Diving manual
DIVING FOR SCIENCE AND
TECHNOLOGY
U.S. DEPARTMENT OF COMMERCE
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Digitized by the Internet Archive
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NOAA DIVING
MANUAL
DIVING FOR SCIENCE AND TECHNOLOGY
October 1991
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U.S. DEPARTMENT OF COMMERCE
Robert A. Mosbacher, Secretary
National Oceanic and Atmospheric Administration
John A. Knauss, Under Secretary
Oceanic and Atmospheric Research
Ned A. Ostenso, Assistant Administrator
Office of Undersea Research
David B. Duane, Director
Mention of a commercial company or
product does not constitute an endorsement
by NOAA. Use for publicity or advertising
purposes of information from this pub-
lication concerning proprietary products or
the use of such products is not authorized.
No photograph appearing in this publication
may be reproduced in any fashion without
prior written permission from NOAA.
Information contained in this Manual was
current as of May 1990.
Library of Congress Cataloging in Publication Data
United States. National Oceanic and Atmospheric
Administration. Office of Undersea Research.
NOAA diving manual.
Bibliography: p.
Includes index.
1. Diving, Scientific. 2. Hyperbaric Physiology.
I. Title.
A publication is of value only if it is kept up to date.
Changes to this publication will be issued periodi-
cally; check your original source for all updates.
Updates will also be available through the Superin-
tendent of Documents.
TABLE OF CONTENTS
V
FOREWORD
vii
PREFACE
ix
CONTRIBUTORS
xiii
LIST OF FIGURES
xxi
LIST OF TABLES
SECTION 1
HISTORY OF DIVING
SECTION 2
PHYSICS OF DIVING
SECTION 3
DIVING PHYSIOLOGY
SECTION 4
COMPRESSED AIR AND
SUPPORT EQUIPMENT
SECTION 5
DIVER AND DIVING
EQUIPMENT
SECTION 6
HYPERBARIC CHAMBERS
AND SUPPORT EQUIPMENT
SECTION 7
DIVER AND SUPPORT
PERSONNEL TRAINING
SECTION 8
WORKING DIVE
PROCEDURES
SECTION 9
PROCEDURES FOR
SCIENTIFIC DIVES
SECTION 10
DIVING UNDER SPECIAL
CONDITIONS
SECTION 11
POLLUTED-WATER DIVING
SECTION 12
HAZARDOUS AQUATIC
ANIMALS
SECTION 13
WOMEN AND DIVING
SECTION 14
AIR DIVING AND
DECOMPRESSION
SECTION 15
MIXED GAS AND OXYGEN
DIVING
SECTION 16
SATURATION DIVING
SECTION 17
UNDERWATER SUPPORT
PLATFORMS
SECTION 18
EMERGENCY MEDICAL CARE
SECTION 19
ACCIDENT MANAGEMENT
AND EMERGENCY
PROCEDURES
SECTION 20
DIAGNOSIS AND TREATMENT
OF DIVING CASUALTIES
APPENDIX A
DIVING WITH
DISABILITIES
111
APPENDIX B
APPENDIX C
APPENDIX D
APPENDIX E
REFERENCES
INDEX
U.S. NAVY AIR
DECOMPRESSION TABLES
TREATMENT FLOWCHART
AND RECOMPRESSION
TREATMENT TABLES
NOAA NITROX I DIVING
AND DECOMPRESSION
TABLES
GLOSSARY
IV
FOREWORD
NOAA, the largest component of the Department of Commerce, is an agency with a broad mission in environ-
mental monitoring, prediction, and understanding of the oceans and the atmosphere. I call NOAA the "earth
systems agency" because it studies the relationship between the natural components of our planet. Among the most
important duties we perform is the monitoring of the oceans and Laurentide Great Lakes.
NOAA operates a variety of sensors and platforms that permit observation and measurement of change in the
seas and Great Lakes. We operate satellites, ships, and submersibles, as well as the world's only underwater
habitat. To add a uniquely human dimension to ocean research and marine services, NOAA conducts wet diving
operations throughout the Great Lakes, the territorial sea, the U.S. Exclusive Economic Zone, and wherever the
agency is involved in marine operations and research.
NOAA numbers among its staff the largest diving complement of any civil Federal agency — more than 250 men
and women. (This number does not include those civilian scientists, engineers, and technicians who dive under the
auspices of NOAA-sponsored research grants, a factor that significantly increases that number.) As befits the
variety of their missions, NOAA's divers are scientists, engineers, technicians, and officers in the NOAA Corps,
and all have volunteered to be divers.
Because the tasks NOAA divers carry out are as varied as those of any group of underwater workers in the world,
this version of the NOAA Diving Manual — greatly expanded and revised — contains instructions, recommenda-
tions, and general guidance on the broadest possible range of underwater living conditions and dive situations.
Thus, while the Manual is directed toward NOAA, it will be useful, as were previous editions, to working divers
who have other affiliations and to those who dive for pleasure only.
Under authority delegated by the Secretary of Commerce, NOAA takes seriously the mandate under Section
21(e) of the Outer Continental Shelf Lands Act Amendments of 1978 to "conduct studies of underwater diving
techniques and equipment suitable for protection of human safety and improvement in diver performance . . . ."
NOAA is proud of its record of safe diving and the assistance it has provided to the diving community.
To continue that record, the Manual has been revised to incorporate recommendations and information obtained
from the entire diving community. The various issues addressed and the procedures recommended reflect the
wisdom, experience, and specialized skills of working and recreational divers, equipment manufacturers, medical
and scientific authorities, and many others.
Under ordinary circumstances, the guidance in this Manual could mean the difference between a successful
mission and a failure. In an extreme situation, however, it could make the difference between life and death. To
those who contributed to this revision, I express, on behalf of all of NOAA, my deep appreciation for their
assistance in making this revision of the Manual a truly useful document for all divers.
John A. Knauss
Under Secretary of Commerce
for Oceans and Atmosphere
PREFACE
This Manual has been developed for use by NOAA divers. It focuses principally on diving to depths that
are shallower than 250 feet (76 m), the depth range in which NOAA divers generally operate. Other sources should
be referred to for information on deep-water mixed-gas diving procedures. As in previous versions, references have
been used liberally to keep this Manual to a manageable size.
This version of the Manual contains many changes from the first and second editions. Immediately noticeable is
the loose-leaf format, which will greatly facilitate revision and additions. This format will permit the Manual to be
updated no matter how large or small the section needing revision, e.g., a section, a paragraph, or a single table.
This edition of the Manual has 25 distinct parts: 20 sections and 5 appendixes. Of these units, 6 are new, 12 have
undergone major revision, and 7 are largely unchanged, as noted below:
New:
Section 1
Section 1 1
Section 13
Appendix A
Appendix C
Appendix E
Substantially revised:
Section 4
Section 5
Section 6
Section 7
Section 9
Section 10
Section 14
Section 15
Section 18
Section 19
Section 20
Appendix D
Largely unchanged:
Section 2
Section 3
Section 8
Section 12
Section 16
Section 17
Appendix B
History of Diving
Polluted-Water Diving
Women and Diving
Diving With Disabilities
Treatment Flowchart and Recompression Treatment Tables
Glossary
Compressed Air and Support Equipment
Diver and Diving Equipment
Hyperbaric Chambers and Support Equipment
Diver and Support Personnel Training
Procedures for Scientific Dives
Diving Under Special Conditions
Air Diving and Decompression
Mixed Gas and Oxygen Diving
Emergency Medical Care
Accident Management and Emergency Procedures
Diagnosis and Treatment of Diving Casualties
NOAA Nitrox I Diving and Decompression Tables
Physics of Diving
Diving Physiology
Working Dive Procedures
Hazardous Aquatic Animals
Saturation Diving
Underwater Support Platforms
U.S. Navy Air Decompression Tables
Although the recommendations and guidelines contained in this Manual are based on the best information
available, they are not intended to replace judgment and expert opinion or to restrict the application of science and
technology that may become available in the future. NOAA also recognizes that some procedures may have to be
modified under controlled experimental conditions to permit the advance of science. Because the information in
this Manual reflects the thinking and experience of many specialists in the field of diving, procedural variations
should be made only on the basis of expert advice.
As stated above, this Manual has been developed for NOAA's divers, whose missions are varied but whose chief
responsibilities are the conduct of oceanic and Great Lakes research and the support of such research activities.
vn
NOAA also recognizes that this Manual will be useful for others who dive because it contains a wealth of
information on applied diving techniques and technology. The information in this Manual, however, should not be
taken to reflect any endorsement or approbation on the part of NOAA or its Undersea Research Program for any
products illustrated, nor can either accept any liability for damage resulting from the use of incorrect or incomplete
information.
The multidisciplinary nature of underwater exploration and research is such that the assistance of numerous
experts in diving-related specialties was essential to the preparation of this Manual. To gain an appreciation of the
number of individuals involved in the task, the reader is referred to the list of contributors and reviewers for this
and previous editions. Special thanks go to all of these contributors and reviewers, but particular gratitude is
extended to: the NOAA Diving Safety Board for its review and comments; Dr. Morgan Wells for his very thorough
editing, including checking of tables and example problem calculations throughout; Dr. James W. Miller for
numerous helpful suggestions, but especially for accepting the task of producing the Glossary; Marthe Kent, whose
persistence, knowledge, and attention to detail drove the entire process; and Marcia Collie, who had to translate
everyone's handwritten notes to intelligible and intelligent prose, cross-check every draft through to galley and the
final page proofs, and in general to see to production.
Comments on this Manual are welcome. They should be directed to:
Director
NOAA's Undersea Research Program, R/OR2
1335 East-West Highway, Room 5262
Silver Spring, Maryland 20910
David B. Duane,
Director
Vlll
CONTRIBUTORS
AND REVIEWERS
Bachrach, Arthur J., Ph.D.
Taos, New Mexico
Bangasser, Susan, Ph.D.
Redlands, California
Barsky, Steven
Diving Systems International
Santa Barbara, California
Bassett, Bruce, Ph.D.
Human Underwater Biology, Inc.
San Antonio, Texas
Bauer, Judy
Hyperbaric Medicine Program
University of Florida
Gainesville, Florida
Bell, George C, Lt. Col., M.C., USAF
Lackland Air Force Base, Texas
Bell, Richard, Ph.D.
Department of Chemical Engineering
University of California
Davis, California
Bennett, Peter, Ph.D.
Duke Medical Center
Durham, North Carolina
Berey, Richard W.
Fairleigh Dickinson University
National Undersea Research Center
National Oceanic and Atmospheric Administration
St. Croix, U. S. Virgin Islands
Black, Stan
Naval Civil Engineering Laboratory
Port Hueneme, California
Bornmann, Robert, M.D.
Limetree Medical Consultants
Reston, Virginia
Bove, Alfred, M.D.
Temple University
Philadelphia, Pennsylvania
Affiliations, titles, and academic degrees are as they were at
the time contribution was made.
Breese, Dennison
Sea-Air-Land-Services
Southport, North Carolina
Busby, Frank
Busby Associates
Arlington, Virginia
Butler, Glenn
International Underwater Contractors, Inc.
City Island, New York
Clark, James D., M.D., Ph.D.
Institute for Environmental Medicine
University of Pennsylvania Medical Center
Philadelphia, Pennsylvania
Clarke, Richard E., M.D.
Department of Hyperbaric Medicine
Richland Memorial Hospital
Columbia, South Carolina
Clifton, H. Edward, Ph.D.
Geological Survey
United States Department of the Interior
Menlo Park, California
Cobb, William F.
Northwest and Alaska Fisheries Center
National Oceanic and Atmospheric Administration
Pasco, Washington
Corry, James A.
Technical Security Division
Department of Treasury
Washington, D.C.
Crosson, Dudley J., Ph.D.
Harbor Branch Oceanographic Institution, Inc.
Fort Pierce, Florida
Daugherty, C. Gordon, M.D.
Austin, Texas
Davis, Jefferson C, M.D.
Hyperbaric Medicine
Southwest Texas Methodist Hospital
San Antonio, Texas
IX
Contributors and Reviewers
Desautels, David
Hyperbaric Medicine Program
University of Florida
Gainesville, Florida
Dingier, John R.
Geological Survey
U.S. Department of the Interior
Menlo Park, California
Dinsmore, David A.
University of North Carolina at Wilmington
National Undersea Research Center
National Oceanic and Atmospheric Administration
Wilmington, North Carolina
Eckenhoff, Roderic G., M.D.
Wallingford, Pennsylvania
Edel, Peter
Sea Space Research Co., Inc.
Harvey, Louisiana
Egstrom, Glen, Ph.D.
Department of Kinesiology
Los Angeles, California
Emmerman, Michael
Lifeguard Systems, Inc.
New York, New York
Farmer, Joseph C, Jr., M.D.
Division of Otolaryngology
Duke University Medical Center
Durham, North Carolina
Feldman, Bruce A., M.
Washington, D.C.
D.
Fife, William, Ph.D.
Hyperbaric Laboratory
Texas A & M University
College Station, Texas
Flynn, Edward T., M.D.,
Capt., Medical Corps
USN Diving Medicine Department
Naval Medical Research Institute
National Naval Medical Center
Bethesda, Maryland
Francis, Art, Lt. (j-g-), NOAA
NOAA Diving Office
Rockville, Maryland
Graver, Dennis
National Association of Underwater Instructors
Montclair, California
Halstead, Bruce W.
World Life Research Institute
Colton, California
Hamner, William M., Ph.D.
Department of Biology
University of California
Los Angeles, California
Hamilton, R.W., Ph.D.
Hamilton Research Ltd.
Tarrytown, New York
Heine, John N.
Moss Landing Marine Laboratory
California State University
Moss Landing, California
Hendrick, Walter, Jr.
Lifeguard Systems, Inc.
New York, New York
Hennessy, T. R., Ph.D.
London, U.K.
High, William L.
Western Administrative Support Center
National Marine Fisheries Services
National Oceanic and Atmospheric Administration
Seattle, Washington
Hobson, Edmund
Tiburon Laboratory
Southwest Fisheries Center
National Oceanic and Atmospheric Administration
Tiburon, California
Hollien, Harry, Ph.D.
Institute for Advanced Study
of Communication Processes
University of Florida
Gainesville, Florida
Hubbard, Dennis, Ph.D.
West Indies Laboratory
Fairleigh Dickinson University
St. Croix, Virgin Islands
Hussey, Nancy R.
Washington, D.C.
Jenkins, Wallace T.
Naval Coastal Systems Laboratory
Panama City, Florida
Kent, Marthe B.
Kensington, Maryland
Contributors and Reviewers
Kinney, Jo Ann S., Ph.D.
Surry, Maine
Lambertsen, Christian J., M.D.
Institute for Environmental Medicine
University of Pennsylvania
Philadelphia, Pennsylvania
Lanphier, Edward H., Ph.D.
BIOTRON
University of Wisconsin
Madison, Wisconsin
Lewbel, George, Ph.D.
LGL Ecological Research Associates
Bryan, Texas
Loewenherz, James W., M.D.
Miami, Florida
Long, Richard W.
Diving Unlimited International, Inc.
San Diego, California
Macintyre, Ian G., Ph.D.
Department of Paleobiology
National Museum of Natural History
Smithsonian Institution
Washington, D.C.
Mathewson, R. Duncan, III, Ph.D.
Summerland Key, Florida
Mayers, Douglas, M.D., MC, USN
Naval Medical Command
Naval Medical Research Institute
Bethesda, Maryland
McCarthy, James
Navy Experimental Diving Unit
Panama City, Florida
Miller, James W., Ph.D.
Big Pine Key, Florida
Miller, John N., M.D.
University of South Alabama
Mobile, Alabama
Murray, Rusty
Moray Wheels
Nahant, Massachusetts
Murru, Frank
Curator of Fishes
Sea World
Orlando, Florida
Newell, Cliff
Chief, Diving Operations
National Oceanic and Atmospheric Administration
Seattle, Washington
Norquist, David S.
University of Hawaii
National Undersea Research Center
National Oceanic and Atmospheric Administration
Waimanalo, Hawaii
Orr, Dan
Academic Diving Program
Florida State University
Tallahassee, Florida
Pegnato, Paul, Lt. Cdr., NOAA
NOAA Diving Program
National Oceanic and Atmospheric Administration
Rockville, Maryland
Pelissier, Michael
Ocean Technology Systems
Santa Ana, California
Peterson, David H., Lt. Cdr., NOAA
National Oceanic and Atmospheric Administration
Rockville, Maryland
Peterson, Russell, Ph.D.
Westchester, Pennsylvania
Phoel, William C, Ph.D.
Sandy Hook Laboratory
Northeast Fisheries Center
National Marine Fisheries Service
National Oceanic and Atmospheric Administration
Highlands, New Jersey
Reimers, Steve, P.E.
Reimers Engineering
Alexandria, Virginia
Robinson, Jill
Jill Robinson & Associates
Arlington, Virginia
Rogers, Wayne, M.D.
Big Pine Key, Florida
Roman, Charles M.
Office of NOAA Corps Operations
National Oceanic and Atmospheric Administration
Rockville, Maryland
Rounds, Richard
West Indies Laboratory
Fairleigh Dickinson University
National Undersea Research Center
St. Croix, U. S. Virgin Islands
XI
Contributors and Reviewers
Rutkowski, Richard L.
Hyperbarics International
Miami, Florida
Schroeder, William W., Ph.D.
Marine Science Program
University of Alabama
Dauphin Island, Alabama
Schane, William, M. D.
West Indies Laboratory
Fairleigh Dickinson University
National Undersea Research Center
St. Croix, U. S. Virgin Islands
Somers, Lee, Ph.D.
Department of Atmospheric and Oceanic Sciences
University of Michigan
Ann Arbor, Michigan
Spaur, William, M.D.
Norfolk, Virginia
Staehle, Michael
Staehle Marine Services, Inc.
North Palm Beach, Florida
Stanley, Chet
NOAA Diving Safety Officer
Rockville, Maryland
Stewart, James R., Ph.D.
Scripps Institution of Oceanography
La Jolla, California
Stewart, Joan, Ph.D.
Scripps Institution of Oceanography
La Jolla, California
Stone, Richard B.
National Marine Fisheries Service
National Oceanic and Atmospheric Administration
Silver Spring, Maryland
Strauss, Michael B., M.D.
Memorial Medical Center of Long Beach
Long Beach, California
Swan, George
Northwest and Alaska Fisheries Center
National Marine Fisheries Service
National Oceanic and Atmospheric Administration
Pasco, Washington
Thompson, Terry
Ocean Images, Inc.
Berkeley, California
Thornton, J. Scott, Ph.D.
Texas Research Institute, Inc.
Austin, Texas
Valentine, Page, Ph.D.
Geological Survey
United States Department of the Interior
Woods Hole, Massachusetts
Vorosmarti, James, Jr., M.D.
Rockville, Maryland
Walsh, Michael, Ph.D.
National Institute on Drug Abuse
U.S. Public Health Service
Rockville, Maryland
Waterman, Stanton A.
East/West Film Productions, Inc.
Lawrenceville, New Jersey
Webb, Paul, M.D.
Webb Associates
Yellow Springs, Ohio
Wells, Morgan, Ph.D.
NOAA Diving Program
Rockville, Maryland
Wicklund, Robert I.
National Undersea Research Center
Caribbean Marine Research Center
Lee Stocking Island, Bahamas
Wilkie, Donald W., Ph.D.
Scripps Institution of Oceanography
University of California
La Jolla, California
Williscroft, Robert, Ph.D.
Williscroft Manuscripts
Dayton, Washington
Workman, Ian
Southeast Fisheries Center
Pascagoula Facility
National Oceanic and Atmospheric Administration
Pascagoula, Mississippi
xn
LIST OF FIGURES
SECTION 1
HISTORY OF DIVING Page
l-l Breath-Hold Pearl Divers 1-2
1-2 Alexander the Great's Descent Into The Sea ... 1-3
1-3 Halley's Diving Bell, 1690 1-3
1-4 Triton Diving Apparatus 1-4
1-5 Rouquayrol-Denayrouse Semi-Self-
Contained Diving Suit 1-5
1-6 Fernez-Le Prieur Self-Contained Diving
Apparatus 1-5
1-7 World War II Military Swimmer Dressed in
Lambertsen Amphibious Respiratory Unit 1-6
SECTION 2
PHYSICS OF DIVING
2-1 Equivalent Pressures, Altitudes, and Depths .... 2-4
2-2 Effects of Hydrostatic Pressure 2-5
2-3 Boyle's Law 2-9
2-4 Gas Laws 2-12
2-5 Objects Under Water Appear Closer 2-13
SECTION 3
DIVING PHYSIOLOGY
3-1 The Process of Respiration 3-1
3-2 The Circulatory System 3-3
3-3 Oxygen Consumption and Respiratory Minute
Volume as a Function of Work Rate 3-4
3-4 Relation of Physiological Effects to Carbon
Dioxide Concentration and Exposure
Period 3-6
3-5 Effects of Hydrostatic Pressure on Location
of Breathing Bags Within a Closed-Circuit
Scuba 3-9
3-6 Principal Parts of the Ear 3-1 1
3-7 Location of Sinus Cavities 3-12
3-8 Pressure Effects on Lung Volume 3-13
3-9 Complications From Expansion of Air in the
Lungs During Ascent 3-15
3-10 Isobaric Counterdiffusion 3-19
3-1 1 Effect of Exposure Duration on Psychomotor
Task Performance in Cold Water 3-26
xiii
List of Figures
Page
SECTION 4
COMPRESSED AIR AND SUPPORT EQUIPMENT
4-1 Production of Diver's Breathing Air 4-6
4-2 Steel Cylinder Markings 4-7
4-3 Aluminum Cylinder Markings 4-8
4-4 Valve Assemblies 4-11
4-5 Gauges 4-12
SECTION 5
DIVER AND DIVING EQUIPMENT
5-1 Open-Circuit Scuba Equipment 5-1
5-2 First-Stage Regulators 5-3
5-3 Breathing Hoses 5-4
5-4 Mouthpieces 5-5
5-5 Check and Exhaust Valves 5-6
5-6 Lightweight Helmet 5-8
5-7 Face Masks 5-12
5-8 Flotation Devices 5-13
5-9 Swim Fins 5-14
5-10 Neoprene Wet Suit 5-15
5-11 Effects of Water Temperature 5-16
5-12 Cold- Water Mitt, Liner Included 5-17
5-13 Open-Circuit Hot-Water Suit 5-18
5-14 Snorkels 5-19
5-15 Dive Timer 5-20
5-16 Depth Gauges 5-20
5-17 Pressure Gauges 5-22
5-18 Diving Lights 5-23
5-19 Signal Devices 5-23
5-20 Shark Darts 5-25
5-21 Shark Screen in Use 5-25
5-22 Diver Communication System 5-26
5-23 Schematics of Diver Communication Systems . 5-26
5-24 Modulated Acoustic Communication System... 5-27
SECTION 6
HYPERBARIC CHAMBERS AND
SUPPORT EQUIPMENT
6-1 A Double-Lock Hyperbaric Chamber —
Exterior View 6-1
6- IB Double-Lock Hyperbaric Chamber —
Interior View 6-2
6-2 Mask Breathing System for Use in Hyperbaric
Chamber 6-3
6-3 Transportable Chambers 6-4
6-4 Certification Plate for Hyperbaric Chamber .... 6-4
6-5 Burning Rates of Filter Paper Strips at an
Angle of 45° in N2-02 Mixtures 6-15
xiv
List of Figures
Page
6-6 Combustion in N->-Ot Mixtures Showing the
Zone of No Combustion 6-16
SECTION 7
DIVER AND SUPPORT PERSONNEL TRAINING
No Figures
SECTION 8
WORKING DIVE PROCEDURES
8-1 Surface-Supplied Diver in Deep-Sea Dress 8-2
8-2 Predive Environmental Checklist 8-3
8-3 Lightweight Surface-Supplied Mask 8-4
8-4 Surface-Supplied Diver In Lightweight Mask
and Wet Suit 8-5
8-5 Major Components of a Low-Pressure
Compressor-Equipped Air Supply System .... 8-10
8-6 Typical High-Pressure Cylinder Bank Air
Supply System 8-10
8-7 Circular Search Pattern 8-12
8-8 Circular Search Pattern for Two
Diver/Searchers 8-12
8-9 Circular Search Pattern Through Ice 8-14
8-10 Arc (Fishtail) Search Pattern 8-15
8-11 Jackstay Search Pattern 8-16
8-12 Searching Using a Tow Bar 8-16
8-13 Diver-Held Sonar 8-17
8-14 Using a Compass for Navigation 8-18
8-15 Underwater Hydraulic Tools 8-21
8-16 Explosive Hole Punch 8-22
8-17 Oxy-Arc Torch 8-22
8-18 Salvaging an Anchor With Lift Bags 8-26
8-19 Aquaplane for Towing Divers 8-30
8-20 Underwater Cameras 8-33
8-21 Basic Equipment for Closeup and Macro
Photography 8-34
8-22 Diurnal Variation of Light Under Water 8-35
8-23 Selective Color Absorption of Light as a
Function of Depth in Clear Ocean Water 8-36
8-24 Lighting Arms and Brackets for Strobe
Systems 8-40
8-25 Video Recording Systems 8-45
8-26 Commercial Underwater Video System 8-46
SECTION 9
PROCEDURES FOR SCIENTIFIC DIVES
9-1 Fiberglass Measuring Tape 9-3
9-2 Bottom Survey in High-Relief Terrain 9-3
9-3 High-Frequency Sonic Profiler 9-5
9-4 Multipurpose Slate 9-6
xv
List of Figures
Page
9-5 Counting Square for Determining Sand Dollar
Density 9-8
9-6 Diver-Operated Fishrake 9-8
9-7 Underwater Magnification System 9-9
9-8 Hensen Egg Nets Mounted on a Single Diver
Propulsion Vehicle 9-9
9-9 A Circle Template for Determining Benthic
Population Density 9-10
9-10 Coring Device With Widemouth Container 9-10
9-1 1 Infauna Sampling Box 9-1 1
9-12 Use of a Hand-Held Container to Collect
Zooplankton 9-12
9-13 Use of a Plexiglas Reference Frame for
Estimating Population Densities
in Midwater 9-13
9-14 Benthic Environment of the American
Lobster 9-14
9-15 Diver With Electroshock Grid 9-15
9-16 Tagging a Spiny Lobster on the Surface 9-15
9-17 Tagging a Spiny Lobster in Situ 9-16
9-18 Elkhorn Coral Implanted on Rocky Outcrop .... 9-17
9-19 Algal Cover of Rock Substrate 9-18
9-20 Diver in Giant Brown Kelp (Macrocystis) Bed .... 9-19
9-21 Fish Using Tires as Habitat 9-21
9-22 An Artificial Reef Complex 9-21
9-23 Underwater Geological Compass 9-23
9-24 Box Cores (Senckenberg) for Determining
Internal Structure in Sand 9-25
9-25 Greased Comb for Ripple Profiling 9-26
9-26 Diver Using Scaled Rod and Underwater
Noteboard 9-26
9-27 Aerial Photograph and Composite Map 9-27
9-28 Dip and Strike of Rock Bed 9-28
9-29 Geologist Measuring Dip (Inclination) of
Rock Outcrop 9-28
9-30 Coring in a Deep Reef Environment With a
Hydraulic Drill 9-28
9-31 Pneumatic Hand Drill 9-29
9-32 Diver Taking Vane Shear Measurement 9-31
9-33 Undersea Instrument Chamber 9-32
9-34 Dye-Tagged Water Being Moved by Bottom
Current 9-35
9-35 Diver Using Water Sample Bottle 9-36
9-36 Water Sample Bottle Backpack 9-36
9-37 Diver Recovering Indian Artifacts 9-37
9-38 Archeologist Exploring the Golden Horn 9-38
9-39 Heavy Overburden Air Lift 9-39
9-40 Prop Wash System Used for Archeological
Excavation 9-41
9-41 Fish Trap 9-42
9-42 Diver Checking Fish Trawl 9-43
9-43 Slurp Gun Used to Collect Small Fish 9-45
xvi
List of Figures
Page
SECTION 10
DIVING UNDER SPECIAL CONDITIONS
lO-l Schematic Diagram of Waves in the Breaker
Zone 10-8
10-2 Near-shore Current System 10-10
10-3 Shore Types and Currents lO-l l
10-4 Entering the Water Using the Roll-In Method 10-12
10-5 Transom-Mounted Diver Platform 10-12
10-6 Side-Mounted Diver Platform 10-13
10-7 Down-line Array for Open-Ocean Diving 10-15
10-8 Three Multiple Tether Systems (Trapezes)
Used for Open-Ocean Diving 10-16
10-9 Safety Reel Used in Cave Diving 10-18
10-10 Water Temperature Protection Chart 10-20
10-1 1 Diver Tender and Standby Diver in Surface
Shelter 10-21
10-12 Cross Section of a Typical Hydroelectric
Dam in the Northwestern United States 10-29
10-13 Diver Protected by Cage and Ready to be
Lowered into Dam Gatewell 10-30
10-14 A Fish Ladder at a Hydroelectric Dam in
the Northwest 10-30
10-15 Creeper — A Device Used to Move Across
Rocky Substrates in Strong Currents 10-32
10-16 Support Ship, Trawl, Diver Sled, and
Support Boat 10-35
SECTION 11
POLLUTED-WATER DIVING
ll-l Diver Working in Contaminated Water 11-2
1 1-2 Diver in Dry Suit 1 1-4
1 1-3 NOAA-Developed Suit-Under-Suit (SUS)
System 1 1-5
1 1-4 Dressing a Diver for Contaminated-Water
Diving 1 1-5
11-5 Decontamination Team at Work 11-6
SECTION 12
HAZARDOUS AQUATIC ANIMALS
l 2-1 Sea Urchin Echinothrix diadema on a
Hawaiian Reef 12-1
12-2 Stinging Hydroid 12-2
12-3 Stinging or Fire Coral 12-2
12-4 Portuguese Man-of-War 12-3
12-5 Large Jellyfish of Genus Cyanea 12-3
12-6 Bristleworm 12-4
12-7 Cone Shell 12-4
12-8 Anatomy of a Cone Shell 12-5
12-9 Rare Australian Blue-Ring Octopus 12-5
xvn
List of Figures
Page
12-10 Dasyatid Stingray 12-6
12-1 1 Myliobatid Stingray 12-6
12-12 Lionfish 12-7
12-13 Surgeonfish 12-7
12-14 Sea Snake 12-8
12-15 Great White Shark 12-8
12-16 Gray Reef Shark 12-9
12-17 Moray Eel 12-10
12-18 Barracuda 12-11
12-19 Torpedo Ray 12-12
12-20 Examples of Pufferfish 12-12
SECTION 13
WOMEN AND DIVING
13-1 Scientist on Research Mission 13-5
SECTION 14
AIR DIVING AND DECOMPRESSION
14-1 Sea States 14-5
14-2A Hand Signals 14-10
14-2B Additional Hand Signals 14-1 1
14-3 Deliverable Volumes at Various Gauge
Pressures 14-16
14-4 Typical High Pressure Cylinder Bank Air
Supply 14-18
14-5 Repetitive Dive Flowchart 14-25
14-6 Repetitive Dive Worksheet 14-26
SECTION 15
MIXED GAS AND OXYGEN DIVING
15-1 Minimum Safe Inspired Gas Temperature
Limits 15-5
15-2 Percentage of Oxygen in Breathing Mixtures
as a Function of Depth and Oxygen Partial
Pressure Relative to Ranges for Hypoxia
and CNS Toxicity 15-6
15-3 Closed-Circuit Mixed-Gas Scuba
(Rebreather) 15-1 1
15-4 Closed-Circuit Oxygen Scuba (Rebreather) 15-1 1
15-5 Air Analysis Kit for On-Site Use 15-14
15-6 Direct-Reading Colorimetric Air Sampler 15-15
SECTION 16
SATURATION DIVING
No Figures
xviii
List of Figures
Page
SECTION 17
UNDERWATER SUPPORT PLATFORMS
17-1 Saturation Diving Complex 17-2
17-2 Open Diving Bell on Deck of Seahawk 17-3
17-3 Bell System 17-4
17-4 Open Bell Showing Control Lines 17-5
17-5 Open Bell Emergency Flow-Chart 17-6
17-6 Cutaway Showing Mating Position With
Deck Decompression Chamber 17-7
17-7 Undersea Habitat Specifications and
Operational Data 17-8
17-8 Edalhab 17-12
17-9 Hydrolab 17-13
17-10 Tektite 17-14
17-11 La Chalupa 17-15
17-12 Aegir 17-16
17-13 Underwater Classroom 17-17
17-14 Aquarius 17-17
17-15A Sublimnos 17-18
17-15B Subigloo 17-19
17-15C Lake Lab 17-19
17-15D Undersea Instrument Chamber 17-19
17-16 Diver Propulsion Vehicle 17-20
17-17 JIM System 17-21
17-18 WASP System 17-21
17-19 ROV System Components 17-22
17-20 Mitsui Engineering and Shipbuilding
RTV-100 17-23
17-21 Examples of ROV David Work Tasks 17-23
SECTION 18
EMERGENCY MEDICAL CARE
18-1 Life-Support Decision Tree 18-2
18-2 Jaw-Lift Method 18-4
18-3 Bag-Valve-Mask Resuscitator 18-6
SECTION 19
ACCIDENT MANAGEMENT AND
EMERGENCY PROCEDURES
19-1 Buddy Breathing 19-6
19-2 Clearing a Face Mask 19-8
19-3 Do-Si-Do Position for Administering
In-Water Mouth-to-Mouth Artificial
Resuscitation 19-1 1
19-4 Mouth-to-Mouth In-Water Artificial
Resuscitation 19-12
19-5 Mouth-to-Snorkel Artificial Resuscitation 19-13
19-6 Towing Position for Mouth-to-Snorkel
Artificial Resuscitation 19-14
19-7 Tank-Tow Method 19-18
xix
List of Figures
Page
19-8 Divers Alert Network (DAN) 19-22
19-9 Modified Trendelenberg Position 19-24
19-10 Diving Accident Management Flow Chart 19-25
19-11 Evacuation by Helicopter 19-27
SECTION 20
DIAGNOSIS AND TREATMENT OF DIVING
CASUALTIES
20-1 Structure of External, Middle, and Inner Ear 20-8
20-2 Summary of Decompression Sickness and
Gas Embolism Symptoms and Signs 20-10
20-3 Decompression Sickness Treatment From
Diving or Altitude Exposures 20-12
20-4 Treatment of Arterial Gas Embolism 20-14
20-5 Treatment of Symptom Recurrence 20-16
xx
LIST OF TABLES
SECTION 1
HISTORY OF DIVING page
No Tables
SECTION 2
PHYSICS OF DIVING
2-1 Conversion Factors, Metric to English Units.... 2-2
2-2 Conversion Table for Barometric Pressure
Units 2-3
2-3 Colors That Give Best Visibility Against a
Water Background 2-16
SECTION 3
DIVING PHYSIOLOGY
3-1 Carboxyhemoglobin as a Function of
Smoking 3-8
3-2 Narcotic Effects of Compressed Air Diving 3-22
SECTION 4
COMPRESSED AIR AND SUPPORT EQUIPMENT
4-1 Composition of Air in its Natural State 4-1
SECTION 5
DIVER AND DIVING EQUIPMENT
No Tables
SECTION 6
HYPERBARIC CHAMBERS AND
SUPPORT EQUIPMENT
6-1 Hyperbaric Chamber Predive Checkout
Procedures 6-5
6-2 Ventilation Rates and Total Air
Requirements for Two Patients and
One Tender Undergoing Recompression
Treatment 6-8
6-3 Chamber Post-Dive Maintenance Checklist 6-9
6-4 Pressure Test Procedures for NOAA
Chambers 6-1 1
6-5 Standard NOAA Recompression Chamber
Air Pressure and Leak Test 6-12
xxi
List of Tables
Page
SECTION 7
DIVER AND SUPPORT PERSONNEL TRAINING
No Tables
SECTION 8
WORKING DIVE PROCEDURES
8-1 Wind Speed and Current Estimations 8-11
8-2 Diver Power Tools 8-19
8-3 Selection Guide for Discharge Pipe and
Air Line 8-28
8-4 Characteristics of Principal U.S. Explosives
Used for Demolition Purposes 8-32
8-5 Color Correction Filters 8-36
8-6 Manual and Through-the-Lens (TTL)
Strobes for Closeup Photography 8-37
8-7 Through-the-Lens (TTL) Mini Strobes for
Automatic and Manual Exposure 8-38
8-8 Exposure Compensation for Underwater
Photography 8-38
8-9 Underwater Photographic Light Sources 8-39
8-10 Still Films Suited for Underwater Use 8-41
8-1 1 Processing Adjustments for Different
Speeds 8-42
8-12 Motion Picture Films Suited for Underwater
Use 8-43
SECTION 9
PROCEDURES FOR SCIENTIFIC DIVES
9-1 Micro-Oceanographic Techniques 9-33
9-2 Levels of Anesthesia for Fish 9-44
9-3 Fish Anesthetics 9-47
SECTION 10
DIVING UNDER SPECIAL CONDITIONS
10-1 Comparison of Differences in Time Limits
(in Minutes of Bottom Time) for
No-Decompression Dives 10-25
10-2 Theoretical Ocean Depth (TOD) (in fsw) at
Altitude for a Given Measured Diving Depth 10-26
10-3 Pressure Variations with Altitude 10-27
SECTION 11
POLLUTED-WATER DIVING
No Tables
xxii
List of Tables
Page
SECTION 12
HAZARDOUS AQUATIC ANIMALS
No Tables
SECTION 13
WOMEN AND DIVING
No Tables
SECTION 14
AIR DIVING AND DECOMPRESSION
14-1 Sea State Chart 14-6
14-2 Signal Flags, Shapes, and Lights 14-9
14-3 Hand Signals 14-12
14-4 Line Pull Signals for Surface-to-Diver
Communication 14-13
14-5 Respiratory Minute Volume (RMV) at
Different Work Rates 14-14
14-6 Air Utilization Table at Depth 14-15
14-7 Cylinder Constants 14-16
14-8 Scuba Cylinder Pressure Data 14-17
1 4-9 Estimated Duration of 7 1 .2 ft3 Steel
Cylinder 14-17
14-10 Flow-Rate Requirements for Surface-
Supplied Equipment 14-19
14-1 1 No-Decompression Limits and Repetitive
Group Designation Table for No-
Decompression Air Dives 14-21
14-12 Residual Nitrogen Timetable for Repetitive
Air Dives 14-22
14-13 Optional Oxygen-Breathing Times Before
Flying After Diving 14-31
SECTION 15
MIXED GAS AND OXYGEN DIVING
15-1 Oxygen Partial Pressure and Exposure Time
Limits for Nitrogen-Oxygen Mixed Gas
Working Dives 15-3
15-2 Depth-Time Limits for Breathing Pure
Oxygen During Working Dives 15-7
1 5-3 NOAA NITROX-I (68% N2, 32% 02) No-
Decompression Limits and Repetitive
Group Designation Table for No-
Decompression Dives 15-8
15-4 Equivalent Air Depths (EAD) and Maximum
Oxygen Exposure for Open-Circuit Scuba
Using a Breathing Mixture of 68%
Nitrogen and 32% Oxygen (NOAA
Nitrox-I) 15-9
15-5 Air Purity Standards 15-11
xxiii
List of Tables
Page
SECTION 16
SATURATION DIVING
16-1 Summary of Air and Nitrogen-Oxygen
Saturation Exposures 16-2
16-2 Characteristics of Three Carbon Dioxide
Absorbents 16-10
1 6-3 Hazardous Materials for Habitat Operations 16-14
SECTION 17
UNDERWATER SUPPORT PLATFORMS
17-1 Desirable Features of Underwater Habitats 17-1 1
SECTION 18
EMERGENCY MEDICAL CARE
No Tables
SECTION 19
ACCIDENT MANAGEMENT AND
EMERGENCY PROCEDURES
19-1 Summary of Probable Causes of Non-
Occupational Diving Fatalities
from 1976-1984 19-5
19-2 Sources of Emergency Assistance 19-21
19-3 Ground-to-Air Visual Signal Code 19-23
19-4 Diving Casualty Examination Checklist 19-26
SECTION 20
DIAGNOSIS AND TREATMENT OF
DIVING CASUALTIES
20-1 Characteristics of Inner Ear Barotrauma and
Inner Ear Decompression Sickness 20-5
20-2 List of U.S. Navy Recompression Treatment
Tables 20-1 1
20-3 General Patient Handling Procedures 20-15
xxiv
SECTION 1
HISTORY OF
DIVING
1.0
1.1
1.2
1.3
1.4
1.5
Page
General 1-1
Free (Breath-Hold) Diving 1-1
Diving Bells 1-1
Helmet (Hard-Hat) Diving 1-2
Scuba Diving 1-3
Saturation Diving 1-6
1.5.1 Saturation Diving Systems 1-6
1.5.2 Habitats 1-7
1.5.3 Lockout Submersibles 1-7
1.6 Summary 1-7
(
(
HISTORY
OF DIVING
1.0 GENERAL
Divers have penetrated the oceans through the centu-
ries for purposes identical to those of modern diving: to
acquire food, search for treasure, carry out military
operations, perform scientific research and explora-
tion, and enjoy the aquatic environment. In a brief
history of diving, Bachrach (1982) identified five
principal periods in the history of diving, from free (or
breath-hold) diving, to bell diving, surface support or
helmet (hard hat) diving, scuba diving, and, finally,
saturation diving. (Atmospheric diving, another div-
ing mode, is discussed in Section 17.5.) All of these
diving modes are still currently in use.
1.1 FREE (BREATH-HOLD) DIVING
Free diving, or breath-hold diving, is the earliest of all
diving techniques, and it has played an historic role in
the search for food and treasure. The Hae-Nyu and
Ama pearl divers of Korea and Japan (Figure 1-1) are
among the better-known breath-hold divers. In his
book, Half Mile Down, Beebe (1934) reports finding
several mother-of-pearl inlays in the course of con-
ducting an archeological dig at a Mesopotamia site
that dated back to 4500 B.C.; these shells must have
been gathered by divers and then fashioned into inlays
by artisans of the period. Beebe also describes the
extensive use of pearl shells among people from other
ancient cultures. The Emperor of China, for example,
received an oyster pearl tribute around 2250 B.C. Free
divers were also used in military operations, as the
Greek historian Thucydides reports. According to
Thucydides, divers participated in an Athenian attack
on Syracuse in which the Athenian divers cut through
underwater barriers that the Syracusans had built to
obstruct and damage the Greek ships. Free or breath-
hold divers sometimes used hollow reeds as breathing
tubes, which allowed them to remain submerged for
longer periods; this type of primitive snorkel was use-
ful in military operations (Larson 1959).
Free diving continues to be a major diving method.
World records were set in 1969 by a U.S. Navy diver,
Robert Croft, who made a breath-hold dive to 247 feet
(75 meters), a record broken in 1976 by a French diver,
Jacques Mayol, who set the current world's breath-
hold dive record at 325 feet (99 meters). Mayol grasped
October 1991 — NOAA Diving Manual
the bar of a weighted line to plunge to this depth and
held his breath for 3 minutes and 39 seconds.
The obvious advantage of free diving as a work method
(and as a recreational method) is its mobility and the
freedom of the breath-hold diver to maneuver; the
obvious disadvantage is that the air supply is necessarily
limited to the amount of air the diver can take in and
maintain in a single breath or can obtain by means of a
snorkel-type reed or tube to the surface. The modern
snorkel is an aid in breath-hold diving but is not used
to provide a continuous supply of air, because on descent
it fills with water that must then be exhaled on surfacing.
1.2 DIVING BELLS
The second principal historical mode of diving is bell
diving. One of the earliest reports of the use of a device
that enabled a diver to enter the water with some
degree of protection and a supply of air involved the
diving bell Colimpha used in Alexander the Great's
descent in approximately 330 B.C., depicted by an
Indian artist in a 1575 miniature (Figure 1-2). An
account of this dive appeared in the 13th century French
manuscript, The True History of Alexander. In his
Problemata, Aristotle described diving systems in use
in his time: "they contrive a means of respiration for
divers, by means of a container sent down to them;
naturally the container is not filled with water, but air,
which constantly assists the submerged man."
In the 1000 years following this period, very few
developments occurred in diving. It was not until 1535
that Guglielmo de Lorena developed a device that can
be considered a true diving bell. Davis (1962) tells of a
diver who worked for about an hour in a lake near
Rome using de Lorena's diving apparatus, which rested
on his shoulders and had much of its weight supported
by slings. De Lorena's "bell" thus provided a finite but
reliable air supply.
In 1691, the British astronomer Sir Edmund Halley
(who was then Secretary of the Royal Society) built
and patented a forerunner of the modern diving bell,
which he later described in a report to the Society. As
Sir Edmund described it, the bell was made of wood
coated with lead, was approximately 60 cubic feet
(1.7 cubic meters) in volume, and had glass at the
top to allow light to enter; there was also a valve to
1-1
Section 1
Figure 1-1
Breath-Hold Pearl Divers
vent the air and a barrel to provide replenished air
(Figure 1-3). In his history of diving, Davis (1962)
suggests that Halley undoubtedly knew of a develop-
ment reported by the French physicist Denis Papin,
who in 1689 had proposed a plan (apparently the first)
to provide air from the surface to a diving bell under
pressure. Papin proposed to use force pumps or bellows
to provide air and to maintain a constant pressure
within the bell. Davis speculates that Halley's choice
of the barrel rather than forced air method of replenish-
ment may have reflected Halley's concern that Papin
(who was also a Fellow of the Royal Society) would
accuse him of stealing his concept. Halley's method
was used for over a century until Smeaton introduced
a successful forcing pump in 1788. In 1799, Smeaton
dived with his "diving chests," which used a forcing
pump to replenish the air supply (Larson 1959).
Diving bells continue to be used today as part of
modern diving systems, providing a method of trans-
porting divers to their work sites while under pressure
and, once at the site, of supplying breathing gas while
the diver works. Both modern-day open (or "wet") and
closed bells are clearly the successors of these ancient
systems.
1-2
Photos courtesy Suk Ki Hong
1.3 HELMET (HARD-HAT) DIVING
Although these early diving bells provided some
protection and an air supply, they limited the mobility
of the diver. In the I7th and 18th centuries, a number of
devices (usually made of leather) were developed to
provide air to divers and to afford greater mobility.
However, most of these devices were not successful,
because they relied on long tubes from the surface to
provide air to the diver and thus did not deal with the
problem of equalizing pressure at depth.
The first real step toward the development of a surface-
supported diving technique occurred when the French
scientist Freminet devised a system in which air was
pumped from the surface with a bellows, allowing a
constant flow of air to pass through a hose to the diver
in the water. This system is considered by many to be
the first true helmet-hose diving apparatus. Freminet
has been credited with diving in 1774 with this device
to a depth of 50 feet (15 meters), where he remained
for a period of 1 hour.
The first major breakthrough in surface-support
diving systems occurred with Augustus Siebe's inven-
tion of the diving dress in 1819. Around the same time,
NOAA Diving Manual — October 1991
History of Diving
Figure 1-2
Alexander the Great's Descent Into The Sea
Figure 1-3
Halley's Diving Bell, 1690
Courtesy National Academy of Sciences
the Deane Brothers, John and Charles, were working
on a design for a "smoke apparatus," a suit that would
allow firefighters to work in a burning building. They
received a patent for this system in 1823, and later
modified it to "Deane's Patent Diving Dress," consisting
of a protective suit equipped with a separate helmet
with ports and hose connections for surface-supplied
air. Siebe's diving dress consisted of a waist-length
jacket with a metal helmet sealed to the collar. Divers
received air under pressure from the surface by force
pump; the air subsequently escaped freely at the diver's
waist. In 1837, Siebe modified this open dress, which
allowed the air to escape, into the closed type of dress.
The closed suit retained the attached helmet but, by
venting the air via a valve, provided the diver with a
full-body air-tight suit. This suit served as the basis
for modern hard-hat diving gear. Siebe's diving suit
was tested and found to be successful in 1839 when
the British started the salvage of the ship Royal
George, which had sunk in 1782 to a depth of 65 feet
(19.8 meters) (Larson 1959).
No major developments occurred in hard-hat gear
until the 20th century, when mixed breathing gases, in
October 1991 — NOAA Diving Manual
Courtesy National Academy of Sciences
particular helium-oxygen, were developed. The first
major open-sea use of helium and oxygen as a breath-
ing mixture occurred in the salvage of the submarine,
the USS Squalus, in 1939. The breathing of mixed
gases such as helium-oxygen permitted divers to dive
to greater depths for longer periods than had been
possible with air mixtures. The hard-hat surface-
supported diving technique is probably still the most
widely used commercial diving method; the use of
heliox mixtures and the development of improved decom-
pression tables have extended the diver's capability to
work in this diving dress at depth. Although surface-
supported diving has several advantages in terms of
stability, air supply, and length of work period, a major
problem with hard-hat gear is that it severely limits
the diver's mobility. This limitation has been overcome in
certain dive situations by the development of self-
contained underwater breathing apparatus (scuba).
1.4 SCUBA DIVING
The development of self-contained underwater breathing
apparatus provided the free moving diver with a portable
1-3
Section 1
Figure 1-4
Triton Diving Apparatus
air supply which, although finite in comparison with
the unlimited air supply available to the helmet diver,
allowed for mobility. Scuba diving is the most fre-
quently used mode in recreational diving and, in vari-
ous forms, is also widely used to perform underwater
work for military, scientific, and commercial purposes.
There were many steps in the development of a suc-
cessful self-contained underwater system. In 1808,
Freiderich von Drieberg invented a bellows-in-a-box
device (Figure 1-4) that was worn on the diver's back
and delivered compressed air from the surface. This
device, named Triton, did not actually work but it did
serve to suggest that compressed air could be used in
diving, an idea initially conceived of by Halley in
1716. In 1865, two French inventors, Rouquayrol and
Denayrouse, developed a suit (Figure 1-5) that they
described as "self-contained." In fact, their suit was
not self contained but consisted of a helmet-using
surface-supported system that had an air reservoir
that was carried on the diver's back and was sufficient
to provide one breathing cycle on demand. The demand
valve regulator was used with surface supply largely
because tanks of adequate strength were not then availa-
ble to handle air at high pressure. This system's demand
valve, which was automatically controlled, represented a
major breakthrough because it permitted the diver to
have a breath of air when needed in an emergency. The
Rouquayrol and Denayrouse apparatus was described
with remarkable accuracy in Jules Verne's classic,
Twenty Thousand Leagues Under The Sea, which was
written in 1869, only 4 years after the inventors had
made their device public (Larson 1959).
The demand valve played a critical part in the later
development of one form of scuba apparatus. Howev-
er, since divers using scuba gear exhaled directly into
the surrounding water, much air was wasted. One solution
to this problem was advanced by Henry Fleuss, an
English merchant seaman who invented a closed-circuit
breathing apparatus in 1879 that used pure oxygen
compressed to 450 psig for the breathing gas supply
and caustic potash to purify the exhaled oxygen. Fleuss'
"closed circuit oxygen-rebreather SCUBA" passed a
crucial test when it was used successfully in 1880 by
the English diver Alexander Lambert to enter a flooded
tunnel beneath the Severn River to secure an iron door
that had jammed open and to make needed repairs in
the tunnel. Although Fleuss' rebreather was successful
in this limited application, the depth limitations
associated with the use of pure oxygen directed most
attention to compressed air as a breathing mixture.
In the 1920's, a French naval officer, Captain Yves
Le Prieur, began work on a self-contained air diving
1-4
Courtesy National Academy of Sciences
apparatus that resulted in 1926 in the award of a
patent, shared with his countryman Fernez. This device
(Figure 1-6) was a steel cylinder containing compressed
air that was worn on the diver's back and had an air
hose connected to a mouthpiece; the diver wore a nose
clip and air-tight goggles that undoubtedly were
protective and an aid to vision but did not permit
pressure equalization. The cylinder on the first Fernez-
Le Prieur model contained around 2000 psi of air and
permitted the wearer to remain less than 15 minutes in
the water. Improved models later supplied sufficient
air to permit the diver to remain for 30 minutes at
23 feet (7 meters) or 10 minutes at 40 feet (12 meters).
The major problem with Le Prieur's apparatus was the
lack of a demand valve, which necessitated a continu-
ous flow (and thus waste) of gas. In 1943, almost
20 years after Fernez and Le Prieur patented their
apparatus, two other French inventors, Emile Gagnan
and Captain Jacques- Yves Cousteau, demonstrated their
"Aqua Lung." This apparatus used a demand intake
valve drawing from two or three cylinders, each
containing over 2500 psig. Thus it was that the demand
regulator, invented over 70 years earlier by Rouquayrol
and Denayrouse and extensively used in aviation, came
into use in a self-contained breathing apparatus that
did not emit a wasteful flow of air during inhalation
NOAA Diving Manual — October 1991
History of Diving
Figure 1-5
Rouquayrol-Denayrouse Semi-Self-Contained
Diving Suit
Figure 1-6
Fernez-Le Prieur Self-Contained Diving Apparatus
Courtesy National Academy of Sciences
(although it continued to lose exhaled gas into the
water). This application made possible the develop-
ment of modern open-circuit air scuba gear (Larson
1959).
In 1939, Dr. Christian Lambertsen began the devel-
opment of a series of three patented forms of oxygen
rebreathing equipment for neutral buoyancy underwater
swimming, which became the first self-contained under-
water breathing apparatus successfully used by a large
number of divers. The Lambertsen Amphibious Res-
piratory Unit (LARU) (Figure 1-7) formed the basis
for the establishment of U.S. military self-contained
diving (Larson 1959).
This apparatus was designated scuba (for self-
contained underwater breathing apparatus) by its users.
Courtesy National Academy of Sciences
Equivalent self-contained apparatus was used by the
military forces of Italy, the United States, and Great
Britain during World War II and continues in active
use today. The rebreathing principle, which avoids
waste of gas supply, has been extended to include
forms of scuba that allow the use of mixed gas (nitrogen or
helium-oxygen mixtures) to increase depth and dura-
tion beyond the practical limits of air or pure oxygen
breathing (Larson 1959).
A major development in regard to mobility in diving
occurred in France during the 1930's: Commander de
Carlieu developed a set of swim fins, the first to be
produced since Borelli designed a pair of claw-like
fins in 1680. When used with Le Prieur's tanks, gog-
gles, and nose clip, de Carlieu's fins enabled divers to
move horizontally through the water like true swimmers,
instead of being lowered vertically in a diving bell or in
hard-hat gear. The later use of a single-lens face mask,
which allowed better visibility as well as pressure equali-
zation, also increased the comfort and depth range of
diving equipment.
Thus the development of scuba added a major work-
ing tool to the systems available to divers; the new
mode allowed divers greater freedom of movement and
access to greater depths for extended times and required
much less burdensome support equipment. Scuba also
enriched the world of sport diving by permitting
recreational divers to go beyond goggles and breath-
hold diving to more extended dives at greater depths.
October 1991 — NOAA Diving Manual
1-5
Section 1
Figure 1-7
World War II Military Swimmer Dressed in
Lambertsen Amphibious Respiratory Unit
Courtesy C. J. Lambertsen
1.5 SATURATION DIVING
Although the development of surface-supplied diving
permitted divers to spend a considerable amount of
working time under water, divers using surface-supplied
systems for deep and/or long dives incurred a substan-
1-6
tial decompression obligation in the course of such
dives. The initial development of saturation diving by
the U.S. Navy in the late 1950's and its extension by
naval, civilian government, university, and commer-
cial laboratories revolutionized scientific, commercial,
and military diving by providing a method that permits
divers to remain at pressures equivalent to depths of up
to 2000 feet (610 meters) for periods of weeks or
months without incurring a proportional decompres-
sion obligation.
Saturation diving takes advantage of the fact that a
diver's tissues become saturated once they have absorbed
all the nitrogen or other inert gas they can hold at that
particular depth; that is, they cannot absorb any addi-
tional gas. Once a diver's tissues are saturated, the
diver can remain at the saturation depth (or a depth
within an allowable excursion range up or down from
the saturation depth) as long as necessary without
proportionately increasing the amount of time required
for decompression.
Divers operating in the saturation mode work out of
a pressurized facility, such as a diving bell, seafloor
habitat, or diver lockout submersible. These subsea
facilities are maintained at the pressure of the depth at
which the diver will be working; this depth is termed
the saturation or storage depth.
The historical development of saturation diving
depended both on technological and scientific advances.
Engineers developed the technology essential to sup-
port the saturated diver, and physiologists and other
scientists defined the respiratory and other physiological
capabilities and limits of this mode. Many researchers
played essential roles in the development of the saturation
concept, but the U.S. Navy team working at the U.S.
Submarine Medical Research Laboratory in New
London, Connecticut, is generally given credit for making
the major initial breakthroughs in this field. This team
was led by two Navy diving medical officers, George
Bond and Robert Workman, who, in the period from
the mid-1 950's to 1962, supervised the painstaking
animal tests and volunteer human dives that provided
the scientific evidence necessary to confirm the valid-
ity of the saturation concept (Lambertsen 1967).
1.5.1 Saturation Diving Systems
The earliest saturation dive performed in the open
sea was conducted by the Link group and involved the
use of a diving bell for diving and for decompression.
Initial Navy efforts involved placing a saturation hab-
itat on the seafloor. In 1964, Edwin Link, Christian
Lambertsen, and James Lawrie developed the first
deck decompression chamber, which allowed divers in
NOAA Diving Manual — October 1991
History of Diving
a sealed bell to be locked into a pressurized environ-
ment at the surface for the slow decompression from
saturation. The first commercial application of this
form of saturation diving took place on the Smith
Mountain Dam project in 1965 and involved the use of
a personnel transfer capsule. The techniques pioneered at
Smith Mountain have since become standard in com-
mercial diving operations: saturated divers live, under
pressure, in the deck decompression chamber on board
a surface vessel and are then transferred to the under-
water worksite in a pressurized personnel transfer cham-
ber (also called a surface decompression chamber)
(Lambertsen 1967). Although saturation diving sys-
tems are the most widely used saturation systems in
commercial diving today, two other diving technologies
also take advantage of the principle of saturation: habi-
tats and lockout submersibles.
1.5.2 Habitats
Habitats are seafloor laboratory/living quarters in
which saturated diver-scientists live and work under
pressure for extended periods of time. Habitat divers
dive from the surface and enter the habitat, or they
may be compressed in a pressure vessel on the surface
to the pressure of the habitat's storage depth and then
be transferred to the habitat. Decompression may take
place on the seafloor or in a surface decompression
chamber after the completion of the divers' work. The
most famous and widely used habitat was NOAA's
Hydrolab, which was based in the Bahamas and Car-
ibbean from 1972 to 1985 and provided a base for more
than 600 researchers from 9 countries during that
time. In 1985, the Hydrolab was retired from service
and now resides permanently in the Smithsonian Insti-
tution's National Museum of Natural History in Wash-
ington, D.C. The Aquarius, a more flexible and
technologically advanced habitat system, has replaced
the Hydrolab as NOAA's principal seafloor research
laboratory. (See Section 17 for a more detailed discus-
sion of habitat-based in-situ research programs.)
1.5.3 Lockout Submersibles
Lockout submersibles provide an alternative method
for diver/scientists to gain access to the underwater
environment. Lockout submersibles are dual-purpose
vehicles that permit the submersible's pilot/driver and
crew to remain at surface pressure (i.e., at a pressure of
1 atmosphere), while the diver-scientist is pressurized
in a separate compartment to the pressure of the depth
at which he or she will be working. The lockout com-
partment thus serves in effect as a personnel transfer
capsule, transporting the diver to and from the seafloor.
The Johnson Sea-Link, which can be pressurized to
2000 fsw (610 msw), has played a central role in NOAA's
undersea research program for years, particularly in
pollution and fisheries research off the Atlantic coast.
1.6 SUMMARY
Humans have explored the ocean depths at least since
the fifth millennium B.C., and the development of the
diving techniques and systems described in this sec-
tion reflects mankind's drive for mastery over all aspects
of the environment. The search for methods that will
allow humans to live comfortably in the marine bio-
sphere for long periods of time continues today, as
engineers and scientists work together to make access
to the sea safer, easier, and more economical.
October 1991 — NOAA Diving Manual
1-7
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SECTION 2
PHYSICS
OF
DIVING
Page
2.0 General 2-1
2.1 Definitions 2-1
2.1.1 Pressure 2-1
2.1.2 Temperature 2-1
2.1.3 Density 2-1
2.1.4 Specific Gravity 2-1
2.1.5 Seawater 2-1
2.2 Pressure 2-2
2.2.1 Atmospheric Pressure 2-2
2.2.2 Hydrostatic Pressure 2-2
2.2.3 Absolute Pressure 2-2
2.2.4 Gauge Pressure 2-3
2.2.5 Partial Pressure 2-3
2.3 Buoyancy 2-3
2.4 Gases Used in Diving 2-6
2.4.1 Air 2-6
2.4.2 Oxygen 2-6
2.4.3 Nitrogen 2-6
2.4.4 Helium 2-6
2.4.5 Carbon Dioxide 2-6
2.4.6 Carbon Monoxide 2-6
2.4.7 Argon, Neon, Hydrogen 2-7
2.5 Gas Laws 2-7
2.5.1 Dalton's Law 2-7
2.5.2 Boyle's Law 2-8
2.5.3 Charles' Law 2-10
2.5.4 Henry's Law 2-1 1
2.5.5 The General Gas Law 2-11
Gas Flow (Viscosity) 2-12
Moisture in Breathing Gas 2-12
2.7.1 Condensation in Breathing Tubes or Mask 2-13
2.7.2 Fogging of the Mask 2-13
Light and Vision Under Water 2-13
2.8.1 The Physics of Light Under Water and the
Consequences for Vision 2-13
2.8.1.1 Refraction 2-13
2.8.1.2 Scatter 2-14
2.8.1.3 Absorption 2-14
2.8.1.4 Insufficient Light 2-15
2.9 Acoustics 2-16
2.6
2.7
2.8
(
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2.0 GENERAL
This section describes the laws of physics as they affect
humans in the water. A thorough understanding of the
physical principles set forth in the following paragraphs is
essential to safe and effective diving performance.
2.1 DEFINITIONS
This paragraph defines the basic principles necessary
to an understanding of the underwater environment.
The most important of these are listed below.
PHYSICS
OF
DIVING
Kelvin (K) = X plus 273.15
Rankine (R) = °F plus 459.67
Temperatures measured in centigrade may be converted
to Fahrenheit using the following formula:
°F = (1.8 X X) + 32
Temperatures measured in Fahrenheit may be converted
to centigrade using the following formula:
C
(°F - 32)
2.1.1 Pressure
Pressure is force acting on a unit area. Expressed
mathematically:
Pressure =
Force
Area
or
P =
Pressure is usually expressed in pounds per square inch
(psi) or kilograms per square centimeter (kg/cm2).
2.1.2 Temperature
Heat is a form of energy that increases the tempera-
ture of the substance or matter to which it is added and
decreases the temperature of the matter from which it
is removed, providing that the matter does not change
state during the process. Quantities of heat are measured
in calories or British thermal units (Btu).
The temperature of a body is a measure of its heat.
Temperature is produced by the average kinetic energy or
speed of the body's molecules, and it is measured by a
thermometer and expressed in degrees centigrade (°C)
or Fahrenheit (°F). The quantity of heat in the body is
equal to the total kinetic energy of all of its molecules.
Temperature values must be converted to absolute
values for use with the Gas Laws. Both the Kelvin and
Rankine scales are absolute temperature scales. Abso-
lute zero is the hypothetical temperature characterized
by the complete absence of heat; it is equivalent to
approximately -273 °C or -460 'F. Conversion to the
Kelvin or Rankine scales is done by adding 273 units to
the temperature value expressed in centigrade or 460
units to the temperature value expressed in Fahrenheit,
respectively.
2.1.3 Density
Density is mass per unit volume. Expressed mathe-
matically:
Density (D) =
Mass
Volume
Density is usually stated in pounds per cubic foot (lb/ft3)
in the English system and in grams per cubic centi-
meter (gm/cm3) in the metric system.
2.1.4 Specific Gravity
Specific gravity is the ratio of the density of a sub-
stance to the density of fresh water at 39.2 °F (4°C).
Fresh water has a specific gravity of 1.0 at 39.2° F
(4°C); substances heavier than fresh water have spe-
cific gravities greater than 1.0, and substances lighter
than fresh water have specific gravities less than 1.0. The
human body has a specific gravity of approximately
1.0, although this varies slightly from one person to
another.
2.1.5 Seawater
Seawater is known to contain at least 75 elements
that occur in nature. The four most abundant elements in
seawater are oxygen, hydrogen, chlorine, and sodium.
Seawater is always slightly alkaline because it con-
tains several alkaline earth minerals, principally sodi-
um, calcium, magnesium, and potassium. The tempera-
ture of seawater varies from 30.2T to 86.0°F (-IX to
30°C).
October 1991 — NOAA Diving Manual
2-1
Section 2
Table 2-1
Conversion Factors, Metric to English Units
The specific gravity of seawater is affected both by
salinity and temperature, and these effects are in-
terrelated. For example, water with a high enough
salt content to sink toward the bottom will float at the
surface if the water is sufficiently warm. Conversely,
water with a relatively low salt content will sink if it is
sufficiently chilled. Seawater also is an excellent elec-
trical conductor, an interaction that causes corrosion
problems when equipment is used in or near the ocean.
The viscosity of seawater varies inversely with tem-
perature and is nearly twice as great at 33.8 °F (1°C)
as at 89.6 °F (32 °C). The impact of this property can
be seen when the same sailboat is able to achieve
higher speeds in warm water than in cold.
In many parts of the world the metric system of
measurement is used rather than the English system
still widely used in the United States. Table 2-1 pres-
ents factors for converting metric to English units.
2.2 PRESSURE
The pressure on a diver under water is the result of two
forces: the weight of the water over him or her and the
weight of the atmosphere over the water. Table 2-2
provides factors for converting various barometric pres-
sure units into other pressure units. The various types
of pressure experienced by divers are discussed in the
following sections.
2.2.1 Atmospheric Pressure
Atmospheric pressure acts on all bodies and struc-
tures in the atmosphere and is produced by the weight
of atmospheric gases. Atmospheric pressure acts in all
directions at any specific point. Since it is equal in all
directions, its effects are usually neutralized. At sea
level, atmospheric pressure is equal to 14.7 psi or
1.03 kg/cm2. At higher elevations, this value decreases.
Pressures above 14.7 psi (1.03 kg/cm2) are often
expressed in atmospheres. For example, one atmosphere
is equal to 14.7 psi, 10 atmospheres is equal to 147 psi,
and 100 atmospheres is equal to 1470 psi. Figure 2-1
shows equivalent pressures in the most commonly used
units for measuring pressure at both altitude and depth.
2.2.2 Hydrostatic Pressure
Hydrostatic pressure is produced by the weight of
water (or any fluid) and acts on all bodies and struc-
tures immersed in the water (or fluid). Like atmospheric
pressure, hydrostatic pressure is equal in all directions
at a specific depth. The most important form of pres-
sure to divers is hydrostatic pressure. It increases at a
rate of 0.445 psi per foot (1 kg/cm2 per 9.75 meters) of
To Convert
From
Metric Units
To English Units
Multiply By
PRESSURE
1 gm/cm2
1 kg/cm2
1 kg/cm2
1 kg/cm2
1 cm Hg
1 cm Hg
1 cm Hg
1 cm Hg
1 cm of fresh water
inch of fresh water
pounds/square inch (psi)
feet of fresh water (ffw)
inches of mercury (in. Hg)
pound/square inch
foot of fresh water
foot of seawater (fsw)
inch of mercury
inch of fresh water
0.394
14.22
32.8
28.96
0.193
0.447
0.434
0.394
0.394
VOLUME AND CAPACITY
1 cc or ml
1 m3
1 liter
1 liter
1 liter
1 liter
cubic inch (cu in.)
cubic feet (cu ft)
cubic inches
cubic foot
fluid ounces (fl oz)
quarts (qt)
0.061
35.31
61.02
0.035
33.81
1.057
WEIGHT
1 gram
1kg
1kg
ounce (oz)
ounces
pounds (lb)
0.035
35.27
2.205
LENGTH
1 cm
1 meter
1 meter
1 km
inch
inches
feet
mile
0.394
39.37
3.28
0.621
AREA
1 cm2
1 m2
1 km2
square inch
square feet
square mile
0.155
10.76
0.386
Adapted from NOAA (1979)
descent in seawater and 0.432 psi per foot (1 kg/cm2
per 10 meters) of descent in fresh water. This relation-
ship is shown graphically in Figure 2-2.
2.2.3 Absolute Pressure
Absolute pressure is the sum of the atmospheric
pressure and the hydrostatic pressure exerted on a
2-2
NOAA Diving Manual — October 1991
Physics of Diving
Table 2-2
Conversion Table for Barometric Pressure Units
atm
N/m2 or
Pa
bars
mb
kg/cm2
gm/cm2
(cm H20)
mm Hg
in. Hg
("Hg)
lb/in2
(psi)
1 atmosphere
=
1
1.013X105
1.013
1013
1.033
1033
760
29.92
14.70
1 Newton (N)/m2 or
Pascal (Pa)
=
9869X10"5
1
105
.01
1.02X10'5
.0102
.0075
2953X10"3
.1451X10"3
1 bar
=
.9869
105
1
1000
1.02
1020
750.1
29.53
14.51
1 millibar
(mb)
=
9869X10"3
100
.001
1
.00102
1.02
.7501
.02953
.01451
1 kg/cm2
=
.9681
9807X105
.9807
980.7
1
1000
735
28.94
14.22
1 gm/cm2
(1 cm H20)
=
968.1
98.07
9807X10'3
.9807
.001
1
.735
.02894
.01422
1 mm Hg
=
.001316
133.3
.001333
1.333
.00136
1.36
1
.03937
.01934
1 in. Hg
=
.0334
3386
.03386
33.86
.03453
34.53
25.4
1
.4910
1 lb/in2 (psi)
=
.06804
6895
.06895
68.95
.0703
70.3
51.70
2.035
1
Adapted from NOAA (1979)
submerged body. Absolute pressure is measured in
pounds per square inch absolute (psia) or kilograms
per square centimeter absolute (kg/cm2 absolute).
2.2.4 Gauge Pressure
Gauge pressure is the difference between absolute
pressure and a specific pressure being measured.
Pressures are usually measured with gauges that are
balanced to read zero at sea level when they are open
to the air. Gauge pressure is therefore converted to
absolute pressure by adding 14.7 if the dial reads in
psi or 1.03 if the dial reads in kg/cm2.
2.2.5 Partial Pressure
In a mixture of gases, the proportion of the total
pressure contributed by a single gas in the mixture is
called the partial pressure. The partial pressure con-
tributed by a single gas is in direct proportion to its
percentage of the total volume of the mixture (see
Section 2.5.1).
2.3 BUOYANCY
Archimedes' Principle explains the nature of buoyancy.
A body immersed in a liquid, either wholly
or partially, is buoyed up by a force equal
to the weight of the liquid displaced by
the body.
Using Archimedes' Principle, the buoyancy or buoyant
force of a submerged body can be calculated by
subtracting the weight of the submerged body from the
weight of the displaced liquid. If the total displace-
ment, that is, the weight of the displaced liquid, is
greater than the weight of the submerged body, the
buoyancy will be positive and the body will float or be
buoyed upward. If the weight of the body is equal to
that of the displaced liquid, the buoyancy will be neu-
tral and the body will remain suspended in the liquid.
If the weight of the submerged body is greater than
that of the displaced liquid, the buoyancy will be negative
and the body will sink.
The buoyant force of a liquid is dependent on its
density, that is, its weight per unit volume. Fresh water
has a density of 62.4 pounds per cubic foot (28.3 kg/
0.03 m3). Seawater is heavier, having a density of 64.0
pounds per cubic foot (29 kg/0.03 m3). Therefore, a
body in seawater will be buoyed up by a greater force
than a body in fresh water, which accounts for the fact
that it is easier to float in the ocean than in a fresh
water lake.
Lung capacity can have a significant effect on the
buoyancy of a submerged person. A diver with full
lungs displaces a greater volume of water and there-
fore is more buoyant than a diver with deflated lungs.
Other individual differences that may affect buoyancy
include bone structure, bone weight, and relative amount
of body fat. These differences help to explain why
certain individuals float easily and others do not.
October 1991 — NOAA Diving Manual
2-3
Section 2
Figure 2-1
Equivalent Pressures, Altitudes, and Depths
Atmospheres (atm)
I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
.0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1.0
Pounds Per Square Inch (psi)
I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — I — i— n
0 2 4 6 8 10 12 14 14.7
Inches of Mercury (in Hg)
i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — n
0 5 10 15 20 25 29.92
Millimeters of Mercury (mm Hg)
i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — i — m
0 100 200 300 400 500 600 700 760
+
Millibars (mb)
I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 P 1
0 100 200 300 400 500 600 700 800 900 1013.2
Newtons Per Square Meter x104(n/m2x104)
I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 P 1
0123456789 10.13
Pressure Altitude Thousands of Feet
iii i i i mi i i i i i i i i i — i — i — i — i — i — i — i 1 i i i i — n — i — i — i — i
100 60 50 40 30 20 10 5 0
30 20 15 10 8 6 3 2 10
Ll_l I I I I I I I I I I I I I I I I
Thousands of Meters
Atmospheres Absolute (ATA)
I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
0123456789 10
Depth in Seawater Meters
I 1 1 1 1 1 1 1 1 1
0 20 40 60 80
0 50 100 150 200 250 300
I ■ I I I I I I I I I
Feet
Adapted from National Aeronautics and Space Administration (1973)
2-4 NOAA Diving Manual — October 1991
Physics of Diving
>
Figure 2-2
Effects of Hydrostatic Pressure
At the Surface
Atmosphere Absolute, 14.7 psi
The flotation device is fully expanded.
■in
At 33 Feet
2 Atmospheres Absolute, 29.4
{Vi Surface Volume) Because of hydrosta
pressure, the same volume of air in
flotation device is reduced to only Vi
surface lifting capacity
psi '
tic
the
Vi its
At 1 32 Feet
5 Atmospheres Absolute, 73.5 psi
XA Surface Volume) Because of hydrostatic
pressure, the same volume of air in the
flotation device is reduced to only Vi its
surface lifting capacity.
October 1991 — NOAA Diving Manual
Adapted from NOAA (1979)
2-5
Section 2
Divers wearing wet suits usually must add diving
weights to their weight belts to provide the negative
buoyancy that allows normal descent. At working depth,
the diver should adjust his or her buoyancy to achieve a
neutral state so that work can be accomplished without
the additional physical effort of counteracting positive
(upward) or negative (downward) buoyancy.
2.4 GASES USED IN DIVING
While under water, a diver is totally dependent on a
supply of breathing gas. Two methods of providing
breathing gases can be used. The diver may be supplied
with gas via an umbilical from the surface or a sub-
merged source, or he or she may carry the breathing
gas supply. The second method is called scuba, an
initialism for "Self-Contained Underwater Breathing
Apparatus."
Many combinations of breathing gases are used in
diving. Compressed air is the most common, but the
use of other mixtures for special diving situations is
increasing. The following paragraphs describe the gases
most commonly found in diving operations.
2.4.1 Air
Air is a mixture of gases (and vapors) containing
nitrogen (78.084%), oxygen (20.946%), argon (0.934%),
carbon dioxide (0.033%), and other gases (0.003%).
Compressed air is the most commonly used breathing
gas for diving (see Section 4).
2.4.2 Oxygen
Oxygen is a colorless, odorless, and tasteless gas that
is only slightly soluble in water. It can be liquefied at
-297. 4°F (-183°C) at atmospheric pressure and will
solidify when cooled to -361.1 T (-218.4°C). Oxygen
is the only gas used by the human body, and it is
essential to life. The other gases breathed from the
atmosphere or breathed by divers in their gas mixtures
serve only as vehicles and diluents for oxygen. However,
oxygen is dangerous when excessive amounts are
breathed under pressure; this harmful effect is called
oxygen poisoning (see Section 3.3).
2.4.3 Nitrogen
Nitrogen is a colorless, odorless, and tasteless gas. It
is chemically inert and is incapable of supporting life.
Its boiling point is -320. 8°F (-196°C). Nitrogen is
commonly used as a diluent for oxygen in diving gas
mixtures but has several disadvantages compared with
2-6
some other diving gases. For example, when nitrogen is
breathed at increased partial pressures, it has a dis-
tinct anesthetic effect called "nitrogen narcosis," a
condition characterized by loss of judgment and
disorientation (see Section 3.2.3.5).
2.4.4 Helium
Helium is found in the atmosphere only in trace
amounts. It has the lowest boiling point of any known
substance, -452.02°F (-268. 9°C). Helium is color-
less, odorless, and tasteless and is used extensively as a
diluent for oxygen in deep diving gas mixtures. Helium
has some disadvantages but none as serious as those
associated with nitrogen. For example, breathing helium-
oxygen mixtures causes a temporary distortion of speech
(producing a Donald Duck-like voice), which hinders
communication. Helium also has high thermal con-
ductivity, which causes rapid loss of body heat in divers
breathing a helium mixture. Helium is used in breath-
ing mixtures at depth because of its lower density and
lack of narcotic effect. However, helium should never
be used in diving or treatment without a full under-
standing of its physiological implications.
2.4.5 Carbon Dioxide
Carbon dioxide (C02) is a gas produced by various
natural processes such as animal metabolism, combus-
tion, and fermentation. It is colorless, odorless, and
tasteless. Although carbon dioxide generally is not
considered poisonous, in excessive amounts it is harm-
ful to divers and can even cause convulsions. Breathing
C02 at increased partial pressure may cause uncon-
sciousness (see Sections 3.1.3.2 and 20.4.1). For example,
a person should not breathe air containing more than
0.10 percent C02 by volume (see Table 15-3); divers
must therefore be concerned with the partial pressure
of the carbon dioxide in their breathing gases. In the
case of closed- and semi-closed-circuit breathing
systems, the removal of the excess C02 generated by
the diver's breathing is essential to diving safety
(see Sections 15.5.1.2 and 15.5.1.3).
2.4.6 Carbon Monoxide
Carbon monoxide (CO) is a poisonous gas. It is color-
less, odorless, and tasteless and therefore difficult to
detect. Carbon monoxide is produced by the incom-
plete combustion of hydrocarbons, which occurs in the
exhaust systems of internal combustion engines. Car-
bon monoxide may also be produced by over-heated
oil-lubricated compressors. A level of 20 parts per
NOAA Diving Manual — October 1991
Physics of Diving
million of CO should not be exceeded in pressurized
breathing systems (see Table 15-3). When scuba cyl-
inders are filled, care should be taken not to introduce
CO from the exhaust system of the air compressor into
the breathing gases. Proper precautions must be taken
to ensure that all areas where cylinders are filled are
adequately ventilated. The compressor's air intake must
draw from an area where the atmosphere is free of
contamination, such as automobile exhaust fumes.
2.4.7 Argon, Neon, Hydrogen
Argon, neon, and hydrogen have been used experi-
mentally as diluents for oxygen in breathing gas mix-
tures, although these gases are not used routinely in
diving operations. However, the results of recent research
suggest that hydrogen-oxygen and helium-hydrogen-
oxygen breathing mixtures may be used within the
next decade in deep diving operations (Peter Edel,
personal communication).
2.5 GAS LAWS
The behavior of all gases is affected by three factors:
the temperature of the gas, the pressure of the gas, and
the volume of the gas. The relationships among these
three factors have been defined in what are called the
Gas Laws. Five of these, Dalton's Law, Boyle's Law,
Charles' Law, Henry's Law, and the General Gas Law,
are of special importance to the diver.
2.5.1 Dalton's Law
Dalton's Law states:
The total pressure exerted by a mixture of
gases is equal to the sum of the pressures
that would be exerted by each of the gases
if it alone were present and occupied the
total volume.
In a gas mixture, the portion of the total pressure
contributed by a single gas is called the partial pres-
sure of that gas. Stated mathematically:
PTotal = PPl + PP2 + PPn
where
PTolal = total pressure of that gas
Ppi = partial pressure of gas component l
Pp2 = partial pressure of gas component 2
Ppn = partial pressure of other gas components.
An easily understood example is that of a container
at atmospheric pressure, 14.7 psi (l kg/cm2). If the
container were filled with oxygen alone, the partial
pressure of the oxygen would be l atmosphere. If the
same container were filled with air, the partial pres-
sures of each of the gases comprising air would con-
tribute to the total pressure, as shown in the following
tabulation:
Percent of Component x Total Pressure (Absolute)
= Partial Pressure
Gas
Percent of
component
Atmospheres
partial pressure
N2
o2
co2
Other
78.08
20.95
.03
.94
0.7808
.2095
.0003
.0094
Total
100.00
1.0000
Example 1
If the same container, for example a scuba cylinder,
were filled with air to 2000 psi, the following steps
would be necessary to calculate the partial pressures
(in ATA's) of the same components listed in the above
table.
Step 1 — Dalton's Law
Percent of component gas X total pressure (abso-
lute) = partial pressure
Percent of com
ponents:
N2
78.08%
.7808 N2
100
o2
20.95%
.2095 02
100
co2
00.03%
.0003 C02
100
Other
00.94%
.0094 Other
100
Step 2 — Convert 2000 psi to atmospheres absolute
(ATA)
(2000 psi)
+ 1 = ATA
14.7 psi
136 + 1 = 137 ATA
October 1991 — NOAA Diving Manual
2-7
Section 2
Step 3 — Partial pressure of constituents at 137 ATA
PpN = 0.7808 X 137 = 106.97 ATA
Pp0 = 0.2095 X 137 = 28.70 ATA
Ppco = 0.0003 X 137 = 0.04 ATA
pP0ther = 00094 X 137 = 1.29 ATA
Observe that the partial pressures of some compo-
nents of the gas, particularly C02, increased significantly
at higher pressures, although they were fairly low at
atmospheric pressure. As these examples show, the
implications of Dalton's Law are important and should
be understood by all divers.
Step 2 — Boyle's Law (at 33 feet of water):
P2V2 = K
P2 = pressure at 33 feet in ATA
V2 = volume at 33 feet in ft3
K = constant.
Step 3 — Equating the constant, K, at the surface and
at 33 feet, we have the following equation:
P.V, = p2v2
Transposing to determine the volume at 33 feet:
P.V,
(
where
2.5.2 Boyle's Law
Boyle's Law states:
At constant temperature, the volume of a
gas varies inversely with absolute pressure,
while the density of a gas varies directly
with absolute pressure (Figure 2-3).
For any gas at a constant temperature, Boyle's Law is:
PV = K
where
P1 = 1 atmosphere (ATA)
V, = 24 ft3
v2 =
2 ATA
24 ft3
1 ATA X 24 ft3
2 ATA
V2 = 12 ft3.
Note that the volume of air in the open bell has been
compressed from 24 to 12 cubic feet in the first 33
feet of seawater.
(
P = absolute pressure
V = volume
K = constant.
Boyle's Law is important to divers because it relates
changes in the volume of a gas to changes in pressure
(depth) and defines the relationship between pressure
and volume in breathing gas supplies. The following
example illustrates Boyle's Law.
Example 1 (Boyle's Law)
An open diving bell with a volume of 24 cubic feet is
to be lowered into the sea from a surface support ship.
No air is supplied to or lost from the bell, and the
temperature is the same at all depths. Calculate the
volume of the air space in the bell at the 33-foot,
66-foot, and 99-foot depths.
Step 1 — Boyle's Law (at surface):
P,V, =K
P( = pressure at surface in ATA
V, = volume at surface in ft3
K = constant.
Step 4 — Using the method illustrated above to deter-
mine the air volume at 66 feet:
P]V,
where
P, = 3 ATA
v3-
1 ATA X 24 ft3
3 ATA
V3 = 8 ft3 .
Step 5 — For a 99-foot depth, using the method illus-
trated previously, the air volume would be:
v4 =
PlV,
where
p4 = 4 ATA
V, = 6 ft3 .
<
2-8
NOAA Diving Manual — October 1991
Physics of Diving
>
Figure 2-3
Boyle's Law
October 1991 — NOAA Diving Manual
Adapted from NOAA (1979)
2-9
Section 2
As depth increased from the surface to 99 feet, the
volume of air in the open bell was compressed from
24 cubic feet to 6 cubic feet.
In this example of Boyle's Law, the temperature of
the gas was considered a constant value. However,
temperature significantly affects the pressure and volume
of a gas; it is therefore essential to have a method of
including this effect in calculations of pressure and
volume. To a diver, knowing the effect of temperature
is essential, because the temperature of the water deep
in the oceans or in lakes is often significantly different
from the temperature of the air at the surface. The gas
law that describes the physical effects of temperature
on pressure and volume is Charles' Law.
Because the volume of the closed bell is the same at the
surface as it is at 99 feet, the decrease in the pressure is
a result of the change in temperature. Therefore, using
Charles' Law:
(volume constant)
where
Pj = 14.7 psia (atmospheric pressure)
T, = 80°F + 460°F = 540 Rankine
T7 = 33 °F + 460° F = 493 Rankine.
2.5.3 Charles' Law
Charles' Law states:
At a constant pressure, the volume of a
gas varies directly with absolute temper-
ature. For any gas at a constant volume,
the pressure of a gas varies directly with
absolute temperature.
Stated mathematically:
(volume constant)
Transposing:
P2 =
P.T2
T,
P, _
14.7 X 493
r2 —
540
P2 =
13.42 psia.
Note that the final pressure is below atmospheric
pressure (14.7 psia) because of the drop in temperature.
V, T,
— = — (pressure constant)
where
P( = initial pressure (absolute)
P2 = final pressure (absolute)
Tj = initial pressure (absolute)
T2 = final pressure (absolute)
V, = initial volume
V2 = final volume.
To illustrate Charles' Law, an example similar to the
one given for Boyle's Law can be used.
Example 2 (Charles' Law)
A closed diving bell at atmospheric pressure and
having a capacity of 24 cubic feet is lowered from the
surface to a depth of 99 feet in the ocean. At the
surface, the temperature is 80 °F; at 99 feet, the tem-
perature is 33 °F. Calculate the pressure on the bell
when it is at the 99-foot level and the temperature is
33°F.
Example 3 (Charles' Law)
To illustrate Charles' Law further, consider the fol-
lowing example:
An open diving bell having a capacity of 24 cubic feet
is lowered into the ocean to a depth of 99 feet. At the
surface, the temperature is 80 °F; at depth, the temper-
ature is 45 ° F. What is the volume of the gas in the bell at
99 feet?
From Example 1 illustrating Boyle's Law, we know
that the volume of the gas was compressed to 6 cubic
feet when the bell was lowered to the 99-foot level.
Applying Charles' Law then illustrates the additional
reduction in volume caused by temperature effects:
where
Vj = volume at depth, 6 ft3
T, = 80 °F + 460 °F = 540 Rankine
T2 = 45 °F + 460 °F = 505 Rankine.
2-10
NOAA Diving Manual — October 1991
Physics of Diving
Transposing:
V —
V,T2
v2
T,
V —
6 X 505
540
V, =
5.61 ft3 .
2.5.5 The General Gas Law
Boyle's and Charles' laws can be conveniently com-
bined into what is known as the General Gas Law,
expressed mathematically as follows:
P.V,
P,V,
where
2.5.4 Henry's Law
Henry's Law states:
The amount of any given gas that will
dissolve in a liquid at a given temperature
is a function of the partial pressure of the
gas that is in contact with the liquid and the
solubility coefficient of the gas in the
particular liquid.
This law simply states that, because a large percentage
of the human body is water, more gas will dissolve into
the blood and body tissues as depth increases, until
the point of saturation is reached. Depending on the
gas, saturation takes from 8 to 24 hours or longer. As
long as the pressure is maintained, and regardless of
the quantity of gas that has dissolved into the diver's
tissues, the gas will remain in solution.
A simple example of the way in which Henry's Law
works can be seen when a bottle of carbonated soda is
opened. Opening the container releases the pressure
suddenly, causing the gases in solution to come out of
solution and to form bubbles. This is similar to what
happens in a diver's tissues if the prescribed ascent
rate is exceeded. The significance of this phenomenon
for divers is developed fully in the discussion of decom-
pression (see Section 3.2.3.2).
The formula for Henry's Law is:
VG
= aP,
VL
where
VG = volume of gas dissolved at STP
(standard temperature and pressure)
VL = volume of the liquid
a = Bunson solubility coefficient at specified
temperatures
P| = partial pressure in atmospheres of that
gas above the liquid.
P, = initial pressure (absolute)
V, = initial volume
T| = initial temperature (absolute)
and
P2 = final pressure (absolute)
V2 = final volume
Tt = final temperature (absolute).
Example 4 (General Gas Law)
Let us again consider an open diving bell having a
capacity of 24 cubic feet that is being lowered to
99 feet in seawater from a surface temperature of 80 °F to
a depth temperature of 45 °F. Determine the volume of
the gas in the bell at depth.
The General Gas Law states:
P,V,
p2v2
T,
where
P, = 14.7 psia
V, = 24 ft3
T, = 80°F + 460°F = 540 Rankine
P2 = 58.8 psia
T2 = 45 °F + 460 °F = 505 Rankine.
Transposing:
V, =
V,
PiV.T2
T,P,
(14.7X24X505)
(540)(58.8)
V, = 5.61 ft3.
October 1991 — NOAA Diving Manual
2-11
Section 2
Figure 2-4
Gas Laws
This is the same answer as that derived from a com-
bination of Example 1 and Example 3, which were used
to demonstrate Boyle's and Charles' Laws. Figure 2-4
illustrates the interrelationships among Boyle's Law,
Charles' Law, and the General Gas Law.
2.6 GAS FLOW (VISCOSITY)
There are occasions when it is desirable to determine
the rate at which gas flows through orifices, hoses, and
other limiting enclosures. This can be approximated
for a given gas by employing Poiseuille's equation for
gases, which is expressed mathematically as:
V =
APr47r
8Lt7
where
V = gas flow, in cm3 • sec1
AP = pressure gradient between 2 ends of
tube, in dynes • cm-2
r = radius of tube, in cm
L = length of tube, in cm
■t] = viscosity, in poise.
This equation can be used only in relatively simple
systems that involve laminar flow and do not include a
number of valves or restrictions. For practical applica-
tions, the diver should note that, as resistance increases,
flow decreases in direct proportion. Therefore, if the
length of a line is increased, the pressure must be
increased to maintain the same flow. Nomograms for
flow resistance through diving hoses can be found in
Volume 2 of the US Navy Diving Manual (1987).
2.7 MOISTURE IN BREATHING GAS
Breathing gas must have sufficient moisture to be com-
fortable for the diver to breathe. Too much moisture in
a system can increase breathing resistance and pro-
duce congestion; too little can cause an uncomfortable
sensation of dehydration in the diver's mouth, throat,
nasal passages, and sinus cavities (U.S. Navy 1988).
Air or other breathing gases supplied from surface
compressors or tanks can be assumed to be dry. This
dryness can be reduced by removing the mouthpiece
and rinsing the mouth with water or by having the
diver introduce a small amount of water into his or her
throat inside a full face mask. The use of gum or candy
2-12
(
Note: Effects of gravity
and water vapor are not
considered in the illustration
because they are so sma
I ATM
80°F
60°F
40°F
l
2
3
20-0
19. 3
18.5
2 ATM
r
4
5
9.3
6
10.0
9.6
(
3 ATM
7
8
9
6.6
6.4
1 r
6.2
Instructions:
(1) A uniform bore sealed-end tube with 20 divisions is in-
verted in a container of water at 80 degrees F and
one atmosphere pressure. The conditions of
temperature and pressure are then changed as il-
lustrated to explain the three gas laws.
(2) Steps 1,2,3; 4,5,6; 7,8,9 (horizontally) illustrate Charles'
Law, i.e., the reduction of volume with reduction in
temperature at a constant pressure.
(3) Steps 1,4,7; 2,5,8; 3,6,9 (vertically) illustrate Boyle's Law,
i.e., at a constant temperature the volume is inversely
related to the pressure.
Steps 1,5,9; 3,5,7 (diagonally) illustrate the General
Gas Law i.e., a combination of Charles's and Boyle's
Laws.
Adapted from NO A A (1979)
NOAA Diving Manual — October 1991
(4)
(
Physics of Diving
Figure 2-5
Objects Under Water Appear Closer
to reduce dryness while diving can be dangerous, because
these items may become lodged in the diver's throat.
The mouthpiece should not be removed in water that
may be polluted (see Section 1 1).
2.7.1 Condensation in Breathing Tubes or Mask
Expired gas contains moisture that may condense in
the breathing tubes or mask. This water is easily blown
out through the exhaust valve and generally presents
no problem. However, in very cold water the condensate
may freeze; if this freezing becomes serious enough to
block the regulator mechanism, the dive should be
aborted.
2.7.2 Fogging of the Mask
Condensation of expired moisture or evaporation
from the skin may cause fogging of the face mask glass.
Moistening the glass with saliva, liquid soap, or
commercially available anti-fog compounds will reduce
or prevent this difficulty. However, it should be noted
that some of the ingredients in chemical defogging
agents can cause keratitis (inflammation of the cor-
nea) if improperly used. Wright (1982) has described
two such cases; symptoms included severe burning,
photophobia, tearing, and loss of vision, which Wright
attributed to the use of excessive quantities of the
defogging solution and inadequate rinsing of the mask.
Rays passing from water into air are retracted away from the
normal, since the refractive index of water is 1.33 times that of
air. The lens system of the eye (omitted for simplicity) forms a
real inverted image on the retina, corresponding to that of an
object at about three-quarters of its physical distance from the
air-water interface. The angle subtended by the image is thus 4/3
larger than in air. Source: NOAA (1979)
2.8 LIGHT AND VISION UNDER WATER
2.8.1 The Physics of Light Under Water and
the Consequences for Vision
To function effectively under water, divers must
understand the changes that occur in their visual per-
ception under water. Many of these changes are caused
simply by the fact that light, the stimulus for vision,
travels through water rather than air; consequently it
is refracted, absorbed, and scattered differently than
in air. Refraction, absorption, and scatter all follow
physical laws and their effects on light can be predicted;
this changed physical stimulus can in turn have pro-
nounced effects on our perception of the underwater
world. Both the physical changes and their effects on
vision are described in detail in Kinney (1985) and are
only summarized here.
2.8.1.1 Refraction
In refraction, the light rays are bent as they pass
from one medium to another of different density. In
October 1991 — NOAA Diving Manual
diving, the refraction occurs at the interface between
the air in the diver's mask and the water. The refracted
image of an underwater object (see Figure 2-5) is
magnified, appears larger than the real image, and
seems to be positioned at a point three-fourths of the
actual distance between the object and the diver's
faceplate.
This displacement of the optical image might be
expected to cause objects to appear closer to the diver
than they actually are and, under some conditions,
objects do indeed appear to be located at a point three-
fourths of their actual distance from the diver. This
distortion interferes with hand-eye coordination and
accounts for the difficulty often experienced by novice
divers attempting to grasp objects under water. At
greater distances, however, this phenomenon may reverse
itself, with distant objects appearing farther away than
they actually are. The clarity of the water has a pro-
found influence on judgments of depth: the more tur-
bid the water, the shorter the distance at which the
reversal from underestimation to overestimation occurs
(Ferris 1972). For example, in highly turbid water, the
2-13
Section 2
distance of objects at 3 or 4 feet (0.9 or 1.2 m) may be
overestimated; in moderately turbid water, the change
might occur at 20 to 25 feet (6.1 to 7.6 m); and in very
clear water, objects as far away as 50 to 75 feet (15.2 to
22.9 m) might be wmferestimated.
It is important for the diver to realize that judgments
of depth and distance are probably inaccurate. As a
rough rule of thumb, the closer the object, the more
likely it will appear too close, and the more turbid the
water, the greater the tendency to see it as too far away.
Training to overcome inaccurate distance judgments
can be effective, but it is important that it be carried
out in water similar to that of the proposed dive or
in a variety of different types of water (Ferris 1973).
In addition, training must be repeated periodically to
be effective .
Changes in the optical image result in a number of
other distortions in visual perception. Mistakes in esti-
mates of size and shape occur. In general, objects
under water appear to be larger by about 33 percent
than they actually are. This often is a cause of disap-
pointment to sport divers, who find, after bringing
catches to the surface, that they are smaller than they
appeared under water. Since refraction effects are greater
for objects off to the side of the field of view, distortion
in the perceived shape of objects is frequent. Similarly,
the perception of speed can be influenced by these
distortions; if an object appears to cross the field of
view, its speed will be increased because of the greater
apparent distance it travels (Ross and Rejman 1972).
These errors in visual perception and misinterpreta-
tions of size, distance, shape, and speed caused by
refraction can be overcome, to some extent, with experi-
ence and training. In general, experienced divers make
fewer errors in judging the underwater world than do
novice divers. However, almost all divers are influ-
enced to some extent by the optical image, and attempts
to train them to respond more accurately have met
with some, but not complete, success.
Although the refraction that occurs between the
water and the air in the diver's face mask produces
these undesirable effects, air itself is essential for vision.
For example, if the face mask is lost, the diver's eyes
are immersed in water, which has about the same refrac-
tive index as the eyes. Consequently, no normal focus-
ing of light occurs and the diver's vision is impaired
immensely. The major deterioration is in visual acuity;
other visual functions such as the perception of size
and distance are not degraded as long as the object can
be seen (Luria and Kinney 1974). The loss of acuity,
however, is dramatic, and acuity may fall to a level
that would be classified as legally blind (generally
20/200) on the surface (Luria and Kinney 1969). While
myopes (near-sighted individuals) do not suffer quite
as much loss in acuity if their face masks are lost as
individuals with 20/20 vision do, the average acuities
of the two groups, myopes and normals, were found to
be 20/2372 and 20/4396, respectively, in one study of
underwater acuity without a mask (Cramer 1975).
2.8.1.2 Scatter
Scatter occurs when individual photons of light are
deflected or diverted when they encounter suspended
particles in the water. Although scattering also occurs
in air, it is of much greater concern under water because
light is diffused and scattered by the water molecules
themselves, by all kinds of particulate matter held in
suspension in the water, and by transparent biological
organisms. Normally, scatter interferes with vision
and underwater photography because it reduces the
contrast between the object and its background. This
loss of contrast is the major reason why vision is so
much more restricted in water than in air (Duntley
1963, Jerlov 1976); it also accounts for the fact that
even large objects can be invisible at short viewing
distances. In addition, acuity or perception of small
details is generally much poorer in water than in air,
despite the fact that the optical image of an object
under water is magnified by refraction (Baddeley 1968).
The deterioration increases greatly with the distance
the light travels through the water, largely because the
image-forming light is further interfered with as it
passes through the nearly transparent bodies of the
biomass, which is composed of organisms ranging from
bacteria to jellyfish (Duntley 1976).
2.8.1.3 Absorption
Light is absorbed as it passes through the water, and
much of it is lost in the process. In addition, the spec-
tral components of light, the wavelengths that give rise
to our perception of color, are differentially absorbed.
Transmission of light through air does not appreciably
change its spectral composition, but transmitting light
through water, even through the clearest water, does,
and this can change the resulting color appearance
beyond recognition. In clearest water, long wavelength
or red light is lost first, being absorbed at relatively
shallow depths. Orange is filtered out next, followed
by yellow, green, and then blue. Other waters, particu-
larly coastal waters, contain silt, decomposing plant
and animal material, and plankton and a variety of
possible pollutants, which add their specific absorp-
tions to that of the water. Plankton, for example, absorb
2-14
NOAA Diving Manual — October 1991
Physics of Diving
violets and blues, the colors transmitted best by clear
water. The amount of material suspended in some harbor
water is frequently sufficient to alter the transmission
curve completely; not only is very little light transmit-
ted, but the long wavelengths may be transmitted bet-
ter than the short, a complete reversal of the situation
in clear water (Jerlov 1976, Kinney et al. 1967, Mertens
1970).
Color vision under water, whether for the visibility
of colors, color appearances, or legibility, is thus much
more complicated than in air. Accurate underwater
color vision requires that divers know the colors involved,
understand the sensitivity of the eye to different col-
ors, know the depth and underwater viewing distance,
and are familiar with the general nature of water and
the characteristics of the specific waters involved. Infor-
mation is available from several investigations about
which colors can be seen best and which will be invisi-
ble under water (Kinney et al. 1967, 1969; Kinney and
Miller 1974; Luria and Kinney 1974; Kinney 1985).
Table 2-3 is a summary of the results of these experi-
ments and shows the colors that were most visible when
viewed by a diver against a water background.
Changes occur too in the appearance of colors under
water. For example, red objects frequently appear black
under water. This is readily understandable when one
considers that red objects appear red on the surface
because of reflected red light. Since clear water absorbs
the red light preferentially, at depth no red light reaches
the object to be reflected, and therefore the object
appears unlighted or black. In the same way, a blue
object in yellowish-green water near the coast could
appear black. Substances that have more than one
peak in their reflectance curve may appear quite dif-
ferent on land and in the sea. Blood is a good example;
at the surface a reflectance maximum in the green is
not noticeable because there is a much larger one in the
red. At depth, the water may absorb the long wave-
length light and blood may appear green. The ghostly
appearance of divers in 20 to 30 feet (6.1 to 9.1 m) of
clear water is another example of the loss of red light.
In general, less and less color is perceived as the
depth and viewing distance under water are increased,
and all objects tend to look as though they are the same
color (the color that is best transmitted by that partic-
ular body of water). Objects must then be distinguished
by their relative brightness or darkness. In Table 2-3,
many of the most visible colors are light, bright colors
that give good brightness contrast with the dark water
background. If the background were different (for exam-
ple, if it were white sand), darker colors would have
increased visibility. Fluorescent colors are conspicu-
ous under water because fluorescent materials convert
short wavelength light into long wavelength colors that
are rarely present under water, which increases the
color contrast.
The use of color coding under water is complicated
by these changes in color appearance, and only a few
colors can be employed without risk of confusion. Green
and orange are good choices, since they are not con-
fused in any type of water. Another practical question
concerns the most legible color for viewing instruments
under water; the answer depends on many conditions,
which are specified in Human Engineering Guidelines
for Underwater Applications (Vaughan and Kinney
1980, 1981). In clear ocean water, most colors are
equally visible if they are equally bright, but in highly
turbid harbor waters, red is best for direct viewing and
green is best for peripheral or off-center viewing.
2.8.1.4 Insufficient Light
Attenuation and scatter dramatically reduce the
amount of natural light available under water, restricting
natural daylight vision to a few hundred feet under the
best of conditions and to l to 2 feet (0.30 to 0.61 m) or
less under the worst or highly turbid conditions. If
there is not enough light (without an auxiliary dive
light) for daylight vision, many visual capabilities that
we take for granted in air will be greatly different; this
includes good acuity, color vision, and good central or
direct vision. In a low-light situation, acuity is very
poor and the diver will be unable to read; he or she will
have no clear vision, because all objects will appear
white, gray, or black; the diver will have to look off-
center to see rather than looking directly at an object.
Moreover, in order to see at all, the diver must dark-
adapt.
In air, an individual can gradually adapt to night-
time light levels during twilight and probably not notice
the change in vision; however, a diver may go directly
from bright sunlight on the boat into a dark underwa-
ter world and be completely blind. To function effectively,
the diver's eyes must adjust to the dim illumination for
as long as 30 minutes if he or she has been in bright
light. Some adaptation will take place while the diver
descends, but the rate of descent cannot be slow enough to
make this a practical solution, and other techniques
are required. This is especially important during dives
in which the bottom time is short and visual observa-
tion important.
The most effective way to become dark-adapted is
to remain in the dark for 15 to 30 minutes before the
dive. If this is impossible, red goggles are recommended.
October 1991 — NOAA Diving Manual
2-15
Section 2
Table 2-3
Colors That Give Best Visibility
Against a Water Background
Water Condition
Natural Illumination
Incandescent Illumination
Mercury Light
Murky, turbid water of low
visibility (rivers, harbors,
etc.)
Fluorescent yellow, orange,
and red
Yellow, orange, red, white
(no advantage in fluorescent
paint)
Fluorescent
yellow-green and
yellow-orange
Regular yellow, orange, and
white
Regular yellow, white
Moderately turbid water
(sounds, bays, coastal
water)
Any fluorescence in the
yellows, oranges, or reds
Any fluorescence in the
yellows, oranges, or reds
Fluorescent
yellow-green or
yellow-orange
Regular paint of yellow,
orange, white
Regular paint of yellow,
orange, white
Regular yellow, white
Clear water (Southern
water, deep water offshore,
etc.)
Fluorescent paint
Fluorescent paint
Fluorescent paint
Note: With any type of illumination, fluorescent paints are superior.
a. With long viewing distances, fluorescent green and yellow-green
b. With short viewing distances, fluorescent orange is also excellent
are excellent.
Adapted from NOAA (1979)
The night vision system of the eye is relatively insensi-
tive to red light; consequently, if a red filter is worn
over the face plate before diving, the eyes will partially
adapt and at the same time there will be enough light
for the day vision system to continue to function. The
red filter should be worn for 10 to 15 minutes and must
be removed before the dive. Because high visual sensi-
tivity is reached sooner when this procedure is used,
visual underwater tasks can be performed at the begin-
ning of the dive instead of 20 to 30 minutes later. If it is
necessary to return to the surface even momentarily,
the red filter should be put on again, because exposure
to bright light quickly destroys the dark-adapted state
of the eye.
2.9 ACOUSTICS
Sound is a periodic motion of pressure change transmitted
through a gas (air), a liquid (water), or a solid (rock).
Since liquid is a denser medium than gas, more energy
is required to disturb its equilibrium. Once this
disturbance takes place, sound travels farther and faster
in the denser medium. Several aspects of underwater
sound are of interest to the working diver.
During diving operations, there may be two or more
distinct contiguous layers of water at different tem-
peratures; these layers are known as thermoclines. The
2-16
colder a layer of water, the greater its density; as the
difference in density between layers increases, less
sound energy is transmitted between them. This means
that a sound heard 164 feet (50 meters) from its source
within one layer may be inaudible a few meters from its
source if the diver is in another layer.
In shallow water or in enclosed spaces, reflections
and reverberations from the air/water and object/water
interfaces will produce anomalies in the sound field,
i.e., echoes, dead spots, and sound nodes. When a diver
is swimming in shallow water, among coral heads, or in
enclosed spaces, periodic losses in acoustic communi-
cation signals and disruption of signals from acoustic
navigation beacons are to be expected. The problem
becomes more pronounced as the frequency of the
signal increases.
The use of open-circuit scuba affects sound recep-
tion by producing high noise levels at the diver's head
and by creating a screen of bubbles that reduces the
effective sound pressure level (SPL). If several divers
are working in the same area, the noise and bubbles
will affect communication signals more for some divers
than for others, depending on the position of the divers
in relation to the communicator and to each other.
A neoprene wet suit is an effective barrier to sound
at frequencies above 1000 Hz, and it becomes more of
NOAA Diving Manual — October 1991
Physics of Diving
a barrier as frequency increases. This problem can be
overcome by exposing a small area of the head cither
by cutting holes 0.79 to 1.18 in. (2 to 3 cm) at the
temples or above the ears of the hood.
The human ear is an extremely sensitive pressure
detector in air, but it is less efficient in water. A sound
must therefore be more intense in water ( + 20 dB to
60 dB, SPL) to be heard. Hearing under water is very
similar to trying to hear with a conductive hearing loss
under surface conditions: a smaller shift in pressure is
required to hear sounds at the extreme high and low
frequencies, because the ear is not as sensitive at these
frequencies. The SPL necessary for effective commu-
nication and navigation is a function of the maximum
distance between the diver and the source (-3 dB SPL
for every doubling of the distance between the source
and the measurement point), the frequency of the signal,
the ambient noise level and frequency spectrum, type of
head covering, experience with diver-communication
equipment, and the diver's stress level.
The use of sound as a navigation aid or as a means of
locating an object in the environment depends prima-
rily on the difference in the time of arrival of the sound
at the two ears as a function of the azimuth of the
source. Recent experiments have shown that auditory
localization cues are sufficient to allow relatively pre-
cise sound localization under water. Moreover, it has
been demonstrated that under controlled conditions
divers are able to localize and navigate to sound bea-
cons (Hollien and Hicks 1983). This research and practi-
cal experience have shown that not every diver is able
to localize and navigate to sound beacons under all
conditions. In general, successful sound localization
and navigation depend on clearly audible pulsed sig-
nals of short duration that have frequency components
below 1500 Hz and above 35,000 Hz and are pulsed
with a fast rise/decay time.
Sound is transmitted through water as a series of
pressure waves. High intensity sound is transmitted by
correspondingly high intensity pressure waves. A diver
may be affected by a high intensity pressure wave that
is transmitted from the surrounding water to the open
spaces within the body (ears, sinuses, lungs). The pres-
sure wave may create increased pressure within these
open spaces, which could result in injury.
The sources of high intensity sound or pressure waves
include underwater explosions and, in some cases, sonar.
Low intensity sonars such as depth finders and fish
finders do not produce pressure waves of an intensity
dangerous to a diver. However, some military anti-
submarine sonar-equipped ships do pulse high inten-
sity pressure waves dangerous to a diver. It is prudent
to suspend diving operations if a high-powered sonar
transponder is being operated in the area. When using
a diver-held pinger system, it is advisable for the diver
to wear the standard 1/4-inch (0.64-cm) neoprene
hood for ear protection. Experiments have shown that
such a hood offers adequate protection when the ultra-
sonic pulses are of 4-ms duration, are repeated once
per second for acoustic source levels up to 100 watts,
and are at head-to-source distances as short as 4 inches
(10 cm).
October 1991 — NOAA Diving Manual
2-17
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SECTION 3
DIVING
PHYSIOLOGY
Page
3.0 General 3-1
3.1 Circulation and Respiration 3-1
3.1.1 Circulatory System 3-1
3.1.2 Mechanism of Respiration 3-2
3.1.2.1 Pulmonary Ventilation 3-2
3.1.2.2 Blood Transport of Oxygen and Carbon Dioxide 3-2
3.1.2.3 Gas Exchange in the Tissues 3-4
3.1.2.4 Tissue Need for Oxygen 3-4
3.1.2.5 Summary of Respiration Process 3-4
3.1.3 Respiratory Problems 3-5
3.1.3.1 Hypoxia 3-5
3.1.3.2 Carbon Dioxide Excess (Hypercapnia) 3-5
3.1.3.3 Carbon Monoxide Poisoning 3-6
3.1.3.4 Smoking 3-7
3.1.3.5 Excessive Resistance to Breathing 3-8
3.1.3.6 Excessive Dead Space 3-8
3.1.3.7 Hyperventilation and Breath-holding 3-8
3.2 Effects of Pressure 3-10
3.2.1 Direct Effects of Pressure During Descent 3-10
3.2.1.1 The Ears 3-10
3.2.1.2 The Sinuses 3-12
3.2.1.3 The Lungs 3-13
3 2.1.4 The Teeth 3-14
3.2.2 Direct Effects of Pressure During Ascent 3-14
3.2.2.1 Pneumothorax 3-14
3.2.2.2 Mediastinal Emphysema 3-14
3.2.2.3 Subcutaneous Emphysema 3-15
3.2.2.4 Gas Embolism 3-15
3.2.2.5 Overexpansion of the Stomach and Intestine 3-16
3.2.2.6 Bubble Formation and Contact Lenses 3-16
3.2.3 Indirect Effects of Pressure 3-16
3.2.3.1 Inert Gas Absorption and Elimination 3-16
3.2.3.2 Decompression Sickness 3-17
3.2.3.3 Counterdiffusion 3-19
3.2.3.4 Aseptic Bone Necrosis (Dysbaric Osteonecrosis) 3-20
3.2.3.5 Inert Gas Narcosis 3-20
3.2.3.6 High Pressure Nervous Syndrome (HPNS) 3-22
3.3 Oxygen Poisoning 3-22
3.4 Effects of Cold (Hypothermia) 3-24
3.4.1 Thermal Protection 3-25
3.4.2 Symptoms of Hypothermia 3-25
3.4.3 Survival in Cold Water 3-26
3.4.4 Rewarming 3-27
3.5 Effects of Heat (Hyperthermia) 3-27
3.6 Drugs and Diving 3-28
3.6.1 Prescription Drugs 3-28
3.6.2 Illicit Drugs 3-28
(
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DIVING
PHYSIOLOGY
3.0 GENERAL
This section provides divers with basic information
about how the body reacts to physiological stresses
that are imposed by diving and how to compensate for
these stresses and other physical limitations. Divers
should become familiar with the terminology used in
this chapter to understand and be able to describe any
diving-related symptoms or physical problems they
experience. Commonly used diving medical terms are
defined in the glossary of this manual (Appendix E).
3.1 CIRCULATION AND RESPIRATION
The activity of each cell of the body involves several
delicate reactions that can take place only under well-
defined chemical and physiological conditions. The
chief function of the circulatory system is to maintain
conditions around the cells at the level that is optimal
for their functioning. The regulation of cardiac output
and the distribution of the blood are central to the
physiology of circulation.
Respiration is the process by which gases, oxygen,
and carbon dioxide are interchanged among the tissues
and the atmosphere. During respiration, air enters the
lungs via the nose or mouth and then traverses the
pharynx, larynx, trachea, and bronchi. Air being exhaled
follows this path in reverse. The bronchi enter the
lungs and divide and re-divide into a branching net-
work, ending in the terminal air sacs (alveoli), which
are approximately one ten-thousandth of an inch
(0.003 millimeter) in diameter. The alveoli are sur-
rounded by a thin membrane, and the interchange of
gases takes place across this membrane, where the blood
in the tiny pulmonary capillaries takes up oxygen and
gives off carbon dioxide. This process is shown sche-
matically in Figure 3-1.
Before discussing diving physiology, a basic under-
standing of circulation, respiration, and certain prob-
lems associated with the air-containing compartments
of the body is necessary. These topics are discussed in
the following paragraphs.
3.1.1 Circulatory System
The heart is divided vertically into the right and left
sides, each consisting of two communicating chambers,
October 1991 — NOAA Diving Manual
Figure 3-1
The Process of Respiration
Conchae
Septum
Hairs
Sphenoidal Sinus
Hard Palate
Tongue
Larynx (Voice Box)
Trachea (Windpipe)
Alveoli Bronchial
Adenoid
(Naso-Pharyngeal Tonsil)
Soft Palate
Tonsil
Pharynx
Esophagus (Food Tube)
Right Lung
Bronchiole
Pulmonary
Venule
Pulmonary
Arteriole
Bronchus
Pulmonary
Vein
Pulmonary
Artery
Cut Edge
of Pleura
(Hilus)
Cut Edge of
Diaphragm
Stomach
Source: NOAA (1979)
the auricles and ventricles. Blood is pumped by the
right ventricle into the pulmonary artery, through the
pulmonary capillaries, and back to the left side of the
heart through the pulmonary veins. The left ventricle
pumps the blood into the aorta, which distributes it to
the body. This distribution is accomplished by a con-
tinual branching of arteries, which become smaller
until they become capillaries. The capillaries have a
thin wall through which gases and other substances are
interchanged between the blood and the tissues. Blood
from the capillaries flows into the venules, the veins,
3-1
Section 3
and, finally, is returned to the heart. In this way,
carbon dioxide produced in the tissues is removed,
transported to the lungs, and discharged. This process
is shown schematically in Figure 3-2.
During exercise, there is an increase in the frequency
and force of the heart beat as well as a constriction of
the vessels of the skin, alimentary canal, and quiescent
muscle. Peripheral resistance is increased and arterial
pressure rises. Blood is expelled from the spleen, liver,
skin, and other organs, which increases circulatory
blood volume. The net result of this process is an increase
in the rate of blood flow to the body organs having a
high demand for oxygen — the brain, the heart, and any
active muscles.
3.1.2 Mechanism of Respiration
The chest wall encloses a cavity, the volume of which is
altered by the rhythmic contraction and relaxation of
muscles. This thoracic cavity contains the lungs, which
are connected with the outside environment through
the bronchi, the trachea, and the upper respiratory
passages and the heart and great vessels. When the
volume of the thoracic cavity changes, a decrease or
increase in pressure occurs within the internal cham-
bers and passages of the lungs. This change causes air
to flow into or out of the lungs through the respiratory
passageways until the pressure everywhere in the lungs
is equalized with the external pressure. Respiratory
ventilation consists of rhythmic changes of this sort.
Respiration is affected by the muscular action of the
diaphragm and chest wall and is under the control of
the nervous system, which itself is responding to changes
in blood oxygen and carbon dioxide levels. The normal
respiratory rate at rest varies from about 12 to 16
breaths a minute. During and after heavy exertion, this
rate increases severalfold.
In the chest wall's normal resting position, that is, at
the end of natural expiration, the lungs contain about
2.5 liters of air. Even when one voluntarily expels all
the air possible, there still remain about 1.5 liters of
residual air. The volume of air that is inspired and
expired during rest is referred to as tidal air and aver-
ages about 0.5 liter per cycle. The additional volume
from the resting expiratory position of 2.5 liters that
can be taken in during a maximal inspiration varies
greatly from individual to individual, ranging from
about 2 to 6 liters. The total breathable volume of air,
called the vital capacity, depends on the size, develop-
ment, age, and physical condition of the individual.
Vital capacity is defined as the maximal volume that
can be expired after maximal inspiration. A reduction
in vital capacity limits the ability of a person to respond
3-2
adequately to a demand for increased ventilation dur-
ing exercise. Because diving often requires strenuous
exercise, cardiovascular or respiratory disorders may
seriously limit or prevent an individual from actively
participating in this activity.
3.1.2.1 Pulmonary Ventilation
Air drawn into the lungs is distributed through smaller
air passages until it reaches the honeycomb-like alveoli or
air sacs through which the exchange of respiratory
gases takes place (see Figure 3-1). The rates at which
oxygen is supplied and carbon dioxide removed from
the lungs depend on several factors: (1) the composi-
tion and volume of the air supplied through the res-
piratory passages; (2) the partial pressures of respiratory
gases in the blood; and (3) the duration for which a
given volume of blood is exposed to alveolar air. In a
normal person in good physical condition, other fac-
tors influencing respiratory exchange are not likely to
be significant.
At rest, about 0.3 liter of oxygen is used by the
tissues per minute. During exercise, an exchange of
about 3.5 liters or more of oxygen per minute may take
place. This flexibility is accomplished by increased
frequency of breathing, increased heart action propel-
ling blood through the pulmonary capillaries, and
increased differences in the partial pressures of oxy-
gen and carbon dioxide during exercise. Figure 3-3
depicts oxygen consumption as a function of work rate.
Normally, despite wide differences in the rates of gas-
eous exchange in the resting and heavy exercise condi-
tions, the blood leaving the lungs is almost completely
saturated with oxygen and in equilibrium with the
alveolar carbon dioxide pressure.
3.1.2.2 Blood Transport of Oxygen and
Carbon Dioxide
Blood can take up a much greater quantity of oxygen
and carbon dioxide than can be carried in simple solu-
tion. Hemoglobin, which is the principal constituent in
red blood cells and gives the red color to blood, has a
chemical property of combining with oxygen and with
carbon dioxide and carbon monoxide. The normal hemo-
globin content of the blood increases the blood's oxygen-
carrying capacity by about 50 times. The reaction
between oxygen and hemoglobin is governed primarily
by the partial pressure of oxygen. At sea level, where
there is normally an inspired oxygen partial pressure
of 150 millimeters of mercury, the alveolar hemoglo-
bin becomes about 98 percent saturated in terms of its
NOAA Diving Manual — October 1991
Diving Physiology
Figure 3-2
The Circulatory System
Right
auricle
Lung capillaries
Tricuspid -f^lt
valve
Veins
Bicuspid valve
Arteries
Body capillaries
Source: Shilling. Werts. and Schandelmeier (1976)
capacity to form oxy-hemoglobin. In the tissues, where
the partial pressure of oxygen is normally about
20 millimeters of mercury, between one-third and
one-half of this oxygen is given up by hemoglobin and
made available to the tissues. It is apparent that the
blood of persons lacking a sufficiency of hemoglobin,
i.e., anemic persons, will be deficient in its capacity
to carry oxygen. As a consequence, anemic people are
generally less fit for diving than people who are not
anemic.
October 1991 — NOAA Diving Manual
The blood contains a small amount of carbon dioxide
in simple solution, but a greater amount is found in
chemical combinations such as carbonic acid, bicar-
bonate, or bound to hemoglobin. All the forms of car-
bon dioxide tend toward chemical equilibrium with
each other. The taking up of oxygen by the hemoglobin
in the lung capillaries favors the unloading of carbon
dioxide at the same time that the absorption of carbon
dioxide into the blood in the tissues favors the release
of oxygen.
3-3
Section 3
Figure 3-3
Oxygen Consumption and
Respiratory Minute Volume
as a Function of Work Rate
0.71
.E (20)
E
"5 ^
= c 1.4
8 I (40)
»s
E *■
2 °
il
o
2.1
(60)
0)
cc
2.8
(80)
SS. I Rest
Sitting Quietly!*
Light
Work
Moderate
Work
Heavy Work
Severe Work
Swim, 0.5 Knot
(Slow)H^
Swim, 0.85 Knot (Average SpeeoV^^
Swim, 1 Knot
Swim, 1.2 Knots^^
\^
\^
"\
I I I I
I I
i i
\
Oxygen Consumption, standard liters/min
Derived from NOAA (1979)
3.1.2.3 Gas Exchange in the Tissues
The exchange of oxygen and carbon dioxide between
the blood and body cells occurs in opposite directions.
Oxygen, which is continuously used in the tissues,
exists there at a lower partial pressure than in the
blood. Carbon dioxide is produced inside the tissue
cells, which increases its concentration relative to that
of the blood reaching the tissues. Therefore, blood
supplied by the arteries gives up oxygen and receives
carbon dioxide during its transit through the tissue
capillaries. The rate of exchange of these respiratory
gases and the total amount of gas movement depend on
their respective partial pressure differences, since the
exposure time of blood in the tissue capillaries is ade-
quate for nearly complete equilibration to be achieved.
When tissues are more active, the need for oxygen is
greater. The increased oxygen is supplied not from an
increase in the oxygen content of the arterial blood but
by the larger volume of blood that flows through the
tissues and by a more complete release of oxygen from
a given volume of the blood. There can be as much as a
ninefold increase in the rate at which oxygen is sup-
plied to active tissues.
3.1.2.4 Tissue Need for Oxygen
All living tissues need oxygen, but tissues that are
especially active during exertion, such as skeletal muscle,
need greater amounts of oxygen. The brain, however, is
made up of tissue that has an extraordinarily high and
nearly steady requirement for oxygen. Although the
nervous system represents only about 2 percent of the
body weight, it requires about 20 percent of the total
circulation and 20 percent of the total oxygen used by
the body per minute at work or at rest. If circulation is
completely cut off, consciousness may be lost in about
one-quarter of a minute and irreparable damage to the
higher centers of the brain may occur within 3 to
5 minutes (see Section 3.1.3.1).
3.1.2.5 Summary of Respiration Process
The process of respiration includes six important
phases:
(1) Breathing or ventilation of the lungs;
(2) Exchange of gases between blood and air in the
lungs;
(3) The transport of gases carried by the blood;
3-4
NOAA Diving Manual — October 1991
Diving Physiology
(4) Exchange of gases between blood and body tissues;
(5) Exchange of gases between the tissue fluids and
cells; and
(6) Use and production of gases by the cells.
Each phase of this process is important to the life of the
cells, and the process must be maintained constantly
by the respiratory and circulatory systems.
3.1.3 Respiratory Problems
Although most physiological problems associated
with diving are related to the breathing of gases at the
high pressures encountered under water, respiratory
problems may occur at the surface as well. These prob-
lems are generally related to the inadequate transport
of oxygen to the cells and to the inadequate removal of
carbon dioxide. Some of the common respiratory prob-
lems are hypoxia, hypercapnia, and carbon monoxide
poisoning. Each of these is discussed in the following
paragraphs.
3.1.3.1 Hypoxia
The term hypoxia, or oxygen shortage, is used to
mean any situation in which tissue cells fail to receive
or are unable to obtain enough oxygen to maintain
their normal functioning. Hypoxia can occur as a result of
interference with any phase of the oxygen transport
process.
Hypoxia stops the normal function of cells. Brain
tissue cells are the most susceptible of all body cells to
hypoxia; unconsciousness and death can occur before
the effects of hypoxia are apparent on other cells.
Hypoxia may cause sudden unconsciousness or, if onset
is gradual, may decrease the ability to think clearly,
orient oneself, or to perform certain tasks. Confusion
and difficulty in standing, walking, and maintaining
coordination often follow. Victims of hypoxia may be
unaware of impending trouble even though they become
drowsy and weak. A particular danger of hypoxia is
that as it progresses, it causes a false sense of well-
being that may prevent the diver from taking correc-
tive action soon enough. If hypoxia is severe and sud-
den, unconsciousness develops almost at once; un-
consciousness usually occurs when the inspired partial
pressure of oxygen falls to 0.10 atmosphere, i.e., equiva-
lent to the oxygen pressure prevailing when a person
breathes a 10 percent oxygen mixture at atmospheric
pressure. Below this level, permanent brain damage
and death occur quickly (US Navy 1985).
If a diver suffering from severe hypoxia is not res-
cued quickly, the interference with brain function will
cause failure of breathing control. If given fresh air
promptly before breathing stops, the diver usually will
regain consciousness shortly and recover completely.
If breathing has stopped but heart action continues,
cardiopulmonary resuscitation may enable oxygen to
reach the brain and revive the breathing control center
so that spontaneous breathing will resume. It is diffi-
cult to know when the heart action has stopped com-
pletely, so efforts at resuscitation must be continued
until medical attendants pronounce a victim dead.
WARNING
There Is No Natural Warning That Tells a Diver
of the Onset of Hypoxia
3.1.3.2 Carbon Dioxide Excess (Hypercapnia)
An excess of carbon dioxide in the tissues can occur
if the process of carbon dioxide transport and elimina-
tion is interrupted or modified. In diving, carbon diox-
ide excess occurs either because there is too much
carbon dioxide in the diver's breathing medium or
because the carbon dioxide that is produced is not
eliminated properly. The diver's own metabolic processes
are generally the source of any excess carbon dioxide.
The proper carbon dioxide level is maintained in the
body by respiration rapid enough to exhale the carbon
dioxide produced and delivered to the lungs. For breath-
ing to be effective, the air inhaled must contain a
minimum of carbon dioxide. Inadequate helmet or mask
ventilation, too large a dead space in mouthpiece or
tubing, or failure of the carbon dioxide absorption
system of closed- or semi-closed-circuit breathing
systems may produce an excess of carbon dioxide in
the gas breathed.
All tissues are affected by an excess of carbon diox-
ide, but the brain is the most susceptible organ to
hypercapnia. Figure 3-4 shows the physiological effects
of different concentrations of carbon dioxide for vari-
ous exposure periods. At the concentrations and dura-
tions represented by Zone I, no perceptible physiological
effects have been observed. In Zone II, small threshold
hearing losses have been found and there is a percepti-
ble doubling in the depth of respiration. In Zone III,
the zone of distracting discomfort, the symptoms are
mental depression, headache, dizziness, nausea, 'air
hunger,' and a decrease in visual discrimination. Zone
IV represents marked physical distress associated with
dizziness and stupor, which is accompanied by an ina-
bility to take steps for self-preservation. The final
stage of the Zone IV state is unconsciousness. Above a
CO., partial pressure (PCOJ of 0.15 ATA, muscle
spasms, rigidity, and death can occur. If an excess of
October 1991 — NOAA Diving Manual
3-5
Section 3
Figure 3-4
Relation of Physiological Effects to Carbon
Dioxide Concentration and Exposure Period
<
<
o
0 10
0.08
0.06
0.04
0.02
\ Zone IV Dizziness, stupor, unconsciousness
\ Zone III Distracting discomfort
^^^^ Zone II Minor perceptible changes """"""■■"■——««»,
0.00
Zone I No effect
I I I I I I I
PC02 ATA
10 20 30 40 50 60 70
Exposure Time, minutes
40 Days
10
<
8 5
6 .£
c
o
«
c
A •
c
o
o
3 CM
O
O
2 .o
0.5
0
Derived from NOAA (1979)
carbon dioxide causes a diver to lose consciousness, he
or she can be revived quickly if the lungs are ventilated
with fresh air. The aftereffects of hypercapnia include
headache, nausea, dizziness, and sore chest muscles.
The bar graph at the right of Figure 3-4 extends the
period of exposure shown to 40 days. It illustrates that,
for exposures of 40 days, concentrations of carbon
dioxide in air of less than 0.5 percent (0.005 ATA
partial pressure) (Zone A) cause no biochemical or
other effects; concentrations between 0.5 and 3.0 per-
cent (0.005-0.03 ATA partial pressure) (Zone B) cause
adaptive biochemical changes, which may be consid-
ered a mild physiological strain; and concentrations
above 3.0 percent (0.03 ATA partial pressure) (Zone
C) cause pathological changes in basic physiological
functions. For normal diving operations, ventilation
rates should be maintained so that carbon dioxide par-
tial pressures are maintained in Zones I and II for
short-term exposures and in Zones A and B for long-
term exposures.
Increased carbon dioxide in the breathing-mixture
stimulates the respiratory center to increase the breathing
rate. Carbon dioxide at a partial pressure of 0.02 atmo-
sphere generally increases breathing noticeably.
When the carbon dioxide level reaches a partial
pressure of 0.05 atmosphere, an uncomfortable sensa-
tion of shortness of breath occurs. There are large
differences in individual responses to increases in car-
bon dioxide. The amount of work, the depth, and the
breathing medium are factors that will also alter the
effect of an increase in carbon dioxide on breathing.
Deliberately reducing one's breathing rate will cause a
carbon dioxide buildup; maintaining an adequate ven-
tilation rate is necessary to remove carbon dioxide
from the lungs effectively. Other conditions that increase
the likelihood of carbon dioxide poisoning include severe
exertion, high partial pressures of oxygen, high gas
density, and the use of breathing apparatus that has
excessive dead space or high breathing resistance.
WARNING
Skip-Breathing Is Not a Safe Procedure
Because Carbon Dioxide Buildup Can Occur
With Little or No Warning
3.1.3.3 Carbon Monoxide Poisoning
Inspired carbon monoxide (CO) combines with hemo-
globin in the red blood cells, rendering them incapable
of carrying oxygen to the tissues. When carbon monoxide
is bound to hemoglobin, a person experiences tissue
hypoxia (oxygen deficiency in the tissues) even though
3-6
NOAA Diving Manual — October 1991
Diving Physiology
the air being breathed has sufficient oxygen. This con-
dition is known as CO poisoning. Hemoglobin com-
bines with carbon monoxide about 210 times more
readily than with oxygen, so very small concentrations
of carbon monoxide can be dangerous to life (US Navy
1985). The hemoglobin-carbon monoxide combination is
red in color and may cause an unnatural redness of the
lips and skin. However, since this redness may not
occur, carbon monoxide poisoning cannot be ruled out
simply because a person has normal coloring. In addi-
tion to its effects on hemoglobin, carbon monoxide
combines with the final respiratory enzyme (cytochrome
oxidase af> in the tissues, causing hypoxia at the tissue
level as well. Because carbon monoxide poisoning inter-
feres with the delivery of oxygen to the tissues, the
symptoms are identical to those of other types of hyp-
oxia. If the concentration of carbon monoxide is high
enough to cause rapid poisoning without the diver's
awareness, he or she may lose consciousness suddenly.
If the carbon monoxide poisoning is more gradual in
onset, pounding headache, nausea, and vomiting may
occur.
A diver's breathing gas can be contaminated by
carbon monoxide if the compressor supplying the breath-
ing gas draws from an area where the air is contami-
nated by the exhaust from a gasoline or diesel engine or
if vapor from the oil used to lubricate the compressor
gets into the air supply. It is essential that the air
intakes on compressors be protected to avoid this source
of carbon monoxide contamination and that oil with an
appropriate flash point is used in any oil-lubricated
compressor that supplies divers' breathing air (see Sec-
tion 4.2.2).
When a diver loses consciousness, it is routine to
administer recompression treatment because of fear
that either decompression sickness or an arterial gas
embolism has caused the loss of consciousness. Occa-
sionally, carbon monoxide poisoning is the cause of
unconsciousness, and recompression treatment, using
either USN Treatment Table 5 (Oxygen Treatment of
Type I Decompression Sickness; US Navy 1985) or a
hyperbaric oxygen treatment table designed specifi-
cally to treat carbon monoxide poisoning, is the treat-
ment of choice in these cases as well. Carbon monoxide
poisoning victims who resume breathing and regain
consciousness quickly have a good chance of complete
recovery.
3.1.3.4 Smoking
Smoking directly affects the oxygen-carrying capabil-
ity of the red blood cells. The smoke of a typical
American cigarette contains about 4 percent carbon
monoxide (40,000 ppm). The average carbon monoxide
concentration inhaled during the smoking of one cigarette
is 400-500 ppm, which produces anywhere from 3.8 to
7.0 percent carboxyhemoglobin (HbCO) in the blood;
in non-smokers, the HbCO level is generally 0.5 per-
cent. The percentage of HbCO blood levels after con-
tinuous exposure to carbon monoxide for 12 hours or
after reaching equilibrium are summarized in the table
below.
Continuous Exposure
Level of
HbCO in Blood
CO, ppm
%
50
8.4
40
6.7
30
5.0
20
3.3
10
1.7
—
0.5 (non-smoker)
Source: NOAA (1979)
Table 3-1 shows the relationship between smoking
and HbCO blood levels. This table shows that the
HbCO level in the blood of divers who smoke is higher
than it would be if the divers had been exposed to
20 ppm carbon monoxide for 12 hours (equivalent to the
maximum carbon monoxide level allowed in divers'
breathing air by the U.S. Navy (see Table 15-6)).
Considering that it takes a heavy smoker approximately
8 hours to eliminate 75 percent of the carbon monoxide
inhaled, it is clear that the HbCO level (0.95 percent)
even for a light smoker diving 8 hours after the last
cigarette is almost twice that of a non-smoker
(0.50 percent). The carboxyhemoglobin blood level of
a passive smoker (i.e., a person who does not smoke but
who is exposed to the smoke of others) can rise to
5 percent after exposure to a smoke-filled environment
(Surgeon General 1986).
The dose of carbon monoxide a smoker receives from
smoking is toxic; it causes changes in neurologic reflexes,
psychomotor test results, sensory discrimination, and
electrocardiograms, as well as fatigue, headache, irri-
tability, dizziness, and disturbed sleep. Other short-
term effects of smoking may also adversely affect the
diver. For example, in addition to accelerating the
atherosclerotic changes in blood vessels, cigarette smoke
also raises blood pressure and increases heart rate.
Smokers have trouble eliminating respiratory tract
secretions, and the accumulation of these secretions
can make equalizing pressure in the ears and sinuses
difficult (Shilling, Carlston, and Mathias 1984). The
irritants in inhaled tobacco smoke can cause an increase
October 1991 — NOAA Diving Manual
3-7
Section 3
Table 3-1
Carboxyhemoglobin as a
Function of Smoking
Median
HbCO
Expired
Smoking Habits
Level, %
CO, ppm
Light smoker (less than Vz pack/
day)
3.8
17.1
Moderate smoker (more than Vz
pack/day and less than 2
packs/day)
5.9
27.5
Heavy smoker (2 packs or more/
day)
6.9
32.4
Source: NOAA (1979)
in bronchial mucus and a chronic inflammatory change in
the bronchial lining. Over a prolonged period, these
conditions may result in structural weakness of the
lung, such as emphysematous bullae, alveoli enlarged
with air, or obstructive lung disease. Lung cysts can
enlarge because of gas trapped by bronchial obstruc-
tion and may then rupture. The resulting tears can
open into pulmonary veins, permitting gas embolism.
Furthermore, nicotine and carbon monoxide increase
the 'stickiness' of blood platelets, causing a clumping
that can interfere with the flow of blood in the small
vessels; this condition may increase a person's suscep-
tibility to decompression sickness. In a study of 93
Navy divers, cigarette smoking was found to be
associated with lung function decrement and to have
an important and adverse effect on divers' health
(Dembert et al. 1984). Other Navy research reported
by Dembert and co-authors suggests that there is an
association between smoking and the risk of decom-
pression sickness.
The deleterious effects of smoking on the cardiore-
spiratory system clearly indicate that divers should
not smoke. If divers are not able to stop smoking alto-
gether, they should at least avoid smoking for several
hours before diving.
3.1.3.5 Excessive Resistance to Breathing
Any breathing apparatus used by a diver under water
will increase the work-of-breathing (i.e., the amount
of work involved in breathing) to some extent. If the
breathing resistance of the apparatus is high, it will be
difficult to breathe adequately even during ordinary
exertion and breathing will become impossible during
hard work. Resistance to the flow of breathing gas is
caused by demand regulators, valves, hoses, and other
appurtenances of a life-support system. Well-designed
equipment minimizes the amount of resistance to the
flow of breathing gas (see Section 5. 1 . 1 . 1 ).
The characteristics of the breathing gases flowing
through tubes of various sizes and configurations influ-
3-8
ence the amount of breathing resistance encountered
by a diver using the equipment. Gases moving through
tubes of optimal design will flow 'in line' or in laminar
flow until restrictions in or the dimensions of the tube
cause the air molecules to begin moving in a disordered
fashion {turbulent flow). The increase in the effort
required to move gas that is in turbulent rather than
laminar flow is significant: the resistance increases in
relation to the square of the increased flow rate; that is,
doubling the flow rate causes a fourfold increase in
resistance (see Section 2.6). This may be a problem
with small-bore snorkels, small-diameter exhaust valves,
or inadequate breathing tubes and mouthpieces. Thus,
snorkels should have diameters approximately 3/4 inch
(1.9 centimeters) with no unnecessary bends, corruga-
tions, or obstructions, and exhaust valves should be
large enough to keep the exhalation resistance as low
as possible (see Sections 5.1.1.4 and 5.6.1).
The position of the demand valve or breathing bag in
relation to the internal pressure in the lungs is critical
in closed-circuit scuba to avoid unbalanced hydrostatic
pressure causing an increase in breathing resistance
(Figure 3-5). As the work-of-breathing increases, the
body reaches a point where it will accept increased
carbon dioxide rather than perform the respiratory
work required to maintain a normal carbon dioxide
level in the tissues (US Navy 1985).
3.1.3.6 Excessive Dead Space
Dead space in a diving system is that space in which
residual exhaled air remains. A diver exhaling into a
snorkel, mouthpiece, or full-face mask may return
some of this exhaled gas to the lungs; the amount
returned depends on the dead space volume within the
system. A well-designed system has minimum dead
space. A casual examination of diving equipment will
not reveal dead space volume; special equipment must
be used to measure the extent of this ineffective vol-
ume by determining how much exhaled gas is actually
rebreathed.
Full-face masks may add as much as 0.5 liter of
dead space; this excess must be ventilated with each
breath (US Navy 1985). Because of carbon dioxide
buildup, the excess can seriously limit a diver's ability
to do work. Free-flow helmets do not have this dead
space problem. The use of oral-nasal masks inside
full-face masks is effective in reducing the amount of
dead space (see Section 5.2.1).
3.1.3.7 Hyperventilation and Breath-holding
The respiratory system utilizes both carbon dioxide
(C02) and oxygen (02) tensions (partial pressures) in
NOAA Diving Manual — October 1991
Diving Physiology
Figure 3-5
Effects of Hydrostatic Pressure on Location
of Breathing Bags Within a Closed-Circuit Scuba
Breathing bag is deeper than the lungs. It is
subject to more hydrostatic pressure,
increasing breathing resistance on
exhalation.
Breathing bag is at the same level as the
lungs. Breathing resistance is the same as
on the surface.
Breathing bag is shallower than the lungs.
It is subject to less hydrostatic pressure,
increasing breathing resistance on
inhalation.
Source: NOAA (1979)
the body to regulate the process of breathing. Rising
CO, tension and falling O, tension are monitored by
biological sensors in the body, which normally trigger
the breathing response when the appropriate levels are
reached. Hyperventilation (rapid, unusually deep breath-
ing in excess of the necessary rate for the level of
activity) interferes with the normal operation of the
respiratory control mechanism. Hyperventilation low-
ers the CO, level in body tissues to levels below nor-
mal, a condition known as hypocapnia, which initially
causes a feeling of lightheadedness and may cause
weakness, faintness, headache, and blurring of vision
over a longer period.
Voluntary hyperventilation, which occurs in distance
underwater swimming or breath-holding competitions, is
a dangerous practice. Hyperventilation lowers the carbon
dioxide level without significantly increasing the oxy-
gen level of the blood. When breath-holding after
hyperventilation, oxygen levels can fall to levels resulting
in unconsciousness before the CO, level is high enough
to stimulate respiration. As a consequence, competi-
tive underwater breath-holding events should be dis-
couraged (Bove 1985).
Hyperventilation is often initiated by anxiety or physi-
cal stress or outright panic and may cause uncon-
sciousness or muscle spasms. If either unconsciousness
or spasm occurs in the water, the diver may drown.
Some individuals are more susceptible to hyperventila-
tion-induced hypocapnia than others; however, suf-
ficiently prolonged hyperventilation induces uncon-
sciousness or muscle spasms in most individuals.
Both scuba and surface-supplied divers should be
aware of the problems associated with hyperventila-
tion. Divers who notice that they are hyperventilating
should take immediate steps to slow their breathing
rate, notify their buddies, and, if feasible, ascend prompt-
ly. After reaching the surface, they should inflate their
buoyancy compensators. Hyperventilating divers should
not attempt to swim to a boat or the shore unaided
because they may lose consciousness in the attempt.
During surface-supplied diving, the tender should
continuously monitor the diver's breathing for signs of
hyperventilation. Divers starting to hyperventilate should
be asked to stop work and rest. Once on the surface, hold-
ing the breath for short periods will aid in replenishing
low CO, levels and may avert further complications.
October 1991 — NOAA Diving Manual
3-9
Section 3
3.2 EFFECTS OF PRESSURE
The effects of pressure on divers may be divided into
two principal categories: (1) those that are direct and
mechanical; and (2) those that come about because of
changes in the partial pressure of inspired gases. With
each 2-foot (0.61 meter) increase in the depth of sea-
water, the pressure increases by almost 1 psi. Each
33 feet (10 meters) of descent in seawater increases the
pressure by an additional atmosphere (14.7 psi).
The lungs and respiratory passages contain air at all
times. In addition to the major air channels, which
include the nose, mouth, throat, larynx, and trachea,
there are a number of side compartments issuing from
the upper respiratory passages that are important in
diving physiology. These include the eustachian tubes,
the middle ear, and the paranasal sinuses. When the
body is exposed to pressure changes, such as those that
occur in diving, air contained in these cavities undergoes
compression because the pressure of the air delivered
by the breathing supply must be equilibrated with the
pressure of the surrounding environment. The pressure
of air breathed into and out of the lungs and respiratory
passages thus also changes in accordance with changes
in the surrounding hydrostatic pressure.
3.2.1 Direct Effects of Pressure During Descent
Humans can tolerate increased pressures if they are
uniformly distributed throughout the body. However,
when the outside pressure is different from that inside
the body's air spaces, this difference in pressure may
distort the shape of the involved tissues, causing inju-
ry. This is called barotrauma.
The pressure in such spaces as the sinuses and the
middle ear must be equalized on descent, or pressure
differences will develop across the walls of these spaces.
Once the pressure at a given depth has been equalized,
it must be allowed to decrease if the external pressure
decreases, as occurs during ascent. The effects of pressure
on various parts of the body are discussed in the following
paragraphs.
3.2.1.1 The Ears
The air-containing external and middle ear gives
humans a device that efficiently transforms airborne
sound energy to the fluid-containing inner ear, where
this energy is transduced into electrical signals. Proper
functioning of this mechanism requires that both the
external ear canal and the middle ear contain air and
that differences in pressure be avoided between these
structures and the ambient atmosphere or inner ear.
The many changes in pressure regularly involved in
diving make a pressure-sensitive middle ear a liability
for a diver.
The effect of immersion on the human ear causes it
to function differently under water than it does in air.
Normally, sound is transmitted in air (which is easily
compressed) in a high-amplitude (HA) low force mode.
In liquid (which is difficult to compress), sound is
transmitted in a low-amplitude (LA) high force mode.
The human ear is designed to convert HA energy to LA
energy (see Figure 3-6) by the mechanical processing
of sound in the external and middle ear. In water,
however, sound arrives at the ear in the LA mode, and
the process of converting sound from LA to HA and
back to LA is not efficient. As a result, the external/
middle ear mechanisms are functionally bypassed under
water and hearing is primarily achieved by bone (skull)
conduction.
When divers experience extreme changes in ambient
pressure, the ears may be injured unless the pressure
between the air-containing cavity and the ambient
atmosphere is equalized. Barotitis media (middle ear
squeeze) resulting from inadequate pressure equaliza-
tion between the middle ear and the ambient pressure
is a fairly common problem among divers. Although
occasionally disabling, it is usually reversible. Because
more people are diving to deeper depths, there have
been more serious and disabling problems involving
the inner ear.
In terrestrial environments, balance and spatial ori-
entation depend on input to the central nervous system
from the visual, proprioceptive (sense of touch), and
vestibular (sense of balance) systems. When people
work beneath the sea, visual and proprioceptive cues
are frequently distorted; thus, spatial orientation and
balance become more dependent on information received
from the vestibular system. Vestibular system dysfunc-
tion may occur in many phases of diving, and the
subsequent vertigo, nausea (and, occasionally, vomiting)
can be life threatening.
The middle ear space (Figure 3-6) connects with air
cell systems in the skull bone containing the ear. With
an intact eardrum membrane, the only communication
between this system and the ambient atmosphere is
through the eustachian tube. This tube is approximately
1.4 to 1.5 inches (3.5 to 3.8 cm) long in the adult and
leads from the middle ear to the nasopharynx (or upper
expanded portion of the throat) behind the nasal cavi-
ties. The nasopharyngeal opening normally is closed
by positive middle ear pressure, or, when opened dur-
ing swallowing, by muscular action on the surrounding
cartilage.
3-10
NOAA Diving Manual — October 1991
Diving Physiology
Figure 3-6
Principal Parts
of the Ear
Semicircular canals
EAR
The air-containing external auditory canal, middle ear, and eusta-
chian tube are noted. The fluid-filled inner ear is subdivided into
the perilymphatic and endolymphatic spaces, which connect to
the subarachnoid space by the cochlear duct and endolymphatic
duct, respectively.
Source: Bennett and Elliott (1982) . with the
permission of Bailliere Tindall, Ltd.
The eustachian tube is lined by epithelium that is
similar to the lining of the nose, sinuses, and nasophar-
ynx. Abnormal nasal function can be caused by acute
or chronic inflammatory diseases, allergy, chronic irrita-
tion from excessive smoking or prolonged use of nose
drops, or chronic obstruction from internal or external
nasal deformities or lesions. Nasal dysfunction may
contribute to inadequate eustachian tube function, which
may cause middle or inner ear barotrauma in divers
(Sections 20.3.2 and 20.3.3).
Descent usually causes greater difficulty in equalizing
the ear than ascent because the air passes from the
middle ear more easily than into the middle ear from
the nasopharynx. As descent or compression proceeds,
middle ear pressure must be equalized constantly to
prevent middle ear barotrauma with possible eardrum
rupture or inner ear injury caused by rupture of the
round window (see Figure 20-1). Successful methods
of equalizing middle ear pressure are swallowing,
yawning, or gently blowing against a closed mouth and
nostrils. Forceful blowing (valsalva maneuver) should
never be done because, if the middle ear pressure is
already negative, forceful blowing, which causes an
increase in cerebrospinal fluid and inner ear pressure,
may rupture the round window. Injuries to the ear-
drum or inner ear may occur with as little as 3 pounds
(1.3 kilograms) of pressure differential, and they may
happen anywhere in the water column.
WARNING
Because Of The Danger Of Round Window
Rupture, A Forceful Valsalva Maneuver Should
Not Be Performed During Descent
The inner ear consists of a system of fluid-filled
bony channels within the temporal bone (Figure 3-6).
Membranous structures that are divided into two parts,
the vestibular system containing the semi-circular canals
and the auditory system, are located in these channels.
These two systems are interconnected and have a common
blood supply. Changes in cerebrospinal fluid pressure
can be transmitted directly to the inner ear compart-
ments, and therefore any maneuver such as straining,
lifting, or trying to clear the ears against closed nasal
passages can cause increased pressure in the ear's fluid-
filled compartments. Marked pressure changes may
cause ruptures between the inner and middle ear, leading
to vertigo and hearing loss; this may happen even in
shallow exposures.
In general, any individual who has difficulty with
middle ear ventilation at the surface should not dive.
Furthermore, individuals who have chronic nasal
obstruction or a history of frequent upper respiratory
infections, nasal allergies, mastoid or ear disease,
or chronic sinus trouble should have a complete
otolaryngological evaluation before diving. Also, indi-
viduals who have an upper respiratory infection of any
kind should not dive until the infection has cleared.
Systemic and topical drugs may improve nasal function
and sinus and middle ear ventilation. However, divers
should use such agents cautiously because the rebound
phenomenon that occurs after the drug, and especially
topical nose drops, wears off may lead to greater nasal
congestion and even greater equalization problems in
the ears and sinuses. Prolonged use of topical nasal
medications can cause chronic nasal irritation.
For safe diving, equalization problems must be
avoided. For example, if a diver cannot clear his or her
ears on the surface, he or she should not dive. Some
steps to be followed during descent are:
• Descend feet first, preferably down the anchor
line or a drop line. It is easier to equalize middle
ear pressure in the upright position because drain-
age is more effective in this orientation.
October 1991 — NOAA Diving Manual
3-11
Section 3
Figure 3-7
Location of
Sinus Cavities
• Clear the middle ear early, actively, and con-
scientiously during descent. Clearing by forceful
blowing against a closed mouth and nose should be
avoided, if possible.
• Stop the descent if ear blockage or fullness devel-
ops; the diver should ascend until these symptoms
have cleared, even if return to the surface is required.
Descent should not be continued until ear pain
develops.
Inner-ear decompression sickness (also called ves-
tibular decompression sickness) has occurred with no
symptoms other than vertigo, ringing in the ears, or
nausea (Farmer 1976). Vestibular decompression sick-
ness is seen more commonly after deep helium-oxygen
dives, particularly after a switch to air in the later
stages of decompression, although it also has occurred
in shallower air diving. Any diver with such symptoms
during descent or compression should be considered as
having inner ear barotrauma, including possible rup-
ture of the oval and round windows, and should not be
recompressed. Recompression would again subject the
diver to unequal middle ear pressures. However, even
if these precautions are heeded, hearing impairment
can develop as a result of diving. For this reason, divers
should have annual audiometric examinations.
NOTE
Any diver with ringing or roaring in the ears,
loss of hearing, vertigo or dizziness, or nau-
sea or vomiting during or shortly after decom-
pression from a dive should be treated as
having inner-ear decompression sickness.
3.2.1.2 The Sinuses
The sinus cavities are shown in Figure 3-7. Although
paranasal sinus barotrauma occurs only rarely in divers,
inflammation and congestion of the nose, nasal deformi-
ties, or masses can cause blockage of the sinus opening.
This blockage leads to a series of changes within the
cavities, consisting of absorption of pre-existing gas,
vacuum formation, swelling, engorgement, inflamma-
tion of the sinus lining, or collection of fluid in the
sinus cavity. When such blockage occurs during descent
in diving or flying, the intra-sinus vacuum becomes
greater and the resulting pathological changes are more
severe; there may be actual hemorrhage into the sinus
in some instances.
Paranasal sinus barotrauma also occurs during ascent;
the mechanism of this trauma appears to be a blockage
of a one-way valve of the sinus by inflamed mucosa,
cysts, or polyps, which permits pressure equalization
3-12
(
Orbit Of Eye
Maxillary
Sinus
(
Maxillary
Sinus
Opening To
Eustachian
Tube
Pharynx
(
Source: NOAA (1979)
NOAA Diving Manual — October 1991
Diving Physiology
during descent but impairs it during ascent. The symp-
toms and management of paranasal sinus barotrauma
are discussed in Sections 20.2.1 and 20.3.
Figure 3-8
Pressure Effects
on Lung Volume
3.2.1.3 The Lungs
As long as normal breathing takes place and the
breathing supply is ample, the lungs and airways will
equalize pressure without difficulty. If divers hold
their breath during a pressure increase, no difficulty
arises until the total volume of air in the lungs is
compressed to less than the residual volume. Once the
volume in the lungs becomes less than the residual
volume, pulmonary congestion, swelling, and hemor-
rhage of the lung tissue occurs; this condition is called
thoracic squeeze. Figure 3-8 graphically illustrates
the effects of pressure on lung volume.
In breath-hold diving, no high-pressure air is avail-
able to the lungs. Pressure compresses the diver's chest
and raises the diaphragm; pressure equalization results
from the fall in lung volume, i.e., the effects of Boyle's
Law (P V =P,VJ. Lung volume limits the extent of
tolerable compression. Descending to 33 feet (10 meters)
will reduce lung volume by one-half. Compression down
to residual volume (the amount of air in the lungs after
forceful expiration) can be tolerated; however, when
chest compression exceeds this limit, tissue trauma
occurs. Fluid from the capillaries and tissues then
enters the alveoli and the air passageways and may
cause gross hemorrhaging. Mild lung barotrauma causes
only pain and a slight exudation, which is quickly
reabsorbed, but in serious cases, the lungs may be
damaged. This form of trauma generally responds well
to conservative treatment consisting of general supportive
care, prevention of infection, and intermittent positive-
pressure inhalation therapy. Spraying with bronchodila-
tors and aerosols and inducing gravitational drainage
may prove beneficial if hemorrhage or bruising has
been severe.
The use of a breathing apparatus that has a high
inspiratory resistance may cause pulmonary edema
(increased fluid in the tissues of the lungs). In an effort
to maintain adequate lung ventilation during moder-
ate activity, the small veins of the lungs may be dam-
aged, fluid may seep through the membranes, and the
alveoli may rupture. In addition, gas exchange can be
hampered, which increases the risk of decompression
sickness. Coughing and shortness of breath are symp-
toms of this condition, and x rays of the chest may show
patchy pulmonary infiltration, which usually clears
within 24 hours without specific therapy.
The lungs can be traumatized during the compres-
sion phase of a dive or treatment if an individual stops
October 1991 — NOAA Diving Manual
At the surface
1 Atmosphere Absolute, 1 4.7 psi. The lungs are fully
expanded with a full breath of air.
At 33 Feet
2 Atmospheres Absolute. 29.4 psi. Because of
hydrostatic pressure, the same volume of air in the
lungs is reduced to only Vi its surface volume.
Source: NOAA (1979)
3-13
Section 3
breathing, either voluntarily by breath-holding or invol-
untarily because of windpipe or tracheal obstruction
or convulsions.
3.2.1.4 The Teeth
Pain in the teeth (harodontalgia) can occur in diving
and may be caused either by referred pain from the
paranasal sinuses or by tooth squeeze. This latter con-
dition, athough uncommon, is caused by a variety of
dental conditions, such as new lesions or a lesion that
has developed around the edge of an old filling (recur-
rent decay) (Rottman 1982). Tooth squeeze is not caused
by air trapped in a filling. Other causes of tooth squeeze
include recent extractions, gum infections that have
formed periodontal pockets, large areas of decay where
the pulp is infected, and recent fillings. Tooth squeeze
can also occur if a person dives while undergoing root
canal therapy. Part of the root canal procedure is to
dry and seal the canal between treatments with a material
that is designed to be adequate at a pressure of one
atmosphere. Exposure to higher pressures, however,
can produce small leaks in this material that are not
able to release air fast enough during subsequent ascent.
Like other squeezes, tooth squeeze usually subsides
when the ambient pressure is reduced to one atmo-
sphere. This mechanism also may be the explanation
for tooth explosion (Rottman 1982). Gas that has accu-
mulated slowly during a saturation dive can cause
tooth explosion during or after decompression.
3.2.2 Direct Effects of Pressure During Ascent
During a pressure decrease (e.g., during ascent), the
air in the body cavities expands. Normally, this air
vents freely and there are no difficulties. If breathing
is normal during ascent, the expanding lung air is
exhaled freely. However, if the breath is held or there
is a localized airway obstruction, the expanding air is
retained, causing overinflation and overpressurization
of the lungs. For example, the air in the lungs at a
depth of 66 feet (20.1 meters) gradually expands to
WARNING
A Diver Who Has Experienced Blowup (or an
Overpressure Accident) Must Immediately
Be Examined by a Physician
three times its volume during ascent to the surface (see
Figure 3-8). The air volume can expand safely to the
point of maximum inspiration, assuming there is no
airway obstruction. If the pressure decreases further,
overexpansion and overpressurization of the lungs may
cause progressive distension of the alveoli. This over-
distension may be general, which occurs with breath-
holding or insufficient exhalation, or localized, which
happens with partial or complete bronchial obstruc-
tion caused by the presence of bronchial lesions, mucus,
or bronchospasm. For this reason, individuals with
bronchial asthma should not do compressed gas diving
of any type. Problems of lung overinflation can occur
during ascent from depths as shallow as 4-6 feet
(1.2-1.8 meters) if the breath is held. Several of the
most commonly encountered physiological difficulties
associated with pressure during ascent are described
in the following paragraphs; each may be prevented by
breathing normally during ascent, providing there is
no localized airway obstruction. Figure 3-9 shows the
possible consequences of overinflation of the lungs.
WARNING
Do Not Hold Breath While Ascending
3.2.2.1 Pneumothorax
Distended alveoli or air-filled blisters (emphysematous
blebs) may rupture the membrane lining of the chest
(pleura), causing pneumothorax. Under pressure, this
is extremely dangerous because trapped intrapleural
gas expands as the diver surfaces, causing increased
pressure in the chest cavity. The lungs may be col-
lapsed by this pressure, and the heart may be pushed
out of its normal position. Symptoms and signs include
sudden severe pain, reduction of breathing capability,
and, rarely, coughing of frothy blood.
The rapid onset of pneumothorax can cause sudden
respiratory and circulatory difficulty, impaired car-
diac function, or death from shock. Early diagnosis
and prompt treatment with thoracentesis (chest punc-
ture) are essential. If recompression is required for
concomitant conditions, the pneumothorax must be
vented or released by a chest tube or other device
before ascent is accomplished.
3.2.2.2 Mediastinal Emphysema
Mediastinal emphysema is the result of air being
forced into the tissues about the heart, the major blood
vessels, and the trachea (windpipe) in the middle of the
chest. Gas trapped in the spaces between tissues may
expand rapidly with continuing decompression, caus-
ing impaired venous return. The symptoms of medias-
tinal emphysema are pain under the sternum (breast-
bone) and, in extreme cases, shortness of breath or
3-14
NOAA Diving Manual — October 1991
Diving Physiology
Figure 3-9
Complications From Expansion
of Air in the Lungs During Ascent
Cerebral Gas Embolism
Air Passes Via
Carotid Arteries
To Brain
Mediastinal
Emphysema
Air Passes Along
Bronchi To
Mediastinum
Air Enters-
Pleural Cavity
(Pneumothorax)
Air Enters
Blood Vessel
Alveoli
Expanded
Alveoli
Normal j^
Source: NOAA (1979)
fainting caused by circulatory interference resulting
from direct pressure on the heart and large vessels. The
treatment for mild cases of mediastinal emphysema is
symptomatic. In more severe cases, oxygen inhalation
may aid resolution of the trapped gas. For severe,
massive mediastinal emphysema, recompression is
required.
3.2.2.3 Subcutaneous Emphysema
Subcutaneous emphysema, which may be associated
with mediastinal emphysema, is caused by air being
forced into the tissues beneath the skin of the neck
extending along the facial planes from the mediasti-
num. Unless it is extreme (characterized by a crack-
ling of the skin to the touch), the only symptoms of
subcutaneous emphysema are a feeling of fullness in
the neck and, perhaps, a change in the sound of the
voice. Having the victim breathe oxygen will acceler-
ate the absorption of this subcutaneous air.
3.2.2.4 Gas Embolism
The most serious result of pulmonary overpressuriza-
tion is the dispersion of alveolar gas into the pulmo-
nary venous system. This gas is carried to the heart and
then into the arterial systemic circulation, causing gas
emboli (gas bubbles) in the coronary, cerebral, and
other systemic arterioles. These gas bubbles continue
to expand as the pressure decreases, which in turn
makes the clinical signs more severe. (Section 20.4.2
describes the symptoms of arterial gas embolism in
detail.)
The clinical features of traumatic arterial gas embo-
lism may occur suddenly or be preceded by dizziness,
headache, or a feeling of great anxiety. Unconsciousness,
cyanosis, shock, and convulsions follow quickly. Motor
and sensory deficits occur in various degrees and in
different combinations. Death is caused by coronary
or cerebral occlusion with cardiac arrhythmia, respira-
tory failure, circulatory collapse, and shock. Physical
examination of a person with a gas embolism may
reveal: (1) focal or generalized convulsions; (2) other
neurological abnormalities; (3) marbling of the skin;
(4) air bubbles in the retinal vessels of the eye;
(5) hemoptysis; or (6) Liebermeister's sign (a sharply
defined area of pallor in the tongue). Temporary obstruc-
tion of an air passage, which can occur with a cold or
bronchitis, increases the risk of gas embolism, and
diving with a respiratory infection should therefore be
avoided. A person with bronchial asthma has hyper-
reactive small airways in the lung. Breathing dry
compressed air, aspiring salt water or cold water,
exercising, or being anxious can all cause a bronchospasm
October 1991 — NOAA Diving Manual
3-15
Section 3
under water. Ascent with local air trapped in the alveoli
could cause a pressure imbalance and rupture, resulting
in gas embolism. For this reason, bronchial asthma is a
strict contraindication for compressed gas diving,
regardless of how well the asthma is controlled by
medication. Coughing or sneezing while in a recom-
pression chamber or while ascending during a dive can
also cause a gas embolism. Divers should stop their
ascents if they feel a cough or a sneeze coming on, and
chamber operators should stop the chamber ascent if
they are notified that an occupant of the chamber is
about to cough or sneeze.
The only effective treatment for gas embolism is
recompression; other treatment is merely symptomatic.
A patient should be kept in the head-down position,
which may help to keep bubbles in the circulation from
reaching the brain. Placing the patient on the left side
helps to maintain cardiac output, which may be impaired
because the gas bubbles have decreased the efficiency
of the pumping action of the heart (see Figure 19-9).
In non-fatal cases, residual paralysis, myocardial necro-
sis, and other ischemic injuries may occur if recom-
pression is not carried out immediately and may even
occur in adequately treated patients if there is a delay
in initiating therapy. Hyperbaric chambers that can-
not be pressurized to 6 ATA are not as effective for
embolism treatment as those with this capacity, but
recompression to 2 or 3 ATA is far better for the
embolism patient than no recompression.
WARNING
Central Nervous System Decompression
Sickness Is Clinically Similar to Gas Embo-
lism and the Treatment of Either Requires a
Recompression Chamber
In cases of gas embolism, administering oxygen and
positioning the body (head-down at a 15 degree angle)
are only partially effective; drugs and fluids also may
be helpful. These measures should be used in the inter-
val before the patient reaches a recompression cham-
ber (see Section 20.4.2).
3.2.2.5 Overexpansion of the Stomach and Intestine
The stomach and large intestine ordinarily contain
1.06 quarts (1 liter) or more of entrapped gas. Since
the intestines are surrounded by soft tissues, the com-
pression and re-expansion of these air bubbles are
ordinarily neither hazardous nor noticeable. If one
swallows air while diving, it may be necessary during
ascent to expel gas by belching or passing it per rec-
tum. An excess of gas in the stomach or intestine
during ascent may cause marked discomfort and vaso-
vagal effects. Eating large amounts of gas-producing
foods before diving is not recommended. If a diver
swallows enough air, he or she may have difficulty
breathing and may then panic. Accordingly, activities
that cause air swallowing, such as gum chewing, should be
avoided during diving.
3.2.2.6 Bubble Formation and Contact Lenses
The use of contact lenses by divers has increased
significantly in recent years. For this reason, studies
have been done to determine the inherent dangers of
using them, especially during decompression (Simon
and Bradley 1981). Three types of contact lenses were
compared, membrane (soft) lenses and two types of
polymethylmethacrylate (hard) lenses. One type of
hard lens (fenestrated) had a 0.016 inch (0.4 millimeter)
hole in the center, while the other type (non-fenestrated)
was solid throughout. During controlled decompres-
sions from 149 feet (45.5 meters) in a hyperbaric cham-
ber, subjects wearing the non-fenestrated hard lenses
developed small bubbles in the precorneal tear film
under the contact lens. These bubbles, first observed at
70 feet (21.3 meters), increased both in number and
size as decompression progressed. The divers wearing
these hard lenses experienced soreness, decreased vis-
ual acuity, and reported seeing halos when viewing
lights. These symptoms were noted at the time of bub-
ble formation and persisted for about 2 hours after
return to sea level (Simon and Bradley 1981). No bub-
bles were noted under the same decompression condi-
tions when the divers wore the fenestrated hard lens,
the soft membrane lens, or no lens at all.
The authors of this study concluded that the bubble
formation was caused by the lack of permeability of
the hard non-fenestrated lens (Simon and Bradley
1981). It is recommended, therefore, that divers electing
to wear contact lenses use either soft membrane lenses
or hard fenestrated lenses.
3.2.3 Indirect Effects of Pressure
The indirect effects of pressure are caused by changes
in the partial pressures of the gases in the breathing
medium. These effects include saturation and desat-
uration of body tissues with dissolved gas and changes
in body functions caused by abnormal gas tensions.
3.2.3.1 Inert Gas Absorption and Elimination
While breathing air at sea level, body tissues are
equilibrated with dissolved nitrogen at a pressure equal to
3-16
NOAA Diving Manual — October 1991
Diving Physiology
the partial pressure of nitrogen in the lungs. During
exposures to altitude (low pressure) or in diving (high
pressure), the partial pressure of nitrogen in the lungs
will change and the tissues will either lose or gain
nitrogen to reach a new equilibrium with the nitrogen
pressure in the lungs. The taking up of nitrogen by the
tissues is called absorption or uptake; giving up nitro-
gen from the tissues is termed elimination. In air div-
ing, nitrogen absorption occurs when a diver is exposed
to an increased nitrogen partial pressure, and elimina-
tion occurs when pressure decreases. This process occurs
when any inert gas is breathed.
Absorption consists of several phases, including the
transfer of inert gas from the lungs to the blood and
then from the blood to the various tissues through
which it flows. The gradient for gas transfer is the
partial pressure difference of the gas between the lungs
and blood and the blood and the tissues. The volume of
blood flowing through the tissues is usually small com-
pared to the mass of the tissue, but over a period of
time the gas delivered to the tissue will cause it to
become equilibrated with that carried in solution by
the blood. The rate of equilibration with the blood gas
depends on the volume of blood flow and the respective
capacities of blood and tissues to absorb the dissolved
gas. For example, fatty tissues hold significantly more
gas than watery tissues and will thus take longer than
watery tissues to saturate or desaturate excess inert
gas.
The process of elimination is the reverse of absorp-
tion. During ascent and after surfacing, the tissues lose
excess inert gas to the circulating blood by diffusion,
the gradient being the difference between the inert gas
partial pressure in each tissue and that in the blood
after the blood has equilibrated to the pressure of the
gas in the lungs. The amount of inert gas that can be
taken up in the blood is limited, so the tissue inert gas
tension falls gradually. As in absorption, the rate of
blood flow, the difference in partial pressures, and the
amount of inert gas dissolved in the tissues and blood
determine the rate of elimination. After decompressing to
the surface or ascending to a shallower level, equilibration
at the new level may require 24 hours or more.
It is assumed that, during decompression, the blood
and tissues can to some degree hold gas in supersaturated
solution without bubbles being formed. A supersaturated
solution is one that holds more gas than would be
possible at equilibrium at the same temperature and
pressure. Because of the ability of the blood and tissue
to become supersaturated for short periods of time, a
diver can ascend a certain distance, depending on the
depth and duration of his or her dive, without bubble
formation. The ascent establishes an outward gradient
and thus causes inert gas to be eliminated from body
tissues; after a sufficient time, enough gas will have
been eliminated to permit the diver to ascend further.
This process is continued until the diver reaches the
surface safely. On surfacing, the diver's body still
contains inert gas in supersaturated solution in some
tissues, but this is normally safe if kept within proper
decompression limits and if further pressure reduc-
tion, such as ascent to altitude, does not occur (see
Section 14.8).
The basic principles of absorption and elimination
are the same for any inert gas breathed. However,
there are differences in the solubility and rates of gas
diffusion in water and fat. Helium is much less soluble
in tissues than nitrogen and diffuses faster. Thus, helium
equilibration occurs somewhat more rapidly than is
the case for nitrogen. The advantages in using helium-
oxygen rather than nitrogen-oxygen mixtures are free-
dom from narcosis and a decrease in breathing resistance.
To develop mathematical models of gas solubility in
tissues, physiological theory postulates that the human
body is composed of several 'tissue compartments,' each
having a different 'half time.' For example, a com-
partment with a half time of 10 minutes is one in which
the tissues are 50 percent saturated with gas after
exposure to pressure for 10 minutes, while a 20-minute
compartment would be 50 percent saturated in 20 min-
utes, and so on. Various characteristics of these theo-
retical compartments, such as their relative fattiness,
are believed to account for these differences in tissue
half times.
3.2.3.2 Decompression Sickness
Decompression sickness (DCS) refers to the illness
that may occur after a reduction in barometric pres-
sure; such a reduction in pressure can occur either
when returning from the depth of a dive to the atmo-
sphere at sea level or when going from the atmosphere
at sea level to the atmosphere at altitude. The cause of
decompression sickness is the release of dissolved gas
from solution in the tissues and blood of the body and
the consequent formation of bubbles in the body. That
bubbles are the cause of DCS is borne out by the facts
that (1) bubbles have been seen and recorded during
incidents of DCS (as well as during decompressions in
which no DCS symptoms occurred), and (2) no other
explanation accounts so well for the success of re-
compression therapy as a treatment for DCS.
These bubbles can cause the symptoms and signs of
DCS through various mechanisms: Intracellular bub-
bles can disrupt the cells and cause loss of function;
intravascular bubbles can act as emboli and block
October 1991 — NOAA Diving Manual
3-17
Section 3
circulation either to a few or many tissues, depending
on where these bubbles lodge; and extravascular bub-
bles can cause compression and stretching of the blood
vessels and nerves. In addition, the blood-bubble inter-
face acts as a foreign surface and activates the early
phases of blood coagulation and the release of vasoactive
substances from the cells lining the blood vessels.
The causes of DCS include inadequate decompres-
sion (either because the decompression table used was
inadequate or was not followed properly), individual
physiological differences, or environmental factors.
Inadequate decompression is an obvious cause of DCS,
but frequently no symptoms occur even when the decom-
pression is obviously inadequate. In addition, decom-
pression sickness may occur even if the decompression
tables used are adequate and are strictly observed.
Moreover, it is common to assume that DCS cannot
occur on a 'no-decompression' dive; however, although it
is uncommon for DCS to occur on no-decompression
dives, it can happen. Differences in individual physi-
ology that may predispose to DCS include factors such
as obesity, fatigue, age, poor physical condition, being
dehydrated, or having an illness that affects the lung
or circulatory efficiency. Environmental factors that
have been implicated in the development of DCS are
cold water, heavy work, rough sea conditions, and the
use of heated suits.
Decompression sickness (colloquially termed 'the
bends') may be divided into two general categories,
Type I and Type II. Type I DCS includes those cases in
which pain, skin itching or marbling, or lymphatic
involvement are the only symptoms. The mildest cases
of DCS are those involving the skin or the lymphatics.
Skin bends are characterized by itching of the skin and
a burning sensation, which may also be accompanied
by the appearance of a mottled rash or marbling of the
skin. Lymphatic involvement is usually signaled by
painless swelling, but such involvement is uncommon.
Some experts also consider the symptoms of anorexia
and excessive fatigue that may follow a dive manifes-
tations of Type I DCS. In addition, 'niggles,' which are
mild pains that begin to resolve within 10 minutes of
onset, are considered symptoms of Type I DCS. These
mild cases of Type I DCS (skin bends, lymphatic
involvement, or niggles) do not require treatment other
than breathing pure oxygen at 1 ATA for a short period
of time, and often even this is not required. However,
any diver with niggles, skin bends, or lymphatic
involvement should be watched closely, because these
symptoms may presage the onset of more serious prob-
lems that will require recompression. It should not sim-
ply be assumed that these symptoms will not progress
to more severe ones.
The most common symptom of DCS is pain, which is
usually localized at a joint. Pain is reported to occur in
70 to 75 percent of DCS cases. The pain of DCS is
often described as a dull, throbbing pain deep in the
joint or tissue. The onset of this pain is usually gradual
and, in the early stages, the diver may not recognize
the pain as being related to DCS. However, the pain
slowly becomes more intense and, in some cases, it may
become severe enough to interfere with the strength of
the limb. In divers, the upper limbs are affected about
three times as often as the lower limbs. Before it is
decided that the case involves Type I DCS only, the
diver should be given a careful examination for any
neurological signs, because the pain may be masking
more serious symptoms. However, if pain is truly the
only symptom, the case falls into the Type I category
and should be treated as such.
Although pain is reported as a symptom in 30 per-
cent of cases of Type II DCS, this form of DCS includes
all cases that have respiratory problems, hypovolemic
shock, or more serious symptoms or signs of central or
peripheral nervous system involvement. Because of the
involvement of the nervous system, Type II DCS may
be associated with many different signs and symptoms.
These usually have their onset during or immediately
after a dive but, as is the case with Type I DCS, may
occur as long as 36 hours after surfacing. The most
common site for Type II DCS is the spinal cord, and
the most common symptoms are similar to those seen
in spinal cord trauma; these include paralysis, loss of
sensation, muscular weakness, loss of sphincter con-
trol, and girdle pain of the trunk. Often the symptoms
or signs of either spinal cord DCS or peripheral nerve
DCS do not follow a typical nerve distribution, and
care must be taken not to dismiss strange neurological
complaints or findings as hysterical in origin. Symp-
toms may be unstable in position and type during the
early stage of spinal or peripheral DCS; this shifting in
symptoms is different from the usual history of trau-
matic nerve injuries.
Cerebral decompression sickness can be manifested
in the form of almost any symptom. Common ones are
headaches or visual disturbances, and others include
dizziness, tunnel vision, confusion, disorientation,
psychotic symptoms, and unconsciousness. The com-
bination of nausea, vomiting, vertigo, and nystagmus
is characteristic of labyrinthine DCS, which is known
as the 'staggers' because its victims have difficulty
walking or maintaining their balance. Tinnitus and
partial deafness may also occur as part of this complex
of symptoms.
Pulmonary DCS is commonly known as the 'chokes.'
It is characterized by substernal distress on inhala-
3-18
NOAA Diving Manual — October 1991
Diving Physiology
Figure 3-10
Isobaric Counterdiffusion
tion, coughing that can become paroxysmal, and severe
respiratory distress that can end in death. This form of
DCS has been reported to occur in about 2 percent of
all DCS cases.
Hypovolemic shock may occur as the sole symptom
of Type II DCS, but it is more commonly associated
with other symptoms. The symptoms of rapid pulse
rate, postural hypotension, etc., are no different from
those found in hypovolemic shock occurring for other
reasons and should be treated in the same manner, that
is, by rehydration. Rehydration should be performed
orally if the patient is conscious or, if unconscious,
intravenously. Mild hypovolemia may be more com-
mon in diving than is generally realized because of the
increased heat load that results from working hard
while dressed in a diving suit, limited access to fluids,
pressure or cold diuresis, etc. Hypovolemic shock should
always be identified and treated, because the treat-
ment of DCS is less effective if the shock condition has
not been corrected. A more complete discussion of the
symptoms of DCS may be found in Elliott and Kindwall
(1982).
(A) Steady State-
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3.2.3.3 Counterdiffusion
Experiments dating back to 1962 have demonstrated
that the sequential use of different breathing gases in a
particular order, determined by their physical proper-
ties, could increase dive time at depth without increas-
ing a diver's decompression obligation. During some of
these experiments, however, it was discovered that a
diver breathing one gas mixture while surrounded by
another could develop serious gas lesions even when
the ambient pressure was maintained at a constant
level (D'Aoust and Lambertsen 1982).
For example, experimental subjects breathing neon
or nitrogen mixtures while surrounded by a helium
environment developed skin lesions, severe nausea,
vomiting, and vestibular derangement. Because this
phenomenon involves the passage of gases at the same
ambient pressure through tissue fluids in opposing
directions, it has been termed isobaric counterdiffusion or
isobaric counterexchange.
Depending on circumstances, counterdiffusion (super-
saturation or subsaturation) can occur in the skin or
between internal tissues and their capillaries. This can
lead not only to serious lesions but also to the forma-
tion of gas emboli even when ambient pressures are
constant. The process is shown in Figure 3-10. The
situation depicted in Figure 3-1 0A is referred to as
'steady state' and occurs when the superficial tissues
of the subject approach saturation with gas 2 (•) except
Source: Bennett and Elliott ( 1982) . with the
permission of Bailliere Tmdall, Ltd.
at the skin, where a gradient sloping to the exterior
exists; note that the superficial skin approaches satu-
ration with gas 1 (°), except for a gradient in gas 1 that
slopes from the exterior to the interior blood capillar-
ies. The process depicted in Figure 3-1 OB occurs in
deep tissue isobaric gas exchange. Deep-tissue isobaric
counterdiffusion occurs if the gas surrounding a diver
is suddenly changed to one that is different from the
one being breathed. In such a situation, gas 1 (c) will
be eliminated via the lungs and initially through the
skin, and gas 2 (•) will be taken up again via the
lungs and through the skin. Unlike the situation in
Figure 3-1 0A, this latter process must be considered
transient, since gas 1 (°) eventually will be reduced
to a negligible level and gas 2 (•) will eventually saturate
the subject at a final pressure that is no greater than
ambient (D'Aoust and Lambertsen 1982).
Depending on depth and the breathing gases being
used, the total gas tensions produced during the tran-
sient can reach levels sufficiently high to cause bubble
formation and decompression sickness. Work in this
complex field is continuing and should lead to the use
of improved gas sequences and improvement in the
efficiency of deep diving and the development of safer
decompression procedures.
October 1991 — NOAA Diving Manual
3-19
Section 3
3.2.3.4 Aseptic Bone Necrosis
(Dysbaric Osteonecrosis)
Exposure to compressed air at elevated atmospheric
pressure is sometimes associated with the death of
portions of the long bones of the exposed individual.
This condition is referred to as avascular necrosis of
bone, caisson disease of bone, or aseptic or dysbaric
bone necrosis. These changes are not of infectious ori-
gin, and they have been seen in patients suffering from
many conditions, such as chronic alcoholism, pan-
creatitis, and sickle-cell anemia, in patients using sys-
temic steroids, and in caisson (compressed air tunnel)
workers and divers. The development of changes in the
hip and shoulder joints of caisson workers, accompa-
nied by crippling effects caused by joint breakdown,
was first noted in 1888, but the disease has not been
particularly prevalent in divers, who generally observe
more conservative decompression procedures than com-
pressed air tunnel workers do.
If the lesions of aseptic bone necrosis occur in the
head of such bones as the femur (long leg bone) or
humerus (bone of the upper arm), the weakened underly-
ing bone that supports the cartilage covering the bone
will collapse under weight-bearing and activity, caus-
ing the joint surface to break down and become irregu-
lar. Pain occurs with movement of these joints and is
accompanied by muscle spasms around the joint and
the inability to use the joint in a normal manner. Since
the lesions often are bilateral and symmetrical, both
femoral heads may collapse, causing severe disability.
Lesions may also occur in the shafts of the long
bones, but these almost never cause symptoms or disa-
bility; however, bony scars that indicate increased density
may appear on x ray after new bone is deposited during
the healing process. Bone necrosis is seldom seen in the
elbows, wrists, or ankles of divers or caisson workers
(Kindwall 1972).
Factors that may be related to the likelihood of
developing bone lesions are frequency of exposure to
pressure, number of cases of bends, adequacy and
promptness of recompression treatment, and the total
amount of exposure to pressure. According to McCallum
and Harrison (1982), "The whole process from the
first radiographic appearance of the lesions to loss of
continuity in the joint surface may take only from 3 or
4 months to 2 or 3 years or perhaps longer."
The cause of aseptic bone necrosis has still not been
demonstrated beyond doubt. There is some evidence
that fat emboli may occlude circulation in the blood
vessels in bone and other tissues and thus may be a
factor in the development of hip lesions in the chronic
alcoholic with a fatty liver. In patients with gout,
lesions of the hip joints have contained sodium urate
3-20
crystals, which may have been a factor in the destruc-
tion of the joint surface. Bone lesions may not become
apparent on x rays for 4 months to 5 years after the
initiating insult. A detailed review of aseptic bone
necrosis may be found in McCallum and Harrison
(1982).
A 3-year survey of 350 full-time divers in the British
Navy showed a 5-percent incidence of aseptic bone
necrosis; half of the affected divers had shown no
evidence of having experienced decompression sick-
ness (Workman, personal communication). In a recent
survey of 934 U.S. Navy divers, 16 positive cases of
aseptic bone necrosis were found by standard radio-
graphic techniques; another 1 1 cases were interpreted
as doubtful (Hunter et al. 1978). The data revealed a
1.71 percent incidence overall and a 6.7 percent inci-
dence for divers over the age of 35. Although the
relationship between aseptic bone necrosis and decom-
pression sickness is not clear, the incidence of oste-
onecrosis in the subjects of this study was found to be
related both to age and number of months of diving.
In another study conducted by the U.S. Navy, the
long-bone radiographs of a group of 177 non-diving
enlisted men were compared to the long-bone radio-
graphs of 93 enlisted divers 35 years of age or over
(Hunter and Biersner 1982). It was found that diving,
as practiced by the U.S. Navy, contributes independently
to the development of aseptic bone necrosis and bone
cysts, as evidenced among divers in the tested group.
This conclusion was qualified by the statement that
the results must be viewed with caution 'because of the
larger number of doubtful films found for the nondiver
group than for the diver group, the small number of
positive and doubtful cases found in either group, the
age of the samples used (35 years of age or older), and
the substantial degree of unreliability demonstrated in
the classification of the films' (Hunter and Biersner
1982). A subsequent study, also by the U.S. Navy,
concluded that the prevalence of bone cysts among
Navy divers is probably related to one or more of
several conditions, including hyperbaric exposure,
genetic predisposition, and increased exposure to adverse
environmental or hazardous conditions (Biersner and
Hunter 1983).
3.2.3.5 Inert Gas Narcosis
Inert gas narcosis is caused by the raised partial
pressure of the inert gas in compressed air (see
Section 20.1.6). In diving, the most common type of
inert gas narcosis is nitrogen narcosis. Although nitrogen
and other inert gases are physiologically inert under nor-
mal conditions, they are able to induce signs and symp-
NOAA Diving Manual — October 1991
Diving Physiology
toms of narcosis or anesthesia at sufficiently raised
pressures. Other inert gases, such as those in the noble
gas series, range in narcotic potency from helium through
neon, nitrogen, argon, and krypton to the surgical anes-
thetic xenon. Recent analyses have demonstrated that
the qualitative behavioral effects are equivalent regard-
less of the specific gas causing the narcosis (Fowler et
al. 1985). Neon has been used satisfactorily for exper-
imental diving procedures but is not used in diving
today. Helium is a gas widely used in diving as a
substitute for nitrogen and to prevent narcosis (see
Section 15.1.3). Helium is such a weak narcotic that
helium narcosis has not been demonstrated.
Although many theories have been developed to
explain the mechanism of inert gas narcosis, it is clear
that it is caused by the physiochemical interaction of
the inert gas with the nerve cell membranes of the
body. A theory widely held that has been proved incor-
rect is that the signs and symptoms of narcosis are
caused by carbon dioxide retention resulting from
respiratory embarrassment occasioned by the breath-
ing of dense inert gas mixtures at raised pressures.
The signs and symptoms of narcosis are noticed first
at approximately 100 feet (30.5 meters) during com-
pressed air breathing and are similar to those of alco-
holic intoxication or the early stages of hypoxia; there
is a wide variation in individual susceptibility. However,
at greater depths the majority of compressed air divers
show impairment of thought, time perception, judg-
ment, reasoning, memory, ability to perform mental or
motor tasks, and increased reaction time (see Table 3-2).
Many measures have been used to assess the perform-
ance decrement resulting from inert gas narcosis.
Cognitive tests are more sensitive measures of narcotic
effects than manual dexterity tests (Fowler et al. 1985).
Intellectual capacities such as short-term memory are
affected to a greater extent than manual dexterity. If
divers expect to dive in situations where they are likely
to become narcotic, they should practice anticipated
tasks well before diving.
Divers experiencing nitrogen narcosis may have feel-
ings of elation and well-being (euphoria) and a sense
of detachment from the environment, accompanied by
a dangerous overconfidence, an uncontrollable desire
to laugh, and a tingling and vague numbness of the
lips, gums, and legs. There may be an inability to make
correct and rapid decisions or to concentrate effectively
on a task. Errors may be made in recording or compil-
ing data or computations. Novices, especially, may-
develop terror rather than euphoria. Narcosis is a sig-
nificant danger to divers because it increases the risk
of an accident and simultaneously diminishes their
ability to cope with an emergency.
The onset of narcosis is rapid. The condition is often
severe when a diver first reaches depth and may there-
after stabilize. Recovery is equally rapid and is accom-
plished by ascending to a shallower depth so that the
narcotic effect of the inert gas is reduced. Divers who
have experienced narcosis on a dive may not remember
events occurring at depth.
High alveolar pressures of N and CO, are additive
in their effects on performance, but CO, has no signif-
icant effect on nitrogen narcosis (Hesser, Adolfson,
and Fagraeus 1971). Factors that can increase the
susceptibility to narcosis include alcohol or the after-
effects of alcohol, fatigue, anxiety, cold, and the effects of
motion sickness remedies and sedatives. At a constant
nitrogen partial pressure, increases in the oxygen par-
tial pressure increase the signs and symptoms of nar-
cosis (Hesser 1963; Frankenhaeuser et al. 1960).
For air dives to depths greater than 100 feet
(30.5 meters), special precautions should be taken;
only experienced, fit, and well-trained divers should
be used. As many decisions as possible should be made
before the dive, including length of bottom time, dura-
tion of ascent, and actions to be taken in an emergency.
Experience, frequent exposure to deep diving, and a
high degree of training may permit divers to dive as
deep as 180-200 feet (54.9-61 meters) on air, but
novices or susceptible individuals are advised to remain
at shallower depths. At depths greater than 180 feet
(54.9 meters), the performance or efficiency of divers
breathing compressed air will be impaired. At 300 feet
(91.5 meters) or deeper, the signs and symptoms of
narcosis are severe and there is the possibility of hallu-
cinations, bizarre behavior, or loss of consciousness.
Furthermore, because of the associated increased oxygen
partial pressure at such depths, oxygen convulsions
may occur.
Experimental work has suggested that divers satu-
rated on compressed air or a mixture of nitrogen and
oxygen tend to adjust to some of the narcotic effects of
nitrogen, thus permitting deeper air breathing excur-
sions to be made (Hamilton et al. 1973, Schmidt et al.
1974, Langley and Hamilton 1975, Miller 1976).
However, divers must have demonstrated their ability
to adjust to elevated partial pressures of nitrogen before
procedures relying on it can be used without taking
extra care and providing additional supervision (Bennett
1976, 1982). Various efforts have been made to use
drugs and other methods to reduce the effects of nar-
cosis. In general, 'the weight of evidence favors the
conclusion that ethanol (alcohol) exacerbates narcosis
and amphetamine ameliorates it. This is consistent
with the view that narcosis depresses the CNS (central
October 1991 — NOAA Diving Manual
3-21
Section 3
Table 3-2
Narcotic Effects of
Compressed Air Diving
Depth
Effect
Feet
Meters
30-100
9.1-30.5
Mild impairment of performance on unpracticed tasks
Mild euphoria
100
30.5
Reasoning and immediate memory affected more than motor coordination and
choice reactions. Delayed response to visual and auditory stimuli
100-165
30.5-50.3
Laughter and loquacity may be overcome by self control
Idea fixation and overconfidence
Calculation errors
165
50.3
Sleepiness, hallucinations, impaired judgment
165-230
50.3-70.1
Convivial group atmosphere. May be terror reaction in some
Talkative. Dizziness reported occasionally
Uncontrolled laughter approaching hysteria in some
230
70.1
Severe impairment of intellectual performance. Manual dexterity less affected
230-300
70.1-91.5
Gross delay in response to stimuli. Diminished concentration
Mental confusion. Increased auditory sensitivity, i.e., sounds seem louder
300
91.5
Stupefaction. Severe impairment of practical activity and judgment
Mental abnormalities and memory defects. Deterioration in handwriting,
euphoria, hyperexcitability
Almost total loss of intellectual and perceptive faculties
300
91.5
Hallucinations (similar to those caused by hallucinogenic drugs rather than alcohol)
Derived from Edmonds, Lowry, and Pennefather (1976)
nervous system)' (Fowler et al. 1985). (Readers are
referred to Bennett (1982) and Fowler et al. (1985) for
more complete discussions of inert gas narcosis.)
3.2.3.6 High Pressure Nervous Syndrome (HPNS)
At diving depths greater than 600 fsw (183 msw),
signs and symptoms of a condition known as the high
pressure nervous syndrome (HPNS) appear and become
worse the faster the rate of compression used and the
greater the depth or pressure attained. HPNS is char-
acterized in humans by dizziness, nausea, vomiting,
postural and intention tremors, fatigue and somnolence,
myoclonic jerking, stomach cramps, decrements in intel-
lectual and psychomotor performance, poor sleep with
nightmares, and increased slow wave and decreased
fast wave activity of the brain as measured by an
electroencephalogram (Bennett et al. 1986).
First noted in the 1960's, HPNS was referred to
initially as helium tremors. Since that time, numerous
studies have been conducted that were designed to
determine the causes of HPNS and to develop means
of preventing it (Bennett 1982). Methods of preventing or
ameliorating HPNS include using a slow and steady
3-22
rate of compression to depth, using a stage compres-
sion with long pauses at selected intervals, employing
exponential compression rates, adding other inert gases
such as nitrogen to helium/oxygen mixtures, and
selecting personnel carefully. At present, the data suggest
that adding 10 percent nitrogen to a helium/oxygen
mixture, combined with the use of a proper compres-
sion rate, ameliorates many of the serious symptoms of
HPNS (Bennett 1982).
3.3 OXYGEN POISONING
Prolonged exposure to higher than normal oxygen
partial pressures causes a variety of toxic effects whose
manifestations are referred to collectively as oxygen
poisoning. It is now believed most likely that oxygen
poisoning is initiated by increased rates of formation
of superoxide, peroxide, and other oxidizing free radi-
cals that ultimately cause critical enzyme inactiva-
tion, lipid peroxidation, and impairment of cell mem-
brane function, with resultant disruption of intracellular
metabolism. These adverse effects of oxidant species
are opposed by anti-oxidant protective mechanisms
NOAA Diving Manual — October 1991
Diving Physiology
until the defenses are overwhelmed by the magnitude
and duration of oxidant stress. Thus, the onset time,
nature, and severity of overt manifestations of oxygen
toxicity are determined by the inspired oxygen pres-
sure and duration of exposure, as well as by unique
characteristics of enzyme function and external mani-
festations of specific disruptions of intracellular metabo-
lism. Since oxygen toxicity is a generalized phenome-
non that affects all living cells, its adverse effects are
ultimately expressed in all organ systems and func-
tions (Lambertsen 1978).
Pulmonary oxygen poisoning will occur during
prolonged exposure to any oxygen partial pressure above
0.5 atmosphere. At the lower end of this range, detecta-
ble degrees of pulmonary intoxication would occur
only after many days to weeks of saturation exposure
(Clark and Lambertsen 1971a). During continuous
administration of 100 percent oxygen, pulmonary symp-
toms have been observed within 12 to 24 hours at
1.0 atmosphere (Comroe et al. 1945), 8 to 14 hours
at 1.5 atmosphere (Clark et al. 1987), 3 to 6 hours at
2.0 atmospheres (Clark and Lambertsen 1971b), and 1 to
3 hours at 3.0 atmospheres (Clark et al. 1987). The
onset of symptoms is usually characterized by mild
substernal irritation that intensifies slowly at first and
then more rapidly until each inspiration is painful.
Coughing also progressively increases in severity until
it cannot be suppressed after deep inspiration. Short-
ness of breath during exertion, or even at rest, may
occur in severe exposures, presumably because of
decreased vital capacity, which can occur before symp-
toms are obvious.
Central nervous system (CNS) oxygen poisoning cul-
minating in generalized convulsions followed by un-
consciousness is a dominant manifestation of oxygen
intoxication during exposures to oxygen partial pres-
sures above 2.0 atmospheres. Convulsions may also
occur while breathing oxygen at lower partial pres-
sures during periods of exertion, particularly when
combined with underwater immersion, during periods
of carbon dioxide accumulation with concurrent incre-
ments in cerebral blood flow and brain oxygen tension,
and in unusually susceptible individuals. Muscular
twitching, especially of the face and lips, or hands,
may precede the onset of convulsions. When this sign
does occur, it should serve as a warning to reduce the
inspired oxygen pressure or to terminate the oxygen
exposure immediately, if possible.
In a group of 18 normal resting men breathing oxy-
gen for up to 3.5 hours at 3.0 atmospheres in a hyperbaric
chamber, constriction of peripheral vision always
occurred prior to convulsions (Lambertsen et al. 1987).
Nausea and dizziness may occur intermittently during
October 1991 — NOAA Diving Manual
continuous oxygen exposure. Other symptoms or signs
of CNS oxygen poisoning include ringing in the ears,
irregularities in breathing pattern, diaphragmatic
spasms, muscular incoordination, fatigue, confusion,
and anxiety. Extreme bradycardia to a degree suffi-
cient to cause cerebral ischemia with transient loss of
consciousness may occur during prolonged oxygen expo-
sure at 3.0 atmospheres (Pisarello et al. 1987).
Oxygen effects on organs other than the lungs and
CNS undoubtedly occur to some degree during expo-
sures that produce overt manifestations of pulmonary
or neurologic oxygen poisoning (Clark 1983, Lambertsen
1978). These effects go unnoticed because they are not
associated with chest pain, convulsions, or other obvi-
ous indications of oxygen poisoning. Although the nature
and degree of such effects are not now known, likely
target sites include the liver, kidney, endocrine organs,
and hematopoietic tissues. In addition, a regular increase
in myopia (near-sightedness) has been noted in some
patients who receive daily hyperbaric treatments (Lyne
1978, Anderson and Farmer 1978). Individuals exposed
to elevated partial pressures of oxygen in saturation
diving conditions also have been found to experience
potent visual effects (Kinney 1985).
In the absence of definitive information regarding
the subtle effects of oxygen toxicity, it is important to
remain aware that organ systems and functions exter-
nal to the lungs and CNS may be adversely affected by
either prolonged and continuous or repeated and
intermittent oxygen exposures. It is likely that such
effects would be most evident either near the end of a
continuous oxygen exposure or within several hours
after exposure termination. During a series of inter-
mittent oxygen exposures, the probability of detection
of subtle adverse effects will increase directly with the
number and duration of exposures.
In humans, recovery from oxygen poisoning after
oxygen pressure-exposure duration combinations that
do not produce overt intoxication appears to be suf-
ficiently complete to allow appropriately spaced,
repeated exposures without fear of cumulative or residual
effects (Lambertsen 1978). Full recovery from such
conditions probably requires relatively limited and rapid
reactivation of critical enzymes and reversal of early
alterations in cellular function. When overt manifesta-
tions of oxygen poisoning are produced, however, recov-
ery probably requires a more extensive and lengthy
reversal of tissue inflammatory reactions and repair of
cellular metabolic or structural defects.
Rates of recovery from the symptomatic and func-
tional effects of oxygen toxicity are variable for different
effects and different individuals. The complete resolution
of most symptoms associated with CNS oxygen poisoning
3-23
Section 3
occurs within minutes after the inspired oxygen pres-
sure is reduced to normal levels. Even after an oxygen
convulsion, recovery can occur within 30 minutes, but
it may require an hour or more in some individuals.
Chest pain and cough associated with oxygen-induced
tracheobronchitis usually resolve within 2 to 4 hours
after exposure termination, but unusual fatigue and
mild dyspnea on exertion may occasionally persist for
several days or even a few weeks after exposure. Although
there is a wide range in individual variability, oxygen-
induced deficits in vital capacity and forced expira-
tory and inspiratory flow rates typically reverse within
1 to 3 days after exposure, while recovery of pulmo-
nary diffusing capacity for carbon monoxide often
requires 1 to 2 weeks or more (Clark et al. 1987).
Hyperoxic exposures for diving and decompression
applications should be planned to remain well within
the known oxygen tolerance limits. They should also be
appropriately spaced to ensure complete recovery
between exposures. This approach will both avoid the
cumulative, residual effects of oxygen poisoning and
maintain a reserve of oxygen tolerance in case hyper-
oxygenation therapy is required for decompression sick-
ness or gas embolism. If (as might occur in a complex
treatment) oxygen therapy makes it necessary to cause
a significant degree of pulmonary intoxication in a
patient, subsequent operational exposures to hyperoxia
should be delayed for at least several weeks to allow
complete recovery.
A variety of conditions, procedures, and drugs can
be used to modify the oxygen tolerance of humans
(Clark and Lambertsen 1971a). These factors may
affect the time of onset, rate of progression, or severity
of one or more of the diverse manifestations of oxygen
poisoning. Of all the factors known to hasten the devel-
opment of oxygen poisoning, the effects of exercise and
carbon dioxide accumulation are most relevant to div-
ing operations.
By mechanisms that are not well understood (apart
from the possible influence of concurrent carbon diox-
ide retention), physical exertion itself exacerbates the
development of CNS oxygen poisoning. This reduction
in CNS oxygen tolerance is expressed both by the
earlier onset of convulsions at oxygen pressures above
2.0 atmospheres and by the occurrence of convulsions
during exposure to oxygen pressures at which oxygen-
induced seizures would otherwise almost never occur
in normal, resting individuals. The adverse effects of
exercise on pulmonary or other non-neurologic mani-
festations of oxygen intoxication have not been de-
monstrated.
Elevated arterial carbon dioxide pressure will also
hasten the onset of convulsions or cause them to occur
at unusually low oxygen pressures. Possible causes of
carbon dioxide retention include faulty CO absorp-
tion in closed-circuit breathing equipment, inadequate
pulmonary ventilation while exercising under condi-
tions of excessive external resistance to breathing, and
intentional hypoventilation to conserve air. Cerebral
vasodilation, which occurs in response to carbon diox-
ide retention, is responsible for the prominent eleva-
tion of brain oxygen tension during oxygen breathing
and accounts for most, if not all, of the associated
decrement in CNS oxygen tolerance.
Extending human oxygen tolerance by means of drugs
that have been shown to delay one or more manifesta-
tions of oxygen toxicity has not to date been shown to
be practical. Since such an agent ideally would have to
be distributed throughout all body tissues and oppose
toxic effects on a variety of enzymatic targets, it is not
likely that any drug now available will ever have more
than a limited potential for practical application (Clark
1983, Lambertsen 1978). At the present time, the most
useful procedure for extending human oxygen toler-
ance employs systematic alternation of hyperoxic and
normoxic exposure intervals to increase greatly the
tolerable duration of exposure to a selected level of
hyperoxia. This procedure takes practical advantage
of the empirical observation that many early, subclini-
cal effects of oxygen toxicity are reversed more rapidly
than they develop. Interrupted exposure as a means of
oxygen tolerance extension was initially studied in ani-
mals (Clark 1983, Lambertsen 1978), and its effective-
ness was later demonstrated directly in man (Hendricks
et al. 1977). Although periodic interruption of oxygen
exposure has been a component of the U.S. Navy oxy-
gen treatment tables (US Navy 1985) for many years,
its potential for oxygen tolerance extension has been
only minimally exploited to date.
3.4 EFFECTS OF COLD (HYPOTHERMIA)
Hypothermia is a condition in which the deep tissue or
core temperature of the body falls below 95 °F (35 °C),
which is the temperature at which malfunctions in
normal physiology begin to occur. If the core tempera-
ture drops below 96.8 °F (36 °C), diving operations
should be terminated because the consequences of con-
tinuing are serious. If the core temperature falls to
93.2°F (34°C), temporary amnesia may occur and
emergency rewarming and medical treatment are
required. Between 86° and 89.6 °F (30° and 32 °C),
cardiac irregularities commence and unconsciousness
may result.
Because water has a specific heat approximately
1000 times greater than that of air and a thermal
3-24
NOAA Diving Manual — October 1991
Diving Physiology
conductivity 24 times greater than that of air, the
body loses heat much faster in water than in air of the
same temperature. Fortunately, the thermoregulatory
system of the body is highly sensitive to stimulation
from the hands and feet, so that the body's heat gener-
ating systems are activated before the core tempera-
ture is affected seriously. The fact that the hands and
feet get cold first is thus, in this sense, an advantage.
With cold skin and with core temperatures below
96.8° F (36°C), the defense mechanisms of the body
are activated. These mechanisms consist of shivering,
which can increase basal body heat production by up to
five times, and vasoconstriction, which reduces blood
flow to the periphery and thus reduces heat loss.
Unfortunately, these mechanisms rarely achieve heat
balance, so that the diver continues to lose heat.
In addition to losing body heat by conductive loss
from the skin, a significant loss (10 to 20 percent of
total body heat loss) occurs by evaporation from the
lungs. The percentage is dependent on the humidity of
the inspired air, since the drier the air the greater the
evaporative heat loss. Further, as divers go deeper and
their breathing gas becomes more dense, convective
heat loss increases. Breathing gas heating is needed
beyond depths of 400 feet (122 meters).
3.4.1 Thermal Protection
Obviously, a diver exposed to cold water or even
moderately warm water for long periods must wear
protective clothing. Because of large individual dif-
ferences in cold tolerance, every diver must determine
the most suitable protection on an individual basis. A
variety of diving suits is available, ranging from standard
foamed neoprene wet suits and dry suits to specially
heated suits (for detailed descriptions of these suits,
see Sections 5.4 and 10.8).
The use of protective equipment, however, creates a
complication because the body's defense mechanism is
modified by the thermal barrier of the clothing. This
complication is only just being recognized as impor-
tant, and divers should be aware that the faster the rate
of heat loss, the smaller the drop in core temperature
for a given quantity of heat loss. Furthermore, whether
or not a person shivers is strongly influenced by: (l) the
rate of body heat loss; (2) the amount of body fat; and
(3) the body size. Larger, fatter people are less affected by
a given cold exposure and less affected by a given
amount of heat loss. For example, because heat trans-
fer is about 100 to 200 times faster in water than in air,
the heat that reaches the skin surface is rapidly trans-
ferred to the water. Generally, the thicker the layer of
subcutaneous fat, the greater the insulation.
October 1991 — NOAA Diving Manual
During swimming, the increase in energy production
resulting from exercise is counterbalanced by the increase
in muscle blood flow resulting in greater heat transfer.
Thus swimming promotes faster transfer of heat from
the core to the periphery, and this heat is in turn lost to
the water (Nadel 1984). This is why persons suddenly
immersed in cold water or divers becoming cold are
better off remaining still than trying to swim. Rapid
heat loss provokes strong shivering, so that the diver is
warned. Gradual heat loss over a long time often will
not cause shivering, yet the accumulated cooling and
the likelihood of hypothermia may be even greater,
with the likely result of impaired performance. Use of
apparently adequate thermal protection in prolonged
dives, or repeated dives over several days, may produce
long slow cooling and undetected hypothermia even in
tropical water. This affects memory and the speed of
reasoning and other cognitive functions, thus reducing
a diver's effectiveness and possibly endangering him
or her. In addition, repeated diving with inadequate
thermal protection may lead to an unwillingness to
dive again or to disabling fatigue — states that are now
known to be associated with being cold (Webb 1985).
3.4.2 Symptoms of Hypothermia
It is easy to recognize that hands and feet are cold by
the familiar sensations of discomfort, numbness, pain,
and diminished usefulness. On the other hand, loss of
body heat is extremely difficult to recognize. Individ-
uals are poor judges of their own thermal state. As
body heat is lost, the body approaches hypothermia;
recognizing hypothermia in its early stages is a serious
problem in diving. Deep hypothermia, meaning a rec-
tal temperature of 95 °F (35 °C) or lower, is dangerous;
at this stage, a diver may become helpless.
Chilling, even if not severe enough to threaten life,
will produce loss of dexterity and sense of touch in the
hands, making it difficult for a diver to do useful work
or even to control diving equipment such as weight
belts and buoyancy compensators. Shivering causes a
lack of coordination and may make it difficult for a
diver to hold the mouthpiece in place. By the time
shivering becomes uncontrollable, oxygen consumption
has increased significantly. Before this, however, the
dive should have been terminated and rewarming started.
The ability to think clearly and short-term memory
also may be affected seriously by cold. Figure 3-1 1
shows the effect of cold water on psychomotor
performance when a diver is wearing a 1/4-inch
(0.63 centimeter) wet suit, with hood, gloves, and
booties. For example, both fine digital manipulation
and the execution of a simple assembly task are affected
3-25
Section 3
Figure 3-11
Effect of Exposure Duration on
Psychomotor Task Performance
in Cold Water
(
Or-
o
E
o
.c
o
>.
CO
Q-
c
o
li
E -
CD
O I
CD
Q
CD
O
c
CO
E
o
20 -
40
60
80
Proper Decrement Curve
Type Task
Water Temperature "[
70
60
50
40
Fine Digital
Manipulation
1
3
6
7
Simple
Assembly
1
2
4
6
Gross Body &
Power Move.
1
2
2
3
,OStang& Wiener (1970)
' * Bowen (1968)
O Weltman & Egstrom Et Al (1970)
D Weltman & Egstrom Et Al (1971)
<
10
20
30
Time(Min)
40
50
Source: Egstrom (1974)
seriously at 50 °F (10°C) and 40 °F (4.5 °C) tempera-
tures, respectively, as shown in Figure 3-11. Studies
also have shown that air consumption can go up by as
much as 29 percent when diving in cold water (Dunford
andHayford 1981).
When diving in cold water, it is essential for the
diver to:
• Wear thermal protection appropriate for the water
temperature (see Figure 5-17)
• Note the first signs of cold hands and feet and loss
of dexterity and grip strength
• Note difficulty in performing routine tasks, con-
fusion, or a tendency to repeat tasks or procedures
• Note feelings of being chilled followed by inter-
mittent shivering, even though routine tasks can
still be performed
• Terminate a dive if any of the above symptoms are
present
• Be aware that even when properly dressed, hypo-
thermia may develop without shivering
• Watch the buddy diver and take heed of any
behavioral changes that may indicate existing or
approaching hypothermia.
3.4.3 Survival in Cold Water
If ship abandonment is necessary, there are proce-
dures that can significantly increase the chances of
survival, even in extremely cold water. Records show
that ship sinkings, even in the worst cases, usually
require at least 15 to 30 minutes. This affords valuable
time for preparation. The following procedures should
be carried out (U.S. Coast Guard 1975):
(
3-26
NOAA Diving Manual — October 1991
Diving Physiology
Locate and don a personal flotation device as quickly
as possible.
Try to enter the water in a lifeboat or raft to avoid
wetting insulating clothing and losing body heat.
Wear several layers of clothing because the trapped
air provides insulation. Even in the water, the extra
layers of clothing will reduce the rate of body heat
loss.
Especially protect the head, neck, groin, and the
sides of the chest, because these are areas of rapid
heat loss.
If it is necessary to enter the water, do so slowly to
minimize the likelihood of increasing breathing
rate, swallowing water, shock, and death. If jumping
is necessary, pinch the nose and hold the breath.
Once in the water, orient yourself with respect to
lifeboats, floating objects, etc. Also button up and
turn on signal lights as quickly as possible before
manual dexterity is lost.
Do not attempt to swim except to a nearby craft,
fellow survivor, or floating object. Swimming will
pump out the warmed water between the body and
clothing layers and cause the blood to move from
the body core to the extremities, thus increasing
body heat loss.
Keep the head and neck out of the water.
The best position to conserve body heat is to hold
the knees against the chest in a doubled-up fash-
ion with the arms tight around the side of the
chest. If others are nearby, huddle together and
maintain maximum body contact.
Board a life raft or floating object as soon as possible.
Keep a positive attitude, because a will to live does
make a difference.
3.4.4 Rewarming
At the end of a dive, a cold diver should be rewarmed.
This can be accomplished by having the diver drink hot
liquids such as soup or coffee, dry off in a warm place,
and bathe in warm water. Studies have shown that
rewarming in 104° F (40°C) water reestablishes nor-
mal body temperature 67 percent faster than rewarming
in 100°F (38°C) air (Strauss and Vaughan 1981).
Cold divers should not make a second dive on the same
day, because it is difficult to know when body heat has
been restored. However, if a second dive is necessary,
it is advisable to overdo the rewarming until sweating
occurs, which indicates that body heat has been restored.
Exercising to generate internal heat is also helpful to
speed up the rewarming process. The diver should then
change into warm, dry clothing and continue some
mild exercise to improve heat production and circula-
tion. Several hours may be required to restore all the
body heat lost. Drinking alcohol is not beneficial, because
it increases circulation of blood to the skin and speeds
the loss of body heat in cold surroundings. A diver who
is so hypothermic that he or she is helpless, irrational,
or lethargic should be rewarmed more vigorously. Ide-
ally, a hot bath should be used, but if none is available,
a hot water suit, electric blanket, or inhalation rewarming
are suitable methods. A hypothermic diver who is help-
less, irrational, lethargic, or unconscious needs medi-
cal attention and immediate and vigorous rewarming,
by any of the prescribed techniques (see Section 18.8.3
for further discussion of rewarming).
WARNING
Divers Who Have Been Chilled on Decompres-
sion Dives (or Dives Near the Decompres-
sion Limit) Should Not Take Very Hot Baths
or Showers Because These May Stimulate
Bubble Formation
3.5 EFFECTS OF HEAT (HYPERTHERMIA)
Unlike hypothermia, hyperthermia rarely is produced
by immersion in water. However, if the water temperature
reaches 85 °F (29.4 °C), there is little or no difference
in temperature between the skin and water and heat
cannot be transferred to the water. If heavy exercise is
performed under such conditions, there can be serious
overheating problems (Bove 1984).
Hyperthermia is encountered more commonly dur-
ing dive preparation where a diver, especially one encased
for a long time in a wet suit in the hot sun, can overheat.
The symptoms of hyperthermia include heat exhaus-
tion (see Section 18.8.1), with accompanying feelings
of dizziness, disorientation, rapid pulse, hyperventila-
tion, and potential loss of consciousness. A more seri-
ous result of hyperthermia is heat stroke, which can
cause death (see Section 18.1.8). An important factor
that increases the risk of hyperthermia is dehydration,
which can develop quickly as a result of excessive
sweating and lack of fluid replacement. Because it
reduces the volume of blood available for circulation
to the skin, dehydration increases the chances of divers
becoming hyperthermic. Dehydration also increases
the likelihood of decompression sickness as a result of
inadequate blood flow to the muscles and tissues. Water
and juices are recommended for ingestion because alco-
hol and other fluids act as diuretics, which will only
make matters worse. Divers who develop hyperthermia
should be put in a cool place, given fluids, and cooled
October 1991 — NOAA Diving Manual
3-27
Section 3
with water poured over the skin until the body temper-
ature returns to normal.
3.6 DRUGS AND DIVING
The use of prescribed or over-the-counter medications
while diving is a complex issue. There are no simple
answers to questions about which drugs are best for
which conditions in a hyperbaric environment. Indi-
vidual variability, existing medical and physical con-
ditions, and the mental and physical requirements of
diving all must be taken into account before phar-
macologically active agents are used.
3.6.1 Prescription Drugs
Drug-induced physiological and psychological re-
sponses often are altered in a hyperbaric environment.
The normal metabolic and excretion patterns of drugs
taken at one atmosphere may be significantly and
pathologically altered once the diver becomes pressur-
ized. An understanding of the types of changes that
occur, the implications of these changes, and the rela-
tionships between and among drugs, the environment,
and the diver are critical if therapeutic accidents are
to be avoided. Specific concerns include the following:
• The manner in which the drug is absorbed, metab-
olized, and excreted by the body in a hyperbaric
environment;
• The physical impact of the type of breathing gas,
increased density of the gases, water temperature,
and other environmental factors, and the degree of
diver exertion all contribute to the total effect of a
medication;
• Acceptable side effects, like drowsiness from
antihistamines, may be tolerated on the surface.
In the hyperbaric environment, however, such side
effects may become unacceptable, leading in some
cases to serious morbidity or even death. Impairment
of cognitive function, neuromuscular strength and
coordination, or integration of thought and action
can have catastrophic results while diving.
In addition to the antihistamines, drugs commonly
used that may adversely affect diver safety and per-
formance include: motion sickness remedies, amphet-
amines, tranquilizers, sedatives, hypertensive drugs,
and decongestants, some of which have been found to
induce impaired coordination, cardiovascular effects,
addiction, and inflammation of the lower airways. It is
noteworthy that the effects of some of these drugs may
appear to have worn off on the surface, only to return
when the diver becomes pressurized (Anonymous 1986).
3-28
While taking medication, therefore, careful consid-
eration should be given to the following elements before
diving:
• Why are the drugs being used, and are there underly-
ing medical conditions that may be relatively or
absolutely contraindicated for divers (Kindwall
1976)?
• What is the half-life of the drug, and for what
period of time before or after its use should the
diver not be exposed to a high-pressure environment?
• Will the side effects of the drug increase the
associated risks of diving to an unacceptable level?
• Will the drug interfere with physical performance?
• Will the drug impair exercise tolerance?
• Does the drug produce rebound phenomena?
A conscientious diver will discuss these questions with
his/her physician before diving while taking prescribed
or over-the-counter medications.
3.6.2 Illicit Drugs
It is obvious that cognitive and motor performance
can be impaired by the abuse of psychoactive agents.
Alcohol and marijuana (and other cannabis products)
are the most commonly abused central nervous system
depressants in the world today. Research clearly indi-
cates that their use is addictive and in some cases (e.g.,
with concurrent administration of barbiturates) can
potentiate other central nervous system depressants.
For example, in addition to being a depressant and
having other subjective effects, alcohol can cause reduced
blood glucose levels, which can lead in turn to weak-
ness and confusion. Alcohol also causes blood vessel
dilation, which can interfere with proper maintenance
of body temperature while diving (see Section 3.4).
Because of its diuretic action, alcohol can contribute
significantly to body dehydration, especially in the
tropics, where divers may combine alcohol with the
consumption of caffeine-containing drinks such as tea,
coffee, and colas.
There are reports that the use of marijuana preced-
ing cold water dives can reduce a diver's cold tolerance
and breath-holding capability, cause general discom-
fort, unexplainable apprehension, and a desire to ter-
minate a dive prematurely (Tzimoulis 1982). It is impor-
tant to note that the effects of smoking marijuana can
last for up to 24 hours (Anonymous 1986).
Cocaine is currently the most commonly abused central
nervous system stimulant. Its relatively short action
belies the hazard it poses to the diver. The hyper-
metabolic state that occurs during the use of cocaine
(it is rarely used alone and is often used with alcohol or
NOAA Diving Manual — October 1991
Diving Physiology
marijuana) may place the diver at risk of subsequent
fatigue, mental depression, acidosis, and the inability
to respond promptly to life-threatening emergencies.
It also increases the likelihood of an oxygen seizure
and can disturb the normal rhythm of the heart (Anon-
ymous 1986).
Divers and their physicians have an obligation to
communicate with one another. The clinician has the
responsibility to explain the nature of his or her treat-
ment to the diver, and the diver has the responsibility
of indicating to the treating clinician that a diving
exposure is anticipated. In general, divers should be
discouraged from using medications before diving. The
sharing of medications among divers also should be
discouraged. A diving exposure is not a good opportu-
nity for either a clinician or a diver to determine whether a
drug will be safe and efficacious for a given individual.
Conservative and safe practices are required for the
well-being and survival of the diver. Abstinence from
diving may be the most conservative approach for an
individual requiring systemic medication (Walsh and
Ginzburg 1984). (For a comprehensive review of the
effects of drugs in a hyperbaric environment, the reader is
referred to Walsh 1980.)
October 1991 — NOAA Diving Manual
3-29
t
<
♦
Page
SECTION 4 4.0 General 4-1
COMPRESSED 4.1 Compressed Air 4-1
AIR AND 4.1.1 General Safety Precautions for Compressed Air 4-1
SUPPORT 4.2 Air Compressors and Filtering Systems 4-2
EQUIPMENT 4.2.1 Maintenance 4-5
4.2.2 Lubricants 4-5
4.3 Compressed Gas Cylinders 4-5
4.3.1 Cylinder Markings 4-5
4.3.2 Cylinder Inspection and Maintenance 4-7
4.3.3 Cylinder Valve and Manifold Assembly 4-10
4.3.4 Low-Pressure Air Warning/Reserve Air Mechanism 4-1 1
4.3.5 Submersible Cylinder Pressure Gauge 4-1 1
c
«
<
COMPRESSED AIR
AND SUPPORT
EQUIPMENT
4.0 GENERAL
This section describes the composition and character-
istics of compressed air, the most commonly used breath-
ing mixture for diving, and the precautions that must
be taken when compressed air is used as a breathing
medium for divers. It also discusses the equipment
used in air diving, including compressors and cylin-
ders, and its maintenance and inspection.
4.1 COMPRESSED AIR
Compressed air is the most frequently used diver's
breathing medium. In its natural state at sea level
pressure, compressed air consists of nitrogen, oxygen,
argon, carbon dioxide, and trace amounts of other
gases. Table 4-1 shows the natural composition of air.
All ambient air does not meet the standards of purity
necessary for use as a diver's breathing medium. For
example, in urban areas the carbon monoxide concen-
tration in the air may be high, and in some cases it may
reach a concentration of 50-100 parts per million (ppm).
Ambient air may also contain dust, sulfur, oxides, and
other impurities. These contaminants derive from indus-
trial sources and automotive exhausts and must be
avoided in the breathing air supplied to a diver.
Scuba cylinders should not be filled from an ambient
air source when an air pollution alert is in effect. The
Environmental Protection Agency (EPA) monitors ozone
and other oxidants in metropolitan areas, and the local
EPA office should be consulted before a diving operation
is undertaken in an area suspected of having high
pollutant levels. The potential hazard presented by
breathing air obtained from ambient sources is under-
lined by the fact that at least 70 metropolitan areas in
the United States were unable to achieve compliance with
Federal limits for carbon monoxide by the end of 1987.
In addition to airborne pollutants, the air compressor
machinery and storage system themselves may intro-
duce contaminants, including lubricating oil and its
vapor, into the breathing medium. Additionally, the
temperature of the gas being compressed can be high
enough at each successive stage to cause pyrolytic
decomposition of any hydrocarbon compounds pres-
ent. This is particularly true if the compressor's interstage
coolers are not functioning properly. Intercooler mal-
function can be caused by excessive condensate, impaired
October 1991 — NOAA Diving Manual
Table 4-1
Composition of Air in its Natural State
Gas
Percent
by volume
Nitrogen 78.084
Oxygen 20.946
Argon .934
Carbon dioxide .033
Rare gases .033
Source: NOAA (1979)
cooling water circulation, or, in the case of air radiator
coolers, by loss of cooling air flow caused by trash, dirt,
or lint getting into the radiator fins.
The free air intake of the compressor must be located to
draw air from an area where there are no contami-
nants. Potential contaminants include engine or venti-
lation exhaust; fumes or vapors from stored chemicals,
fuel, or paint; and excess moisture.
No compressor should be allowed to operate with its
intake or first-stage suction blocked, because this will
produce a vacuum within the cylinders that can rap-
idly draw lubricating oil or oil vapor from the compressor
crankcase into the air system. Some effective methods
of preventing the intake of contaminated air are discussed
below.
4.1.1 General Safety Precautions for
Compressed Air
There are three primary safety concerns associated
with the use of compressed air or any compressed gas.
These are:
• That the gas be sufficiently pure and appropriate
for its intended use;
• That compressed gas cylinders or storage cylin-
ders be properly labeled and handled;
• That cylinders be protected from fire and other
hazards.
Compressed air is available from many sources. Most
of it, however, is produced for industrial purposes and
is therefore not of the purity necessary for use as a
4-1
Section 4
diver's breathing medium. When compressed air is
purchased from a manufacturer, it is essential that the
gas be certified by the manufacturer to be of high
purity, free of oil contaminants, and suitable for breath-
ing. Compressed air suspected of being contaminated
should not be used for diving until tested and found
safe.
Proper identification and careful handling of com-
pressed gas cylinders are essential to safety. Compressed
gas cylinders used to transport gas under pressure are
subject to Department of Transportation (DOT) regu-
lations. These regulations include design, material,
inspection, and marking requirements (see Section 4.3).
Compressed gas cylinders can be extremely hazardous
if mishandled and should be stored securely in a rack,
preferably in the upright position.
When in transit, cylinders should be secured against
rolling. Standing an unsecured cylinder on end or
allowing it to roll unsecured could result in the explo-
sive rupture of the cylinder. Cylinders can become
deadly projectiles capable of penetrating a wall, and
they can propel themselves at great speeds over long
distances.
Scuba cylinders are often fitted with a rubber or
plastic boot that has holes in it to permit draining.
These boots fit over the base of the cylinder and help to
keep the cylinder in an upright position. However,
cylinders equipped with such boots should not be left
unsecured in an upright position, because the boot
alone does not provide sufficient protection against
falling.
any attempt is made to repair the leak. Leaks can
sometimes be detected by painting a 20 percent deter-
gent soap solution (called a snoop) over the external
parts of the valve with a brush. Even small leaks will be
obvious because they will cause a froth of bubbles to
form. After the leak has been repaired, the soap solu-
tion used for leak detection must be removed completely
with fresh water and the valve dried carefully before
reassembly.
Scuba cylinders generally are not color-coded or
labeled as to type of gas contained; however, large gas
cylinders may be color-coded and labeled. The label
should be used to identify the contents of a gas cylin-
der, because color-coding is not standardized.
WARNING
Because Colors Vary Among Manufacturers,
the Content of Large Cylinders Should Always
Be Identified By Label— Do Not Rely on Cyl-
inder Color
Several special safety precautions to be observed
when using compressed gas are noted on the label of
gas cylinders. In general, these precautions concern
the flammability of the gas and its ability to support
combustion. Although not in itself flammable, com-
pressed air does support combustion and should there-
fore not be used or stored in an area where open flames,
hot work, or flammable gases are present.
NOTE
Cylinder boots should be removed periodi-
cally and the cylinder checked for evidence
of corrosion.
Compressed gas cylinders are protected against exces-
sive overpressure by a rupture disk on the valve. Because
regulators or gauges may fail when a cylinder valve is
opened to check the cylinder pressure, it is important
to stand to the side rather than in the line of discharge
to avoid the blast effect in case of failure.
WARNING
Do Not Stand in the Line of Discharge When
Opening a High-Pressure Cylinder
If a cylinder valve is suspected of having a thread or
seal leak, it should be completely discharged before
4-2
4.2 AIR COMPRESSORS AND
FILTERING SYSTEMS
Air compressors are the most common source of diver's
breathing air. The compressor used for umbilical div-
ing is generally backed up by a bank of high-pressure
gas storage cylinders to reduce the possibility of
interrupting the diver's breathing gas supply because
of loss of power or compressor malfunction.
There are two main types of compressors: high-
pressure, low-volume, for use in filling scuba cylin-
ders; and low-pressure, high-volume, used for umbili-
cal diving. A compressor is rated at the pressure at
which it will unload or at which the unloading switches
will activate. A compressor must have the output vol-
ume to provide sufficient breathing medium and to
provide pressure above the range equivalent to the
ambient pressure the diver will experience at depth.
When evaluating compressor capacity, the different
overbottom pressure and volume requirements of dif-
ferent types of underwater breathing apparatus and/or
NOAA Diving Manual — October 1991
Compressed Air and Support Equipment
helmets must be taken into consideration, as well as
umbilical length and diameter.
Any air compressor used for a diver's surface-supplied
system must have an accumulator (volume cylinder) as
an integral part of the system. The accumulator will
provide a limited emergency supply of air if the com-
pressor fails.
As the number of scientific, educational, and sport
divers increases, there is a concomitant rise in the num-
ber and variety of air compressors being used to supply
breathing air. Operators should become thoroughly
familiar with the requirements associated with the
production of breathing air. To ensure proper mainte-
nance and care, organizations using compressors should
assign the responsibility for the operation of compres-
sors to a specific individual.
Air compressors are generally rated by two parame-
ters: the maximum pressure (measured in pounds per
square inch gauge, or psig) they can deliver and the
output volume (measured jn standard cubic feet per
minute, or scfm) that can be delivered at that pressure.
To be effective, both the output volume and pressure
must be equal to or exceed the requirements of the
system they supply.
Air compressors commonly used to provide divers'
breathing air may be classified in the following groups:
• High-Volume, Low-Pressure Air Compressors.
These compressors are most often used to support
surface-supplied operations or to supply hyperbaric
chambers. They are generally found at sites where
large-scale diving operations are being conducted
or aboard surface platforms fitted out for diving.
Units commonly used have output volumes of
between 50 and 200 scfm at maximum discharge
pressures of between 150 and 300 psig. These units
may be either permanently installed or portable.
Portable units are generally built into a skid assem-
bly along with a power source (diesel engine, gaso-
line engine, or electric motor), volume cylinder,
filter assembly, distribution manifold for divers'
air, and a rack for storing divers' umbilical as-
semblies.
• Low-Volume, High-Pressure Air Compressors.
These compressors are used for filling scuba cyl-
inders and high-pressure air storage systems that
provide support for surface-supplied diving and
hyperbaric chambers. Portable units used for fill-
ing scuba cylinders are commonly available with a
volumetric capacity of 2 to 5 scfm at a discharge
pressure adequate to fully charge the cylinders
(2250 or 3000 psig, depending on the type of
cylinder).
Large, high-pressure cylinders are advantageous to
use as a source of breathing gas when there is conven-
ient access to a high-pressure compressor for recharging.
Using cylinders as the gas source reduces the chance of
losing the primary supply, since the entire volume of
gas needed for a dive is compressed and stored before
the dive. Most lockout submersibles carry the diver's
gas supply in high-pressure cylinders incorporated into
the system. Compressed gas cylinders are also gener-
ally mounted on the exteriors of underwater habitats,
submersibles, and diving bells to provide a backup gas
supply in case of emergency, and divers using the habitat
as a base can refill their scuba cylinders from these
mounted cylinders.
Many types of compressors are available: centrifu-
gal, rotary screw, axial flow, and reciprocating. The
most commonly used type in the diving industry is the
reciprocating, or piston-in-cylinder, type. These
compressors are further classified as "oil-lubricated"
or "non-oil-lubricated," depending on whether or not
they require lubrication of their compression cylinders.
In an oil-lubricated compressor, the oil in the crank-
case assembly also lubricates the pistons and cylinder
walls. As a result, some of the oil may come into direct
contact with the air being compressed. The lubricants
used in machines that provide breathing air must be of
the quality specified for breathing air and be so desig-
nated by the equipment manufacturer. One lubricant
should not be substituted for another unless the manu-
facturer's directions so specify. Chlorinated lubricants,
synthetics, or phosphate esters (either pure or in a
mixture) should never be used. Oil-free compressors
usually employ a standard oil-lubricated crankcase
assembly similar to that of oil-lubricated machines;
however, the pumping chambers in oil-free machines
are designed to run either with water lubrication or
with no lubrication at all. For this reason, some manu-
facturers describe their machines as oil-free, even
though the breakdown of such compressors could still
result in oily breathing air. The mechanical connec-
tions between the pumping chambers and the crank-
case on oil-free machines are carefully designed to
prevent the migration of crankcase oil into the pump-
ing chambers. The all-purpose crankcase lubricant
recommended by the manufacturer can usually be used
for oil-free compressors. The compressors used to pro-
vide breathing air in hospitals are of the oil-free type,
but these machines are still not widely used in opera-
tional diving.
The production of compressed air is a complex proc-
ess. The process begins as the piston in the first/second
stage head strokes upward in its cylinder. At that
point, the intake valve to the first stage closes and the
October 1991 — NOAA Diving Manual
4-3
Section 4
intake valve to the second stage opens. At the point of
maximum compression, the exit valve from the first
stage opens and compressed air is admitted to the
first-stage intercooler. Intercoolers cool the air before
further recompression and cause water and oil vapors
to condense and collect as the air passes through the
air/liquid separator at the discharge end of the inter-
cooler. The separator is fitted with a drain valve that
must be opened periodically to drain off accumulated
liquids. Each intercooler assembly is also fitted with a
relief valve that opens if the pressure rises above a safe
level.
The second stage of compression takes place on the
downstroke of the piston, during which the second-
stage inlet valve closes and the air is further com-
pressed. At the moment of maximum compression, the
exit valve to the second stage opens and compressed air
is admitted to the second-stage intercooler.
In a typical three-stage compressor, the air is taken
from ambient pressure to approximately 2250 psi. Com-
pressors typically use a ratio of 6:1, although this may
vary with different makes and models of compressors.
Each succeeding cylinder is proportionately smaller in
volume than the previous one. Some efficiency (approxi-
mately 10 percent) is lost because of the volume of the
intercoolers and residual cylinder volumes; this factor
is called volumetric efficiency.
Air leaving a compressor must be cooled and passed
through an air/liquid separator to remove any con-
densed water and oil vapors before storage or immedi-
ate use. Air from an oil-free compressor does not gen-
erally require any further treatment unless the applica-
tion requires that it be further dried or there is concern
about possible contamination of the intake air. Air
from an oil-lubricated compressor must be carefully
filtered to remove any possible oil mist, oil vapors,
possible byproducts from oil oxidation in the compres-
sor (predominantly carbon monoxide), or odors. Sev-
eral types of filtration systems are available. To use
most filtration agents properly, it is necessary to place
them in the filtration system in a specific order. To do
this, the direction of the air flow through the filter
system must be known, and, if there is any doubt, it
should be checked. Like other high-pressure compo-
nents, filter canisters should be inspected visually for
corrosion damage (High 1987). An inspection protocol
can be helpful when performing filter canister in-
spections.
For purposes of dehydration and adsorption, sub-
stances known as molecular sieves are often used. A
molecular sieve is a material having an extremely large
surface area to enhance its capacity for adsorption.
Since it removes harmful contaminants by causing
4-4
them to adhere to its surface, the sieve itself remains
inert and virtually unchanged physically during the
purification process. With appropriate periodic re-
generation processes, most molecular sieves are capa-
ble of removing a wide range of contaminants, includ-
ing nitrogen dioxide and most odors. However, the
most effective way to remove hydrocarbons and odors
is still with the use of activated carbon, which acts
much like a molecular sieve.
Another popular filtration system involves the fol-
lowing components, which are used in the sequence
shown:
• coalescing section to remove oil mist;
• dessicant section to remove water vapor, nitrogen
dioxide, hydrocarbons, and other contaminants re-
movable by adsorption;
• activated charcoal section for removal of resid-
ual odors and tastes; and
• Hopcalite® section for carbon monoxide removal.
The Hopcalite® oxidizes the carbon monoxide to car-
bon dioxide. Hopcalite® is a true catalyst in this reac-
tion and is neither consumed nor exhausted in the
process. The amount of carbon dioxide produced by
the catalytic action is so small as to be physiologically
insignificant. The amount of oxygen used up is approxi-
mately 0.5 part of oxygen per million parts of carbon
monoxide, which has no appreciable effect on the air
produced. The lifetime of this system is usually
determined by the lifetime of the dessicant, since
Hopcalite® is quickly "poisoned" and rendered ineffective
by excessive water vapor. An aspect of this process
that is not widely understood is that the carbon monoxide
oxidation process releases substantial quantities of heat.
If a Hopcalite® filter becomes extremely hot or shows
signs of discoloration, the compressor output air should be
checked for elevated carbon monoxide levels.
In addition to Hopcalite®, the use of activated alu-
mina in combination with Multi-sorb® is also widespread.
No matter what technique is employed, the location of
the compressor intake with respect to possible sources
of contamination is an important factor in ensuring
satisfactory air quality. Compressors should not be
operated near the exhausts of internal combustion
engines, sewer manholes, sandblasting or painting opera-
tions, electric arcs, or sources of smoke. Plastic con-
tainers of volatile liquids can give off fumes even when
they are tightly closed. Intakes must be provided with
filters for removing dust and other particles. Proper
orientation to wind direction is also critical in setting
up air compressor systems.
The final step in the production of pure air is the
filling station, usually located in a dive shop, on board
NOAA Diving Manual — October 1991
Compressed Air and Support Equipment
ship, or near a diving installation. It is important for
the diver to inspect the filling station to ensure that
proper safety precautions are being observed and that
Federal, state, and local regulations are being followed.
Figure 4-1 is a schematic of the processing of air from
the intake to the scuba cylinder. (Note that the system
depicted in Figure 4-1 includes a high-pressure booster
pump, which can increase the efficiency of cylinder
filling operations by providing air at the filling station
at a pressure above that of the air storage cylinder.)
For some diving operations, air is supplied by the
manufacturer in banks of high-pressure cylinders. These
cylinder banks are fitted with valves and manifolds
and may be used to provide breathing air in surface-
supplied diving operations and for filling scuba cylinders.
4.2.1 Maintenance
Both the compressor and filter system must be
maintained properly. When running, the compressor
must be cooled adequately, because the primary factor
causing the breakdown of lubricants and contamina-
tion of the compressed air is high temperature in the
compressor cylinder. Cylinder heads may be cooled by
air blowers or water spray systems or by cooling sys-
tems integral to the compressor machinery. A cylinder
head temperature controller is valuable in eliminating
the possibility of excessive cylinder temperatures. Partic-
ular attention should be paid to draining the interstage
and final-stage separators. Compressors and filters
are usually given routine maintenance on an hours-of-
operation basis. Filters should be examined and replaced
in accordance with the manufacturer's specifications.
The compressor lubricant and mechanical parts should be
replaced on a rigorous schedule, based on the manu-
facturer's recommendations or the results of an air
analysis. Analysis of the output air from oil-lubricated
compressor systems should be performed on a periodic
basis. Oil mist analyses are difficult to perform and
require careful collection techniques as well as quali-
fied laboratory analysis of the samples. However, car-
bon monoxide analyses, by far the most important, can
easily be performed in the field using colorimetric
tubes. (See Section 15.4 for information on contami-
nant analysis.)
A log should be kept for each compressor. The log
should record all time in service, maintenance, and air
analysis information.
4.2.2 Lubricants
Oil-lubricated compressors always have a small
amount of oil on the interior of the cylinder's walls, and
October 1991 — NOAA Diving Manual
some of this oil mixes with the air being compressed.
This oil is filtered out by the compressor's filtering
system. Because an improperly functioning filter can
raise temperatures sufficiently to decompose or ignite
the oil, it is important to select oil to be used as a
lubricant carefully.
The oil's flashpoint (the temperature of the liquid oil
at which sufficient vapors are given off to produce a
flash when a flame is applied) and auto-ignition point
(the temperature at which the oil, when mixed with air,
will burn without an ignition source) are both impor-
tant considerations. The most desirable compressor
lubricants have higher-than-average flashpoints and
low volatility. The oils recommended by the manufac-
turer of the compressor are generally the safest and
most efficient lubricants for this equipment.
4.3 COMPRESSED GAS CYLINDERS
The scuba cylinder or cylinders are secured to the
diver's back by an adjustable harness or form-fitting
backpack assembly equipped with a clamping mecha-
nism. Regardless of which model is employed, all straps
securing the apparatus should be equipped with cor-
rosion-resistant, quick-release buckles to permit rapid
opening under emergency conditions.
Scuba cylinders contain the compressed breathing
gas (usually air) to be used by a diver. Most cylinders
for diving are of steel or aluminum alloy construction,
specially designed and manufactured to contain com-
pressed air safely at service pressures from 2250 to
3000 psig (158 to 21 1 kg/cm2) or greater.
4.3.1 Cylinder Markings
Regardless of cylinder type, data describing the cyl-
inder must be clearly stamped into the shoulder of the
cylinder, which must be manufactured in accordance
with the precise specifications provided by the Inter-
state Commerce Commission (ICC) (until 1970), there-
after by the DOT, and most recently reflected on cyl-
inders as CTC/DOT, which indicates equivalency with
requirements of the Canadian Transport Commission
(High 1986a).
Regulatory changes in the more than 35 years since
scuba cylinders entered service in the United States
have produced a variety of code markings. Typically,
steel cylinders carry the code DOT (or ICC). 3AA
(steel type), and a service pressure of 2250 psig
(158 kg/cm2) or higher on the first line. These marks are
followed by the serial number, cylinder manufactur-
er's symbol (before 1982, the symbol of the user or
equipment distributor), the original hydrostatic test
4-5
Section 4
Figure 4-1
Production of Diver's Breathing Air
<
Pressure Gauge
Priority
Back Pressure
Valve
Magnetic Starter
& Hour Meter
Relief Valve
Final Moisture Separator
%
a
FT- . .
Pressure Switch
%-M
Isolation
Valve
-i i ! i i : !_
Bleed
Valve
Check Valve
Check Valve
Chemical Filters
* ' i i i i i_
— Moisture Separator
fS>-Auto Condensate Dump
"Compressor
Low Oil Level Switch
High Pressure Lines
■ Electrical Lines
Auto Air Distribution Panel
High Pressure Air Booster
X
Auto Air
Fill Panel
Fill Hoses
»
Air Storage Cylinders
Courtesy Skin Diver Magazine
date with testor's symbol, and a plus ( + ) mark, which
indicates that a 10 percent fill over-service-pressure
is allowed for the 5-year period of the original hydro-
static test.
Additional hydrostatic test dates, with the testors'
codes, will be added on successful retest at required
5-year or shorter intervals. However, since hydrostatic
test facilities rarely retest scuba cylinders appropri-
ately to permit inclusion of the plus mark ( + ) for
continued 10 percent overfill, few steel cylinders are
filled in excess of the designated service pressure
after the initial period. (Figure 4-2 shows steel scuba
cylinder markings.) Current practice allows a cylinder
submitted for the plus ( + ), that is the 10 percent
overfill, to fail the elastic expansion test and to be
reevaluated at the lower service pressure on the basis
of the permanent expansion test (High 1986b).
Aluminum alloy scuba cylinders entered U.S. com-
mercial service in 1971 and are code-marked in a
somewhat different manner than steel cylinders. Ini-
tially, DOT issued special permits or exemptions for
4-6
the manufacture of aluminum cylinders. These are
indicated in some code markings as SP6498 or E6498,
followed by the service pressure, which typically ranges
from 2475 to 3000 psi (174 to 211 kg/cm2). No plus
( + ) or overfill allowance is used with aluminum alloy
cylinders. Currently, aluminum cylinders reflect DOT
and CTC equivalency, a new material designation (3AL),
the service pressure, and a mark indicating volume and
that the cylinder is intended for scuba service (S80), as
shown in Figure 4-3.
NOTE
Aluminum alloy cylinders should never be
filled in excess of marked service pressure,
and steel cylinders without a plus ( + ) after
the current hydrostatic test date should also
not be filled over their marked service pres-
sures.
i
NOAA Diving Manual — October 1991
Compressed Air and Support Equipment
Figure 4-2
Steel Cylinder Markings
Initial Hydrostatic
Test Company
Serial Number
Steel Alloy Specification
£ 073440
PST
(DACOR)
4-83 +
Manufacturer
Distributor
NOTE There are four major manufacturers of scuba cylinders in (he United States
Their names and symbols are shown below
Manufacturer
Manufacturer's
Symbol
Inspector's
Official Mark
Name of
Inspection Service
Luxfer
0
A
Authorized Testing
Pressed Steel
PST
G
T. H. Cochrane Laboratory
Walter Kidde
(k) of WK
or WK&Co
& ®
Arrowhead Industrial Service
or Hunt Inspection
Norns Industries
<S>
C
T H Cochrane Laboratory
Derived from NOAA (1979)
The internal volume of a cylinder is a function of its
physical dimensions and may be expressed in cubic
inches or cubic feet. Of more interest is the capacity of
the cylinder, which is the quantity of gas at surface
pressure that can be compressed into the cylinder at its
rated pressure. The capacity usually is expressed in
standard cubic feet or standard liters of gas. Cylinders
of various capacities are commercially available. Steel
scuba cylinders generally have a rated working pres-
sure of 2250 psig (158 kg/cm:, or 153 atm) and contain
64.7 standard cubic feet (1848 standard liters) of gas.
Cylinders with capacities from 26 standard cubic feet
(742 standard liters) to over 100 standard cubic feet
(2857 standard liters) are used for scuba diving.
October 1991 — NOAA Diving Manual
WARNING
Do Not Fill Cylinders Beyond Their Service
Pressure
4.3.2 Cylinder Inspection and Maintenance
The exteriors of most steel cylinders are protected
against corrosion by galvanized metal (zinc), epoxy
paint, or vinyl-plastic coating. The zinc bonds to the
cylinder and protects it from air and water. Galva-
nized exteriors are recommended for protection against
corrosion; however, epoxy paint or plastic is unsatis-
factory for use over bare steel cylinders, because even
4-7
Section 4
Figure 4-3
Aluminum Cylinder Markings
Agency Responsible
for Standard
Aluminum Alloy
Specification
Service Pressure
Scuba Service
Serial Number
Manufacturer-
3AL
/ SP6498 \
\ E6498 )
3000 S8oAr-
(OmittedA
Cylinder Volume
CTC/DOT
(DOT) ,
\ First Hydrostatic
P71841^Luxfer 2 A85 ^prest
(Distributor) (A5081)<^ark
2/^v85 "*\Test and Company
NOTE There are four major manufacturers of scuba cylinders in the United States
Their names and symbols are shown below
Manufacturer's
Inspector's
Name of
Manufacturer
Symbol
Official Mark
Inspection Service
Luxfer
o
A
Authorized Testing
Pressed Steel
PST
G
T.
H. Cochrane Laboratory
Walter Kidde
(k) or WK
or WK&Co.
& £>
Arrowhead Industrial Service
or Hunt Inspection
Norns Industries
<8>
C
T.
H. Cochrane Laboratory
■Initial Test
Showing Testor's
Mark, With
Manufacturer's
Mark Separating
Test Month
and Year.
Courtesy William L. High
minor abrasions may penetrate these two coatings and
expose the underlying metal, allowing oxidation (rusting)
to begin immediately. Epoxy paint or plastic is accept-
able, however, over zinc-galvanized surfaces because
it reduces electrolytic corrosion of the zinc by salt
water and imparts an attractive appearance. With proper
preventive maintenance, electrolytic corrosion is rela-
tively insignificant on bare zinc coating.
Since internal rusting is a problem, manufacturers
formerly applied protective linings on the interiors of
cylinders. The use of internal coatings has only been
relatively successful, because even a small flaw in the
lining allows moisture in the cylinder to penetrate to
bare metal. Corrosion under the lining cannot be seen
4-8
or assessed. Also, the lining tended to loosen and, in
some cases, the resulting flakes clogged the valve or
the regulator. Damaged linings must be removed.
A corrosion-inhibiting epoxy-polyester finish usu-
ally is applied to the exterior of aluminum cylinders
both to protect them and to give them an attractive
color. If this coating scrapes off, an oxide layer forms
that tends to protect the cylinder from further corro-
sion. Often the interiors of aluminum cylinders have a
protective layer over the base metal, such as Alrock® or
Irridite®, which is applied during the fabrication process.
Air cylinders and high-pressure manifolds should
be rinsed thoroughly with fresh water after each use to
remove traces of salt and other deposits. The exterior
NOAA Diving Manual — October 1991
Compressed Air and Support Equipment
of the cylinder should be visually inspected for abra-
sion, dents, and corrosion. If the cylinder has deep
abrasions or dents, it should be tested hydrostatically
before refilling; external corrosion should be removed
and a protective coating applied to prevent further
deterioration of the cylinder wall. Care also must be
taken to prevent moisture accumulation inside high-
pressure cylinders. When a cylinder is completely drained
of air while being used with a single-hose regulator,
water may enter the cylinder through the regulator if
the purge button is depressed, allowing the second-
stage valve to open. Cylinders used under water as a
source of air for power tools or for lift bags often
become contaminated by moisture returning through
the valve. Cylinders should be stored with about
100 psi of air remaining in the cylinder to keep water from
entering the cylinder.
Cylinders should never be submerged completely
before the filler assembly is attached, because small
amounts of water may be trapped in the valve orifice
and injected into the cylinder. Moisture in a cylinder
often can be detected by (1) the presence of a whitish
mist when the valve is opened; (2) the sound of sloshing
water when the cylinder is tipped back and forth; or
(3) a damp or metallic odor to the air in the cylinder.
Water in a cylinder can create a particularly danger-
ous condition in cold water diving, because ice can
form in the first stage or in the hose prior to the second-
stage valve, causing the flow of air to the diver to be
interrupted.
Both steel and aluminum cylinders should be inspected
internally by a trained technician at least once a year
for damage and corrosion. Cylinders should be inspected
more frequently, and perhaps as often as every 3 months,
if they are used in a tropical climate or aboard ship, or
if they receive especially hard service. A special rod-
type low-voltage light that illuminates the entire inside of
the cylinder should be used for internal visual inspec-
tion. Standards and procedures for the visual inspec-
tion of compressed gas cylinders are discussed in detail
in High (1987).
Two forms of inspection are used, depending on the
interval since the previous inspection or the nature of
the suspected problem. An informal inspection is a
cursory look at a scuba cylinder's exterior and interior
to determine if there is a reason to examine it further.
A formal inspection is a complete evaluation against
standards, in which a judgment is reached and evi-
dence of the inspection is affixed to the cylinder in the
form of a sticker that attests to the cylinder's suitabil-
ity for continued use. The sticker should indicate the
standard used, the date of inspection, and the facility
conducting the inspection.
October 1991 — NOAA Diving Manual
The visual cylinder inspection procedure is neither
complex nor time consuming, but it should be performed
only by persons properly trained and using appropriate
tools. In general, the cylinder exterior should be com-
pared to standards for:
(1) cuts, gouges, corrosion (general, pitting, line),
and stress lines;
(2) dents or bulges;
(3) signs of heat damage;
(4) general abuse;
(5) condition of plating; and
(6) current hydrostatic test date.
Interior cylinder evaluations to standards should assess:
(1) type and amount of cylinder contents (if any);
(2) magnitude of general, pit, or line corrosion;
(3) thread integrity;
(4) defects in interior coating (if any);
(5) sign(s) of substantial material removal;
(6) presence of manufacturer's re-call items
(if any); and
(7) internal neck cracks.
There are several methods of hydrostatic testing of
cylinders, including direct expansion, pressure reces-
sion, and the water jacket method. The most common
method is the water jacket method, which involves
filling the cylinder with water, placing it in a water-
filled pressure chamber, raising the pressure inside the
cylinder with a hydraulic pump, and measuring the
amount of cylinder expansion in terms of water column
displacement. The pressure is increased to five-thirds
the rated pressure of the cylinder. According to DOT
regulations, a permanent expansion of 10 percent or
more of the total expansion indicates that the cylinder
is unsafe for use and should be condemned.
Scuba cylinders may be stored at full pressure for
short periods of time. However, it has been traditional
to store cylinders over longer periods with low pressure
to ensure that the valve is not inadvertently opened.
There is a potential for moist ambient air to pass through
the open valve into the cylinder as air temperatures
change. If there is moisture in the cylinder, air at the
higher pressure (higher partial pressure of oxygen)
accelerates corrosion.
However, a greater danger exists when partially filled
aluminum cylinders are exposed to heat, as might occur
during a building fire. The metal can soften before the
temperature-raised pressure reaches that necessary to
burst the frangible safety disk. An explosion may occur
well below the cylinder service pressure.
4-9
Section 4
Rules for the use of scuba cylinders are:
(1) Do not fill high-pressure cylinders if the date of
the last hydrostatic test has expired (5 years for
steel and aluminum cylinders) or if more than
1 year has passed since the last formal visual
inspection.
(2) Charge cylinder at a slow rate to prevent exces-
sive heat buildup.
(3) Never exceed the maximum allowable pressure
for any particular cylinder.
(4) Never perform maintenance or repairs on a
cylinder valve while the cylinder is charged.
(5) Handle charged cylinders carefully. Handling
by the valve or body is preferred. Handling by
straps or backpack may allow the cylinder to
slip or drop.
(6) Store charged cylinders in an upright position
in a cool, shady place to prevent overheating.
(7) Secure cylinders properly to prevent falling or
rolling.
(8) Internal inspections, hydrostatic tests, and repair
work should be performed only by those formally
trained to do so.
(9) Have cylinders visually inspected for interior
deterioration annually (or more frequently,
depending on use).
(10) Inspect cylinders externally before and after
each dive for signs of general pitting or line cor-
rosion, dents, cracks, or other damage. Never use
a welded, fire-damaged, uninspected, gouged,
or scarred cylinder.
(11) Remove cylinder boot periodically to inspect
for corrosion and rusting. Boots that inhibit rapid
draining and drying should not be used because
they allow water to remain in contact with the
cylinder, forming corrosion.
(12) Do not completely drain the cylinder of air
during dives. This prevents moisture from enter-
ing the cylinder.
WARNING
Aluminum Cylinders Should Not Be Heated
Above 350° F (177° C) Because This Reduces
the Strength of the Cylinder and Could Cause
Rupture
4.3.3 Cylinder Valve and Manifold Assembly
Open-circuit scuba cylinders are normally worn on
a diver's back with the manifold/valve assembly up. In
4-10
this configuration, the demand valve of the double-
hose regulator rides at the back of the diver's neck. The
demand valve of the single-hose regulator is positioned at
the diver's mouth, regardless of cylinder orientation.
The demand valves of both types must be kept in close
proximity to the diver's lungs to ensure a minimum
hydrostatic pressure differential between demand valve
and respiratory organs, regardless of diver orientation.
If this is not achieved, the diver's respiratory system
must work harder than necessary to overcome this
differential during inhalation (or exhalation, depending
on orientation). Thus, the position of the cylinders on
the diver's back is especially important when a double-
hose regulator is employed.
If diver's air is to be supplied by two or more cylin-
ders simultaneously, a manifold assembly is employed
to join the cylinders and provide a common outlet. The
manifold consists of sections of high-pressure piping
and appropriate fittings specially configured and
threaded to incorporate two or more cylinders, a valve,
and frangible burst disks into a single functional unit.
In addition, it may also contain a reserve valve.
The cylinder valve assembly is a simple, manually
operated, multiple-turn valve that controls the flow of
high-pressure gas from the scuba cylinder. It also is
the point of attachment for the demand regulator.
After the regulator has been clamped to the cylinder
valve and just before using the apparatus, the valve is
opened fully and then backed off one-fourth of a turn.
It remains open throughout the dive. On completion of
the dive, the cylinder valve is closed and should be bled
to atmospheric pressure, which prevents the O-ring
from blowing out while the regulator is removed.
When a single cylinder supplies diver's air, the cyl-
inder valve unit is generally sealed directly into the
neck of the cylinder by a straight-threaded male con-
nection containing a neoprene O-ring on the valve body.
Most cylinders placed in service before 1960 were
fitted with a valve having a 0.5-inch tapered thread
without O-rings. When a single cylinder is utilized, the
cylinder valve assembly houses a high-pressure burst
disk as a safety feature to prevent cylinder pressure
from reaching a critical level during charging or under
conditions of elevated temperature. Old-style lead-filled
blowout plugs must be replaced with modern frangible
disk assemblies. When a pair of cylinders is employed,
two burst disks are installed in the manifold assembly.
Valve manufacturers use burst disks designed to rup-
ture at between 125 and 166 percent of the cylinder
service pressure. The rating may be stamped on the
face of the burst disk assembly to prevent confusion,
and disks of different pressure ratings must not be used
interchangeably. Valves are not interchangeable between
NOAA Diving Manual — October 1991
Compressed Air and Support Equipment
Figure 4-4
Valve Assemblies
cylinders having different service pressures unless their
respective burst disk assemblies are also interchanged.
NOTE
The standard cylinder valve assembly de-
scribed above is known as a K-valve. A
cylinder valve that incorporates a low-air
warning/reserve air mechanism is known as a
J-valve.
4.3.4 Low-Pressure Air Warning/Reserve
Air Mechanism
Several mechanisms are used in open-circuit scuba
to perform the important function of warning divers
that the air supply is approaching a critically low level.
Some of these devices also provide a reserve air supply
that allows the diver to proceed safely to the surface.
Such a device is generally one of the following: J-valve,
submersible cylinder pressure gauge, or auditory warning
device. These mechanisms may be incorporated into
the cylinder valve/manifold assembly or into the demand
regulator. These devices and their limitations are
discussed in the following paragraphs.
Reserve Valve
The reserve valve (also called a J-valve), illustrated
in Figure 4-4, is a spring-loaded check valve that
begins to close as the cylinder pressure approaches a
predetermined level, generally 300 or 500 psi (23 or
30 kg/cm:). Until this pressure is approached, the
reserve valve permits an unrestricted flow of air to the
regulator throughout the dive. At the predetermined
pressure, a spring forces a flow check against the port
orifice and restricts the air flow, causing increased
breathing resistance. This is followed by total obstruc-
tion of air flow if the reserve air is not manually released.
The remaining or reserve air can be released by manually
overriding the spring-loaded check valve.
NOTE
The reserve valve lever must be in the down
position when charging cylinders.
When a diver depresses the cylinder valve/manifold-
mounted reserve lever, a plunger pin within the reserve
valve advances, forcing the flow check to back off the
orifice against the action of the spring. The remaining
October 1991 — NOAA Diving Manual
A. Cylinder Valve
B. Reserve Valve
Source: NOAA (1979)
300 or 500 psi (23 or 30 kg/cm2) of air is then made
available to the diver.
Divers should be aware that the availability and
duration of the reserve air supplied through a reserve
valve are dependent on the number of cylinders carried
as well as the depth of the dive. The 300 psi (23 kg/cm2)
reserve available is at actual cylinder pressure; it is not
300 psi above ambient pressure. Thus, at a depth of
100 feet (ambient pressure of approximately 50 psi),
only 250 psi (17 kg/cm2) is available until the diver
starts to ascend. Also, the reserve valve mechanism
retains a reserve air supply only in one cylinder of a
twin set of cylinders; the other cylinder or cylinders
are at a lower pressure when the reserve valve trips.
When the reserve mechanism is activated, the reserve
air distributes itself proportionately in all cylinders.
For this reason, the reserve valve mechanism employed
with twin cylinders must be set to provide a 500-psi
reserve. Unfortunately, though generally reliable, the
reserve valve mechanism is subject to physical damage
or mechanical failure and, if moved as little as 1/8" to
1/4", may be tripped inadvertently early in the dive,
which allows the reserve air to be exhausted without
the diver's knowledge.
NOTE
Reserve valves should be inspected annually
for defects or whenever a malfunction is
suspected.
4.3.5 Submersible Cylinder Pressure Gauge
Use of a submersible cylinder pressure gauge (Fig-
ure 4-5) is a requirement in nearly all recreational and
scientific diving. These gauges have largely replaced
constant reserve valves and audio systems. When reading
4-11
Section 4
Figure 4-5
Gauges
Courtesy William L. High
a gauge is difficult, as is the case in low-visibility
conditions, a constant reserve valve can be carried as
well. In addition, dial faces that glow in the dark
increase gauge readability under marginal light condi-
tions. Some newer gauges are able to provide data on
the amount of time remaining for the dive at the cur-
rent breathing gas consumption rate. This feature cal-
culates the pressure drop in the cylinder over time and
predicts the amount of air time remaining, assuming a
continued constant rate of use. However, divers should
be aware that changing their respiration rates can
dramatically alter the amount of time remaining at
low cylinder pressures.
The use of consoles that allow other types of gauges
to be added to the submersible pressure gauge has
increased the amount of information that can be obtained
when a diver monitors the submersible cylinder pres-
sure gauge. Maximum depth indicators, bottom tim-
ers, and compasses are now commonly associated with
pressure gauges. However, this use of console gauge
holders has added considerably to the mass of the
high-pressure hose end, and the hose and gauge must
be positioned carefully as a result; the high-pressure
hose can be run inside the waist strap on the back pack
so that the gauges are located on the thigh in a read-
able position. When worn improperly, a submersible
pressure gauge positioned at the end of a 2- to 3-foot
(0.7 to 1 m) length of high-pressure hose can increase
the chance that a diver will foul on bottom debris .or
become entangled with equipment. The gauge supply
hose muSt be connected to a high-pressure port with
compatible threads or be used with an adapter.
The high-pressure hose normally has brass fittings
with a restricting orifice. Should the high-pressure
hose rupture, this orifice prevents rapid loss of cylin-
der air and allows the diver time to abort the dive and
surface. Care must be taken to keep water from getting
into the first stage of the regulator before the cylinder
valve is opened, because otherwise water could be blown
into the submersible pressure gauge and other regula-
tor parts. Divers also should never submerge their
scuba cylinders when the valve is off and there is no
pressure in the attached regulator.
Gauge readings that err by as much as 300 psi
(23 kg/cm2) or more may occur because gauge accuracy
declines with use, especially if small amounts of water
have entered the mechanism. Divers should therefore
compare their gauges to known cylinder pressures reg-
ularly; gauges should be checked at various pressures.
Professional dive facilities often use gauges in their
high-pressure air systems that are accurate to 1 or
2 percent so they can make cylinders with known pres-
sures available to their customers for comparison. At
all NOAA diving units, pressure gauge testing devices
are available that can be used for gauge calibration
and to assess erratic needle movement.
WARNING
Do Not Look Directly At the Face of Any Pres-
sure Gauge When Turning on the Cylinder
Because of the Possibility of Blowout
Because the accuracy of the slow indicator needle
declines during normal use, the needle on a defective
unit might stick, which could cause the pressure read-
ing to be higher than it actually is. Divers in the field
can assess the adequacy of submersible gauge needle
function by releasing pressure from the gauge over a
3-minute period while they observe the needle for
erratic movement. Defective gauges must be returned
to the manufacturer for replacement of parts.
4-12
NOAA Diving Manual — October 1991
SECTION 5
DIVER AND
DIVING
EQUIPMENT
Page
5.0 General 5-1
5.1 Open-Circuit Scuba 5-1
5.1.1 Demand Regulators 5-1
5.1.1.1 Two-Stage Demand Regulators 5-2
5.1.1.2 Breathing Hoses 5-4
5.1.1.3 Mouthpieces 5-4
5.1.1.4 Check Valves and Exhaust Valves 5-5
5.1.1.5 Preventive Maintenance for Regulators 5-5
5.2 Surface-Supplied Diving Equipment 5-6
5.2.1 Free Flow/Demand Masks 5-6
5.2.2 Lightweight Free Flow Helmets 5-8
5.2.3 Lightweight Free Flow/Demand Helmets 5-8
5.2.4 Umbilical Assembly 5-8
5.3
5.2.4.1
5.2.4.2
5.2.4.3
5.2.4.4
5.2.4.5
5.2.4.6
5.2.4.7
5.2.4.8
5.2.4.9
5.2.4.10
Diver Equipment.
5.3.1
5.3.2
5.3.3
5.3.4
5.3.5
Gas Supply Hoses 5-9
Communication Cables 5-9
Pneumofathometer Hoses 5-9
Strength Members 5-9
Hot-Water Hoses 5-10
Assembly of Umbilical Members 5-10
Coiling and Storage of Umbilical Hose 5-10
Umbilical Maintenance 5-10
Harness 5-1
Weighting Surface-Supplied Divers 5-1
5-1
Face Masks 5-1
Flotation Devices 5-1
Weight Belts 5-13
Diver's Knife 5-14
Swim Fins 5-14
5.4 Protective Clothing 5-14
5.4.1 Wet Suits 5-15
5.4.2 Dry Suits 5-16
5.4.2.1 Dry Suit Insulation 5-17
5.4.2.2 Variable-Volume Neoprene or Rubber Dry Suits 5-17
5.4.3 Hot-Water Suit Systems 5-18
5.4.3.1 Open-Circuit Hot-Water Suits 5-18
5.4.3.2 Hot-Water Heater and Hoses 5-18
5.4.3.3 Closed-Circuit Hot-Water Suits 5-19
5.5 Diver's Accessory Equipment 5-19
5.5.1 Snorkels 5-19
5.5.2 Timing Devices 5-20
5.5.3 Depth Gauges 5-20
5.5.4 Wrist Compass 5-21
5.5.5 Pressure Gauges 5-21
5.5.6 Underwater Slates 5-22
5.5.7 Diving Lights 5-22
5.5.8 Signal Devices 5-22
5 5.9 Safety Lines 5-24
5.5.10 Floats 5-24
5.5.1 1 Accessories That Are Not Recommended 5-24
5.6 Shark Defense Devices 5-24
5.7 Underwater Communication Systems 5-25
5.7.1 Hardwire Systems 5-25
5.7.2 Acoustic Systems 5-26
5.7.3 Modulated Acoustic Systems 5-26
5.7.4 Non-acoustic Wireless Systems 5-27
♦
4
<
DIVER AND
DIVING
EQUIPMENT
5.0 GENERAL
This section describes diving equipment that has proven
to be reliable in a wide variety of underwater environ-
ments. New models and new types of diving equipment
come on the market regularly, and divers should be
careful when selecting equipment to ensure that the
equipment they have chosen is both safe and efficient.
Diving equipment must be maintained properly to per-
form at its best; selection and maintenance are funda-
mental to safe, effective diving.
5.1 OPEN-CIRCUIT SCUBA
Self-contained underwater breathing apparatus (scuba)
was developed to allow the diver freedom of movement
under water. In this diving mode, divers carry their
breathing medium on their backs, which allows dives
to be conducted without surface support.
A typical open-circuit scuba system consists of a
compressed air cylinder (tank) that contains high-
pressure air, a regulator that reduces the pressure of
the air in the tank to a pressure equal to that of the
diver's environment (ambient pressure), and a means
of attaching the tank and regulator to the diver.
A standard open-circuit scuba system is shown in
Figure 5-1.
Three major categories of scuba are currently in use:
• Open-circuit demand;
• Semi-closed-circuit (for mixed gas applications);
and
• Closed-circuit.
To select equipment that is appropriate for a particu-
lar dive, divers must know and understand the differ-
ence between self-contained diving (open-circuit air)
and surface-supplied diving.
The advantages of open-circuit scuba are:
• It permits diver mobility;
• The equipment needed can be carried or trans-
ported easily;
• It can be conducted from small boats (i.e., this
mode requires little support equipment); and
• Training for this mode is widely available.
The disadvantages of open-circuit scuba are that it:
• Cannot be used at great depths:
October 1991 — NOAA Diving Manual
Figure 5-1
Open-Circuit Scuba Equipment
Courtesy U.S. Divers
• Cannot supply breathing gas for dives of long
durations;
• Does not permit communication between the diver
and the surface;
• Cannot be used under conditions of poor visibility;
• Cannot be used for cold-water diving; and
• Requires a minimum of two divers (i.e., use of the
buddy system) for safety.
5.1.1 Demand Regulators
Demand regulators are used to reduce the pressure
of the breathing gas coming from high-pressure cylin-
ders to ambient pressure and to provide gas to a diver
on demand; the pressure differential created by the
respiratory action of the diver's lungs is the signal to
5-1
Section 5
the regulator to provide gas to the diver. Most regula-
tors automatically adjust to changes in the diver's
depth or respiration rate and conserve the gas supply
by delivering only the quantity of breathing gas required.
The function of "upstream" and "downstream" valves
is critical to the operation of regulators. An upstream
valve is one that opens against the air flow coming
from the high-pressure gas in the cylinder. Because
this valve is forced closed by gas of higher pressure, it
increases breathing resistance. If a major regulator
malfunction occurs, the upstream valve is closed by
the higher pressure gas, which, in turn, shuts off the
diver's supply. As a consequence of this feature, these
valves are only rarely manufactured today. A down-
stream valve, on the other hand, opens in the same
direction as the airflow, which causes such valves to be
forced open by the higher pressure air. This method of
operation results in smoother operation and reduced
inhalation effort. Almost all commercially available
regulators are now equipped with downstream second-
stage valves. Many different demand regulators are
available that deliver breathing gas at remarkably
consistent, low-differential pressures.
5.1.1.1 Two-Stage Demand Regulators
Two-stage regulators are designed to reduce the
breathing gas in a cylinder to ambient pressure in two
stages. The first stage reduces the pressure to approx-
imately 110 to 160 psi above ambient pressure, and the
second or demand stage reduces the pressure from this
level to ambient pressure. The major advantage of the
second stage is that air is supplied to the demand stage
at a nearly constant pressure, which allows both a
reduction in breathing resistance and fewer fluctua-
tions caused by changes in depth and decreasing cylin-
der pressure. Breathing resistance is reduced because
the demand valve works against a controlled pressure
(1 10 to 160 psi above ambient from the first stage).
All single-hose regulators are two-stage demand
regulators. A few two-stage, two-hose regulators are
still in use, and single-stage, two-hose regulators can
be seen occasionally. The original two-stage regulator
is the double-hose model similar to the original Aqua-
lung developed by Gagnon and Cousteau in 1943, in
which both pressure reduction stages are combined
into one mechanical assembly that mounts on the tank
manifold. Two flexible low-pressure hoses lead from
either side of the regulator to a mouthpiece that con-
tains both the inhalation and exhaust non-return valves.
The hose that leads over the right shoulder supplies the
breathing (inhalation) gas at ambient pressure, and
the exhaled gas exits through the mouthpiece and is
5-2
exhausted at the regulator through the hose leading
over the left shoulder. The two-hose regulator is no
longer widely used, and it is not currently in commer-
cial production.
The single-hose regulator is designed so that the
first pressure reduction stage mounts directly on the
tank manifold or valve, and the second pressure reduc-
tion stage is contained in an assembly that also includes a
mouthpiece and exhaust ports. The first and second
stages are connected by an intermediate pressure hose.
Air is delivered from the first stage at intermediate
pressure (110-160 psi over ambient) and from the
second stage at ambient pressure. The exhaust gas is
released into the water from the mouthpiece through
the exhaust port (non-return valve). The single-hose,
two-stage regulator is the most common regulator in
use because of its reliability, simplicity, and ease of
maintenance (Cozens 1980). Lighter weight plastics
are being used in second-stage housings, and silicone
rubber components have largely replaced less durable
materials. The performance characteristics of second-
stage components have also been improved by elimi-
nating metal-to-metal interfaces.
First-stage regulators are available in two types,
diaphragm and piston; both types are produced in two
configurations, unbalanced and balanced (Figure 5-2).
The diaphragm first-stage regulator (Figure 5-2a)
contains an unbalanced upstream valve (i.e., high-
pressure air acts to close the valve). A spring applies a
force that opposes that of the high-pressure air and
acts against a flexible diaphragm. The forces exerted
by the spring, the water (ambient), and the high-pressure
air combine to activate the valve. During descent, the
increasing hydrostatic pressure in the free-flooding
chamber displaces the diaphragm and opens the valve
until equilibrium is restored. When the diver inhales,
the reduced pressure in the intermediate chamber dis-
places the diaphragm and opens the valve until equi-
librium is achieved.
The balanced diaphragm first-stage regulator (Fig-
ure 5-2b) is designed so that the valve stem extends
completely through the high-pressure chamber; the
operation of the balanced valve is thus independent of
the tank (supply) pressure. In both balanced and unbal-
anced configurations of the diaphragm first-stage
regulator, failure of the diaphragm causes the valve to
close.
The unbalanced piston first-stage regulator (Fig-
ure 5-2c) contains a downstream valve (i.e., higher
pressure air acts to open the valve). A bias spring
in the free-flooding chamber controls the intermediate
pressure, and a hole in the shaft of the piston allows
NOAA Diving Manual — October 1991
Diver and Diving Equipment
Figure 5-2
First-Stage Regulators
a. Unbalanced Diaphragm
Valve Seat
• Diaphragm
HP Air-
[BM
Ambient
—Water
Pressure
Upstream Adjustable
Valve To 2nd Tension
Stage Spring
b. Balanced Diaphragm
"O" Ring
Seal\
HP Air-
a»
Ambient
* Water
Pressure
Valve To 2nd Diaphragm
Seat Stage
Adjustable
Tension
Spring
c. Unbalanced Piston
Valve
Seat
HP Air
Hollow
Stem
Piston
"O" Ring To 2nd \ Ambient
Seals Stage x Water
Pressure
d. Balanced Piston Adjustable
Hollow /Tension
Stem / Spring
Valve
Seat
HP Air
'O" Ring Ambient
Seals Water
Pressure
To 2nd
Stage
Piston
Source: NOAA (1979)
the dry side of the piston to be equalized at the inter-
mediate pressure. During descent, the increasing hydro-
static pressure in the free-flooding chamber displaces
the piston, opening the valve until equilibrium is
restored. When the diver inhales, the reduced pressure
in the intermediate chamber displaces the piston,
opening the valve until equilibrium is achieved.
The balanced piston regulator (Figure 5-2d) is
designed so that the piston movement is isolated from
the high-pressure chamber by an 0-ring: the operation
of the valve is therefore independent of tank (supply)
pressure. In both the balanced and unbalanced config-
uration, failure of the piston seal tends to cause the
valve to fail in the open or free-flow mode.
The second-stage regulator, located in the mouth-
piece, is connected to the first stage by a medium-
pressure hose; this hose, in turn, supplies a constant
medium pressure to a valve in the mouthpiece. The
reduction in pressure in a low-pressure chamber in the
mouthpiece caused by inhalation results in distortion
of a diaphragm. This distortion applies pressure to a
stem or linkage that is connected directly to the medium-
pressure air inlet valve, opening the valve and admit-
ting air into the mouthpiece at ambient pressure. As
long as a diver inhales, air will continue to flow into the
mouthpiece. In addition, most regulator manufactur-
ers incorporate aspirators (venturi's) into their designs
to improve the dynamic breathing characteristics of
the regulator; the venturi effect tends to pull the dia-
phragm inward, which reduces inhalation effort. On
exhalation, the diaphragm returns to a neutral posi-
tion, releasing pressure on the stem or linkage, which
returns to its normal position, closing the medium-
pressure valve. As exhalation increases the pressure in
the low-pressure chamber to levels above ambient, a
one-way mushroom valve is unseated, which allows
the exhaled gas to be exhausted into the surrounding
water. A properly constructed second stage has a min-
imum of dead space, which limits the amount of air
that will be rebreathed.
The pilot valve second stage also has been used with a
number of regulators; it incorporates an air supply
valve that is opened and closed by air pressure rather
than by mechanical leverage. The opening pressure is
generated by air flow through a diaphragm-activated
downstream pilot valve. A simple mechanical linkage
is used between the diaphragm mechanism and the
pilot valve. Because the pilot valve is very small, the
amount of spring tension needed to counterbalance the
pressure is small and less force is necessary to open and
close the valve. The pilot valve opens only a little way
to permit the air supply valve to pass a small amount of
air into a control chamber. With this system, air supply
valve openings larger than those used in conventional
leverage systems can be used in the second stage.
Because there is a piston opposite the valve opening
that exactly counteracts the opening force of the air
pressure, the supply valve is balanced and therefore is
not affected by intermediate pressure variations. The
system can be described as a pneumatically amplified
second stage; this means that a small force, the pilot
valve, is pneumatically amplified to move a larger
force, the air supply valve.
October 1991 — NOAA Diving Manual
5-3
Section 5
The aspirator port, mentioned previously, is directed
toward the mouthpiece inside the regulator and gener-
ates a slight vacuum within the regulator case when air
is flowing. As a result, less effort is required to main-
tain air flow during inhalation. Although normally set
for demand breathing, the aspirator can be set for
positive-pressure breathing. The regulator is so sensi-
tive to pressure variations that, in some cases, a
dive/predive switch is incorporated to decrease the
response of the regulator. Normally, a regulator requires
a pressure or suction equivalent to that of a 2-inch
(5.1 cm) water column to activate air flow; the pilot
system requires a pressure equal to that of a 0.5-inch
(1.3 cm) water column.
The operation of the regulator is initiated by a slight
inhalation effort that causes the regulator diaphragm
to be drawn downward. The resulting linkage move-
ment opens the pilot valve, and air flows to pressurize
the control chamber; this, in turn, opens the air supply
valve. The structural arrangement between the pilot
and air supply valves provides a controlling feedback
that allows the air supply valve to move only in exact
response to the pilot valve. The pilot valve acts as a
safety relief valve in the event of first-stage malfunc-
tion. A mechanical override also is incorporated into
the system to ensure operation in case the pilot valve
malfunctions.
5.1.1.2 Breathing Hoses
In double-hose scuba, the breathing hoses (Fig-
ure 5-3A) are flexible, large-diameter rubber ducts that
provide passageways for air from the cylinder to the
diver. Corrugated rubber hoses are common, but hoses
may also be made of rubberized fabric with metallic
rings or spiral stiffening. To provide minimum resist-
ance to breathing, the hose should have an inside diameter
of at least 1 inch (2.5 cm) and should be long enough in
the "relaxed" state to allow full freedom of body move-
ment. The hose must be capable of stretching to twice
its relaxed length without collapsing or buckling.
Single-hose scuba, with the second stage of the
demand regulator mask mounted or mouthpiece mount-
ed, does not require the large-bore, ambient pressure
breathing hose described above because the gas in the
hose is at medium pressure (110 to 160 psi above
ambient) rather than at ambient pressure (Figure 5-3B).
The second-stage or demand valve is connected to a
cylinder-mounted first-stage regulator by a single,
medium-pressure hose of relatively small diameter.
Exhaled gases are discharged directly into the water
through an exhaust valve in the mask or mouthpiece.
Breathing hoses should be checked for cracks or
chafing before every dive. Divers should check the
5-4
Figure 5-3
Breathing Hoses
A. Corrugated Hose
B. Low-Pressure Hose Fitting
Source: NOAA (1979)
connections that are covered by hose protectors espe-
cially carefully before diving, because the protectors
sometimes conceal damage.
5.1.1.3 Mouthpieces
The mouthpiece (Figure 5-4) provides a channel for
the flow of breathing gas between the diver and the
life-support system. The size and design of the mouth-
piece differ among various manufacturers, but the
mouthpiece generally is molded of neoprene, silicone
rubber, or other materials that have a low deteriora-
tion rate. (Silicone rubber has the added advantage of
being hypoallergenic.) Typically, the mouthpiece con-
sists of a flange that fits between the diver's lips and
teeth. Bits, one on either side of the opening, serve to
space the jaws. The mouthpiece should fit comfortably
and be held in place when a slight pressure is exerted
by the lips and teeth. The novice diver often forgets
that the bits are spacers and should not, under normal
conditions, be used as grips. In an emergency, the bits
will provide a reliable grip, but continuous force exerted
through the teeth will weaken the bits and cause con-
siderable fatigue of the muscles around the jaws.
Many individuals have difficulty with temporal man-
dibular joint (TMJ) pain when gripping the mouth-
piece tabs too firmly during a dive. Mouthpieces that
spread the load to the rear teeth are more comfortable.
Learning to relax the jaw is probably the most effec-
tive deterrent to TMJ pain.
On a two-hose regulator, the mouthpiece assembly
incorporates a system of one-way check valves, and
clamps are provided for the breathing hoses. In a single-
hose scuba regulator, the mouthpiece is incorporated
into the second-stage demand valve housing. In some
cases, the mouthpiece assembly can be replaced entirely
by a full face mask. The use of a full face mask in lieu
of a mouthpiece facilitates voice communication by
freeing the diver's mouth; however, with this configu-
ration, an oral nasal mask must be used to prevent
carbon dioxide buildup.
NOAA Diving Manual — October 1991
Diver and Diving Equipment
Figure 5-4
Mouthpieces
A. Double Hose
B. Single Hose
Courtesy U.S. Divers
5.1.1.4 Check Valves and Exhaust Valves
Check valves and exhaust valves (Figure 5-5) are
designed to permit gas flow in one direction only. Check
valves direct the flow of inhaled and exhaled gases
through the breathing system. During inhalation, pres-
sure decreases in the mouthpiece chamber (now lower
than ambient), which seats the exhalation check valve
but opens the inhalation check valve. During exhala-
tion, the air is directed out through the mouthpiece
and exhalation tube to the exhaust valve. This pair of
valves within the mouthpiece assembly minimizes dead
air space within the system, and this, in turn, mini-
mizes the rebreathing of exhaled gases. The inhalation
check valve also prevents water from entering the demand
regulator when the mouthpiece floods.
An exhaust valve is a special check valve that per-
mits the discharge of exhaled gas from the breathing
system and prevents the entrance of water. A flapper
valve (also called a flutter valve) is typically used as an
exhaust valve in the double-hose regulator, while a
mushroom valve generally fulfills this function in the
single-hose model. A flapper valve is simply a soft
rubber tube collapsed at one end; when ambient water
pressure is greater than the air pressure within the
valve, the valve remains in the collapsed condition.
During exhalation, however, the increase in pressure
above ambient pressure forces the flapper open, allowing
the gas to escape. Water cannot enter the valve while
the higher pressure gas escapes, and when the pressure
equalizes, the flapper returns to the relaxed or closed
position.
The mushroom valve on single-hose models is made
of extremely soft, flexible rubber, which renders it
very sensitive to changes in pressure across the check
valve. A wheel-shaped valve seat is fashioned to hold
the rubber mushroom in place. Rigid spokes of the
valve seat support the mushroom valve against a clos-
ing pressure but permit the flow of air when pressure
within the mouthpiece exceeds ambient pressure.
5.1.1.5 Preventive Maintenance for Regulators
Because regulators are one of the primary compo-
nents of a life-support system, they require careful
maintenance. An essential element of maintenance is
to ensure that no foreign matter has entered any of the
regulator's components; introducing foreign matter into
an area of close tolerance or into a perfect seal could
cause a malfunction. The primary entry point for for-
eign matter is the high-pressure inlet in the first stage.
For this reason, the dust cap should be kept in position
over the high-pressure inlet whenever the regulator is
not in use. Salt water entering the high-pressure inlet
will leave deposits of salt that can prevent proper oper-
ation or pit valve surfaces. The addition of a few drops
of salt water into the high-pressure filter on several
successive days can substantially degrade the perform-
ance of most regulators.
Divers should be alert for early symptoms of equip-
ment malfunction. For example, increased breathing
resistance may be caused by the corrosion of internal
moving parts, and water leakage in the mouthpiece can
occur as the result of deterioration of the second-stage
exhalation valve. Other signs that indicate problems
are rusting or clogging of the first-stage filter, free
flowing, and 0-ring leaks. These and other signs of
trouble should be thoroughly evaluated before any
further dives are made.
The most important maintenance to be performed on
a regulator is a fresh water rinse after each use; this
procedure removes salt and other debris (sand, dirt,
etc.) from the regulator and prevents deterioration.
Rinsing should be done within a few hours of the com-
pletion of a dive, regardless of whether the dive was
conducted in fresh or salt water. Procedures for washing
single- and double-hose regulators vary significantly
and are discussed below.
With a single-hose regulator, the first stage should
be held under a stream of warm, fresh water for at least
2 minutes while the dust cap remains sealed in place,
and water should be allowed to flow freely through any
open ports. This is especially important with piston-
type regulators, because it prevents the buildup of
salt on the piston tracks. Because the dust caps pro-
vided with some regulators are not watertight, the
diver must make sure the cap is watertight before
rinsing the regulator.
When rinsing the second stage of a single-hose regula-
tor, the diver should permit water to enter through the
mouthpiece and exit via the exhaust. Allowing water to
flow in the direction of the non-return exhaust valve
washes sand, dirt, etc., out of the mouthpiece. The
purge button should not be pushed unless the system is
October 1991 — NOAA Diving Manual
5-5
Section 5
Figure 5-5
Check and Exhaust Valves
Source: NOAA (1979)
pressurized, since doing so opens the air inlet valve and
might allow dirty water to pass through the middle-
pressure hose to the high-pressure stage. If the regulator
is to be stored for a long period of time, it may be
desirable to remove the band holding the two sections
of the second stage and the diaphragm in place and to
rinse each separately. Rinsing procedures for the double-
hose regulator are more complicated than for the single-
hose model. As with the single-hose regulator, rinsing
should be conducted with the watertight dust cap in
place. The exhaust side of the regulator has a series of
holes, and water should be allowed to flow freely through
this section.
Care must be taken when rinsing the hose and mouth-
piece assembly because any water that is forced under
high pressure into the mouthpiece may bypass the soft
rubber non-return valve and enter the intake side,
which may cause corrosion. During rinsing, the mouth-
piece should be held with the air inlet valve up, and
water should be allowed to enter the mouthpiece, flow
through the exhaust valve and hose, and exit at the
main body of the regulator. To remove water from the
corrugations in the hose, the hose should be stretched
lightly and the diver should blow through the mouth-
piece, allowing excess water to pass out through the
exhaust. The regulator should not be hung by the mouth-
piece, because this will stretch and weaken the hose.
To avoid cultivating bacteria in the corrugations, the
interior of the hoses should be dried periodically. Scuba
regulators should be tested functionally on a regular
basis and at least as often as every 6 months. Perform-
ing this test usually requires nothing more than a
manometer.
NOTE
Hoses (especially exhaust hoses) should be
removed periodically and should then be
washed with surgical soap to prevent bac-
terial buildup.
5-6
5.2 SURFACE-SUPPLIED DIVING
EQUIPMENT
One of the major constraints of scuba diving is the
limited quantity of breathing gas the diver can carry;
with umbilical (surface-supplied) diving, divers have
a continuous air supply, which allows them to spend
more time on the bottom. The increased safety pro-
vided by umbilical equipment is also important. In this
mode, the diver is tethered and has direct voice com-
munication, which permits safe operation under condi-
tions considered too hazardous for the self-contained
diver. If a surface-supplied diver becomes fouled or
disabled, a continuous air supply can be maintained
from the surface and a standby diver can locate the
diver by following the entrapped diver's tether. In
addition, if strong currents are a problem, the tethered
diver can use additional weights to increase his or her
stability.
Surface-supplied diving can be conducted from many
locations: from the surface, a habitat, a personnel transfer
capsule, or a lockout submersible. An umbilical to the
diver that runs from the gas storage cylinders of the
habitat, capsule, or submersible provides the diver's
breathing gas, hot water (if required), and a communi-
cations link. The major disadvantage associated with
surface-supplied diving is that this mode requires more
support equipment and personnel than is the case for
the scuba mode.
Many safe and efficient diving masks and helmets
are available commercially. All masks and helmets
provide the diver with a continuous supply of breath-
ing gas, and some models allow the diver to elect either
the free flow or demand operating mode. A communi-
cation system is standard equipment on modern surface-
supplied helmets.
5.2.1 Free Flow/Demand Masks
The free flow/demand mask is designed to be used
with an umbilical hose that supplies breathing gas
from the surface, an underwater habitat, or a person-
nel transfer capsule (submersible decompression cham-
ber). Free flow systems supply sufficient ventilation
for heavy work and also provide divers with an adjust-
able-flow, off-on supply to the interior of the mask
through the muffler deflector. In addition to supplying
the diver with a steady flow of breathing gas, the
deflector directs gas across the viewing lens to prevent
fogging. When the umbilical hose is pressurized with
breathing gas, the demand regulator is pressure-loaded
at all times. The regulator provides a demand breath-
ing system, similar to that of standard open-circuit
NOAA Diving Manual — October 1991
Diver and Diving Equipment
scuba, which is adjustable for gas supplied at pressures
ranging from 60 to 180 psi over ambient pressure.
Demand systems are preferred for light to moderate
work because they economize on gas requirements and
enhance communication. A nose-blocking device is
incorporated into demand systems to facilitate sinus
and middle-ear equalization, and an oral-nasal mask
assembly is used to reduce dead air space and elimi-
nate the possibility of a dead air space carbon dioxide
buildup.
Some lightweight masks and helmets conventionally
used for surface-supplied diving are equipped with
regular scuba demand regulators and can be adapted
easily for use with self-contained air supply (scuba
tanks). Divers using these masks consume more air
than they do with regular scuba mouthpieces, and each
diver's air consumption rate should be determined at
several different work loads before actual diving oper-
ations begin. To permit buddy breathing, an octopus
second-stage regulator can be added to the first stage.
The advantages of this setup are greater comfort around
the mouth and jaws during long exposures and the
ability to utilize a tape recorder or diver-to-diver
communication.
Face masks may be equipped with nose-blocking
devices to facilitate equalization of pressure during
descent. Blocking off the nose to aid in equalizing
pressure in the ears is accomplished easily either by
pushing upward on the bottom of the mask to create a
seal or gripping the nose when using masks with nose
pockets. Masks also may be equipped with a purge
valve to aid in clearing water from the mask. Only
high-quality masks with large purge valves are recom-
mended, because purge valves are subject to failure or
leakage.
Face mask selection is a matter of individual prefer-
ence, fit, comfort, and other diver requirements. Masks
are available in a variety of sizes and shapes that will
accommodate different lens configurations. The closer
the lens is located to the eye, the wider the peripheral
visual field (Egstrom 1982). Selection of a mask that
fits well can provide easy clearing and an optimal
visual field. A problem with some of the new clear
plastic or clear rubber masks is that they allow light to
enter from the side, which may cause a mirror effect on
the lens.
The following features should be looked for when
selecting a face mask:
• Light weight
• Comfortable fit
• Wide-angle vision
• Easy closure of nostrils for equalization
• Low volume
• Easy strap adjustment
• Secure strap fasteners
• Hypo-allergenic material
• Tempered safety glass.
Divers who must wear eyeglasses on land generally
need some form of optical correction under water.
Several methods for accommodating corrective lenses
in divers' face masks have been developed:
• Individual prescription lenses can be inserted into
goggle-type masks;
• Prescription lenses can be incorporated into the
faceplate;
• Large-size prescription lenses can be bonded perma-
nently to the inner faceplate surface;
• Lenses can be mounted in a special frame and be
secured to the inside of the faceplate;
• Standard glasses can be mounted inside the face-
plate with stainless steel spring wire; and
• Soft or fenestrated contact lenses can be worn.
Each of these methods has advantages and disadvan-
tages. Glasses generally cannot be worn inside a mask
because the temples cause the mask to leak. Wearing
lens inserts inside the face mask is simple and inexpen-
sive but provides an extra surface to fog. Some off-
the-shelf masks are available with built-in correction;
whether or not these are useful to a given individual
depends on several factors, including the type and
amount of refractive error, the similarity of error in
the two eyes, and the interpupillary distance.
The use of contact lenses under the face mask pro-
vides good vision under water, offers a wide field of
view, and eliminates problems with fogging. However,
some people do not tolerate contact lenses well, and
some lenses cause corneal edema. The signs and symp-
toms of corneal edema, which include discomfort, haloes
around lights, and loss of visual acuity, have been
found to occur when unfenestrated hard contact lenses
are used; soft lenses or fenestrated hard lenses do not
cause this condition, which has been attributed to the
inability of hard lenses to "breathe" (Simon and Bradley
1978, 1980). Because a dislodged lens can be very
painful and debilitating, Cotter (1981) has suggested
that dive buddies establish a signal that means "lens or
eye trouble" if either diver wears contact lenses. (The
options available to individuals who have different
types of refractive error but wish to dive, and the
advantages and disadvantages of the various methods,
are discussed fully in Kinney (1985).)
Ventilation across the faceplate generally is poor,
and the glass tends to fog easily. To minimize fogging.
October 1991 — NOAA Diving Manual
5-7
Section 5
Figure 5-6
Lightweight Helmet
the inside of the faceplace should be smeared with
saliva and then be rinsed before wearing. Anti-fogging
solutions (such as a mild liquid soap or a special com-
mercial preparation) may be applied to the inside of
the faceplate. The faceplate should be washed frequently
in detergent to remove oils or surface film, both of
which enhance fogging. If the mask fogs during use,
drops of water should be let into the mask and should
then be rolled across the fogged areas to clear them.
If the mask has a purge valve, the valve should be
thoroughly washed out to remove any sand that might
prevent it from sealing properly. The mask should not
be left in the sun for any extended period because
sunlight will make the headstrap and sealing edge
brittle. Although the headstrap can be replaced easily
and economically, cracking of the sealing edge will
make the mask useless.
Self-contained emergency gas supply systems (or
bailout units) are used in conjunction with surface-
supplied diving equipment to perform work at depths
in excess of 60 feet (18.3 m), when working in tunnels,
pipes, etc., or where there is the danger of entangle-
ment. These units consist of a scuba cylinder assembly,
a reduction regulator (i.e., first stage of a standard
single-hose regulator), and a backpack-harness assem-
bly. The capacity of the scuba cylinder assembly varies
from 10 ft3 to 140 ft3, depending on the diver and the
situation. Emergency gas may be fed directly into the
diver's mask through a special attachment on the side
valve or be introduced directly into the diver's air hose
assembly. In the latter case, a check valve must be
located between the intersection of the emergency gas
supply hose and the primary surface supply hose. A
completely separate bailout system, which includes a
scuba tank and regulator, may be used. If the umbili-
cal air supply is lost, the full face mask must be removed
before the diver ascends to the surface using the scuba
tank and mouthpiece. If an emergency gas supply sys-
tem is selected, a second face mask should also be
carried. The advantage of this configuration is com-
plete redundancy; the disadvantages are loss of com-
munication and difficulty in putting on the face mask
and locating the regulator.
5.2.2 Lightweight Free Flow Helmets
Many lightweight free flow diving helmets have been
designed and manufactured in recent years. Some manu-
facturers have constructed helmets of the traditional
spun copper, which emphasizes indestructibility, while
others use fiberglass and emphasize comfort, light
weight, and maneuverability. In general, modern light-
weight helmets (Figure 5-6) feature streamlined design,
5-8
®Diving Systems International
1990 All Rights Reserved.
standardized interchangeable fittings, improved valves,
unbreakable faceplates, better ventilation (low C02
buildup), improved visibility, better communication,
versatility because they can be used with any type of
dress, bailout capability, and simplicity of use and
maintenance. Modern helmets can be used with a
neoprene wet suit, a hot-water suit, or a variable-
volume suit. Some helmets attach to the neck bands of
specially adapted dry suits for use in cold or contami-
nated water.
5.2.3 Lightweight Free Flow/Demand Helmets
Free flow/demand system dry helmets combine the
advantages of full head protection, communications,
and the breathing characteristics of a standard dry
helmet with the gas economy and comfort of a demand
mask. Weight is distributed throughout the helmet
to achieve balance and optimum performance without
neck strain or effort. The helmet is designed to be
neutrally buoyant in seawater. It is equipped with an
auxiliary (or emergency) system valve and a non-return
valve and with communication earphones and microphone.
An oral-nasal mask reduces the potential for C02 buildup.
5.2.4 Umbilical Assembly
The umbilical assembly for surface-supplied light-
weight helmets and free flow/demand masks generally
consists of a gas supply hose, a pneumofathometer
NOAA Diving Manual — October 1991
Diver and Diving Equipment
hose, a communications wire, and a strength member.
Depending on dive requirements, a hot-water supply
hose may also be included. Umbilical members are
assembled in continuous lengths; for example, in shal-
low water diving operations (i.e., to depths less than
90 fsw (27 m)), a 150-foot (45 m) assembly may prove
satisfactory. Regardless of length, all members should
be in continuous lengths because umbilical assemblies
designed with fittings and connectors have a greater
likelihood of failing or separating.
5.2.4.1 Gas Supply Hoses
A 3/8-inch (1.2 cm) or larger synthetic rubber,
braid-reinforced, heavy-duty hose is generally used to
carry the diver's air supply. The hose must have a
working pressure of at least 200 psig (this pressure
must exceed the diver's required supply pressure). The
outer cover of the hose must be durable and resistant to
abrasion, weathering, oil, and snag damage. The inside
tube of the hose must be non-toxic and impervious to
any breathing gas to be used. Hoses must be flexible,
kink resistant, and easy to handle. Although a hose
may have a sufficient pressure rating, it may shrink
considerably in length because it increases in diameter
when pressurized, which causes looping of the other
members of the umbilical assembly. To avoid prob-
lems, the percentage of shrinkage should be determined
before purchasing the hose, and the assembly should
be taped while the hose is pressurized. At pressures
less than 150 psig, the change in length should not
exceed 2 percent.
To facilitate recordkeeping, all air supply hoses
should be tagged with a serial number. A metal tag-
ging band that is resistant to damage and unlikely to be
lost during use is desirable. Purchase, test, and usage
records should be maintained for each hose assembly.
5.2.4.2 Communication Cables
Communication cables must be durable enough to
prevent parting when a strain is placed on the umbili-
cal assembly; they must also have an outer packet that
is waterproof and oil- and abrasion-resistant. Multi-
conductor shielded wire (size 14 to 18) that has a
neoprene outer jacket is satisfactory for shallow water
diving. In normal service, only two conductors are used
at any one time. The wire-braid shielding adds consid-
erable strength to the umbilical assembly. The cable
should be in a continuous length, with an additional
few feet at the diver's end and the surface end to allow
room to install connectors, make repairs, and connect
the communication equipment.
The wire is fitted with connectors that are compati-
ble with those on the helmet or mask. A four-conductor,
waterproof, "quick-connect" connector is often used;
these connectors have a socket-type configuration.
When joined together, the four electrical pin connec-
tions are established and a watertight seal is formed,
which insulates the wire from the surrounding seawa-
ter. To be secure and waterproof, these connectors
should be molded to the communication cable. Profes-
sional installation is desirable. For field installation,
rubber electrical tape overlaid with plastic electrical
tape has been successful, although it is less satisfac-
tory than special molding processes. The surface end
of the wire should be fitted with an appropriate con-
nector, generally of the standard terminal post type,
that is compatible with the communications unit. Many
divers use simple terminal or binder post connections
on masks and helmets. The ends of the wire are pre-
pared with solder, inserted into the binder post termi-
nal, and secured. Although less satisfactory than the
special connectors mentioned above, the use of termi-
nal or binder post connections is satisfactory and
economical.
Standard two-wire "push-to-talk" communicators
are commonly used in diving. By using all four wires in
the communication wire, the system can be set up so
that the diver's voice is "live" at all times. All commu-
nication wires should be tagged or coded for record-
keeping purposes, and lines should be checked before
being issued for use on any dive.
5.2.4.3 Pneumofathometer Hoses
The pneumofathometer hose is a small hose that is
open at the diver's end and connected to an air source
and pneumofathometer at the surface. Pneumofathom-
eters are precision pressure gauges that are calibrated
in feet of seawater and are used to determine the pre-
cise depth of the diver under water. Pneumofathometers
must be protected from abuse and should be calibrated
regularly. Lightweight air or oxygen hose (0.24-in.
(0.6 cm) i.d., 200 psig working pressure) is generally
used. Standard oxygen fittings are used for surface
connections.
5.2.4.4 Strength Members
The U.S. Navy recommends the use of a strength
member in the umbilical assembly. The lines used as
strength members include:
• 3/8-in. (1.2 cm) nylon braided line
• 3/8-in. (1.2 cm) synthetic polyolefin braided or
3-strand twisted line
October 1991 — NOAA Diving Manual
5-9
Section 5
• 3/8-in. (1.2 cm) manila line
• thin stainless aircraft-type cable.
Each type of line has advantages and disadvantages.
Braided nylon line is commonly used and has accepta-
ble strength, durability, and handling qualities, although
it stretches under high load conditions; many organi-
zations, including the U.S. Navy, use this type of line.
Polyolefin line floats and thus reduces the in-water
weight of the umbilical assembly somewhat, but this
type of line can be abrasive to the hands. Manila line is
readily available and is the least expensive, but it
deteriorates rapidly. Aircraft-type cable is strong, com-
pact, lightweight, and expensive. Some divers use hollow-
core polyolefin line, with the communications line run-
ning through the hollow core, to combine the strength
and communication members. A few combination
strength member/communicator wire lines are com-
mercially available.
5.2.4.5 Hot-Water Hoses
When hot-water wet suits are worn on a dive, a
specially insulated hose is required. This hose can be
obtained in either 1/2- or 3/4-inch (1.2 or 1.8 cm)
inside diameter size, depending on the depth and vol-
ume of water to be supplied to the diver. The insulation
reduces the loss of heat to the open sea, which allows a
lower boiler operating temperature. The hose should
be equipped with a quick-disconnect female fitting
that is compatible with the manifold attached to the
suit. To prevent handling problems, the hot-water hose
should be joined to the diver's gas and communications
umbilical.
5.2.4.6 Assembly of Umbilical Members
The various members of the umbilical assembly should
be bound together with pressure-sensitive tape. Two-
inch (5 cm) wide polyethylene cloth-laminated tape or
duct tape is commonly used. Prior to assembly, the
various members should be (1) laid out adjacent to
each other, and (2) inspected for damage or abnormal-
ities; all fittings and connections should be installed in
advance. The gas supply hose and pneumofathometer
hoses should be connected to the air supply and should
be pressurized to about 150 psig to ensure that shrink-
age does not cause looping.
The following guidelines should be observed when
assembling umbilical members:
• The strength member should terminate in a position
to hook to the diver's safety harness, generally on the
left-hand side, so that the strain of a pull from the
surface is placed on the harness and not on the diver's
helmet, mask, or fittings.
• If a lightweight, more flexible "whip" (short length
of hose) is used between the helmet and the main
umbilical air supply hose, the communication line
and the supply hose should also be adjusted
accordingly.
• If a whip and special auxiliary air supply line valve
are used for helmet diving, their length should be
adjusted.
The diver should have sufficient hose and cable length
between the safety harness attachment point and the
mask (or helmet) to allow unrestricted head and body
movement without placing excessive stress on the hose
connections. Excessive hose should not, however, form
a large loop between the harness connection and the
mask.
The communication line should be slightly longer
than the rest of the assembly to permit repairs at the
diver's end. The diver's end should be fitted with a
snap hook that is secured to the strength member and
the rest of the assembly to facilitate attachment to the
safety harness. The surface end of the strength mem-
ber and other components also are secured to a large
D-ring, which allows the assembly to be secured at the
diving station.
5.2.4.7 Coiling and Storage of Umbilical Hose
After the umbilical hose is assembled, it should be
stored and transported; protection should be provided
for hose and communications fittings during these proce-
dures. The hose ends should be capped with plastic
protectors or be taped closed to keep out foreign mat-
ter and to protect threaded fittings. The umbilical hose
may be coiled on take-up reel assemblies, "figure-
eighted," or coiled on deck with one loop over and one
loop under. Incorrect coiling, all in the same direction,
will cause twist and subsequent handling problems.
The tender should check the umbilical assembly at the
end of each dive to ensure that there are no twists, and
the coil should be secured with a number of ties to
prevent uncoiling during handling. Placing the umbil-
ical assembly in a large canvas bag or wrapping it in a
tarpaulin will prevent damage during transport.
5.2.4.8 Umbilical Maintenance
After a day's diving, the umbilical should be washed
with fresh water, be visually inspected for damage,
and be carefully stored to prevent kinks. If the umbili-
cal is to be stored for a long period of time, the hoses
should be blown dry and the connectors should be
5-10
NOAA Diving Manual — October 1991
Diver and Diving Equipment
capped to prevent foreign matter from entering. Con-
nectors should be lubricated with silicone spray after
capping.
required for weight belts is fresh-water washing after
use and predive checks of the quick-release mechanism
to ensure that it is operating properly.
5.2.4.9 Harness
The diver should wear a harness assembly to facili-
tate attachment of the umbilical assembly. The har-
ness should be designed to withstand a minimum of a
1000-pound (454 kg) pull in any direction, and it must
prevent strain from being placed on the diver's mask or
helmet when a pull is taken on the hose assembly. The
location of the attachment depends on the type of
harness assembly worn by the diver, but the harness
should not be attached to the weight belt in case the
latter needs to be dropped.
WARNING
Never Attach the Diver's Umbilical Directly
to the Weight Belt. A Separate Belt or Har-
ness is Required To Permit the Weight Belt
To Be Dropped If Necessary
5.2.4.10 Weighting Surface-Supplied Divers
To weight the diver properly, lead weights (3, 5, or
8 lbs (1.4, 2.3, or 3.7 kg) each) are secured to the belt
with bolts. The belt is approximately 4 inches (10.2 cm)
wide and is fitted with a quick-release fastener. The
weight belts used for arctic diving are heavier than
most belts because of the bulk and positive buoyancy
of cold-water exposure suits. A shoulder harness that
is similar in configuration to a fireman's suspenders
is the best method of preventing the heavy, unwieldy
belts from slipping off. If a leather belt is used, it
should be coated regularly with neat's-foot oil.
Weighted shoes or leg weights may be used in con-
junction with the weight belt (primarily by tethered
divers) to overcome positive buoyancy and to give sta-
bility to the diver. Standard weighted shoes consist of
a lead or brass sole, leather straps to hold the shoe in
place, and a protective brass toe piece.
Leg weights consist of one large or several small
weights attached to leather or nylon straps. The straps
are fitted with buckles for securing the weights to the
diver's legs near the ankle. The weights vary from
2 to 10 pounds (0.9 to 4.5 kg) each, depending on the
diver's preference. Leg weights provide improved sta-
bility and protection against blowup, because divers
wearing variable-volume suits can swim with relative
ease while wearing fins and leg weights. For safety,
the weight belt should be worn outermost so that it
can be freed easily when released. The only maintenance
5.3 DIVER EQUIPMENT
The on-scene dive master determines which items of
equipment are required to accomplish the particular
underwater task. Unnecessary equipment should be
left on the surface because excessive equipment can
become a hazard rather than an asset. This is particu-
larly true when diving in a strong current, under condi-
tions of limited visibility, or in heavy surge, because
each additional item of diving equipment (especially
additional lines) increases the probability of fouling
the diver.
Diver equipment considered in this section includes
face masks, flotation devices, weight belts, knives, and
swim fins. The sections below discuss each of these
items in turn.
5.3.1 Face Masks
Face masks are used to provide increased clarity and
visibility under water by placing an air space between
the diver's eyes and the water. There are two general
classes of face masks: separate face masks and full
face masks (Figure 5-7) (Hall 1980a). The separate
mask, which covers only the eyes and nose, is generally
used for scuba diving (when equipped with a mouthpiece)
or for skin diving. Full face masks are used with special
scuba and surface-supplied diving apparatus. Full face
masks consist of a faceplate, a frame, and a headstrap.
The faceplates are made of highly impact-resistant,
tempered safety glass. (Glass is still better than plas-
tic, because plastic faceplates are subject to discolora-
tion, abrasive damage, and fogging.) The frame is
designed to hold the faceplate and to provide a water-
tight seal; it is usually made of plastic. Silicone rubber
has largely replaced less durable materials as face seal
components; the widespread use of silicone materials
in diving has significantly extended the useful life of
most rubber components. The mask should be sufficiently
rigid to hold the rubber plate away from the diver's
nose and should be pliable enough to ensure perfect fit
and still retain its shape. An adjustable rubber headstrap
approximately l inch (2.5 cm) wide and split at the
rear holds the mask to the diver's head.
5.3.2 Flotation Devices
A flotation device is an essential part of a diver's
life-support and buoyancy control system; it is also an
October 1991 — NOAA Diving Manual
5-11
Section 5
Figure 5-7
Face Masks
A. Separate Masks
Courtesy Glen Egstrom
B. Full Face Mask
'BDiving Systems International
1990 All Rights Reserved
item of rescue and safety equipment. Many different
buoyancy compensators have been developed during
the past few years, including those with the popular
stabilizing jacket and compensators using the horse
collar designs (Figure 5-8). These devices are available
as vest units, backpack-mounted units, stabilizer jackets,
and in a wide range of variable-volume dry suits.
Although almost all divers would agree that some type
of buoyancy compensation is necessary, they would not
agree about which configuration or design is best.
When selecting a buoyancy compensator (BC), a
number of factors must be considered, including: type
of exposure suit, type of scuba cylinder, diving depth,
characteristics of the breathing equipment, nature of
diving activity, and type of accessory equipment and
weight belt (Snyderman 1980a, 1980b). The BC must
be compatible with the exposure suit.
NOTE
Buoyancy compensators should not be used
as a substitute for swimming ability and physi-
cal fitness.
Flotation devices should be designed so that a diver,
even when unconscious, will float with face up. The
inflating mechanism of the device should be constructed
of corrosion-resistant metal, and a relief valve should
be part of the device when it is used for buoyancy
compensation. Most devices are designed to inflate
automatically either when a C02 cartridge is punc-
tured or when filled with air supplied by a low-pressure
hose from the scuba cylinder. Regardless of their method
of inflation, all flotation devices should be equipped
with an oral inflation tube. The oral inflation tube
should have a large diameter and be able to be oper-
ated with either hand.
Recent studies have determined that a minimum of
25 pounds (11 kg) of positive buoyancy is required to
support a fully outfitted diver operating in Sea State 1
conditions. To achieve this, a 19-25 gram C02 car-
tridge must be used with a properly designed buoyancy
compensator. U.S. Coast Guard regulations require
life vests to have a positive buoyancy of 24.5 pounds
(11 kg) to support a fully clothed adult. Divers and
boat operators should keep themselves informed about
the status of life vests (personal flotation devices),
because, for example, the Coast Guard recently issued
a warning cautioning against the use of Type III life
vests in rough water because they will not keep a diver's
head clear in choppy water. Flotation devices that use
5-12
NOAA Diving Manual — October 1991
Diver and Diving Equipment
Figure 5-8
Flotation Devices
Courtesy Glen Egstrom
larger cartridges than those required, multiple car-
tridges, and one or two inflation compartments are also
available; these models can be used as buoyancy com-
pensators if the diver partially inflates the device through
the oral or power inflation tube while he or she is still
submerged.
Specially designed buoyancy compensators that have
large oral inflation tubes and separate inflatable cham-
bers are commercially available. A large cylinder of
compressed air that is chargeable from a standard
scuba air cylinder is an integral part of some buoyancy
compensators; this arrangement allows for partial or
complete inflation while the diver is submerged. Pres-
sure relief valves are provided for each compartment
to prevent overinflation.
Training divers in the use of specific BC devices is
essential because these devices vary widely in terms of
control locations, control operation, and potential buoy-
ancy. Regardless of the diver's choice, training and
practice under controlled conditions are required to
master buoyancy compensation procedures. Divers must
be trained not to use excessive weights or to be overly
dependent on a BC to compensate for diving weights.
Because rapid, excessive inflation can cause an un-
controlled ascent, divers must learn to vent air from
the compensator systematically during ascent to maintain
proper control.
After each use, the exterior of the device should be
rinsed thoroughly with fresh water. Special attention
should be given to the C02 release mechanism, oral
and power inflators, and other movable mechanical
parts to ensure that they operate freely and easily. The
C02 actuating lever, with cartridge removed, should
be worked up and down while fresh water is being
flushed through the mechanism. The mechanical parts
should be allowed to dry and should then be lubricated
with a silicone lubricant. The threads on the CO, car-
tridge should also be lubricated.
The most frequent cause of flotation device mal-
function is corrosion caused by salt water entering the
inflation compartments; the resulting residue can block
the passage of C02 and cause significant deterioration
of the inflation-release mechanism. If this occurs, the
device should be filled approximately one-third full of
warm fresh water, the water should be circulated rap-
idly through the vest, and the water should then be
drained out through the oral inflation tube. Fresh water
also should be flushed through the passage between
the vest and the C02 cartridge.
NOTE
Buoyancy compensators should not be worn
with a variable-volume dry suit if the BC hin-
ders easy access to the suit's valves.
Periodic checks of the inflation device are also
required. The device should be inflated and hung up
over night and/or be submerged periodically to check
for leaks. If leaks are observed, they should be repaired
before the device is used again. The C02 cartridges
should be weighed frequently to ensure that they have
not lost their charge; if their weight is more than 3
grams less than the weight printed on the cylinder, the
cartridge should be discarded. The cartridge used in a
flotation device should be the one designed to be used
with that device. Cartridges should also be inspected
to ensure that the detonating mechanism has not punched
a pinhole into the top of the cartridge that has allowed
the C02 to escape.
WARNING
Buoyancy Compensators Should Not Be Used
As Lift Bags Unless They Are Not Attached
To the Diver
5.3.3 Weight Belts
Divers use weight belts to achieve neutral buoyancy;
they should carry enough weight so that their buoy-
ancy at the surface is slightly negative with a full tank
and becomes slightly positive as air is consumed. The
positive buoyancy provided by the diver's suit is prob-
ably the largest contributing factor in determining
appropriate weight requirements. Without an exposure
suit, most divers can achieve neutral buoyancy with
October 1991 — NOAA Diving Manual
5-13
Section 5
Figure 5-9
Swim Fins
less than 5 pounds (2.3 kg) of weight, whereas 10 to
30 pounds (4.5 to 13.5 kg) may be required, depending on
depth, if a full suit is worn. Dry suits may require even
more weight. Divers must accurately determine their
weight requirements in shallow water before undertaking
a working dive. Failure to establish the proper buoy-
ancy can consume air and energy unnecessarily. The
following test can be performed to determine the proper
amount of weight to be carried: a full lung of air at the
surface should maintain a properly weighted diver at
eye-level with the water; exhalation should cause the
diver to sink slowly, while inhalation should cause a
slow rising back to eye-level with the water. (This test
should only be performed on the last dive of the day
because it will influence the diver's repetitive dive
status.) As a general rule, the deeper the dive, the less
weight will be required to achieve the desired buoy-
ancy because of the exposure suit's compressibility.
When using exposure suits with increased thickness or
air spaces, care should be taken to ensure that the diver
has adequate weight to permit a slow, easy ascent,
especially during the last 10 feet (3 m) of ascent.
5.3.4 Diver's Knife
A diver's knife serves a variety of purposes, the most
common being to pry and probe at underwater rocks,
organisms, etc., and to free the diver in the event of
entanglement (Boyd 1980). A diver's knife should be
constructed of a corrosion-resistant metal, preferably
stainless steel. Handles must provide a good, firm grip
and be resistant to deterioration. The knife should be
worn where it is easily accessible in an emergency;
knives are worn on the inside of the calf or on the upper
arm. Carrying the knife on the inside of the calf is
popular because this position makes it readily accessi-
ble with either hand and lessens the likelihood that the
knife itself will foul. This placement also maintains a
clear drop-path for the weight belt. After each use, the
knife should be rinsed with fresh water, dried, and
coated with a layer of light oil prior to storage. The
knife must be checked frequently to ensure that the
blade is sharp; if properly maintained, the material
used in most diving knives will retain a good cutting
edge for a long time.
5.3.5 Swim Fins
Swim fins (Figure 5-9) increase the propulsive force
of the legs and, when used properly, conserve the diver's
energy and facilitate underwater movement. They are
available in a variety of sizes and designs.
In general, there are two styles of fins: swimming
and power (Hall 1980b). Swimming fins are smaller, of
5-14
Courtesy New England Divers, Inc.
lighter weight, and are slightly more flexible than the
power style, and they use approximately as much force
on the up-kick as on the down-kick. The swimming-
style fin is less fatiguing for extensive surface swim-
ming, less demanding of the leg muscles, and more
comfortable. Power-style fins are longer, heavier, and
more rigid than swimming fins. They are used with a
slower, shorter kicking stroke, with emphasis on the
down-kick. This style of fin is designed for maximum
power thrusts of short duration, and these fins sacri-
fice some comfort; power fins are the preferred style
for working divers. A narrow, more rigid fin provides
the best thrust-to-energy cost ratio. The fin must fit
comfortably, be sized properly to prevent cramping or
chafing, and be selected to match the individual's physi-
cal condition and the nature of the task to be performed.
Swim fins with adjustable heel straps either should
have the straps reversed, with the bitter ends inside, or
the ends of their straps taped down before diving in
kelp beds, surf grass, or pond weeds. If this is not done,
plants may catch in the straps and impede further
progress. A number of plastic fins have gained popu-
larity because of their good propulsion characteristics
and light weight; these fins couple a plastic blade with
a neoprene rubber foot pocket and an adjustable heel
strap.
5.4 PROTECTIVE CLOTHING
Divers usually require some form of protective cloth-
ing. This clothing, known as a suit or insulation, mini-
mizes thermal exposure effects. In addition, it pro-
tects the diver from abrasions and minor bites.
Suits must be selected with certain diving condi-
tions in mind; elements to consider include water tem-
perature, depth, and activity level. The following points
should be considered when evaluating thermal needs:
NOAA Diving Manual — October 1991
Diver and Diving Equipment
Figure 5-10
Neoprene Wet Suit
• All insulation is trapped air or gas.
• Cold water absorbs heat 25 times faster than air.
• Fifty percent of the average diver's energy is con-
sumed just trying to keep the body warm.
• The greater the temperature difference between
the body and the surrounding water, the faster
heat leaves the body.
• The larger the body mass, the better the heat
retention.
• It takes time, rest, and food to replace lost heat
energy.
5.4.1 Wet Suits
The neoprene wet suit is the most common form of
protective clothing in use (Figure 5-10). It provides
thermal protection, as well as protection against coral,
stinging coelenterates, and other marine hazards. Wet
suits are constructed of closed-cell foamed neoprene
and generally are 3/ 16- or 1/4-inch (approximately
0.6 cm) thick, although suits as thin as 1/8 (0.3 cm)
and as thick as 3/8 of an inch (1.2 cm) are available.
Wet suits rely on air bubbles in the closed foam to act
as insulation. Because the foam is compressible, how-
ever, the suit rapidly loses its insulative capability as
depth increases. For example, one-half of a wet suit's
insulating capacity is lost at 33 feet (10 m), two-thirds
at 66 feet (20 m), and three-fourths at 99 feet (30 m).
Consequently, wet suits are recommended only for
shallow water diving or snorkeling and generally are
not recommended for diving in water at temperatures
below 60°F (15. 6°C).
The wet suit used in warm water consists of neoprene
pants and jacket, with optional boots, gloves, hood,
and vest. For warm-water (80°F; 26.7°C) diving, a
brief vest that covers only the body's trunk is available.
Full-length styles that cover the entire body (includ-
ing the hands, feet, and head) except the face are
available for use in colder waters. Fit is important to
the effectiveness of a wet suit; some divers may need a
custom suit to achieve proper fit. Thinner suits provide
more freedom of movement, while suits of thicker mate-
rial provide better thermal protection. Most suits use a
nylon liner on the inside surface of the neoprene to
limit tearing and to facilitate easy entry. Models are
available with nylon on both the inner and outer sur-
faces to minimize tears and damage to the suit; howev-
er, the added layer of nylon further restricts the diver's
movements, as do elbow and knee pads. Although wet
suits with nylon inside offer easier entry into the suit,
they also allow water to seep in, which may be a prob-
lem in cold water. Nylon on the outside cuts down on
suit abrasions but tends to hold water, which acts as an
Courtesy Diving Unlimited International
evaporative surface and causes chilling when the diver
is on the surface.
The sections of a wet suit are joined by neoprene
glue. The seams on better models are sewn together to
prevent separation. Neoprene glue is available in small
cans for quick and easy wet suit repair. However, double-
surface nylon does not repair well with ordinary cement,
so tears in this material should be sewn. A wet suit may
have as many as five zippers, one in each ankle and
sleeve and one in the front of the jacket. In colder
waters, zippers can become a significant source of heat
loss, and care should be taken either to minimize zipper
length and number or to provide waterproof zippers
if extended cold-water work is anticipated. Some
suits are flexible and strong enough to be constructed
without ankle and sleeve zippers.
When water temperatures approach 60 °F (15.6°C),
the hands, feet, and head lose heat at a rate that makes
October 1991 — NOAA Diving Manual
5-15
Section 5
Figure 5-11
Effects of Water Temperature
diving without protective gloves, boots, and a hood
impractical. Even in tropical climates, divers often
elect to wear some form of boot and glove for abrasion
protection. In colder waters, loss of body heat from
these body areas may significantly affect diver per-
formance unless some form of thermal protection is
worn (Figure 5-1 1).
Thermal protection of the hands is necessary because
loss of dexterity significantly reduces a diver's effec-
tiveness. Most divers in temperate climates prefer cot-
ton gloves because these gloves do not severely restrict
finger movement and touch. Five-fingered foamed neo-
prene gloves are available in 1/8- or 3/16-inch (0.3 to
0.4 cm) thicknesses that permit a satisfactory degree
of finger movement. Three-fingered "mitts" are used
in cold water (Figure 5-12). Proper fit is important
because too tight a fit will restrict blood circulation
and increase the rate of heat loss.
Failure to wear a hood in cold water can result in
numbing of the facial areas and a feeling of extreme
pain in the forehead immediately on entering the water,
phenomena that persist until the head becomes accli-
mated to the cold. Fifty percent of body heat can be
lost from the head and neck during submersion in cold
water. Hoods that are attached to jackets generally
provide better thermal protection than separate hoods.
The hood should have an adequate skirt, one that extends
at least midway onto the shoulders, to prevent cold
water from running down the spine. In extremely cold
water, a one-piece hooded vest is recommended. Fit is
important when selecting a hood because too tight a fit
can cause jaw fatigue, choking, headache, dizziness,
and inadequate thermal protection.
Wet suits must be properly cared for and maintained
if they are to last for a reasonable length of time. After
each use, the suit should be washed thoroughly with
fresh water; it should then be allowed to dry before
being stored. The suit should be inspected carefully for
rips; if any are found, the suit should be repaired
before being used again. A suit can be used approxi-
mately 10 minutes after it has been repaired, but for
best results it should not be used for several hours. Suit
zippers and metal snaps should be inspected frequently
and be kept corrosion free.
Special silicone greases are available for use as equip-
ment lubricants; petroleum-based products will cause
neoprene materials to deteriorate. Suits should be hung
on wide, specially padded hangers to prevent tearing.
They may also be rolled up or laid flat, but they should
not be folded because prolonged folding may cause
creasing and deterioration of the rubber at the folds.
Suits should be stored out of direct sunlight because
prolonged exposure to the sun will cause the neoprene
Normal Body
Temperature
0)
Comfortable
During
Moderate
Work
Diver s
Underwear
May Suffice
Suits etc.
Required
°C
35
30-
25H
20-
15-
10-
— 4 Resting
-90
4 Working
Diver
Will
Overheat
-5-
-80
-70
60
-50
-40
Resting Diver Chills
In 1 -2 Hours
'Approximate
Tolerance Time
Of Working
Diver Without
Protection
I
1 2
Hours
-30
Fresh
Water
Sea
Water
Freezing
Point
Source: NOAA (1979)
to rot, become brittle, and crack. Storing suits in hot,
dry environments also can lead to deterioration.
5.4.2 Dry Suits
Dry suits that are made of waterproof materials are
becoming more widely used than wet suits. Commonly
called shell suits, these fabric suits are designed to be
worn with undergarments; they are usually used with
hoods and gloves and are relatively easy to doff and don.
Dry suits can be inflated via the inlet valve on the
diver's air supply at the low-pressure fitting on the
regulator, and air inside the suit can be expelled through
an exhaust valve. Some valves are equipped with an
adjustable over-pressure relief mechanism, which allows
for automatic buoyancy control. By manipulating the
valves, a properly weighted diver can maintain buoy-
ancy control at any depth. A power exhaust valve can
evacuate excess air from the suit, which makes the suit
easier to deflate. Because shell suits have no inherent
flotation capability, a buoyancy compensator that does
not cover the suit's valves should be worn.
Dry suits must be maintained properly. They should
be washed with fresh water after each use, and water
5-16
NOAA Diving Manual — October 1991
Diver and Diving Equipment
Figure 5-12
Cold-Water Mitt, Liner Included
Courtesy Trelleborg/Viking Inc.
should be sprayed directly into the suit's valves to
wash out sand. If the suit develops mildew spots, it
should be washed with soap and water. Finally, the suit
should be allowed to dry while hanging so that it will
dry thoroughly inside and out.
Dry suits should be stored away from sunlight and
from ozone-producing sources, such as cars or gas-
fired household water heaters. The life of the suit's
seals can be extended by storing the suit in a dry plastic
bag with talcum powder during long periods of non-
use.
5.4.2.1 Dry Suit Insulation
The amount of suit insulation needed for a particu-
lar diver to remain comfortable on a given dive is
determined by water temperature, duration of the dive,
and the age, body size, sex, and exercise rate of the
diver. However, many suits are insulated with materi-
als that trap air and stabilize it. The most common
insulation materials in use are synthetic fibers made of
polyester, nylon, and polypropylene. These fibers, used
in piles, buntings, and batting, are selected because of
their low water absorption.
Underwear made of such material provides primary
thermal protection when divers wear a dry suit because
the shell of the suit loses its insulation with depth and a
diver's other outer garments have little inherent insu-
lation. Leaks can always be a problem with shell suits;
however, divers equipped with dry suits and nylon pile
or Thinsulite® undergarments have been able to work
intermittently for 6 hours in 2°C (35 °F) water (Zumrick
1985).
5.4.2.2 Variable-Volume Neoprene or Rubber Dry
Suits
Variable-volume dry suits differ from dry fabric-
shell suits. They are one-piece suits that are made of
closed-cell foamed neoprene or rubber compounds.
These suits are designed to conserve body heat in
extremely cold water for an extended period of time
(Hall 1980c). Variable-volume rubber suits are light
and require no surface support, which makes them
ideal for use at remote locations. These suits also are
simple and reliable, which greatly reduces their main-
tenance and repair requirements. Operations have been
conducted in arctic regions using suits of this type for
long-duration dives (2 hours) under ice in 28.5 °F to
30°F(-1.9°C to -l.rC) water.
Most suits are constructed of 3/ 16- or 1/4-inch
(0.4 or 0.6 cm) closed-cell foamed neoprene and have a
nylon interior and exterior lining. One style is availa-
ble that is made from a rubber compound over a tricot
material. All suits of this type are designed to be worn
with thermal underwear, are of one-piece construc-
tion, and are entered through a water- and pressure-
proof zipper. The hood and boots usually are an inte-
gral part of the suit, but the gloves are separate. To
prevent separation, all seams are glued and sewn. Because
the knees of the suit are the point of most frequent
abuse, knee pads often are attached permanently to the
suit to reduce the likelihood of leaks.
The suit may be inflated via an inlet valve connected
to the diver's air supply at the low-pressure fitting on
the regulator. Air inside the suit can be exhausted
either by a valve on the opposite side of the chest from
the inlet valve or one on the suit's arm. By manipulat-
ing these two valves, a properly weighted diver can
maintain buoyancy control at any depth.
When diving in cold weather, care must be taken to
avoid icing of the suit's inlet and exhaust valves. The
inlet valve may be frozen in the open position if the suit
is inflated with long bursts of expanding air instead of
several short bursts. When the inlet valve freezes in the
open position, the suit may overexpand and cause an
uncontrolled ascent. If there is more air in the suit than
October 1991 — NOAA Diving Manual
5-17
Section 5
Figure 5-13
Open-Circuit Hot-Water Suit
the exhaust valve can exhaust, the diver should hold up
one arm, remove his or her tight-fitting glove, and
allow the excess air to escape under the suit's wrist
seal.
The disadvantages of variable-volume dry suits are:
• Long suits are fatiguing because of the suit's bulk;
• Air can migrate into the foot area if the diver is
horizontal or head down, causing local overinflation
and loss of fins;
• Inlet and exhaust valves can malfunction; and
• A parting seam or zipper could result in sudden
and drastic loss of buoyancy, as well as significant
thermal stress.
Divers planning to use any type of variable-volume
dry suit should be thoroughly familiar with the manu-
facturer's operational literature and should perform
training dives under controlled conditions before wearing
the suit on a working dive.
Maintaining variable-volume dry suits is relatively
simple. After every use, the exterior of the suit should
be washed thoroughly with fresh water, and the suit
should then be inspected for punctures, tears, and seam
separation, all of which must be repaired before reuse.
The zipper should be closed, cleaned of any grit, and
lubricated. The zipper should be coated with water-
proof grease after every few uses. The inlet and outlet
valves should be washed thoroughly and lubricated
before and after each dive. Cuffs, collar, and face seals
also require lubrication with pure silicone spray before
and after each dive. The inflation hose should be
inspected before each dive.
5.4.3 Hot-Water Suit Systems
Hot-water suit systems are designed to keep divers
warm by encapsulating them in warm water. A hot-
water system heats and closely controls the tempera-
ture of the water that is pumped through a specially
insulated hose to the diver; the system then distributes
the heated water evenly over the diver's body inside
the passive insulation of the specially constructed suit
(Figure 5-13). An open-circuit hot-water suit allows the
heated water to flow back to the open sea after use,
while a closed-circuit hot-water suit returns the warm
water to the heater for rewarming. Hot-water systems
can be used to protect more than one diver at a time
and to heat a diving bell.
5.4.3.1 Open-Circuit Hot-Water Suits
Open-circuit hot-water suits are loose fitting and
are made of passive insulation material; they are
equipped with a control manifold and tubing to dis-
courtesy Diving Unlimited International
tribute warm water to the diver's arms, hands, legs,
feet, and front and back torso. The suit allows used
water to leak out through the suit's arm, leg, and neck
seals. The control manifold must have a single valve to
allow water to bypass the diver and to return directly to
the surrounding water.
The hot water that supplies suits of this type may
originate on the surface and be pumped directly to the
diver or be passed to the diver from a diving bell,
submersible, or habitat. To maintain body heat, a con-
tinuous flow of 2.5 to 3.5 gallons per minute of 95 °F to
110°F (35 °C to 43 °C) water is required. This system
does not recirculate the warm water; instead, water is
dumped into the sea through the suit's vents. If the
water supply is interrupted, the non-return valve retains
the hot water in the suit, which allows the diver up to
1 8 minutes to return to the bell or surface.
5.4.3.2 Hot-Water Heater and Hoses
The heater unit of these systems contains water pumps,
a heat source, and controls that deliver hot water at a
5-18
NOAA Diving Manual — October 1991
Diver and Diving Equipment
Figure 5-14
Snorkels
prescribed temperature. The heat source may use a
diesel fuel flame, electric cal-rod heaters, live steam,
or a combination of these. The heat exchanger gener-
ally transfers heat from the heat source through an
intermediate fresh water system to the diving water
system. The intermediate system isolates the diving
water system from temperature surges and reduces
heater maintenance by controlling scaling and corro-
sion. For operational convenience, the controls that
operate the heat source can be located remotely.
Hot-water suits require both a bell hose and a diver's
hose. The bell hose carries hot water from the heater to
the bell, and the diver's hose carries hot water either
from the heater or the bell.
5.4.3.3 Closed-Circuit Hot-Water Suits
Closed-circuit hot-water suits consist of a dry suit
and a special set of underwear; heated water is circu-
lated through the underwear. Water is pumped from a
heater, through a series of loops in the underwear, and
back to the heat source. Hot water may originate either
from a heater carried by the diver or from a surface
heater. The primary advantages of closed-circuit hot-
water systems are that they keep the diver dry and
retain their insulating ability for some period of time if
the hot-water source fails. The major disadvantages of
suits of this type are that the special underwear severely
restricts the diver's movement and that these suits are
more fragile than the open-circuit system.
5.5 DIVER'S ACCESSORY EQUIPMENT
There are numerous items of accessory equipment that
have special uses and are valuable to a diver to accom-
plish underwater tasks. The following sections describe
several of these items.
5.5.1 Snorkels
A snorkel is a rubber or plastic breathing tube that
allows a diver to swim comfortably on the surface
without having to turn his or her head to the side to
breathe. Snorkels allow scuba divers to survey the
bottom in shallow water without having to carry a
scuba tank.
Snorkels are available in a wide variety of designs
(Figure 5-14), and selection is a matter of individual
preference (Murphy 1980). The most commonly used
snorkel has three segments: a barrel that protrudes
above the water, a mouthpiece tube, and a mouthpiece.
The mouthpiece should be selected to fit easily under
the lips and should be capable of being held without
Courtesy TEKNA SCUBA
excessive biting force. Soft rubber models are availa-
ble, and some have a swivel feature. Other models are
bent to conform to the configuration of the diver's
head or to have a flexible length of hose at the breath-
ing end that allows the mouthpiece to drop away when
not in use. Although widely distributed, snorkels with
a sharp bend should not be used because they increase
airway resistance. Those with shallow bends, such as
the wraparound models, reduce this resistance to a
minimum. Snorkels with corrugated flexible tubes,
however, are difficult to clear of water and addition-
ally cause air to move in turbulent flow, which increases
breathing resistance. Snorkels should have an opening
of the same size at the intake as at the mouthpiece;
they should not have a divider in the mouthpiece, because
the divider also will cause turbulent flow.
Ideally, the inside diameter of the snorkel should be
5/8 to 3/4 inch (1.3 to 1.8 cm), and it should not be
more than 15 inches (38.1 cm) in length. Longer snor-
kels increase breathing resistance, are more difficult
to clear, increase dead air space, and cause additional
drag when the diver is swimming under water. Snor-
kels flood when the diver submerges, but these devices
can be cleared easily by exhaling forcefully through
the tube. With some snorkels, especially those with
flexible tubing near the mouthpiece, it is difficult to
clear the snorkel completely, and small amounts of
water may remain in the curve or corrugations of the
tube. Snorkels of this type can be cleared easily when
the diver surfaces.
October 1991 — NOAA Diving Manual
5-19
Section 5
Figure 5-15
Dive Timer
5.5.2 Timing Devices
A watch is essential for determining bottom time,
controlling rate of ascent, and assisting in underwater
navigation; it is imperative for dives deeper than
30 feet (9 m). A diver's watch must be self-winding,
pressure- and water-proof (a screw-type sealing crown is
recommended), and should have a heavily constructed
case that is shock-resistant and non-magnetic. An
external, counter-clockwise-rotating, self-locking bezel
is required for registering elapsed time. The band should
be of one-piece construction and should be flexible
enough to fit easily over the diver's arm. A flat, scratch-
proof crystal and screw-down and lock stem also are
recommended. Electronic (battery-powered) diving
watches are now common, but divers should remember
that batteries run down and that some of these watches
are sensitive to external temperatures, which could
affect their reliability during cold-water diving.
Dive timers are miniature computers that use micro-
processor chips to count the number of dives in a day,
the current bottom time, and the current surface interval
(Figure 5-15). Some timers also can count the hours
after the last dive to let the user know when it is safe to
fly. Models are available that can operate for as long as
5 years without battery replacement. Dive timers are
activated automatically when the diver descends to a
depth below a certain depth (approximately 5 to 9 feet
(1.5 to 2.7 m)). During ascent, timers stop automati-
cally at a depth of about 3 to 5 feet (0.9 to 1.5 m).
As with other diving equipment, watches and timers
must be handled with care and be washed in fresh
water after they have been used in salt or chlorinated
water. An important requirement for any dive timer is
that it have a high-contrast face to facilitate reading
under poor-visibility conditions.
5.5.3 Depth Gauges
Depth gauges (Figure 5-16) are small, portable,
pressure-sensitive meters that are calibrated in feet
and allow divers to determine their depth while sub-
merged. Depth gauges are delicate instruments and
must be treated carefully to avoid decalibration. Accu-
racy is extremely important and should be checked at
regular intervals. Only a few models of depth gauges
can be calibrated in the field; most models can be
returned to the manufacturer if they need replacement
parts. During evaluation and regular use, gauges should
be checked to ensure that rough gears or internal cor-
rosion does not cause the indicator hand to stick at par-
ticular depths.
(
«
Courtesy TEKNA SCUBA
Figure 5-16
Depth Gauges
4
5-20
Courtesy New England Divers, Inc.
NOAA Diving Manual — October 1991
Diver and Diving Equipment
Most commercially available depth gauges operate
either on the capillary, diaphragm, or bourdon tube
principle. Capillary depth gauges consist of a plastic
tube that is open to the water at one end and is attached
to a display that is calibrated in feet. As depth increases,
the pocket of air trapped in the tube decreases and the
depth is read from the water level in the tube. The
diaphragm model has a sealed case, one side of which is
a flexible diaphragm. As pressure increases, the dia-
phragm is distorted, which causes the needle to which
it is linked to move. Bourdon tube depth gauges are the
most fragile of these types of gauges; they require more
frequent calibration than the other types. With bour-
don tubes, water pressure causes a distortion of the
tube, which in turn moves a needle that indicates depth.
Both bourdon tube and diaphragm depth gauges are
available in models that are sealed and oil-filled for
smooth, reliable operation.
Combination depth gauges are also available; these
generally consist of combinations of a conventional
bourdon tube with a capillary gauge around the perim-
eter of the face. Capillary gauges generally give more
accurate readings at shallower depths, and these gauges
can also be used as a reference for measuring the
accuracy of a bourdon tube gauge. If the bourdon tube
has been damaged, the readings provided by the two
gauges at shallow depths will differ significantly.
Bourdon tube gauges tend to retain salt water in the
tube, which may cause salt deposition or corrosion. To
prevent this, the tube should be sucked free of water
and the gauge should be stored in a jar of distilled
water. Helium-filled depth gauges leak and lose accu-
racy if they are not kept completely submerged in
water whenever they are exposed to high-pressure
conditions.
Depth gauges are delicate, finely tuned instruments
and must be used, stored, and maintained with great
care. They are an essential part of a diver's life-support
equipment, and careless handling on the part of the
diver could prove fatal.
For surface-supplied divers, depth is usually meas-
ured with a pneumofathometer, which is a pressure
gauge located on the surface. To determine a diver's
depth, air is introduced into the pneumo hose at the
surface. The pneumo hose is one of the members of a
diver's umbilical assembly and is open to the water at
the diver's end. The air introduced at the surface dis-
places the water in the hose and forces it out the diver's
end. When the hose is clear of water, excess air escapes.
The gauge connected to the hose on the surface indi-
cates the pressure (in feet or meters of seawater equiv-
alent) required to clear the hose of water.
October 1991 — NOAA Diving Manual
5.5.4 Wrist Compass Cylinders
An underwater compass consists of a small magnetic
compass that is housed in a waterproof and pressure-
proof case and is worn attached to a diver's wrist by a
band. Compasses are useful for underwater naviga-
tion, especially in conditions of reduced visibility, and
they are also helpful when divers are swimming back to
a boat while submerged. Compasses do not provide
precise bearings, but they do provide a convenient,
reliable directional reference point. To limit magnetic
interference, compasses should be worn on the oppo-
site wrist from the diver's watch and depth gauge.
Compass models are available that allow a diver to
read them while holding them horizontally in front of
them when swimming. Compasses do not have to be
recalibrated, and the only maintenance they need is a
fresh-water rinse after use.
5.5.5 Pressure Gauges
Two styles of pressure gauges can be used to deter-
mine the amount of air in a scuba tank. A surface
cylinder pressure gauge (Figure 5-1 7 A) is used to check
the amount of air in a tank on the surface. This type of
gauge fits over the cylinder manifold outlet, attaches
in the same manner as a regulator, and provides a
one-time check of the pressure in a tank. A pressure-
release valve is installed on the gauge so that air trapped
in the gauge after the valve on a tank has been secured
can be released and the gauge removed. These small
dial gauge movements are designed with an accuracy
of ± 100 psi, but they may become less accurate with
use.
The submersible cylinder pressure gauge attaches
directly to the first stage of a regulator by a length
of high-pressure rubber hose; these gauges provide
divers with a continual readout of their remaining
air. Many units have a console that holds the compass,
depth gauge, and tank pressure gauge (Figure 5-1 7B);
these consoles free the diver's arms for other dive
activities. Submersible pressure gauges are essential
pieces of diving equipment; most of these devices
operate on the same principle as the bourdon tube.
One end of the submersible pressure gauge is sealed
and is allowed to move; the other end is held fixed
and is connected to a high-pressure air supply. As the
air pressure increases, the bourdon tube tends to
straighten out or to uncurl slightly. The gauge's dial
face should be easy to read and should have high-contrast
markings. Although gauges currently in use are designed
to be accurate and reliable, they are not precision
laboratory instruments. Divers should not expect accu-
racies better than ± 250 psig at the upper end of
5-21
Section 5
Figure 5-17
Pressure Gauges
A. Cylinder Gauge
Courtesy Dacor Corporation
B. Submersible Cylinder Pressure Gauge
Courtesy TEKNA SCUBA
the gauge range and ± 100 psig at the lower end
between 500 and 0 psig (Cozens 1981a).
NOTE
Submersible pressure gauges are recom-
mended for all divers and all dives.
The only maintenance that a submersible pressure
gauge needs is a fresh-water rinse after use. To pre-
vent internal deterioration and corrosion of a surface
gauge, care must be taken to ensure that the plastic
plug that covers the high-pressure inlet is firmly in
place. Submersible pressure gauges should be handled
with care and should be stored securely when not in
use.
5.5.6 Underwater Slates
A slate may be a useful piece of equipment when
underwater observations are to be recorded or when
divers need a means of communication beyond hand
signals. A simple and useful slate can be constructed
from a 1/8- or 1/4-inch (0.3 to 0.6 cm) thick piece of
acrylic plastic that has been lightly sand-papered on
both sides; these slates can be used with an ordinary
pencil.
Semimatte plastic sheets can be placed on a clip
board or in a ring binder. These sheets (about 1/32-inch
(0.01 cm) thick) may be purchased in sizes up to 6 x
10 feet (1.8 to 3.0 m). They may be cut as needed, and no
sanding is required. Ordinary lead pencils can be used,
and marks can be erased or wiped off with a rubber
eraser or an abrasive cleanser. Some underwater slates
are equipped with a compass, depth gauge, and watch
that are mounted across the top. When slates are used,
they should be attached to the diver with a loop or
lanyard made of sturdy line to keep them from being
lost.
5.5.7 Diving Lights
A waterproof, pressure-proof diving light is an impor-
tant item of equipment when divers are operating in
areas of restricted visibility. Lights are used most fre-
quently for photography, night diving, cave diving,
wreck diving, exploring holes and crevices, or diving
under ice. Regardless of the power of an underwater
light, it will have only limited value in murky, dirty
waters where visibility is restricted by suspended matter.
When selecting a light, there are several factors to
consider, such as brightness and beam coverage, type
of batteries (disposable or rechargeable), size and shape,
burn time, and storage time (Figure 5-18) (Cozens 1981b).
Most divers prefer the light to have a neutral or slightly
positive buoyancy because it is easy to add a small
weight to keep the light on the bottom, if necessary.
As with all other pieces of diving equipment, lights
should be washed with fresh water after every use. The
0-ring should be lubricated with a silicone grease and
should be checked for debris every time the light is
assembled. When not in use, the batteries should be
removed and stored separately. Before a diving light is
used, it should be checked thoroughly to ensure proper
operation. The batteries should be replaced any time
they show any signs of running low, and spare light
bulbs and batteries should be available at the dive site:
5.5.8 Signal Devices
Signal devices are an important but frequently ignored
item of diving safety equipment for divers. They are
5-22
NOAA Diving Manual — October 1991
Diver and Diving Equipment
Figure 5-18
Diving Lights
Figure 5-19
Signal Devices
A. Diver's Pinger
Courtesy Battelle-Columbus Laboratories
particularly valuable when a diver surfaces at a great
distance from the support platform or surfaces prema-
turely because of an emergency. Several types of sig-
naling devices are available (Figure 5-19).
Whistles are valuable for signaling other swimmers
on the surface. For easy accessibility, they may be
attached to the oral inflation tube of the buoyancy
vest by a short length of rubber strap.
The military-type flare (MK-13, Mod 0, Signal Dis-
tress, Day and Night) can be carried taped to the
diver's belt or knife scabbard. One end of the flare
contains a day signal, a heavy red smoke, while the
opposite end holds a night signal, a red flare. Both ends
are activated via a pull ring. After either end of the
signal has been pulled, the flare should be held at arm's
length, with the activated end pointed away from the
diver at an angle of about 45 degrees. The diver's body
should be positioned upwind of the signal. If the flare
does not ignite immediately, waving it for a few sec-
onds may assist ignition. After activation, the flare
will work after submergence, although it will not ignite
if activated under water. After every dive, the flare
should be flushed with fresh water and should then be
checked for damage or deterioration.
NOTE
Red flares and smoke signals should be used
only as distress signals or to signal the ter-
mination of a dive.
At night, divers can carry a flashing rescue light that
is attached to their belt, harness, or arm. Rescue lights
of this type are compact, high-intensity, flashing strobe
lights that are generally visible for 1 0 to 15 miles
(16 to 24 km) from a search aircraft flying at an altitude
B. Diver's Flasher
Courtesy Dacor Corporation
of 1500 feet (457.2 m). These lights are waterproof and
can operate submerged at depths up to 200 fsw (61 m),
depending on the make and model. Some rescue lights
have an operational life of as much as 9 hours; the
operational life of these units can be extended greatly
by using the light only intermittently.
Some divers use chemical light tubes; these small
tubes contain two separated chemicals. When the tube
is bent, the chemicals discharge and mix, causing a
soft green light that glows for several hours. Some
divers attach these tubes to their scuba cylinders, mask
straps, or snorkels as an aid to tracking their buddies,
while others carry them as an emergency light source.
Signal devices should be carried so that they are
easily accessible and will not be lost when equipment is
discarded. Buoyancy compensators frequently have a
built-in ring that will accommodate a whistle or strobe
light, and flares are often taped to the scabbard of the
diver's knife with friction tape.
October 1991 — NOAA Diving Manual
5-23
Section 5
5.5.9 Safety Lines
Diver safety lines should be used whenever divers
are operating under hazardous conditions; examples of
such situations are cave diving, working under ice, or
diving in strong currents. Diver-to-diver lines should
be used when the working conditions of the dive could
separate the divers who are working under water. Safety
lines provide divers with a quick and effective (although
limited) means of communications. Under special condi-
tions, a surface float can be added to the line to aid
support personnel in tracking the diver.
The most commonly used types of safety line are
nylon, dacron, or polypropylene. These materials are
strong, have nearly neutral or slightly positive buoy-
ancy, and are corrosion resistant. A snap can be spliced
into each end of these lines to facilitate easy attach-
ment to a float or to a diver's weight belt.
Maintenance of safety lines requires only that they
be inspected and that their snaps be lubricated. Reels
and lines used in cave diving must be dependable;
these lines require additional maintenance and careful
inspection. Any safety line should be replaced if it
shows signs of weakness or abrasion.
5.5.10 Floats
A float carrying the diver's flag should be used any
time a diver is operating from a beach or in an area that
is frequented by small boats. Floats also provide the
dive master with quick and accurate information about
the diver's location and provide the diver with a point
of positive buoyancy in an emergency. Floats range in
size and complexity from a buoy and flag to small
rafts; the type most frequently used is an automobile
innertube whose center portion is lined with net. Float
should be brightly colored and should carry a diver's
flag positioned at the top of a staff; bright colors make
the raft noticeable, and the flag tells boaters that a
diver is in the water.
5.5.11 Accessories That Are Not
Recommended
Several pieces of equipment are sold commercially
but should not be used because they can cause injury to
the diver or convert a routine situation into an emer-
gency. Earplugs should never be used while diving;
they create a seal at the outer ear, which prevents
pressure equalization and can lead to serious ear squeeze,
ruptured eardrum, and, possibly, total loss of hearing
(if the plug is forced deeply into the ear cavity).
Goggles also should not be used in diving because
they do not cover the nose and thus do not permit
equalization of pressure. The increase in pressure inside
the goggles as depth increases during the dive may
cause the rim of the goggles to cut deeply into the face
or the eyes to be forced against the glass plates; either
of these events can cause severe and painful tissue or
eye squeeze.
Regulator neckstraps should also not be worn because
these straps are difficult or impossible to remove in an
emergency. Some single-hose regulators come equipped
with these straps as standard equipment; the straps
should be removed and discarded before diving.
In addition to the specific items mentioned above,
any equipment that is not necessary for the particular
dive should be considered hazardous because extra
equipment increases a diver's chances of fouling. Excess
gear should be left on the surface.
5.6 SHARK DEFENSE DEVICES
In areas where sharks are frequent, many divers carry
some form of shark defense. Several types of devices
are available and have been shown to be effective.
These devices are designed to be used only as defense
mechanisms; they are not effective and should not be
used as offensive weapons.
The oldest anti-shark device is a wooden club that is
counter-weighted to facilitate underwater use and is
commonly called a "shark billy." It is used to fend off
or to strike a shark, preferably on the nose. Shark
billies are made from 3/4-inch (1.8 cm) round fiber-
glass stock and are 4 feet (1.2 m) long. A hole is drilled
in one end to accommodate a lanyard and a loop of
surgical tubing, and the other end is ground to a point
and coated with fiberglass resin. Instruments of this
length and diameter can be moved through the water
quickly because they afford little drag under water.
If a shark is circling a diver, the diver should use the
billy to prod the shark; the butt end should be kept
against the diver's body and the sharp end should be
used against the shark. This defense should discourage
the shark from coming closer than about 4 feet (1.2 m)
from the diver. Sharks that have been prodded leave
the immediate area hastily (although they return to
the area almost immediately). Although brief, the shark's
retreat usually provides sufficient time for the diver to
leave the water (Heine 1985).
If a diver wishes to kill rather than discourage a
shark, a power head can be used. These devices, com-
monly called "bang sticks," consist of a specially
constructed chamber designed to accommodate a power-
ful pistol cartridge or shotgun shell. The chamber is
attached to the end of a pole and is shot or pushed
5-24
NOAA Diving Manual — October 1991
Diver and Diving Equipment
Figure 5-20
Shark Darts
against the shark, where it fires on impact. Although
power heads have a built-in positive safety, they should
be handled with extreme caution; they also should not
be carried in water with poor visibility or at night. It
also is dangerous to carry loaded power heads when
several divers are working closely together in the water.
Devices known as "shark darts" are available com-
mercially; these instruments are designed to disable or
kill sharks by injecting a burst of compressed gas.
Shark darts consist of a hollow stainless steel needle
approximately 5 inches (12.5 cm) long that is con-
nected to a small carbon dioxide (C02) cylinder or
extra scuba tank; they are available in dagger or spear
form (see Figure 5-20). To use these devices, the dart is
thrust against the shark's abdominal cavity, where it
penetrates into the animal's body cavity and discharges
the contents of the C02 cartridge. The expanding gas
creates a nearly instantaneous embolism and forces
the shark toward the surface. The size of the C02
cylinder varies from model to model; a 12-gm cylinder
is effective to a depth of 25 feet (8 m), a 16-gm cylin-
der to 40 feet (13 m), and a 26-gm cylinder to 100 feet
(30 m). Multiple-shot compressed-air models are also
available.
NOTE
In some localities, it is illegal to carry com-
pressed-air weapons such as shark darts in
automobiles or on the person. Divers are
therefore advised to check with local authori-
ties before carrying these devices.
One of the most effective methods of protecting
divers in shark-infested waters is the Shark Screen, a
lightweight synthetic bag that has three inflatable
collars (Figure 5-21). In the water, the diver blows up
the collars, gets into the bag, and fills it with seawater;
the bag then conceals the occupant from the sea below
and keeps any effusions (e.g., blood or sweat) that
might attract sharks in the bag. When not in use, the
bag is folded into a small package and carried in a life
vest or kept with other survival gear.
5.7 UNDERWATER COMMUNICATION
SYSTEMS
Several underwater communication systems have been
developed and are available commercially. These sys-
tems vary in effectiveness because of their inherent
deficiencies and use constraints. Studies have shown
that, regardless of the efficiency of these systems, the
Photo William High
Figure 5-21
Shark Screen in Use
Photo Scott Johnson
intelligibility of messages transmitted through any type
of diver communication system is less than optimal as
a result of the effects of pressure, interference from
the life support system, and the need for a diver to
concentrate on behaviors other than communication.
Message intelligibility improves significantly, howev-
er, if divers are trained to be better talkers and listeners in
the underwater environment (Hollien and Rothman
1976). The four principal types of diver communica-
tion systems are described in the following sections.
5.7.1 Hardwire Systems
Hardwire systems employ a closed loop that is com-
parable to a telephone and includes a microphone, an
October 1991 — NOAA Diving Manual
5-25
Section 5
Figure 5-22
Diver Communication System
earphone/receiver, and a cable over which the signal is
transmitted. These units require a physical connec-
tion, i.e., umbilical, between the talker and the listener.
Hardwire systems of the type used for surface-supplied or
scuba diver communication provide the greatest degree
of intelligible communication of the systems discussed
here. Figure 5-22 shows the surface control panel of a
hardwire diver communication system.
Most hardwire systems can be configured either for
two-wire or four-wire operation. In a two-wire sys-
tem, the diver usually is the priority signal path and
the tender listens to the diver. If the tender wishes to
talk to the diver, a switch must be thrown. The ear-
phone and microphone on the diver's end are wired in
parallel (Figure 5-23A). When two divers are operating
on the same radio, the tender must push a cross-talk
switch to enable the divers to talk to each other. A
four-wire system (Figure 5-23B) allows the tender and
divers to participate in open-line (round robin) com-
munication, similar to that in a conference telephone
call.
Most hardwire units are powered by internal 6- or
12-volt lantern-type batteries that provide continu-
ous operation on moderate volume output for 25 hours
or more. Some units feature connections for an exter-
nal power supply; others incorporate redundant batteries
so that a spare is always available in an emergency.
5.7.2 Acoustic Systems
The acoustic system includes a microphone, ampli-
fier, power supply, and transducer; it transduces speech
directly into the water by means of the projector (under-
water loudspeaker). The signal produced can be received
either by a hydrophone placed in the water or by divers
without any special receiving equipment. Some of these
systems also incorporate alarms or signals that can be
used to recall divers.
5.7.3 Modulated Acoustic Systems
Several units of the modulated acoustic type have
been manufactured, and these have performance charac-
teristics that vary from poor to excellent. The most
widely used modulated acoustic systems employ ampli-
tude modulation (AM), a technique also used by com-
mercial AM broadcast stations. However, since radio
signals are absorbed rapidly by seawater, the acoustic
carrier rather than the radio frequency carrier is mod-
ulated in diving situations. A typical system of this
type consists of a microphone, power supply, amplifi-
er, modulator, and underwater transducer (Figure 5-24).
Acoustic signals produced by such systems can be
5-26
\
Photo Michael Pelissier, Ocean Technology Systems
Figure 5-23
Schematics of Diver
Communication Systems
A. Two-Wire Mode
(
P^ 5^f
&_
B. Four-Wire Mode
MICROPHONE
i
Courtesy Michael Pelissier, Ocean Technology Systems
NOAA Diving Manual — October 1991
Diver and Diving Equipment
Figure 5-24
Modulated Acoustic
Communication System
Photo Michael Pelissier. Ocean Technology Systems
understood only by a diver or a topside listener equipped
with an appropriate receiver and demodulator. In one
such unit, for example, a 31.5-kHz carrier signal is
modulated by the speech signal, amplified, and projected
into the water via an acoustic transducer. The acoustic
signal is then picked up by another acoustic transduc-
er, amplified, demodulated, and heard in the normal
speech mode. The power output of a typical 31.5-kHz
communicator is 1/2 watt. Generally, a range of
1/4 mile (0.4 km) can be expected in good ocean
conditions. However, range and clarity can change
dramatically because of acoustic background noise, a
shadow effect (caused by the tank, buoyancy compen-
sator, wet suit, etc.), or thermoclines.
Other modulated acoustic systems involve frequency
modulation (FM) or single sideband (SSB). FM sys-
tems generally require a high ultrasonic frequency to
obtain the frequency deviation necessary for intelligi-
ble communication. Generally, the higher the frequency,
the greater the absorption of sound in water. As a
result, few FM systems adapted to underwater use are
commercially available.
Single sideband has an advantage over AM, because
AM puts one-half of the total output power in the
carrier, and this power is ultimately lost. SSB commu-
nicators have greater range than AM systems for the
same output power and frequency. A major drawback
to SSB is that it requires more complicated electronics
and higher initial cost than other systems, and, as a
result, most presently used underwater communica-
tion systems utilize the AM technique.
Poor intelligibility has been a problem for many
users of wireless diver communications. In the late
1960's, researchers at the University of Florida sponsored
a series of tests designed to elucidate this problem.
During the tests, divers read phonetically balanced
word lists using various masks, microphones, and com-
municators; test results showed intelligibility scores in
the 50 percent range at best. It is now known that many
human and equipment factors contribute to an increase in
intelligibility. The key elements are the microphone,
mask, earphone, transmitter/speech filter design, and
diver training.
5.7.4 Non-acoustic Wireless Systems
Another approach to underwater communication
involves a non-acoustic wireless system that uses an
electric current field. Because it is non-acoustic, this
system is not affected by thermoclines, natural or man-
made barriers, or reverberation. Range is determined
by the amount of power applied to the field platers and
by the separation between them. Separation generally
is limited to the diver's height, and power output is
limited by what the diver can tolerate because the
diver "feels" a mild shock when transmitting. This
mode is limited, at best, to a range of a few hundred
feet or meters. With modification, this system can be
used to transmit physiological data.
October 1991 — NOAA Diving Manual
5-27
♦
i
SECTION 6
HYPERBARIC
CHAMBERS
AND SUPPORT
EQUIPMENT
Page
6.0 General 6-1
6.1 Hyperbaric Chambers 6-1
6. 1 .1 Transportable Chambers 6-2
6.2 Design and Certification 6-3
6.3 Operation 6-3
6.3.1 Predive Checklist 6-3
6.3.2 Gas Supply 6-3
6.3.3 Chamber Ventilation and Calculation of Gas Supply 6-6
6.3.4 Mask Breathing System 6-7
6.3.5 Oxygen Analyzers 6-8
6.3.6 Electrical System 6-9
6.4 Chamber Maintenance 6-9
6.5 Fire Prevention 6-10
6.5.1 Ignition 6-10
6.5.2 Combustion 6-14
6.5.3 Materials 6-14
6.5.4 Management of a Fire 6-14
6.5.4.1 Detection 6-17
6.5.4.2 Extinguishment 6-17
6.5.4.3 Breathing Masks and Escape 6-17
6.5.5 Summary of Fire Protection Procedures 6-17
♦
«
HYPERBARIC
CHAMBERS
AND SUPPORT
EQUIPMENT
three terms generally describe 'chambers used prima-
rily to treat diving casualties), and decompression cham-
bers (a term used to indicate that their primary use is
for the surface decompression of divers). Engineers
refer to these as PVHO's (Pressure Vessels for Human
Occupancy).
6.1 HYPERBARIC CHAMBERS
Early models of hyperbaric chambers were single-
compartment (single-lock) chambers that allowed one
patient and a tender to enter and be pressurized. NOAA
does not recommend the use of single-lock chambers
because they do not allow medical and tending person-
nel to have access to the patient during treatment. All
modern chambers are of the multilock type (see Fig-
ure 6-1). The multilock chamber has two or more com-
partments that are capable of being pressurized in-
dependently; this feature allows medical personnel and
6.0 GENERAL
Hyperbaric chambers were developed to permit
human beings to be subjected to an increased pressure
environment. Such chambers are vessels capable of
accommodating one or more occupants and of being
pressurized so that the environment inside the chamber
simulates water depth while the pressure outside the
chamber remains at normal (l atmosphere) pressure.
Hyperbaric chambers are used in research on the ef-
fects of pressure, in the treatment of pressure-related
conditions, and in the decompression of divers. For
example, hyperbaric chambers are used in several sit-
uations that occur in diving: surface decompression;
omitted decompression; treatment of diving accidents
such as gas embolism and decompression sickness; and
pressure and oxygen tolerance tests. Terms used inter-
changeably to denote these chambers include recom-
pression, compression, or hyperbaric chambers (these
Figure 6-1A
Double-Lock Hyperbaric Chamber— Exterior View
Oxygen
Nitrox Regulator Inert Gas Inner Lock Analyzer Communications Outer Lock Outer Lock
Lifting Eye (Therapy Gas) Regulator Gauge j / y Gauge Viewport
Viewport
C02 Scrubber
Controls
Design and
Cert. Plate
E.K.G.
02 Overboard
Exhaust
Air Exhaust
Oxygen and Therapy
Gas Cylinders
Photo Dick Rutkowski
October 1991 — NOAA Diving Manual
6-1
Section 6
Figure 6- 1B
Double-Lock Hyperbaric Chamber— Interior View
Emergency
Air/Therapy
Gas Mask
nterior Light
Photo Dick Rutkowski
tenders to enter the chamber to treat the patient and
then to leave, while the patient remains at the desired
pressure in the inner compartment.
A chamber should be equipped with the following:
• A two-way communication system
• A mask breathing system for oxygen (normally of
the demand type, although ventilation hoods are
gaining acceptance for clinical treatment) (Fig-
ure 6-2)
• Emergency air/mixed gas breathing masks
• Pressurization and exhaust systems
• A fire extinguishing system
• External lighting that illuminates the interior
• Viewports
• Depth control gauges and control manifolds
• Heating and air conditioning systems (highly
desirable)
• Stop watches (elapsed time with hour, minute, and
second hands)
• Gas sampling ports.
Multiplace chambers are designed to accommodate
several occupants at the same time. Deck decompres-
sion chambers (located on the deck of the surface
platform or support ship) and land-based chambers
used for recompression treatment and diving research
or for clinical hyperbaric treatment and research are
examples of multiplace chambers.
6.1.1 Transportable Chambers
Small portable chambers, varying in size and shape
from single-person, folding chambers made from modern
lightweight materials (Figure 6-3) to L-shaped, two-
person capsules, have been used in emergencies to
recompress divers being transported to a large well-
equipped chamber. Transportable chambers are most
valuable when they are of the two-person type and are
capable of being mated to a larger chamber, because
these features allow the patient to be continuously
tended and pressurized. Small one-person transportable
6-2
NOAA Diving Manual — October 1991
Hyperbaric Chambers and Support Equipment
Figure 6-2
Mask Breathing System for Use in Hyperbaric
Chamber
C02 Scrubber Motor
Sound Powered
Phone
Viewport
Oxygen
Exhaust
C02 Scrubber
Canister
Photo Dick Rutkowski
chambers, although better than no recompression
capability at all, have major shortcomings because an
attendant outside the chamber has no way to perform
lifesaving measures, such as maintaining an airway,
performing cardiopulmonary resuscitation, or reliev-
ing a pneumothorax.
6.2 DESIGN AND CERTIFICATION
Several codes and standards apply to man-rated pres-
sure vessels, including current standards set by the
American National Standards Institute, the American
Society of Mechanical Engineers, the National Fire
Protection Association, and, under certain circum-
stances, the U.S. Coast Guard. These codes are com-
prehensive where the structural integrity of the vessel
is concerned and include all aspects of material selec-
tion, welding, penetrations into the pressure vessel
walls, flanges for entry or exit, and testing. Only high-
quality pressure gauges and ancillary equipment should
be used in outfitting a hyperbaric chamber. All such
equipment should be tested and calibrated before a
diving operation. Figure 6-4 is an example of a certifi-
cation plate and shows various specifications and
certifications.
NOTE
If structural modifications such as those
involving welding or drilling are made, the
chamber must be recertified before further
use.
Hyperbaric chambers used in diving usually are cylin-
drical steel pressure vessels that are designed to with-
stand an internal working pressure of at least 6 atmo-
spheres absolute (ATA) (165 fsw). Modern chambers
generally are 54-60 inches (137-152 centimeters) in
inside diameter but may have inside diameters ranging
from 30 inches (76 centimeters) to as large as 10 feet
(3 meters). Large chambers used to house and decom-
press divers for long saturation exposures are outfitted
with toilet facilities, beds, and showers, but such com-
fortable chambers usually are found only at sites where
large-scale diving operations or experimental dives
are conducted.
6.3 OPERATION
6.3.1 Predive Checklist
A predive check of each chamber must be conducted
before operation. If pressurized by a compressor, the
gas source must be checked to see that the intake is
clean and will not pick up exhaust from toxic sources.
The predive checklist (see Table 6-1) should be posted
on the chamber itself or on a clipboard next to the
chamber.
6.3.2 Gas Supply
A chamber treatment facility should have a primary
and a secondary air supply that will satisfy the follow-
ing requirements:
Primary supply — sufficient air to pressurize the cham-
ber twice to 165 fsw and to venti-
late throughout the treatment:
Secondary supply — sufficient air to pressurize the
chamber once to 165 fsw and to
ventilate for l hour.
October 1991 — NOAA Diving Manual
6-3
Section 6
Figure 6-3
Transportable Chambers
A. Total system
Courtesy Draegerwerk AG
C. Lightweight one-person transportable chamber
♦
B. Schematic showing victim and tender
Photo Butch Hendrick
Technical Data:
Max. operating pressure: 5 bar
Test pressure: 7.5 bar
Total volume: 700 liters
Total outside length: 2540 mm
Total outside height: 1520 mm
Total outside width: 860 mm
Outside height (without mobile base): 1200 mm •
Total inside length: 2350 mm •
Largest inside diameter: 640 mm •
Total weight: approx. 500 kp
Weight of the complete base: approx. 275 kp
Weight of the complete pressure
chamber without base: approx. 225 kp
Acceptance: Techn. Inspect. Agency (TUV)
Courtesy Draegerwerk AG
72.5 pounds/sq. in.
■ 108.75 pounds/sq. in.
■42,714 cu. in.
•100.00 in.
■ 59.84 in.
• 33.86 in.
47.24 in.
92.52 in.
25.20 in.
1102.5 pounds
606.4 pounds
496.1 pounds
♦
Figure 6-4
Certification Plate for Hyperbaric Chamber
Maximum Working Pressure.
ASME Stamp (Chamber manufactured
in accordance with ASME Code) for,
Unfired Pressure Vessel
Division of Code (Manufactured
according to Section 8, Division 1).
Arc or Gas Welded Construction.
Manufacturer .
77 PSI 150°F
Uj SERIAL NO
DIV I 1973
W «
b USCG CLASS
MIA 73 25
DESIGNED AND BUILT BY
PERRY SUBMARINE BUILDERS
RIVIERA BEACH, FLORIDA
Maximum Working Temperature
Manufacturer's Serial Number
^.Year of Construction
.U.S. Coast Guard Stamp:
Class II designates either Working
Pressure between 30 and 600 psi or
working temperature between 275°
and 700 °F
U.S. Coast Guard Office in charge of
Marine Inspection
MIA — Miami Office
73 — Year of inspection
25 — Sequential number of
inspection (e.g., 25th
chamber inspected in
1973)
I
6-4
Source: NOAA (1979)
NOAA Diving Manual — October 1991
Hyperbaric Chambers and Support Equipment
Table 6-1
Hyperbaric Chamber Predive
Checkout Procedures
Before every operation of the chamber, a predive check of
ELECTRICAL SYSTEM
the facility must be conducted. This procedure should take
Lights operational
only a few minutes, provided that the personnel are experienced
Wiring approved, properly grounded
and the chamber is properly maintained.
Monitoring equipment (if applicable)
calibrated and operational.
Predive Checklist
COMMUNICATION SYSTEM
CHAMBER
Primary system operational
Clean
Secondary system operational.
Free of all extraneous equipment
Free of noxious odors
FIRE PREVENTION SYSTEM
Doors and seals undamaged, seals lubricated
Water and appropriate fire extinguisher in chamber. For
Pressure gauges calibrated, compared.
chambers with installed fire suppression system,
pressure on tank
AIR SUPPLY SYSTEM
Combustible material in metal enclosure
Primary air supply adequate for two pressurizations to
Fire-resistant clothing worn by all chamber occupants
165 feet plus ventilation
Fire-resistant mattress and blankets in chamber.
Secondary air supply adequate for one pressurization
and 1 hour of ventilation
MISCELLANEOUS — INSIDE CHAMBER
Supply valve closed
Slate, chalk, and mallet
Equalization valve closed
Bucket and plastic bags for body waste
Supply regulator set at 350 psig or 250 psig, depending
Primary medical kit
on working pressure (200 or 100 psi) of chamber
Ear protection sound attenuators/aural protectors
Fittings tight, filters clean, compressors fueled.
(one pair per occupant) .
OXYGEN SUPPLY SYSTEM
MISCELLANEOUS— OUTSIDE CHAMBER
Cylinders full; marked as BREATHING OXYGEN;
Stopwatches
cylinder valves open
Recompression treatment time
Replacement cylinders on hand
Decompression time-personnel leaving chamber
Inhalators installed and functioning
Cumulative time
Regulator set between 75 and 100 psig
Spare
Fittings tight, gauges calibrated
U.S. Navy recompression treatment tables
Oxygen manifold valves closed.
U.S. Navy decompression tables
Log
NITROX (Therapy Gas)
List of emergency procedures
Cylinders full; marked 60% N2/40% 02;
Secondary medical kit
cylinder valves open
Oxygen analyzers functioning and calibrated.
Replacement cylinders on hand
Inhalators installed and functioning
CLOSED-CIRCUIT OPERATIONS (WHEN APPLICABLE)
Regulator set between 75 and 100 psig
C02 scrubber functional
Fittings tight, gauges calibrated
Adequate C02 absorbent
NITROX valves closed.
C02 analyzer functional.
Both the primary and secondary supply may be pro-
vided by any combination of stored and compressor
capacities that will provide the required amounts of air
at the appropriate pressure in the required times.
If it is not feasible to have a high-pressure system
available as a backup, two low-pressure systems may
be used. In addition to having an adequate volume of
stored gas, it is important to be aware of the possibility
of power failures and, wherever possible, to keep an
emergency generator available to provide continuous
power if service is interrupted. Personnel at chamber
installations should be familiar with local fire and
rescue units that can provide emergency power and air.
October 1991 — NOAA Diving Manual
The compressor should have a card in a conspicuous
place showing the date of service and type of lubricant
used. Before activating a hyperbaric chamber, the opera-
tor must ensure that the predive checklist shown in
Table 6-1 has been completed.
WARNING
Compressors Should Be Lubricated With
Lubricants That Will Not Break Down Under
Heat or High Pressure, and Filters Should Be
Changed According to Required Maintenance
Procedures
6-5
Section 6
6.3.3 Chamber Ventilation and Calculation of
Gas Supply
Unless the chamber is equipped with a scrubber, it is
necessary to ventilate the chamber with fresh air to
maintain safe levels of carbon dioxide and oxygen inside
the chamber. The rate at which air must be circulated
through the chamber depends on the number of per-
sonnel inside the chamber, their level of activity, the
chamber depth, and the breathing gas being used.
NOTE
The abbreviation acfm refers to actual cubic
feet per minute at the chamber pressure in
use at the time; scfm refers to standard cubic
feet per minute, defined as cubic feet per
minute at standard conditions at one atmo-
sphere pressure and 0° C [acfm = (scfm)/
(chamber pressure in atmospheres absolute,
usually expressed as (D + 33)/33), where
D = chamber depth in fsw].
The following procedures reflect various scenarios
encountered in chamber operations:
(1) When occupants are breathing air in the chamber:
(a) 2 acfm for each person at rest
(b) 4 acfm for each person not at rest.
(2) When occupants are breathing oxygen by mask
in a chamber without an overboard dump system:
(a) 12.5 acfm for each person at rest
(b) 25.0 acfm for each person not at rest
(c) Additional ventilation is not necessary for
occupants who are not breathing oxygen.
(3) Interrupted ventilation:
(a) Should not exceed 5 minutes during any
30-minute period.
(b) When resumed, should use twice the required
acfm for twice the period of interruption, and
then the normal rate should be resumed.
(4) When oxygen monitoring equipment is available:
(a) Ventilation should be used as required to
maintain oxygen concentration in the chamber
below 23 percent.
(5) With an installed overboard dump system:
(a) The ventilation rates for air breathing given
in Step 1 above should be used.
The quantity of air ventilated through the chamber
is controlled by regulating the precalibrated exhaust
valve outside the chamber. Once the exhaust rate has
been established, the air supply valve can be regulated
to maintain a constant chamber pressure.
6-6
The chamber air supply should be maintained at a
minimum supply pressure of 100 psig over maximum
chamber pressure. Regulator settings for oxygen depend
on the type of oxygen breathing masks installed in the
chamber; most masks should be supplied with gas at
between 75 and 100 psig above the chamber pressure.
Knowing the amount of air that must be used does
not solve the ventilation problem unless there is some
way to determine the volume of air actually being used
for ventilation. The standard procedure is to open the
exhaust valve a given number of turns (or fractions of a
turn), which provides a certain number of actual cubic
feet of ventilation per minute at a specific chamber
pressure, and to use the air supply valve to maintain a
constant chamber pressure during the ventilation period.
• The exhaust valve handle should be marked
so that it is possible to determine accurately
the number of turns and fractions of turns.
• The rules in this paragraph should be checked
against probable situations to determine the rates
of ventilation at various depths (chamber pressures)
that are likely to be needed. If the air supply is
ample, determination of ventilation rates for a
few depths (30, 60, 100, 165 fsw) may be suffi-
cient, because the valve opening specified for a
given rate of flow at one depth normally will pro-
vide at least that much flow at a deeper depth.
• The necessary valve settings for the selected flows
and depths should be determined with the help of
a stopwatch by using the chamber itself as a
measuring vessel.
• The ventilation rate can be calculated by using
this formula:
R =
V X 18
t X
(P + 33)
33
where
R
V
t =
chamber ventilation rate in acfm;
volume of chamber in cubic feet;
time for chamber pressure to change 10
fsw in seconds;
P = chamber pressure (gauge) in fsw.
Chamber pressure in the unoccupied chamber should
be increased to 5 fsw beyond the depth in question. The
exhaust valve should then be opened a certain amount
NOAA Diving Manual — October 1991
Hyperbaric Chambers and Support Equipment
and the length of time it takes to come up to 10 fsw
below this maximum depth should be determined. (For
example, if checking for a depth of 165 fsw, the
chamber pressure should be taken to 170 fsw and the
time it takes to reach 160 fsw should be measured.)
The valve should be opened different degrees until the
setting that approximates the desired time is known;
that setting should then be written down. Times for
other rates and depths should be calculated and set-
tings determined for these in the same way. A chart
or table of the valve settings should be made and a
ventilation chart using this information and the venti-
lation rates should be prepared.
Primary system capacity (for a chamber not equipped
with a mask overboard discharge system and assuming
there are two patients and one tender in the chamber)
is calculated as follows:
where
Cp
V
10
Cp = 10V + 48,502
total capacity of primary system (scf);
chamber volume (ft3);
atmospheres needed to pressurize twice
from the surface to 165 fsw;
48,502 = total air (in scf) required to ventilate during
a treatment using USN Treatment Table 4.
Table 6-2 shows ventilation rates and total air
requirements for two patients and one attendant
undergoing recompression treatment (US Navy 1985).
As indicated, the maximum air flow rate that the sys-
tem must deliver is 70.4 scfm (with an oxygen stop at
60 fsw).
Secondary System Capacity
To calculate secondary system capacity, the formula is
Cs = 5V + 4,224
where
Cs = total capacity of secondary system (scf);
V = chamber volume (ft3);
5 = atmospheres required to pressurize from
the surface to 165 feet once;
4,224 = maximum ventilation rate of 70.5 scfm
for 1 hour.
The exhaust intake must be placed inside the cham-
ber as far away from the supply inlet as practical to
ensure maximum circulation within the chamber and
to prevent fresh air from being drawn from the cham-
ber during ventilations.
6.3.4 Mask Breathing System
The oxygen system provides oxygen for that part of
the decompression/recompression schedule requiring
pure oxygen. It also provides a source of known clean
air in the event of fouling of the air in the chamber. The
system should be inspected carefully and checked for
leaks. Smoking in the vicinity of a chamber is prohibited.
A hyperbaric chamber may be equipped with both
standard and overboard discharge breathing masks.
The standard mask is generally used with air but can
be used with mixed gas or treatment gas. Overboard
discharge masks are generally used for oxygen breath-
ing during recompression or treatments. The standard
breathing mask consists of an oral-nasal mask, demand
regulator for oxygen or air supply, appropriate hoses
and fittings, and an in-board dump (or discharge)
system (see Figure 6-2). A breathing mask with an
overboard discharge system consists of the same basic
components as the standard mask, with the addition of
a mask-mounted demand exhaust regulator and appro-
priate hoses and fittings to exhaust the diver's exhaled
breath outside the recompression chamber; overboard
dump systems are usually used for oxygen breathing.
The oxygen cylinder pressure is reduced to approxi-
mately 75 psig over chamber pressure by a pressure
regulator. This pressure differential is maintained by a
suitable tracking regulator or by operator manipula-
tion of a standard regulator as required by changes in
chamber depth. The resulting low-pressure oxygen or
air flows through a lightweight, flexible hose to a demand
regulator located on the mask. A control knob on the
demand regulator allows adjustment of the regulator
to minimize breathing resistance or to permit constant
flow, if this is desired. The gas delivery pressure also
may be adjusted from outside the chamber to enhance
flow characteristics.
With the overboard discharge units, the diver's exhala-
tion is removed through a regulator that is mounted on
the side of the mask. The regulator exhaust is con-
nected by a hose to the outside of the chamber. For a
pressure differential in excess of 60 fsw, an auxiliary
regulator must be connected between the hose and the
chamber wall to limit the differential pressure at the
outlet of the mask-mounted regulator. The unit should
not be pressurized to a depth greater than 60 fsw unless
it is fitted with an auxiliary vacuum regulator or the
October 1991 — NOAA Diving Manual
6-7
Table 6-2
Ventilation Rates and Total
Air Requirements for Two
Patients and One Tender
Undergoing Recompression Treatment
Section 6
Depth Ventilat
on
of Rate (scfm)
Ventilation Air Required at Stop (scf)
Using 02
Stop Air
°2
'
Treatment Table
from 60'
(fsw) Stop
Stop 5
6
6A
1A
2A
3
4
4
165 47.9
1437
1437
1437
5749
5749
140 41.9
503
503
1256
1256
120 37
139
444
444
1111
1111
100 32.2
966
386
386
966
966
80 27.3
328
328
328
821
821
60 22.5
70.4 2929
4561
4561
675
675
675
8104
25344
50 20.1
62.9
603
603
603
7234
22644
40 17.7
55.3 1772
1772
1772
530
530
530
6363
19908
30 15.3
47.7 1107
6183
6183
916
1831
10996
10996
34344
20 12.8
40.2
770
1540
1540
1540
7236
10 10.4
32.6 1090
1090
1090
1250
2501
1250
1250
5868
Total for Ventilation
6898
13606
15182
6038
10778
18692
45390
125247
NOTE: Total air requirements are dependent on chamber size.
Depth of Stop
Duration
A
r Required
60'
4 Hr. 02
4 Hr. Air
4 Hr. 02
16,903
5,400
16,903
60'
4 Hr. Air
3,672
to
4 Hr. 02
14,430
30'
2 Hr. Air
1,922
30'
2 Hr. Air
1,776
to
4 Hr. 02
10,012
10'
4 Hr. Air
2,726
10'
4 Hr. 02
6,262
to
4'
at 4'
2 Hr. Air
624
2 Hr. Air
499
2 Hr. 02
1,563
4'
4 Min.
26
to Surface
82,718 (min)
Adapted from US Navy (1985)
discharge hose has been disconnected from the exter-
nal port.
These units should be inspected by the inside tender
or supervisor before each use. Hose fittings should be
inserted into properly labeled connectors on the wall of
the chamber. After testing, the internal and external
valves should be closed until mask breathing gas is
required.
The mask must be cleaned with an antiseptic solu-
tion (antibacterial soap and warm water, alcohol, and
sterilizing agent) after each use, air-dried, and stored
in a sealed plastic bag or be reinstalled for subsequent
use. Routine inspection and preventive maintenance
are required annually or when malfunctioning is evident.
Generally, inspection and repair service is provided by
6-8
the manufacturer. For further information, consult the
appropriate manufacturer's instruction manual (see
the predive checklist in Table 6-1).
6.3.5 Oxygen Analyzers
An oxygen analyzer is useful for monitoring oxygen
concentrations in chambers where oxygen is used for
therapy, surface decompression, or research. The oxy-
gen level in a hyperbaric chamber should be maintained
between 21 and 23 percent to reduce the danger of
fire (see Section 6.5). An absolute upper limit of
25 percent should be observed, in accordance with
current National Fire Protection Association rules.
Several oxygen analyzers are available. For units
placed outside the chamber with a remote sensor located
NOAA Diving Manual — October 1991
Hyperbaric Chambers and Support Equipment
Table 6-3
Chamber Post-Dive Maintenance Checklist
AIR SUPPLY
Close all valves
Recharge, gauge, and record pressure of air banks
Fuel compressors
Clean compressors according to manufacturer's
technical manual.
VIEWPORTS AND DOORS
Check viewports for damage; replace as necessary
Check door seals; replace as necessary
Lubricate door seals with approved lubricant.
CHAMBER
Wipe inside clean with vegetable-base soap and
warm fresh water
Remove all but necessary support items from chamber
Clean and replace blankets
Encase all flammable material in chamber in
fire-resistant containers
Restock primary medical kit as required
Empty, wash, and sanitize human waste bucket
Check presence of sand and water buckets in chamber
Air out chamber
Close (do not seal) outer door. Preferably leave one light
on inside chamber to keep moisture out.
SUPPORT ITEMS
Check and reset stopwatches and lock them in control
desk drawer
Ensure presence of decompression and treatment tables.
list of emergency and ventilation procedures, and the
NOAA Diving Manual
_ Restock secondary medical kit as required and stow
Clean and stow fire-retardant clothing
Check that all log entries have been made
Stow log book.
OXYGEN SUPPLY
Check inhalators, replace as necessary
Close 02 cylinder valves
__ Bleed 02 system
Close all valves
Replace cylinders with BREATHING OXYGEN, as required
Ensure spare cylinders are available
Clean system if contamination is suspected.
NITROX (Therapy Gas) SUPPLY
Check inhalators, replace as necessary
Close NITROX cylinder valves
Bleed NITROX system
Close all valves
Replace cylinders with 60% N2/40% 02, as required
Ensure spare cylinders available.
COMMUNICATIONS
Test primary and secondary systems; make repairs as
necessary.
ELECTRICAL
Check all circuits
Replace light bulbs as necessary
If lights encased in pressure-proof housing, check
housing for damage
Turn off all power
Check wiring for fraying
If environmental monitoring equipment is used, maintain
in accordance with applicable technical manual.
inside the chamber, an appropriate chamber penetra-
tion is required. Small, portable, galvanic cell-type
units, however, may be placed directly in the chamber.
When choosing portable units for hyperbaric use, the
manufacturer's instructions should be consulted to be
certain that the unit is compatible with hyperbaric
environments. Since nearly all units read out in response
to partial pressures of oxygen relative to a pressure of
1 ATA, mathematical conversions must be made to
ascertain the true reading at depth. The manufacturer's
instructions should be consulted for detailed informa-
tion on specific oxygen analyzers.
6.3.6 Electrical System
The electrical system in a chamber varies in com-
plexity, depending on the capability and size of the
chamber. Whenever possible, it is best to keep all
electricity out of the chamber, to provide lights through
fiber optics or through port windows, and to have the
actual electrical system controls located outside the
chamber. When chambers have electrical systems and
October 1991 — NOAA Diving Manual
lights inside, they must be inspected to ensure that the
system is properly grounded and that all fittings and
terminals are in good order and encased in spark-proof
housings (see the predive checklist in Table 6-1).
WARNING
Lights Inside the Chamber Must Never Be
Covered With Clothing, Blankets, or Other
Articles That Might Heat Up and Ignite
6.4 CHAMBER MAINTENANCE
Proper care of a hyperbaric chamber requires both
routine and periodic maintenance. After every use or
no less than once a month, whichever comes first, the
chamber should be maintained routinely in accordance
with the Post-Dive Maintenance Checklist shown in
Table 6-3. At this time, minor repairs should be made
and supplies restocked. At least twice a year, the chamber
should be inspected both outside and inside. Any deposits
6-9
Section 6
of grease, dust, or other dirt should be removed and the
affected areas repainted (steel chambers only).
Only steel chambers are painted. Aluminum cham-
bers normally are a dull, uneven gray color that per-
mits corrosion to be recognized easily. Painting an
aluminum chamber will serve only to hide (and thus
encourage) corrosion. Corrosion is best removed by
hand-sanding or by using a slender pointed tool, being
careful not to gouge or otherwise damage the base
metal. The corroded area and a small area around it
should be cleaned to remove any remaining paint or
corrosion products. Steel chambers should then be
painted with a non-toxic, flame-retardant paint.
All NOAA hyperbaric chambers must be pressure
tested at prescribed intervals. The procedures to be
followed are shown in Table 6-4, and Table 6-5 pres-
ents a checklist for chamber pressure and leak tests.
6.5 FIRE PREVENTION
A hyperbaric chamber poses a special fire hazard because
of the increased flammability of materials in compressed
air or an environment otherwise enriched in oxygen.
Fire safety in hyperbaric chambers requires basically
the same practices as it does in other locations. The
chamber environment, however, involves two special
considerations — the atmosphere is an "artificial" one,
and people are confined with the fire in a relatively
small space. The traditional trio of conditions neces-
sary for a fire, in a chamber or anywhere else, are a
source of ignition, combustible materials, and an oxidizer.
There are four steps in chamber fire safety in addition
to preventive measures: detecting the fire, extinguishing
it, using a mask for breathing, and — if possible — escaping.
A safe chamber begins in the design stage. Various
codes and design handbooks deal with this complex
subject, and it can only be touched on here (Naval
Facilities Engineering Command 1972, National Fire
Protection Association 1984). After safe design, the
manner in which the chamber is used is next in impor-
tance. This section reviews chamber fire safety, cover-
ing both basic principles and operational techniques.
For a more thorough treatment of the subject and
additional references, consult the section on fire safety
in The Underwater Handbook (Shilling, Werts, and
Schandelmeier 1976, pp. 646-664).
6.5.1 Ignition
Possible sources of ignition in a hyperbaric chamber
include:
• Electrical wiring or apparatus
• Cigarettes or other smoking materials
6-10
• Heat of compression
• Electrostatic sparks.
The most common sources of chamber fires in the
past have been lighted cigarettes, faulty electrical
wiring, and sparks from electrically powered devices.
Electrical fires, however, can start either from over-
heating caused by a defective component, a short
circuit, a jammed rotor in a motor, sparks produced by
making or breaking a load-carrying circuit, or from a
device with arcing brushes.
The safe use of electrical devices in a chamber is
primarily a design factor, requiring proper installation
of the supply wiring and properly designed devices.
Wiring should be insulated with mineral materials or
Teflon® and be shielded in metal conduit (which can be
either rigid or flexible). The housings of electrical de-
vices such as instruments can be purged with an
oxygen-free inert gas during operation and may or
may not be pressure proof. Lights may be enclosed and
purged, or they may be external to the chamber and
have the light directed inside with a "light pipe" or
fiber optic cable. Even an enclosed light can generate
enough heat to start a fire, a fact to be considered at
both the design and operational stages. A fire protec-
tion plan should include the capability to disconnect
all electrical power instantaneously. Auxiliary lighting
must be available.
At some installations, control of the electrical haz-
ard is achieved by allowing no electricity in the cham-
ber at all. When electricity is used, however, it requires
protection of the occupants from electrical shocks.
This may be accomplished by employing protective
devices such as ground fault detectors and interrupt-
ers. Use of low voltages (e.g., 12 or 24 volts) avoids this
hazard, but it is a dangerous misunderstanding to think
such voltages cannot start a fire if high-current flow is
possible. Devices tolerant of pressure and qualifying
as intrinsically safe may be used. Low-current, low-
voltage devices such as headsets and microphones gener-
ally are considered safe. There is a fundamental dif-
ference between the concepts behind "explosion-proof
devices and those required for chamber safety. Ex-
plosion-proof housings are made to prevent the igni-
tion of flammable gases or vapors by sparks generated
by electrical equipment; this is not the expected prob-
lem in a diving chamber. Junction boxes and other
equipment made to explosion-proof standards may pro-
vide the kind of protection afforded by mechanical
housings (mentioned above), but this equipment is
designed for a purpose different from the enriched-
oxygen hyperbaric environment and may in fact be
inadequate. Also, most explosion-proof boxes are much
NOAA Diving Manual — October 1991
Hyperbaric Chambers and Support Equipment
Table 6-4
Pressure Test Procedures for NOAA Chambers*
A pressure test must be conducted on
3. Repeat Steps 1 and 2
every NOAA recompression chamber:
until all the leaks
have been eliminated.
1, When initially installed;
2. When moved and reinstalled;
4. Pressurize lock to
3. At 2-year intervals when in place
maximum chamber operating
at a given location.
pressure (not hydrostatic
pressure) and hold for 5
The test is to be conducted as follows:
minutes.
1, Pressurize the innermost lock to
5. Depressurize the lock to
100 feet (45 psig) . Using soapy water or
165 feet (73.4 psig).
an equivalent solution, leak test all shell
Hold for 1 hour. If
penetration fittings, viewports, dog
pressure drops below
seals, door dogs (where applicable) ,
145 feet (65 psig) ,
valve connections, pipe joints, and
locate and mark leaks.
shell weldments.
Depressurize chamber and
repair leaks in accordance
2. Mark all leaks. Depressurize the lock
with Step 2 above and
and adjust, repair, or replace components
repeat this procedure
as necessary to eliminate leaks.
until final pressure
is at least 145 feet
a. Viewport Leaks - Remove the viewport
(65 psig) .
gasket (replace if necessary) , wipe.
6. Repeat Steps 1 through 5,
CAUTION
leaving inner door open
and the outer door closed.
Acrylic viewports should not be lubricated
Leak test only those
or come in contact with any lubricant.
portions of the chamber
Acrylic viewports should not come in contact
not previously tested.
with any volatile detergent or leak detector
(non-ionic detergent is to be used for
leak test) . When reinstalling viewport, take
up retaining ring bolts until the gasket
just compresses the viewport. Do not
overcompress the gasket.
b. Weldment Leaks - Contact appropriate
technical authority for guidance on
corrective action.
restricted to a maximum pressure of 100 psig, regardless of design
pressure rating.
*AII NOAA standard recompression chambers are
too large and heavy for efficient use in the crowded
conditions of a chamber.
Although static sparks should be avoided, the atmo-
sphere in a chamber is usually humid enough to sup-
press sparks. Also, static sparks are only a hazard with
vapors, gases, or dry, finely divided materials, none of
which should be present in a chamber. Static sparks
usually can be prevented by using conductive materi-
als and by grounding everything possible. In some
medical hyperbaric chambers, the patient himself is
grounded with a wrist strap.
Although the heat of compression is more of a prob-
October 1991 — NOAA Diving Manual
lem in the piping of oxygen-rich gases, it is also a
factor in chamber safety. Because gases heat up when
compressed, the sudden opening of a valve, which allows
an oxygen mixture to compress in the pipes, can cause
an explosion. A different but related hazard is the gas
flow through a filter or muffler in the air supply. If the
air is produced by an oil-lubricated compressor, some
oil may collect on the filter or muffler and be ignited
by compression or sparks generated by flowing gas.
Incredible as it may seem, a major source of cham-
ber fires has been smoking. This is less of a hazard now
than before the risks were widely known, but the pro-
6-11
Table 6-5
Standard NOAA Recompression Chamber
Air Pressure and Leak Test
Ship/Platform/Facility
Type of Chamber: Double Lock Aluminum
Double Lock Steel
Portable Recompression Chamber
Other*
* (Description)
Section 6
i
Manufacturer
NAME PLATE DATA
Date of Manufacture
Serial Number
Maximum Working Pressure
Date of Last Pressure Test .
Test Conducted by
(Name/Rank/Title)
1. Conduct visual inspection of chamber to determine if chamber is ready for test.
Chamber satisfactory Initials of Test Conductor
Discrepancies of inoperative chamber equipment:
Satisfactory
2. Close inner lock door and with outer lock door open, pressurize inner lock to 100 fsw (45 psig) and verify that the following
components do not leak:
(Note: If chamber has medical lock, open inner door and close and secure outer door.)
Inner lock leak checks
A. Shell Penetrations and Fittings
B. Viewports
C. Door Seals
D. Door Dog Shaft Seals
E. Valve Connections and Stems
F. Pipe Joints
G. Shell Welds
Satisfactory
Satisfactory
Satisfactory
Satisfactory
Satisfactory
Satisfactory
3. Increase inner lock pressure to 225 fsw (100 psig) operating pressure (not hydrostatic pressure) and hold for 5 minutes.
Record Test Pressure
Satisfactory
(NOTE: Disregard small leaks at this pressure)
Initials of
Test Conductor
6-12
NOAA Diving Manual — October 1991
Hyperbaric Chambers and Support Equipment
Table 6-5
(Continued)
4.
Ci
5.
6.
7.
A.
B
C.
D.
E.
F.
G.
8.
9.
10
Depressurize lock slowly to 165 fsw (73.4 psig)
Secure all supply and exhaust valves and hold for 1 hour.
Start time
Pressure
165 fsw
fsw
Fnd timp
Pressure
iterion: If pressure drops below 145 fsw (65 psig) , locate and mark leaks. Depressurize, repair, and retest inner I
Innpr Inrk prpssurp drop tpst passpd
ock.
Depressurize inner lock and open inner lock door. Secure in open position. Close outer door and
(NOTE: If chamber has medical lock, close and secure inner door and ope
Repeat tests of sections 2. 3, and 4 above when setup per section 5. Leak test only
tested in sections 2, 3, and 4.
Outer Lock Checks
Shpll Penptrations and Fittings
secure.
n outer door)
those portions
of the char
nber not
Initials of
onductor
165 fsw
fsw
Initials of
onductor
Satisfactory
Vipwports
Satisfactory
Door Seals
Satisfactory
Door Dog Shaft Spals
Satisfactory
Valve Connections and Stems
Satisfactory
Pipe Joints
Satisfactory
Shell Welds
Satisfactory
Maximum Chamber Operating Pressure Test (5 minute hold)
Satisfactory
Inner and Outer Lock Chamber Drop Test (Hold for 1 Hour)
Start time
TestC
Pressure
Fnd time
Pressure
Inner and Outer Lock Pressure Drop Test Passed Satisfactorily
. All above tests have been satisfactorily completed.
TestC
Test Director
Signature
Date
Diving Officer/ UDS
Date
Director, NDP
Date
October 1991 — NOAA Diving Manual
6-13
Section 6
hibition against smoking in and around chambers must
be strictly enforced.
no combustion, there is a broad pressure-oxygen per-
centage zone of incomplete or reduced combustion.
6.5.2 Combustion
The primary factor increasing the risk of fire in a
hyperbaric chamber is the increased combustibility
caused by the enriched oxygen atmosphere. An enriched
oxygen atmosphere is one that either has a partial
pressure or an oxygen percentage that is greater than
that of air at sea level pressure. The burning rate
(determined in a laboratory with paper strips) when
the pressure is equivalent to 75 fsw is twice that of sea
level air, and it is 2.5 times as fast at 165 fsw.
An additional hazard is introduced when the gas
mixture in the chamber also has an increased percent-
age (i.e., fraction) of oxygen. The relationships among
flammability, partial pressure, and oxygen fraction
are complex and non-linear, but show a consistent
trend toward faster burning with increased oxygen
percentage or with an increasing pressure at the same
oxygen percentage (Figure 6-5). The nature of the
background gas is important, too, with helium requir-
ing higher ignition temperatures but allowing faster
burning.
Because of the greatly increased risk when oxygen is
added to the chamber atmosphere, it is now considered
essential to use an overboard dump system for exhaled
gas when divers are breathing oxygen by mask during a
decompression or treatment. It is also considered accept-
able if a low oxygen level can be maintained by venti-
lating or purging the chamber with air, but this is a less
desirable option because the gas used for purging is
itself fairly rich in oxygen. It takes high flows to keep
the oxygen within accepted limits, and high flows may
be accompanied by excessive noise and compressor
wear and tear. The "zone of no combustion" concept is
helpful in the management of fire safety in chambers.
This concept takes into account the fact that, although
changes in pressure at a constant oxygen percentage
affect burning rate, changes in the percentage of oxy-
gen have a greater effect. As a result, there is a "zone"
of pressure and oxygen percentage that provides ade-
quate oxygen for respiration but that will not support
combustion (Shilling, Werts, and Schandelmeier 1976;
Rodwell and Moulton 1985). This is illustrated in Fig-
ure 6-6. An important consequence of the zone of no
combustion is that the chamber environment in most
saturation dives is fire safe except in the later stages of
decompression. The existence of this zone allows for
controlled combustion, such as that of welding, to be
performed safely at pressure. In addition to the zone of
6-14
6.5.3 Materials
The third element required to make a fire is fuel, i.e.,
something to burn. Chamber fire safety requires that
all combustible materials in the chamber be kept to a
minimum, and that, where possible, materials that are
not flammable in enriched oxygen be used. Some materi-
als regarded as non-flammable in air will burn in a
high oxygen mixture, so it is best to rely on materials
known to be safe or relatively safe in oxygen.
Metals are safe, as are ceramics. For wiring insula-
tion, TFE (Teflon®) is probably the best all-around
material, but there are mineral insulations and fiber-
glass, as well as some hard plastics like Bakelite® and
Melmac® that are usable in some circumstances. Some
fluorine-based elastomers are relatively safe in high
oxygen mixtures, but their conductive properties are
poor and they are expensive. For clothing, the popular
choice is Durette®, but Nomex® is also adequate. Beta
fiberglass is suitably flameproof but has undesirable
wearing properties (Dorr 1971).
Although chamber design is important to fire safety,
even the well-designed chamber needs to be used prop-
erly to be safe. Good housekeeping is mandatory; all
loose clothing, papers, and other flammable materials
must be stowed or removed from the chamber when it
is being operated beyond the fire-safe zone. Particu-
larly important to eliminate are fuzzy or powdered or
finely divided materials and flammable liquids and
gases.
One flammable gas that may come into increasing
use in diving is hydrogen. The use of this gas is being
explored for deep diving because of its physiological
properties (primarily its low density, which results in
low breathing resistance). Hydrogen can be used with-
out danger of explosion (once it is properly mixed)
when a mixture contains less than 5 percent oxygen,
making it suitable for diving deeper than 100 fsw.
Most of the safety problems associated with the use
of hydrogen as a diving gas occur during handling
and mixing.
6.5.4 Management of a Fire
The preceding sections addressed the prevention of
chamber fires. Another component of fire safety requires
that the people involved be able to deal with a fire once
it starts. Although some past chamber fires have spread
rapidly (National Fire Protection Association 1979),
many others have been extinguished without loss of
NOAA Diving Manual — October 1991
Hyperbaric Chambers and Support Equipment
Figure 6-5
Burning Rates of Filter Paper Strips at an Angle
of 45° in N2-02 Mixtures
4.5
o
CO
E
o
LU
DC
CD
P02=2Atm
99.6% 02
0 1.00
2.51
4.03
5.54
7.06
8.57
10.1 ATA
50
1 00 1 50
PRESSURE
200
250
300 FSW
October 1991 — NOAA Diving Manual
6-15
Section 6
Figure 6-6
Combustion in N2-Oo Mixtures Showing
the Zone of No Combustion
LU
o
rr
LU
Q_
LU
_l
o
Z
LU
O
>
X
o
O COMPLETE COMBUSTION
A INCOMPLETE COMBUSTION
O SLIGHT COMBUSTION
Q NO COMBUSTION
COMPLETE COMBUSTION
o
4 8 12
TOTAL PRESSURE, ATMOSPHERES ABSOLUTE
Combustion zones are defined by solid lines and normal respiration
by dashed lines. The area A-D-E is compatible with respiration for
prolonged periods, while the area represented by A-B-C is safe to
6-16
breathe for short periods only (adapted from Shilling, Werts, and
Schandelmeier 1976) .
NOAA Diving Manual — October 1991
i
Hyperbaric Chambers and Support Equipment
life. It is therefore essential that chamber personnel be
trained in fire safety techniques.
6.5.4.1 Detection
Numerous fire detection mechanisms are available
for routine fire protection. Many of these systems are
usable in a pressure chamber, particularly ones operating
at the relatively low pressures used with compressed
air. The detection mechanisms most suitable for chamber
use are those involving infrared or ultraviolet sensors.
Ionization or smoke detectors may also be of value.
There are two problems with fire detection systems:
false alarms and failure to detect a fire quickly enough.
Any detection system needs to be studied thoroughly
in the context of the uses and needs of the particular
installation. Most experts feel, for example, that a
clinical hyperbaric chamber treating patients with open
wounds should have an alarm system only, rather than
one that automatically deluges the chamber; a pre-
ferred approach is to have both a hand-held directable
fire hose inside and switches to activate a general
deluge system easily available to both chamber occu-
pants and the topside crew. Whether a deluge or alarm
system is used, it should be thoroughly tested at the
time of installation and periodically thereafter.
The best protection against fire is an alert chamber
crew that is backed up by detectors. During certain
welding operations in compressed air, the only dependa-
ble detection system is another person standing by to
watch the operation. It is best if the designated "fire
watch" person stands inside the chamber rather than
outside (Hamilton, Schmidt, and Reimers 1983).
6.5.4.2 Extinguishment
Fire extinguishment is accomplished by physical, or
a combination of physical and chemical, actions involving
four basic mechanisms:
• The combustible material can be cooled to a tem-
perature below that required for ignition or the
evolution of flammable vapors.
• The fire can be smothered by reducing the oxygen
or fuel concentration to a level that will not sup-
port combustion.
• The fuel can be separated from the oxidizer by
removing either the fuel or the oxidizer or by
mechanically separating the two. Mechanical protein
foams operate in this fashion by blanketing the
fuel and separating it from the oxidizers.
• The reactions occurring in the flame front or just
before the flame front can be inhibited or inter-
fered with through the use of chemicals.
October 1991 — NOAA Diving Manual
At present, the best fire extinguishing agent for use
in hyperbaric chambers is water. Water extinguishes
primarily by cooling and works best if it strikes the
flame or wets the fire in spray form. The pressure at the
spray nozzle must be 50 psi or more above chamber
pressure to produce the desired degree of atomization
and droplet velocities. Simultaneous with the discharge of
water, all electrical power to the chamber should be
shut off to prevent shorting and electrical shocks to
personnel in the chamber; lights must of course remain
on. A manually directable fire hose will permit occu-
pants of a chamber to control small localized fires. The
fire suppression system should be tested periodically
under chamber operating conditions.
6.5.4.3 Breathing Masks and Escape
Most fire fatalities are caused by smoke inhalation
rather than burns. Accordingly, the first thing the
occupants of a chamber with a fire should do unless
immediate escape is possible is to don a breathing
mask. The masks should be handy and should have a
breathable gas on line or be controllable by the occu-
pants at all times. If it is possible for occupants to flee
quickly to another chamber or compartment that can
be sealed off from the fire, they should do so rather
than donning masks and trying to extinguish the fire.
6.5.5 Summary of Fire Protection Procedures
A summary of chamber fire prevention procedures
follows:
• Maintain oxygen concentration and partial pres-
sure as low as possible, preferably within the region
of non-combustion. Use an overboard dump sys-
tem whenever pure oxygen is breathed by mask in
a chamber.
• Eliminate ignition sources.
• Minimize combustibles, with the complete exclu-
sion of flammable liquids and gases.
• If combustible materials must be employed, the
type and quantity and their arrangement in the
chamber must be carefully controlled.
• Firewalls and other containment techniques should
be utilized to isolate high-risk fire zones.
• The extinguishing system should involve a water
deluge spray that can be activated either by occu-
pants or topside operators and a hand fire hose
that can be controlled and directed by the cham-
ber occupants.
• A mask with an appropriate gas on line should be
available for each chamber occupant at all times.
• Escape to another chamber or directly into the sea
should be the first option in the fire safety opera-
tions plan, whenever feasible.
6-17
♦
♦
<
SECTION 7
DIVER AND
SUPPORT
PERSONNEL
TRAINING
7.0
7.1
7.2
7.3
7.4
7.5
7.6
Page
General 7-1
NOAA Divers 7-1
7.1.1 Selection Standards 7-1
7.1.2 Physical Examination 7-1
7.1.3 Swimming Skills 7-3
7.1.4 Scuba Training 7-3
7.1.4.1 Classroom 7-4
7.1.4.2 Pool and Open-Water 7-4
7.1.5 Umbilical Dive Training 7-5
7.1.6 Special Equipment Training 7-6
7.1.7 Mixed-Gas Training 7-6
7.1.8 Saturation Training 7-7
7.1.9 Chamber Operator Training 7-7
Training of Diving Supervisors 7-8
Diving Medical Technicians 7-8
Hyperbaric Physicians 7-9
Research Divers 7-10
7.5.1 Selection 7-10
7.5.2 Curriculum 7-1 1
Equipment Maintenance 7-1 1
«
<
DIVER AND
SUPPORT
PERSONNEL
TRAINING
7.0 GENERAL
This section describes the general content of diver
training programs, the training involved in preparing
to dive under specialized circumstances, and basic
approaches to diver training. It does not prescribe
specific training procedures or attempt to teach divers
how to perform specific underwater tasks.
Many organizations offer diver training. NOAA and
the Navy are among those government agencies that
train divers in support of agency missions. Many col-
leges and universities offer diver training to students
and faculty members who use diving as a research tool.
Diver training also is available from diver certifica-
tion organizations and local dive shops. Commercial
diving schools offer extensive diver training for divers
in the commercial diving industry. These training organi-
zations select students on the basis of their personal
motivation, physical fitness, and basic swimming skills.
This section emphasizes the training of NOAA divers
and other personnel, but many of the principles described
here apply to the training of all divers.
7.1 NOAA DIVERS
NOAA-certified divers include NOAA Corps officers,
researchers, diving technicians, and individuals from
universities and organizations involved in NOAA-
sponsored programs that require diving skills. NOAA
also trains divers from other Federal agencies. All of
the candidates who apply to NOAA's diving program
are volunteers.
The amount and type of diving involved in the dif-
ferent NOAA programs can vary greatly: NOAA divers
include senior researchers who dive only occasionally
in shallow water as well as divers who are required to
dive regularly as part of their normal duties. The selection
and training of NOAA divers are monitored carefully
by the NOAA Diving Program.
7.1.1 Selection Standards
NOAA divers are selected from volunteers on the
basis of their psychological and physical fitness and
their water skills. The psychological evaluation for
acceptance into the program consists of a personal
interview, an assessment of motivation, and a general
October 1991 — NOAA Diving Manual
screening by experienced NOAA divers to identify
individuals who are unlikely to be able to handle the
stresses of operational and research diving. The evalu-
ation interview helps to identify any misconceptions
the candidate may have about training or the require-
ments, conditions, and responsibilities of subsequent
NOAA diving work.
7.1.2 Physical Examination
The physical examination of divers to determine if
they are medically qualified to dive requires evalua-
tion by a trained hyperbaric physician. Military, com-
mercial, and scientific divers are evaluated according
to standards set forth by their respective agencies or
organizations. NOAA has developed and enforces medi-
cal standards for its divers.
Many medical conditions disqualify a person for
diving with compressed gas, and other medical condi-
tions increase the risk of serious injury or disability in
the diving environment. The guidelines below present
a framework for individual dive fitness evaluations;
they are not established standards. These guidelines
are organized in accordance with a systems approach,
and no attempt is made to rank systems in terms of
their relative importance.
Skin
• Any chronic or acute dermatitis adversely affected
by prolonged immersion should be disqualifying.
• Allergy to materials used in diving equipment that
comes into contact with the skin is a relative
contraindication.
• History of sensitization or severe allergy to marine
or waterborne allergens should be disqualifying.
Psychiatric
• Acute psychosis should be disqualifying.
• Chronic or acute depression with suicidal tenden-
cies should be disqualifying.
• Chronic psychosis in partial remission on medica-
tion should be disqualifying.
• Substance use or abuse, including abuse of alcohol
or use of mood-altering drugs, should be disqualify-
ing.
• Careful attention should be paid to the maturity of
prospective candidates, their ability to adapt to
7-1
Section 7
stressful situations, their motivation to pursue div-
ing, and their ability to understand and follow
decompression tables and directions.
Neurologic
• Closed head injury; following full recovery, any
neurologic deficit (including an abnormal EEG or
post-traumatic seizures) should be disqualifying.
• Spine injury, with or without cord damage, may
carry an increased risk of decompression sickness
and attendant lower extremity paralysis. Prior cord
decompression sickness with residual symptoms
should be disqualifying. Herniated nucleus pulposis
of the lower back (if corrected) should be evalu-
ated on an individual basis, as should peripheral
neuropathy.
• Any disorder that causes or results in loss of con-
sciousness should be absolutely disqualifying. This
includes any form of seizure, previous gas embo-
lism, or prior cerebrovascular accident (due to
regional perfusion abnormalities that would pre-
dispose to decompression sickness).
• Diving after intracranial surgery should be evalu-
ated individually; however, it is not an absolute
contraindication. Issues to be considered include
absence of seizures, presence of residual neurologic
deficit, and impairment of regional perfusion.
Ophthalmologic
• Candidates should demonstrate adequate visual
acuity to orient themselves in the water and on a
boat. Corrective lenses, either fixed to the face
mask or soft contact lenses (which allow for gas
transfer), are acceptable.
• Narrow-angle glaucoma, aphakia with correction,
motility disorder, cataract, and retinitis pigmentosa
are relative disqualifications for diving; a skilled
ophthalmologist should be consulted.
• Because color vision is required for certain diving
tasks, deficiencies in color vision may be dis-
qualifying.
Otolaryngologic
• As a prerequisite to diving, candidates must have
intact tympanic membranes and be able to auto-
inflate the middle ear. Performing a Valsalva or
Toynbee maneuver can be used to indicate whether
the candidate can inflate his or her middle ear
(inability to do so predisposes to rupture of the
tympanic membrane or round window).
• Tympanic membrane perforations should be dis-
qualifying (an opening in the tympanic membrane
would allow water to get into the middle ear). If a
tympanic membrane rupture is completely healed
7-2
or has been surgically repaired and the candidate
is able to auto-inflate, he or she may be condition-
ally cleared for diving with the warning that the
perforation may recur.
• Active ear infection should be temporarily dis-
qualifying.
• Chronic or acute otitis externa should be dis-
qualifying until healed.
• Meniere's disease and other conditions that are
associated with vertigo should be disqualifying.
• Extensive mastoid surgery, stapedectomy, or arti-
ficial cochlear implant should be disqualifying.
• Barotitis should be disqualifying until all middle
ear inflammation and fluid have resolved and tym-
panic membrane motility has returned to normal.
Nose and Paranasal Sinuses
• A patent nasal passage and the absence of sinus and
nasal congestion are essential in diving.
• Nasal polyps, deviated nasal septum, and other
obstructive nasal lesions should be corrected before
diving is permitted.
• Acute or chronic infection should be disqualifying.
• A history of long-term decongestant use should
trigger a search for the cause of the congestion, d
and candidates should be warned about the dangers \
of the chronic use of chemical agents while diving.
Oral and Dental
• Candidates must be able to be fitted with and hold
a scuba mouthpiece.
• Where there is a danger that trapped gas could get
under a tooth and rupture it, diving should not be
permitted.
• Badly decayed or broken teeth should be dis-
qualifying.
Pulmonary
• Because any abnormality in pulmonary system func-
tion can cause arterial gas embolism, pneumotho-
rax, or pneumomediastinum, the following condi-
tions should be absolute disqualifications for diving:
— Bronchial asthma;
— History of traumatic or spontaneous pneumo-
thorax;
— Previous penetrating chest trauma or surgery of
the chest;
— Chronic obstructive lung disease;
— Active pneumonia or lung infection, including
active tuberculosis; and
— Mycotic (fungal) disease with cavity formation. A
• Long-term cigarette smoking increases the risk ^
of pulmonary complications while diving.
NOAA Diving Manual — October 1991
Diver and Support Personnel Training
• All candidates should be given a screening chest x
ray to determine if they have a disqualifying lesion.
Cardiovascular
• Cardiovascular defects can be disqualifying be-
cause they predispose the individual to unaccept-
able risks. Conditions that should be disqualify-
ing are:
— Cyanotic heart disease;
— Aortic stenosis or coarctation of the aorta;
— Prosthetic heart valves;
— Exercise-induced rhythm disorders, including
disorders that manifest as paroxysmal tachy-
cardias despite control with drugs;
— Heart block;
— Cardiac or pulmonary A-V shunts;
— Candidates with pacemakers should be indi-
vidually evaluated and generally should be dis-
qualified.
• Coronary artery disease should be evaluated by
an expert.
• Peripheral vascular disease requires case-by-case
evaluation.
• Candidates taking cardiovascular drugs (including
blood pressure medication) should be evaluated
on a case-by-case basis. The use of beta blockers
increases the risk of bronchospasm and suppresses
the stress response.
• Hypertension should be considered on a case-by-
case basis.
Hematological
• Sickle cell anemia should be disqualifying.
• Leukemia or pre-leukemia manifesting as myelofi-
brosis and polycythemia should be disqualifying.
• Anemia is relatively disqualifying and requires
case-by-case evaluation.
• Intoxication that has caused methemoglobinemia
should be disqualifying.
Gastrointestinal
• Any disorder that predisposes a diver to vomiting
should be disqualifying (including Meckel's di-
verticulum, acute gastroenteritis, and severe sea
sickness).
• Unrepaired abdominal or inguinal hernia should
be disqualifying.
• Active peptic ulcer disease, pancreatitis, hepatitis,
colitis, cholecystitis, or diverticulitis should be dis-
qualifying until resolution.
Endocrinological
• Diabetes mellitus should be disqualifying unless it
is diet controlled.
October 1991 — NOAA Diving Manual
• Obesity increases the relative risk of developing
decompression sickness because of the decrease in
gas diffusion through adipose tissue.
• Other endocrine abnormalities should be evaluated
on a case-by-case basis.
Musculoskeletal
• Paralytic disorders should be relatively disqual-
ifying.
• Bone fractures that are incompletely healed and
osteomyelitis that is actively draining should be
disqualifying.
• Deformities, either congenital or acquired, that
impair the candidate's ability to use scuba equip-
ment should be disqualifying.
• Inadequate physical fitness to handle the physical
work of diving should be disqualifying.
Obstetric and Gynecological
• Pregnancy should be absolutely disqualifying be-
cause of the risk of bubble formation in the de-
veloping fetus during decompression.
7.1.3 Swimming Skills
All applicants for diver training should perform the
following swimming exercises without face masks, fins, or
snorkels and with confidence and good watermanship:
• Swim 300 yards (274 meters) using the crawl,
sidestroke, and backstroke
• Swim under water for a distance of 50 feet
(15.2 meters) without surfacing
• Stay afloat for 30 minutes.
7.1.4 Scuba Training
Although NOAA has its own diver training and
certification program, NOAA personnel often receive
basic scuba training before they become NOAA diver
candidates. Regardless of the training organization,
however, there are basic practices and procedures that
should be included in any scuba training program. For
example, any diver training program should produce:
• Divers who reach a level of competence that will
permit safe open-water diving
• Divers who can respond to emergency situations
and make appropriate decisions when faced with
problems under water
• Divers who can execute assigned underwater tasks
safely and efficiently.
Diving procedures, particularly those of a lifesaving
nature, should be overlearned to ensure automatic
response in emergencies, which reduces the likelihood
7-3
Section 7
of the diver losing control and panicking (Bachrach
and Egstrom 1986).
Although training courses vary widely among organi-
zations with respect to length, content, complexity,
and water skills required, all courses should include
both classroom sessions and in-water training. The
core of a training program for working divers should
follow the guidelines discussed in Sections 7.1.4.1 and
7.1.4.2.
7.1.4.1 Classroom
Classroom lectures using multimedia presentations
should be developed to provide the candidate with as
much knowledge as possible. It is important for the
candidate to develop a general understanding of diving
principles and the diving environment, and the self-
confidence (but not overconfidence) necessary to operate
safely in the field.
Formal training courses are only the first step in
becoming a safe and efficient diver. With this in mind,
diver training should expose the trainee to a wide vari-
ety of diving-related experiences in addition to teach-
ing the basics. Details of various diving systems and
ancillary equipment will be learned as part of on-the-
job training. Topics to which working and research
divers should be exposed during basic and advanced
training include:
• Diving physics: pressure, temperature, density, spe-
cific gravity, buoyancy, diving gases, the kinetic
theory of gases, and the gas laws and their practi-
cal application in diving;
• Diving physiology and medicine: the anatomy and
mechanics of circulation and respiration, the effects
of immersion on the body, hypoxia, anoxia, hyper-
capnia, hypocapnia, hyperpnea, apnea, hyperthermia,
hypothermia, the direct effects of pressure (squeeze,
lung overpressure, and "diver's colic"), the indi-
rect effects of pressure (decompression sickness,
gas embolism, inert gas narcosis, oxygen toxicity,
bone necrosis), breathing gas contaminants, drown-
ing, near-drowning, overexertion, exhaustion,
breathing resistance, "dead space," and psycho-
logical factors such as panic;
• Equipment: selection, proper use, and care of
personal gear; air compressors and compressor sys-
tems; operation and maintenance; tank-filling
procedures; requirements for testing and inspec-
tion of specific types of equipment (including scuba
cylinders); and air purity standards and testing;
• Diving platforms: shore, small boat, and large vessel
platforms; fixed structures; safety precautions and
7-4
surface-support requirements in vessel diving; and
water entry and exit;
• Operations planning: objectives, data collection,
definition of tasks, selection of equipment, selec-
tion of dive team, emergency planning, special
equipment requirements, and setup and check out
of support platforms;
• Principles of air diving: introduction to decom-
pression theory, definition of terms, structure and
content of diving tables, single and repetitive div-
ing principles, practical decompression table prob-
lems (including decompression at altitude), and
calculation of air supply requirements;
• Diving procedures: relationship of operations plan-
ning to diving procedures; warning signal require-
ments; hand and line signals; recall; water emer-
gencies; buddy teams; tending; precautions required
by special conditions, e.g., pollution, restricted
visibility, currents; "dive safe ship" requirements;
boating safety; dangers of diving at high altitude
or flying after diving; dive station setup and post-
dive procedures; work procedures for search and
recovery; salvage and object lifting; instrument
deployment and maintenance; and underwater navi-
gation methods;
• Accident prevention, management, and first aid:
basic principles of first aid, cardiopulmonary
resuscitation (CPR), use of oxygen resuscitators,
development of accident management plans, recov-
ery of victims and boat evacuation procedures,
recognition of pressure-related accident signs and
symptoms, patient handling en route to treatment,
introduction to recompression chambers and treat-
ment procedures, and procedures for reporting acci-
dent investigations (see Sections 18 and 19); and
• Diving environment and hazardous marine life:
tides and currents (surf; thermoclines; arctic, tem-
perate, and tropical conditions); waves and beaches;
rip currents; and river, harbor, and marine life
hazards.
7.1.4.2 Pool and Open-Water
A program of work in the water that progresses from
pool to protected open water and then to a variety of
open-water situations is essential to diver training.
Students should be exposed to open-water conditions
while diving at night, under conditions of reduced
visibility, and in cold water (see Section 10 for details
of diving under special conditions). An understanding
of the proper use of mask, fins, and snorkel; surface
swimming; surface dives; underwater swimming; pressure
equalization; and rescue techniques is required to master
skin (breath-hold) and scuba diving.
NOAA Diving Manual — October 1991
Diver and Support Personnel Training
Breath-hold or skin diving is hazardous, and work-
ing and research divers using this technique must be
competent swimmers in excellent physical condition.
The skin diver is subject to barotrauma of the ears and
sinuses, just as any other diver is; however, air embo-
lism and related complications are a problem only if
the skin diver breathes air from a scuba cylinder, a
habitat, or an underwater air pocket. Since breath-
holding can cause serious problems, divers should
thoroughly understand the potential hazards of prolonged
breath-holding under pressure.
Specific skills to be learned in a pool and open-water
program should include but not be limited to:
• Skin diving skills
— equalization of air spaces
— mask clearing and equalization
— snorkel clearing
— proper use of buoyancy compensator
— proper use of weight belt (including how to
ditch it)
— proper kicks with and without fins
— distance swimming with full skin-diving gear
— water entries and surface dives
• Skin diving confidence drills
— recovery of mask, snorkel, and fins
— clearing the ears
— one-finned kicks over a distance
— snorkeling without mask
• Lifesaving skills
— search and recovery
— proper rescue entries
— rescue techniques with and without a buoyancy
compensator
— rescue carries
— in-water mouth-to-mouth artificial resuscita-
tion
• Skills involving the use of scuba equipment
— air sharing
— "ditch and don" exercises
— mask clearing
— regulator recovery and clearing
— emergency ascent
— station breathing
— scuba entries
— buoyancy control
— gauges and other special life support equipment
— scuba rescues.
October 1991 — NOAA Diving Manual
Experience and experimental data have shown that
the diver should be trained to maintain a reasonably
constant respiration rate with a nearly complete inha-
lation and exhalation pattern. This slow deep-breathing
pattern permits good air exchange at relatively low
flow rates. Keeping the flow rate at lower levels results
in more comfortable breathing; higher respiration rates
can cause discomfort and anxiety (Bachrach and Egstrom
1986).
7.1.5 Umbilical Dive Training
Umbilical diving is also referred to as surface-supplied
diving. In umbilical diving, the diver's breathing gas is
supplied via an umbilical from the surface, which pro-
vides the diver with an unlimited breathing gas supply.
Preliminary selection procedures and criteria for
umbilical dive training are essentially the same as
those for basic scuba. In NOAA, divers applying for
umbilical training must be certified as advanced working
divers, which requires the completion of at least 100
logged dives. Before qualifying as umbilical divers,
trainees should receive instruction and training in:
• The general purpose and limitations of surface-
supplied (umbilical) diving;
• Use of masks and helmets;
• Assembling and disassembling of the gas supply
system;
• Use of accessory tools and equipment basic to
umbilical procedures and specific to the particu-
lar tasks being contemplated;
• Methods of achieving intelligible communication;
• Equipment repair and maintenance;
• Water entry, descent, and ascent procedures and
problems.
When initial training is completed, an open-water
qualification test that includes both general diving
techniques and actual working procedures should be
given.
Qualification Test
To pass the qualification test, candidates must
demonstrate the ability to:
• Plan and organize an air surface-supplied diving
operation to depths between 30 and 50 fsw
(9.1 and 15.2 msw), including calculation of hose
pressure and air requirements and instruction of
surface personnel;
• Demonstrate ability to rig all surface and under-
water equipment properly, including air supply,
mask/helmet, communications, and other support
equipment;
7-5
Section 7
• Demonstrate proper procedures of dressing-in and
dressing-out, using the particular pieces of equip-
ment needed for the working dive;
• Tend a surface-supplied diver;
• Demonstrate knowledge of emergency procedures
(these may differ for each project or exposure) as
determined by the instructor or dive master;
• Participate in at least two practice dives, as described
below:
— Properly enter water that is at least 10 fsw
(3 msw) deep and remain submerged for at least
30 minutes, demonstrating control of air flow,
buoyancy, mobility, and facility with communi-
cation systems.
— Ascend and leave water in a prescribed manner.
— Properly enter water that is between 30 and
50 fsw (9.1 and 15.2 msw) deep and conduct
work-related tasks.
After successful completion of this test, the instruc-
tor should evaluate the diver's performance and estab-
lish a phased depth-limited diving schedule to ensure
a safe, gradual exposure to deeper working depths.
Detailed descriptions of umbilical diving equipment
and its use appear in Sections 5.2 to 5.2.4.10.
7.1.6 Special Equipment Training
In addition to learning how to operate and maintain
diver life-support scuba and umbilical equipment, divers
may be called on to use special equipment in the per-
formance of their duties. In such instances, new tech-
niques and procedures must be learned from divers
who are already experienced in their use, from techni-
cal personnel (such as manufacturers' representatives), or
by test and evaluation. Examples of types of equip-
ment that are used by divers and whose use requires
special training are: variable-volume suits; thermal
protection diving suits; protective suits, clothing, sup-
port equipment, and breathing apparatus for diving in
contaminated water; photographic/video equipment;
scientific equipment; and underwater tools.
Many training programs prepare divers to use spe-
cial equipment and protective clothing. The topics
addressed include:
• Operational Diver Training
— Search and recovery techniques
— Wireless communications
— Lifting of objects
— Ships husbandry
— Underwater television systems
— Pinger/sonar locators
— Underwater tools
7-6
Variable- Volume Dry Suit Training
— Suit selection, preparation, and maintenance
— Emergency procedures for blowups, weighting,
buoyancy control
— Control of operational problems
— Hypothermia/hyperthermia
— Accessories
— In-water training
— Cleanup and decontamination after polluted-
water dives
Contaminated-Water Diving Training
— Protective systems
— Donning and doffing
— Buoyancy control
— Hyperthermia
— Training as a tender
— Work performance while fully suited
— Decontamination procedures.
7.1.7 Mixed-Gas Training
Mixed-gas diving involves the use of a breathing
medium other than air; this mixture may consist of
nitrogen-oxygen, helium-oxygen, or oxygen and one
or more inert gases.
The curriculum for NOAA's mixed-gas training pro-
gram includes coverage of the following topics:
• Oxygen partial pressure limits
• Nitrogen-oxygen breathing mixtures
• Depth/time limits for oxygen during working dives
• Central nervous system and pulmonary oxygen
toxicity
• Nitrogen/oxygen breathing media mixing pro-
cedures
• Analysis of mixed-gas breathing media
• Mixed-gas diving equipment (open-circuit systems)
• NOAA Nitrox I no-decompression limits and
repetitive group designation table for no-decom-
pression dives
• NOAA Nitrox I equivalent air depths for open-
circuit scuba
• NOAA Nitrox I decompression tables
• NOAA Nitrox I residual nitrogen table
• NOAA Nitrox I surface interval table.
NOAA mixed-gas trainees attend classroom sessions
and then progress to open-water dives, during which
they use a nitrox (68 percent nitrogen, 32 percent
oxygen) breathing mixture. Divers enrolled in a com-
mercial diving mixed-gas course or those being trained
by their companies receive classroom and open-water
NOAA Diving Manual — October 1991
Diver and Support Personnel Training
training in the use of heliox (helium-oxygen) breath-
ing mixtures. Heliox is a widely used breathing medium
in deep mixed-gas diving and in saturation diving.
7.1.8 Saturation Training
Although the basic requirements for saturation div-
ing are the same as those for surface-based diving, there
are some important differences that need to be addressed
during training. The diver's "home base" during satu-
ration usually is either a seafloor habitat or a diving
bell system (see Section 17). For this reason, the satu-
ration diver needs a fundamental reorientation to the
environment. For example, the saturation diver must
constantly be aware that returning to the surface will
complicate, rather than improve, an emergency situa-
tion. This factor has specific implications with respect
to the selection and use of certain pieces of saturation
diving equipment. For example, in saturation diving:
• Weight belts without quick-release mechanisms
or weight harnesses should be used;
• Buoyancy compensators with oral inflation tubes
rather than a cartridge or tank inflation system
should be used;
• Adequate diving suits should be worn because the
extended diving time involved in saturation may
cause chilling even in tropical regions;
• A self-contained backup breathing gas supply should
be used when umbilical equipment is utilized;
• Extra precautions must be taken when filling scuba
cylinders to avoid admitting water into the valves.
Because the consequences of becoming lost are so
serious, a saturation diving training program also should
include training in underwater navigation techniques.
Divers should be instructed in the use of navigational
aids, such as grid lines, string highways, ripple marks,
topographical features, and navigation by compass.
Because compasses are not always accurate, divers
should be trained to use the compass in combination
with topographical and grid line information.
Training in habitat operations, emergency procedures,
and local diving restrictions usually is conducted on
site. Such training includes instruction in: communi-
cation systems; use of special diving equipment; habi-
tat support systems; emergency equipment; regional
topography; underwater landmarks; navigational grid
systems; depth and distance limitations for diver/
scientists; and operational and safety procedures used
by the surface support team.
Other features related to seafloor habitation also
need to be identified during saturation training. Some
of these relate to housekeeping chores inside the habi-
tat. For example, water boils at a higher temperature
under water than on the surface: 262°F (128°C) at
50.5 feet (15.4 meters) and 292°F (144X) at 100 feet
(30.5 meters); cooking procedures must be altered,
because burned food not only constitutes a fire hazard
but produces toxic gases at depth. (For additional infor-
mation on underwater habitation, see Miller and Koblick
(1984).)
A slight loss in speech intelligibility also occurs as a
result of the denser atmosphere at depth. The amount
of speech distortion depends on the habitat breathing
mixture and the depth. Other factors directly affect-
ing the saturated diver or a habitat diving program
include: the necessity to pay special attention to per-
sonal hygiene, e.g., to take special care of the ears and
skin. Because of the high humidity encountered in
most habitats, the growth of certain pathogens and
organisms is stimulated and recovery is prolonged.
Proper washing, drying, and care of diving suits is
essential to prevent skin irritation or infections. Trainees
should be aware that there are restrictions with respect
to the use of toxic materials in a closed-environment
system such as a habitat. This applies not only to the
use of scientific preparations but also to the use of
normally harmless things such as rubber cement (used
for the repair of wet suits) and aerosol sprays.
Training for saturation diving from underwater habi-
tats should teach divers the procedures for making
ascending and descending excursions from the storage
depth. Special diving excursion tables have been
developed for excursions from the saturation depth.
These tables are designed to consider storage depth,
oxygen dose, nitrogen partial pressures, and other fac-
tors. Trainees should become familiar with these tables
and their limitations.
A unique feature of saturation diving is the diver's
ability to make upward excursions. However, upward
excursions constitute a decompression, and divers must
be careful to remain within the prescribed excursion
limits. This applies not only to the divers themselves
but also to certain types of equipment; for example, if a
camera is opened and reloaded in a habitat, an upward
excursion of 10 to 15 feet (3.0 to 4.6 meters) can cause
flooding because such equipment is not designed to
resist internal pressure. Students should be instructed
to check all equipment to be used in a habitat to deter-
mine whether it is designed to withstand both internal
and external pressures.
7.1.9 Chamber Operator Training
The operation and maintenance of recompression
chambers are a necessary part of a diving program; it is
October 1991 — NOAA Diving Manual
7-7
Section 7
therefore important to ensure that all personnel oper-
ating recompression chambers are properly trained
and certified as chamber operators.
A training program for chamber operators should
include the following topics:
• Introduction to hyperbaric chambers;
• Chamber setup and subsystems;
— Pre- and post-dive procedures
— Plumbing
— Controls
— Life-support and emergency procedures
— Breathing and communication systems
— Maintenance procedures
Recordkeeping;
Introduction to the physics of pressure;
Decompression theory and calculation of decom-
pression tables;
Recompression theory and treatment tables;
Barotrauma;
Examination and handling of patients;
Emergency management of decompression sickness
and air embolism;
Inside tending procedures;
Chamber medical kit contents and use;
Review of case histories;
Hands-on experience with simulated treatments;
Chamber operation procedures.
7.2 TRAINING OF DIVING SUPERVISORS
Many organizations, including NOAA, the Navy, and
commercial diving companies, designate certain experi-
enced divers as supervisors. NOAA has four supervi-
sory diving categories: Line Diving Officer, Unit Div-
ing Supervisor, Diving Instructor, and Divemaster.
Each organization provides training that is specifi-
cally related to the goals of the organization; however,
all diving supervisors are required to have a broad
range of diving experience. In addition, every supervi-
sor must have the working knowledge to plan diving
projects, oversee diving activities, conduct inspections,
and investigate accidents. Diving supervisors receive
advanced training in dive planning, the use of special
equipment, first aid, communications, and accident
management.
7.3 DIVING MEDICAL TECHNICIANS
Although there are obvious advantages in having
a qualified hyperbaric physician at a diving site, this
7-8
is often not practical. As an alternative, a Diving
Medical Technician (DMT) trained in the care of
diving casualties can be assigned to the site. An in-
dividual so trained can respond to emergency medical
situations and can also communicate effectively with a
physician located at a distance from the diving site
(see Section 19.6.1).
The development of emergency medical service
organizations began in the United States in the mid-
1970's in response to the need for improved national
emergency medical care. The National Highway Traf-
fic Safety Administration of the Department of Trans-
portation developed and implemented a program to
train Emergency Medical Technicians (EMT's) at vari-
ous levels of certification. These services, coordinated
by the Department of Transportation, are offered and
managed at the state level.
Courses in various aspects of emergency medical
care are offered by organizations such as the American
Red Cross, the American Heart Association, and local
fire and rescue groups. Individuals successfully com-
pleting these courses are certified by the sponsoring
agency as having fulfilled the course requirements.
Courses may lead to different levels of certification,
e.g., national, state, local, or regional, and thus may
reflect different levels of proficiency.
In the late-1970's, the need for medical technicians
specializing in the emergency treatment of diving cas-
ualties was recognized; this specialized need arose
because existing EMT training programs were heavily
oriented toward urban ambulance-hospital emergency
systems. The interest in diving medical technicians
grew with the development of offshore oil and gas
well drilling platforms. Experts decided that the most
workable solution to this need was to cross-train work-
ing divers as medics rather than to train medics to
treat diving casualties. This choice to train working
divers as medical technicians was also driven by eco-
nomic considerations, since using a diver as a medic
made it unnecessary to have a person standing by. The
National Association of Diver Medical Technicians
(NAMDT) was founded in 1981 and, by 1985, a number
of training organizations were approved to provide
DMT training. NOAA has adopted DMT training for
its medical personnel and has a representative on the
NAMDT Board of Directors.
The approved DMT training program is an extensive
303-hour course and includes training in the following
areas:
Lecture (158 hours)
• orientation, anatomy, medical terminology, legal
problems
NOAA Diving Manual — October 1991
Diver and Support Personnel Training
• basic life support, shock, use of oxygen
• systemic diseases and injuries
• medical, environmental, thermal, diving, and de-
compression aspects
• equipment use, patient handling, emergency com-
munications
• drugs and fluids
Laboratory and Practical Experience (115 hours)
• patient assessment and care, suturing
• animal laboratory (optional)
• autopsy (optional)
• diving treatment, neurological examination
• chamber operations
Clinical Observation (30 hours)
• mixed ambulance/emergency room experience.
DMT training is based on the EMT Level I Program
but includes a number of important additions. Because
it may be hours or even days before medical help
arrives in an emergency diving situation, the DMT
must be capable of delivering more advanced support
than a medical technician in an urban area. Accord-
ingly, DMT's receive training in parenteral drug
administration, intravenous infusion techniques, pneu-
mothorax stabilization, simple suture techniques, and
other special procedures.
DMT's must be recertified every 2 years and must
attend 24 hours of lectures and serve 24 hours in an
ambulance/emergency room situation to maintain their
certification. Serving under the diving supervisor, the
trained DMT brings enhanced diagnostic and clinical
skills to medically and geographically remote worksites.
DMT's also have the ability to implement expert advice
received from medical specialists belonging to organi-
zations such as the national Divers Alert Network
(see Section 19.6.1), even though these experts are
geographically distant from the scene of the diving
accident or illness.
7.4 HYPERBARIC PHYSICIANS
A hyperbaric physician is a medical doctor with spe-
cial training in the treatment of medical problems
related to diving and/or elevated atmospheric pres-
sure. Such a physician may be a general practitioner or a
specialist in any branch of medicine. In many cases,
the personal impetus to become an expert in hyperbaric
medicine derives from the fact that the physician is
also a diver. Historically, the U.S. Navy and U.S. Air
Force have been the primary sources of expertise and
trained personnel in hyperbaric medicine.
Because of the increase in the number of divers,
however, the need for physicians trained to treat div-
ing casualties has increased. In response to this need,
several organizations offer specialized training. These
courses range from a series of lectures to more inten-
sive courses lasting several weeks. The best source of
information on the availability of courses in hyperbaric
medicine is the Undersea and Hyperbaric Medical
Society, Inc., which is located in Bethesda, Maryland.
One of the most respected and comprehensive train-
ing courses in hyperbaric medicine is the 3-week pro-
gram offered by NOAA. Started in 1977 with finan-
cial support from the Department of Energy and the
cooperation of the U.S. Navy, this program has trained
over 269 physicians to date. The course includes train-
ing in the following areas:
diving physics
basic diving physiology
fundamentals of inert gas exchange
stress physiology and behavior
oxygen toxicity
air embolism
vestibular problems related to diving
saturation diving
commercial diving equipment
decompression tables
decompression sickness and treatment
helium-oxygen tables and recompression treatment
recompression chamber operation and safety
procedures
gas analysis systems
pressure exposures in recompression chambers
hyperbaric oxygen therapy
emergency treatment of diving casualties
orientation to the national Divers Alert
Network (DAN)
basics of diving accident management
case histories of diving accidents and treatment
polluted-water diving
treatment of near-drowning victims
evaluation and assessment of scuba diver injuries
and illnesses.
Physicians trained in hyperbaric medicine are an
important resource for the diver. Every diver should
learn the name, address, and phone number of the
nearest hyperbaric facility and/or hyperbaric physi-
cian in his or her area. In the event of a diving accident
related to pressure, such as an embolism or decompres-
sion sickness, it is essential to have located a physician
trained in hyperbaric medicine before beginning the
dive. Hyperbaric chambers are described in Section 6,
and the treatment of diving casualties is discussed in
Section 20.
October 1991 — NOAA Diving Manual
7-9
Section 7
7.5 RESEARCH DIVERS
Research diver training is offered by NOAA and a
number of educational institutions and marine labora-
tories. Although the course content and style differ
with different organizations, the objective of such courses
is either to train experienced divers in scientific tech-
niques and methods to enable them to act as underwa-
ter scientific technicians or to train experienced scien-
tists in the techniques and methods of underwater work.
In either case, the curriculum should include advanced
instruction in diving physiology, uses of underwater
equipment, and a review of the potential hazards faced
by divers.
Each of these factors should be related to the prob-
lems faced by diving scientists and their impact on the
conduct of underwater investigations. Diving safety
should be emphasized throughout the course so that on
completion of training the divers feel completely com-
fortable in the water and are able to concentrate their
energies on the work or scientific tasks at hand. This
degree of competence can be achieved only if the basic
diving skills are learned so thoroughly that routine
operations and responses to emergencies become
automatic.
University research diver training programs have
historically lasted for a minimum of 100 hours and
required candidates to complete 12 open-water dives.
In 1984, the Occupational Safety and Health Admin-
istration (OSHA), which had promulgated regulations
in 1978 governing commercial diving operations, spe-
cifically exempted from these regulations those scien-
tific and educational diving programs that could meet
certain requirements. A research organization or
educational entity wishing exemption from the Fed-
eral OSHA standard must have in place a diving pro-
gram that has developed a diving manual, has a diving
control officer and diving safety board, and has developed
procedures for emergency diving situations. The pro-
gram used by many research organizations to fulfill
these requirements for exemption was originally de-
veloped at the Scripps Institution of Oceanography in
the 1950's and has been updated since then as new
technologies and techniques have become available.
The safety record of the research diving community
reflects the effectiveness of current diver training and
certification procedures. Individuals or organizations
wishing information about scientific diving programs
should contact the American Academy of Underwater
Sciences (947 Newhall Street, Costa Mesa, California
92627). As a result of the combined experience of
scientific diving organizations, a set of standards has
been developed to ensure that the high level of quality
and the success of scientific diving are maintained
(American Academy of Underwater Sciences 1987).
7.5.1 Selection
Selecting individuals for research diver training
depends on the objectives of the particular course. The
acceptance of individuals for such training should be
based on need, academic background, personal moti-
vation, and the ability to pass certain swimming and
fitness requirements. If possible, individuals with com-
mon objectives should be grouped together and trained
in a single class.
Selection criteria should require research diver-
candidates to demonstrate evidence of:
• Diver certification from a recognized organization
• Satisfactory completion of a physical examination
• Good physical condition
• Need for the specialized training
• Training in the basics of first aid, including CPR
• Training or equivalent experience in research
methods
• Ability to pass diving and swimming skill tests to
the satisfaction of the examiner.
Research divers must be comfortable in the water and
know their limitations and those of their equipment.
To accomplish these ends, a series of pretraining tests
are used to predict likely success in the diving envi-
ronment. The following phases are included in the
pretests:
Phase 1 — Swimming Pool
This series of activities is to be completed within a
15-minute period and should be done without mask,
fins, or snorkel and in the following sequence:
1. Perform a 75 foot (22.9 meter) underwater swim
on a single breath.
2. Perform a 1000 foot (304.8 meter) swim on the
surface in less than 10 minutes, using the breast
or side stroke.
3. Perform a 150 foot (45.7 meter) underwater swim,
surfacing for no more than 4 single breaths dur-
ing the swim.
The 75 foot (22.9 meter) underwater swim simulates
a 75 foot (22.9 meter) emergency ascent, except that
the exhaling is omitted. The 1000 foot (304.8 meter)
surface swim simulates a swim back to the beach. The
150 foot (45.7 meter) underwater swim, surfacing for 4
single breaths, simulates surf passage, where one has
to surface, take a breath, and get back under water
before the next wave.
7-10
NOAA Diving Manual — October 1991
Diver and Support Personnel Training
The candidates are then required to swim 75 feet
(22.9 meters), dive to the bottom of the pool, recover,
and tow a person of similar size 75 feet (22.9 meters).
Phase 2 — Open-Water Test
An ocean or other open-water swim involves a
1000 foot (304.8 meter) open-water swim and a dive to
the bottom in a depth of at least 15 feet (4.6 meters).
This open-water exercise often reveals potential problems
that are not apparent when the candidate swims in a
swimming pool. The diver training success rate among
those screened by means of these two tests at the Scripps
Institution of Oceanography has been nearly 100 per-
cent (Stewart 1987).
Operational planning, including diver supervision,
scheduling, and emergency plans;
First aid, including CPR;
Diving accident management procedures;
Underwater navigation and search methods, includ-
ing methods of locating, marking, and returning to
research sites;
Collection techniques, including introduction to
sampling, testing, and harvesting systems, tagging,
preserving, transporting of specimens, and data
recording methods;
Photographic documentation, including the use of
still, video, movie, and time-lapse photography
for scientific investigations.
7.5.2 Curriculum
Research diver training should cover dives conducted
in as many different environments as possible. Addi-
tionally, students should gain experience using a vari-
ety of different platforms, such as small boats, ships,
piers, docks, and jetties, and should make water entries
under as many shore conditions as practical.
The curriculum should be tailored to the local area
and the particular needs of the researcher. However,
the following outline identifies topics that are usually
addressed in a practical scientific diving course:
• A review of diving physiology and physics as they
relate to field operations;
• Surface-supplied diving techniques, including
tending, communications, capabilities of surface-
supplied diving systems, and emergency procedures;
• Small boat handling, including the uses and limi-
tations of small craft as diving platforms, load
limits and distribution, securing procedures, minor
field repairs, and legal responsibilities;
• Equipment handling, including safe use, field main-
tenance, and storage of diving and scientific
equipment;
• Underwater rigging, including emplacement, mov-
ing, and securing of research equipment in the water;
• Environmental hazards, such as: diving in currents,
polluted water, blue water, restricted areas such
as caves, under ice, and in wrecks, and under con-
ditions of limited visibility;
• Thermal protection problems, including the use of
wet suits, variable-volume dry suits, and hot water
suits, and the advantages and disadvantages of
each;
• Diver communication, including diver tending,
hardwire, and acoustic and diver recall systems;
7.6 EQUIPMENT MAINTENANCE
Training in equipment maintenance is an important
element in any diving program. Although fatal diving
accident statistics show that equipment failure is rarely
the cause of death (see Section 19.2), equipment mal-
function does cause near-misses, lost time, inconven-
ience, and premature dive termination. Only trained
and qualified personnel should perform maintenance
and repair of diving equipment, especially regulators,
scuba cylinders, and other life support systems.
NOAA and other organizations have instituted a
training and certification program for scuba cylinder
inspectors. The objective of these programs is to ensure
that uniform minimum inspection standards are used
at diving facilities. People who successfully complete
the course are certified as cylinder inspectors. The
issuance of visual cylinder inspection stickers is tightly
controlled.
The cylinder inspection course covers the following
topics:
• Reasons for cylinder inspection;
• Frequency of inspection;
• Types of inspection;
• Analysis of cylinder structure and accessories;
• Criteria of inspection, e.g., wall thickness, mate-
rial and valve specifications;
• Evaluation of cylinder interior and exterior;
• Use of inspection equipment, e.g.. lights, probes,
flushing solutions;
• Detailed inspection sequence (this is an 18-step
process describing each step of a cylinder inspec-
tion); and
• The inspection of a minimum of 10 cylinders under
the supervision of an instructor.
October 1991 — NOAA Diving Manual
7-11
«
«
SECTION 8
WORKING
DIVE
PROCEDURES
Page
8.0 General 8-1
8.1 Surface-Supplied Diving Procedures 8-1
8.1.1 Planning the Dive 8-1
8.1.2 Selecting the Dive Team 8-2
8.1.3 Dressing the Surface-Supplied Diver 8-3
8.1.4 Tending the Surface-Supplied Diver 8-4
8.1.5 The Dive 8-4
8.1.5.1 Diver Emergencies 8-5
8.1.6 Ascent 8-7
8.1.7 Post-Dive Procedures 8-8
8.1.8 Umbilical Diving From Small Boats 8-8
8.1.9 Basic Air Supply Systems 8-9
8.1.10 Rates of Air Flow 8-9
8.1.1 1 Supply Pressures 8-10
8.2 Search and Recovery 8-10
8.2.1 Circular Search 8-12
8.2.2 Arc Pattern (Fishtail) Search 8-13
8.2.3 Jackstay Search Pattern 8-13
8.2.4 Search Using a Tow Bar 8-15
8.2.5 Search Without Lines 8-16
8.2.6 Recovery 8-16
8.3 Underwater Navigation 8-16
8.4 Underwater Tools 8-18
8.4.1 Hand Tools 8-18
8.4.2 Pneumatic Tools 8-20
8.4.3 Hydraulic Tools 8-20
8.4.4 Electric Tools 8-21
8.4.5 Power Velocity Tools 8-21
8.4.6 Cutting and Welding Tools 8-22
Maintenance and Repair Tasks 8-23
Instrument Implantation 8-23
Hydrographic Support 8-24
8.7.1 Hazards to Navigation 8-24
8.7.2 Locating and Measuring Least Depths 8-25
8.7.3 Resolving Sounding Discrepancies 8-25
Wire Dragging 8-25
Salvage 8-26
8.9.1 Lifting Devices 8-26
8.9.2 Air Lifts 8-27
Diving From an Unanchored Platform 8-27
8.10.1 Liveboating 8-28
8.10.2 Drift Diving 8-30
Underwater Demolition and Explosives 8-31
Underwater Photography 8-33
8.12.1 Still Photography 8-33
8.12.1.1 Lenses and Housings 8-33
8.12.1.2 Light and Color 8-34
8.12.1.3 Selection of Film 8-38
8.12.1.4 Time-Lapse Photography 8-41
8.12.2 Motion Picture Photography 8-42
8.12.2.1 Selection of Film 8-42
8.12.2.2 Procedures 8-42
8.12.3 Special Procedures 8-44
8.13 Underwater Television 8-44
8.5
8.6
8.7
8.8
8.9
8.10
8.11
8.12
«
i
WORKING
DIVE
PROCEDURES
8.0 GENERAL
This section describes some of the techniques and pro-
cedures used by scientific and academic divers engaged in
routine underwater work operations. The diving mode
of choice for underwater work that requires the diver
to remain submerged for extended periods of time is
supplied air. This mode is also called umbilical diving.
8.1 SURFACE-SUPPLIED DIVING
PROCEDURES
The surface-supplied air diving mode is widely used
by NOAA divers and by diver-scientists because it
gives them the flexibility they need to perform many
different underwater tasks. In surface-supplied div-
ing, the diver's breathing mixture is supplied from the
surface by means of a flexible hose; thus, divers using
this mode have a continuous breathing gas supply.
The surface-supplied mode is generally used when
divers need to remain under water for an extended
period of time to accomplish the dive's objectives. The
advantages of surface-supplied diving over scuba div-
ing are that it:
• provides greater safety;
• permits dives to greater depths;
• permits divers to stay on the bottom for longer
periods;
• provides thermal protection (if diving in cold water);
• permits communication between the diver and the
surface; and
• provides an unlimited air supply.
Another advantage of the surface-supplied mode is
that it can be undertaken using a variety of support
platforms, including piers, small boats, barges, and
ships. The disadvantages of this mode, compared with
the scuba mode, are: (l) that the umbilical diver's
mobility and operational range are restricted by the
length of the umbilical; and (2) that a large amount of
equipment is required to support umbilical diving.
Surface-supplied diving gear includes both deep-
sea and lightweight equipment. When a diver-scientist
needs maximum protection from the physical or ther-
mal environment or when the dive is deep (i.e., to
190 fsw (57 m)), the deep-sea diving outfit shown
in Figure 8-1 is the diving dress of choice. For dives
October 1991 — NOAA Diving Manual
to shallower depths that do not require maximum
protection from pollution, temperature extremes, or
underwater objects, a lightweight diving outfit may
be used. (Section 5 describes diver and diving equip-
ment of various types in detail.)
8.1.1 Planning the Dive
The success of any dive depends on careful pre-dive
planning, which must consider the goals of the dive,
the tasks involved in achieving these goals, environ-
mental conditions (both surface and subsurface), the
personnel needed to carry out the dive, the schedule for
the dive, the equipment needed to conduct the dive
safely and efficiently, and the availability of emer-
gency assistance. Figure 8-2 is a checklist that can be
used to evaluate environmental conditions that may
affect the dive.
For every surface-supplied dive, the dive supervisor
should complete this checklist (or one adapted to the
specific conditions of a particular dive) before decid-
ing on personnel and equipment needs. Different envi-
ronmental conditions affect members of the dive team
differently. For example, divers are generally not affected
by surface waves except when entering or exiting the
water; however, divers operating in very shallow waters,
in surf, or in exceptionally large waves can be affected
by wave action at the surface.
Air temperature and wind conditions at the surface
also may have a greater effect on the tender and other
surface support personnel than on the diver, because
these individuals are more exposed than the diver to
surface conditions. It is important to remember, how-
ever, that the surface crew should be able to operate
with maximal efficiency throughout the dive, because
reductions in the performance of topside personnel
could endanger the diver.
Visibility at the surface can affect the performance
and safety of the diver and the surface crew. For exam-
ple, a diver surfacing under low- or no-visibility con-
ditions might not be able to find the support craft.
The underwater environment can influence many
aspects of a dive, from crew selection to choice of
diving mode. All diving operations must consider:
• depth;
• bottom type;
8-1
Section 8
Figure 8-1
Surface-Supplied Diver
in Deep-Sea Dress
ill
.Jocking Harness
/ Yvr^^rlrfu".
^^Front
Jocking
Strap
Hip Weight
W -i iv*'
Pocket > — ^
^SPii^^oidS.
Thigh Weight
Pocket
Calf Weight
Pocket
Umbilical
•Crotch
Jocking
Strap
, Boots
Adjustable
Exhaust
Valve
Rear Jocking
Straps
Dry Suit
Boot Safety
Straps
Helmet
Assembly
Air Whip
Communication
Whip
Thigh Retainer
Calf Retainer
Source: US Navy (1988)
• temperature of the water;
• underwater visibility; and
• tides and currents.
In addition, the presence of contaminants in the water
(see Section 11), underwater obstacles, ice, or other
unusual environmental conditions can affect planning
for some dives.
Dive depth must be measured using two different
methods before the dive begins. To obtain an accurate
depth profile of the area of the dive, a series of depth
measurements must be plotted. Methods of measuring
depth that may be used include lead line sounding,
pneumofathometer, high-resolution sonar, or ship-
mounted fathometer. Depth readings on maps or charts
are useful for general screening purposes but are not
sufficiently accurate to be used to measure dive depths.
Samples should be taken of the bottom in the general
area of the dive; in some instances, in-situ observa-
tions can be made before the dive. Bottom conditions
affect a diver's mobility and visibility under water; a
sandy bottom allows maximum mobility, and the diver's
movements do not stir up so much sediment that visi-
bility is restricted. By comparison, working in an area
with a muddy and silty bottom can be dangerous, because
the diver may become entrapped in the mud and usu-
ally generates sufficient silt to interfere substantially
with visibility.
Currents must be considered in dive planning, whether
the surface-supplied scientist-diver is working in a
river or the ocean. The direction and velocity of river,
8-2
ocean, and tidal currents vary with such factors as the
time of year, phase of the tide, bottom conditions,
depth, and weather.
Underwater visibility and water temperature also have a
major influence on dive planning. For a detailed descrip-
tion of underwater conditions in major U.S. geographi-
cal regions, see Section 10.1.
8.1.2 Selecting the Dive Team
The size of the team needed for a surface-supplied
dive depends on the number of divers on the dive team,
the type of equipment available, the dive's safety
requirements, environmental conditions, dive depth,
dive mission, and the surface support platform availa-
ble. The optimal number of dive team personnel for a
large and complex surface-supplied dive is six: a dive
supervisor, diver, standby diver, tender, standby ten-
der, and timekeeper/recorder. If all members of the
team are fully trained, a job rotation system can be
used that permits all team members to take turns serv-
ing as divers; this approach allows for maximum in-water
working time and is thus both logistically and econom-
ically efficient.
The dive supervisor is responsible for planning,
organizing, and managing all dive operations; the dive
supervisor remains at the surface at all times. This
individual also determines equipment requirements,
inspects the equipment before the dive, selects team
members, ensures that emergency procedures and first
aid supplies are available, conducts pre-dive briefings,
NOAA Diving Manual — October 1991
Working Dive Procedures
Figure 8-2
Predive Environmental
Checklist
Surface
Atmosphere
Visibility
Sunrise/Set
Moonrise/Set
Temperature (air)
Humidity
Barometer
Precipitation
Cloud Description/Cover
Wind Direction/Force
Other:
Sea Surface
Sea State
Wave Action:
Height
Length
Direction
Current:
Direction
Velocity
Type
Visibility
Water Temperature _
Local Characteristics
Subsurface
Underwater and Bottom
Depth
Water Temperature:
degrees at
degrees at
degrees at
depth
depth
depth
Visibility
Underwater:
feet at
feet at
feet at
Bottom
degrees at bottom
feet at
depth
depth
depth
depth
Thermoclines:
at
at
Bottom Type:
depth
depth
Obstructions:
Current:
Direction
Source
Velocity
Pattern
Tides:
High Water
Low Water
Ebb Direction Velocity
Flood Direction _ Velocity _
Marine Life:
Other:
/
time
time
Adapted from US Navy (1988)
monitors the progress of the dive, debriefs the divers,
prepares reports of the dive, and checks equipment and
diver logs at the completion of the dive.
The diver(s) must be qualified and trained in the
equipment and diving techniques needed for the dive.
During the course of the dive, the diver must keep
surface personnel informed of the progress of the dive,
bottom conditions, and any problems (actual or poten-
tial). Every diver is responsible for ensuring that his or
October 1991 — NOAA Diving Manual
her diving gear is complete, in good repair, and ready
for use. In addition, all divers must know both line pull
signals and voice signals and must respond to and
comply with instructions from surface personnel.
The standby diver must be as well trained and quali-
fied as the diver; a standby is required for all surface-
supplied operations, regardless of size. It is the responsi-
bility of the standby diver to be ready to provide
emergency or backup support to the diver any time the
diver is in the water.
The tender is the member of the surface team who is
responsible for tending the diver while the diver is in
the water. Every diver in the water must have a tender.
Before the diver enters the water, the tender:
• checks the diver's equipment;
• checks the air supply; and
• dresses the diver.
Once the diver is in the water, the tender takes care of
the diver's lines to ensure that no excess slack or ten-
sion is on the line. In addition, the tender maintains
communication with the diver and keeps the diving
supervisor informed of the diver's progress. All ten-
ders should be fully qualified divers.
On complex dives, a standby tender may be needed.
The standby tender should be fully trained as a diver
and should be instructed in all of the required duties of
the tender. It is the standby tender's job to be ready to
assist the tender or to replace him or her at any time.
The timekeeper may be dedicated to keeping the
diver's time during the job or, on dives involving a
limited number of dive team members, the tender may
also serve as the timekeeper. The timekeeper's respon-
sibilities involve keeping an accurate record of dive
times and noting all of the important details of the
dive. On some dives, the dive supervisor acts as the
timekeeper.
8.1.3 Dressing the Surface-Supplied Diver
Surface-supplied divers use either a diving mask or
a helmet, and the supervisor and diver must decide
whether a dry suit, wet suit, or bathing suit is appro-
priate for a particular dive. Factors to be considered
when making these choices include:
• Personal preference;
• Depth of the planned dive;
• Nature of the work to be performed;
• Length of the planned dive;
• Environmental conditions (temperature of the water,
speed of current, underwater visibility, etc.); and
• Condition of the water, i.e., polluted or clean.
8-3
Section 8
The dressing procedures followed by the diver and his
or her tender depend on the type of dress selected for
the dive.
At least one tender assists in dressing a diver wear-
ing a lightweight surface-supplied diving system (dry
suit) or a wet suit. If a dry suit is to be worn, the diver
applies a lubricant to the suit's zipper and then, while
seated, inserts his or her legs into the suit. The diver
then stands and works both arms into the suit's sleeves.
The tender holds the breech ring while the diver is
performing these procedures. Then the tender:
Wraps the harness chest strap tab around the left
shoulder strap and presses it into place;
Pulls the crotch strap to the front and fastens the
weight belt latch;
Adjusts the waist belt and shoulder straps and
secures both rear jocking straps;
Inserts thigh and calf weights and secures the
thigh and calf restrainers;
Ensures that air is available to the helmet and that
the air supply valve is opened;
Lowers the helmet into place on the diver's head
and aligns it with the lower breech ring lugs;
Presses the quick-release locking pins, slides them
into place, and ensures that all pins are locked;
Positions the umbilical and whips under the diver's
left arm and secures them;
Performs a communications check; and
Establishes the appropriate air flow.
If a lightweight mask (Figure 8-3) is to be used with
a wet suit or bathing suit, dressing procedures are
simpler than those described above. For divers wearing
a wet suit or a bathing suit, the tender assists the diver
to perform the following steps:
• Don the harness;
• Place the lower breech ring with neck dam over the
diver's head;
• Secure the ring to the jock strap; and
• Place the helmet on the diver's head and secure it.
Figure 8-4 shows a surface-supplied diver dressed and
ready to dive in a wet suit.
8.1.4 Tending the Surface-Supplied Diver
The tender is the dive team member in closest com-
munication with the diver during the dive. Before the
dive begins, the tender checks the diver's diving dress,
paying particular attention to the valves on the helmet,
the helmet locking device, the helmet seal, and the
harness. The tender then dresses the diver and helps
the diver to position himself or herself on the diving
8-4
Figure 8-3
Lightweight Surface-Supplied
Mask
Steady Flow
Valve (defogger)
'Dial-a-Breath"
"Adjustment knob
Waterproof
Communication
Connector
(Male)
Source: US Navy (1988)
stage or ladder. The tender must always keep a hand on
the diver's lifeline close to the helmet to steady the
diver and to prevent a fall.
As the diver enters the water, the tender pays out the
umbilical at a steady rate, being careful to avoid sharp
edges. Throughout the dive, the tender must keep slack
out of the line; at the same time, the tender must be
careful not to pull the line taut. Maintaining approxi-
mately 2 or 3 feet (0.7 to 1 m) of slack on the line
permits the diver the right degree of freedom and
prevents him or her from being pulled off the bottom
by currents or by the movement of the support craft.
Too much slack in the line interferes with effective line
communication between the diver and tender and
increases the likelihood of line fouling.
Throughout the dive, the tender continuously observes
the descent line and monitors the umbilical to receive
any line-pull signals from the diver. If an intercom
system is not in use, the tender periodically signals the
diver (using line pulls) to ensure that the diver's condi-
tion is good. If the diver fails to respond to two pull
signals, the situation must be treated as an emergency
and the dive supervisor must be notified immediately.
8.1.5 The Dive
Once the diver is dressed and ready for the dive, the
tender helps the diver to prepare for water entry. The
entry technique used depends on the staging area or
type of vessel involved in the operation. If a stage is
used for diver entry, the diver should stand or sit squarely
NOAA Diving Manual — October 1991
Working Dive Procedures
Figure 8-4
Surface-Supplied Diver
In Lightweight Mask
and Wet Suit
Source: US Navy (1988)
on the stage platform and maintain a good grip on the
rails. If the diver makes a jump or roll entry into the
water, he or she must maintain a grip on the face mask
while the tender maintains sufficient slack on the line
and air hose.
When the diver is positioned for descent, the follow-
ing procedures, as appropriate, should be followed by
various members of the dive team.
• The diver should adjust his or her buoyancy, if
necessary. Whether the diver is weighted neutrally or
negatively will depend on the dive's objectives.
• The tender should re-verify that the air supply
system, helmet (or mask), and communications
are functioning properly. If not, corrections must
be made before the diver's descent. The tender
should check for any leaks in the air supply fittings
or suit and also should look for air bubbles. No
diver should dive with malfunctioning equipment.
• The tender should also re-verify that all equip-
ment is functioning satisfactorily.
• The diving supervisor should give the diver per-
mission to descend.
• The diver should descend down a descent or "shot"
line. The descent rate used depends on the diver;
however, it should not exceed 75 ft/min (22.9 m/min).
The air supply should be adjusted for breathing
ease and comfort.
October 1991 — NOAA Diving Manual
• The diver must equalize pressure in both ears and
sinuses during descent. If equalization is not pos-
sible, the dive must be terminated.
• When descending in a tideway or current, the diver
should keep his or her back to the current so that
he or she will be forced against the descent line.
• When the diver reaches the bottom, the tender
should be informed of the diver's status and the
diver should ensure that the umbilical assembly is
not fouled in the descent line.
• If necessary, buoyancy and air flow should be reg-
ulated before releasing the descent line; adjust-
ments to air control valves should be made in small,
cautious increments.
• The diver should attach a distance line (if one is
used) and should then proceed to the work area. A
distance line should be used when visibility is
extremely poor and the diver cannot see the descent
line from a distance.
• After leaving the descent line, the diver should
proceed slowly to conserve energy. It is advisable
for divers to carry one turn of the umbilical hose in
the hand.
• The diver should pass over, not under, wreckage
and obstructions.
• If moving against a current, it may be necessary
for the diver to assume a crawling position.
• If the diver is required to enter wreckage, tunnels,
etc., a second diver should be on the bottom to tend
the umbilical hose at the entrance to the confined
space.
• The tender must constantly inform the diver of the
bottom time. The diver should be notified a few
minutes in advance of termination so that the task
can be completed and preparations made for ascent.
If the diver experiences rapid breathing, panting, or
shortness of breath, abnormal perspiration, or an unu-
sual sensation of warmth, dizziness, or fuzzy vision, or
the helmet ports have become cloudy, there is probably
an excess of carbon dioxide in the helmet. To get rid of
this excess, the air flow in the helmet should be increased
immediately by simultaneously opening the air control
and exhaust valves.
8.1.5.1 Diver Emergencies
Fouling
A surface-supplied diver's umbilical may become
fouled in mooring lines, wreckage, or underwater struc-
tures, or the diver may be trapped by the cave-in of a
tunnel or the shifting of heavy objects under water. In
8-5
Section 8
such emergencies, surface-supplied divers are in a
better position to survive than scuba divers, because
they have a virtually unlimited air supply and can
communicate with the surface, both of which facilitate
rescue operations. Fouling may result in fatigue, expo-
sure, and prolonged submergence, and it may also neces-
sitate an extended decompression. Divers who are fouled
should:
• Remain calm;
• Think clearly;
• Describe the situation to the tender;
• Determine the cause of fouling and, if possible,
clear themselves; and
• Be careful to avoid cutting portions of their umbilical
assembly when using their knife.
If efforts to clear themselves are unsuccessful, divers
should call for the standby diver and then wait calmly
for his or her arrival. Struggling and other panicky
actions only make the situation worse by using up the
remaining air supply at a faster rate.
Blowup
Blowup is the uncontrolled ascent of a diver from
depth; this is a hazard for divers using either a closed
dress (deep-sea or lightweight helmet connected to a
dry suit) or variable-volume dry suit (UNISUIT® or
equivalent). Blowup occurs when the diving dress or suit
becomes overinflated or the diver loses hold of the bot-
tom or descending line and is swept to the surface.
During blowup, the diver exceeds the rate of ascent
(25 ft/min (8 m/min)) that must be maintained to be
decompressed successfully at the surface. Accidental
inversion of the diver, which causes the legs of the suit
to fill with air, also may result in uncontrolled blowup.
Accidental blowup can cause:
• Cerebral gas embolism;
• Decompression sickness; and/or
• Physical injury (if the diver's head strikes an object,
such as the bottom of a ship or platform).
Before descending, the diver must be certain that all
exhaust valves are functioning properly. The diving suit
or dress should fit the diver well to avoid leaving exces-
sive space in the legs in which air can accumulate; air in
the legs of the suit presents a serious hazard, particu-
larly with variable-volume suits. Divers must be trained
under controlled conditions, preferably in a swimming
pool, in the use of all closed-type diving suits, regard-
less of their previous experience with other types of
suits. Some divers have attempted to use a technique
called "controlled blowup" for ascent; however, this
8-6
method of ascent should never be used because losing
control of the rate of ascent can have fatal consequences.
After surfacing, blowup victims should not be allowed
to resume diving. If a diver who has experienced a
blowup appears to have no ill effects and is still within
the no-decompression range prescribed by the tables,
he or she should return to a depth of 10 feet (3.0 m) and
decompress for the amount of time that would normally
have been required for ascent from the dive's working
depth. The diver should then surface and dress, after
which he or she should be observed for at least an hour
for signs of delayed-onset air embolism or decompres-
sion sickness.
Blowup victims who are close to the no-decompression
limit or who require decompression should first be
recompressed in a chamber and then be decompressed in
accordance with surface decompression procedures; if
the available surface decompression tables are not ade-
quate, the victim should be recompressed in a chamber
to 100 feet (30.5 m) for 30 minutes and then be treated
in accordance with U.S. Navy Treatment Table 1A (see
Appendix C). If no chamber is available, conscious vic-
tims should be treated in accordance with recompression
procedures for interrupted or omitted decompression; .
unconscious victims should be handled according to the m
recompression table in Appendix C that is designed for
cases of air embolism or serious decompression sickness.
Loss of Primary Air Supply
Although losing the primary air supply is an infre-
quent occurrence in surface-supplied diving, it does
occasionally occur. In the event of a primary air supply
malfunction or loss, the panel operator should switch
immediately to the secondary supply, notify the tender
and diver, and call for the termination of the dive.
(Secondary air supply systems on the surface are
discussed in Sections 4.2 and 14.5 for both air com-
pressor and high-pressure cylinder air supplies.)
The use of self-contained emergency air supplies in
surface-supplied diving has significantly reduced the
hazard associated with primary air supply failure. In
an emergency, a diver equipped with such a supply can
simply activate his or her emergency supply and pro-
ceed to the surface. Divers faced with the loss of their
surface supply should close their helmet free-flow valves
to conserve air, and the surface crew should be alerted
to the situation as soon as it develops. If, because of
fouling, the diver is forced to cut the air supply line, a
check valve incorporated into the reserve manifold
will prevent loss of the reserve air supply. The diver a
must immediately terminate the dive if it is necessary fl
to switch to the emergency supply; under no conditions
should the diver attempt to complete the work task.
NOAA Diving Manual — October 1991
Working Dive Procedures
If the primary air supply fails when a diver is diving
without a self-contained emergency air supply, the
diver can drop his or her weight belt (without removing
the mask) and then ascend to the surface, exhaling
throughout the ascent to prevent air embolism. A diver
with a fouled hose should release his or her weight belt
and harness (or harness attachment) and then remove
the mask by grasping it and pulling it forward, up, and
over the head. The surface-support team should han-
dle a diver who surfaces in this way in the same manner
as a blowup emergency, because air embolism or decom-
pression sickness is a possibility.
Loss of Communication or Contact with the Diver
If contact with the diver is lost, the following proce-
dures should be implemented:
• If intercom communication is lost, the tender should
immediately attempt to communicate with the diver
by line-pull signals (see Section 14.2).
• Depending on diving conditions and the arrange-
ments made during dive planning, the dive may
either be terminated or continued to completion
(using line-pull signals for communication). In
research diving, it is generally best to terminate
the dive so that the problem can be resolved and
the dive plan revised.
• If the tender does not receive an immediate line-
pull signal reply from the diver, greater strain
should be taken on the line and the signal should
be sent again. Considerable resistance to the ten-
der's pull may indicate that the umbilical line is
fouled, in which case a standby diver should be
dispatched as soon as possible.
• If the tender feels sufficient tension on the line to
conclude that it is still attached to the diver but
continues to receive no reply to line-pull signals,
the diver should be assumed to be unconscious. In
this event, the standby diver should be dispatched
immediately.
• If no standby diver is available, or if for some
reason it is considered unwise to use one, the diver
must be pulled to the surface at a rate of 60 feet
(18.3 m) per minute or less, and the tender and the
dive team should be prepared to administer first
aid and recompression as soon as the diver sur-
faces. If the diver is wearing closed dress or a
variable-volume dry suit, pulling him or her to the
surface is likely to cause blowup unless another
diver is available to assist with the ascent. It is
thus essential that a standby diver be ready at all
times to enter the water when divers wearing
variable-volume dry suits are in the water.
October 1991 — NOAA Diving Manual
Loss From View of Descent or Distance Line
Occasionally a diver will lose sight of the descent
line or lose contact with the distance line. If the dis-
tance line is lost, the diver should search carefully
within arm's reach or within his or her immediate
vicinity. If the water is less than 40 feet (12.2 m) deep,
the tender should be informed and should haul in the
umbilical assembly and attempt to guide the diver
back to the descending line. In this situation, the diver
may be hauled a short distance off the bottom. When
contact with the descent line is regained, the diver
should signal the tender to be lowered to the bottom
again. In water deeper than 40 feet (12.2 m), the tender
should guide the diver to the descent line in a system-
atic fashion.
Falling
Falling is an especially serious hazard for divers
using deep-sea or helmet equipment to work on the
hull of a ship. A diver falling off a diving stage or work
platform wearing such equipment is much more likely
to be injured than a diver falling a greater distance in
open water. The principal danger from falling is the
sudden increase in pressure, which may not be com-
pensated for by the overbottom pressure of the air
supply; this could result in helmet or mask squeeze.
The diver and tender must therefore always be alert to
the possibility of a fall. Should the diver start to fall,
the tender should take an immediate strain on the
umbilical assembly to steady the diver.
The likelihood of a faceplate being cracked during a
fall when a modern helmet is being used is relatively
small. If the faceplate does crack, however, the diver
should continue to wear it, and the air pressure should
be increased slightly to prevent water leakage.
If a tear develops in a variable-volume suit, the dive
should be terminated immediately because the chilling
effect of water entering the suit can be severely debili-
tating to a diver. If a closed suit with the helmet
attached is torn in a fall, the diver should remain in an
upright position and ascend to the surface at a safe rate
of ascent.
8.1.6 Ascent
When the diver's bottom time has expired or the task
has been completed, the diver should return to the
ascent line and signal the tender to prepare for ascent.
The following procedures should be used;
• The tender should pull in any excess umbilical line
and exert a slight strain on the line; he or she
8-7
Section 8
should then exert a slow and steady pull at the
prescribed rate (generally 60 ft/min (18.3 m/min));
• The tender should start a timer on the surface and
should then monitor this timer (along with the
pneumofathometer) to control the diver's ascent
rate;
• The diver controls his or her buoyancy by using
either a buoyancy compensator or adjusting the
air in his or her closed- or variable-volume suit
(the diver must be careful not to overinflate the
suit, which could cause an accidental blowup);
• The diver should continuously hold onto the line
during ascent;
• The tender or diving supervisor should inform the
diver well in advance of his or her decompression
requirements (a diving stage may be required for
long decompressions);
• When decompression is completed, the tender assists
the diver to board the support platform.
8.1.7 Post-Dive Procedures
Divers should be helped from the water and should
then be assisted by surface-support personnel in remov-
ing their equipment. The following procedures are
recommended:
• Remove the weight belt;
• Remove the helmet and secure the air flow valve;
• Unbuckle and remove the emergency backpack;
• Remove the neckring assembly;
• Unbuckle and remove the jocking belt.
If the diving system is not to be used again that day:
• Close the supply valve and vent the primary air
hose;
• Close the emergency air cylinder valve, open the
reserve air valve to vent the line, and close the
reserve air valve again;
• Disconnect the primary air hose from the emer-
gency manifold;
• Disconnect the hose from the helmet inlet and
disconnect the communication cable;
• Place the helmet in an upright position, rinse external
surfaces with fresh water, and wipe them dry; clean
the interior, if necessary, with a damp sponge and
then wipe it dry;
• Rinse the jocking belt in fresh water and hang it up
to dry.
The divers should be observed for any signs of sick-
ness or injury caused by the dive, and warming proce-
dures should be commenced as soon as possible if the
8-8
divers are chilled. The divers and tenders should report
any equipment defects noted during or after the dive,
and defective equipment should be tagged for correc-
tive maintenance. The divers should then be debriefed
and the log completed. Divers should establish their
own standard of care for their masks, depending on the
conditions of use. For example, using a mask in fresh
water requires different maintenance procedures and
cleaning frequencies than are required when a mask is
used in seawater. The type of underwater activity also
influences maintenance requirements. When diving in
seawater, the exterior of the mask should be rinsed in
fresh water after each dive, taking care not to flood the
microphones. The interior of the mask should then be
wiped clean with a cloth or sponge. An alcohol solution
is useful for cleaning and disinfecting the oral-nasal
mask. (Inhibisol® or similar solvents should not be
used, because they will harm the acrylic port.) The
interior of the mask should be completely dry when the
mask is stored, even if the storage time is very short.
Some masks should be placed in the face-down posi-
tion to allow water to drain from the face seal.
Masks of some types require additional maintenance.
For example, the interior of masks that are fitted with
a cold-water hood are difficult to clean and dry unless
the hood is first removed. After the hood is removed,
the mask should be turned inside out and the water in
the open-cell foam face seal should be squeezed out.
The interior of the hood and mask should be dried
completely before reassembling. Installing a zipper in
the back of the hood simplifies maintenance because it
reduces the number of times the hood has to be removed.
Monthly (or between-dive) maintenance and repair
should be performed on all masks in accordance with
the manufacturer's instructions and the service man-
ual supplied with each mask.
8.1.8 Umbilical Diving From Small Boats
Although most surface-based umbilical diving is
conducted from large vessels or fixed platforms, the
umbilical system can be adapted readily to small boat
operations. When working from small boats, i.e., at
depths of 16 to 30 feet (4.9-9.1 m), a bank of high-
pressure cylinders is usually used to supply breathing
air, which enables the team to operate without an air
compressor and its accompanying bulk and noise. The
number and size of the high-pressure cylinders required
depend on the size of the boat and on operational
requirements. For small boats, two or more sets of
standard twin-cylinder scuba tanks can be connected
by a specially constructed manifold that is, in turn,
connected to a high-pressure reduction regulator or
NOAA Diving Manual — October 1991
Working Dive Procedures
small gas control panel. The umbilical is then con-
nected to the pressure side of the pressure reduction
unit. In larger boats, air may be carried in a series of
240- or 300-cubic foot (6.8 or 8.5 m3) high-pressure
cylinders. Regardless of the cylinder configuration used,
all cylinders must be secured properly, and the valves,
manifold, and regulator must be protected to prevent
personnel and equipment damage. The umbilical may
be coiled on top of the air cylinders or in the bottom of
the boat. For the convenience of the tender, the com-
municator is generally placed on a seat or platform.
Communications equipment must be protected from
weather and spray. Because small boats can only be
used to support shallow water work, the umbilical from
the boat to the diver is usually 100 to 150 feet (30.5-
45.7 m) in length. It is generally wise to limit diving
depths to less than 100 feet (30.5 m) when working
from a small boat.
The diving team for a surface-supplied dive from a
small boat usually consists of a diver, tender, and
standby diver. The tender, who is a qualified diver,
also serves as the supervisor on such dives. If properly
qualified, all personnel can alternate tasks to achieve
maximum operational efficiency. The standby diver
may be equipped with a second umbilical and mask or,
as is frequently the case, be equipped with scuba; he or
she should be completely dressed and capable of don-
ning scuba and entering the water in less than a min-
ute. A standby using scuba should be fitted with a
quick-release lifeline (readily releasable in the event
of entanglement). Some divers use a heavy-duty com-
munication cable as a lifeline, which allows the standby-
diver and tender to stay in communication. This line is
also constructed so that it may be released readily in
case of entanglement.
Many divers consider high-pressure cylinder air supply
systems safer and more dependable than systems
incorporating a small compressor and a volume or
receiver tank, and some divers prefer to have a small
tank incorporated into the system to provide air for
surfacing in an emergency. Most experts agree that a
diver should carry a small self-contained emergency
scuba tank for use in the event of primary system
failure. An emergency supply of this type is mandatory
when a diver will be working around obstructions or
inside submerged structures.
8.1.9 Basic Air Supply Systems
The two basic types of air supply systems used for
surface-supplied diving are:
• Air compressors; and
• High-pressure cylinder systems.
When properly configured, either of these air sources
is able to supply breathing gas that is:
• Of specified purity (see Table 1 5-3);
• Of adequate volume;
• At the proper pressure; and
• Delivered at a sufficient flow rate to ensure ade-
quate ventilation. Regardless of the type of sys-
tem, it is imperative that it be in good repair, be
serviced at regular intervals, and be manned by
trained personnel.
Air compressors are discussed in more detail in Sec-
tion 4.2. When the air supply system for surface-supplied
diving operations incorporates an on-line air compressor,
the general system configuration is similar to that
shown in Figure 8-5. When surface-supplied diving
operations utilize a high-pressure cylinder system for
diver air supply, the general system configuration used
is the one shown in Figure 8-6.
8.1.10 Rates of Air Flow
The rate at which air must flow from the air supply-
to the diver depends on whether the breathing appara-
tus (helmet or mask) is operated in a free-flow or
demand mode. With free-flow equipment, the primary-
requirement of the air supply system is that it have a
capacity (in acfm) that will provide sufficient ventila-
tion at depth to prevent the carbon dioxide level in the
mask or helmet from exceeding safe limits at normal
work levels and during extremely hard work or emer-
gencies. By ensuring that the apparatus is capable of
supplying at least 6 acfm (170 liters) under all circum-
stances, divers can be reasonably certain that the inspired
carbon dioxide will not exceed 2 percent. To compute
the ventilation rate necessary to control the level of
inspired C02, the following equation should be used:
R = 6(Pa)(N)
where R = ventilation flow rate in scfm; Pa = abso-
lute pressure at working depth in ATA; N = number of
divers to be supplied.
Example:
What ventilation rate would be required for two
divers using lightweight helmets at 80 fsw (24.4 m)?
R = 6(Pa)(N)
R = 6(3.42)(2)
R = 41.04 scfm
For demand equipment, the air requirement for res-
piration is based on the maximum instantaneous (peak)
flow rate under severe work conditions. The maximum
October 1991 — NOAA Diving Manual
8-9
Section 8
Figure 8-5
Major Components of a Low-Pressure
Compressor-Equipped Air Supply System
Moisture
Separation
Back
.Pressure
^i+J Regulator
LP
Compressor
/Valve /W\
^^^^ Air Intake
D*0— I J to Weather
Pressure
Regulator
(if req)
From
Secondary
Source
Volume Tank
Divers
Manifold |
Drain
Valve
"C£<|_ Drain
'Valve
Source: US Navy (1985)
instantaneous flow is not a continuous demand but
rather the highest rate of air flow attained during the
inhalation part of the breathing cycle. A diver's air
requirement varies with the respiratory demands of
the work level. Consequently, the rate at which com-
pressed air is consumed in the system is significantly
lower than the peak inhalation flow rate.
Computing the rate of flow that the air supply sys-
tem must be able to deliver for demand breathing
equipment is essentially the same as calculating the
consumption rate at depth (see Section 14.3).
Example:
What rate of flow will a diver require using a demand
mask and doing moderate work at 75 fsw (22.9 m)?
Cd = RMV (Pa)
Cd = (1.1 acfm) (3.27 ATA)
Cd = 3.6 scfm
For demand equipment, the rate of air flow must meet
or exceed the diver's consumption rate at depth.
8.1.11 Supply Pressures
The air supply system must be capable at all times of
delivering air to the diver at a pressure that overcomes
the water pressure at the working depth (overbottom
pressure) and the pressure losses that are inherent in
any surface-supplied diving system (hoses, valves, and
8-10
Figure 8-6
Typical High-Pressure
Cylinder Bank Air Supply System
Air Supply to Divers
From
Secondary
Supply
— t>~0-
<X—
Pressure Regulator
Source: US Navy (1985)
regulators). The supply pressure must always exceed
the ambient pressure at the working depth to provide a
safety factor in case an accidental rapid descent from
below the planned working depth must be made.
When using a free-flow mask or lightweight helmet,
a hose pressure of at least 50 psi is required for dives in
water less than 120 fsw (36.6 m) in depth, and a pres-
sure 100 psi greater than ambient pressure is necessary
for depths exceeding 120 fsw (36.6 m). In addition, a
loss through the valves of at least 10 psig should be
anticipated. Simple calculations give the supply pres-
sures necessary for most free-flow masks and light-
weight helmets.
For depths less than 120 fsw (36.6 m):
Ps = 0.445D + 65 + Pj
where Ps = supply air pressure in psig; D = depth in
fsw; 65 = absolute hose pressure (50 psi + 14.7 psi);
and Pj = pressure loss in system.
For depths greater than 120 fsw (36.6 m):
ps = 0.445D + 115 + P;
where 115 = absolute hose pressure (100 psi + 14.7 psi).
8.2 SEARCH AND RECOVERY
Search techniques all rely on one common element: the
adoption and execution of a defined search pattern.
The pattern should commence at a known point, cover
a known area, and terminate at a known end point.
Search patterns are implemented by carrying out
search sweeps that overlap. To be efficient, the overlap
NOAA Diving Manual — October 1991
Working Dive Procedures
Table 8-1
Wind Speed and Current Estimations
should be minimal. The initial step in a search is to
define the general area and the limits to be searched. If
the search is being conducted to locate a specific object,
the last known position of the object is the starting
point for defining the search area. The drift in the open
sea resulting from sea and wind currents, the local
wind condition at the time the object was lost, and the
leeway (movement through the water from the force of
the wind) should be studied. Sea currents can be esti-
mated for a particular area using current NOAA Tidal
Current Tables and Tidal Current Charts and the U.S.
Navy's current Atlas of Surface Currents. Wind cur-
rents can be estimated using Table 8-1.
The leeway generally is calculated at 0 to 10 percent
of the wind speed, depending on the area of the object
exposed to the wind and the relative resistance of the
object to sinking. The direction of leeway is downwind,
except for boats that have a tendency to drift up to
40 percent off the wind vector. Calculation of the value
and direction of leeway is highly subjective for objects
that float or resist sinking; however, if the average
wind velocity is relatively low (under 5 knots (2.5 m/s)),
or the object is heavy enough to sink rapidly, the
leeway has little or no effect on the calculation of a
probable location.
After the vectors of water current, wind current, and
leeway have been added vectorially and applied to the
last known position of the object, a datum point is
defined. The datum point is the most probable position
of the object. Once the datum point has been defined,
the search radius around the datum point is selected.
The search radius, R, is equal to the total probable
error of position plus a safety factor, as defined by the
following formula:
where
R = radius
k = safety factor (between 0
C = total probable error
R = (1 + k)C
and 1.5)
The total probable error is a mathematical combination
of the initial error of the object's position (x). the
navigation error of the search craft (y), and the drift
error (de). The drift error is assumed to be one-eighth
of the total drift. The total probable error, C, is:
C = (de: + x2 + y2)'/2
Each factor included in the total probable error is
somewhat subjective. Selecting conservative values has
the effect of enlarging the search radius; sometimes, a
small search radius is selected, and repeated expan-
Wind Speed,
knots (m/s)
Wind Current,
miles/day (km)
1-3
(0.5- 1.5)
2 (3.2)
4-6
(2.0- 3.0)
4 (6.4)
7-10
(3.5- 5.0)
7 (11.3)
11-16
(5.5- 8.0)
11 (17.7)
17-21
(8.5-10.5)
16 (25.8)
22-27
(11.0-13.5)
21 (33.9)
28-33
(14.0-16.5)
26 (41.9)
Adapted from NOAA (1979)
sions are made around the datum point until the object
is located. Searching the area around the datum point
can be implemented using a variety of patterns,
depending on the search equipment, visibility, or number
of search vehicles involved.
Systematic searching is the key to success. A good
search technique ensures complete coverage of the
area, clearly defines areas already searched, and
identifies areas remaining to be searched. The visibili-
ty, bottom topography, number of available divers,
and size of the object(s) to be located are prime factors
in selecting the best method for a particular search.
There are two acoustic approaches to underwater
object location. The first is to traverse the area being
searched with a narrow beam fathometer, keeping track
of the ship's position by normal surface survey meth-
ods. This approach is suitable for returning to the
position of a known object that has high acoustic relief
and is located in an otherwise relatively flat area, such
as a wreck, significant rock outcrop, or a mount. The
second acoustic method involves the use of side-scan
sonar. When using side-scan sonar, a transponder
receiver unit is towed either from the surface or a
submersible. Acoustic beams are broadcast left and
right, and the signals received are processed to present
a picture of the bottom on both sides of the transponder-
receiver unit. Approximate object position can be deter-
mined by knowing the ship's position, heading, and
speed, and the approximate position of the transponder-
receiver unit with respect to the ship.
Onboard microprocessors to control the range/gain
necessary to produce optimum display contrast are
beginning to replace manual adjustment of the gain;
the use of microprocessors simplifies the task of the
observer and increases the effectiveness of a search. If
more precise determination is necessary, one of the
October 1991 — NOAA Diving Manual
8-11
Section 8
Figure 8-7
Circular Search Pattern
acoustic surveying methods described in Section 9.1.3
can be used. Underwater object location using acous-
tic techniques involves divers only after the object has
been detected. The following diver search techniques
have been useful for such purposes.
8.2.1 Circular Search
In conditions where the bottom is free of projections,
the visibility is good, the object to be located is reason-
ably large, and the area to be searched is small, use of
the circular search technique is recommended. Under
such favorable conditions, a floating search line is
anchored to the bottom or tied with a bowline around
the bottom of the descent line and is used to sweep the
area. To determine when a 360-degree circle has been
made, a marker line should also be laid out from the
same anchor as the search line. This marker line should
be highly visible and should be numbered with the
radial distance from the anchor.
Where current is noticeable, the marker line should
be placed in the downcurrent position so that the diver
always commences the search from the position having
the least potential for entanglement. When more than
one circle is to be made with tethered divers, the direc-
tion of travel should be changed at the end of each
rotation to prevent the possibility of fouling lines.
The circular search has many modifications, depending
on the number of divers and the thoroughness required.
The standard technique is to station one or more divers
along the search line close to the center of the search
area. The marker line can be used to assign precise
distances. The divers hold the search line and swim in a
circle until they return to the marker line, which ensures
that a full 360 degrees has been covered. The divers
increase the radius for the next search, moving out a
distance that permits good visual coverage. This pro-
cedure is continued until the outermost perimeter is
reached (see Figure 8-7).
When two divers are searching, search effectiveness
can be increased by having one diver hold the circling
line taut and swim the outside perimeter of the area to
be cearched while another diver sweeps back and forth
along the taut circling line. As shown in Figure 8-8A,
the first search will cover a full circle bounded by the
outside diver's path. The search starts and finishes at
the marker line. The search may be extended by the
pattern shown in Figure 8-8B, in which case the cir-
cling line is marked at the point where the outside
diver was previously stationed. The outside diver then
moves to a new position, farther out on the circling
line, and the inside diver sweeps back and forth between
the marker and the outside diver's new position. Posi-
8-12
,, Descending Line
If* — —
, ^ , j
rft. \ Marker Line VwTT^
M7==4s===_-L /AD "■
^V J JSS^==:==V IA Weight
First Search Circle ^-^«_
^>v Search Line
Second Search Circle
Descending Line Anchor
Courtesy Skin Diver Magazine
Figure 8-8
Circular Search Pattern for Two Diver/Searchers
(A)
Previously
Searched
Area
Source: NOAA (1979)
tions may be changed at regular intervals if the divers
become fatigued. Changing positions can be done at
the end of each sweep by having the outside diver hold
NOAA Diving Manual — October 1991
i
Working Dive Procedures
position after moving out one visibility length; the
other diver then moves outside, taking up his or her
position for the next sweep. If the search is conducted
in murky water, using a weighted line may be advisa-
ble; if the lost object is shaped so that it will snag the
moving line, a pull on the line will tell the diver that the
object has been found.
Circular search techniques also may be used for
diving through the ice in waters that have no current,
such as inland lakes and quarries. The following pro-
cedure has been used successfully by the Michigan
State Police Underwater Recovery Unit (1978). When
the ice is covered with snow, a circle is formed in the
snow, using the under-ice entry hole as the center
pivot point. The radius of the circle is determined by
the length of line used to tend the diver. The circle on
the snow indicates the area being searched and the
approximate location of the diver who is searching
under the ice. If the object of the search is not recovered
within the first marked-off area, a second circle that
slightly overlaps the last circle is formed on the sur-
face. This procedure is continued until the complete
area has been searched. The circular pattern involves
only one diver, with a backup diver standing by; before
entering the hole, the diver is secured by one end of the
line, and the other end is held by the tender. The diver
in search of an object will go directly below the hole
and make a search of the immediate area. If the object
is not found directly below, the diver returns to the
surface and describes the underwater conditions. The
diver then proceeds just under the ice to the full length
of the line (approximately 75 feet (25 m)). With the
use of rope signals, the diver begins circling, keeping
the line taut and staying about 6 or 8 inches (15-20 cm)
below the ice. After the diver completes one circle
without encountering any resistance, the tender sig-
nals the diver to descend to the bottom. With the line
taut, the diver begins the first circle on the bottom.
After the diver completes one circle, the tender sig-
nals the diver and pulls him or her to a new location
(within the limits of visibility). The diver commences
searching in a second circle, and the pattern is repeated
until the diver again reaches the hole. If the diver's
physical condition continues to be satisfactory, a sec-
ond hole is cut in the ice and the procedure is repeated;
otherwise, the standby diver takes over and a second
standby diver is designated. Figure 8-9 illustrates this
through-the-ice search technique.
8.2.2 Arc Pattern (Fishtail) Search
The arc pattern search technique is used to perform
an under-ice search in water that has a current. The
October 1991 — NO A A Diving Manual
diver is secured with a descending line in the same
manner described above for a circular search. The
diver descends to the bottom (using a weighted line, if
necessary) and searches the immediate area. After
reporting to the surface, the diver again descends,
going downstream to the extended length of the line.
At this point, the diver begins moving sideways in an
arc-type swing. As the diver circles in the pattern, he
or she will feel some resistance on the upward swing of
the arc. When this occurs, the diver signals the tender,
who pulls in the line the distance of the diver's visibili-
ty. The diver then swings back along the bottom in the
opposite direction until he or she again meets the resist-
ance of the current. The pattern is repeated until the
diver is back at the original starting point. This pattern
can also be used in open water, including rivers and
lakes, and can be conducted from bridges, boats, and
off the shore. The fishtail technique is shown in
Figure 8-10.
A variation on the arc pattern search can be used to
relocate objects in waters with fast-moving currents.
After reaching the general vicinity of the object, the
diver searches large areas of the river bottom by swinging
in widening arcs from a line attached to a heavy pivotal
object, such as an anchor, a stake driven into the bot-
tom, or a creeper. The diver's body can be used as a
rudder, allowing the current to force it across the river
bottom in alternating directions. When initiating the
search, the diver has slack in the line and swims to the
right (or left) until the line becomes taut. The diver
then turns onto his or her right side, grasps the line
with the right hand (both hands are needed in very
strong currents), and stiffens his or her body, turning it
at an oblique angle so that the current sweeps it rapidly
to the left. As the arc slows, a conventional swimming
position is assumed and the diver swims upstream and
shoreward. When swimming against the current becomes
difficult, the diver shifts the line to his or her left hand,
turns on his or her left side, and repeats the procedure
in reverse mode. As progress is made across the bot-
tom, the diver slips backward along the line, gradually
making larger and larger arcs. The size of the arc
depends on current velocity and line length. If the
object of search is not found, the diver returns up the
line to the pivotal point, relocates the anchor, and
begins again.
8.2.3 Jackstay Search Pattern
In the jackstay search pattern, a rectangular search
area is laid out and buoyed (see Figure 8-11 A). Buoy
lines run from the bottom anchor weights to the sur-
face, and a ground line is stretched along the bottom
8-13
Section 8
Figure 8-9
Circular Search Pattern
Through Ice
8-14
Courtesy Clifford Ellis
NOAA Diving Manual — October 1991
Working Dive Procedures
Figure 8-10
Arc (Fishtail) Search Pattern
B. Offshore Search
A. Search in Waters
with Currents
Courtesy Clifford Ellis
between the weights. The divers conducting the search
descend on the buoy line and search along the ground
line, beginning at one of the anchor weights. When the
searching diver reaches the other anchor weight, the
weight is moved in the direction of the search. The
distance the weight is moved depends on visibility; if
visibility is good, the weight is moved the distance the
searching diver can comfortably see as he or she swims
along the line. If visibility is poor, the line is moved
only as far as the searching diver can reach. The searching
diver then swims back toward the first anchor weight
along the ground line (Figure 8-llB). The length of the
ground line determines the area to be covered. The
jackstay search pattern is the most effective search
technique in waters with poor visibility.
8.2.4 Search Using a Tow Bar
The tow-bar partem is similar to the aquaplane method
illustrated in Figure 8-21. It involves the use of a
metal bar 4 to 10 feet (1.2-3.0 m) long that permits two
divers to be towed behind a boat (liveboating). The
area to be searched is marked off with four diving flag
buoys, one at each corner, to form a square or rectan-
gle. The distance between the buoys depends on the
size of the area to be searched and the maneuverability
of the boat. After the buoys are in place, the divers
grasp the tow bar and are pulled parallel to two of the
buoys at a slow rate of speed. After the divers have
passed the last buoy, the boat is brought about through
the center of the square and parallel to the buoys. A
second pass is made along the buoys, one boat width
away. This pattern is continued until the buoyed area
has been searched completely. Two of the buoys can
then be moved to the far side of the second set of buoys,
forming another square. This technique is shown in
Figure 8-12. (The procedures and safety precautions
associated with liveboating are described in Sec-
tion 8.10.1.)
October 1991 — NOAA Diving Manual
8-15
Section 8
Figure 8-11
Jackstay Search Pattern
6 Rectangular Search t
^\ Buoy
Buoy /" \
(
N^Buoy
BuoyV
'
'
'
|.C
\.Buoy
~~~—~rr
^ I
J
Buoy ''^
J |
'
' ;
I
' J
Source: NOAA Diving Pn
jgram
Figure 8-12
Searching Using a Tow Bar
Courtesy Clifford Ellis
8.2.5 Search Without Lines
When conditions are such that search lines cannot
be used, a search can be conducted using an underwa-
ter compass. There are many search patterns that will
ensure maximum coverage; however, simplicity of pat-
tern is important. Divers should use the cardinal points —
N, E, S, W — and the length of a side — one-minute
intervals or 50 kicks — and should turn the same way
each time.
In addition to observing the usual safe diving prac-
tices, divers conducting searches should consider the
following:
• When plastic-coated steel wire is used as a line
marker, a small pair of wire cutters should be
carried to permit escape from entanglement.
• To prevent line fouling when two tethered divers
are used in search patterns, one should be desig-
nated as the inside diver; this diver always remains
under and inside the position of the other tethered
diver.
• When untethered divers are involved, it is advisa-
ble to use contrasting materials for radius, bound-
ary, and distance lines to decrease the possibility
of a diver becoming lost. Polyethylene line pro-
vides a good contrast to plastic-coated stainless
steel wire and is recommended for boundary lines.
8.2.6 Recovery
The method chosen to recover a lost object depends
on its size and weight. Small items can be carried
directly to the surface by the diver, while larger items
require lifting devices (see Section 8.9.1). When a lift
is used, the diver must attach lifting straps and equip-
ment to the item being recovered. A line that is longer
than the depth of the water being searched and that has
a small buoy attached should be carried to the spot to
mark the located object.
8.3 UNDERWATER NAVIGATION
At present, all readily available diver navigation or
positioning systems rely on surface position for their
origin. If navigational or geodetic positions under water
were used, the origin would have to be extrapolated,
which would introduce an additional margin of error.
Recently, acoustic telemetry techniques, which use
microprocessor-controlled methods, have been applied to
diver navigation. These systems can be used to track
divers from the surface and to guide them to particular
locations. Newer methods will allow divers to take the sys-
tem along to monitor their own position (Woodward 1982);
however, dead reckoning is still the most common form
of underwater navigation. This procedure has a long
8-16
NOAA Diving Manual — October 1991
Working Dive Procedures
Figure 8-13
Diver-Held Sonar
history and is used because it is impractical for divers
to carry and operate cumbersome and complex navi-
gation equipment. An acoustic-based navigational system
has recently been developed that uses a person's sensory
ability to differentiate the time-of-arrival of under-
water sounds at the two ears. If a sequence of sounds is
produced along a line, a person interprets them as
deriving from a moving sound source, just as a person
perceives the lights being sequentially turned on and
off on a theater marquee as moving. A diver can quite
accurately perceive the center of a sound array and
swim to it from distances as great as 1000 feet (303 m).
This technique can be used in habitat operations and
when diving in murky water.
Sonar is another method of increasing a diver's abil-
ity to navigate under water. Divers may find carrying a
compact active sonar useful for avoiding obstacles.
Underwater diver-held sonars have been used with
some success for years (Figure 8-13). The effectiveness of
sonar operations is related directly to the level of a
diver's training; many hours of listening to audio tones
in a headset are required before a diver can "read" the
tones. When using diver-held sonar, the diver makes a
slow 360-degree rotation until the object is located
and then notes the compass heading. The active range
of most diver-held sonars is about 600 feet (182 m). In
the passive or listening mode, pingers or beacons some-
times can be detected as far away as 3000 feet (909 m).
For shorter ranges, there are units that allow a diver
to point the device ahead and obtain a direct readout
in feet for distances up to 99 feet (30 m) with a
reported accuracy of 6 inches (15.2 cm) (Hall 1982).
Acoustic pingers are battery-operated devices that,
when activated, emit a high-frequency signal. Pingers
are the companion units to pinger locators; locators are
used in the passive mode. Pingers can be attached to
any underwater structure, including:
• Habitats;
• Submersibles;
• Pipelines;
• Wellheads;
• Hydrophone arrays;
• Wrecks; and
• Scientific instruments.
Divers have had some success in locating underwa-
ter structures with acoustic beacons that emit signals
within the audible frequency range. In some cases,
single beacons have been as accurate as dead reckon-
ing; however, the sequentially activated acoustic array
system has been shown to be superior to either pingers
or dead reckoning.
Courtesy Dukane Corporation
For relatively short underwater excursions, howev-
er, the compass, watch, and depth gauge are still the
simplest navigational devices available. Once a com-
pass bearing has been ascertained, the diver swims
along the line of bearing, holding the compass in a
horizontal position in front of him or her. Progress is
timed with the watch, and the depth is noted. To swim
a good compass course, the axis of the compass must be
parallel to the direction of travel. A simple and reliable
method of achieving this is for divers to extend the arm
that does not have the compass on it in front of them
and then to grasp this arm with the other hand (i.e., the
arm to which the compass is strapped) (Figure 8-14).
Swimming with the arms in this position helps divers to
follow the desired course and, in low visibility, pre-
vents them from colliding with objects. Practicing on
land by walking off compass courses and returning to
the starting point helps to train divers for underwater
navigation. Because the accuracy of a compass is affected
by the presence of steel tanks, it is advisable to deter-
mine a compass's deviation in a pool with a second
diver swimming alongside and varying the course. A
depth gauge or watch should not be worn on the same
arm as the compass because it may cause a deviation in
compass heading.
A diver can calculate his or her transit time by using
the following formula to estimate distance:
D
T = -
S
where
T = transit time in minutes
D = distance to be covered in feet
S = speed of advance in feet per minute.
October 1991 — NOAA Diving Manual
8-17
Section 8
Figure 8-14
Using a Compass for Navigation
A diver can estimate speed by swimming at a pace
easily maintained over a known distance and slightly
modifying the formula to:
D
S = -
T
For example, a diver traversing a 1000-foot (305 m)
course in 10 minutes is swimming at a speed of 100 feet
(30.5 m) per minute, or approximately 1 nautical
mile (1.85 km) per hour.
Some underwater topographical navigation aids that
can be used are underwater landmarks (and turns made
with respect to them), the direction of wave ripples in
the sand, and the direction of the current (if it is known
that the current will not change during the dive). Some
areas require the use of a transect line because they
lack distinct bottom features. Divers often use the
increase in pressure against their ears and masks or
changes in the sound of exhaust bubbles to identify
changes in depth.
8.4 UNDERWATER TOOLS
A fundamental aspect of accomplishing work under
water is the selection of proper tools and equipment. In
all operations, the relative advantages and disadvan-
tages of power tools and hand tools must be considered.
The amount of effort that will have to be expended is
an important consideration in underwater work, and
power tools can reduce the amount of physical exertion
needed. Having to supply tools with power and to trans-
port them, however, may be a substantial disadvantage.
The performance of divers under water is degraded
by several factors, including water resistance, diver
buoyancy, equipment bulk, the confined space envi-
ronment, time limitations, visibility restrictions, and a
diver's inability to provide a proper amount of reaction
force without adequate staging, hand grips, or body
harnesses. A diver's performance may therefore decrease
significantly compared with his or her performance on
land. Even a relatively simple task like driving a nail
can be difficult because of limited visibility, water
viscosity, and other environmental factors; however,
some tasks are easier to accomplish under water because
of the diver's ability to move easily in three dimen-
sions. Because diver safety is a primary consideration
in any underwater operation, hazards such as electric
shock, excessive noise, and other potential causes of
injury must be taken into account when selecting under-
water tools.
Table 8-2 lists some common tools used under water,
along with their sources of power and available acces-
Photo by Bonnie J. Cardone
sories. Most pneumatic and hydraulic tools can be
adapted for underwater use. The information supplied
by the tool's manufacturer contains detailed use specifi-
cations that should be observed faithfully.
8.4.1 Hand Tools
Almost all standard hand tools can be used under
water. Screwdrivers are generally available in three
configurations: the machine (or straight-slotted) type,
the phillips type, and the alien type. Of the three, the
alien screwdriver is easiest for a diver to use, because
only torque is required to operate it and the linear
reaction force necessary is minimum. Also, the alien
type provides a longer lever arm. The other types of
screwdriver have a tendency to slip out of the screw
head or to damage the screw by twisting. A single
multipurpose tool can be made by welding a screw-
driver blade and a pair of pliers to an adjustable wrench.
When using a hand saw under water, it is difficult to
follow a straight line. An added complication is the
tendency of the blade to flex, which increases the like-
lihood that the blade will break. Because it is easier for
8-18
NOAA Diving Manual — October 1991
Working Dive Procedures
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October 1991 — NOAA Diving Manual
8-19
Section 8
a diver to pull than push under water, it is useful to put
the blade in the saw so that the sawteeth are oriented
toward the diver and the cut is made on the draw.
A 2- to 4-lb short-handled hammer is a commonly
used underwater tool. Because considerably more effort is
required to swing a hammer under water than on land,
it is easier to develop force by pounding with the heavy
weight of a sledge hammer than by swinging and hit-
ting with a lighter hammer.
Because it is easy to lose or drop tools under water,
they usually are carried to the work site in a canvas bag
and are then attached to the diver's belt with a line.
They also can be attached to a descending line with a
shackle and be slid down this line to the job site from
the surface. Tasks involving grinding, chipping, pound-
ing, or reaming with hand equipment are arduous and
time consuming, and the use of hand tools for these
tasks is not practical unless the task is small. To pro-
tect hand tools after use, they should be rinsed with
fresh water and lubricated with a protective water-
displacing lubricant.
8.4.2 Pneumatic Tools
Although pneumatic tools are rarely designed spe-
cifically for use under water, they need little, if any,
alteration to be used in this medium. According to
Hackman and Caudy (1981), the power available in air
motors ranges from 1/8 to 25 hp, and loaded speeds
range from 40 to 6000 rpm; some of these tools have
even higher speeds. Most pneumatic tools require 90
psig of air pressure to operate, and they exhaust into
the water. A disadvantage of these tools is that they
exhaust bubbles that may disturb divers or impair
their visibility under water. In addition, the amount of
pressure available for power decreases at depth. Pneu-
matic tools can be modified to include a hose attach-
ment on the exhaust that is larger in diameter than the
supply hose. Often, the exhaust hose is routed back to
the surface, where it discharges to atmospheric pres-
sure. Even with these modifications, surface-supplied
pneumatic power can be used only to depths of 100 to
150 feet (30.5-45.7 m). Although closed-circuit pneu-
matic tools would not be as wasteful of energy at depth
as open-circuit tools, they have not been developed
because the entire system would have to be pressurized
or the tool would have to be designed to withstand
ambient water pressure. The extensive maintenance
requirements of pneumatic tools can be minimized by
using in-line oilers to meter oil automatically into the
air supply hose. After each day's diving, oil should be
poured into the air inlet of the tool until it completely
8-20
fills the motor section; the tool should then be sub-
merged in an oil bath before being turned on once to
displace any water trapped in the tool.
8.4.3 Hydraulic Tools
Hydraulic tools are the most popular kind of tool
with working divers because they provide consistent
closed-cycle power, are safer to use under water, have
little or no depth limitation, are much lighter per unit
of power output, do not produce bubbles that obscure
the diver's vision, and require relatively little mainte-
nance. As with pneumatic motors, hydraulic systems
have the capability to start and stop rapidly, and they
can be operated at different speeds.
Tools such as drills (Figure 8- 15 A), impact wrenches
(Figure 8-1 5B), chain saws, disc grinders (Figure 8-1 5C),
and cable or pipe cutters usually are modified versions
of hydraulic tools designed for use on land. To convert
tools for underwater use, different seals are used,
internal voids are compensated to withstand ambient
pressure, external surfaces are painted or coated with
a corrosion inhibitor, and dissimilar metals are insulated
from each other.
To facilitate the field use of hydraulic tools in areas
where hydraulic oil is not readily available or where
environmental restrictions prohibit the discharge of
oil, hydraulic tool systems are being developed that
use seawater as the working fluid in place of oil. The
Navy has supported a program, called the "Multi Func-
tion Tool System," that involves the development of a
seawater hydraulic grinder, band saw, impact wrench,
and rock drill specifically for underwater use.
Hydraulic tools require a power source at the sur-
face or a submersible electrohydraulic power source
that can be located at the work site near the diver.
These power sources are compensated to operate at all
depths but require built-in batteries or an electrical
umbilical from the surface to run the motor. The tools
normally operate at pressures from 1000 psi to 3000 psi.
To use them, divers usually work standing on the bottom
or on some structure. When working with these tools on
the side of a structure or in the midwater column, a
diver can use harnesses or a diver's stage for support.
The U.S. Navy has adapted and developed a variety
of diver-operated hydraulic tools for construction and
salvage work. These tools include:
1. An abrasive saw (2000 psi, 6-14 gpm, 10-in. dia.
by 1/8-in. thick blade);
2. A grinder (2000 psi, 11 gpm, used with discs,
cups, or wire brush);
NOAA Diving Manual — October 1991
Working Dive Procedures
Figure 8-15
Underwater Hydraulic Tools
Courtesy Stanley Hydraulic Tools
3. A come-along (1500 psi, 2000 lb. force, moves
cable 1.5 in. per stroke, used as a rigging aid);
4. A hurst tool (input of 5000 psi and .07 gpm, jaws
of tool open and close with force of 6 tons through
a distance of 32 inches);
5. Impact wrenches (2000 psi, 5 gpm, used for dril-
ling, tapping, or for make/break of nuts and bolts);
6. Linear actuators (10,000 psi rams, 8 ton pull-
cylinders, 10,000 psi cutters or 2 1/2 in. wire
rope, rebars, or splitting nuts);
7. A pump (2000 psi, 5 gpm hydraulic fluid; 100 psi,
400 gpm water flow, used for jetting, washing,
and dredging); and
8. Hose reels and different hydraulic power supplies.
(An excellent source of information on the operation
and maintenance of the Navy's hydraulic tool systems
isNAVSEA 1982.)
Some hydraulic tools have been designed solely for
underwater use. There is, for example, a hydraulic
hammer that operates on 2000 psi, 0.5 to 3.0 gpm, and
develops a 40-foot-pound force per blow; output speed
ranges from 1 to 300 blows per minute. The unique
design uses compressibility of the hydraulic fluid to
generate and store the impact energy.
October 1991 — NOAA Diving Manual
Hydraulic tools that minimize diver fatigue and dis-
comfort should be selected. Most tools can be recon-
figured or redesigned to increase diver comfort. More
attention should be given to underwater human engi-
neering principles in the design of new tools. Areas
where progress could be made include weight reduc-
tion, special grips and triggers, placement of handles
at the center of gravity or wherever they will best
counteract torque, and reduction of vibration and reac-
tion forces.
Hydraulic tools are easy to maintain. They should be
rinsed thoroughly with fresh water after each use and
then be sprayed with a protective lubricant such as
WD-40.
8.4.4 Electric Tools
Underwater tools that operate by electric power have
been designed, developed, and manufactured, but they
are seldom used. The AC motor, stator, and control
electronics of such tools are potted in epoxy, and the
motor is water cooled and water lubricated. Electric
tools require only a small umbilical, have no depth
limitation, and are reasonably light in weight. Although
ground-fault detector circuitry is provided, the fear of
electric shock persists, and most divers consequently
prefer to use hydraulic tools despite their greater weight
and support equipment requirements.
8.4.5 Power Velocity Tools
Power velocity tools are actuated by the firing of an
explosive cartridge, which increases the pressure behind a
piston to accelerate a stud or a cutter into the work
piece (Figure 8-16). Power velocity tools are used to
attach padeyes, studs, and hollow penetrations in plate
steel. Different configurations are used to cut cable,
rebar, hydraulic/electrical umbilicals, and to drive an
impact socket for loosening jammed nuts. Studs are
available to penetrate steel that is at least 1/4-inch
thick (0.64 cm). The cutters can sever 1.5-inch (3.8 cm)
in diameter cables or 2-inch (5.1 cm) in diameter
composite umbilicals.
WARNING
Only Properly Trained Personnel May Han-
dle Explosive Cartridges. Trained Divers Also
Should Use These Tools Only When The Proper
Safety Precautions Have Been Taken
Power velocity tools are well suited to most under-
water work. Their weight is comparable to that of
8-21
Section 8
Figure 8-16
Explosive Hole Punch
Figure 8-17
Oxy-Arc Torch
Courtesy Broco, Inc.
Courtesy Battelle-Columbus Laboratories
hydraulic tools, but they require no umbilical or power
line. Some models of underwater stud guns feature
barrels that can be replaced easily by the diver. The
heavier duty models, as well as most cutters, require
that reloading be performed on the surface.
8.4.6 Cutting and Welding Tools
Cutting and welding are often required both in sea-
water and in dry underwater enclosures or habitats.
Since habitat welding involves techniques and tools
similar to those of atmospheric welding, this manual
addresses only cutting and welding tools that are used
in seawater. Underwater cutting and welding processes
emit toxic gases that rise to the surface and, since they
are heavier than air, collect in any low-lying confined
areas. Ventilation during underwater cutting and welding
is thus essential to protect both divers and surface
personnel.
The most popular cutting torch is oxy-arc (Fig-
ure 8-17); the process is learned with less training than
oxy-hydrogen, oxy-acetylene, or shielded metal arc
cutting. The oxy-arc process uses electric power to
heat the work piece to ignition temperature; a jet of
oxygen is then directed at the heated spot and the
metal burns or oxidizes very rapidly. Electric current
is not required for oxy-hydrogen, but an air hose is
required to fill a shield cup around the tip to stabilize
the flame and to hold water away from the area of
8-22
metal being heated. The metal is heated to ignition
temperature by a hydrogen/oxygen flame, and pure
oxygen is then directed at the heated spot to start the
cutting action. Although acetylene also has been used
as a fuel gas for cutting, it is considered unsafe to use
at depths greater than 30 feet (9.1 m). Shielded metal-
arc cutting is a process in which metal is severed sim-
ply by melting and physically pushing the metal out of
the kerf. An electric arc is formed between the elec-
trode and the work piece to provide the heat for melting.
The process is used in situations where no oxygen is
available. Some believe that shielded metal-arc cut-
ting is superior to oxygen cutting on steel plates less
than 1/4 inch (0.64 cm) thick or when cutting brass,
copper, or copper-based alloys. Oxy-arc is used to cut
steel up to 2 inches (5.1 cm) thick.
The most widely used underwater welding process is
shielded metal-arc welding. The weld is produced by
heating with an electric arc between a flux-covered
metal electrode and the work piece. The heat developed
by the arc causes the base metal parts, the core wire of
the stinger, and some of the flux covering to melt.
Other constituents of the flux decompose to gases,
which shield the molten metals somewhat from con-
tamination. When welding under water, technique is
important and special training is required. Generally,
underwater welds are not as strong as surface welds
because of water quench and contamination. Also, it is
vitally important that the diver be aware at all times of
the severe shock hazards associated with electric cut-
ting and welding processes. Metal helmets must be
insulated.
NOAA Diving Manual — October 1991
Working Dive Procedures
WARNING
Diver Training and Experience Are Essential
in Underwater Cutting or Welding
8.5 MAINTENANCE AND REPAIR TASKS
Maintaining and repairing equipment, structures, and
instruments under water requires skill and an under-
standing of the work to be done. In addition, underwa-
ter maintenance should be performed only when envi-
ronmental conditions are acceptable.
If practical, divers should practice underwater tasks
in shallow water before attempting them in deep water.
The time that will be needed to accomplish the task
must be known to enable the diver to complete the task
(or a major portion of it) within the constraints of the
air supply. For strenuous tasks, the work should be
divided into subtasks and several divers should take
turns carrying them out.
To accomplish underwater work, four task phases
are involved:
• Inspection of the work site and determination of
the condition of the equipment that needs mainte-
nance or repair;
• Selection of appropriate tools;
• Performance of the repair or maintenance task;
and
• Reinspection to ensure that the work has been
accomplished successfully.
Most underwater maintenance and repair tasks that
a diver is asked to perform are associated with the
inspection and repair of a ship's rudder, propeller, sea
chest, or cathodic protection system. When a diver is
working over the side of a ship to perform a mainte-
nance task, the ship's propeller should be locked out
and the rudder should be held in static position. The
appropriate international code flag should be hoisted.
Divers should be careful to avoid skin contact with
the hull of the ship on which they are working, because
toxic paints are often used on the hull to inhibit marine
growth (barnacles, algae). These paints retain their
toxic qualities for months after the freshly painted
ship has been returned to the water.
Maintenance and repair tasks can be accomplished
more easily if a restraining system is used. Such a
system can be as simple as a line for the diver to hold
onto that is attached to a convenient point or as elabo-
rate as a jacket with magnets or suction cups that
attach to a shear plate.
8.6 INSTRUMENT IMPLANTATION
The proper implantation of scientific instruments is
important to the success of underwater scientific investi-
gations. Instruments that are implanted on the sea
bottom include lights, cameras, positioning stakes, radi-
ometers, recording current meters, thermistors, oxy-
gen sensors, and acoustical devices. Factors affecting
the success of implantation are:
• The instrument's size and weight, mounting dimen-
sions, fragility, and attachment points
• The available power supply and instrument read-
out cables, or (if self-contained) the frequency
with which the instrument's batteries must be
changed or the instrument must be serviced or
replaced
• The alignment of the instrument in position, its
height above the bottom, and its sensitivity to
misalignment
• Bottom conditions, the bearing strength of the
bottom, anticipated currents, and the type of marine
life
• The precise markings of instrument location and
the methods used for recovery at completion of the
mission.
The size and weight of the instrument and its physi-
cal dimensions and fragility affect the type of anchor
used and the techniques chosen to move the instrument
to the site. For small instruments, a concrete block
may be an appropriate anchor. The blocks can be
predrilled, fitted with fasteners on the surface, and
moved to the site as a unit and positioned. In other
cases, the concrete block and instrument can be moved
to the site separately, and a diver can then position and
align the instrument in the water. A concrete block
anchor can be lowered directly into position using a
winch, or it may be fitted with flotation devices and
guided into position by a diver, who removes the flota-
tion device when the anchor is in position.
For large instrument packages, anchors can be made
of metal piles that are driven into the bottom by a diver
using a sledgehammer or pneumatic impact hammer.
Steel pilings create magnetic anomalies that can affect
instrument readings; instruments should therefore be
used only after the effect of the pilings on the instru-
ment's functioning has been calibrated. Pilings may be
grouted in place with concrete supplied from the sur-
face. Embedment anchors can be used to stabilize an
instrument installation and can be driven into the bot-
tom to secure the lines. Chains or wires equipped with
turnbuckles can be run over the instrument package
between anchors to secure the installation further. The
October 1991 — NOAA Diving Manual
8-23
Section 8
foundation package should be designed to accept the
instrument package easily so that it is as easy as possi-
ble for the diver to attach the package. When the
foundation is complete, a line or lines should be run to
the surface to assist in lowering and guiding the instru-
ment into place.
Many underwater instruments require outside power to
operate and to transmit data to outside receivers. Dur-
ing the installation of instrument cables, a diver usu-
ally is required to anchor the cable at various points
along the cable run. The first point of anchor should be
near the instrument package. To reduce the possibility
that the cable will topple the instrument or that move-
ment of either the cable or instrument will break the
cable connection, the diver should allow a loop (called
a bight) of extra cable between the first anchor and the
instrument. The diver should guide the instrument
cable around any rocks or bottom debris that might
abrade the cable covering. Anchors should be placed
at frequent intervals along the length of the cable,
wherever the cable turns, and on each side of the cable
where it runs over an outcropping or rise in the bottom.
Cable anchors can either be simple weights attached to
the cable or special embedment anchors.
The alignment of the foundation is important to
successful implantation. A simple technique to achieve
alignment is to drive a nonferrous stake into the bot-
tom that has a nonferrous wire or line attached and
then to hang a compass from the line or wire. A second
nonferrous stake is then driven into the bottom when
the compass indicates that the alignment is correct.
The two stakes and the attached line then act as the
reference point for aligning the foundation or instru-
ment. A tape is used to translate measurements from
the reference stakes and line to the foundation or the
instrument.
Before selecting a location for an instrument, bot-
tom conditions should be analyzed to identify the appro-
priate foundation. The instrument site should be
reinspected at frequent intervals to monitor the condi-
tion of the instrument and to clear away sediment or
ma-ine growth that may affect instrument readings.
Unmanned instrumentation is increasingly used for
long-term data-gathering and environmental monitoring
tasks. Because many unmanned instruments are self-
contained and expensive, they must be equipped with
reliable relocation devices. Although surface or sub-
surface buoys (used in combination with LORAN-C
or satellite navigation systems) are the most common
relocation devices, at least for short-term implanta-
tion, these buoys are subject to vandalism, fouling in
ship propellors, and accidental release. Many users
therefore equip these instruments with automatic pinger
devices in addition to marker buoys (see Section 8.3).
If a pinger-equipped instrument is believed to be
lost in the vicinity of implantation, a surface receiver
unit operated from a boat can guide divers to the
approximate location; they can then descend and search
with a hand-held locator unit. This technique works
especially well in murky water when the divers are
surface supplied and use liveboating techniques (see
Section 8.10.1), particularly if the pinger is weak and a
long search is necessary.
8.7 HYDROGRAPHIC SUPPORT
In hydrographic operations, divers can be used to con-
firm the existence and/or location of hazards to navi-
gation, locate and measure least depths, and resolve
any sounding discrepancies identified by different
surface-based measurement techniques. When using
divers for this type of work, it is essential to consider
the skills of the divers, water conditions, the nature of
the work, special equipment requirements, and the
availability of diver support. Because hydrographic
operations are frequently conducted in open water, it is
important to mark the dive site using buoys, electronic
pingers, or fathometers; this precaution becomes increas-
ingly important under conditions of reduced visibility
and high currents.
8.7.1 Hazards to Navigation
A significant portion of hydrographic support div-
ing is conducted to identify hazards to navigation.
Once the general location of a navigational hazard has
been identified, its precise location can be determined
using the search techniques described in Section 8.2.
When the object has been found, it should be marked
with a taut-line buoy and its geographic position should
be noted. If the depth is shallower than about 50 feet
(15.2 m), a lead line depth should be recorded, along
with the time of notation.
Diving operations that are designed to prove that no
navigational hazard exists in a particular area are
extremely time consuming and require painstaking doc-
umentation of search procedures and location. The
reported location and geographic position of the haz-
ard should be marked precisely; a taut-line buoy should
be used to mark the search control point. Any time the
control point is moved, the move should be documented
and the geographic position of the new control point
should be noted. Documentation of the search should
include the geographic position of control points, the
type of search, the equipment used, water conditions,
8-24
NOAA Diving Manual — October 1991
Working Dive Procedures
and problems encountered, what was found or not found,
and a statement describing the area that has been
searched and any area that may have been missed.
8.7.2 Locating and Measuring Least Depths
Divers can be used to determine least depths accu-
rately, especially in such areas as rocky shoals, coral
reefs, and wreck sites. After the general location to be
studied has been identified, a diver is sent down to
mark precisely the least depth by tying off a line on the
bottom so that a buoy floats directly overhead. Care
must be taken to ensure that the lead line is plumb and
that the time of marking is recorded. A taut-line buoy
can be used to mark the geographic position of the
least depth so that it can be noted and recorded by
surface personnel.
8.7.3 Resolving Sounding Discrepancies
When measurements of undersea features are dis-
crepant, divers can be used to inspect the site, resolve
the discrepancies, and mark the site correctly. Dis-
crepant measurements are most likely to occur in areas
such as rocky substrates, faulted or volcanic bottoms,
and reefs.
8.8 WIRE DRAGGING
Wire dragging is a method of ensuring that surface
ships can pass through an area safely. The method
involves deploying a wire between two ships and hold-
ing it at depth with weights ranging from 50 to
250 pounds (22.7-113.4 kg). The objective of this proce-
dure is to tow the wire in such a manner that hydrody-
namic forces induce an arc-shaped curve. As the ships
move through the water, the wire will snag on obstruc-
tions protruding above the depth of the drag. Divers
supporting wire-dragging operations are used to identify:
• The objects on which the wire hangs;
• The least depth over the obstruction; and
• The highest protrusion that could be caught from
any direction.
Divers also can identify underwater features that pose
a hazard to fishing nets and trawling or ground tackle
and assist in the removal of minor obstructions. Another
task performed by divers is assessing the areal extent
of wreckage. If the least depth cannot be determined
accurately, the approximate depth needed for clear-
ance is sought.
Divers need to exercise extreme caution when work-
ing around wire drag hangs because, in addition to the
hazards associated with any wreck diving operation,
the wire itself poses a hazard. For example, if the wire
slips on an obstruction, it could pin a diver; if the
strands of the wire are broken, the wire can cut a diver
severely; and if a diver holds the wire and it pulls loose,
it can sever the diver's fingers.
When an underwater obstruction needs to be inves-
tigated, the support boat must be tied off to the buoy
nearest the obstruction. After agreeing on all proce-
dures, the divers swim to the buoy and descend to the
bottom wire. Depth gauges are checked, and the depth
of the obstruction is noted on a slate.
Because of forces acting on both the wire and the
upright to the buoy, the depth at the weight can vary
from its setting by as much as 10 feet (3 m). Once on
the bottom, the divers proceed hand-over-hand along
the wire, one behind the other, taking care to stay
outside the bight of the wire. This may be difficult
because most drags are run with the current, which
tends to push the diver into the bight. The recommended
procedure is to "crab" into the current, making every
effort to stay as much above the wire as possible.
WARNING
Divers Must Be Extremely Careful When Work-
ing Inside the Bight of a Ground Wire
After arriving at the obstruction, wire depth is
recorded. The divers then try to find the least depth of
the obstruction; this procedure requires the divers to
leave the wire. If the obstruction is not substantial, the
divers should be several feet above the obstruction's
depth when they enter the bight. Once the least depth
point is found, the divers record the depth and deter-
mine whether the high point could cause the ship to
hang at any point. If the object is intact or is a candi-
date for recovery, the divers select a suitable place to
tie off a small buoy. The buoy must be tied off inside
the bight so as not to be torn away when the drag wire is
recovered.
The depth information recorded is verified by a
surface-tended pneumatic pressure gauge. Because
the equipment involved is cumbersome, this technique
is rarely used during the initial investigation. In rela-
tively calm seas and slack current, a lead line may be
used to verify depth information.
Because divers following a wire do so in single file, it
is easy for one diver to lose track of his or her buddy.
A buddy-check should therefore be carried out every
50 feet (15.2 m); this procedure also may prevent diver
entanglement when there is poor visibility.
October 1991 — NOAA Diving Manual
8-25
Section 8
Figure 8-18
Salvaging an Anchor
With Lift Bags
NOTE
Wire-drag support diving should be done
only by experienced divers who are well
trained in the techniques and fully aware
of the hazards involved.
8.9 SALVAGE
Salvage of a ship or craft, its cargo, or its equipment
requires a knowledge both of the technical aspects of
recovery and the legal aspects of ownership of the
salved items and claims for salvage. A salvor who
recovers a ship or craft or its cargo without prior agree-
ment with the owner must file a claim in the United
States District Court nearest to the port in which the
salved items are landed.
Salvage techniques vary considerably with the size,
value, and condition of the item to be salved, the depth
of the object and seafloor conditions, and the equip-
ment available to conduct the salvage. Salvage tech-
niques that are used commonly are direct lifts using a
winch or crane, floating lifts using a device to compen-
sate for the negative buoyancy of the ship or craft, and
repairing and restoring the inherent buoyancy of the
salved object itself.
Individual divers often salvage instruments or instru-
ment arrays, anchors, or other small structures. In the
majority of these cases, the diver simply carries the
item to the surface. In other situations, the diver atta-
ches a flotation device (Figure 8-18) or, for heavy
items, a line or wire that will facilitate a direct lift to
the surface.
In some salvage operations such as archeological
excavations, it may be necessary to clear bottom sedi-
ment from around the item before it can be recovered.
This procedure is necessary to ensure that the item is
free of entanglement. A water jet or air lift commonly
is used to clear away entangling debris (see Sec-
tion 9.12.2).
When working with heavy or overhead items with
cables, lines, or chains under tension, divers must develop
a sixth sense for safety. Divers should avoid positioning
themselves or their umbilicals under heavy objects
that might fall or placing themselves above lines that
are under tension. The buoyancy or the weight of water
displaced from a container by the compressed air nec-
essary to raise an object is equal to the weight of the
object in water plus the weight of the container. It is
important to remember that:
• The container should be vented to prevent excess
air from rupturing it;
• The air will expand if the object is raised from the
bottom before all the water has been displaced
8-26
Photo by Geri Murphy
from the container; this will displace more water
and may increase the speed of ascent to an uncon-
trollable rate;
• The weight of the object in water is reduced by an
amount equal to the weight of the water it displaces.
8.9.1 Lifting Devices
Many objects can be used as lifting devices, includ-
ing a trash can or bucket inverted and tied to the
object, a plastic bag placed in a net bag, a 55-gallon oil
drum, or a commercially available lift bag (shown in
Figure 8-18). If the object is lying on a soft bottom, it
may be necessary to break the suction effect of the
mud by using high-pressure hoses or by rocking the
object back and forth; a force equal to 10 times the
weight of the object may be necessary to break it free.
Raising and lowering can be accomplished with
commercially available lift bags of various sizes and
lifting capacities or with ordinary automobile tire inner
tubes. One regular-sized inner tube will lift about
100 pounds (45.4 kg). The tube or tubes are rigged with
a short loop or rope holding them together and with the
valves pointing toward the bottom. (The valve caps
and cores must be removed.) A rope loop is attached to
the object to be lifted and is then pulled down as close
to the object as possible, because inner tubes have a
tendency to stretch to about twice their original length
before lifting starts. An ordinary shop air nozzle with a
spring-loaded trigger is attached to a short length of
low-pressure air hose and is then plugged into the
low-pressure port of a single-hose regulator first-stage
NOAA Diving Manual — October 1991
Working Dive Procedures
mechanism. This device is attached to a separate air
cylinder for transport to the work site. The end of the
nozzle is inserted into the tire valve opening and pushed so
that air will not escape. The tube fills, and the object
rises to the surface. Care must be taken to leave the
valve open, because the expanding air on surfacing
could burst a closed system. With practice, objects can
be raised part-way to the surface and moved under
kelp canopies, etc., into clear water, where they can be
surfaced and towed. Divers using this technique should
try to accompany the object to the surface and should
not stay on the bottom or in any way expose themselves
to the drop or ascent path of the object. This technique
is especially useful to biologists lifting heavy bags of
specimens.
Although the innertube method works, commercially
available lift bags are preferred. These bags are designed
for heavy duty use, come in a variety of sizes ranging
from 100 to 20,000 lbs (45.4-9080 kg) in lifting capacity,
and have built-in overpressure relief and/or dump
valves. They also are lightweight and readily trans-
portable, e.g., a bag capable of lifting 100 lbs (45.4 kg)
weighs only 6 lbs (2.7 kg), and a 1/2-ton-capacity bag
weighs only 14 lbs (6.4 kg).
When lifting an object, the lift bag should be inflated
slowly from a spare scuba cylinder or other air source.
Inflation should cease as soon as the object begins to
lift off the bottom. Because air expands as it rises, the
rate of ascent may increase rapidly, causing the diver
to lose control. Loss of control is dangerous, and it also
can cause the bag to tip over when it reaches the
surface, spilling the air out and sending the object
back to the bottom. The bag's dump valve, therefore,
should be used carefully to control ascent.
WARNING
Do Not Use Your Buoyancy Compensator as
a Lifting Device While Wearing the Compen-
sator
In addition to the type of lift bags shown in Fig-
ure 8-18, special computer-controlled lifting systems
have been developed for large salvage jobs (Kail 1984).
These systems are relatively insensitive to surface
weather conditions and permit both ascent and descent
velocities to be held constant even for loads as great as
15 tons. Such systems can be used for emplacing and
retrieving heavy instrumentation packages as well as
for salvage.
If the object cannot be lifted to the surface directly
by winching or lift devices, the rise of the tide can be
used if a large vessel or pontoon is available. At low
tide, lines are connected tautly to the object and the
surface platform; as the tide rises, the load rises with
it.
Every salvage project must be planned and executed
individually. Novice divers should not attempt under-
water salvage tasks for which they are not properly
trained or equipped.
8.9.2 Air Lifts
An air lift is used to lift mixtures of water, grain,
sand, mud, and similar materials from the holds of
ships during salvage operations. In some cases of
stranding, an air lift may be used to clear away sand
and mud from the side of the vessel (Figure 9-39);
An air lift works on the pressure-differential princi-
ple. Air is introduced into the lower end of a partially
submerged pipe. The combining of air bubbles with the
liquid in the pipe forms a mixture that is less dense
than the liquid outside the pipe. The lighter density
results in less head pressure inside the pipe than out-
side, which causes the mixture to rise in the pipe. The
amount of liquid lifted depends on the size of the air
lift, submergence of the pipe, air pressure and volume
used, and the discharge head.
An air lift consists of a discharge pipe and a foot
piece or air chamber. The size of the discharge pipe
ranges from approximately 3 to 14 inches (7.6-35.6 cm)
in diameter, depending on the amount of work to be
done and the service intended. The air chamber
should be located approximately 20 to 30 inches
(50.1-76.2 cm) from the end of the pipe. Table 8-3
may be used as a guide in selecting the size of dis-
charge pipe and air line, taking into consideration the
air available and the job to be done.
An air lift operates as follows: the discharge pipe is
submerged in the mixture to be lifted to a depth of
approximately 50 to 70 percent of the total length of
the pipe. The air is turned on, and the lifting operation
commences almost immediately. Occasionally, consider-
able experimentation is necessary to determine the
amount of air required to operate the lift efficiently.
The use of air lifts in archeological excavation is
described in Section 9.12.2.
8.10 DIVING FROM AN UNANCHORED
PLATFORM
Diving from an unanchored barge, small boat, or
vessel can be an efficient method of covering a large
October 1991 — NOAA Diving Manual
8-27
Table 8-3
Selection Guide For Discharge Pipe and Air Line
Section 8
Diameter of
Diameter of Compressed
Gallons per
Cubic Feel: of
Pipe, inches
Air
Line, inches
Minute
Air
3
.50
50-
-75
15-40
4
.75
90-
-150
20-65
6
1.25
210-
-450
50-200
10
2.00
600-
-900
150-400
Source:
NOAA
(1979)
area for search or survey purposes. When a diver is
towed from a boat that is under way, the technique is
referred to as liveboating. When a boat accompanies the
diver but the diver is not attached to the boat and is
being propelled by current alone, the technique is called
drift diving. There are procedures and safety precau-
tions that apply to both kinds of diving; these are
described below.
WARNING
When Liveboating or Drift Diving, the Engines
of Both the Small Boat and Large Vessel (if
Any) Should Be in Neutral When the Divers
Are Close to the Boat or Are Entering or Leav-
ing the Water
8.10.1 Liveboating
Some underwater tasks require great distances to be
covered in a minimum amount of time. These tasks
include inspecting a pipeline, surveying a habitat site,
searching for a lost instrument, observing fish popula-
tions over a wide area, or any number of similar opera-
tions. Free-swimming divers are inefficient at carry-
ing out such tasks, and quicker methods of search or
survey are needed. Devices such as swimmer propul-
sion units, wet subs, or towed sleds may be used to
increase diver efficiency.
Towing a diver behind a small boat is another method
of searching a large area. This technique is called diver
towing; the divers hold onto a line attached to the boat
and vary their depth according to the contour of the
bottom, which allows them to make a closeup search of
the area over which the boat is traveling.
WARNING
Liveboat Divers Should Be Careful to Moni-
tor and Control Their Depth to Avoid Devel-
oping an Embolism
8-28
When liveboating is used, the following safety pre-
cautions are recommended:
• If possible, the boat should be equipped with a "jet
dive" propulsion system, which has no rudder or
propeller.
• If the boat is equipped with a propeller, a propeller
cage or shroud should be fabricated to protect the
divers.
• A communications system should be set up between
the diver and the boat, with signals agreed on and
practiced prior to diving. A line separate from the
tow or descent line may be employed.
• Divers being towed should carry signal devices
(whistle, flare, etc.) especially in adverse weather
conditions such as fog, in case they become separated
from the boat and tow line.
• Unless there is danger of entanglement, the divers
should carry a surface float to assist the boat crew
in tracking them. The float line also can be used
for signaling the divers while they are on the bottom.
• If diving with scuba, two divers should be towed
together.
• If diving with surface-supplied equipment, one
diver should be towed while the other remains in
the boat suited up and ready to dive.
• A ladder or platform should be available for
boarding.
• The boat should be equipped with charts, radio,
first aid kit and resuscitator, emergency air sup-
ply, and all equipment required by the Coast Guard
for safe boating operations.
• The boat operator should know the procedure for
alerting the Coast Guard in case of an accident.
• All personnel on board should be thoroughly briefed
on the dive plan.
One practical and inexpensive method of liveboating
involves the use of a single towline with loops, a tow
bar, or a fluked anchor for the divers to hold. Divers
using such an apparatus should be towed at a comfort-
able speed that will not dislodge their masks. The
height above the bottom at which the divers travel is
NOAA Diving Manual — October 1991
Working Dive Procedures
controlled by the speed of the boat and the ability of
the divers to arch their bodies and to plane up or down.
A single towline, rather than a bridle, leading back to a
yoke with a short line for each diver works best. There
should be two crew members in the tow boat, one to
operate the vessel and the other to watch for surfacing
divers and to keep the towline from fouling in the boat
propeller.
The equipment necessary for towing divers is readily
available. The boat should have at least a 30-hp engine
and should be large enough to accommodate three or
more people and the diving equipment. A towline of
1/2 or 5/8 inch (1.3 or 1.6 cm) nylon line about
200 feet (61 m) long used with about 75 pounds
(34 kg) of weight permits divers to reach depths of
up to 90 fsw (27.4 m). The towing weight should be
made of two or three pieces of lead, steel, or concrete.
Three 25-pound (11.3 kg) lead balls are ideal because
there is less likelihood that a ball will hang up on
submerged objects. A return line of 1/2 inch (1.3 cm)
nylon 50 feet (15.2 m) long should be tied to the
towline at the weights. Polypropylene line should not
be used because it is buoyant. The return line will
trail behind the towed divers, who hang onto the
towline at or near the weights.
Any time one diver leaves the towline, the partner
should monitor the departing diver's actions until he or
she has again made contact with the return line. If the
diver fails to regain the return line, the partner must
abandon the towline and both divers must surface
together.
Another liveboating method uses the aquaplane (Fig-
ure 8-19). The simplest version is a board that, when
tilted downward or sideways, provides a dynamic thrust
to counter the corresponding pull on the towing cable.
The addition of a broom-handle seat and proper bal-
ancing of the towing points permit one-handed control
of the flight path. With an aquaplane, which can be
made in a few hours from off-the-shelf materials, a
team of divers can be towed behind a small boat; as
with other towing methods, the maximum speed must
be such that the diver's mask is not torn off. The dive
team may operate either in tandem off the same board,
which requires some practice and coordination, or each
diver may have a separate board attached to a yoke.
As in the swimming traverse (see Section 10.16.5),
the diver keys observation to time. At the same time, a
surface attendant notes the location of the tow boat or
escort boat as it moves along the traverse, with hori-
zontal sextant angles marking locations versus time.
Later, the position of the diver at times of recorded
observations can be determined by subtracting the
length of the towline from the position of the surface
boat at the time of observation.
In areas where entanglement is not a problem, divers
may wish occasionally to drop off the towline during
traverses to investigate objects of interest. A 50-foot
(13.4 m) return line attached to and trailing behind the
aquaplane can be used to permit a diver who drops off
the sled to grasp the line and return to the sled. It is
important for those in the boat to know what the divers
are doing, especially if they intend to drop off the line
to observe the bottom. A sled or aquaplane released by
a diver may continue planing downward by itself and
crash into the bottom. Some tow rigs have a small wire
built into the towline, with a waterproof pushbutton
switch, so that the divers can communicate by buzzer
with the tow boat.
One of the best methods of towing divers, especially
if they intend to drop off the towline, is to equip each
arm of the yoke with a large cork float, such as those
used on fishing nets or mooring pickup poles. The diver
merely straddles the cork and hangs onto the line ahead.
The towing pull is then between the legs and not on the
hands and arms. Maneuvering by body flexing is easy,
and when the divers wish to leave the line they merely
release their grip and spread their legs, allowing the
cork to rise rapidly to the surface to let personnel in the
boat know the divers are off the line. As soon as the
cork breaks the surface, the boat stops, backs up along
the line to the cork (the boat must not pull the cork and
line to the boat), and hovers, with the engine in neutral,
near the bubbles until the divers surface. The divers
can then hand over samples, relate findings, and resume
the tow. Experience has shown that there is little or no
danger of losing the bubbles using this method, because
the relatively slow towing speed of the boat allows the
cork to surface within seconds of being released. The
cork should surface at a point very close to the place
where the divers dropped off the line. If this method is
not used and if, after the divers drop off a tow, their
bubbles cannot be seen from the tow boat, there is a
chance that they are temporarily lost. In this case, a
standby buoy with an adequate anchor should be ready
to be lowered slowly and carefully overboard, so as not
to hit the divers below. The towboat should stand by at
the buoy until the divers surface. This technique pre-
vents the surface boat from being carried away from
the survey area by current or wind.
The scope of the towline may be as much as 10-to-l,
and in deep water this could place a diver far behind
the tow boat. If a weighted line is used, as described
earlier, the scope can be reduced to about 4-to-l. If
the diver is a long distance behind the tow boat, a
October 1991 — NOAA Diving Manual
8-29
Section 8
Figure 8-19
Aquaplane for Towing Divers
Source: iMOAA (1979)
safety boat may be used to follow the towed divers to
assist them if they become separated from the towline.
Whenever a towing operation is planned, regardless
of the equipment or method used, it is advisable to
conduct a series of practice runs to determine the best
combinations of boat speed, towline-yoke length, and
diver-boat signals.
Although towing is a useful way to cover a great deal
of terrain, there are limitations and drawbacks to this
technique. It is difficult to take notes or photographs
while under tow, unless enclosed sleds are used. There
may be considerable drag on the body, so one should
not carry bulky equipment either in the hands or on the
weight belt. Until the diver leaves the towline, the
hands should not be used for anything but holding on.
Sample bags, cameras, etc., should be attached to the
towline with quick-release snaps. The amount of work
to be accomplished and the equipment to be carried
can be determined in predive practice.
Liveboating also can be used when surface-supplied
umbilical systems are provided. Under such conditions,
the speed of the boat must be slow (0.5-1.5 k (0.25-
0.75 m/s)), carefully controlled, and determined by the
experience of the divers. Precautions must be taken to
avoid fouling the diver's umbilical in the propeller.
Generally, the propeller is covered by a specially
constructed wire or metal rod cage, and the umbilical
is "buoyed" so that it floats clear of the stern. When
liveboating from a large vessel, it may be desirable to
tow a small boat behind the vessel and to tend the
towed diver from the smaller boat. The tender must be
especially cautious to keep the umbilical clear, and
positive communications must be maintained between
the bridge on the large vessel and the tender. The
bridge also may wish to incorporate a system that
allows monitoring of the diver's communication. If
diver-to-surface communication is interrupted for any
reason, the engines must be stopped.
8.10.2 Drift Diving
Drift diving is used occasionally to cover a large
area when there are strong currents. Divers are put
into the water upstream and drift with the boat, which
trails a buoy with a clearly visible diver's flag. If the
operation must be conducted in heavy currents, divers
should enter the water as far upcurrent as necessary
and drift with the current, holding onto a line attached
to the drifting boat. Drift diving should be carried out
only when observers in the drifting boat can see the
diver's bubbles. If the drift involves a large vessel, a
small boat should be used to track the divers and to
pick them up. As with liveboating, drift divers should
carry appropriate signaling devices (see Section 8.10.1).
During pickup, the boat operator should not (except
in an emergency) approach the divers until the entire
dive team is on the surface and has given the pickup
signal. The boat's operator should bring the boat along-
side the dive party on a downwind or downcurrent side,
and the dive tender should assist the divers aboard. In
all cases, the boat's motor should be in idle during
pickup, with the propeller in neutral.
8-30
NOAA Diving Manual — October 1991
Working Dive Procedures
WARNING
Liveboating or Drift Diving Should Never Be
Conducted With Inexperienced Personnel
8.11 UNDERWATER DEMOLITION AND
EXPLOSIVES
Many underwater tasks require the use of explosives.
Several different types of explosives are available, and
these can be applied in a variety of ways. Because
explosives are powerful and dangerous tools, they should
be used only by trained personnel. To achieve accurate
results in underwater applications, the explosive must
be selected carefully and positioned properly.
Explosives are used under water to remove obstruc-
tions, to open new channels or widen existing ones, and
to cut through steel, concrete, or wooden pilings, piers,
or cables. They are also used to trench through rock or
coral.
Explosives suitable for underwater use include prima-
cord, various gelatins, plastics, precast blocks, and some
liquids. Such charges are relatively safe to use if the
manufacturer's instructions are observed and general
safety precautions for explosives handling are followed.
Bulk explosives (main charges) generally are the most
stable of the explosive groups; there is progressively
less stability with the secondary (primers) and initia-
tor (detonators/blasting caps) groups. Initiators and
secondary explosives always should be physically
separated from bulk explosives.
WARNING
Only Properly Trained and Certified Person-
nel Are Permitted to Handle Explosives
explosion, losing its intensity with distance. Less severe
pressure waves follow the initial shock wave very closely.
For an extended time after the detonation, there is
considerable turbulence and movement of water in the
area of the explosion. Many factors affect the intensity
of the shock wave and pressure waves; each should be
evaluated in terms of the particular circumstances in
which the explosion occurs and the type of explosive
involved.
Type of Explosive and Size of the Charge. Some
explosives have high brisance (shattering power in the
immediate vicinity of the explosion) with less power at
long range, while others have reduced brisance and
increased power over a greater area. Those with high
brisance generally are used for cutting or shattering
purposes, while low-brisance (high-power) explosives
are used in depth charges and sea mines, where the
target may not be in immediate contact and the ability
to inflict damage over a greater area is an advantage.
The high-brisance explosives therefore create a high-
level shock wave and pressure waves of short duration
over a limited area. High-power explosives create a
less intense shock and pressure waves of long duration
over a greater area. The characteristics of the explo-
sive to be utilized need to be evaluated carefully before
use to estimate the type and duration of the resulting
shock and pressure waves. The principal characteris-
tics of the most commonly used explosives for demoli-
tion are shown in Table 8-4.
WARNING
Before Any Underwater Blast All Divers Should
Leave the Water and Move Out of Range of
the Blast
An underwater explosion creates a series of waves
that propagate in the water as hydraulic shock waves
(the so-called "water hammer") and in the seabed as
seismic waves. The hydraulic shock wave of an under-
water explosion consists of an initial wave followed by
further pressure waves of diminishing intensity. The
initial high-intensity shock wave is the result of the
violent creation and liberation of a large volume of gas,
in the form of a gas pocket, at high pressure and tem-
perature. Subsequent pressure waves are caused by
rapid gas expansion in a noncompressible environment,
which causes a sequence of contractions and expan-
sions as the gas pocket rises to the surface.
The initial high-intensity shock wave is the most
dangerous; it travels outward from the source of the
If a diver must remain in the water, the pressure of
the charge a diver experiences from an explosion must
be limited to less than 50 to 70 pounds per square inch
(3.5-4.9 kg/cm2). To minimize pressure wave effects,
a diver should also take up a position with feet pointing
toward the explosion and head pointing directly away
from it. The head and upper section of the body should
be out of the water, or divers should float on their back
with their head out of the water.
For scientific work, very low-order explosions are
occasionally used to blast samples loose or to create
pressure waves through substrata. Each use must be
evaluated in terms of diver safety and protection. Bot-
tom conditions, the degree of the diver's submersion,
and the type of protection available to the diver can
October 1991 — NOAA Diving Manual
8-31
Section 8
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8-32
NOAA Diving Manual — October 1991
Working Dive Procedures
modify the effects of an explosion and must be consid-
ered in planning a dive involving the use of explosives.
Divers also should be cautioned against diving in the
vicinity when sub-bottom profiling using high-pressure
air or high electrical discharges is being conducted.
8.12 UNDERWATER PHOTOGRAPHY
Scientists can use three methods to document under-
water events: written records, tape recordings, and
photography/television. This section describes the use
of photography and television in underwater work.
Either diver-held cameras or remotely operated cam-
eras can be used, and each has certain advantages.
Diver-held cameras allow the photographer greater
mobility and permit more precise positioning in rela-
tion to the subject than can be achieved with remotely
controlled cameras. On the other hand, the remote
camera disturbs underwater subjects less than the pres-
ence of a diver, and such cameras can operate at depths
difficult for divers to reach.
8.12.1 Still Photography
8.12.1.1 Lenses and Housings
A 35-mm camera is a good starting point for under-
water photography; cameras of this type can then be
modified as necessary to meet task requirements. Two
categories of camera can be used under water: instru-
ments specifically designed to operate in the sea and
that have water-tight sealing, such as the Nikonos®, or
cameras designed for air use that are then housed in a
watertight casing (Figure 8-20). Cameras designed
for underwater use are easily portable and are rela-
tively simple to use, while land-use cameras that have
been adapted for underwater use are more versatile
because they can be modified easily.
The choice of lens for any camera to be used under
water is dictated by the required field of view and the
clarity of the water. Because the distance from camera
to subject must be short compared with that in air
(Figure 2-5), a photographer who wishes to photograph a
broad expanse must use a lens that has a wide degree of
coverage. A good rule of thumb is that photographic
visibility is only about one-third as good as eye visibil-
ity, which means that a wide-angle lens is an impor-
tant tool even in clear water.
Wide-angle lenses create optical problems in under-
water use. When used through a plane parallel port
facing the water, these lenses produce distortions and
color aberrations, narrow the angle of view, and lose
sharpness at the periphery. The optical characteristics
October 1991 — NOAA Diving Manual
Figure 8-20
Underwater Cameras
A. Watertight Camera
Courtesy Nikon
B. Standard Camera in Watertight Housing
C. Motor-Driven and Motor Winder Camera in Watertight Housing
Courtesy Ikelite Underwater Systems
of water require that wide-angle lenses be corrected
before they are used under water; a correction for
underwater use can be designed into the lens formula
(an expensive but effective approach), or corrective
ports can be placed in front of the lens. Attaching a
Plexiglas® dome (part of a hemisphere) and making
an allowance for closer focusing of the lens than is
necessary in air solves the underwater wide-angle lens
8-33
Section 8
problem at lesser cost. Several commercial underwa-
ter housings have built-in corrective capabilities, and
sealed cameras can be fitted with lenses that range
from 15 to 80 mm in width.
When close-up photography of small objects is
required, a plane parallel port coupled with lenses of
longer focal length is useful. This type of photography
demands ground glass focusing for precise framing,
whisker sharpness of the image, a lens that can focus
closely on the object, and at least one light source
coupled to the camera. Plane parallel ports are helpful
when using a longer lens because they enhance the
telephoto effect without noticeably destroying the
sharpness or color quality of the picture. For example,
the use of a Nikonos® close-up kit with a standard
35 mm lens allows clear pictures to be obtained at a focal
distance of 9.25 inches (23 cm); with the 35 mm lens
alone, this distance must be 33 inches (84 cm). This
ability is achieved through the use of an optically
matched auxiliary magnifier lens that is placed over
the primary lens.
Another method of obtaining close-ups is macro
photography. This technique involves placing an exten-
sion tube between the camera's body and the lens to
extend the focal length. A framer extension is attached
in front of the lens to ensure proper framing and focal
distance, which allows pictures to be obtained at dis-
tances as close as 2.5 inches (6.3 cm) from the subject.
In addition to the high magnification, macro photog-
raphy offers maximum color saturation, sharp focus
due to the strong flash illumination, and minimal sea
water color filtration because of the short focal dis-
tance (usually 3-7 inches (7.6-17.8 cm)). Figure 8-21
shows the basic equipment needed for closeup and
macro photography.
Unmodified off-the-shelf underwater cameras or
simpler housings for air cameras only permit a pho-
tographer-scientist to work in the mid-distance range;
although useful data can be collected at this distance,
long distance, closeup, and macro photography can
provide valuable additional information. Well-designed
and engineered housings for air cameras are heavier
and bulkier and require more maintenance than sealed
underwater cameras; however, housed cameras can be
more flexible and have a broader range of wide angle
and closeup capabilities than underwater cameras.
Another disadvantage of sealed cameras is that the
diver must work within a rigidly defined distance from
his or her subject and must rely on mechanical framing
rods to determine distance. Few fish will tolerate a
metal framing rod in their territory, and these rods
often cause unnatural behavior in fish and other marine
Figure 8-21
Basic Equipment for Closeup
and Macro Photography
Wire Framer
Locking Screw
Support Rod
Locking Screw.
Close-Up Lens
9.25 Inches
(23.4 cm)
i
A
Locking Knob
/
Locking Screw
Framer Bracket
A. Closeup
Locking Screw
Extension Tube Lens Wire Framer
Courtesy Geri Murphy
B. Macro
life. In comparison, the ground glass focusing of the
housed camera and its longer lenses allow photograph-
ers to work farther away from their subjects. The under-
water photographer must weigh the advantages and
disadvantages of each technique to determine which is
most suitable. An excellent series of articles compar-
ing closeup and macro photography was recently
published in Skin Diver Magazine (Murphy 1987-1988).
8.12.1.2 Light and Color
Light and color go hand in hand in underwater pho-
tography (Figure 8-22). Color films balanced for either
daylight or tungsten light are relatively blind to the
color subtleties that the eye can distinguish within the
blue and green spectra of water. When using^ available
light in shallow depths, filtration offers some compen-
sation. A color-correction filter (Table 8-5) over a
lens will break blue color up enough so that a certain
amount of color is restored. The color red disappears at
approximately 22 feet (6.7 m), orange vanishes at
8-34
NOAA Diving Manual — October 1991
Working Dive Procedures
Figure 8-22
Diurnal Variation of
Light Under Water
When the sun is 90° above the
horizon, its light is only reflected
by three percent as it enters the
water; nearly all the light will be
transmitted below the surface.
0sable Angle of Sunlight
Low-angle sunlight is nearly
totally reflected by the water's
surface.
Water s surface
Source: NOAA (1979)
approximately 40 feet (12.2 m), and yellow disappears
at approximately 80 feet (24.4 m) of water, and no
filtration of the lens can restore it (Figure 8-23). Color
correction filters that selectively subtract ultraviolet
light and correct the blue shift found in seawater are
readily available (Murphy 1987). These filters, which
are designed and color-balanced for available light at
depths ranging from 15-50 feet (4.6-15.2 m), can be
attached to and removed easily from the camera while
under water. Because such filters subtract from the
amount of light reaching the film, however, slightly
longer exposure times are required when they are used
(Murphy 1987). For additional information on the
absorption and transmission of light under water, see
Section 2.8.
Artificial light illuminates underwater situations and
also brings out the color inherent in the subject. To be
effective in water, artificial light must be used much
closer to the subject than would be necessary in air.
The closer and more powerful the light, the more it will
compensate for the inherent blue of seawater. By vary-
ing distance and power, different balances can be
obtained; a water-blue background with a slight hint
of color can be achieved as easily as brilliantly illumi-
October 1991 — NOAA Diving Manual
8-35
Section 8
Table 8-5
Color Correction Filters
Underwater path
length of the
light (feet)
1 .
2 .
5 .
8 .
12
15
Filter
CC 05R
CC 10R
CC 20R
CC 30R
CC 40R
CC 50R
Exposure
increase
in stops
1/3
1/3
1/3
2/3
2/3
1
For distances of greater than 15 feet (4.5 m), composite filter with
the appropriate number of filter units can be used.
Adapted from NOAA (1979)
nating the subject and completely obliterating the water
quality.
Many good electronic flash units are made for under-
water use. Some offer an underwater wide beam for use
with wide-angle lenses, others a narrow beam that
may penetrate the water column more effectively. (For
a list of underwater strobe units, see Table 8-6.) The
variance in exposure when using different strobe units
is caused by:
• The light beam angle;
• The strobe reflector material;
• The watt-seconds; and
• The guide number of the strobe.
Most strobes designed for underwater use come with
an exposure guide (see Table 8-6).
When using macro photography under water, divers
have a choice between manual and through-the-lens
(TTL) flash systems. Although each has its advantages
and disadvantages, the manual system is less expen-
sive, has underwater quick-disconnect features, and
offers better exposure control. In general, the manual
system is the preferred flash method for macro photogra-
phy. The automatic TTL system does, however, have
some advantages. For example, because the length of
the flash is controlled by the amount of light reflected
from the subject back through the lens, the system
automatically compensates for varying distances and
reflectivity. This system also provides a visual signal
confirming that the correct exposure was used. Auto-
matic TTL systems can be switched readily to the
manual mode as needed; Table 8-7 lists some TTL
mini strobes that are suitable for macro photography.
Tests should be made before the dive to establish
correct exposures with any unit that uses films of vari-
ous speeds. It is advisable when shooting with availa-
ble light to use shutter speeds of 1/100 or 1/125 of a
second, if possible. These shutter speeds should freeze
Figure 8-23
Selective Color Absorption
of Light as a Function of Depth
in Clear Ocean Water
(
i
Derived from Church 1971
Derived from Church (1971)
the action and reduce the amount of blur caused by
movement of the camera during exposure.
Table 8-8 lists exposure compensations for under-
water photography that should be used as a starting
point for work with adjustable cameras. These recom-
mendations are based on the following conditions: bright
sunshine between 10 a.m. and 2 p.m., slight winds, and
underwater visibility of about 50 feet (15.2 m). The
degree of visibility, the amount of particulate matter
in the water, the reflective qualities of the bottom, and
other factors can significantly affect photographic
results, and thus it is important to conduct tests before
(
8-36
NOAA Diving Manual — October 1991
Working Dive Procedures
Table 8-6
Manual and Through-the-Lens
(TTL) Strobes for Closeup
Photography
Mfg.
Model
Head
Size
Weight
In Air
Depth
Tested
Beam
Angle
Beam
Spreader
Color
Temp.
Batteries
Power
Modes
No. of
Flashes
Recycle
Time
U/W
Guide
Slave
Mode
TTL
Mode
Akimbo
Subatec
S-100
6 x 3.5"
2.75 lbs.
500 ft.
96
No
4,500 K
Removable
Rechargeable
Pack
1
1/2
1/4
1/8
150
250
350
500
4 sec.
3 sec.
2 sec.
1 sec.
22
16
11
8
No
No
Akimbo
Subatec
S-200 TTL
6 x 3.5"
2.75 lbs.
500 ft.
96
No
4,500 K
Removable
Rechargeable
Pack
1
1/2
1/4
1/8
150
250
350
500
4 sec.
3 sec.
2 sec.
1 sec.
22
16
11
8
No
Yes
Berry
Scuba
Whale Strobe
TTL II
7 x 4"
2.3 lbs.
165 ft.
65
Yes
(95)
5,600 K
4 AA
Dry Cells
Full
1/4
130
450
7 sec.
2 sec.
32
16
No
Yes
Helix
Aquaflash
28
6 x 5"
3.8 lbs.
165 ft.
65
Yes
(95)
5,600 K
6 AA
Dry Cells
Full
1/4
80
300
10 sec.
1 sec.
40
22
Yes
No
Helix
Aquaflash
28 TTL
6 x 5"
3.8 lbs.
165 ft.
65
Yes
(95)
5,600 K
6 AA
Dry Cells
Full
1/4
80
300
10 sec.
1 sec.
40
Yes
Yes
Ikelite
Substrobe
150 TTL
10 x 6"
7 lbs.
300 ft.
110
No
4,800 K
Removable
Rechargeable
Pack
Full
1/2
1/4
150
300
600
6 sec.
3 sec.
2 sec.
22
16
11
Yes
Yes
Ikelite
Ikelite
225 TTL
10 x 6"
8 lbs.
300 ft.
110
No
4,800 K
Removable
Rechargeable
Pack
Full
1/2
1/4
125
250
500
6 sec.
3 sec.
2 sec.
32
22
16
Yes
Yes
Nikon
SB-103
7 x4"
2 lbs.
160 ft.
65
Yes
(95)
5,500 K
4 AA
Dry Cells
Full
1/4
1/16
130
450
1,400
12 sec.
4 sec.
1 sec.
24
12
5.6
No
Yes
Nikon
SB-102
8.5 x 5.5"
4.3 lbs.
160 ft.
79
Yes
(95)
5,500°K
6C
Dry Cells
Full
1/4
1/16
120
400
1,200
14 sec.
5 sec.
2 sec.
33
16
8
Yes
Yes
Oceanic
3000 Master
9 x 5.7"
4.8 lbs.
300 ft.
110
No
5,700 K
Built-in
Rechargeable
Pack
High
Low
350
650
3 sec.
1 sec.
22
16
Yes
Yes
See
& Sea
YS-150
9.5 x 5"
5.4 lbs.
350 ft.
100
No
5,400 K
Removable
Rechargeable
Pack
Full
1/2
100
200
5 sec.
3 sec.
22
16
Yes
No
See
& Sea
YS-100 TTL
6 x 4"
2 lbs.
200 ft.
65
Yes
(80)
5,400 K
4 AA
Dry Cells
Full
1/2
1/4
1/8
130
250
450
900
12 sec.
12 sec.
12 sec.
12 sec.
32
22
16
11
Yes
Yes
Graflex
Subsea
Subsea
Mark 150RG
11 x 6"
8.5 lbs.
350 ft.
150
No
5,500 K
Removable
Rechargeable
Pack
150
100
50
175
250
325
5 sec.
3 sec.
2 sec.
22
16
11
Yes
No
Courtesy Gen Murphy
starting to photograph; these variables can cause
exposures to vary by as much as 4 or 5 stops (see
Section 2.8.1.3).
Although most underwater photographers now use
strobe flash systems, flash bulbs (clear bulbs for dis-
tance and blue bulbs for closeups) can still be used
effectively under water (Table 8-9). The longer water
column effectively filters the clear bulbs with blue so
October 1991 — NOAA Diving Manual
that the light balances for daylight film. Divers should
be aware that the pressure at great depth can cause
bulbs to implode; divers have been cut when changing
bulbs in deep water.
Incandescent lights that are powered either by bat-
tery or by a topside generator and that are a must for
motion picture work can also be used in still photogra-
phy. Incandescent light does not penetrate water as
8-37
Section 8
Table 8-7
Through-the-Lens (TTL) Mini
Strobes for Automatic and
Manual Exposure
Mfg.
Model
Head Size
(diameter)
Beam
Angle
(degrees)
Beam
Spreader
Color
Temp.
u/w*
Guide
No.
Batteries
Manual
Power
Modes
Recycle * '
Time
(seconds)
No.
Flashes
Extras
Depth
Tested
(feet)
Berry
Scuba
Whale Strobe
TTL II
7x4"
65
Yes
(95 degrees)
5,600 K
32
4AA
Full
1/4
7
2
130
450
• Confirm
Signal
• Test Fire
165
Helix
Aqua Flash
28 TTL
6x5"
70
Yes
(95 degrees)
5,600 K
40
6AA
Full
1/4
10
1
80
300
• Slave
• Confirm
Signal
• Test Fire
165
Ikelite
Substrobe MV
4.5 x 3.5"
" 65
No
5,800 K
20
4 AA
Full
5
250
• Inter-
changeable
sync cords
300
Nikon
SB-103
Speedlight
7x4"
65
Yes
(95 degrees)
5,500 K
24
4 AA
Full
1/4
1/16
12
4
1
130
450
1,400
• Confirm
Signal
160
Sea &
Sea
YS-100TTL
6x4"
65
Yes
(80 degrees)
5,400 K
32
4 AA
Full
1/2
1/4
1/8
12
12
12
12
130
250
450
900
• Slave
• Audio
Ready
• Exposure
Calculator
200
Sea &
Sea
YS-50 TTL
6x3"
72
No
5,400 K
22
4 AA
Full
10
140
200
*U/W Guide Number based on ISO 50 film with strobe set on full power manual.
* 'Recycle times and number of flashes based on alkaline batteries. Rechargeable nickel-cadmium batteries produce faster recycle times but fewer flashes.
Courtesy Geri Murphy
Table 8-8
Exposure Compensation for
Underwater Photography
Number of f-Stops to
Increase Lens Opening
Over Normal Above-Water
Depth of Subject
Exposure
Just under surface
1 1/2f-stops
6 feet (1.8 m)
2 f-stops
20 feet (6.0 m)
2 1/2 f-stops
30 feet (9.0 m)
3 f-stops
50 feet (15.0 m)
4 f-stops
Adapted from NOAA (1979)
well as electronic or flash bulb light, and these lights
are also clumsier to use.
Lighting arms and brackets or extension cords allow
off-camera light to be placed in many positions (Fig-
ure 8-24). Lights should not be placed on the camera
lens axis, because lighting suspended particles in the
water directly can curtain off the subject matter and
increase backscatter. Underwater exposure meters, pri-
marily of the reflected-light type, are manufactured
8-38
with brackets that permit them to be either mounted or
hand held.
8.12.1.3 Selection of Film
Depending on the quality of the documentation required
by the diver/scientist, a wide variety of both black-
and-white and color films is available (Table 8-10).
The sensitivity of film is measured according to an
American Standards Association (ASA) rating that
ranges for most purposes from 25 to 400 ASA. There
are slower and extra high-speed emulsions available
for special purposes and techniques.
Film is merely a base on which an emulsion of light-
sensitive, microscopic grains of silver halide has been
placed. These particles react to light in various ways
that affect the following:
• Grain, which is the clumping of silver halides.
High-speed film clumps more rapidly than slower
film, and enlargements show graininess more than
small pictures. Grain tends to destroy the sharpness
and detail of a photograph, but it can be reduced
or increased in processing. To obtain sharp pic-
tures, film of the finest grain should be used, unless
the light is insufficient and a high-speed film is
necessary.
NOAA Diving Manual — October 1991
Working Dive Procedures
Table 8-9
Underwater Photographic
Light Sources
Type of
Lighting
Depth
Limit(ft)
Factors
Limiting
Visibility
Accuracy
of Color
Rendition
Ability to
Light Subject
for the Human
Eye as Camera
Will See If
Control
of Effects
From
Light
Scattering
Duration
(sec)
Intensity
Means of
Determining
Exposure
Power
Requirement
Extent
of Use
Remarks
Noturol
50 to 100
absorptivity
scattering
poor
(predominantly
green)
very good
fair to
good
continuous
good at surface
but decreases
with depth
meter
none
general
Flood
none
absorptivity
scattering
fairly good
very good
/ery good
continuous
relatively low
guide number
determined
by experiment
high ( 1 2
to2kw)
general,
especially
at greater
depths
Flash bulbs
none
absorptivity.
scottermg
fairly good
poor
fair
1 50 to 1 100
h.gh
guide numbers
self-
contained
battery
general
Diver must
replace
bulbs
Electronic
flash
none
absorptivity
scattering
foirly good
poor
fair to
very
good
1 1 000 to
1 2 000 or
faster
very high
guide numbers,
automatic
self-
contained
battery
general
Electronic
flash is
probably
better
than
regular
flash for
use under
water
Adapted from NOAA (1979)
• Resolving power, which is the ability of the film to
hold fine details; resolving power is measured in
the number of lines per millimeter that the film
will record distinctly. It is related directly to grain:
the finer the grain, the higher the resolving power.
• Latitude is the over- and under-exposure toler-
ance of a film. Wide-latitude film is best under
water because a picture can be obtained even when
the exposure is not exact. For example: black-and-
white negative film will allow sufficient exposure
with a 4 f-stop variance, while color transparen-
cies of short latitude will tolerate only a 1/2 f-stop
deviance. A wide-latitude film should be used
whenever a good picture is necessary and bracket-
ing is impractical. Color negative films, which are
used to make color prints, offer better latitude
than color reversal films, which are used to pro-
duce color slides.
• Color balance, which is a problem only of color
film. Films are made to match the color tempera-
tures of different light sources-daylight, tung-
sten, strobe, etc. Processing and printing greatly
affect the ultimate color balance. Both color reversal
and color negative films are daylight films; both
are color-balanced for outdoor use in sunlight and
for use with electronic flash systems.
• Contrast is the difference in density between darkest
shadow and brightest highlights. Under water, con-
trast is low because of the diffused light. For best
results, film with high contrast should be used
under water.
October 1991 — NOAA Diving Manual
• Color reversal. Color reversal (positive color) film
is used most commonly for still work under water.
Slides or black-and-white or color prints can be
made from this film, and the resulting picture can
be viewed in its true perspective shortly after the
film is developed.
• Storage and shelf-life. The storage and shelf-life
of film is often an important consideration. For
example, over the counter films can withstand rel-
atively high storage temperatures but may shift
color with aging. Professional films, however, remain
constant in color but must be stored under temper-
ature-controlled conditions.
A fast film, such as Eastman Kodak Ektachrome
film that has an ASA value of 200, can produce very
acceptable results, with good depth of field at moder-
ate light levels. In low light conditions, the effective
ASA value may be increased four times to ASA 800.
although this film speed requires special processing
(see Table 8-11). Black-and-white films are available
that can be processed to achieve an ASA of 1200. As
higher ASA's are approached, however, black-and-white
films lose shadow detail during developing.
When taking underwater pictures with a flash or
strobe, both the f-stop generated by the strobe or flash
and the available light (f number registered on the
light meter) must be considered. In this case, the aper-
ture must be adjusted to accommodate the stronger of the
two light sources or a flash distance must be selected
that will equalize the natural and artificial light levels.
8-39
Figure 8-24
Lighting Arms and Brackets
for Strobe Systems
Section 8
Top: Sea & Sea YS 100 TTL Strobe Insert: Sea & Sea Motormarine
Hydro Vision International
Photo Cobra Flash Arm
Nikonos Speedlight SB-102 and SB-103
8-40
Helix Aquaflush 28TTL Insert: Helix Universal Slave Strobe
Courtesy Sea & Sea, Hydro Vision International, Nikonos®, and Helix
NOAA Diving Manual — October 1991
i
Working Dive Procedures
Table 8-10
Still Films Suited
for Underwater Use
Film Type
Dayligh
ASA
t
Description
Sharpness
Grain
Resolving
Power
Eastman Kodak Ektachrome 64
Daylight
Daylight
64
Color
A medium-speed color slide film for
general picture-taking purposes, e.g.,
macro, closeup, flash, available light
high
very
fine
high
Eastman Kodak Ektachrome 200
Daylight
200
A high-speed color slide film for
general picture-taking purposes (e.g.,
deep available light)
high
very
fine
high
Eastman Kodak Ektachrome 400
Daylight
400
A very high-speed color slide film for
general picture-taking purposes (e.g.,
deep available light)
~
Eastman Kodak Kodachrome 25
Daylight
25
Moderate speed, daylight balanced
(e.g., macro photography)
high
extremely
fine
high
Eastman Kodak Kodachrome 64
Daylight
64
A medium-speed color slide film for
general picture-taking (e.g., closeup,
flash, available light)
high
extremely
fine
high
Eastman Kodak Kodachrome 400
Daylight
400
A very high-speed color slide film for
general picture-taking (e.g., deep
available light)
"
extremely
fine
very
high
Vericolor II S
100
Professional color negative film for
short exposure times (1/10 sec. or
shorter)
~
~
~
Panatomic X
Black and White
32 Slow-speed film for a very high degree
of enlargement
very
high
extremely
fine
very
high
Plus-X Pan
125
Medium-speed film for general purpose
photography where a high degree of
enlargement is required
very
high
extremely
fine
high
Tri-X Pan
400
Fast, general purpose film when the
degree of enlargement required is
not great
very
high
very
fine
medium
Verichrome Pan
125
Medium-speed film for general purpose
photography where a high degree of
enlargement is required
very
high
extremely
fine
high
Note: Proper color balance occurs when colors are reproduced as they actually are. Making warmer or colder tones is an
aesthetic decision of the cameraman. All color films should be exposed properly and have good color acceptability at
± 1/2 stop. At more than ± Vfc stop, color reproduction differs noticeably from the original color.
Adapted from NOAA (1979)
Infrared film has opened up new possibilities in under-
water photography; however, because of drastic color
changes, infrared film is not suitable for scientific
color documentation. Kodak recommends starting at
ASA 100, but underwater tests have shown that ASA
50 exposed at 1/60 sec at an f-stop of 5.6 on a sunny
day in 20 feet (6.1 m) of water will give proper expo-
October 1991 — NOAA Diving Manual
sure. A yellow filter should be used to exclude exces-
sive blue saturation.
8.12.1.4 Time-Lapse Photography
Many biological and geological events occur so slowly
that it is neither possible nor desirable to record them
8-41
Table 8-11
Processing Adjustments
for Different Speeds
Section 8
Kodak
Ektachrome 200
Film
(Daylight)
Kodak
Ektachrome 160
Film
(Tungsten)
Kodak
Ektachrome 64
Film
(Daylight)
Kodak
Ektachrome 50
Professional
(Tungsten)
Change the time
in the first
developer by
800
400
Normal 200
100
640
320
Normal 160
80
250
125
Normal 64
32
200
100
Normal 50
25
+ 51/2 minutes
+ 2 minutes
Normal
— 2 minutes
For Kodak Ektachrome film chemicals, Process E-6.
Adapted from NOAA (1979)
continuously on film. Time-lapse photography, which
permits the scheduling of photographic sequences, is
the solution in such cases. This technique has been
used widely for years for studying plant growth, weather
patterns, and many other phenomena. It is particularly
useful for underwater studies, where, in addition to
investigating slow processes, the inconvenience and
cost of frequent site visits make other photographic
techniques impractical.
Modern technology has greatly improved underwa-
ter camera systems that are triggered automatically
by means of standard timing devices or by remote
command. The time-lapse interval (the time between
photographs) is determined by the nature of the event
being studied, the available equipment, environmental
conditions, and cost. The time interval can vary from
seconds or minutes to hours or even days. An example
of a long-term study using current technology is the
record being made of the scouring and erosion of sand
around offshore platforms and pipeline installations
during storms in the North Sea. In this instance, three
pictures per day were taken over a period of 1 month,
using a stereo-camera system (Photosea Systems Inc.
1984).
Because time-lapse systems remain unattended for
long periods, they must be thoroughly checked out for
reliability, leaks, buoyancy, and anchoring before
deployment. They must also be maintained and stored
carefully when not in use.
8.12.2 Motion Picture Photography
Almost all motion picture cameras can be adapted
for underwater use; such cameras should be confined
in rugged, reliable underwater housings that will with-
stand rough handling. All camera controls should be
outside the housing and should be as simple as possi-
ble. The camera also should be balanced properly to be
neutrally buoyant. The underwater cinematographer
must position the camera himself or herself and must
be able to swim in and out of scenes with as little
unnecessary movement as possible.
To cover a single subject adequately, several dives
should be planned. An average for topside shooting in
good amateur work is 1:5 (1 foot (0.3 m) used for every
5 feet (1.5 m) exposed). Photographers should consider
using a tripod if the objects to be photographed are
generally in one area. Artificial lighting is critical
for motion picture work deeper than approximately 30
feet (9.1 m). Surface-powered lights are cumbersome
but more reliable and longer-lasting than battery-
powered lights. Ideally, a buddy diver should handle
the lights, which frees the photographer to concentrate
on filming techniques.
8.12.2.1 Selection of Film
A wide range of motion picture film is available for
underwater photography in both 100 foot (30.5 m) and
in 400 foot (121.9 m) rolls (see Table 8-12). Eastman
Color Negative Film 7291 should yield the best pic-
ture information in both highlight and shadow por-
tions of the film. This film also has a broad range of
color correctability that can be applied during print-
ing and is faster and has more latitude than Eastman
Ektachrome Commercial 7252. Eastman 7294 also is
used frequently for filming at greater depths and on
darker days because it has a higher ASA rating, it can
be processed as easily as 7291 can, and it has a fine
quality that allows it to be edited with 7291 scenes.
Eastman Video News films 7239, 7240, and 7250 are
improvements over Eastman Ektachrome EF (daylight)
7241 and Eastman Ektachrome EF (tungsten) 7242,
both with respect to speed and warmer tone (highlight)
characteristics, which lend a pleasing overall effect to
the photographs.
8.12.2.2 Procedures
Because all film is sensitive to heat, it should not be
stored in the sun or in hot enclosures. In addition, film
should always be loaded in subdued light. Other pro-
8-42
NOAA Diving Manual — October 1991
Working Dive Procedures
Table 8-12
Motion Picture Films
Suited for Underwater Use
Film Type
ASA
Description
Reversal Eastman Plus-X 7276 . .
Reversal Eastman Tri-X 7278 . . .
Black and White
. 50 Daylight
A medium-speed panchromatic reversal film characterized by
a high degree of sharpness, good contrast and excellent
tonal gradations
. 200 Daylight
A high-speed panchromatic reversal film that provides excel-
lent tonal gradations and halation control
Reversal Eastman 4-X 7277
. 400 Daylight
A very high-speed panchromatic reversal film
Negative Eastman Plus-X 7231 . .
. 80 Daylight
A medium-speed panchromatic negative film for general pro-
duction
Negative Eastman Double X 7222
. 250 Daylight
A high-speed panchromatic negative film representing the
latest advances in speed granularity ratio
Negative Eastman 4-X 7224
. 500 Daylight
An extremely high-speed panchromatic negative film
Reversal Eastman Ektachrome . .
Commercial 7252 (Tungsten)
Color
. Daylight 16 w/85 filter
A color reversal camera film designed to provide low-contrast
originals from which color release prints (duplicates) of
good projection contrast can be made
Reversal Eastman Ektachrome . .
EF7241 (Daylight)
.160
A high-speed color reversal camera film, balanced for day-
light exposure, intended primarily for direct projection
(after processing). However, satisfactory color prints can
be made if they are balanced properly
Reversal Eastman Ektachrome . .
EF 7242 (Tungsten)
. w/85 filter - 80
A high-speed color reversal camera film balanced for tung-
sten exposure, intended primarily for direct projection (after
processing). However, satisfactory color prints can be made
if they are balanced properly
Reversal Eastman Ektachrome . .
Video News 7239 (Daylight)
. 1 60
A high-speed color reversal camera film balanced for daylight
exposure, intended for use under low-level illumination
both for color news photography and for high-speed pho-
tography. Satisfactory color prints can be made if they are
balanced properly
Reversal Eastman Ektachrome . .
Video News 7240 (Tungsten)
. w/85 B filter = 80 . . .
.A high-speed color reversal film, intended for use in daylight.
Satisfactory color prints can be made if they are properly
balanced
Reversal Eastman Ektachrome . .
Video News High Speed 7250
(Tungsten)
. w/85 B filter = 250 . .
. No data
Negative Eastman Color
Negative II 7291 (Tungsten)
. w/85 filter - 64
A high-speed color negative camera film designed for use in
tungsten light and in daylight with an appropirate filter. It
is characterized by accurate tone reproduction, excellent
image structure, and wide exposure latitude. Excellent
prints (duplicates) can be made from the original
Adapted from NOAA (1979)
October 1991 — NOAA Diving Manual
8-43
Section 8
cedures to be observed when taking motion pictures
are:
• When using 16-mm equipment, photographers
should film at 24 frames per second (FPS) to achieve
real-time action. At 24 FPS, most motion picture
cameras attain a shutter speed of approximately
1/50 of a second. Such a shutter speed is necessary
for interpreting f-stops when using an exposure
meter.
• When starting to film, the housed camera should
be put in the water, taken down to 30 fsw (9.1 m),
returned to the surface, and checked for leaks.
• The camera should be held as steadily as possible;
if feasible, a tripod (custom-made or commercially
bought and heavily weighted) should be used.
• Photogiaphers should overshoot at the beginning
and end of each scene to establish the scene and to
aid in the editing process.
• The length of scenes should be varied (some short,
some long); this can be done in editing, but film
can be saved if the value and length of each scene
are considered during the shooting.
• Different distances, angles, and exposures of each
scene should be shot.
• Scenes should not be rushed because the beauty of
the sea can be lost if the photographer is hurried.
• Only a few special effects should be used, and then
only when they are exceptional and an integral
part of the picture.
• The shooting script should generally be followed,
but it is important to be flexible enough to deviate
from it if the situation so dictates.
• Photographers should know their cameras thoroughly
so that they can be used most effectively.
8.12.3 Special Procedures
Underwater photographers may find the following
hints helpful:
• Overweighting with plenty of lead makes a diver a
much steadier photographic platform.
• A wet suit protects against rock and coral injuries
even when it is not needed for thermal protection.
• Photographic equipment should not be suspended
from lines on boats in a rough sea unless the line
has a shock absorber incorporated into it.
• To the extent possible, photographic sequences
should be planned before the dive.
• Cameras should be taken down to a habitat open
unless the housing has a relief valve; pressure pre-
vents cameras from opening at depth. The camera
housing should be taken up open, regardless of
relief valves, because the housing can flood when
external pressure is released.
• A basic tool kit should be set up for camera main-
tenance, and spare parts (0-ring grease, WD 40 or
equivalent, towels, etc.) should also be on hand.
• Wearing a wool watch cap can keep water from the
diver's hair from dripping into the camera during
reloading.
• Protective shock-absorbing cases lined with foam
rubber are essential for transporting photographic
gear in a boat.
• Actual underwater experience and experimenta-
tion are often more informative than photography
books, many of which contain errors.
• If a camera floods in salt water, the best immedi-
ate action is to pack the equipment in ice and to
keep it frozen until it can be delivered to a repair
facility. If ice is not available, the camera should
be flushed thoroughly by immersing it in fresh
water or alcohol.
• At the end of the day's work, all camera equipment
should be washed with fresh water.
• When the camera and housing are removed from
the water, they should be placed in the shade imme-
diately; this is especially true in the tropics, where
even a minimal exposure to the sun can cause heat
inside the camera housing to damage the film.
8.13 UNDERWATER TELEVISION
Significant advances continue to be made in underwa-
ter television systems. These advances offer great promise
for the scientific and working diver with respect to
recording natural phenomena, conducting surveys,
documenting experimental procedures, ship hull inspec-
tion, damage assessment, improving working procedures
and techniques, and diving safety. Excellent solid-state
underwater color systems now are on the market that
permit small, compact television cameras to be:
(l) held in the hand, (2) mounted on tripods, (3) worn as
an integral part of a diving helmet (Figure 8-25),
(4) mounted on manned submersibles, or (5) used as an
integral part of remotely controlled systems. Under-
water video systems capable of operating at depths as
great as 35,000 feet (10,668 m) are now available. This
capability, when coupled with the high quality of cur-
rent video systems, has resulted in television replacing
photography as the method of choice for underwater
scientific and technical documentation.
When selecting an underwater video system, it is
best to choose a system designed specifically for
underwater operation rather than to select a "surface"
8-44
NOAA Diving Manual — October 1991
Working Dive Procedures
Figure 8-25
Video Recording Systems
A. Handycam® System With
Underwater Housing
B. Underwater Housing With
Angle Lens Attached
Courtesy Sony Corp. of America
Courtesy Ikelite Underwater System
C. Diver Using Underwater Video System
Photo by Jim Churcn
October 1991 — NOAA Diving Manual
8-45
Section 8
Figure 8-26
Commercial Underwater
Video System
Courtesy Hydro Vision International, Inc.
system packaged for underwater use. Surface televi-
sion cameras normally operate at high light levels and
often are not sensitive enough for underwater condi-
tions. Further, surface cameras are sensitized to red
light, while underwater cameras for use in the open sea
have maximum sensitivity in the blue-green region of
the spectrum. The dynamic range of an underwater
camera also is critical if it is to be used effectively
under the broad range of light intensities commonly
encountered.
To achieve these underwater needs, specifically
designed low-light-level television cameras often are
used; such cameras can record images at light levels as
low as 0.0005 foot-candle at the camera tube while
maintaining a horizontal resolution of 500 lines. In
addition to operating at low light levels, these cameras
can significantly extend the viewing range. Such sys-
tems offer great potential for working under condi-
tions of low visibility, where the diving scientist needs
to observe or record the behavior of marine life without
either artificial light or the veiling effect of backscat-
ter that occurs with lighted systems. In addition to the
optical characteristics of video cameras, other impor-
tant features to consider include: size, weight, and
buoyancy control; type of viewfinder; automatic ver-
sus zone focusing; automatic exposure control with
manual override; and automatic white balance. Other
options to consider are built-in microphones, zoom
lenses, focusing for macro photography, housings, and
general ease of operation.
8-46
The selection of a lighting system for underwater
television Filming is just as critical (and often as expen-
sive) as the selection of a camera. Although quartz
iodide lights are often used for underwater work, their
lights are not as efficient as mercury or thallium dis-
charge lamps because quartz provides a high red spec-
tral output that is absorbed rapidly in seawater. On the
other hand, quartz iodide light is the only source that
produces enough red to allow good underwater color
filming. Another alternative is a water-cooled quartz
halogen lamp that offers burn times of up to 3 1/2
hours at 100 watts at depths to 250 feet (76 m). Like
cameras, underwater lights are designed to operate at
depths of several thousand feet (i.e., several hundred
meters). Specific factors to consider when selecting a
lighting system for a video camera include the size and
location of the battery pack, burn and recharge times,
the size of the underwater beam angle, and an arm and
bracket mounting system. Rapid advances continue in
the development and miniaturization of videotape for-
mats. Miniature camcorders weighing less than 3 pounds
(1.4 kg) have reduced the bulk of video systems and
permitted the use of high-quality 8 mm video tapes.
Underwater TV systems can operate from 12 volts
DC, 115 vac, or 230 vac input power, which provides
the flexibility to operate either from large or small
diving support platforms. As with other television sys-
tems, data can be viewed in real time on the surface or
be stored for later viewing. The combination of a diver-
held or helmet-mounted camera, a surface-based moni-
NOAA Diving Manual — October 1991
Working Dive Procedures
tor, and a good diver-to-surface communication sys-
tem permits the diver to act as a mobile underwater
platform under the direction of the diving supervisor
or a scientist on the surface. This arrangement not only
permits real-time recording of events but greatly
enhances diving safety by allowing the surface support
team to monitor the activities of the diver continuously.
This monitoring can be done either at the site on the
surface or at a remote station or laboratory.
Computer microprocessing technology also permits
digital displays to be overlaid on the output of the
video camera. For the diving scientist, this means that
a wide variety of data can be recorded, including
information on such things as environmental conditions,
weather, water conditions, and the results of experiments.
Underwater TV is used in a variety of modes, including
(1) attached to submersibles, (2) lowered by cable for
use as a remote instrument, or (3) placed on or near a
structure or habitat for long-term monitoring. Within
working depth limitations, divers may be asked to attach,
detach, or service a TV camera in the monitoring mode
or to carry the camera-light module. The best results
are obtained when the camera is manipulated by a
diver using either umbilical diving gear with hard-
wire communications or a scuba diver with reliable
wireless communication. In either case, the diver's
narrative is recorded on videotape, along with the picture.
Commercial systems are available that are designed
as an integral unit, including a full face mask, helmet-
mounted or hand-held camera, monitor, and complete
facilities for two-way communications and videotaping
(Figure 8-26). Divers usually can work with cable
lengths up to 500 feet (152.4 m) if floats and buoys are
used to reduce the drag and the possibility of fouling.
Underwater television technology has reached the stage
where it is preferable, in most cases, to underwater
photography. Its advantages include: on-the-spot evalu-
ation of results; instant replay; communication with
surface support personnel both for safety and assis-
tance in the evaluation of results; and cost-effective
duplicate films.
October 1991 — NOAA Diving Manual
8-47
<
(
SECTION 9
9.0
PROCEDURES
9.1
FOR
SCIENTIFIC
DIVES
9.2
9.3
9.4
9.5
9.6
9.7
9.8
9.9
9.10
9.11
9.12
9.13
9.14
Page
General 9-1
Site Location 9-1
9.1.1 Traditional Methods 9-1
9.1.2 Electronic Methods 9-2
Underwater Surveys 9-2
9.2.1 Direct Survey Methods 9-2
9.2.2 Indirect Survey Methods 9-3
9.2.2.1 Underwater Photographic Surveys 9-3
9.2.2.2 Underwater Acoustic Surveys 9-4
Underwater Recording Methods 9-5
Biological Surveys 9-6
9.4.1 Estimating Population Densities 9-7
Biological Sampling 9-8
9.5.1 Plankton Sampling 9-8
9.5.2 Benthic Organism Sampling 9-9
9.5.3 Airlift Sampling 9-1 1
9.5.4 Midwater Sampling 9-1 1
Shellfish Studies 9-12
9.6.1 Collecting Techniques 9-13
Tagging and Marking Techniques 9-14
Botanical Sampling 9-17
9.8.1 Field Procedures 9-18
9.8.2 Collecting Techniques 9-18
9.8.3 Specimen Preparation and Preservation 9-19
Artificial Reefs 9-20
Geology 9-22
9.10.1 Mapping 9-22
9.10.2 Sampling 9-26
9.10.3 Testing 9-31
9.10.4 Experimentation 9-31
Microphysical Oceanography 9-32
9.11.1 Emplacement and Monitoring of Instruments 9-32
9.1 1.2 Planktonic Studies 9-33
9.11.3 Use of Dye Tracers 9-34
9.1 1.4 Water Samples 9-34
Archeological Diving 9-36
9.12.1 Shipwreck Location and Mapping 9-37
9.12.2 Shipwreck Excavation 9-37
9.12.3 Artifact Preservation and Salvage Rights 9-40
9.12.4 Significance of Shipwreck Archeology 9-40
Capture Techniques 9-41
9.13.1 Nets 9-42
9.13.2 Seines 9-42
9.13.3 Trawls 9-42
9.13.4 Diving on Stationary Gear 9-42
The Use of Anesthetics in Capturing and Handling Fish 9-42
9.14.1 Response to Anesthetics 9-43
9.14.2 Selecting an Anesthetic 9-43
9.14.3 Application of Anesthetics 9-43
9.14.4 Diver-Operated Devices 9-46
<
i
PROCEDURES
FOR
SCIENTIFIC
DIVES
9.0 GENERAL
Diving is widely performed to observe underwater
phenomena and to acquire scientific data, and this use
of diving has led to significant discoveries in the marine
sciences. In some instances, diving is the only method
that can be used to make valid observations and take
accurate measurements. Using equipment and tech-
niques designed specifically for underwater use, the
diving scientist can selectively sample, record, photo-
graph, and make field observations. Some research,
such as ecological surveys, benthic inventories in shallow
water, and fish behavior studies, requires diving to be
used throughout the entire project, while other research
may require diving only as an adjunct to submersible,
remote sensing, or surface ship surveys. Regardless of
the project or the role that diving plays, marine research
using diving as a tool has been important in understanding
the ocean, its organisms, and its dynamic processes.
The diving scientist or technician's working time is
measured in minutes and seconds instead of hours
(unless the saturation diving mode is used). Long
underwater work periods necessitate decompression
times twice as long as the actual work time on the
bottom: the cost-effectiveness of scientific diving
therefore depends on how efficiently scientists can
perform their tasks. Efficiency under water requires
good tools, reliable instruments that can be set up
rapidly, and a well-thought-out task plan. Until recently,
there was almost no standardization of the equipment
and methods used to perform scientific research under
water, and in many cases the instruments, tools, and
techniques were (and still are) improvised by individual
scientists to meet the specific needs of the project.
However, now that the value of scientific diving has
been widely recognized, scientists are becoming con-
cerned about the accuracy and replicability of their
data and results and are increasingly using statistically
valid and standardized methodologies. Through neces-
sity, scientists who want to work under water must be
proficient both in their scientific discipline and as
divers, inventors, and mechanics.
The purpose of this section is to describe some of the
procedures used in diver-oriented science projects.
These methods are intended as guidelines and should
not be construed as the best or only way to perform
underwater surveys or to gather data.
October 1991 — NOAA Diving Manual
9.1 SITE LOCATION
To study any region carefully, it is necessary to plot on
a base map the precise location from which data will be
obtained (Holmes and Mclntyre 197 1 ). This is especially
important if there is a need to return to the same
location several times during a study. The scale of the
base map depends on the detail of the study and the
size of the area to be investigated. In geological mapping
of the seafloor, a scale of 1 inch to 200 yards (2.5 cm to
183 m) is adequate for reconnaissance surveys. In
archeological and some biological studies, a much more
detailed base map, with a scale of 1 inch to 30 feet
(2.5 cm to 9 m), may be required. If existing charts do not
contain the proper scale or sounding density, it may be
necessary to use echosounder survey techniques to
construct a bathymetric map of the bottom before
starting the dive. Gross features can be delineated and
bottom time used more efficiently if the diver has a
good bathymetric map of the study area. If published
topographic charts are inadequate, the sounding plotted
on original survey boat sheets of a region (made by
NOAA's National Ocean Service) can be contoured
and will usually provide adequate bathymetric control
for regional dive surveys. If the survey plan requires
bottom traverses, it will be necessary to provide some
means of locating the position of the diver's samples
and observations on the base chart.
Techniques used to search for underwater sites fall
into two general categories: visual search techniques
and electronic search techniques. The results from the
latter must be verified by divers after the specific site
has been located.
9.1.1 Traditional Methods
The great majority of diving is carried out in nearshore
waters where surface markers, fixed by divers over
strategic points of the work site, may be surveyed from
the shore using well-established land techniques,
including the theodolite, plane table, and alidade, or
from the sea, using bearings from a magnetic compass
or, preferably, measuring horizontal angles between
known points with a sextant. Small, inexpensive, and
rugged plastic sextants are commercially available,
and techniques for using them are simple to learn.
Although sextants have limitations, especially when
9-1
Section 9
they are used from a small boat, they are generally
sufficiently accurate to be useful.
At the other extreme in terms of complexity is a site
relocation method used successfully by many scientists; in
this method, lineups and landmarks on shore are sighted
visually, without the use of artificial aids. Basically,
once the site is located and the boat anchored over it,
scientists take a number of sightings of various nearshore
landmarks (such as trees, hills, and power poles) and
align them visually so that when the boat is repositioned
the landmarks line up the same way. The only drawbacks
to this method are that the work must be conducted
near shore and the visibility must be good in order for
the shoreside landmarks to be seen. When several lineups
have been established and proven, they should be
diagrammed in a notebook that is kept in the boat.
These methods allow divers to establish the locations
of major features in the working area accurately. If
buoys are used for location, particular care is needed
to ensure that the surface floats used during the initial
survey lie directly over the weights anchoring them to
the selected underwater features; the best plan is to
wait for a calm day at slack tide.
In some cases it may be advisable to leave the seabed
anchors in place after the floats have been cut away. If
this is contemplated, the anchors should be constructed to
rise slightly above the surrounding terrain so that they
may be seen easily on the next visit. Small floats made
of syntactic foam may be tied to the anchors below the
surface with a short length of polypropylene line to aid
in relocation. However, because biological fouling soon
obscures any structure used, expensive, highly painted
markers generally are not appropriate. Floating markers,
even if they are small and badly fouled, usually can be
seen if they protrude a short distance above the
surrounding substrate. Once the transect, grid, or other
system of markers is established and fixed relative to
permanent features on the shore, the diver should record
the position of selected features within the working
area in relation to the buoy array.
9.1.2 Electronic Methods
Electronic positioning methods are excellent, but
they are also expensive. If cost is no object or extreme
accuracy of station positioning and marking is required,
several highly sophisticated electronic ranging instru-
ments may be used. Satellite positioning equipment can
position a scientist within a few meters of the desired
location. Loran equipment, although less accurate, is
readily available at relatively low cost.
9-2
9.2 UNDERWATER SURVEYS
A variety of methods is used to survey the underwater
landscape; these include direct and indirect surveying
methods. Direct methods require diver-scientists to
measure distances themselves, while indirect approaches
use photography or acoustic means to determine
distances, angles, and other features.
9.2.1 Direct Survey Methods
With the exception of long distance visual triangula-
tion, many of the methods used in land surveying can
also be used under water. A review of a standard college
text on surveying will provide the scientist with some
basic surveying concepts, while Woods and Lythgoe
(1971) give an excellent description and review of
methods that have been devised specifically for work
under water. In most diving surveys, distances are
measured with a calibrated line or tape. However,
measurements done under water seldom need to be as
accurate as those on land, and the use of an expensive
steel tape is unnecessary. Additionally, most ropes or
lines will stretch and should be used only if the
measurement error resulting from their use is accept-
able. A fiberglass measuring tape that has a minimum
of stretch and is marked in feet and inches on one side
and meters and centimeters on the other is commercially
available (see Figure 9-1). These tapes come in an
open plastic frame with a large metal crank to wind the
tape back onto the reel. They are ideal for most purposes
and require no maintenance except for a fresh water
rinse and lubrication of the metal crank. No matter
what measuring method is used, especially if long
distances are involved, the lines or tapes must be kept
on reels to prevent tangling or fouling. In clear waters,
optical instruments can and have been used to measure
both distance (range finder) and angles between objects
for triangulation.
The first step in surveying any area is to establish a
horizontal and vertical control network of accurately
located stations (bench marks) in the region to be
mapped. Horizontal control is the framework on which
a map of features (topography, biology, or geology) is
to be constructed; such a control provides a means of
locating the detail that makes up the map. Vertical
control gives the relief of the region and may be obtained
by stadia distance and vertical angles or by spirit leveling.
Rough measurements can be made by comparing
differences in depth using a diver's depth gauge, but
measurements may be inaccurate if the irregular sea
surface is used as the reference point.
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-1
Fiberglass Measuring Tape
Figure 9-2
Bottom Survey
in High-Relief Terrain
Courtesy Forestry Suppliers, Inc.
One method that has worked well in areas of high
relief where echosounders are not satisfactory is
described below (Hubbard 1978).
• Along a convenient axis (N-S, E-W, etc.), place
two permanent poles, one on either end of the
survey area.
• Stretch a line between them to serve as a fixed
centerline.
• At intervals prescribed by the size of the area and
the irregularity of the terrain, place additional
poles identified by some sort of coding. The use of
a taut-line buoy may make the sites more visible.
• Lay out the lines perpendicular to the centerline
by using the centerline poles as tie-in points. If a
permanent grid is desired, place poles at intervals
comparable to those between the centerline poles.
If the terrain has significant relief, horizontal
changes can be measured by moving away from
each centerline pole, as shown in Figure 9-2.
• In areas of significant terrain, it is difficult to
maintain an accurate horizontal measurement.
Knowing the difference in depth (y) between the
two points (from a calibrated depth gauge or several
depth gauges) and the measured slope distance
(z), the horizontal distance (x) can be calculated
easily using the formula:
x= V z2 - y2 .
When using a depth gauge over a period of hours,
tidal fluctuations must be taken into account. A reference
staff or bench mark should be established at the begin-
ning of the survey, and readings should be taken at the
reference during the period over which depths are being
measured in the survey area. By going in either direction
from each of the centerline poles, a complete Dathymetric
survey can be conducted with considerable accuracy.
October 1991 — NO A A Diving Manual
Source: NOAA (1979)
Determining the two end points of the centerline by the
methods described in Section 9.1.1 locates the site
with respect to surface positions.
The detail to appear on the finished map is located
by moving from the control networks (bench marks) to
the features to appear on the finished map. On some
surveys, the control is located first and the detail is
located in a separate operation after the control survey
has been completed. On other surveys, the control and
the detail are located at the same time. The former
method is preferable if long-term observations are to
be carried out in an area, for example, around a
permanently established habitat. The latter technique
is preferable if reconnaissance studies are being made
in remote regions or in areas that will not require the
re-establishment of stations.
9.2.2 Indirect Survey Methods
Indirect underwater surveying involves techniques
that do not require the diver physically to measure
angles and distances using tapes, lines, protractors,
etc. Indirect underwater surveying currently is performed
using either photographic or acoustic methods.
9.2.2.1 Underwater Photographic Surveys
Obtaining reliable measurements by means of
photography — photogrammetry — though not as advanced
9-3
Section 9
under water as on land — is a tool being used with
increasing frequency. Limited visibility is one of the
major drawbacks in its application.
Photographs with appropriate scales in the field of
view can be useful in measuring objects on the seafloor
and in recording changes with time. Subtle changes
often recorded on sequentially obtained exposures of
the same area or station can be missed if memory
alone is relied on.
Photographic transects are useful in showing varia-
tions over an area or changes that occur with depth. In
the past, little true photogrammetry was conducted
because of the technical difficulties in producing
corrected lenses and maintaining altitude and constant
depth and because of the high relative relief of many
bottom features. However, improved techniques have
been developed that allow increased accuracy and
flexibility. Recent computerization of photogrammetric
plotting equipment has reduced technical difficulties
considerably.
To improve mapping for detailed archeological studies,
photographic towers may be used (Bass 1964, 1968;
Ryan and Bass 1962). The progress of excavation in
each area can be recorded with grid photographs taken
through a hole in the top of the tower. This approach
produces a consistent series of photos that can be
compared easily when analyzing the data. The tower
ensures that each photo is taken from the same point of
view, thus simplifying follow-on dark room procedures. A
photograph is, however, a perspective view that requires
correction for the difference in scale and position of
objects.
A series of stereophoto pair photographs may be
taken of sites for three-dimensional viewing under a
stereo-viewer. More important, it is possible to make
three-dimensional measurements from such photos.
The use of wide-angle lenses, such as a 15-mm lens,
permits detailed photographs to be taken that cover
large areas from short distances. Bass (1978) recom-
mends that rigid metal grids be constructed and divided
into 6.6 foot (2 m) squares. These squares are then
excavated and photographed individually.
9.2.2.2 Underwater Acoustic Surveys
Another method for conducting bottom surveys
involves the use of sonic location beacons (pingers).
These devices are particularly useful if there is a need
to return to specific locations. The system may consist
of small (the size of a roll of quarters) pingers, which
can be placed at the site of interest, and a diver-held
receiver. The pingers can be tuned by the diver to
specific frequencies to differentiate between sites.
More complex and costly systems can be used to
avoid some of the problems that arise with these simpler
methods. A high-frequency sonic profiler (Figure 9-3)
can rapidly measure underwater sites (Dingier et al.
1977). Such a device, however, requires electronic and
technical support beyond the means of most researchers.
If cost is not a factor, the sonic profiling method is by far
the best way of obtaining an accurate representation of
small-scale subaqueous bed forms.
Acoustic Grid. This method of underwater survey is
the acoustic equivalent of direct trilateration. In its
simplest form, three acoustic transponders are placed at
known positions on the sea bottom. These transponders
are interrogated sequentially from within their estab-
lished grid, and the time delay before each response
occurs is measured and recorded. If the velocity of
sound in seawater is known for that area and time, the
delay in time can be related to the distance between the
interrogator and each of the transponders.
Transponders are implanted and their positions are
determined using direct underwater survey methods.
The interrogator is a small, hand-held directional sonar
device that has a digital readout of the time delay. The
diver, positioned above the point to be surveyed, aims
visually at the first transponder and takes three readings.
The process is repeated for the other two transponders.
Ideally, the data are sent to the surface via an underwater
communications link. In the absence of this equipment,
the data should be recorded on a writing slate attached
directly to the interrogator. The accuracy of this system
can be increased significantly by using four or five
transponders.
Because so many variables affect the velocity of
sound in seawater, errors in measurement can have a
significant effect on the resulting mathematical anal-
ysis. For example, sound velocity measurements in
very shallow water can be affected seriously by errors
in recording temperature. Accurate results depend on
keeping the salinity and temperature measurement errors
small enough so that the errors in velocity are below
the inherent equipment-introduced errors.
More sophisticated versions of the acoustic grid survey
system are available, and many of these read out range
directly. Although more convenient to use, system
inaccuracy may still be created by variability in speed
of sound. Compact and reasonably priced sound veloci-
meters are now available that permit in-situ measure-
ments to be used immediately as survey system correctors.
The acoustic grid is particularly valuable when a
site is visited repeatedly to measure features that vary
over time, such as the motion of sand waves. Another
advantage of this system is its internal completeness. If
the geodetic location of the site is not important and
9-4
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-3
High-Frequency
Sonic Profiler
Photo Tom Harman
only relative position and motion within the site are to
be measured, the acoustic grid is an appropriate method.
It is also possible to relate the grid measurements to a
geodetic map at a later time.
Phase Measurement. Unlike the acoustic grid method,
which determines the position of an object relative to a
fixed network of transponders, phase measurement
systems are contained within the support ship except
for a single mobile transponder. Three receiving elements
are located precisely with respect to each other on the
underside of the support craft; they are usually attached
to a mast extended over the side of the craft. A diver
places a transponder on the object whose position is to
be determined, and an interrogator located on the ship
queries the transponder. A phase analysis is performed
by the receiver on the return signal, which is displayed
as deflection angle and line-of-sight range to the object
with respect to the receiver element mast. The only
variable is velocity of sound, which must be determined
by the method discussed previously.
Small transponders are available that can be strapped
to a scuba cylinder so that the position of the diver can
be monitored continuously by personnel in the support
craft. When continuous communication is available,
the diver can be directed through a geodetically fixed
survey pattern if the ship's position is known accurately.
This system is suited to applications where a large
area must be surveyed or where there are only one or
two sites of interest. Although the system has the
disadvantage of requiring a surface-support platform.
its inherent mobility and flexibility are distinct advan-
tages except in situations where job requirements make
the acoustic grid or one of the direct methods preferable.
Under certain conditions, the phase measurement
system can be more fully utilized if diver towing tech-
niques are employed. In this case the position of the
diver relative to the support ship must be monitored
continuously, which increases both ease of operation
and accuracy. Combining the phase measurement system
with a good diver-to-surface communication system
results in an excellent survey procedure.
9.3 UNDERWATER RECORDING METHODS
The simplest and most widely used method for recording
data under water involves using a graphite pencil on
a white, double-sided plastic board. These records
are sufficiently permanent to withstand normal handling
during a dive. Since most divers use abbreviations
and shorthand in recording observations and species
names, however, the notes should be transcribed as
soon as possible. Wax pencils are usually not satis-
factory because they become brittle and break in cold
water, and pencil holders have metal parts that will
corrode. Ordinary pencil lead can be cleaned off easily
with scouring powder, but wax smears and often must
be removed with a solvent. Mechanical pencils are
unsatisfactory, since the metal parts will soon corrode.
The best writing instrument is an off-the-shelf, readily
available plastic pencil that uses bits of sharpened lead
encased in plastic butts.
Slates can be made multipurpose by adding compasses,
rulers, or inclinometers (see Figure 9-4). Because there is
a risk of misinterpreting the often rather erratic notes
made under water, a list of tasks to be undertaken and
the form to be used for all measurements should be
developed before the dive. These lists and tables may
be inscribed on the plastic pads. In some cases it is
desirable to retain the original records (this is particularly
important in the case of archeological drawings, for
instance); drawings then are made with wax crayons on
waterproof paper attached to the plastic board by screws
or rubber bands. There are several types of underwater
paper, including a fluorescent orange paper. Standard
formats can be duplicated ahead of time to facilitate
recording during a dive. A simple and inexpensive
technique for underwater data sheets is to prepare the
sheets on regular typing paper and then have each
sheet laminated in the same way that drivers' licenses
and other important identification are preserved.
Where precise measurements are to be made, it is
good practice for two observers to take independent
October 1991 — NOAA Diving Manual
9-5
Section 9
Figure 9-4
Multipurpose Slate
Photo Robert Dill
measurements and to check them with each other for
agreement before returning to the surface. If there is
disagreement, the measurements should be repeated.
Tape recording is another useful, although somewhat
specialized, method of documenting data under water.
The most satisfactory and reliable system includes a
cassette tape recorder as part of the hardwire two-way
communication system used in umbilical diving; the
alternative is a self-contained unit carried by a diver
in the scuba mode. The position of the microphone and
the way in which it is waterproofed is critical in
determining the usefulness of an underwater tape
recorder.
Some commercial systems feature a special mouth-
piece unit into which a microphone is built and to
which the scuba regulator is attached. Standard
mouthpiece bits, however, do not allow the lips to move
sufficiently to form anything more than simple words
or noises, which are usually intelligible only to the
speaker immediately after the recording is made. This is
especially true for biologists giving long lists of scientific
names or for scientists reading numbers from instruments.
NOTE
The most critical factor to consider in a voice-
recording system for data gathering is the
ability of the diver to speak and enunciate
clearly enough to be understood and trans-
cribed accurately.
The best equipment configuration is a full-face mask,
equipped with a microphone that is located away from
the immediate mouth area; this position diminishes
9-6
breathing noise and increases voice fidelity by picking
up sounds from the resonating chamber formed by the
mask rather than from the high-sibilance area in front
of the lips. Several commercially available masks are
equipped with demand regulators that can be used
with standard scuba cylinders or with an umbilical air
supply. When an umbilical is used, most diver-tender
communications systems can be wired to accept a tape
recorder so that both sides of the conversation can be
recorded. Regardless of the unit selected, divers should
practice using the system in shallow water until they
can produce intelligible transcriptions routinely.
To optimize recording fidelity and minimize distortion
and interference, cassette tapes of the highest quality
should be used. At present, commercial tapes are
available that have 60 minutes of recording time on
each side, and this capacity is generally sufficient for
most scuba missions. Maintenance is especially important
for tape recorders; special care must be taken (checking
O-rings, seals) to prevent corrosion.
9.4 BIOLOGICAL SURVEYS
Biological surveys generally have the same requirements
and involve the same techniques as those described in
Section 9.2; however, some specific aspects should be
mentioned. Biological surveys are used for many pur-
poses, including determining the environmental impact of
placing man-made objects on the seafloor and assessing
the effects of ocean dumping on marine resources. In
most marine environments, it is not possible to evalu-
ate the impact of man-made changes without performing
special baseline surveys designed to obtain specific
information about the biota and the physical environ-
ment. To be meaningful, these studies must be made
before structures are emplaced on the seafloor or material
is discharged into the area. When baseline information
cannot be obtained before the natural undersea envi-
ronment has been altered by human actions, biological
surveys can be used to determine the incremental impacts
of subsequent activities.
Baseline studies must be designed so that they can
be monitored at prescribed intervals. Control stations
placed outside the area being studied are necessary to
provide data on environmental changes occurring
naturally (e.g., seasonal effects).
The techniques of underwater biological surveying
involve establishing a standardized methodology to
make the results of the survey quantitatively meaningful
and ecologically acceptable. This is done by choosing
stations at specific depth intervals along a transect
line and dropping an anchor at each station to serve as
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
the center of a circle of study. Quantitative observa-
tions are then made within the circle; general bottom
topography and biological features of the areas beyond
the circles are also noted.
The amount of bottom area covered does not need to
be the same for every station; water clarity and the
complexity of the biota will affect the size of the study
circle. The poorer the visibility, the more restricted the
amount of bottom that can be surveyed. In West Coast
regions and for sand stations having a limited macrobiota,
a 10.2 foot (3.1 m) line is generally used to produce a
323 square foot (30 m2) area of study. In rocky areas,
where the biota is more diverse, a 7.2 foot (2.2 m) line
can be used to define the radius of the circle of study.
In addition, using tools such as plankton nets and
bottom cores, scientists can estimate the number of
plants and animals, take quantitative samples of life
forms, and take photographs of general bottom conditions
and of each quadrat.
Environmental factors that must be considered when
surveying the establishment and growth of underwater
communities include exposure to wave or swell action,
type and slope of substrata, water temperature, dissolved
oxygen and nutrient content, and extent of grazing.
Variations in the intensity and spectral composition of
light under water also have a significant effect on plant
communities, but it is often difficult to obtain accu-
rate light measurements. The illumination at or within
a given plant community can be obtained with accuracy
only by actual in-situ light measurements; photographic
light meters are not satisfactory for this purpose.
Underwater spectroradiometers, which are probably the
most effective means of measuring light in the sea,
are available. Submersible spectroradiometers have
been used in studies of photosynthesis and calcification
rates of corals.
Most underwater investigators have used transect or
simple quadrat methods for the analysis of benthic
communities. A reasonable description of the change
in biota relative to depth and other factors can be
obtained by measuring the area of cover along a strip
or band transect. Accurate quantitative data on standing
crops can best be obtained by collecting the entire
ground cover from a quadrat and sorting this into
component species in the laboratory for subsequent
analysis.
9.4.1 Estimating Population Densities
When estimating the biological content or density of
a given region, it is necessary to take surface area into
account. An irregular surface can greatly increase the
area; to the extent that the surfaces sampled depart
from the horizontal, area will be underestimated, which
will cause density to be overstated. This bias becomes
particularly important as the scale of the surface vari-
ation approaches the scale of the distribution being
measured. Dahl (1973) describes a technique designed
to quantify the estimation of irregular surfaces in the
marine environment. Briefly, the technique consists of
making some simple height, frequency, and surface
length measurements and then applying a surface index
formula to determine the surface area. The technique
has been applied to coral reefs, benthic algal substrata,
Thalassia, sand and rubble zones, reef crests, and patch
reefs.
A simple method for estimating populations of sessile
organisms is described by Salsman and Tolbert (1965),
who used it to survey and collect sand dollars (Fig-
ure 9-5). At each location sampled, the authors spent 10
to 15 minutes making observations, taking photographs,
and sampling population density. To facilitate counting
and to ensure a random sample, a counting cell was
constructed by bending an aluminum rod into a square
11.8 inches (30 cm) long on each side. Inexpensive
counting squares also can be constructed using PVC
tubing. As divers approached the seafloor, they released
the square, allowing it to fall to the bottom. The organ-
isms within this square were counted and collected for
later size determination; this procedure was then repeated
at least two more times at each location sampled. The
same method can be used to take a random sample of
any sessile organism.
A device used for surveying epifauna is the diver-
operated fishrake (Figure 9-6). It has been used to
obtain information on the small-scale distribution
patterns and estimates of population densities of demersal
fishes and invertebrates. The apparatus consists of a
metal tubular frame fitted with a handle, a roller of
rigid PVC tubing into which stainless steel wire "staples"
are fixed, and an odometer made of a plastic tracking
wheel and removable direct-drive revolution counter.
It is pushed along the bottom by a diver who makes
visual counts, size estimates, and other observations
on animals that occur within the path traversed by the
roller.
In some underwater situations involving observations
of animal behavior, it is necessary to remain a reasonable
distance from the subject so as not to interfere with
normal behavior. Emery (1968) developed an underwater
telescope for such situations by housing a rifle scope in
PVC tubing with acrylic plastic ends. The underwater
scope described by this author functioned satisfactorily at
depths as great as 180 feet (55 m). An underwater
telephoto camera lens was used during the Tektite II
October 1991 — NOAA Diving Manual
9-7
Section 9
Figure 9-5
Counting Square for Determining
Sand Dollar Density
Figure 9-6
Diver-Operated Fishrake
•MP"
Courtesy U.S. Navy
experiments to avoid interfering with animal behavior
(VanDerwalker and Littlehales 1971).
At the other end of the magnification continuum is
an underwater magnifying system (Pratt 1976). This
device, referred to as the Pratt Macrosnooper, has a
magnification power of seven and permits the diver to
study marine organisms too small to be comfortably
observed with the naked eye. It is a three-element lens
system designed specifically for use under water and
consists of three lenses with appropriate spacers inserted
into a 2 inch (5 cm) plastic pipe (see Figure 9-7). Holes
are then drilled through the housing and the spacers to
permit the entry of water for equalization at depth.
When in use, the Macrosnooper is held against the
mask faceplate. It should be cleaned and rinsed carefully,
along with other diving equipment, after each use.
Soap, mineral, or fungus deposits, which may be removed
by an overnight soak in either bleach, vinegar, or laun-
dry detergent, may form on the lenses after prolonged
use.
9.5 BIOLOGICAL SAMPLING
Although a discussion of research design for a sampling
program is outside the scope of this volume, careful
attention should be given to the implementation of
sampling methods. Chapters on the design of sampling
programs can be found in Holmes and Mclntyre (1971).
As Fager and his colleagues have noted (Fager et al
1966),
Underwater operations have several advan-
tages over sampling from the surface for
ecological studies involving quantitative
sampling or observations of behavior. Prob-
9-8
s j* \s /-Z
J^y \^~~^SF
/ ss. yy~~~--~~~A\)
gv
< REVOLUTION
COUNTER
y
* yyyy copper pipe
yy PLASTIC ROLLER
Photo Art Flechsig
ably the most important practical one is the
ability to observe the sampling apparatus in
operation, to make estimates of its effec-
tiveness, and to improve the design or pro-
cedure in situ. In some cases, such as with
small demersal fish, underwater sampling
is considerably more effective than from
the surface. Direct observation gives one a
feeling for the types and magnitudes of the
errors associated with the sampling and allows
one to decide whether the sampling site is
unusual or representative of a larger area.
With the less common species, it may be
particularly important to be able to make
repeated population estimates without im-
posing unnatural mortality by the removal
of individuals.
Because a diver using marker buoys, stakes, or pingers
can return repeatedly to the same location, changes in
both environment and the biota can be followed for
considerable periods. In addition, changes can be imposed
on the environment by selective removal of species, by
alteration of substrata, and so on, and the effects of
these experimental manipulations can be followed in
detail.
9.5.1 Plankton Sampling
Planktonic organisms that live within 3.2 feet (1 m) of
the bottom can be sampled with a skid-mounted
multilevel net apparatus that is pushed by a diver over
a predetermined distance. Hand-operated butterfly
valves are used to isolate the collection bottles located
in the cod end of the net.
Plankton sampling nets 11.8 inches (30 cm) in
diameter, with a mesh size of 0.08-0.12 inch (2-3 mm)
are used to collect plankton selectively in reef areas.
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-7
Underwater Magnification System
A. Optical System
Figure 9-8
Hensen Egg Nets Mounted on
a Single Diver Propulsion Vehicle
B. Complete System
Photo Harold Wes Pratt
Air-filled bottles also can be inverted in appropriate
areas to suck up plankton and water samples.
Several methods of sampling plankton have been
developed. Ennis (1972) has employed a method using
two diver propulsion vehicles on which a 19.7 inch
(50 cm) plankton net was mounted. A similar method was
used during a saturated dive in the Hydrolab habitat
at Grand Bahama Island, when two 3.2 foot (1 m) long
Hensen egg nets were mounted on a single diver
propulsion vehicle that was operated at a speed of
about 2 to 3 knots (1 to 1.5 m/s) (Figure 9-8). At the
end of every run, each net should be washed separately
and the sample should be concentrated into the cod end
by holding the net up inside a trapped bubble of air
under a plastic hemisphere having an 18 inch (45.8 cm)
radius. The cod end should then be removed, and the
contents of the net should be poured into a glass jar.
The jar should be filled, except for a small volume at
the top, with filtered seawater, and plastic wrap should
be placed over the top of the jar to trap a small bubble
of air. The jar is then removed from the hemisphere
and carried to a work area at the base of the habitat.
The work area should be deeper than the hemisphere so
that hydrostatic pressure will help to keep the air bubble
from escaping. A syringe filled with formalin is then
pushed through the plastic wrap, the jar is capped,
immediately secured, and labeled. When this procedure is
October 1991 — NOAA Diving Manual
Photo William L High
carried out properly, there is no sample loss. Before a
net is reused, it should be turned inside out and back-
flushed.
9.5.2 Benthic Organism Sampling
Quantitative sampling of the epifauna can be accom-
plished by counting the animals within a randomly
located circle or square quadrat. A circle template,
fixed center rod, and movable arm may be constructed
of brass, with the center rod and movable arm marked
with grooves at 0.4 inch (1 cm) intervals (Figure 9-9).
The position of an animal within the circle can be
defined by three numbers: the distance along the center
rod from a standard end; the distance from the center
rod along the movable arm; and the half of the circle
within which the animal was observed. To study details
of the distribution pattern of individuals of sedentary
species, the "distance of the nearest neighbor" tech-
nique can be used. This method involves preassembling a
large, lightweight metal or PVC square and dropping
it at the appropriate location. Within the square, divers
place short brass or plastic rods with fabric flags on
them at predetermined positions in relation to the
individuals of the species being examined. After the
positions of all individuals have been marked, distances to
nearest neighbors are measured, and reflexives are
counted.
Samples of the substrate and infauna can be collected
with no loss of sediment or organisms by using a simple
coring device with a widemouth sample container (a
jar) attached to the top (Figure 9-10). The corer is
pushed a given distance, e.g., 2 inches (5 cm), into the
sand, tipped slightly, and an aluminum plate is slipped
under it through the sand. The apparatus is inverted
and the sediment is allowed to settle into the jar. Once
all sediment and organisms are inside the jar, the coring
attachment is removed and the jar is capped.
9-9
Section 9
Figure 9-9
A Circle Template for Determining
Benthic Population Density
Figure 9-10
Coring Device
With Widemouth Container
Photo Art Flechsig
Another simple soft-bottom sampling device, es-
pecially good for small infauna and meiofauna, is a
thin-walled coring tube of transparent plastic, the
diameter of which is based on a predetermined sample
designed to gather the desired substrate and organisms
most efficiently. Most organisms obtained by this type
of device will be found in the top 3.9 to 4.7 inches (10 to
12 cm) of the sample. For ease of handling, the tube
should be at least 11.8 inches (30 cm) long and sealed
with rubber corks, one of which has a small hole drilled
through it. With both corks off, the tube should be
rotated carefully into the sand to the desired depth,
and the cork with the small hole should then be used to
cap the tube. While gripping the tube for removal, the
scientist's thumb should be held over the hole to create
a suction that keeps the sediment from falling out.
When the tube is free of the sediment, the bottom cork
should be inserted. Samples accurate to any depth can
be taken with this device, and depth lines can be marked
on the outside of the tube. To remove the core, the
scientist places a finger over the hole in the top cork,
removes the bottom cork, and allows the plug to fall out.
To remove discrete segments of the core, the plug may
be pushed out the end and cut into desired lengths or
quick-frozen in dry ice immediately upon surfacing
(to prevent migration of animals) and later cut with
a hacksaw.
A multilevel corer is used for studying the depth
distribution of infauna. This corer samples an area of
about 1 inches square (45 cm2) to a depth of 2.4 inches
(6 cm). The corer consists of a square brass box fitted
with a funnel adapter at the top to accept widemouth
sample containers. The front side of the corer is slotted
to permit thin metal slide plates to be inserted to
separate the sample into five separate layers, which
can then be transferred under water to separate sample
containers.
Photo Art Flechsig
Another coring device for obtaining quantitative
samples of the infauna is a square stainless steel box
with handles and a screen covering one end (Fig-
ure 9-11). Its rugged construction allows scientists
forcibly to penetrate hard substrates, such as sand or
vegetated bottoms, as well as softer sediments. The
sampler, currently in use by NOAA/NMFS divers, can
obtain a 0.17 square foot (1/64 m2) sample to a depth of
9.1 inches (23 cm). After the corer is pushed into the
substrate to the desired depth, one side of the device is
excavated and the device is tilted over, after which the
corer and sample are pulled free. To prevent any loss of
sample, the diver holds the open end of the corer against
his or her body while ascending. The contents are then
placed in a sieve of appropriate mesh size (Fig-
ure 9-11), washed free of most of the sediments, and the
residue containing the organisms is placed in jars of
preservative. A red dye (usually Rose Bengal) is added
to the preservative to facilitate the sorting and identi-
fication process.
A Multiple Disc Sampling Apparatus for collecting
epibenthic organisms has been developed by NOAA/
9-10
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-11
Infauna Sampling Box
0 701 mm2
Mesh Screen
Stainless Steel
1.2 cm Diameter
0701 mm2
Mesh Screen
1.6 mm
Stainless Steel
Plug Sampler
Source: NOAA (1979)
NMFS divers. Each collecting unit consists of a disk
9.7 inches (24.6 cm) in diameter with a surface area of
0.54 square feet (1/20 m2). Various kinds of material
have been used in the construction of the disks (wood,
glass, steel, rubber, cement). Rubber and cement
generally are superior substrates for most sessile
invertebrates. The disks are wired to a galvanized pipe
frame placed on the bottom by divers. Individual disks
are removed at intervals by divers who place a canvas
collecting bag over the disk and cut the wire holding
the disk to the frame. This procedure minimizes the
loss of motile organisms. Individual bags containing
the disks are filled with a narcotic solution (7.5%
magnesium chloride mixed 1:1 with seawater) for 1
hour and the disks are then preserved in a 10 percent
formalin solution. Wiring disks rather than bolting
them simplifies the operation and eliminates the problem
of corroded fastenings. The experimental design — col-
lecting frequency, substrate material to be tested, or
other epifaunal survey requirements — dictates the
number of disks to be used. Because of the large size of
disks, the epifaunal assemblages that are collected by
this method are more typical of those found on natural
substrates. However, only a portion of each disk is
examined and enumerated.
Some knowledge of geological techniques is helpful
when sampling. For example, on rocky substrates it is
important to know how to measure angles of inclines on
overhangs or shelves, because this angle influences the
orientation of many organisms (see Section 9.10.1).
Similarly, knowing the composition of the rock is
important in determining whether or not organisms
can bore into it or merely attach to it, and the rock's
composition will also determine its resistance to erosion
over long periods. In soft bottoms, it is useful to describe
sediment grain size and bottom configurations; deter-
minations of grain size, chemical composition, and
other physical characteristics are best done by scientists
especially equipped to handle these tasks. Situations
vary, and it may be helpful to consult geologists for
recommendations on where to obtain the appropriate
geological data.
9.5.3 Airlift Sampling
An airlift is a sampling device that consists of a long
plastic pipe equipped with a device to supply air at the
lower end. The airlift carries sediment and organisms
to the top of the pipe in a stream of air and water, so
that they can then be emptied into a mesh bag of a
certain size (see Section 8.9.1). Large areas of soft
bottom can be collected in a very short time with this
device, and the samples can be screened through the
bag in the process. When used with a diver-held scraping
device, an airlift is also useful on hard substrates,
especially to collect the small organisms that tend to
escape when attempts are made to "scrape and grab."
9.5.4 Midwater Sampling
Although plastic bags have been used successfully
to sample swarming copepods and small aspirators
have been used to sample the protozoan Noctiluca,
animals in midwater must generally be collected using
October 1991 — NOAA Diving Manual
9-11
Section 9
Figure 9-12
Use of a Hand-Held Container
to Collect Zooplankton
other techniques. It is difficult to sample even very
small animals, such as the copepod Oithona, without
disturbing them. Although small, copepods swim rapidly
for short distances and readily dodge water bottles,
nets, or aspirators. If nets must be used, they are deployed
most effectively by divers swimming the nets by hand
or guiding diver-propulsion units to which the nets are
attached (see Figure 9-8). No objects should obstruct
the mouth of the net, because even monofilament bridles
cause zooplankton to avoid nets.
The diver can easily capture larger, less motile
zooplankton that range from several millimeters to a
few centimeters in size, such as the gelatinous medusae,
ctenophores, salps, pteropods, and chaetognaths, etc.,
by permitting the animals to swim into a hand-held
container, preferably of clear plastic or glass (see Fig-
ure 9-12). This is the preferred method of data collection
for all aspects of laboratory marine research, because
it is the way to collect these delicate animals without
the damage that normally occurs even with the most
carefully handled net.
Estimating density of planktonic aggregations. For
many kinds of organisms, density and distribution can
be determined photographically without disturbing the
aggregation. The use of an 80-mm lens and extension
tubes provides a small measured field of view some
11.8 to 15.7 inches (30 to 40 cm) from the camera.
Depth of field varies systematically with f-stop (see
Section 8.13). Instructions for some underwater cameras
provide these calculations, but investigators can make
them for their own cameras by photographing underwater
targets at a series of known distances in front of the
camera with different f-stops and determining the
depth of field in the resulting photographs. Density of
organisms such as copepods within swarms is determined
by counting all of the animals in focus in the photograph,
i.e., within a known volume determined by area of field
times depth of field. When the number of organisms in
focus is large, density can be estimated by measuring
the distance from one individual to its closest in-focus
neighbor for each of some 20 individuals within a
single plane. These distances are averaged and the
density of the aggregation is estimated by entering this
average into the formula for close packing of spheres
or of isohedronic arrays. Use of the formula
1,000,000 cm3/0.589 x (average nearest neighbor's
distance in cm)3 =
Number of organisms per meter3
is preferred because isohedrons pack symmetrically
along all three axes, whereas spheres do not.
9-12
ftp' * • ~WM
^^y
y^w
B^afl
Photo Al Giddings
Density measurements for animals sparsely distributed
can be obtained more easily by swimming line transects
between tethered buoys while counting the number of
animals that pass through a grid of selected size (see
Figure 9-13). Divers also may drift slowly on a tether
with the ship and estimate densities by measuring the
drift rate and counting the number of organisms that
pass through a grid in a specified time.
Replicated measurements permit the application of
most normal statistical procedures used in quantitative
ecology. Some tests are of questionable validity because
many statistics depend on presupposed patterns of normal
distributions, patterns that may not apply to three-
dimensional arrays. Nonetheless, many of the sampling
procedures used by the terrestrial ecologist may be
applied to underwater sampling. Biological oceanogra-
phers now use these new techniques frequently.
9.6 SHELLFISH STUDIES
The use of diving as a research tool to study lobsters,
crabs, scallops, and other types of shellfish has increased
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-13
Use of a Plexiglas Reference Frame for
Estimating Population Densities in Midwater
Courtesy ^National Geographic Society
Photo Al Giddings
as a result of both the commercial importance of these
living resources and the difficulty of sampling these
organisms effectively with conventional surface-oriented
equipment. In general, shellfish studies have been
directed toward the ecology of these organisms, their
behavior in relation to sampling gear, the efficiency of
sampling gear, and the potential effects of conventional
sampling techniques on the bottom environment and
its fauna.
Historically, more underwater studies have been
conducted on the American lobster of the New England
coast than on any other single species of shellfish. In
addition, extensive studies have been done in Florida
and California on the spiny lobster (Herrnkind and
Engle 1977, Marx and Herrnkind 1985).
Direct in-situ observation of lobsters is the most
effective way to study lobster ecology and behavior.
Comparative studies of lobsters in the laboratory-
aquarium environment have shown that their behavior
is altered significantly when they are in captivity. For
example, lobsters held in captivity are highly canni-
balistic, but cannibalism is rare in the natural environ-
October 1991 — NOAA Diving Manual
ment. In addition, lobsters less than one-half pound
(0.22 kg) in size generally are not nocturnally active in
their natural environment but are active at night in the
confines of an aquarium tank. Lobsters spend most of
their first 3 years of life in a labyrinth of tunnels
projecting as many as 3 feet (0.9 m) into the boulder-
rock substrate of the ocean bottom (see Figure 9-14).
Replicating this substrate in an aquarium is difficult.
9.6.1 Collecting Techniques
Many shellfish (crabs, lobsters, and clams) inhabit
tunnels and burrows on the bottom. Others (scallops,
oysters, and abalone) live in beds and reefs or creep
across the seafloor and rocks. When collecting shellfish,
divers should always wear gloves and carry catch bags.
Lobsters inhabit burrows, tunnels, and caves in shallow
coastal waters and in ocean depths that are beyond the
range of surface-supplied diving. Those more than
one-half pound in size are nocturnal in their movements;
during daylight hours, they remain in their homes.
When picked up, spiny lobsters and bulldozer lobsters
should be held by the back; if grabbed around the
abdomen (tail), the tail can cut a diver's fingers. The
American lobster can be collected easily by grabbing
it from the back, behind the claws. Lobsters can also be
grabbed by their ripper claws and held for l to 2
seconds; if held longer, their crusher claws will be
brought into action. Lobster claws should be inactivated
by banding or pegging before the animal is put in a
catch bag; this will prevent animals from crushing
each other. Lobsters frequently will autotomize (drop)
antennae and claws when handled; American lobsters
do this especially during the winter months, when
water temperatures range between 28.5° and 34.0° F
(-1.94° and 1.1°C).
The conventional method for commercial harvesting
of the spiny and New England clawed lobster is the
wire or wooden trap. Divers should assess the efficiency
and design of this gear before using it, bearing in
mind that spiny lobsters move much faster than
American lobsters and are much more sensitive to
being disturbed.
Commercial crabs are found in waters ranging from
shallow estuaries to ocean depths that are beyond
conventional diving limits. Gloved divers can catch
them easily by hand with short-handled scoop nets and
tongs. Caution should always be exercised when
collecting crabs because they can pinch with their
claws; depending on the size and species, such injuries
can vary from a cut finger (blue crab or Dungeness
crab) to a broken finger (stone crab or Alaskan King
crab).
9-13
Section 9
Figure 9-14
Benthic Environment
of the American Lobster
Surface
Distance from Shore (Meters)
100 150 200
National Marine Fisheries Service
Blue crabs live in the shallow, temperate waters of
estuaries, bays, and sounds in the Gulf of Mexico and
Atlantic Ocean. When frightened, they will burrow
quickly into the bottom or swim away with great speed.
These fast swimming, pugnacious crabs can be collected
easily with a short-handled scoop net. They can be
found partially buried and lying around shells and
rocks or walking along the bottom.
Stone crabs inhabit burrows, depressions, and shell
houses in the coastal waters along the South Atlantic
and Gulf of Mexico states. An 18 inch (45.7 cm) pair of
tongs is useful to extricate them from burrows and
shell houses. Their claws can be brought into action
quickly and can easily crush fingers, so they should be
handled carefully. Stone crabs should be handled by
their rear legs.
The Alaskan King crab lives in the cold waters of the
North Pacific Ocean and the Bering and Okhotsk Seas.
Young crabs (2 to 3 years old) inhabit shallow waters
in large "pods" of 2000 to 3000 individuals and migrate to
deeper water as they mature. Mature crabs (males
range up to 6.6 feet (2 m) and 22 pounds (10 kg))
migrate seasonally between deep and shallow water to
spawn. As the crabs walk across the bottom, divers can
collect them by grabbing them cautiously from behind.
Dungeness crabs are found in shallow inshore,
estuarine, and offshore waters from southern California
to Alaska and the Aleutian Islands; they live in waters
that are up to 328 feet (100 m) deep. These large crabs,
which range up to 9.4 inches (24 cm) across the back
and up to 2.2 pounds (1 kg) in weight, can move quickly,
occasionally even faster than a diver can swim. Individual
crabs can be captured from behind and placed in a
mesh bag, if this is done cautiously.
Oysters inhabit relatively shallow waters in estuaries,
bays, and sounds in the Gulf of Mexico, off the Atlantic
coast states, and in the North Pacific. They occur
individually, in clusters attached to rocks and pilings,
and together, in large beds of thousands of individuals.
These sedentary shellfish are easy to collect by hand. A
pry bar can be used to collect samples that are attached.
Oysters can temporarily be piled loosely on the bottom
during harvesting.
Scallops live in bays, sounds, and ocean bottoms in
depths up to 328 feet (100 m). Density varies from one
or two individual scallops to dozens per square meter.
They are collected easily by hand or scoop net. Loose
piles of scallops should not be left on the bottom because
the scallops may swim away. Getting one's fingers
stuck in the shell of a live scallop is painful.
Abalone inhabit rocky coasts from Alaska to southern
California. They are nocturnal foragers of algae and
rest during the day at their "homespots" on a rock. An
iron pry bar can be used to pull them loose, and they
can sometimes be pried loose quite easily with a quick
motion.
9.7 TAGGING AND MARKING TECHNIQUES
Tagging aquatic organisms can provide information on
many aspects of underwater life, including coastal migra-
tion, nearshore to offshore movement, seasonal distri-
bution, and growth rate. Because tagging can damage
the animal, the value of the information gained from a
return should be carefully considered.
There are two different methods of tagging marine
organisms: The animal can either be tagged in situ or
be captured and brought to the surface for tagging.
Figure 9-15 shows an electroshocking grid used to
collect fish for tagging. Although more traumatic for
the organism, the latter method has the advantage of
allowing the animal to be weighed, measured, and
examined in detail before release. Methods are availa-
ble to take measurements in situ under water. Although
body dimensions can be measured under water, a
satisfactory method for determining body mass (weight)
has not been developed.
Ebert (1964) described a fish-tagging gun that
inserted a standard dart tag into bottom-dwelling fishes
and which could be adjusted to account for skin or
scale thickness. More recently, the plastic "T" tag,
originally designed for marking clothing (Figure 9-16),
has been used. The needle of the tagging gun is placed
against the organism and the tag is inserted into the
body tissue. With practice, the depth of tag penetration
can be controlled by the tagger. Because this particular
gun has many metal parts, it must be washed and oiled
carefully to avoid corrosion.
9-14
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-15
Diver With Electroshock Grid
Courtesy Diving Systems International
Photo Steven M. Barsky
Lobsters have been tagged within their natural envi-
ronments with short-term (lost at shedding) and long-
term (retained at shedding) tags and marks. Lobster
dens may be marked with styrofoam floats, numbered
carefully to note specific locations. Color-coded tags
may be inserted into the dorsal musculature between
the abdomen and thorax of the lobster with the aid of a
No. 20 syringe needle (Figure 9-17). A secondary mark
may be made by punching a small hole (0. 1 6 in. or 4 mm)
into one of the five tail fan sections; this mark will
be retained through at least one molt and will permit
recognition of a lobster that has lost its primary tag.
Movements and locations of lobsters at night may be
determined by using small sonic tags (pingers). These
tags are small (about 1.2 x 2.0 x 0.4 in. or 3 x 5 x 1 cm)
and weigh only a few grams. Several types are availa-
ble commercially. They operate in the general frequency
range of 70 kHz and may be picked up as far away as
1200 feet (363 m) on an open bottom and 60 feet (18.4 m)
when the tagged lobster is in a crevice.
When conducting a survey of lobsters, it should be
kept in mind that the very presence of the diver and the
tagging procedures may affect overall behavior. In one
study, a significant alteration of the population dis-
tribution was noted during the course of several weeks
of capturing and tagging (Miller et al. 1971).
Long-term and short-term tags also have been used
by divers in crab population studies. Long-term dart
and spaghetti tags can be inserted at the isthmus of the
carapace and abdomen, the point from which the crab
exits when shedding. Short-term tags can be applied
to the legs or carapace. Carapace tags for blue crabs
consist of an information-bearing plastic spaghetti
tag with a loop of stainless leader wire at each end. A
loop is put around each of the lateral spines of the
October 1991 — NOAA Diving Manual
Figure 9-16
Tagging a Spiny
Lobster on the Surface
Courtesy Floy Tag and Manufacturing Inc
carapace, adjusted, and then crimped with a leader
sleeve. Other methods of short-term tagging include
staining by injection or dipping with vital stains, fluo-
rescent dyes, or phosphorescent dyes.
Tagging of oysters, scallops, and abalone can be
accomplished by attaching Petersen tags with glue or a
wire, painting the shell, using colored quick-setting
cement, or staining the shell with vital stains. The
excurrent holes on abalone shells are very convenient
points of attachment for tags. A method for tagging
abalone has been reported by Tutschulte (1968). This
technique involves attaching a small battery-powered
luminous beacon to the shell. During the night, the
movements of the abalone with the light source on
its shell are recorded on sensitive film by a camera
fixed several meters above the seafloor. Movement
of a marked animal may be recorded either as light
streaks (in time exposures taken with a still camera)
or as a moving point of light (in time-lapse cinema-
tography). Animals studied by this method are subjected
to a constant, low-intensity light and are not illumi-
nated by the periodic flashes of high-intensity light
required for direct observation in night diving; be-
havioral changes caused by unnatural light flashes
are therefore probably eliminated with this method.
A technique has been developed for tagging echino-
derms (Lees 1968). This method involves drilling. a
tiny hole completely through the sea urchin and inserting
an inert filament (monofilament line or high-quality
stainless steel line) that has been strung with small
pieces of color-coded vinyl tubing. The urchin first is
carefully removed from its hole or crevice and placed
in a holding device made from a weighted plastic bowl
lined with thick polyurethane foam; this enables the
diver to press the urchin down into the foam to hold it
still during the drilling operation. An ordinary hand
drill fitted with an 18-gauge, 4 1 /2-inch-long
(11.4 cm) hypodermic needle is used to drill completely
9-15
Section 9
Figure 9-17
Tagging a Spiny Lobster in Situ
Source: NOAA (1979)
through the test and body cavity. After the filament or
wire has been threaded through the needle, the entire
drill/needle assembly is slowly withdrawn, pulling the
wire through the body cavity and leaving wire and tags
in place on the urchin. The ends of the wire are then
twisted together to form a loop, and the loose ends are
trimmed.
The same technique can be used to tag sea cucum-
bers, except that the wire can be pushed through by
hand instead of with a drill. Animals tagged in this
fashion seem to be unaffected, and tags have been
known to last for 6 to 8 months. With sea cucumbers,
trimming the tags short is important because fish may
otherwise nibble on the long loose ends.
Tagging finfish requires special skill and handling.
The size of the fish must be sufficient so that the tag
will not impair the ability of the fish to navigate,
forage, or avoid predators. Lake (1983) lists several
guidelines for tagging finfish:
• use barbless hooks to catch the fish
• avoid the use of bait
• don't tag fish that have been tired by a long fight
• hold fish with a wet rag over their heads
• keep gills free of sand and dirt
• don't tag fish that are bleeding from the gills
• tag during cold water season whenever possible
• during tagging, make sure that fish are not out of
the water for more than 60 seconds.
A number of techniques have been used to tag finfish.
Three common methods involve Petersen disk tags,
spaghetti tags, and dart tags. Disk tags are about 3/8
or 1/2 inch (0.95 to 1.27 cm) in diameter and come in a
variety of colors. They can be attached to the back of
the fish with monofilament line. This type of tag should
not be used on fish that will grow to a large size because
the tag will cause pressure on the fish as it grows
9-16
(Randall 1961). Spaghetti tags are made of soft tubu-
lar vinyl plastic about 1/16 inch (0.16 cm) in diameter,
with monofilament nylon in the center. This type of tag
can be attached by running the line through the fish's
back beneath the rear of the dorsal fin. Because this
type of tag can snag on rocks or coral, the method is not
recommended for reef fishes. Dart tags consist of a
vinyl plastic tube with a nylon tip and barb. They can
be inserted into the back of the fish with a hollow
needle so that the plastic streamer bearing the legend
trails posteriorly, with a slight upward tilt. Although
this technique permits fairly rapid tagging, these tags
tend to come loose more easily than those implanted
via the first two methods.
Another method of tagging finfish involves injecting
colored dyes subcutaneously (Thresher and Gronell
1978). This technique has been used successfully in
situ for studying the behavior of reef fish. The dye can
be injected via disposable plastic syringes and dispos-
able needles. Although several different dyes have been
used, plastic-based acrylic paints are the most satis-
factory and apparently do not harm the fish or signifi-
cantly affect their behavior. Two methods have been
used, depending on the size of the species to be tagged.
For small-scaled and scaleless species, the needle is
inserted from the rear, parallel to the body surface, so
that the tip enters the skin, runs underneath it for a
short distance, and then emerges. This in-and-out
technique ensures that the tag is placed immediately
below the skin, the best position for producing a long-
lasting tag. Slight pressure should be placed on the
syringe to start the flow of dye (and ensure that the
needle is not plugged), and then the needle should be
pulled back under the skin and withdrawn. The smooth
motion results in an even line of color below the skin.
For large-scaled species, the needle should be inserted
under the rear edge of a scale and moved gently from
side to side while pressure is applied to the syringe,
which causes a small pocket of dye to be deposited
under the scale. Acrylic paint tags inserted in this
manner have lasted as long as 16 months; durability
depends in part on the color of the paint.
Scallops have been marked successfully using a quick-
setting calcium carbonate cement (Hudson 1972). This
material meets four criteria: 1) it does not harm living
tissue; 2) it is easy to apply and readily visible; 3) it
adheres to a wet surface and hardens under water; and
4) it makes a durable mark. The recommended mixture
for this purpose is:
• seven parts Portland gray (or white) cement
(Portland Type II is best because it is formulated
especially for use in seawater)
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-18
Elkhorn Coral
Implanted on Rocky Outcrop
• one part moulding paste
• two parts builder's sand (fine grain).
This mixture will start to harden in 3 to 5 minutes (or
sooner if less moulding paste is used). The materials
should be thoroughly mixed while dry, and three parts
of water should be added to 10 parts of dry mix. If
colored cement is desired, no more than 10 percent
additive by volume should be used, so that the strength
of the cement is not reduced. The final consistency
should be similar to that of a firm putty.
To apply cement to a scallop, the organism should be
removed from the water and the upper valve should be
pressed into a soft sponge to remove excess water. A
small quantity of cement (about 1/2 cc for scallops 0.4
to 0.8 inch (10 to 20 mm) in shell height and 1 cc for
scallops 1.2 inch (3 cm) or larger) is placed near the
lip and then rubbed firmly across the shell at right
angles to the ribs. This tightly grouts the depression
between the ribs and leaves a thin coating of cement
over the shell. Several quick thumb strokes are necessary
to distribute cement evenly out to the lip so that new
shell growth can be measured accurately. Only enough
cement should be applied to fill the inter-rib areas;
the upper surface of the ribs should be visible through
the coating. Marked scallops can be returned immedi-
ately to the holding tank, where they should be held
for several hours to allow further hardening. Scallops
marked in this way have retained this marking material
for 15 months or more.
The same type of cement has been used to transplant
live coral in reef areas and to mark large marine
gastropods and other delicate bivalve molluscs (Hudson
1978). Figure 9-18 shows a living elkhorn coral, Acropora
palmata, implanted on a rocky outcrop. Another method
for marking marine organisms involves the use of
various dyes. Alizarian Red dye has increasingly been
found useful for making permanent growth line marks
in living corals and other invertebrates. The dye does
not harm the coral, and subsequent growth can be
measured after the coral is sliced with a saw.
9.8 BOTANICAL SAMPLING
Studies of benthic macroalgae and seagrasses in their
natural environments focus on both nearshore intertidal
zones and depths. This is the region where sufficient
light can penetrate the water to support the growth of
diverse and often dense associations of photosynthetic
organisms that grow attached to bottom substrates
(Figure 9-19). Benthic algae can occur at depths greater
than 656 feet (200 m), but few species occur in these
"A*
Photo J. Harold Hudson
relatively deep habitats. The sites where most research
involving algal and angiosperm vegetation takes place
are shallow enough to be accessible with scuba equip-
ment.
Wherever stable substrates occur nearshore, on rocky
beaches, in estuaries or bays, or on coral reefs, various
forms of plants will develop. As with all underwater
work, however, site-specific features limit and strongly
influence the choice of sampling method. Large-scale
biologic studies may include samples or catalogues of
plants, recorded with estimates of area covered. Data
may sometimes be combined for forms or species (crusts,
Iridaea spp., for example), depending on the need for
taxonomic precision. Large discrete thalli, such as
taxa of brown kelp, usually are counted. In some cases
only indicator taxa, selected on the basis of economic
value, dominance, or ease of identification or counting,
are of interest. Sampling programs that are designed
to record abundance and distribution patterns of plants
and other sessile organisms are described in Sec-
tions 9.5.1 and 9.5.2.
Presence/absence data or estimates of abundance
are utilized for experimental studies as well as for
descriptive investigations. The methods employed for
these various objectives rely on sampling procedures
that have largely been adapted from terrestrial or
intertidal studies. Their applicability to subtidal work
depends on their efficiency under conditions where
time, mobility, and visibility are often severely limited.
These factors must be assessed independently for every
situation.
October 1991 — NOAA Diving Manual
9-17
Section 9
Figure 9-19
Algal Cover
of Rock Substrate
Photo Bill Bunton
9.8.1 Field Procedures
As with any ecological project, the objectives and
constraints of the study and the features of underwater
sites determine which techniques are appropriate. In
recent years, subtidal biological methods have been
summarized in books that draw on hundreds of scientific
and technical publications. These sources provide up-to-
date reviews of methods, as well as discussions of their
relative advantages and disadvantages. Accordingly,
the following paragraphs represent only a brief review
of botanical field procedures.
Generally, underwater botanical sampling, whether
of data or specimens, depends on the use of transect
lines, grids, and quadrats arranged in fixed, systematic, or
haphazard ("random" is rarely practical) positions.
Recently, circular sampling designs have been found
useful in sites of heavy surge, rough water, or low
visibility. In circular sampling, a radius-length line
attached to a central fixture is used to partition the
area and guide the diver. Underwater sites are usually
located on the surface by sighting or buoys and on the
bottom by a variety of fixed markers. Data can be
recorded by notations on data sheets treated for
underwater use, by collections of organisms, photog-
raphy, voice recorder, or television camera (see
Section 9.3).
Methods suitable for sessile animals are particularly
appropriate for investigating marine plants. Studies
that rely on these methods seek, in general, to dif-
ferentiate and classify plant communities and to analyze
the data to identify changes. As an index of productivity,
standing crop data can be obtained by collecting the
entire vegetation from a given area and sorting the
material into component species in the laboratory. These
specimens can then be dried, weighed, and reduced to
ash for analysis of organic content.
For ecological studies or census (.data, the size and
number of quadrats to be used must be determined by
appropriate tests, such as species accumulation curves,
and researchers often find it advisable to use an area
somewhat larger than the minimal one to be confident
of establishing statistically significant differences
between samples.
Seasonal variations in the diversity and abundance
of plants is very conspicuous in certain parts of the
world. To get complete coverage of events in an area
and to gain understanding of the natural cycles, it is
necessary to sample repeatedly throughout the year. It
is best to return to the same station to monitor changes
over time.
Some plants have a narrow temperature tolerance,
and these may act as indicator species because their
presence or absence suggests certain environmental
characteristics. North latitude kelp taxa, for example,
do not live in warm water and are not found in tropical
latitudes except where cold currents or deep cold water
provide suitable circumstances.
9.8.2 Collecting Techniques
Before beginning a study that requires the collection
of plants, an investigator should survey local environ-
mental conditions so that he or she will know where
and how to sample. Most macroalgae require a hard
substrate for attachment, and the diversity of plants on
rock surfaces usually is far greater than in soft sediment
or sandy areas. Pilings, shells, dead corals, barnacles,
shipwrecks, and mangrove roots are other places algae
are likely to attach. Marine vascular plants (seagrasses)
follow the reverse pattern; most species grow on soft or
sandy substrates, although some, such as Phyllospadix,
grow on the rocky shores of the western United States.
Frequently, seagrasses and larger algae themselves
provide substrates for a great array of smaller epiphytic
plants.
Because benthic plants are attached to the substrate, a
tool such as a putty knife, scraper, or knife is usually
needed to remove entire plants if these are required for
voucher specimens or for later study. Mesh bags or
small plastic vials with attached lids are useful for
holding samples. If plant samples are necessary for
identification, portions or selected branches are often
adequate. If there is no reason for collecting material,
a non-destructive sampling or experimental design
can be implemented. If small thalli are needed for
laboratory examination, it is often more efficient to
9-18
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-20
Diver in Giant Brown
Kelp (Macrocystis) Bed
collect pieces of rock or substrates than to remove and
handle plants during the dive.
When several divers are involved in a study, a system
for incorporating "unknowns" (specimens that cannot
be identified in the field) should be included in the
planning stage. Vouchers for such data as well as for
all critical taxa should be assembled and retained with
the raw data.
If an investigator wishes to obtain a census of an
area, collections from diverse substrates should be
sampled. Because some plants live only in intertidal
or shallow water, while others live only in deep water,
collections should be made over a broad depth range.
Data for large plants, such as the kelp Macrocystis
(Figure 9-20), that may be 100 feet (30 m) in length,
with holdfasts 3 feet (0.9 m) in diameter and as many
as 400 or 500 stipes, are usually based on in-situ
observations and measurements. Care should be exer-
cised when placing several types of marine plants in
a common container, because plants that have extremely
high acidic content may damage other forms of algae
in the container.
A clipboard with waterproof paper and pencil for
notes and a field notebook should be used to record
data immediately after diving. Diving observations
should be recorded as soon as possible. Ideally, field
data should include notes on depth, substrate, terrain,
water temperature, current, visibility (clarity), con-
spicuous sessile animals, herbivores, the date, time,
methods used, and the collecting party. If possible,
information on available light, salinity, and other
environmental factors should be obtained. Census data
become more useful if the relative abundance of each
species is at least estimated, i.e., whether common,
occasional, or rare. Many marine species are incon-
spicuous, and these require careful microscopic exami-
nation and identification in follow-up work.
Accurate light measurements within a given plant
community can be obtained by using small, self-
contained light meters. The use of photographic light
meters that incorporate selenium photocells is unsatis-
factory unless restricted spectral regions, isolated with
colored filters, are measured. This is because a sensing
system that responds differently to different wavelengths
is being used to measure light that is becoming
increasingly monochromatic with depth. The introduc-
tion of colored filters in front of the meter greatly
reduces its sensitivity. An opal cosine collector can be
added to make the system behave more like the plant's
surface does in terms of light absorption, but such
collectors can only be used in shallow, brightly lit
waters. The apparatus needed to make such measure-
ments generally incorporates a selenium photocell of
October 1991 — NOAA Diving Manual
Source: NOAA (1979)
increased surface area, which augments the current
output per unit of illumination; a system for easily
changing the colored filters; and a sensitive ammeter
whose range can be altered by current attenuation
circuitry.
9.8.3 Specimen Preparation and Preservation
To determine the kinds of plants present, notes should
be made on the collected specimens while they are still
fresh. Herbarium and voucher specimens can be made
from either fresh or preserved material. Plants prepared
soon after collection tend to retain their natural color
better than those that have been preserved, because
alcohol bleaches thalli more than formalin does.
Although procedures for drying and mounting large
algal and seagrass specimens are described in many
easily obtained and standard guides, a few simple
procedures are described here. Most marine algae have a
gluelike substance on the outside of the cells that makes
specimens more or less self-adherent to most kinds of
paper. Standard herbarium paper will preserve a
9-19
Section 9
collection permanently, but this paper is not a pre-
requisite for making a useful set of voucher specimens.
Formalin (2.5-5%) will preserve small or delicate forms,
and permanent slides are useful for ongoing work.
Time and place of collection and the name of the study
or collector should be associated with every specimen
by label, with a numbered reference to a field book or
data set.
There are standard herbarium methods for pressing
plants and some special variations for marine algae.
The usual approach is to float specimens in large, flat
trays and to slide them carefully onto sheets of heavy-
weight herbarium paper. Using water, the plants are
arranged on the paper; the paper is placed on a sheet of
blotting paper and topped with a square of muslin or
other plain cloth or a piece of waxed paper. This is
covered with another blotter, and a corrugated card-
board "ventilator" is placed on top. Another layer of
blotter — paper — plant — cloth — blotter — cardboard is
stacked on top. When 20 or 30 layers have been stacked,
the pile should be compressed, using a weight or the
pressure from heavy rocks or from straps wrapped
around the plant press. The top and bottom pieces
should be stiff; boards slightly larger than the herbarium
paper and blotters are generally used. After several
hours (or overnight), the stack should be taken apart,
and the damp blotters should be replaced with dry
ones. Many small algae dry in one day using this tech-
nique, but some, such as the large brown algae, may
take a full week to dry completely, depending on air
humidity.
The usual method for preserving specimens for later
detailed examination and herbarium preparation is
simple and effective. For each station, one or more
large plastic bags can be used to hold samples of larger
plants. Small bags or vials should be used for selected
fragile or rare plants. The best general preservative is a
solution of 3 to 4 percent formalin in seawater buffered
with 3 to 4 tablespoons of borax per gallon. Ethyl
alcohol (70%, made up with fresh water) is recommended
for longer storage. Plant and animal specimens should
not be mixed.
Permanent slides may be made of microscopic spe-
cies. One common method uses a solution of 80 percent
clear corn syrup and 4 percent formalin. The slides
should be allowed to dry slowly; as the syrup dries,
more should be added. The edges of the slide can be
sealed with clear nail polish.
Plants collected for histological study should be
preserved in a manner that is appropriate for the
particular technique to be used. In all cases, preserved
specimens should be kept in a dark place, because
exposure to light causes preserved plants to fade.
9-20
Samples obtained from many stations can be kept in
separate bags in a single large storage drum that can
be sealed tightly to prevent formalin from leaking out.
For shipping, most of the preservative can be drained
off, because the plants, once preserved, remain in good
condition for several weeks if they are kept damp.
An alternative method for preserving whole large
plants involves soaking them for several hours or days
in a solution consisting of 10 percent carbolic acid and
30 percent each of water, alcohol, and glycerin. Spec-
imens thus preserved may be dried and then rolled up
for storage. The glycerin helps to keep the plants flexi-
ble indefinitely. Another technique involves partially
air-drying giant kelp on newspaper (in the shade) and
rolling the plants, beginning with the holdfast. Rolls
are tied, labeled, wrapped in paper, and left to finish
drying. Specimens so prepared can later be resoaked
for examination.
If possible, one wet preserved specimen should be
kept for each pressed specimen. This is especially impor-
tant for unidentified species, because taxonomic clas-
sification often depends on cell structure. Some small
plants can be preserved with general collections, but
delicate specimens should be isolated. Retaining small
pieces of rock with encrusting algae attached helps
keep the plants intact. Coralline algae and rock-
encrusting species require special attention. Articu-
lated corallines may be pressed on paper and then
brushed with a diluted solution of white glue as an
alternative to older methods of storing in boxes.
Plants collected for particular purposes (electron
microscopic study, chemical analyses, culture inocula)
require special treatment. It is important to fix or
preserve such specimens as soon as they are removed
from seawater. Because algae are photosynthetic organ-
isms and the deleterious effects of surface light on
the pigment systems of specimens from subtidal habitats
can affect other metabolic processes, they should be
kept relatively cool and dark until placed in a killing
(fixing) solution or used for physiological work.
9.9 ARTIFICIAL REEFS
Artificial reefs are manmade or natural objects in-
tentionally placed in selected areas of marine, estua-
rine, or freshwater environments to provide or improve
fish habitats. Much of the ocean, estuarine, and fresh-
water environment has a relatively barren, featureless
bottom that does not provide the habitat that reef fish
need. Natural reefs and rock outcrops are limited; less
than 10 percent of the continental shelf can be classi-
fied as reef habitat. Even if rough bottom consists of
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-21
Fish Using Tires
as Habitat
Figure 9-22
An Artificial Reef Complex
Photo Dick Stone, National Marine
Fisheries Service
low-profile rock outcrops, it can provide a habitat for
fish and invertebrates.
Properly sited and constructed artificial reefs can
provide the same benefits as natural reefs. They can
enhance fish habitat, provide more accessible and high-
quality fishing grounds, benefit the anglers and eco-
nomies of shore communities, and increase the total
number of fish within a given area. Artificial reefs
function in the same manner as natural reefs. They
provide food, shelter, spawning and nursery habitat,
and orientation in an otherwise relatively featureless
environment.
Many non-toxic solid wastes or surplus materials
have been used in the United States to build reefs —
junked automobiles and streetcars, scrap tires
(Figure 9-21), damaged concrete pipe and building
rubble, surplus or derelict ships, and numerous other
materials, including gas and oil structures. Rocks,
tires, Christmas trees, and brush piles have been popular
reef materials in fresh water. More recently, fabricated
structures such as Japanese-style fish houses, concrete
structures, and fiberglass-coated plastic units have been
tested in the United States. Figure 9-22 shows an
artificial reef complex. Fabricated units are commonly
used in Japan and Taiwan. Fish aggregating devices
(FAD's) also are becoming popular in the United States;
these have been used for many years in the western Pacific.
Although artificial reefs can enhance recreational
and commercial fishing opportunities, creating a suc-
cessful reef involves more than placing miscellaneous
materials in ocean, estuarine, and freshwater envi-
ronments. Planning is needed to ensure the success of
artificial reefs. If materials are improperly placed or
constructed, all or part of a reef can disappear or break
apart and interfere with commercial fishing operations or
damage natural reefs in the vicinity.
October 1991 — NOAA Diving Manual
Source: Grove and Sonu (1985)
Divers can play a key role in documenting the suc-
cess of an artificial reef. The charting of reef material
on the site and any changes that occur over time are
important pieces of information to researchers and
managers. Also, diver estimates of reef fish popula-
tions can be made by direct counts of the number and
species at the reef sites. Species, number of individu-
als, mean lengths, and behavioral observations should
be recorded on waterproof data sheets (see Section 9.3).
When visibility is 4 feet (1.2 m) or more, these
observations can be made by two or more divers. Each
observer makes counts by species for sections of the
reef, and these are then totaled for the entire reef. The
totals obtained by all observers are averaged for a
mean species count of territorial and schooling fish,
such as black sea bass, Atlantic spadefish, snappers,
grunts, and most porgies. For seclusive fish, such as
cardinalfish, morays, and certain groupers, the highest
count obtained by any one observer is used. Although
the accuracy of fish population estimates varies with
visibility, species, and time of day, it is assumed that,
if conditions remain constant, the counts represent
population density. Photographs taken at intervals from
the same location also can be used to count and iden-
tify species. In this case, the photo print should be
placed on a soft surface and a pin hole put through
each identified fish; the print should then be turned
over and the holes counted. Visibility should be meas-
ured after taking the picture to compare the areas
covered by different photographs.
Diver-biologists have used direct observation tech-
niques to demonstrate that artificial reefs can be used
to augment productive natural reef and rough bottom
areas. They have also shown that these structures increase
9-21
Section 9
total biomass within a given area without detracting
from biomass potential in other areas.
9.10 GEOLOGY
Diving is an invaluable tool for many aspects of geologic
research. The advent of scuba in the late forties and
early fifties permitted easy access to the shallow
subaqueous environment for the first time. The results
of in-situ underwater studies soon began to appear in
the literature. Since that beginning, the scientific
applications of diving have increased to the extent that
many geologists now routinely use scuba as a research
tool. Although most underwater geologic research has
taken place in shallow marine waters, the same tech-
niques generally are applicable to research in lakes
and rivers.
The topics in this section are grouped into two general
categories — characterization and experimentation.
Geological characterization includes mapping, sampling,
and testing parts of the underwater environment, while
experimentation deals with the real-time analysis of
specific geologic processes. Experimental geological
studies rely in part on information obtained from
characterization studies, but they go much further in
that they require extensive interplay between geology
and other disciplines such as biology or fluid mechanics.
Initially, underwater geologic research primarily
involved the characterization of existing conditions,
but such studies now routinely entail experimentation
as well.
Although sophisticated methods have greatly ex-
panded scientists' sampling abilities, careful observa-
tion is still the mainstay of most underwater geological
studies. In some projects, observations may constitute
the main data collected; in other cases, careful docu-
mentation may be important either to select sampling
sites later or to place a chosen study site into the
larger context of its surrounding environment. One of
the most important elements of underwater geological
research, therefore, is accurate note-taking, coupled
with agreement on what was seen. It is advisable to
supplement notes with a debriefing immediately after
the dive and to record debriefing results along with
the underwater notes.
Although most research projects require specific
equipment, there are some basic tools that a diving
geologist should carry routinely. These include a com-
pass, inclinometer, depth gauge, noteboard, ruler, and
collecting bag. These are small items, and many of
them can be combined into a single tool. For example,
a small, oil-filled plastic surveying compass with in-
9-22
clinometer can be cemented to a clipboard or to a
plastic writing surface and a pencil can be attached
with rubber tubing; a plastic ruler can also be mounted
on the edge of the board (Figure 9-23). Other useful
equipment of a general nature might include: a still,
movie, or video camera; an assortment of small sampling
bags or vials; lights; and small coring tubes.
9.10.1 Mapping
Three basic types of mapping can be accomplished
under water: bathymetric, surficial, and geologic.
Bathymetric maps display the depth contour of the
seafloor. Surficial maps show the two-dimensional
character and distribution of the material that com-
prises the seafloor, and geologic mapping projects a
three-dimensional analysis of the rocks that crop out
on the seafloor.
Bathymetric mapping is best done from a surface
craft with echo sounding equipment. Multibeam swath
sonar systems are available in hull-mounted and towed
fish configurations; although expensive, their accuracy
is unsurpassed. A diver under water generally cannot
match the range and efficiency, the accuracy of location,
or the precision of depth determination and recording
possible from a surface craft. However, in unnavigable
water, or when taking precise measurements of a highly
irregular bottom or of features too small to be resolved
from the surface, underwater mapping may be the only
practical means of compiling the bathymetry.
Bathymetric mapping can also be done in detail over
a small bottom area to determine the area's microrelief.
Small-scale bed forms are an example of an important
geologic feature too small to be resolved from surface
craft. These forms develop in response to near-bottom
currents, and their presence indicates aspects of the
dynamics of the environment that otherwise may not
be readily apparent. Moreover, such features may be
preserved in the geologic record, where they are of
considerable use in deciphering ancient environments.
Scaled photographs of bed forms provide important
information on shape and orientation. In mapping
features such as sand ripples, however, the geologist
needs to determine the average size of the bed forms
over a section of seafloor. The small size of the bed
forms, the nature of the sediment, and the fact that bed
forms often are located in areas of strong wave-induced
or unidirectional currents create difficult sampling
problems.
Peterson's Wheel-Meter Tape Trianguiation Method.
This trianguiation method requires a wheel that is
mounted on a vertical shaft and that has a rim marked
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-23
Underwater Geological Compass
Photo Robert Dill
in degrees. The shaft is driven into the bottom at selected
locations. The 0-degree mark on the rim is aligned
with magnetic north. A meter tape, pulled out from the
top of the shaft, measures the distance to any point,
with the direction read on the wheel rim where it is
crossed by the tape. A slightly larger wheel, mounted
over and perpendicular to the first so that it can pivot
around it, allows elevations to be calculated from
simultaneous readings of upward or downward angles.
This is a simple method of making measurements under
limited visibility conditions, using two divers equipped
with voice communication.
Meter Tape Triangulation Method. This triangulation
method is preferable to Peterson's wheel method when
small areas need to be surveyed under conditions of
reasonable visibility. Although this method is time
consuming, it is inexpensive, requires little equipment
and only a few divers, and is especially adaptable to
level and uncomplicated sites. Control points at known
distances from each other are selected and marked on
the seafloor around the site. Horizontal measurements
with a meter tape made from two of these control
points to any object or point on the site provide the
necessary information for plotting the position on a
plane.
Plane Table Triangulation Method. This triangulation
method may be used in clear water or on land, both for
position triangulation and for taking elevations. Simple
plane tables are necessary. They consist of a wooden
table, three movable legs, and a weight. A simple alidade
is constructed by combining a sighting device, a tube
with cross hairs at each end, and a straightedge on a
weighted base. Sheets of frosted plastic are then tacked to
the table tops and the alidades are set on these. Two
plane tables are placed on the bottom, one on each side
of the site, and leveled. Initial sightings are made on a
previously selected reference or primary fixed control
point and across the site from one table to the other.
Lines are inscribed on each plastic drawing surface
with ordinary lead pencils and are then labeled. The
resultant vectors, plus a measurement of the distance
between the two points, establish the position of both
tables on a horizontal plane. If the tables are not at the
same elevation, the relationship is determined by placing
a 19.7 foot (6 m) long calibrated range pole, weighted
at the lower end and buoyed at the top with a float, on
the lower table. A sighting is made from the upper
plane, and the distance between the sighted point on
the length of the pole and the lower table provides the
vertical elevation relationship.
A diver mans each of the two plane tables. A third
diver moves the range pole from point to point on the
site, and sightings are taken from each table and labeled
consecutively. Elevations are measured by the third
diver, who moves a marker up or down the pole until he
or she receives a stop signal from the diver manning
one of the plane tables. The distance is then measured
from that point to the object being positioned. The
plane table diver uses the horizontal element of the
cross hairs for this measurement. The efficiency of this
method is limited by the clarity of the water and the
requirement that three divers record each point.
Dumas Measuring Frame Method. This method of
precision mapping for small areas has been successfully
used by archeologists. A 16.4 foot (5 m) square metal
frame is fitted with four telescopic legs and extension
couplings. The telescopic legs enable the frame to be
leveled a few meters above a sloping site, and the
extension couplings allow the size to be indefinitely
doubled by fitting new sections into place. Using two
sides of the frame as tracks, a horizontal crossbar
mounted on wheels can be moved from one side of the
frame to the other. This crossbar, in turn, is traversed
by a yoke holding a vertical pole. The mobile crossbar,
the vertical pole, and the frame are calibrated in
centimeters. The vertical pole is adjusted to touch any
object within the frame.
The coordinates of the point are recorded from three
measurements read on the frame, the beam, and the
elevation pole. The details around the point must be
drawn by a diver hovering over portable 6.6 foot (2 m)
grids placed directly on the site materials. These simple
grids are divided into 7.9 inch (20 cm) squares, which
are designated by numbers and letters marked on the
sides of the grids. The measuring frame is used to fix
October 1991 — NOAA Diving Manual
9-23
Section 9
the positions of the corners of the grid. Although this
method and the Dumas Measuring Frame method are
no longer used extensively, they may be useful in certain
circumstances.
Merifield-Rosencrantz Method. A simple method of
determining the three-dimensional positions of a number
of ground control reference marker stakes has been
developed and tested by Merifield and Rosencrantz
(1966). Two divers are used for the survey. The procedure
consists of the following operations:
1 . A rough sketch of the approximate locations of the
points to be surveyed is drawn on a frosted plastic sheet
for underwater recording. Using a tape measure, the
slant distance between the various points is determined. A
lattice work of measurements should be made, forming
a triangular net (three sides of all triangles); this
eliminates the need for making angle measurements.
When possible, more than the minimum set of measure-
ments should be taken. For example, if surveying a
square that has a point at each corner, all four sides
and both diagonals should be measured. One of these
measurements is redundant, but it will enable the divers
to check the accuracy of the measurements and to
detect errors. (Errors can easily happen when a large
number of points is being measured.)
2. The vertical height of each point is measured
using a simple but extremely accurate level. A stake
is driven into the ground in the middle of the array of
points. A clear plastic hose with an inner diameter of
0.37 inch (0.95 cm) is fastened to the top of the central
stake, with one end of the hose pointing down. The hose
should be long enough to reach the farthest point to be
measured. To set up the level, a diver first works all the
air bubbles out of the hose. The free end is held at the
same level as the end attached to the stake. The diver
then blows into the free end and fills the hose with air.
As it fills, the hose will rise and form an inverted "u" in
the water. The diver then swims to each point to be
surveyed with the free end of the hose. A measuring
stick is placed on the point and held vertically. The
free end of the hose is placed alongside the stick and
pulled down until bubbles are seen rising from the
fixed end of the hose. When this occurs, the water level
at the measuring stick is even with the mouth of the
fixed end, and the vertical measurements can be read
off the stick. If visibility conditions prevent seeing the
fixed end, the hose at the free end should be pulled
down slowly until the water level remains steady with
respect to the measuring stick. When this occurs, bubbles
will come out of the free end, even if poor visibility
keeps them from being seen.
9-24
3. True horizontal survey distances and vertical heights
are then calculated from these data using basic trigo-
nometry and a hand-held scientific calculator. The
microrelief of a small section of seafloor covered by
unconsolidated sediment can be measured from one or
a set of adjoining box cores (the basic box coring tech-
nique is shown in Figure 9-24). Because the surficial
sediment in the box core may be modified during the
coring process, additional steps must be taken when
surface relief is desired. Newton (1968) covered the
sediment surface with a layer of dyed sand followed by
a layer of native sand to provide a protective covering
before coring. After the core was impregnated with
casting resin, the microrelief was obtained from slabs.
This type of box coring is not only time consuming but
is also extremely difficult to accomplish under the
influence of strong currents.
Ripple height and wave length can be established
under water and, where closely spaced, the resulting
profiles can be used to create a three-dimensional map
of a section of the seafloor. The sophistication of the
equipment used to establish ripple profiles differs greatly,
and the corresponding resolution of the data varies
accordingly. Inman (1957) used a greased "comb"
(Figure 9-25) to obtain a profile of the large ripples
that form in medium and coarse sand. In principle, this
technique should give a fairly accurate profile of the
ripples as long as the spacing of the comb elements is
small compared with the ripple wave length. In practice,
the comb is awkward to use because it has to be
handled carefully to prevent grease from fouling divers
and equipment and to ensure that the adhered grains
are not lost before the trace can be measured. If visibility
permits, photographing a scaled rod laid transverse to
the ripples produces a quick but accurate measure of
ripple wave length (Figure 9-26). To measure the small
ripples that form in fine sand, Inman (1957) laid a
Plexiglas® sheet on top of the ripples and marked off the
crests with a grease pencil. Using this method, ripple
heights could only be estimated, and the problem of
ripple distortion by the Plexiglas® was always present.
Furthermore, reliability decreases markedly when the
current velocity increases because of scour around the
sheet and the diver's inability to hold position long
enough to mark the Plexiglas®.
Underwater surficial mapping requires identifica-
tion and delineation of the materials and features that
compose the seafloor. In a small area, this can be
accomplished more accurately by a diver at the
underwater site than by instruments from a surface
craft. Surficial features (such as rock outcrops, coral
reefs, unconsolidated sediment, and textural and
compositional variations in the sediment) must be
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-24
Box Cores (Senckenberg) for
Determining Internal Structure in Sand
y\ /
(^
/ -V /
BOTTOM
TOP
Taking and processing of sand box cores to identify internal structure, a — Senckenberg boxes aligned in o series, shown here as normal
to a northtrending shoreline (L). Box 81 is nearly completely emplaced boxes 82 and 3 partly emplaced. Spiral anchor screwed m sond
behind boxes provides stability and leverage for diver b — Box filled with sand bottom plate secured with elastic band Box sides were
taped together prior to sampling to prevent their spreading apart during emplacement c — Box on side in laboratory bottom pier
moved d — Upper side of box detached and uppermost 2 to 3 cm of sand removed by careful troweling, e — Metal tray inverted and
pushed into sand surface Orientation data transferred to tray f — Tray removed and sand leveled and dried. Orientation data ot
side of tray g — Sand within tray impregnated with about 120 cc of epoxy resin. When resin has set orientation data is transferred to
the sand slab, h — Sand slob removed from tray, internal structure outlined by surface relief provided by preferential penetration o
through individual beds Orientation data on underside of slab
Source: NOAA (1979)
identified, and their distribution must be traced and
plotted to scale.
The problems of locating underwater features accu-
rately and of covering a sufficiently large area can be
minimized by towing the diver-observer with a surface
craft equipped for precise navigation and communication
with the divers. To ensure accurate location of features,
the towed diver should mark the features with a float.
In areas where the bottom can be seen clearly from
above water, aerial photographs are useful to establish
the general bottom configuration. The details can then
be completed under water (Figure 9-27). Geologic
mapping of the rocks that compose the seafloor is best
accomplished by using seismic profiling techniques
from a surface craft. If a specific question arises — such as
the identification of a rock unit or the location of the
October 1991 — NOAA Diving Manual
9-25
Section 9
Figure 9-25
Greased Comb for
Ripple Profiling
Figure 9-26
Diver Using Scaled
Rod and Underwater Noteboard
' / / m
'V
■^*',-^.*B^.
Photo David Klise
surface trace of a fault — direct underwater observa-
tion must be used to answer it. For example, a geologist
may need to know the attitude (strike and dip) of
sedimentary strata or of fractures, joints, and faults in
the rock.
The strike of a rock bed is the compass direction that
the bed would make when projected to a horizontal
plane on the earth's surface. To fix the orientation of
the bed, however, it is also necessary to know the dip.
The dip is the angle in degrees between a horizontal
plane and the inclined angle that the bed makes,
measured down from horizontal in a plane perpendicular
to the strike. Dip is measured with a clinometer. These
relationships are illustrated in Figure 9-28.
Rock outcrops on the seafloor may be located by
noting irregularities in bottom profiles, anomalous shoals
or reefs, or the presence of organisms such as kelp that
normally grow on rocks. The rock outcrop may be so
encrusted by bottom flora and fauna that recognition
of features, such as stratification surfaces, fractures,
and joint planes, is difficult. In such cases the diving
geologist must clean off the encrustations, search for
freshly scoured surfaces, or collect oriented samples in
the hope of establishing the three-dimensional fabric
of the rock in the laboratory. In some areas, differential
weathering or erosion makes stratification surfaces
and fractures more readily visible under water.
To measure the attitude of planar elements in the
rocks, the diver needs an adequate compass with an
inclinometer. Underwater housings can be built for the
relatively large surveying compasses commonly used
on shore. A hollow plastic dish almost completely Filled
with fluid (plastic petri dishes work well) and marked
with perpendicular crosshairs on the flat surfaces is a
useful adjunct to underwater mapping. The dish is
placed in the plane of the feature whose attitude is to
be measured and rotated until the enclosed air bubble
Photo David Klise
coincides with a crosshair. The other crosshair, which
is now horizontal, defines the strike of the feature, and
the downward direction of the crosshair coincident
with the bubble defines the dip and dip bearing.
Some outcrops are located in water too deep to be
sampled by these methods unless the diver is operating
in the saturation mode. Where underwater sampling
cannot be done, a photograph of the outcrop that includes
a scale (like the one in Figure 9-29) can yield a
considerable amount of information.
For any kind of underwater mapping, it is useful to
prepare a base map on which the outlines of previously
established features are drawn in indelible ink on a
sheet of plastic material. New features can be sketched in
pencil on the base and, as they are confirmed, inked
onto the map.
9.10.2 Sampling
Diving geologists sample everything from unconsoli-
dated sediments to surface and subsurface rock forma-
tions. Although standard land techniques can be used
directly in a few underwater situations, they usually
must be modified (or new techniques must be developed)
to cope with the underwater environment. Diving allows
selective sampling, which is not possible when using
boat-based methods. The diver sees exactly what is
collected and how it relates to other aspects of the
submarine environment. Compromised samples can be
discarded and easily replaced. Also, diving may be the
only way of sampling the seafloor in areas, such as the
high-energy surf zone, inaccessible to surface craft.
Rock sampling may be required in the compilation
of an underwater geologic map or to answer other
9-26
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-27
Aerial Photograph and Composite Map
Courtesy U.S. Geological Survey
questions. Samples broken directly from the outcrop
are the most reliable, although talus fragments may be
adequate if they can be traced to a particular outcrop.
Breaking through the external weathered or encrusted
rind of a submarine outcrop may be difficult because
water makes swinging a hammer impossible; a pry bar
or geological pick can be used in existing fractures or
can be driven against an outcrop with better effect.
Explosives may be practical in some cases but must be
used with extreme care (see Section 8.12). Pneumatic,
electric, or hydraulic drills are available for underwater
work (see Section 8.4).
Macintyre (1977) describes a hydraulically powered,
diver-operated drill used in water depths up to 49 feet
(15 m) (Figure 9-30). The drill consists of a Stanley
hydraulic impact wrench (modified for consistent
rotation) that is powered by a hydraulic pump on the
surface. The drill rotates at a maximum of 600 rpm and
provides sufficient torque to core under any reasonable
conditions (Macintyre and Glynn 1976, Macintyre 1977).
The unit will recover cores roughly 2 or 3.5 inches
(5 or 9 cm) in diameter, using a double-walled core barrel.
Macintyre's original unit was powered by a Triumph
4-cylinder industrial motor, which limited the type of
surface vessel used for support. Smaller units have
been designed that utilize 5-10 hp motors. The result
is a more portable unit, weighing about 350 pounds
(159 kg), that can be operated from a small boat.
Although this approach reduces the flow rate over that
of Macintyre's original design, cores over 82 feet (25 m)
in length have been retrieved with these newer systems
(Halley et al. 1977, Hudson 1977, Shinn et al. 1977.
Marshall and Davies 1982, Hubbard et al. 1985).
For use in water less than 6.6 feet (2 m) deep or on
exposed reefs, a tripod is required to support the drill
(Figure 9-30). In deeper water, a lift bag can be used
in place of the tripod. Using the habitat Hydrolab in
the U.S. Virgin Islands as a base, Hubbard and his
coworkers (1985) were able to core horizontally into
the reef face in water depths of 98 feet (30 m). On such
deep operations, bottom time is usually the limitation.
In addition to tending the normal operation of the drill,
a diver is needed to monitor the progress of the coring
and to note anything that would be useful in logging
October 1991 — NOAA Diving Manual
9-27
Section 9
Figure 9-28
Dip and Strike
of Rock Bed
Figure 9-30
Coring in a Deep Reef
Environment With a Hydraulic Drill
Block diagram illustrating dip and strike. Direction of dip
due east, shown by arrow; amount of dip, angle abc. Notice
that arrow extends horizontally as it would if placed flat on
a map. Direction of strike is north-south, shown by cross-
arm of symbol; it represents a horizontal or level line
drawn on inclined bedding plane.
Photo Holmes (1962)
Figure 9-29
Geologist Measuring
Dip (Inclination) of Rock Outcrop
Photo Larry Bussey
the core at the surface. A submersible drilling frame
can solve some of these problems when divers are working
in deeper water. Adjustable legs allow deployment on
an irregular, sloping bottom. The frame securely holds
the drill in place, while a lift bag can be used either to
place pressure on the drill or to lift it out of the hole. By
using a video camera, the drill can be monitored remotely,
and divers are needed only to set up and recover the
cores.
9-28
Photo Eugene Shinn
The hydraulic drill is also useful in obtaining shorter
samples through large coral heads for the purpose of
examining internal growth bands. A larger diameter,
single-walled barrel is fitted to the same drill and is
used to remove a plug from the coral colony. Because
this method is meant to be non-destructive, great care
must be taken not to damage the surrounding colony.
Some researchers have inserted a concrete plug into
the hole they have drilled to promote overgrowth of the
colony by algae.
The drill (Figure 9-3 la), which can operate at about
100 psi (7 kg/cm2), is attached to a neoprene hose
that is fitted to the low-pressure port of the first stage
of a regulator, which is attached to a standard scuba
cylinder. The drill bit is designed so that the core
sample is forced up into the middle of a core barrel
attached to the bit. This barrel, in turn, is designed to
retain the core sample when the barrel is removed from
the bit. The barrels containing the sample can be
removed, and new barrels can be attached by the diver
under water. The best cores can be obtained by running
NOAA Diving Manual — October 1991
Procedures Tor Scientific Dives
Figure 9-31
Pneumatic Hand Drill
A. Drill and Attachment
B. X Ray of Core
Photo Collin W. Stearn
the drill at its maximum speed, with maximum pressure
on the bit to make the hole quickly. When the full
penetration of the bit is completed, a slight rocking
motion of the bit in the hole will break the core free and
permit it to be removed from the hole. Complete
unfractured cores 0.39 inch (1 cm) in diameter and up
to 33.5 inches (85 cm) long have been obtained with
this method. A single 72 cubic foot (2 m3) scuba cylin-
der is sufficient to drill 4 holes in the coral Montastrea
annularis at depths up to 23 feet (7 m) (see Fig-
ure 9-3 lb). Because this equipment is not designed for use
in salt water, extra care must be taken after use to rinse
and clean it to avoid corrosion. Further details concerning
this technique can be found in Stearn and Colassin
(1978).
Sampling unconsolidated sediment generally is easier
than sampling solid rock, but it may also present
problems. The collection technique used depends on
the purpose of the study. For example, if samples are
collected for compositional or textural analysis, the
primary concern is to obtain material representative of
a larger entity. On the other hand, if internal structure
or engineering properties are the goal, the sample should
be as undisturbed as possible (see Section 9.10.2).
Collecting a representative sample creates a number
of problems that must be resolved. For example, how
deep below the surface should the sampler penetrate?
October 1991 — NOAA Diving Manual
The sediment beneath the seafloor may have been
deposited under conditions markedly different from
those producing the surface sediment; if so, its character
will differ accordingly. How does one sample a sediment
containing interlayered sand and mud? How large a
sample is required to be representative of a specific
particulate trace component, such as placer gold, without
biasing the sample by the loss of some component, such
as the finest or densest material? Many of these questions
have been addressed in conjunction with subaerial
sampling, and the techniques employed in this form of
sampling are applicable to underwater sampling as
well (Clifton et al. 1971).
Surficial samples taken with a small core tube circum-
vent many sampling problems and permit a highly
consistent collection program. Plastic core tubes several
centimeters in diameter with walls a millimeter or so
thick are ideal and inexpensive. Cut into short tubes
several centimeters long, they can be numbered and have
rings drawn (or cut) on them 0.39 to 0.78 inches (1 to 2 cm)
from the base and top (depending on the thickness of
the sediment to be cored). Two plastic caps for each
tube complete the assembly. The tubes are carried
uncapped by the diver to the collection site. A tube
is pushed into the sediment until the ring on the side
coincides with the sediment surface, and a cap is placed
carefully over the top of the tube. Its number is recorded,
along with a description of the sample location. A trowel
or rigid plate is slipped under the base of the tube, and
the tube is then removed from the sediment and inverted.
The second cap is placed on the base, and both caps
are secured. This simple arrangement can be improved
by adding a removable one-way valve to the top end
and a removable core catcher to the bottom. These
items allow the diver to insert and remove the core
without capping it. Capping is done at a convenient
time, and the end pieces are then transferred to another
tube for reuse.
An inexpensive alternative to a core tube is to cut
one end off a 50-cc disposable syringe and to use it
as a small piston core. The sampler is pushed into the
sediment while the syringe plunger is being withdrawn
slowly to keep the sampler at the sediment surface.
The plunger provides enough suction to permit the small
sampler to be removed quickly from the bottom without
losing any sediment. The sample can then be extruded
into a sample bag, or it can be kept in the core tube
by capping the tube with a small rubber stopper.
Undisturbed samples of seafloor sediment are valu-
able for identifying internal structures, such as strati-
fication or faunal burrows, and for making measurements
of certain engineering properties. Compared with the
9-29
Section 9
brief view of the seafloor possible during a single dive,
analysis of these structures provides a broader per-
spective on processes through time. Internal stratifi-
cation, considered in light of sediment texture, can be
used to infer the strength of prevailing currents during
the time of deposition. The orientation of cross-strati-
fication indicates the direction of the stronger currents in
the system and may indicate the direction of sediment
transport. The degree to which mixing by faunal
burrowing disrupts these structures is indicative of the
rate of production or stratification, which in turn reflects
the rate of the occurrence of physical processes and/or
the rate of sedimentation.
Internal structures of modern seafloor sediment also
provide a basis for interpreting ancient sedimentary
environments. Direct comparison of depositional features
in a rock outcrop with those in an individual core may
be difficult because of the limited view permitted by a
core. This problem can be overcome, to a degree, by
taking oriented cores in an aligned series, which yields
a cross section that is comparable with that in the
outcrop.
The collection of undisturbed samples from the
seafloor requires special coring techniques. Diver-
operated box cores have been used successfully to core
the upper 3.9 to 7.8 inches (10 to 20 cm). Cans or
similar containers from which the bottoms have been
removed are useful in muddy sediments. With their
tops off, they can be pushed easily into the mud until
the top is at the sediment surface level (the surface
layer can be lost if the container is pushed below the
sediment surface). The opening at the top of the container
is sealed by a screw cap or stopper after the can is
emplaced in the sediment, and the sediment remains
intact as the core is withdrawn. A wedge-shaped or
spade corer permits the taking of somewhat larger
surficial cores.
Cores can be taken in sandy sediment with a variety
of devices, ranging in design from very simple to quite
complex. Cores more than 6.6 feet (2 m) long can be
taken by driving thin-walled tubing several centimeters
in diameter into the sediment. A simple apparatus
consists of a removable collar that can be attached
firmly to a 3 inch (7.6 cm) in diameter thin-walled
irrigation pipe. A pounding sleeve consisting of a
3 inch (7.6 cm) inside diameter pipe with two pipe handles
welded to it is slipped over the irrigation pipe above the
collar. By forcefully sliding the pounding sleeve down
onto the collar, a 3.3 to 6.6 foot (1 to 2 m) core can be
taken (the core tube must be long enough to allow for
the core and enough pipe above the collar to slide the
pounding sleeve). Adding a removable piston attached
9-30
to a stationary pole so that the piston remains at the
sediment surface during coring can increase the pene-
tration of this apparatus to several meters. Recently,
scientists have constructed a coring apparatus that
used a hydraulic jack hammer. The jack hammer is
attached to one end of a section of 3 inch (7.6 cm) in
diameter aluminum irrigation tubing cut into the
necessary lengths. The attaching device is a slip-fit
made by press-fitting a collar to a standard jack hammer
chisel shaft. Slits are also cut into the upper 6 inches
(15.2 cm) of the core tube to allow for the escape of
water. During operation, the entire device is suspended in
the water with an air bag or air-filled plastic garbage
can. Holding the core pipe in a vertical position, the
diver releases air from the air bag and descends slowly
until the tube makes contact with the bottom. After
ascertaining that the core tube is oriented vertically,
the trigger is pressed and the tube is jack-hammered
into the bottom. Generally, 19.7 feet (6 m) of penetra-
tion is attained in about 30 seconds. Experience has
shown that loss due to compaction is less than 10
percent. Cores up to 29.5 feet (9 m) in length have been
obtained using this method.
A different type of apparatus used for underwater
coring is the vibracore, which relies on high-frequency
vibrations rather than pounding to push the core tube
through the sediments. The core tube is driven as deeply
into the bottom as possible and is then extracted; dur-
ing extraction, the vibration source is turned off.
Several excellent but costly commercial units are
available; a less-expensive unit can be constructed by
attaching a simple concrete vibrator to the top of a
3 inch (7.6 cm) piece of irrigation pipe. The unit can be
powered by a small motor located in the support boat;
cores 32.8 feet (10 m) long have been taken with this
type of unit.
Subaqueous cores are saturated with water when
they are removed from the bottom and must be handled
carefully to avoid destroying them. For example, unless
great care is taken, the sediment may be washed from
the corer as it is removed from the water, be liquefied
by excessive agitation, or collapse during removal from
the corer. The careful geologist avoids these frustrations
by planning core retrieval and transport as an integral
part of the coring system.
Other types of geologic samples can be collected by
divers. For example, gas escaping from seafloor seeps
may be collected more easily by a diver/scientist
operating at the seafloor site than by scientists working
from a surface craft. Hydrocarbons in the sediment can
be analyzed with greater precision when the samples
have been taken by divers. These containers can be
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-32
Diver Taking
Vane Shear Measurement
sealed immediately after sterilization, be opened under
water, and then be resealed with the sample inside
before being returned to the surface.
9.10.3 Testing
In the context of this section, testing means determin-
ing some variable of the sediment in situ that cannot be
identified accurately on the surface from a sample of
the same sediment. For example, Dill and Moore (1965)
modified a commercial torque screwdriver by adding a
specially designed vane to the shaft. The vane was
inserted carefully into the sediment, and torque was
slowly and constantly increased until sediment failure
occurred (Figure 9-32). From this simple test, these
authors were able to determine the maximum shear
strength of surface sediments. They also measured the
"residual strength" of the sediment by continuing to
twist the dial after initial shear occurred. Use of this
equipment generally is restricted to currentless locales
because the diver has to remain motionless during the
test to be able to operate the apparatus correctly and
accurately.
9.10.4 Experimentation
The underwater environment is a superb natural
laboratory, and diving permits the geologist to study a
number of processes in real-time experiments. Most
studies of this type begin with a careful characterization
of the study area, followed by an experiment (usually
carried out over an extended period of time) designed
to explore the interrelationships among geological, bio-
logical, physical, and chemical processes.
The experimental technique may be simple or sophis-
ticated, depending on the nature of the phenomenon
studied and the resources of the experimenters. Repeated
observations at a selected site can produce much
information on processes, such as bed-form migration
or bed erosion and deposition. When visibility permits,
real-time video, cinephotography, or time-lapse photog-
raphy produces a permanent record of an ongoing process
that can later be analyzed in great detail. Monitoring a
site with sophisticated sensors can, for instance, yield
quantitative information on the interaction of perti-
nent physical and geologic variables.
Since many experimental studies in nature involve
making serial observations of the same site, the
experimental site may have to be reoccupied to continue
the study or to service equipment. Relocating the site
can be difficult and must be planned ahead of time. A
buoy, stake, or prominent subaqueous landmark may
suffice in clear, quiet water, while more sophisticated
October 1991 — NOAA Diving Manual
Photo Lee Somers
equipment such as sonic pingers (see Section 8.3) may
be needed under adverse conditions. Current technol-
ogy has advanced to the point where Loran C navigation
systems can guide a boat to within less than 20 feet
(6.1 m) of a previously visited site. Such units are readily
available and can be used on small boats. Surface
buoys tend to arouse the curiosity of recreational boaters,
who may tamper with or even remove them, and land-
marks are seldom close enough to the actual site to be
useful, especially when visibility is poor. Emplacing
stakes at the actual site must be done carefully so as
not to alter the current flow enough to compromise
experimental results.
Some experiments involve the emplacement of
unattended sensors that monitor conditions at specific
times or whenever certain events occur. The data from
such sensors are either recorded in situ or transmitted
by cable or radio to a recording station. Relocation is
necessary to maintain or recover the equipment used in
such experiments.
Characterization studies will continue to be the main-
stay of underwater geologic research because most of
them can be completed without elaborate equipment.
In-situ experimental studies, however, will undoubtedly
become increasingly important as more geologists dis-
cover the advantages they offer in answering funda-
mental questions about the geologic environment.
9-31
Section 9
Figure 9-33
Undersea Instrument Chamber
9.11 MICROPHYSICAL OCEANOGRAPHY
Micro-oceanographers have so far not taken full advan-
tage of diving techniques; to date, in-situ measurements
and observations of water mass processes have not
been widely used. Turbulent cells, boundary layers,
and flow regimes have not been studied extensively.
Notable among published accounts are the studies of
visual indications of the thermocline, the use of dye
tracers to reveal flow patterns (Woods and Lythgoe
1971), and the study of internal waves and the formation
of bubbles in sound attenuation (LaFond and Dill 1957).
Work by Schroeder (1974) in Hydrolab has shown that
divers can be used to do more than emplace, tend, and
recover oceanographic instruments. Divers are the best
means of ascertaining the scale of measurements of the
physical nature of the water column. The oceanographic
scientist today dives to implant instruments in the
active parts of the water column and to ensure that
these instruments are measuring the real underwater
world.
Table 9-1 summarizes some of the micro-oceano-
graphic variables and problems that involve the use of
divers in data collection. As better methodology develops,
the diver's role in micro-oceanography will expand.
9.11.1 Emplacement and Monitoring
of Instruments
The implantation, reading, and maintenance of
instruments and instrument arrays and the recovery of
samples and data are important jobs divers can perform in
oceanographic surveys. Instruments implanted at a
site to measure current flow, direction, or other phe-
nomena may be damaged by marine growth or the
buildup of sand or bottom debris. If the instruments
are read remotely, these conditions may alter the validity
of the data measured by the instrument. Divers should
routinely check the condition of implanted instruments to
ensure that they are operating correctly.
Undersea laboratories are of great advantage in exper-
imental studies requiring the use of many instruments
and dives of long duration. The Undersea Instrument
Chamber (USIC) provides a stable underwater hous-
ing for instruments that record oxygen, temperature,
light, pH, conductivity, and sound. The USIC can be
entered by divers as necessary for data retrieval equip-
ment, calibration, and monitoring (Figure 9-33).
A good diver-managed oceanographic instrumentation
program was carried out during a Hydrolab underwa-
ter habitat mission in 1972 (Schroeder 1975). The
objective was to evaluate a continuously deployed
shallow-water current and hydrographic monitoring
system. Divers set up thermometers, current meters,
(
Photo Morgan Wells
pressure gauges for tidal measurements, and instru-
ments for measuring depth, temperature, conductivi-
ty, salinity, dissolved oxygen, and pH using a taut line
buoy array. Data were obtained by reading the instru-
ments and/or by a direct readout display inside the
habitat. When reading a vertical array of the ther-
mometers, the procedure was to swim at an angle to the
top thermometer, read it, and then to descend the buoy
line to read the remaining thermometers. The data
were transferred onto a slate secured to the anchor
weight of the buoy system. This procedure prevented
the aquanaut's exhalation bubbles from disrupting the
thermal structure.
(
9-32
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Table 9-1
Micro-Oceanographic Techniques
Variable
Instrument/
Technique
Diving
Mode*
Placement
Problems
Remarks
Temperature
Thermometer array
as
Taut-line buoy,
pier, piling,
oil rig.
Where to position ther-
mometers. Pre and post use
calibration. Reduires
repetitive observation.
Limited by bottom
time in conventional
modes.
Recording
thermograph
C.S
Same as above
but secure to
bottom.
Equipment flooding.
Electronic failure.
Only one data point unless
multiple units used.
Relocation of units.
Remote readout
C.S
Same as above.
Same as above
Excellent for use in
habitat.
Salinity
Water samples
C.S
Bottle rack
carried by
diver.
Number of samples.
Processing procedures.
Limited by bottom
time in conventional
modes
Recording salino-
meter
Same as for Temperature, above
Remote readout
Same as tor Temperature, above
Dissolved
Oxygen
Water samples
C.S
Bottle rack
carried by
divers.
Outgassing when brought
to surface.
Best used from
a habitat
Remote readout
Same as for Temperature, above
Multiple
Sensor Unit
Recording
Same as for Temperature, above
Remote readout
C.S
Reverse vertical
profiling using
floats and pulley
system.
Fouling of cables.
Interface at surface.
Excellent for
habitat operations.
Currents
Recording
Same as for Temperature, above
Remote readout
Same as for Temperature, above
Dye studies
Tides
Recording (waves)
Same as for Temperature, above
Ambient pressure
gauge inside
habitat
S
Gauge inside
habitat.
"C = conventional diving
S = saturation diving
Source: NOAA (1979)
9.11.2 Planktonic Studies
Diving techniques have long been an integral part of
in-situ experiments on the effects of controlled nutri-
ent enrichment of phytoplankton and zooplankton popu-
lations. In Lake Michigan, divers implanted large plastic
bags at various depths, which required placement of a
October 1991 — NOAA Diving Manual
screw-type anchor or other anchoring device in the
lake bottom and attachment of a collapsed bag held in
a vertical position by a submerged float (Somers 1972).
Divers could then insert a hose into each bag to facili-
tate filling with lake water and nutrient solutions.
After the filling process was completed, the divers
9-33
Section 9
disconnected the hoses and secured the filling tubes.
Water samples were taken periodically by divers using
a hose and pump.
The role of zooplankton in a coral reef system was
studied by divers working from the Hydrolab under-
water habitat during three saturation missions (Schroeder
et al. 1973). Plankton samples were obtained by divers
using small nets attached to a hand-held diver pro-
pulsion vehicle (see Section 9.5.1). Several variations
on this technique have been used and are described in
Schroeder (1974). To quantify the volume of water
filtered by the sampling nets, the area of the net mouth
was multiplied by the distance traveled. Samples were
preserved by pouring the contents of the cod end of
the net into a jar filled with filtered seawater and
sealing it with plastic wrap. The sample was then
preserved by injecting formalin through the plastic
by syringe and capping the jar immediately.
A second method of sampling zooplankton in inac-
cessible areas, such as small caves in coral, involves a
suction system utilizing air from a scuba tank to create
a vertical water current in a 7.9 inch (20 cm) plastic
tube with a plankton net secured to the top. When used
properly, the device is capable of capturing even fast-
moving small reef fish.
9.11.3 Use of Dye Tracers
In addition to the emplacement and monitoring of
instruments, divers have used dye tracer techniques to
measure currents, internal waves, thermoclines, and
various turbulent components of the water column
(Woods and Lythgoe 1971). Water masses tagged with
fluorescein dye can be followed and photographed to
provide an accurate measurement of current speed and
direction. If a point source of dye (a bottle full of dyed
water) is released into the current, accurate measure-
ments can be made at speeds lower than those of most
current meters commonly employed. To understand
the generation of turbulence inside a thermocline and
within the water column, it is necessary to know both
the density gradient and the velocity shear. The most
convenient technique for laying a shear streak is to
drop a tiny pellet of congealed fluorescein through the
layer under study. Disk-shaped pellets, 0.12 inch
(3 mm) in diameter and 0.6 inch (1.5 mm) thick, are
particularly useful. These pellets are attached to a
light line and dropped through a thermocline. The
dispersion of the dye by the ambient flow can then be
photographed.
The only disturbance to the existing flow caused by
the pellet's passage through the water column is caused
by the formation of a small vortex wake, whose indi-
9-34
vidual vortexes rapidly lose their own motion and fol-
low the ambient flow. The pellets are sealed in water-
proof polyethylene strips until needed. Three sizes,
each with the same aspect ratio, are used: the smallest,
described above, gives the most regular wake but lasts
only for about 5 minutes. The largest, 0.24 inch (6 mm)
in diameter by 0.09 inch (2.3 mm) thick, can lay a
streak through the whole thermocline. The speed of
these pellets is comparable to the difference in hori-
zontal velocity encountered along any streak, and their
drop path is often quite complex, which means that the
velocity profile cannot be determined from a single
photograph. Instead, the mean shear across any given
layer is obtained in successive frames of a timed sequence
of still photographs or motion pictures.
The general procedure is as follows: after identify-
ing the area of interest by dropping a trial pellet, the
photographer positions himself or herself above the
chosen level and then signals an assistant who is float-
ing above and upstream to release a second pellet. As
the second pellet begins to fall, the assistant increases
his or her buoyancy, which permits the assistant to
move away from the dye streak without disturbing it.
Whenever possible, the assistant is positioned above
the sheet overlaying the layer being filmed; this sheet
isolates the assistant's movements from the dye. The
photographer then films the dye streak, keeping the
sun behind the camera to increase contrast.
Current can also be measured near the bottom by
using dye tagging techniques (Figure 9-34). Care must be
taken not to kick up sediment or to create artificial
vortexes by swimming in the area during such studies.
9.11.4 Water Samples
When taking measurements or samples in the water
column, care should be taken to minimize the amount
of activity around the study sites to avoid unnecessary
mixing of the water column caused by vertical water
currents from the diver's exhaled bubbles. Instruments
should be placed well away and upstream of all bubble
activity.
Divers can collect bulk water samples by swirling
large plastic bags through the water until filled, sealing
the mouths of the bags, and carrying the bags to the
ship. Because large water samples are heavy, the bags
should be put into rigid underwater containers that are
then attached to the boom of the ship. The plastic bag
sampler can be modified to collect more precise water
samples by gluing or stapling a strip of wood or plastic
to each edge of the bag opening, so that it will extend
from the corner to about two-thirds the length of the
opening. The remaining third of the open end is then
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-34
Dye-Tagged Water Being
Moved by Bottom Current
y^>
/
/
Courtesy U.S. Navy
folded back against one of the supports and lightly
closed with tape or a rubber band to prevent water
from entering the bag. To begin sampling, the diver
pulls the two mouth supports apart, breaking the tape
or rubber band, and opens the bag to form a triangular
mouth. The bag will fill entirely as the diver pushes it
forward. The diver then closes the supports, refolds the
loose end back against one of the supports, and rolls
the edge tightly toward the bottom of the bag to seal in
the water sample. Large plastic bags also can be filled
using hand-operated pumps. When shipboard analysis
requires uncontaminated samples, new, acid-washed,
hand-operated plastic bilge pumps can be used to collect
samples.
Smaller water samples, up to 1.06 quart (1 L), can
be taken with extreme precision using a plastic or glass
jar with a 2-hole stopper, one hole of which is fitted
with a flexible sampling tube of selected length and
diameter. At the desired depth, the diver inverts the
unstoppered jar, purges it with air, and then inserts the
stopper. The jar is then righted and, as the air bubbles
out of the open hole in the stopper, the diver manipu-
lates the sampling tube to vacuum the water sample,
organisms, or detritus into the jar. After evacuating all
the air, the diver seals the jar by inserting the tip of the
sampling tube into the open hole of the stopper or by
swiftly replacing the stopper with a cap. A bubble of
air remains in the top of the sampling jar and is replaced
with water when the stopper is removed. Contamina-
tion is generally insignificant. Bottles larger than
1.06 quart (1 L) are inconvenient because the buoyancy
of the air-filled jar is sufficient to disturb the buoyancy
of the diver, requiring constant attention to depth reg-
ulation and distracting the diver from the task at hand.
When standard ship-operated water samplers are used,
the divers and ship personnel can precisely position
and trigger the samplers under water.
It is difficult to obtain accurate measures of dis-
solved oxygen in seawater because the changes in pressure
to which a sample of seawater is subjected as it is
brought to the surface affect the chemical nature of
the solution. Liquids and solids are relatively insen-
sitive to pressure effects, but dissolved gases are sensi-
tive to pressure changes. Even if the container is protected
as it is raised through the water column, oxygen may be
taken up when the container is opened on the surface.
To overcome this limitation, a sampler that is portable,
versatile, and inexpensive has been developed (Cratin
et al. 1973). This sampler and technique are equally
effective for operations from the surface or from an
ocean floor laboratory.
The sample bottles (Figure 9-35) are constructed
from PVC tubing that is 2.4 inches (60 mm) o.d.,
1.9 inch (48 mm) i.d., and 4.7 inches (12 cm) long, which
provides a volume of about 0.24 quart (225 ml). Screw
caps made of plastic and fitted with PVC inner linings
and rubber O-rings effectively seal both ends of
the sample bottle from their surroundings. A hole,
0.59 inch (15 mm) in diameter, is drilled into the side of
each sampler and a piece of PVC tubing 0.59 inch
(15 mm) long is sealed into it. Finally, a rubber membrane
is fitted into and over the small PVC tubing. When
taking large numbers of samples, a backpack designed
to fit over double scuba tanks is a useful accessory
(Figure 9-36).
A sample collection proceeds as follows: the open
bottle, i.e., without the screw caps, is moved to the
underwater location, tapped several times to ensure
complete removal of all trapped air, and one of the
caps is screwed on. A marble is placed into the sample
bottle and the second cap is then screwed firmly into
place.
To prevent oxygen from ongassing when the sample
is brought to the surface, two chemical "fixing" solu-
tions are added in the following manner: a venting
(hypodermic) needle is placed into the membrane and
.0042 pint (2 ml) of manganese (II) sulfate and alka-
line potassium iodide solution are injected into the
bottle by hypodermic syringe. (Special care must be
taken to make certain that no bubbles of air are present
in any of the syringes.) The bottle is shaken several
times to ensure complete mixing. (The dissolved oxygen
gas is converted through a series of chemical reactions
October 1991 — NOAA Diving Manual
9-35
Section 9
Figure 9-35
Diver Using
Water Sample Bottle
Figure 9-36
Water Sample Bottle Backpack
Source: NOAA (1979)
Photo William L. High
into a white insoluble solid — manganese III hydroxide.)
When the samplers are taken to the laboratory, they
must be kept under water as added insurance against
leakage.
Once in the laboratory (with the bottle still under
water), a venting needle is inserted into the membrane
and .0042 pint (2 ml) of concentrated sulfuric acid is
added via a hypodermic syringe. The bottle is shaken
several times to ensure complete reaction. The sampler
is then removed from under the water, one of the caps
is carefully unscrewed, and known volumes of solution
are withdrawn. A knowledge of the volumes, concen-
trations of reacting chemicals, and other pertinent
data enables the analyst to calculate quantitatively the
oxygen content in seawater. Use of this sampling tech-
nique is limited only by the depth at which a diver may
safely work. Oxygen analysis of samples taken from
much greater depths requires more complicated and
expensive equipment that can be operated remotely.
9.12 ARCHEOLOGICAL DIVING
Over the last 20 years, diving methodology and tech-
nology have had an enormous impact on the scientific
development of underwater archeology in the Americas
(Burgess 1980). Archeological procedures developed
in the 1960's for use on shipwrecks in the Mediterra-
nean by Bass (1966, 1970, 1972, 1975) and his associ-
ates have been adopted and modified by professional
archeologists in the United States to study both sub-
merged prehistoric and historic sites. Since then, many
archeologists have conducted historical and/or anthro-
pological research on shipwrecks. Thousands of recrea-
tional divers and professional salvors have also become
involved with wreck diving in their search for historic
9-36
artifacts. As more people have discovered the adven-
ture and monetary rewards of shipwreck diving, gov-
ernment resource managers and scientists have become
increasingly aware of the need to preserve and protect
historic shipwrecks.
Although this section deals primarily with shipwreck
archeology, research on prehistoric remains that are
under water is conducted for other purposes as well.
For example, extensive work has been done in Warm
Mineral Springs (Cockrell 1978) and Salt Springs
(Clausen 1975), Florida, to depths of more than 200
feet (61 m), to obtain information on the area's early
animal and human inhabitants, who date back more
than 10,000 years. Figure 9-37 shows a diver recovering
Indian artifacts off the coast of California.
The real boom in archeological diving in the United
States has involved shipwrecks. It is estimated that, of
the more than 2.5 million certified recreational divers
in the country, about 200,000 are wreck divers. In
addition to recreational divers, there are more than
1000 active salvor divers in the country. Professionally
trained marine archeologists, who number no more
than 100 in the United States, thus comprise the smallest
group of wreck divers.
It is estimated conservatively that there are well
over 100,000 shipwrecks in United States waters. Availa-
ble data indicate that close to 90 percent of known
shipwrecks on the Continental Shelf are located in
depths of less than 60 feet (18.3 m). Along some parts
of the coastline, shipwrecks are clustered in large num-
bers within a few hundred meters of the beach. Most
harbors and inlets are rich in shipwreck sites. The
Great Lakes, rivers, estuaries, and navigable channels
of the inland waterway also contain thousands of ship-
wrecks from many different periods.
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-37
Diver Recovering
Indian Artifacts
Courtesy Diving Systems International
Photo Steven M. Barsky
9.12.1 Shipwreck Location and Mapping
Underwater archeologists use many of the same tech-
niques and much of the same equipment as other marine
scientists. The two principal methods of locating
shipwrecks involve the use of visual search and remote
sensing techniques. Visual search procedures are
discussed in Sections 8.2 and 9.1 to 9.3. Within the last
decade, remote sensing techniques have become highly
sophisticated with respect to locating and defining
shallow water shipwreck remains scattered over miles
of open ocean (Mathewson 1977, 1983, 1986).
Marine archeologists use a number of different
techniques to survey underwater sites. The primary
objective of these techniques is to obtain reliable
measurements that accurately reflect the horizontal
and stratigraphic relationships between different types
of artifacts within overall artifact scatter patterns. Many
of these mapping techniques, such as baseline offsets.
artifact triangulation, plane table and grid mapping,
and photomosaic surveys, are well-known procedures
on land sites and are described in detail in archeologi-
cal publications (see Sections 9.2.1 and 9.10.1). Although
the method and theory of underwater archeology are
similar to those used to conduct excavations on land,
operating procedures for mapping sites can be very
different because of underwater conditions. The best
way for archeologists to learn how to modify these
techniques is by borrowing from the experiences of
marine biologists and geologists and by experimenting
with various methods to ensure that reliable descrip-
tive data are obtained.
9.12.2 Shipwreck Excavation
Every historic shipwreck presents unique problems
with respect to the archeological methods required to
excavate. The depositional environment of each site
largely governs how shipwreck remains are to be uncov-
ered and recorded in situ. No two wreck sites are
exactly the same. Shipwreck discoveries made since
the early I960's along the coasts of Florida, Bermuda,
the Bahamas, and throughout the Caribbean have
shown that ancient wooden-hull shipwrecks do not
stay intact for as long as formerly believed. Shallow
water shipwreck remains are subjected continuously to
the onslaught of the sea. Because the vessels' super-
structures are degraded by the impact of currents,
storms, and shifting overburden, visual remains often
are not easily recognizable on the sea bed. The ship's
contents, along with its ballast and lower hull struc-
ture, may be covered by tons of sand, mud, or coral.
Figure 9-38 shows a marine archeologist exploring the
wreck of the Golden Horn.
Before excavation, it is essential to determine the
general character of the environment, which helps to
make the operation more efficient and to avoid unnec-
essary expenditures, accidents, and mistakes. Exam-
ples of the environmental and logistical information
needed include:
• Measurements of the bottom topography and rates
of sedimentation to determine the type of excava-
tion equipment needed
• Sub-bottom profiles to determine sediment layers
relative to wreck or site, and/or coring requirements
• Number of work days and best time of year to work
at the site and the weather conditions to be expected
• Movement of suspended materials, underwater visi-
bility, wave action, current, and temperature
• If near shore, usefulness of shore area as land base.
work area, and living area.
October 1991 — NOAA Diving Manual
9-37
Section 9
Figure 9-38
Archeologist Exploring
the Golden Horn
Courtesy Diving Systems International
Photo Steven M. Barsky
Before excavation, all possible information about
the attitude and extent of a shipwreck and its cargo
must be known. Once the preliminary survey has been
completed, a site excavation plan is formulated and
systematic layer-by-layer surveying and artifact
removal can begin. Care is needed to avoid damaging
the artifacts or removing them without documenting
their position; archeological excavation requires tech-
nique, appropriate equipment, and a great deal of
patience.
Excavation methods range from hand-fanning with
pingpong paddles to the application of large-diameter
prop washes, more commonly referred to as deflectors
or "mail boxes." Each digging procedure has its own
advantages and disadvantages.
Airlift excavation involves the use of a long discharge
pipe (usually made of PVC or aluminum) and an air
manifold bottom chamber (Figure 9-39). Although
the size of the airlift can range anywhere from
9-38
3 to 14 inches (7.6 to 35.6 cm) in diameter, airlifts with a
diameter greater than 8 inches (20.3 cm) are very
difficult for individual divers to handle. When deep
sand or mud needs to be removed from a wreck site, the
larger diameter pipe is more effective. When uncovering
fragile artifacts, particularly in the presence of large
amounts of organic matter, however, a 3 or 4 inch
(7.6 or 10.2 cm) airlift is essential. The principle of
airlift operation is described in Section 8.9.2.
Airlift efficiency increases with water depth because
the trapped air expands as it ascends in the pipe; air-
lifts are consequently not very effective in water depths of
less than 15 feet (4.6 m). Exploratory test holes 6 feet
(1.8 m) deep and 10 feet (3 m) in diameter can be dug
quickly with a 6 inch (15.2 cm) airlift in 45 feet (13.7 m)
of water to define the perimeter of a site. When
excavating around fragile artifacts, the airlift should
be used more as an exhaust for removing loose overburden
than as a digging instrument. Instead of using the
suction force of the airlift to cut into the sea bed, divers
should expose artifacts by carefully hand-fanning the
bottom deposits into the pipe. In this way, fragile artifacts
can be uncovered without being sucked up the pipe.
Because even experienced divers lose artifacts up the
pipe, the use of a basket or grate at the other end is
essential. The most common problem with airlifts is
that large pieces of ballast, coral, or bedrock get drawn
into the mouth of the pipe and become jammed as they
ascend.
Water jet excavation involves the use of a high-
pressure water pump, a fire hose long enough to reach
the sea bed, and a tapered nozzle. The nozzle should
have small holes for permitting a backward thrust of
water to eliminate the recoil so that the operator can
stabilize the hose. The water jet creates a high-pressure
stream that can cut through and remove hard-packed
clays and sand, but its use as an excavating tool is
limited to situations where the water jet will not dam-
age artifacts or the integrity of archeological deposits
before they are mapped.
The venturi pump excavation technique, sometimes
referred to as a Hydro-dredge, involves the use of a
10 foot (3 m) length of metal or PVC tube, 3 to 6 inches
(7.6 to 15.2 cm) in diameter, that is bent in a 90° elbow
at the suction end. A hose from a high-pressure water
pump on the surface is attached to the elbow juncture
at the end of the tube. When high-pressure water flows
along the length of the tube, a venturi effect causes a
suction, which draws bottom sediment into the tube
and out the other end, where it is discharged off the
site. This excavation technique is ideal in shallow water,
particularly in areas that are not accessible to the large
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-39
Heavy Overburden Air Lift
LOW PRESSURE
AIR COMPRESSOR 7ffV&%2)
October 1991— NOAA Diving Manual
Courtesy: NOAA (1979) and Duncan Mathewson
9-39
Section 9
vessels needed to support airlifts or a prop wash. In
water over 50 feet (15.2 m) deep, a similar hydraulic
dredging tool called a Hydro-flo can be used by lower-
ing it over the side and controlling it from the deck. As
with all underwater excavation tools, hydraulic dredges
must be used carefully to avoid damaging artifacts.
Prop wash excavation (also known as a "blower" or
"mailbox") involves a 90° elbow-shaped metal tube
mounted on the transom of a vessel (Figure 9-40). The
metal elbow, slightly larger in diameter than the ves-
sel's propeller, is lowered over the propeller, where it is
locked into position. With the vessel anchored off the
bow and stern, the engines are started so that the
horizontal discharge of the water thrust that normally
pushes the vessel forward is deflected downward. This
surge of water blows away the bottom sediment. As
successive overlapping holes are dug by shifting the
position of the boat on its anchor lines, an archeologi-
cal picture of the artifact scatter pattern slowly emerges.
The key to using the prop wash as an effective arche-
ological tool is to control the engine speed properly. At
slow speeds, the prop wash can remove overburden
very delicately from wreck sites in 15 to 50 feet (4.6 to
15.2 m) of water without damaging the archeological
integrity of the deposits. It can do great damage, how-
ever, if the engines are raced for too long a time. When
operating a prop wash, experience and good judgment
are needed to ensure that artifacts are not lost or
damaged. It is essential to maintain good communica-
tion between the divers on the sea bed and the operator
at the throttle to ensure safe, well-controlled excavation.
In proper hands, a prop wash can be very effective in
defining the anatomy of a wreck site by determining
the extent of its artifact scatter pattern. Even in deep
sand, where it is impossible to record exact provenance
data, artifact clusters mapped as coming from the
same prop wash hole may aid in the interpretation of a
site. Marine archeologists in Texas, Florida, North
Carolina, and Massachusetts have successfully used
prop washes to excavate wrecks.
The use of flotation gear is an inexpensive and effec-
tive method of lifting. Lift bags are available in differ-
ent sizes and forms, ranging from large rubberized
bags and metal tanks capable of lifting several tons to
small plastic and rubberized nylon bags for lifting
50 to 500 pounds (22.7 to 226.8 kg). Larger bags should
be equipped with an air relief valve at the top. For
archeological work, smaller rubberized nylon bags are
recommended; these self-venting bags have a lifting
capacity of 100 pounds (45.4 kg) and are useful in all
underwater operations. Lifting bags are described further
in Section 8.9.1.
9.12.3 Artifact Preservation and Salvage Rights
The recovery of submerged artifacts is only the first
step in enjoying the rewards of research, diving, and
hard work. Many divers, either by accident or by design,
recover valuable or historic artifacts, only to lose them
because they do not take proper care of them. The first
rule for preserving submerged artifacts is to keep them
wet until proper preservation procedures can be initi-
ated. If a diver is uncertain about what to do, he or she
should consult local experts or publications on artifact
treatment (Murphy 1985). Special preservation pro-
cedures are required for iron and steel artifacts, including
the use of rust and corrosion inhibitors, acid treat-
ment, sealants, chemical and electrolytic reduction,
and encapsulation (Murphy 1985). Some of these tech-
niques require soaking or treatments lasting weeks or
months, depending on the nature and size of the arti-
fact. Non-metallic artifacts must be preserved by the
use of entirely different procedures.
In addition to preserving artifacts, it is essential that
the states and the courts establish the rightful owner-
ship of artifacts recovered on submerged bottomlands.
Generally, the U.S. Government controls operations
on or under navigable waters, while the states own the
waters and their submerged beds, which gives them
authority over most finds. Non-navigable waters are
usually privately owned or are controlled by local gov-
ernments. There are many laws affecting the recovery
of historical artifacts or the salvage of abandoned proper-
ty, and these are often complex. Divers involved in
such activities must be aware of applicable laws, both
to protect themselves and their historical finds.
9.12.4 Significance of Shipwreck Archeology
The archeological significance of shipwreck sites is
best determined by their physical integrity and their
potential for providing historical and cultural data
that are not available elsewhere. Information that can
be gleaned from shipwreck sites includes: overseas
trading patterns and maritime adaptation to New World
cultural processes; maritime life styles and patterns of
cultural change; and information regarding the evolu-
tion of European vessels and the development of New
World shipbuilding techniques.
Like terrestrial sites, historic shipwrecks are not
distributed on a random basis. The temporal and spa-
tial patterning of shipwrecks is primarily a function of
environmental factors, seafaring cultural traditions,
maritime technology, and socio-political variables.
Recent studies have demonstrated that the preserva-
tion potential for shipwrecks is highest in areas of low
9-40
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-40
Prop Wash System Used
for Archeological Excavation
LOOSE SHELLY SAND
.••U.Y.
energy (less wave action) and/or high rates of sedi-
mentation. Thus, a knowledge of oceanography and
aquatic geology is important when searching for sub-
merged artifacts.
Shipwrecks should be considered not only as cul-
tural resources but also as a source of valuable
educational and recreational experiences. Wrecks to
be explored for recreational purposes should be situ-
ated in clear water less than 30 feet (9.1 m) deep, have
a visible hull structure, and be accessible by small
boats. Heavily disturbed sites with little or no remaining
physical integrity can. in certain cases, be used to
teach students how to perform underwater archeologi-
cal operations without distorting the archeological record
(Mathewson 1981). Similarly, heavily disturbed sites
and those of more recent date can be developed into
archeological parks to provide new underwater experi-
ences for sport divers. By promoting such recreational
dive sites, user pressure on some of the more archeo-
logically significant sites can be reduced.
October 1991 — NOAA Diving Manual
Courtesy: Duncan Mathewson
9.13 ANIMAL CAPTURE TECHNIQUES
A wide variety of devices is used by scientists and
commercial fishermen to aggregate, concentrate, or
confine aquatic animals. Trawls, seines, traps, grabs,
and dredges have all been used successfully by scuba-
equipped scientists interested in animal and gear behav-
ior. Diver-scientists who will be diving near such cap-
ture systems should train under simulated conditions
before participating in open-water dives. Marine sci-
entists can help to improve the design of trawls and
other such equipment by evaluating its underwater
performance, observing how animals behave in rela-
tion to the gear, and then conveying this information to
equipment designers.
In the FLARE and Hydrolab undersea programs,
divers were able to observe fish near stationary traps
25 to 80 feet (7.6 to 24.4 m) below the surface for up to
8 hours per day (Figure 9-4 1) and to devise methods to
alter catch rates and the species captured (High and
9-41
Section 9
Figure 9-41
Fish Trap
Source: NOAA (1979)
Ellis 1973). Divers from the National Marine Fisher-
ies Service were also able to estimate accurately the
populations of fish attracted to experimental submerged
structures during studies designed to develop automated
fishing platforms.
draw the bottom closed, which seals off the fish's escape
route.
9.13.3 Trawls
Trawls are nets constructed like flattened cones or
wind socks that are towed by one or two vessels. The
net may be operated at the surface, in midwater, or
across the seafloor. Specific designs vary widely,
depending on the species sought. A 9.8 foot (3 m) long
plankton net having a 1.6 foot (0.5 m) mouth opening
may be towed at speeds up to 3.5 knots (1.7 m/s), while
a 202 foot (61.5 m) long pelagic trawl with an opening
40.3 by 10.5 feet (12.3 by 21.5 m) may filter water at
1 knot (0.5 m/s). Figure 9-42 shows a trawl diver. Trawls
may be opened horizontally by towing each wingtip
from a separate vessel, by spreading the net with a
rigid wooden or metal beam, or by suspending paired
otterboards in the water to shear out away from each
other horizontally when towed.
9.13.1 Nets
Nets vary in size, purpose, materials, and methods
of use. Divers working close to an active net (one which
is being towed) can interfere with its operation, espe-
cially if it is small, if they swim too near to it or
touch it. Any net is considered large if direct diver
contact does not appreciably influence its configura-
tion or operation. Plankton nets typify small nets both
in physical size and in the lightweight web required to
retain micro-organisms. At the larger extreme, high-
sea tuna seines often are 3600 feet (1098 m) long, with
4.5 inch (11.4 cm) long meshes stretching 200 feet
(61 m) or more down into the water. Gill nets are designed
to entangle fish attempting to push through the meshes;
webbing mesh and thread size vary, as do net length
and depth, in accordance with the size and species of
fish sought. Gill nets use fine twine meshes hung
vertically in the water between a corkline and a leadline.
The net may be suspended at the surface or below the
surface or be weighted to fish just above bottom and
across the expected path of migratory fish. Divers and
their equipment can easily become entangled in gill
net webbing, which is difficult to see in the water.
9.13.2 Seines
Seines are similar to gill nets in that a wall of web is
held open vertically in the water by the opposing forces
of a corkline and leadline; however, the seine is set in a
circle to confine fish within the web rather than to
entangle the fish. Seines often have rings along the
leadline through which a line or cable can be pulled to
9-42
9.13.4 Diving on Stationary Gear
Diving on stationary gear such as traps, gill nets,
and some seines presents few problems. Experienced
divers can dive either inside or outside the net to observe
animal behavior or to carry out work assignments.
Divers must be alert to the entanglement hazard
presented by loose diving gear, such as valve pull rods,
valves, mask rims, knives, vest inflator mechanisms,
and weight belt buckles. A buddy diver can usually
clear the entanglement more readily than the fouled
diver. Fouled divers must avoid turning or spinning
around, which will entrap them in the web. It is
occasionally necessary for a fouled diver to remove the
tank, disengage the caught mesh, and replace the tank
assembly before continuing with the task at hand.
9.14 THE USE OF ANESTHETICS IN
CAPTURING AND HANDLING FISH
Anesthesia has been defined as a state of reversible
insensitivity of the cell, tissue, or organism. In connec-
tion with fish, the terms narcosis and anesthesia are
often used interchangeably, although not all chemi-
cals characterized as fish anesthetics also act as nar-
cotics. Anesthetics should be used for surgical inter-
vention or to perform other painful manipulations.
Fish anesthetics have been used in conjunction with a
multitude of operations, including capture, transport,
tagging, artificial spawning, blood sampling, moving
fish in aquaria, surgical intervention, and photographic
sessions. There is a wealth of published information in
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-42
Diver Checking Fish Trawl
Photo Ian K. Workman
the popular and scientific literature on a wide variety
of chemicals and their applications.
The use of anesthetics does have an impact on the
surrounding environment, and extreme care must be
exercised to minimize this effect. The subsequent
monitoring of an area in which anesthetics have been
used must take this into account, because census and
other data are affected by the use of anesthetics.
9.14.1 Response to Anesthetics
Fish anesthetics are administered most commonly
by adding them to the water, which is then taken up by
the gills. As the fish proceeds into anesthesia, it usu-
ally follows a series of definable stages that are useful
to know in evaluating the depth of the anesthesia. A
simplified scheme defining the levels of anesthesia,
which is devised largely from the work of McFarland
(1959) and Schoettger and Julin (1967), is presented
in Table 9-2.
The response of a particular fish to an anesthetic
depends on a number of factors, including the species
and size of fish, water temperature, salinity or hard-
ness, pH, and state of excitability of the fish, as well as
on the dosage and type of anesthetic. With some anes-
thetics, not all of the stages mentioned in Table 9-2 are
observable; for example, with quinaldine there is gen-
erally no definitive sedation stage. Recovery begins
when the fish is removed from the anesthetic bath and
transferred to untreated water, where recovery then
proceeds, usually in reverse order, through the stages
shown in Table 9-2.
9.14.2 Selecting an Anesthetic
Factors to consider in choosing an anesthetic are
purpose, toxicity, repellent action, ease of application,
and cost. It may be helpful to refer to the literature to
choose a suitable anesthetic for the species and pur-
October 1991 — NOAA Diving Manual
pose concerned. In the absence of applicable data, it is
often advisable to conduct a preliminary experiment,
since even closely related species may not respond to
the same anesthetic in the same manner. Species-specific
intolerance has been demonstrated with some anesthetics.
Many chemicals exhibit toxic effects that are unrelated
to their anesthetic action, and these may be transitory
or sustained. Some chemicals that exhibit toxic effects
during long-term exposure may be satisfactory to use
for short-term anesthesia.
The therapeutic ratio TR = LC50/EC is sometimes
used in evaluating an anesthetic, where LC50 = the
concentration lethal for 50 percent of the specimens
and EC = the concentration necessary to provide the
desired level of anesthesia. Generally, a TR of 2 or
more is considered desirable, but since time of expo-
sure and a variety of other factors affect the validity of
the TR, its usefulness is somewhat limited.
The toxicity of the anesthetic to humans also must
be considered. A given anesthetic may be dangerous to
handle because of its acute toxicity or carcinogenic
potential, or it may toxify fish flesh, rendering it dan-
gerous or fatal to eat. This last consideration is impor-
tant in cases where the fish will later be released to the
wild, where fishermen might catch it.
In addition, the specific responses of fish to an anes-
thetic may be important, and the stages of anesthesia
can vary with the anesthetic. As mentioned above,
quinaldine generally cannot be used to induce the seda-
tion stage, and some chemicals are much more repel-
lent to fish than others. Other anesthetics may initially
cause an increase in activity.
Several anesthetics have low solubility in water and
must first be mixed with a carrier such as acetone or
alcohol to increase their solubility. The need to premix
may be inconvenient, particularly in field work. Final-
ly, cost must be considered, especially when large field
collections are concerned.
9.14.3 Application of Anesthetics
Rapid immobilization. If an anesthetic is administered
in high enough dosages, fish may be immobilized rap-
idly for capture or handling. The fish is then removed
to untreated water for recovery. The chemical may be
sprayed in the vicinity of the fish or added to a con-
tainer holding the fish, or the fish may be removed to a
separate bath, depending on the circumstances. Sev-
eral anesthetics that are unsuitable for sustained
anesthesia are satisfactory for rapid immobilization,
provided the exposure is of short duration.
Sustained Anesthesia. Under suitable conditions, fish
can be sustained safely under anesthesia for several
9-43
Section 9
Table 9-2
Levels of Anesthesia
for Fish
Stage
Description
Behavior
0
Unanesthetized
Normal for the species.
1
Sedation
Decreased reaction to visual stimuli and/or tapping on the tank; opercular rate
reduced; locomotor activity reduced; color usually darker.
2
Partial loss of equilibrium
Fish has difficulty remaining in normal swimming position; opercular rate usually
higher; swimming disrupted.
3
Total loss of equilibrium
Plane 1 —Fish usually on side or back; can still propel itself; responds to tap on tank
or other vibrations; opercular rate rapid.
Plane 2 — Locomotion ceases; fins may still move but ineffectively; responds to
squeeze of peduncle or tail; opercular rate decreased.
4
Loss of reflex
Does not respond to peduncle squeeze; opercular rate slow — often may be erratic.
This is the surgical level.
5
Respiratory collapse
Operculum ceases to move; cardiac arrest (death) will occur within one to several
minutes unless fish revived in untreated water.
Source; NOAA (1979)
days. Choosing the proper anesthetic with regard to
toxicity and stability is critical. Before the anesthetic
is administered, the fish should be starved for 24 to
48 hours to prevent regurgitation of food.
To perform surgery on captured fish, it is simplest to
anesthetize the fish to the surgical level; the fish should
then be placed in a trough or other restraining device,
and its head should be immersed in an anesthetic bath
for the duration of the procedure. For longer term
surgery, more sophisticated procedures are required.
One successful system employs two water baths, one
containing untreated water and the other the anes-
thetic solution. The level of anesthesia can be con-
trolled carefully by selectively recirculating water from
the baths over the fish's gills. Steps should be taken to
maintain the oxygen content near the saturation level
and the ammonia concentration at the minimal level.
Filtration may be required to maintain water quality
(Klontz and Smith 1968).
Recovery. To revive fish in deep anesthesia, it may
be necessary to move them gently to and fro in their
normal swimming position. It is helpful to direct a
gentle stream of water toward the fish's mouth, which
provides a low-velocity current over the gills. It is not
advisable to use a strong current or to insert a hose
directly into the mouth because this may cause, rather
than alleviate, hypoxia. The water in which the fish is
being revived must be of good quality.
Some species recovering from certain anesthetics
may undergo violent, uncontrolled swimming move-
ments, and steps must be taken in such a situation to
prevent self-inflicted injuries. For example, this is
usually the case when the yellowtail Seriola dorsalia
recovers from quinaldine anesthesia. Various physio-
logical changes, some of which may persist for more
9-44
than a week, have been observed in fish after anesthe-
sia (Houston et al. 1971). During this post-treatment
period, additional stress may result in mortality and
should therefore be minimized.
NOTE
Anesthetics administered to food fish must
be approved by the Food and Drug Adminis-
tration, and those using anesthetics are
advised to be thoroughly familiar with all
pertinent regulations. Violations of these
regulations carry severe penalties.
Tidepools and Ponds. Anesthetics are useful when
collecting fish in tidepools. The water volume in the
pool must first be estimated, and then the desired dose
of anesthetic is calculated and added to the pool. As
the fish become immobilized, they are removed to
untreated water as quickly as possible. It is desirable
to collect fish from tidepools as the tide is rising,
because a moderate amount of surge in the pool helps
to flush anesthetized fish out of crevices, and diluting
the pool water with incoming water will prevent the
killing of specimens that are not going to be collected.
With the proper anesthetic and dose, the mortality of
uncollected specimens can be reduced to a negligible
level (Gibson 1967, Moring 1970).
Reef and Shore. Many species of reef and shore fish
can be collected with anesthetics. Quinaldine (10-20%) is
used widely for this purpose. One-half to 1.05 quart
(0.5 to 1 L) of the solution is generally used for each
collection. Species susceptibility is highly variable.
For example, angelfish and butterflyfish are highly
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Figure 9-43
Slurp Gun Used
to Collect Small Fish
susceptible, squirrelfish are moderately susceptible,
and moray eels are highly resistant. The effectiveness
of the anesthetic also varies with the physical situation
as well as the skill and experience of the collector.
Most anesthetics are at least somewhat repellent, and
the fish usually need to be in a situation, e.g., in small
caves, short crevices, or under rocks, where they can be
confined within the anesthetic's influence for several
seconds. The anesthetic is usually dispensed from a
squeeze bottle in sufficient quantity to immobilize or
partially immobilize specimens on the first applica-
tion. The fish can then be collected with a hand net or,
in the case of small specimens, with a manual "slurp"
gun (Figure 9-43).
A power syringe is available that allows oral anes-
thetics to be delivered through a probe. This device
permits the diver to deliver the anesthetic at closer
range to more species of fish than can be done using a
squeeze bottle, and this delivery system may make the
more expensive anesthetics practical to use for collecting.
Sedentary specimens can sometimes be collected by
slowly trickling a light anesthetic dose downstream
toward them. Fish in burrows are often difficult to
collect with anesthetics because the burrows are so
deep that the fish cannot be reached by discharging
anesthetic from a squeeze bottle. Attaching tubing,
such as a piece of aquarium air line, to the bottle may
provide an adequate extension to reach into the bur-
row. The anesthetic should have repellent qualities
that will cause the fish to emerge, because otherwise
the fish might become anesthetized in the burrow and
remain out of range. A noxious chemical can be added
to some non-repellent anesthetics to ensure that the
fish emerges.
Scientists at the Scripps Aquarium have developed
a successful system for collecting garden eels of the
Taenioconger species, which were previously difficult
to collect. A piece of clear plastic, 6.6 feet (2 m)
square, is placed over the area of the eels' burrows and
weighted down along the edges with sand. Approxi-
mately 1.05 quart (1 L) of 13 percent quinaldine
solution in ethanol is applied under the plastic. The
area is then left undisturbed for 20 minutes, after
which the sedated and immobilized eels are gathered
gently by hand. A single collection in a well-developed
colony may yield more than 20 eels. This technique can
be applied to other burrowing species, although the
dosage and time of exposure may have to be varied.
Fish can also be anesthetized by injection. Although
earlier attempts at collecting fish with projectile-
mounted syringes were limited in their success, a recently
developed technique utilizing Saffan®, a veterinary anes-
thetic, administered by a laser-sighted underwater
October 1991 — NOAA Diving Manual
Photo ■ National Geographic Society
dart gun, shows much promise. Harvey, Denney,
Marliave, and Bruecker (1986) have successfully immo-
bilized small sharks and ratfish with this technique,
while Harvey (1986) has used it to collect moray eels
and jacks.
Coral heads. It usually is advantageous to enclose
coral heads with a loose-fitting net before applying the
anesthetic. Some species of fish such as wrasse and
hawkfish reside in coral at night and can be collected
easily at that time with the aid of anesthetics.
Large-scale collections. One technique used to col-
lect fish over a large portion of a reef is to enclose the
desired area with a seine and to administer a large
enough quantity of anesthetic to immobilize the enclosed
population rapidly. Divers should work as a team to
recover the fish because of the danger of the divers
becoming entangled in the net. Procedures to free
entangled divers should be planned in advance.
Handling large fish. Sharks or other large fish cap-
tured by hook may be immobilized by spraying a strong
anesthetic solution directly over their gills before bring-
ing them aboard. Gilbert and Wood (1957) used a
1 000-ppm tricaine solution successfully in this situation.
Transportation. Anesthetics have been used, with
conflicting results, to immobilize fish during transit.
The effectiveness of this approach depends on a num-
ber of factors, including the type of anesthetic, species
of fish, temperature, time in transit, preconditioning
of fish, and water quality. Since most fish can be
transported successfully without the use of anesthet-
ics, information on the appropriateness of using anes-
thetics during transit should be obtained from the
literature or by experimentation before attempting the
procedure.
Summary. The use of anesthetics as collecting agents
for aquarium fish is controversial, primarily because
9-45
Section 9
of concern about the delayed toxicity of the anesthetic
agents. A survey of the literature indicates that, in the
majority of species experimentally subjected to repeated
anesthetization, delayed mortality is negligible. Pro-
fessional aquarists at Scripps Aquarium, Steinhart
Aquarium, and other institutions have also demonstrated
that many other species that have not yet been subjected
to formal experimentation can be collected safely and
handled without significant mortality.
Most aquatic biologists concerned with collecting
agree that judiciously applied anesthetics are useful
collecting agents. However, the misuse of these chemi-
cals, especially if widespread, can be very harmful. For
example, the practice of using sodium cyanide to col-
lect aquarium fish, which is sometimes done in under-
developed countries, is ill-advised and has resulted in
human deaths, as well as high mortality among the fish
and other organisms in the vicinity.
Recommendations. Tricaine® (MS-222) is a highly
soluble and virtually odorless powder that is easy to
use. It has proved to be a successful anesthetic in a
wide variety of applications under a broad range of
conditions in both fresh water and seawater, and there
is an extensive literature on its properties and use.
Tricaine® is a good choice where sustained sedation or
surgical-level anesthesia is required, but high cost
generally precludes its use as a collecting agent.
Quinaldine has been used widely to collect or handle
fish. It is of low solubility in water and is generally
dissolved in acetone, ethyl alcohol, or isopropyl alco-
hol before use in water. Quinaldine is not useful where
sedation-level anesthesia is the goal, and it should not
be used for major surgery or other painful procedures
because it is a poor pain killer. Liquid quinaldine can
be converted readily to a water-soluble salt, which
greatly facilitates its use. When a mixture of the salt
and tricaine is prepared in proper proportions, it com-
bines the desirable properties of both chemicals and is
effective at lower doses than either alone. Propoxate®
and its analog Etomidate® are two relatively new and
highly potent fish anesthetics that have potential as
anesthetics for fish collection. Table 9-3 shows the
commonly used fish anesthetics, including their recom-
mended dosages.
9.14.4 Diver-Operated Devices
The capture of live fish poses no special problems for
divers. Some fish are territorial and maintain discrete
regions, while others live in schools and roam widely.
Diurnal variations may also cause the fish to change
their habitats during a 24-hour period.
Conventional methods of capture such as seining,
trawling, and long-lining are not appropriate for cap-
turing fish around coral reefs, and a number of special
techniques must be used instead. An array of suction
devices called slurp guns has been on the market for
some time. These are powered either by rubber tubing,
springs, or other means. After cornering a fish, the
diver using a slurp gun (Figure 9-43) pulls the trigger,
drawing the plunger back and sucking a large volume
of water in through a small opening and thus pulling
small fish (1-3 inches (2.54-7.6 cm)) into the gun. The
fish are then moved into a holding container, and the
gun is readied for another shot. The disadvantages of
slurp guns are: the small size of the fish that can be
captured, the necessity for the diver to be very close
to the fish, and the need to corner the fish, usually
in a hole, to capture it.
Glass or plastic bottles also may be used to entrap
small fish; however, fish may react to the pressure
wave created by the moving jar and swim away. All
bottles must be flooded fully with water before being
submerged. A better technique than the bottle is the
use of a piece of plastic core liner or plastic tube with a
screen across one end, which can be slipped over fish
more easily. Divers on the bottom can also use small
gill nets. Animals such as sea urchins may be broken
up and placed near the net to attract fish, or divers may
herd fish into the net. Once entangled, fish may be
withdrawn and placed in bags or wire cages.
As discussed earlier, fish traps may also be effective
if baited appropriately and placed at a proper point
either on the bottom or in the water column. Divers can
then remove fish from the trap and rebait it while it
remains on the bottom.
Deepwater fish can be caught on hook and line and
reeled to 60 to 100 feet (18.3 to 30.1 m), where divers
can insert hypodermic needles into those with swim
bladders and then decompress the fish. There is an 80
percent recovery rate on many species of rock fish
when this technique is used. A dip net fastened to the
end of a pole spear is useful in collecting fish near the
bottom. The fish may be pinned against a rock or sand
bottom, taken out of the net, and placed in an appro-
priate container; again, needle decompression may be
helpful.
Many larger fish such as rays, skates, or harmless
sharks may be caught either by hand or by a loop of
heavy monofilament line on the end of a pole (such as a
snake stick). Electric fish and rays should not be taken
with metal poles or rods because of the shock potential
(see Section 12.4).
Invertebrates may be collected by divers wearing
gloves. A pry bar, screwdriver, putty knife, or diving
9-46
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
Table 9-3
Fish Anesthetics
Anesthetic
Qualities
Dosage (varies
with species,
temperature, etc.)
Common
Use
Remarks
References
Benzocaine*
Powder,
soluble
in
ethanol
25-100 mg/L
Immobilization,
deep anesthesia
Widely used
in human
medicine; safe
and effective
with fish.
Caldarelli 1986
Chloral
hydrate
Solid, soluble,
inexpensive
1-4 g/L
Sedation
Low potency;
not widely used.
McFarland 1959
McFarland 1960
Bell 1967
Cresols
Liquid; mix
50:50 with
acetone to
facilitate
solution.
20-40 mg/L for
immobilization
Collection
Cresols have
undesirable
toxic effects;
para-cresol is
the most effec-
tive isomer.
Howland 1969
Etomidate5
Make 1 percent
solution in
propylene
glycol.
2-10 mg/L
Immobilization
High potency;
analog of
Propoxate®;
longer seda-
tion times
and safer than
quinaldine and
MS-222 mixture.
Amend et al. 1982
Limsowan et al.
1983
Methylpentynol
(Oblivon®,
Dormison ')
Liquid.
moderately
soluble
0.5-2 ml/L
1500-8000 mg/L
Sedation or deep
anesthesia
Widely used but
less desirable
than other
anesthetics;
low potency.
Bell 1967
Klontz and Smith
1968
Howland and
Schoettger 1969
Phenoxyethanol
(2-phenoxye-
thanol)
Oily liquid
0.1-1 ml/L
Immobilization
Used frequently
with salmonids.
Klontz and Smith
1968
Bell 1967
Propoxate®
(McNeil R7464)
Crystalline;
soluble
1-4 mg/L
Collection,
immobilization
Good collecting
agent.
Thienpoint and
Niemegeers 1965
Howland 1969
Quinaldine
(Practical
grade)
Oily liquid,
soluble with
difficulty; dis-
solve in 10-50
percent acetone,
ethanol, or
isopropyl alcohol
to facilitate
solution.
5-70 ml/L
Widely used
for collection,
immobilization
No sedation
state; poor
analgesic;
efficacy varies
widely with
species and water
characteristics;
long exposures
toxic.
Schoettger and
Julin 1969
Locke 1969
Moring 1970
Gibson 1967
Howland 1969
October 1991 — NOAA Diving Manual
9-47
Section 9
Table 9-3
(Continued)
Dosage (varies
with species,
Common
Anesthetic
Qualities
temperature, etc.)
Use
Remarks
References
Quinaldine
Crystalline
15-70 mg/L
Collection,
Prepared from
Allen and Sills
sulfate
solid
immobilization
liquid quinaldine
1973
(QdS04)
and has same
properties.
Gilderhus, Berger,
Sills, Harman
1973a
Rotenone®
Powder or emul-
0.5 ppm
Ichthyocide;
Used to salvage
Tate, Moen,
sion
occasionally
used for
collecting
fish from fresh-
water ponds.
Limited use in
seawater for
live collecting.
Severson 1965
Sodium
Solid
DO NOT USE
Used in
Dangerous to humans;
cyanide
Philippines
and elsewhere
for collecting
causes high
mortality in
fish.
Styrylpy-
White powder;
20-50 mg/L
Immobilization,
Not widely used
Klontz and Smith
ridine (4-
soluble
deep anesthesia
but a successful
1968
styrylpy-
anesthetic.
ridine)
Tricaine®
White crystalline
15-40 mg/L for
Immobilization,
Expense bars its
Klontz and Smith
(MS-222, tri-
powder; readily
sedation
deep anesthesia;
use for collecting;
1968
caine meth-
soluble
40-100 mg/L for
most widely used
used extensively
Bell 1967
anesulfonate)
deep anesthesia
100-1000 mg/L
for rapid
immobilization
anesthetic
in surgery, fish
handling,
transport.
Urethane
Carcinogenic
DO NOT USE
Immobilization,
deep anesthesia
Carcinogenic.
Wood 1956
Mixtures of
Powder, readily
Various, e.g., 10:20
Immobilization,
Combines desirable
Gilderhus, Berger,
MS-222 and
soluble
ppm QdS04: MS-222
deep anesthesia
properties of each
Sills, Harman
QdS04
equals 25 ppm QdS04 or
80-100 ppm MS-222
anesthetic;
combination can be
used in lower
concentration than
1973b
either anesthetic
alone.
Source: Donald Wilkie
9-48
NOAA Diving Manual — October 1991
Procedures for Scientific Dives
knife may be useful in removing some specimens from
their substrate. Delicate animals such as nudibranches
may be placed in separate plastic jars, vials, or ziplock
bags. Vials and jars should be open at the beginning of
the dive but be completely filled with water before
being returned to the surface.
Traps are effective for crabs, lobsters, and, occa-
sionally, octopus. Nylon net bags are more easily used
for collecting than bottles or plastic bags. Animals
that are neutrally buoyant will float out of the bottle or
plastic bag when it is reopened to add another specimen.
Animals that live in the upper few centimeters of
sediment or sandy bottom may be sampled by using
either a scoop, which has a line inscribed showing a
given volume, or a cylinder made of plastic, stainless,
aluminum, or other material that can be forced into
the soft substrate. A simple cake server or spatula can
be inserted from the side to provide a closure as the
core of sediment is withdrawn from the bottom. The
diameter of the cylinder should be such that it fits
snugly over the mouth of the collecting bottle so the
material can be forced into a labeled jar.
Nylon or other plastic screens can be obtained in a
variety of mesh sizes. These may be tied over ends of
plastic tubes as a sieve or be sewn into a bag to be used
to hold sediment samples.
October 1991 — NOAA Diving Manual
9-49
(
SECTION 10
DIVING UNDER
SPECIAL
CONDITIONS
10.0
10.1
10.2
10.3
10.4
10.5
10.6
10.7
10.8
10.9
10.10
10.11
10.12
10.13
10.14
10.15
10.16
Page-
General 10-1
Geographic Regions 10-1
10.1.1 Northeast Coast 10-1
10.1.2 Mid-Atlantic Coast 10-2
10.1.3 Southeast Coast 10-3
10.1.4 Gulf of Mexico 10-3
10.1.5 Northwest Coast 10-3
10.1.6 Mid-Pacific Coast 10-4
10.1.7 Southwest Coast 10-5
10.1.8 Central Pacific Ocean 10-6
10.1.9 Arctic and Antarctic 10-6
10.1.10 Tropics 10-6
10. 1.1 1 Diving in Marine Sanctuaries or Underwater Parks 10-7
Diving From Shore 10-7
10.2.1 Through Surf 10-7
10.2.2 Through Surf on a Rocky Shore 10-9
10.2.3 Through Shore Currents 10-9
10.2.4 From a Coral Reef 10-10
Diving From a Stationary Platform 10-10
Diving From a Small Boat 10-1 1
10.4.1 Entering the Water 10-12
10.4.2 Exiting the Water 10-12
Fresh Water Diving 10-13
10.5.1 Great Lakes 10-13
10.5.2 Inland Lakes 10-14
10.5.3 Quarries 10-14
Open-Ocean Diving 10-14
Cave Diving 10-17
Cold-Water Diving 10-19
Diving Under Ice 10-21
Kelp Diving 10-22
Wreck Diving 10-23
Diving at High Elevations 10-24
10.12.1 Altitude Diving Tables Currently in Use 10-24
10.12.2 Comparison of Existing Tables 10-25
10.12.3 Recommendations for Altitude Diving 10-25
10.12.4 Calculations For Diving at Altitude 10-25
10.12.5 Correction of Depth Gauges 10-26
10.12.6 Hypoxia During Altitude Diving 10-27
Night Diving 10-27
Diving in Dams and Reservoirs 10-28
10.14.1 Diving at Dams 10-28
10.14.2 Diving at Water Withdrawal and Pumping Sites 10-30
River Diving 10-31
Diving From a Ship 10-32
10.16.1 Personnel 10-32
10.16.2 Use and Storage of Diving and Related Equipment 10-32
10.16.3 Safety Considerations 10-33
10.16.4 Using Surface-Supplied Equipment 10-33
10.16.5 While Underway 10-33
(
DIVING
UNDER
SPECIAL
CONDITIONS
10.0 GENERAL
The characteristics of underwater environments, such
as temperature, visibility, and type of marine life, vary
significantly from geographic region to region and
influence the amount and type of diving work that can
be carried out under water. The following paragraphs
describe the diving conditions most typical of U.S.
coastal and other areas and provide an overview of the
diving characteristics of these regions.
WARNING
When Diving in an Unfamiliar Region, Infor-
mation About Local Conditions Should Be
Obtained From Divers Who Are Familiar With
Local Waters. A Checkout Dive Should Be
Made With a Diver Familiar With the Area
10.1 GEOGRAPHIC REGIONS
For purposes of discussion, the coastal regions are
classified as shown on the following table. The princi-
pal characteristics of each region are described in the
following sections of this chapter.
Region
Area Encompassed
Northeast Coast
Maine to Rhode Island
Mid-Atlantic Coast
Rhode Island to Cape Hatteras
Southeast Coast
Cape Hatteras to Florida
Gulf of Mexico Coast
West Coast of Florida to Texas
Northwest Coast
Subarctic Alaska to Oregon
Mid-Pacific Coast
Northern and Central California
Southwest Coast
Point Conception to the
Northern Baja Peninsula
Central Pacific Ocean
Hawaiian and Leeward Islands
Polar
Arctic and Antarctic
Tropics
Caribbean and Florida Keys
10.1.1 Northeast Coast
Diving in northeastern waters is an exciting and
chilling experience. Generally, the best diving condi-
tions in terms of water temperature, sea state, and
underwater visibility occur from June through Octo-
October 1991 — NOAA Diving Manual
ber. As one progresses north along the New England
coast, water temperature decreases and underwater
visibility increases.
Water temperatures near the surface during the spring
and summer, when a substantial thermocline exists,
range from 50 to 70°F (10 to 21 °C). Temperatures at
100 feet (30.5 m) range from 48 to 54 °F (9 to 12'C).
During the winter months, the temperature of the water
column is essentially homogeneous, with temperatures
reaching as low as 28.5 °F (-2°C). Subzero air tempera-
tures and strong winds cause wind chill factors as low
as -70 to -80 °F (-57 to -62 °C). Wet suits and variable-
volume dry suits have become standard for winter
diving in the Northeast (see Section 5.4).
Underwater visibility is primarily a function of sea
state and vertical turbulence in the water column. In
the Northeast, horizontal visibility of 50 to 80 feet
(15 to 24.4 m) may occur occasionally throughout the
year, usually in connection with calm seas. Proximity to
a land mass or to estuaries or harbors is associated with a
decrease in visibility because the load of suspended
material in the runoff from the land mass and the
processes associated with the mixing of fresh and salt
water greatly elevate turbidity. During the summer,
biologically caused 'red tide' conditions may occur,
lowering visibility to less than 1 foot (0.3 m). Coastal
waters within the Gulf of Maine have an average range
in visibility of 25 to 35 feet (7.6 to 10.7 m), while
visibility in waters south of Cape Cod averages 10 to
15 feet (3.0 to 4.6 m).
Several species of brown algae comprise the large
kelp of the New England coast. Unlike the kelp of
California, these kelp do not form surface canopies
(see Section 10.11). New England kelp occasionally
extend as much as 25 feet (7.6 m) off the hard ocean
bottom and, although they look impenetrable, they do
not in fact present a significant entanglement hazard.
Generally, these algal plants are sparsely distributed
and seldom project more than 6 to 8 feet (1.8 to 2.4 m)
from the bottom.
Currents along the New England coast are primarily
tidal in origin and generally do not exceed 0.5 knot
(0.25 m/s). Faster currents may be encountered in
channels and in river mouths. Divers should be cau-
tious in the waters off the New England coast, espe-
cially when diving in strong currents and cold water,
10-1
Section 10
because of the potential for overexertion. The surf in
this region is modest compared with the surf in Cali-
fornia, but it is especially hazardous along rocky, pre-
cipitous coastlines such as the coast of Maine. Short-
period waves as high as 5 to 10 feet (1.5 to 3.0 m) can
create very rough and turbulent sea states along these
coasts and can push divers into barnacle-covered rocks.
Hazardous marine animals. Relatively few species of
fish and invertebrates in the waters off the New England
coast are potentially harmful to divers. Sharks of sev-
eral species are occasionally seen, but they are gener-
ally not harmful to divers (see Section 12.3.1). These
are the mako, dusky, tiger, great white, hammerhead,
and blue shark; occasionally, the filter-feeding basking
shark is mistakenly identified as a dangerous shark.
The torpedo ray (electric ray) (see Figure 12-19), cow-
nosed ray, and stingray are found off southern New
England (Cape Cod and south). Documented diver-
shark or diver-ray encounters are relatively rare along
the New England coast.
The most bothersome fish in this region is the goose-
fish, which may weigh as much as 50 pounds (23 kg)
and grow to 4 feet (1.2 m) in total length. It is the habit
of the goosefish to lie partially buried on the ocean
floor waiting for unsuspecting 'meals' to pass by. This
fish is approximately one-half head and mouth and
one-half tail. The sight of a goosefish is enough to
startle even a seasoned diver, but these fish do not
generally attack unless they are provoked. The wolffish is
another bottom-oriented creature that is highly respected
by fishermen and divers for its strength and aggressive-
ness when bothered. The wolffish's six large canine
tusks are capable of inflicting considerable damage, as
many fishermen have discovered when trying to boat
this species.
The green sea urchin, which has many stout spines
that can easily puncture a rubber wet suit, can also
injure divers. Unless the tip of the urchin's spine is
surgically removed from the diver's flesh, it will cause
a painful 'lump' under the skin that may last for months or
years. The green sea urchin is found in very dense
concentrations on hard substrates to depths of 50 to
60 feet (15.2 to 18.3 m).
10.1.2 Mid-Atlantic Coast
Waters off the coasts of the mid-Atlantic states are
characterized by low visibility and cold bottom tem-
peratures. Bottom topography generally consists of
flat sand clay or gravel and occasional low-relief rocky
outcroppings. Wrecks are found frequently off the New
York-New Jersey coasts and off Cape Hatteras.
10-2
Water temperatures on the surface range during the
summer months from 72-75 "F (22-24 °C) and from
40-60 °F (4-1 6 °C) on the bottom, depending on depth,
proximity to the shore, and general location. In the
mid-Atlantic Bight (Montauk Point, N.Y. to Cape
May, N.J.), a large bottom 'pool' of cold winter water
is trapped every summer. This pool or cell contains the
coldest summer water on the entire eastern continental
shelf. Tidal and wind movement of cold bottom water
can cause a significant and sudden change in the bot-
tom temperature of the water off the New Jersey coast.
A chief characteristic of the mid-Atlantic water
column in the summer is the thermocline. The rapid
decrease in temperature at the thermocline may cause
an unsuspecting and unprepared diver enough discom-
fort to abort the dive. Plankton gathered at the ther-
mocline also can decrease the light so drastically that
artificial lights occasionally are needed in water depths
beyond 70 feet (21.3 m). In the Cape Hatteras area,
eddies from the Gulf Stream often bring warm clear
water to the coast. Bottom temperatures are warmest
in October and early November after the cold bottom
water mixes with the warmer upper layers. Winter
temperatures in the northern range drop as low as 35 °F
(2°C) near shore and are relatively homogeneous
throughout the water column, with slightly warmer
temperatures on the bottom.
Underwater visibility is best during September-
October, when it is common to be able to see for dis-
tances of up to 60 feet (18.3 m). Many of the inshore
waters of the northern area and the waters near the
major estuaries, such as the Hudson and Chesapeake,
have poor visibility throughout most of the year. Visi-
bility can range from 0 to 15 feet (4.6 m) in these areas,
but improves with distance offshore. Tides may cause
large changes in visibility for as much as 3 miles
(4.8 km) offshore near bays and rivers.
Tides and currents. Strong tidal currents can be
expected in the Chesapeake Bay, parts of the New
York Bight, off the outer banks of North Carolina, and
in Long Island Sound. Diving in these areas can be
especially hazardous if the diver becomes lost because
of low visibility and is swept away from the planned
exit area.
Waves. Long-period open ocean waves in the mid-
Atlantic are generally not hazardous to divers, although
summer squalls can cause quick 'chops' that may be a
problem. Waves pose the greatest danger to divers
attempting to dive off the end of a rock jetty in a
moderate to heavy surf; divers too close to the end of a
jetty can be picked up and thrown into the rocks by a
wave. The surf in these waters is generally moderate,
and most beaches are composed of sand rather than
NOAA Diving Manual — October 1991
Diving Under Special Conditions
rock, which makes entry from the shore relatively easy
for divers.
Although sharks are numerous off the coasts of the
mid-Atlantic states, there have been few diver-shark
encounters. However, divers carrying speared fish
have been molested by sharks, and divers are therefore
advised to carry fish on a long line, especially in murky
water.
As in the Northeast, the goosefish is probably the
area's most troublesome marine creature for divers.
Divers swimming close to the bottom to see their way
in murky water often inadvertently place a hand or
foot in the mouth of a goosefish lying camouflaged on
the bottom and thus run the risk of being bitten. Sting-
ing jellyfish are so abundant in estuaries, especially
during the summers in the Chesapeake Bay, that max-
imum protection against them is necessary.
10.1.3 Southeast Coast
For the most part, the waters off the coasts of the
southeastern states are tropical. Warm temperatures
prevail and can reach as high as 75 to 80° F (24 to
27 °C) during the summer months. In the most north-
ern portions of this region of Georgia, South Carolina,
and southern North Carolina, less tropical conditions
prevail. Water temperature during the summer in this
area is about 70°F (21 °C). In the area just south of
Cape Hatteras, the Gulf Stream passes close to land,
causing the water temperature to be warmer near shore
than it is to the south. During the winter, water tem-
perature in the southernmost areas remains 65 to 70 °F
(18 to 21 °C); in the more northerly waters, however,
temperatures drop as low as 50 °F (10°C). In the tropi-
cal and subtropical waters of the Southeast, there are a
vast number of different species of marine animals.
Visibility in southern waters is good to excellent in
the offshore areas; closer to shore, however, it drops to
25 to 30 feet (7.6 to 9.1 m), and in harbors and bays, it
can be poor. Farther north, both offshore and nearshore
visibility drops drastically and averages 20 to 25 feet
(6.1 to 7.6 m).
When diving at the boundary of major oceanic cur-
rent systems such as the Gulf Stream, special care
must be exercised because of the episodic turbulent
eddies that occasionally spin off the main mass of
moving water. Extra precautions also must be taken
because of the meandering nature of the current's edge;
relatively quiet water near the edge may suddenly
change to water with a current velocity of 1 knot or
more. Dives in boundary regions must be planned to
anticipate high current speeds, and appropriate sur-
face support must be provided. As the diver descends,
October 1991 — NOAA Diving Manual
there are often sharp boundaries between water masses
in the water column that have different current veloci-
ties. The current generally slows about 1-2 feet
(0.3-0.6 m) above the bottom, and if divers hug the bot-
tom contours they can work without interference from
the current. However, the tending boat operator must
be aware of the current differential and must establish
a reference for the diver's position to prevent the boat
from being carried away from the dive site. Dropping a
well-anchored buoy over the side at the beginning of
the dive is a good means of establishing such a refer-
ence. Carefully monitoring the bubbles of the diver is
extremely important in this type of diving. Some means of
diver recall must be established in case the crew on the
surface boat loses sight of the diver's position (see
Section 14.2.2).
10.1.4 Gulf of Mexico
Water temperature in the Gulf of Mexico drops to a
low of about 56 °F (13°C) during the winter months
and rises to about 86° F (30°C) in the summer. Visibil-
ity offshore is generally good to excellent and may
even exceed 100 feet (30.1 m) around some reefs. Under-
water visibility near shore is poor, particularly in areas
near river outfalls, in bays and estuaries, and off some
beaches. Occasionally, a mass of clear offshore water
may move inshore and increase the near-shore visibil-
ity up to 75 feet (22.9 m) in regions southeast of Mobile,
Alabama.
Currents in the gulf are generally negligible but
should still be of concern to divers. At times, strong
currents may occur around offshore oil platforms, and
local knowledge must be relied on in this situation.
Weather conditions and running seas are unpredict-
able in the gulf. Unforecasted storms with 6- to 12-foot
(1.8 to 3.6 m) seas have curtailed diving operations in
this region of the country in the past.
10.1.5 Northwest Coast
Diving activities in the northwest take place off the
coast of subarctic Alaska and extend to areas offshore
from Oregon. Water temperatures in subarctic Alaska
range from 34 to 38 °F (l to 3°C) during the winter
months and average 45 to 50° F (7 to 10°C) during
the summer. Divers in these waters must give serious
consideration to their choice of diving dress so that
dive duration is not affected by the cold. During the
winter, temperature and wind conditions may combine
so that some bays, inlets, and near-shore waters freeze
over.
Visibility in Alaskan waters varies drastically from
place to place and from time to time. The best visibility
10-3
Section 10
occurs along coastlines and in the Aleutians, where it
may range, at best, from 40 to 80 feet (12.2 to 24.4 m).
Visibility in the waters of bays and straits is usually
15 to 30 feet (4.6 to 9.1 m). At any location, visibility may
become temporarily limited by storms or phytoplank-
ton blooms. Late each spring in southeast Alaska, the
visibility in the upper 30 to 40 feet (9.1 to 12.2 m) of
the water column may be near zero because of phyto-
plankton, but below that layer the water may be very
clear (visibility of 40 feet (12.2 m) or more). Although
this deep, clear water is often dark because of the
shading effect of the overriding low-visibility water,
there is usually sufficient ambient light to work.
Currents and tides are strong and unpredictable in
subarctic Alaskan waters. Tides are extremely heavy
and can cause currents as high as 10 knots in narrows.
Currents also vary significantly and have been observed
to change direction within a period of minutes.
Much of the Alaskan coastline is steep and rocky;
many areas are too steep to allow divers either to enter
or leave the water. Entry and exit points must be care-
fully selected before a dive. Most sections of coastline
are accessible only from boats. During times of heavy
seas or swells, many near-shore diving locations become
completely unworkable.
Alaskan waters harbor relatively few hazardous marine
organisms. Those that cause divers the most trouble
are the urchins, barnacles, and jellyfish, with their
potential to cause punctures, abrasions, and stings.
Dense beds of floating kelp can cause some problems
for divers, especially during surface swimming. Sharks
and whales are common but are rarely, if ever, seen
under water and generally do not influence diving activity
in any way. The presence of killer whales, which are
common, is an exception to this general rule.
Although no known diver/killer whale encounters
have taken place in Alaska, general caution should
keep divers out of the water if these animals are known
to be near. Steller sea lions are very abundant in some
areas of Alaska; although there are no reports that
these animals have ever harmed divers in Alaska, Cali-
fornia sea lions have been known to injure divers. Because
sea lions are large, fast, and agile and are attracted to
divers, they can disrupt an otherwise routine dive. In
addition to being a psychological distraction, the activity
of sea lions often causes serious roiling of bottom sed-
iments and a reduction of visibility.
Farther south, in the waters off Washington and
Oregon, water temperatures range from about 43 to
60 °F (6 to 16 °C) over the year in protected areas such
as Puget Sound. In open ocean waters, depending on
the water masses moving through, temperatures rang-
ing from 40 to 60 °F (4 to 16 °C) may be encountered
10-4
throughout the year. Visibility usually is low, ranging
from 5 to 25 feet (1.5 to 7.6 m) in coastal water near
beaches and from 0 to 70 feet (0 to 21.3 m) in protected
Puget Sound waters.
Currents in certain areas may be strong and unpre-
dictable. This is especially true in river diving, where
very low visibility can cause orientation problems. Logs,
stumps, wrecked automobiles, fishing hooks and lines,
and other bottom trash also pose distinct dangers to
divers working in Alaskan rivers (see Section 10.15).
10.1.6 Mid-Pacific Coast
The mid-Pacific coastal region includes the waters
of Northern and Central California. From San Francisco
north, the best diving conditions in terms of underwa-
ter visibility as well as water temperatures generally
occur from June through September. From San Francisco
south to Point Conception, good diving conditions may
continue through December.
From San Francisco north to the Oregon border,
summer temperatures generally range from about
48 to 56 °F (9 to 13°C). Fall and early winter tempera-
tures vary from 52 to 60 "F (11 to 16 °C), and late
winter and spring temperatures from 45 to 54 °F (7 to
13 °C). A thermocline generally exists at depths from
20 to 40 feet (6.1 to 12.2 m) during late spring and
summer. The difference in surface and bottom tem-
peratures during this period ranges between 2 and 5°F
(-17 and -15°C). A full wet suit, including hood,
boots, and gloves, is a necessity when diving in these
waters.
Underwater visibility varies quite drastically through-
out the area from summer to winter. From Fort Bragg
to the Oregon border, late spring and summer under-
water visibility ranges between 10 and 15 feet (3.0 and
4.6 m). In the late summer and fall, underwater visibility
increases to about 15 to 25 feet (4.6 to 7.6 m). During
the winter and early spring, visibility decreases to 0 to
10 feet (0 to 3.0 m). South of Fort Bragg down to San
Francisco, visibility ranges from 10 to 20 feet (3.0 to
6.1 m), increasing to 30 feet (9.1 m) in the fall. From
Santa Cruz north to San Francisco, visibility ranges
from 5 to 15 feet (1.5 to 4.6 m) in the early spring and
summer, 10 to 25 feet (3.0 to 7.6 m) in late summer and
fall, and 0 to 10 feet (0 to 3.0 m) during the winter and
early spring. From Point Conception to Santa Cruz,
visibility ranges from 15 to 25 feet (4.6 to 7.6 m)
during the late spring and summer and from 15 to
50 feet (4.6 to 15.2 m) in the fall and may occasionally
reach 100 feet (30.5 m) near Carmel Bay. During
winter and early spring, one can expect visibility to
extend 5 to 20 feet (1.5 to 6.1 m). The main factors
NOAA Diving Manual — October 1991
Diving Under Special Conditions
controlling underwater visibility in this area are the
huge plankton bloom, which occurs during upwelling
in the spring and summer, and the dirty water condi-
tions caused by rough seas and river runoffs during the
winter and early spring.
Three species of surface-canopy-forming brown
algae — kelp — occur on the Pacific coast. From Monterey
north, the dominant kelp is the bull kelp. This particu-
lar species forms large beds but, because of its struc-
ture, does not pose the same entanglement hazard to
divers as the giant kelp (see Section 10.10).
North of Point Conception, surf conditions are proba-
bly the most important consideration in planning a
dive. Divers can expect 2- to 3-foot (0.6 to 0.9 m) surf
in most areas even on calm days, and on rough days it is
not uncommon to see waves 10 feet (3.0 m) or more
high. Divers should always scout the proposed dive
area before going into the water to determine the safest
area of entry and, in case conditions change, to choose
alternate exit sites (see Section 10.2.1).
Long-shore currents and tidal currents are common
and tend to be severe in northern and central Califor-
nia. On very windy days, divers should watch for strong
currents around headlands, off rocky shores, and near
reefs. Rip currents are very common along beaches
and in coves (see Section 10.2.3).
Hazardous marine animals. As in other areas, divers
must watch for sea urchins, jellyfish, and rockfish, but
shark attacks in this area are not common. In the last
15 to 20 years, fewer than 2 dozen shark attacks involving
divers have been recorded; however, diving around the
Farallon Islands, Bodega Bay, Tomales Bay, and off
San Francisco is not recommended except when under-
water visibility is ideal. Stingrays and electric rays are
also found in the mid-Pacific coastal region (for appro-
priate precautions, see Section 12.4).
There are five ecological reserves in this area, where
all animals and plants are protected: Point Lobos State
Reserve, Point Reyes Seashore area, Salt Point State
Park, Estero de Limantour Reserve in Marin County
north of San Francisco, and Del Mar Landing in Sonoma
County. Divers should consult with the park authori-
ties to determine the boundaries of these marine reserves
and the restrictions that apply to them.
10.1.7 Southwest Coast
The waters of the Southwest include the area from
Point Conception to the northern Baja Peninsula. Water
temperatures range from 50 to 60 °F (10 to 16°C) in
winter and 55 to 70 °F (13 to 21 °C) in summer, with
some localized areas made colder by upwelling. Dur-
ing much of the year, temperatures at depths below
100 feet (30.5 m) are fairly stable in the 50's and low
October 1991 — NOAA Diving Manual
60's (10 to 16°C). In fall and winter there is a great
deal of mixing in the upper layers and discrete temper-
ature zones do not exist. However, a distinct summer
thermocline at 40- to 60-foot (12.2 to 18.3 m) depths
causes a sharp temperature drop that should be con-
sidered in dive planning.
Horizontal visibility under water ranges from 5 to
10 feet (1.5-3.0 m) along much of the mainland coast to
as much as 100 feet (30.5 m) around the offshore
islands. The best visibility conditions occur in the late
summer and fall. During spring and early summer,
underwater visibility is generally less (30-50 feet
(9.1-15.2 m)) around the islands, at least in part because
of prevailing overcasts and heavy fogs. Winter storm
conditions and rain runoff can reduce the visibility to
zero for miles along the mainland coast, because the
prevailing long-shore current distributes suspended
material from storm drains and river mouths.
Shore conditions along the mainland coast of south-
ern California range from sand beaches to high pali-
sade cliffs. Ocean access from these areas is often
impossible, and a careful check of charts and maps,
supplemented by a preliminary site visit, is highly
recommended before initiating a dive. The offshore
islands generally are accessible to divers only by boat.
Moderate-to-heavy surf prevails along the entire main-
land coast and on the windward sides of the offshore
islands. Under certain weather conditions, the normally
calm leeward sides also may present hazardous diving
conditions.
Currents and tides are not of prime importance in
the southwest coastal region, although there are local
exceptions. Currents around the islands, especially during
tidal changes, may attain speeds of 3 to 4 knots (1.5 to
2 m/s). The direction and relative strength of nearshore
currents can be observed both topside and under water
by watching the degree and direction of kelp layover.
Hazardous marine organisms in this region include:
sharks (especially around the offshore islands) such as
the blue, horned, swell, angel, and leopard; whales
(including killer whales); moray eels; sea urchins; and
jellyfish. Divers should be aware of the habitats, appear-
ance, and habits of these species (see Section 12).
Sewer outfalls are common along the mainland coast,
and direct contact with sewer effluent should be avoided
(see Section 1 1 ). The outfall discharge point may occur
from a few hundred feet to several miles offshore, in
from 60 to several hundred feet (18.3 to several hun-
dred meters) of water. The effluent sometimes rises to
the surface in a boil characterized by elevated temper-
atures, paper and other debris, and an unpleasant odor.
If diving must be conducted in outfall areas, precau-
tions such as immunization, use of full-face gear, and
10-5
Section 10
scrupulous post-dive hygiene must be observed (see
Section 11 for polluted-water diving procedures). Most
outfall discharge points are marked on charts and can
be identified on the surface by a boil or by an orange-
and-white striped spar buoy anchored near the pipe
terminus.
As in Northern California, ecological reserves that
have various restrictions have been established in the
southwestern coastal region. The local office of the
California Department of Fish and Game is the best
source of information about the location of these reserves
and any restrictions that pertain to them.
Diving in northern Mexican (upper Baja California)
waters is similar to that in lower southern California.
However, Mexico imposes heavy fines and impounds
the boats of people diving in Mexican waters without
proper permits; permits can be obtained through the
Mexican government or from Mexican customs offi-
cials in San Diego.
10.1.8 Central Pacific Ocean
The most accessible diving in this area is around the
Hawaiian Archipelago, which consists of the major
Hawaiian Islands and the lesser known Leeward Islands.
The major islands are: Hawaii, Maui, Kahoolawe, Lanai,
Molokai, Oahu, Kauai, and Niihau. The Leeward Islands
are a group of rocks, shoals, and islets that are rem-
nants of ancient islands and seamounts that extend
from Kauai to Midway Island. They are all wildlife
reserves and generally are inaccessible except to gov-
ernment personnel or authorized visitors.
The average water temperature around the major
islands is 76 °F (24 °C) and changes very little with the
seasons. Underwater visibility is almost always excel-
lent, ranging from 50 to 100 feet (15.2 to 30.5 m) or
more. Currents can sometimes be a problem in chan-
nels and near points and may reach speeds of up to
3 knots (1.5 m/s). High surf is also a potential hazard
and may vary widely with the seasons.
It is possible to make shore entries from all the
islands, but rocks, surge, and surf must always be
considered when planning entries and exits (see Sec-
tion 10.2.1). Since drop-offs occur very near shore and
continue for several hundred feet, it is easy to get into
deep water quickly after making a shore entry. Cau-
tion must always be exercised when making repetitive
dives.
Although most forms of dangerous marine life can
be found in Hawaiian waters, they are uncommon.
There have been a few recorded shark attacks over the
years, but they are extremely rare and usually involve
swimmers or surfers. Eel bites, sea urchin punctures,
and coral abrasions are the most common types of
injury. No license is needed to harvest fish or crusta-
ceans for home consumption; however, game laws in
most states place season and size limitations on some
species.
10.1.9 Arctic and Antarctic
The two most important factors to be considered in
arctic and antarctic environments are the effects of
cold on the diver and the restricted access to the sur-
face when diving under ice. These topics are covered in
detail in the sections dealing with diving in cold water
(Section 10.8) and diving under ice (Section 10.9).
Temperature in arctic waters can be as low as 28 °F
(-2°C), but the air temperature and its associated
chill factor may be more limiting to divers than the
cold water itself. Often, surface temperatures as low as
-40 to -50 °F (-40 to -46 °C) are reached, with accom-
panying wind velocities that bring the chill factor to a
temperature equivalent to -100°F (-73°C) or less. In
such conditions, protecting divers from the extreme
cold is paramount both before and after the dive, although
the problem is greater after the dive because the diver
is then both wet and chilled. When diving is being
conducted under the ice, the dive should begin and end
in a heated shelter positioned over the entry hole. If
such a shelter cannot be positioned over the hole, one
should be located within a few steps of the entry point.
The heated interior of an airplane parked nearby may
satisfy this requirement. When exposed to extremely
low air temperatures for longer than a few minutes,
divers should wear heavy, loose-fitting hooded parkas.
Gloves (in the case of dry suits) or entire wet suits can
be flooded with warm water to forestall the chilling
effects of air and to provide greater initial comfort in
the water. Hot water can be carried in insulated con-
tainers such as thermos jugs.
In polar regions the marine species of concern are
seals, walrus, killer whales, and polar bears. A predive
reconnaissance by an experienced observer will indi-
cate if any of these animals is in the vicinity or is likely
to cause a problem (see Section 12.5).
10.1.10 Tropics
Tropical waters provide the most interesting envi-
ronment for diving, because underwater visibility is
usually excellent and marine life abounds. The visibil-
ity in tropical waters is generally 50 feet (15.2 m) or
more. There is little variation throughout the year,
although the waters may become murky and silty after
a storm, during plankton blooms, or from silting near
10-6
NOAA Diving Manual — October 1991
Diving Under Special Conditions
shore. Water temperatures hover around 70° F (21 °C)
during the winter months and may be as high as 82 °F
(28 °C) in shallower waters during the summer.
Marine life is abundant, and some forms are dangerous
to divers. Sharks thrive in these waters and precau-
tions should be taken when they are sighted. A wide
variety of poisonous marine animals (jellyfish, scorpi-
onfish, sea snakes) also abounds (see Section 12).
10.1.11 Diving in Marine Sanctuaries or
Underwater Parks
Divers may on occasion dive for recreation or work
in sanctuaries or underwater parks. These marine sanctu-
aries have been set aside for the purpose of preserving
or restoring recreational, ecological, or esthetic val-
ues. Examples include the Key Largo National Marine
Sanctuary, Biscayne National Park, John Pennekamp
Coral Reef State Park in Florida, and Buck Island in
the Virgin Islands National Park.
Marine sanctuaries are built around distinctive marine
resources whose protection and proper use require
comprehensive, geographically oriented planning and
management but do not necessarily exclude use by
people. It is important when diving in these areas to
follow the rules and regulations established for sanc-
tuary management. Accordingly, when conducting work-
ing or scientific dives in designated marine sanctuaries
and parks, it is important to check with local authori-
ties before beginning operations.
contours or features, or triangulation methods using
known shore positions should be used initially in locat-
ing a dive site.
When commercial diving operations are being con-
ducted from shore without a boat, OSHA regulations
require that the international code flag alpha be dis-
played at the dive location. If entry conditions permit,
divers should carry and/or tow the flag with them
during the dive (see Section 14.2.4). It is also advisable
to equip each diver with a day/night signal flare for
signaling the shore in an emergency. These flares pro-
vide a quick means of accurately locating a diver on
the surface (see Section 5.6.8).
Entering the water from a smooth, unobstructed
shoreline where the water is relatively quiet poses no
problem. Most lakes, rivers (where currents near shore
are not swift), bays, lagoons, quarries, and ocean coast-
lines (where surf is negligible) have shorelines of this
type.
10.2.1 Through Surf
Entering the water even through moderate surf when
burdened with diving equipment is a difficult and poten-
tially hazardous operation. A careful analysis of surf
conditions should be made and, if conditions are con-
sidered too severe to allow safe passage to open water,
the dive should be terminated.
WARNING
10.2 DIVING FROM SHORE
A diver should expect to encounter a wide variety of
conditions when entering the water from shore. Shore-
lines vary greatly, and diving from a particular shore
requires individual preparation and planning.
Before entering the water from shore, special atten-
tion should be given to the predive equipment check-
out. Since diving equipment is often placed on the
ground near the water, small dirt particles may have
entered a space in the equipment that requires a per-
fect seal or has a close tolerance. Even the smallest
amount of dirt in a regulator or reserve valve may
cause a serious air leak or a valve malfunction. Extra
care must be taken to ensure that diving equipment is
kept as free from dirt as possible.
If the dive from shore is to be made to a precise
underwater location, it is advisable to mark the spot
clearly at the water surface. This can be done by using
a marker buoy or surface float. A small marker buoy
floating on the surface, however, may be difficult for a
diver to see; therefore, compass bearings, underwater
October 1991 — NOAA Diving Manual
Before Diving Through Surf From an Unfa-
miliar Beach, Local Divers Should Be Con-
sulted About Local Conditions
Before entering the water, divers should observe the
surf. Waves traverse vast expanses of ocean as swell,
with little modification or loss of energy. However, as
the waves enter shallow water, the motion of the water
particles beneath the surface is altered. When a wave
enters water of a depth equal to or less than one-half of
its wavelength, it is said to "feel bottom." The circular
orbital motion of the water particles becomes ellipti-
cal, flattening with depth. Along the bottom, the particles
oscillate in a straight line parallel to the direction of
wave travel.
As the wave feels bottom, its wavelength decreases
and its steepness increases. As the wave crest moves
into water whose depth is approximately twice that of
the wave height, the crest changes from rounded to a
higher, more pointed mass of water. The orbital veloc-
ity of the water particles at the crest increases with
10-7
Section 10
Figure 10-1
Schematic Diagram of Waves
in the Breaker Zone
A diver standing on the shore and looking seaward would observe and note: (1) Surf zone; (2) limit of uprush; (3) uprush;
(4) backrush; (5) beach face; (6) inner translatory waves; (7) inner line of breakers, (8) inner bar; (9) peaked-up wave; (10) reformed
oscillatory wave; (11) outer translatory waves; (12) plunge point; (13) outer line of breakers; (14) outer bar (inner at low tide);
(15) breaker depth, 1.3 x breaker height; (16) waves flatten again; (17) waves peak up but do not break on this bar at high tide;
(18) deep bar (outer bar at low tide); (19) still-water level; and (20) mean low water. Adapted from US Army Corps of Engineers (1984)
increasing wave height. This sequence of changes is
the prelude to the breaking of the wave. Finally, at a
depth of approximately 1.3 times the wave height,
when the steepest surface of the wave inclines more
than 60 degrees from the horizontal, the wave becomes
unstable and the top portion plunges forward. The
wave has broken; this turbulent form is called surf
(Figure 10-1). This area of "white water," where the
waves finally give up their energy and where system-
atic water motion gives way to violent turbulence, is
called the surf zone. The surfs white water is a mass of
water containing bubbles of entrapped air; these bub-
bles reduce the normal buoyancy of the water. Having
broken into a mass of turbulent foam, the wave contin-
ues landward under its own momentum. Finally, at the
beach face, this momentum carries it into an uprush or
swash. At the uppermost limit, the wave's energy has
diminished. The water transported landward in the
uprush must now return seaward as backwash, i.e., as
current flowing back to the sea. This seaward move-
ment of water is generally not evident beyond the
surface zone or a depth of 2-3 feet (0.6-0.9 m).
By watching the surf for a short period of time, water
entry can be timed to coincide with a small set of
waves. When ready to enter, the diver should approach
the water, fully dressed for diving. At the water's edge,
the diver should spit on the faceplate, rinse and adjust
it to the face, and place the snorkel in the mouth. With
one hand on the faceplate, the diver should then turn
around and back into the water with knees slightly
bent and body leaning back into the wave. If conditions
10-8
are good, the diver should begin swimming seaward on
the surface, using a snorkel. If heavy sets of waves are
encountered, it may be necessary to switch to scuba
and to swim as close to the bottom as possible. If the
bottom is rocky, divers can pull themselves along by
grasping the rocks; on a sandy bottom, a diver can
thrust a knife into the bottom to achieve the same
purpose. Ripples on a sandy bottom generally run par-
allel or somewhat obliquely to shore, and they can be
used to navigate through the surf zone by swimming
perpendicular to them. Divers entering with a float
should pull it behind them on 10 to 30 feet (3.0 to 9.1 m)
of line and should be aware of the possibility that
turbulence may cause the line to wrap around a leg,
arm, or equipment.
WARNING
Divers Near the Surface Should Not Hold Their
Breath When a Wave Is Passing Overhead
Because the Rapid Pressure Drop at the
Diver's Depth When the Wave Trough Passes
Overhead May Be Sufficient to Cause a Lung
Overpressure Accident
Swimming over breakers should not be attempted.
As breakers approach, the diver should duck the head
and dive under and through them. Diving at the base of
the wave is advantageous because the water molecules
will carry the diver up behind the wave.
NOAA Diving Manual — October 1991
Diving Under Special Conditions
A group of divers may make a surf-entry in buddy
teams and meet beyond the surf zone at the diver's
flag. Once safely through the surf, all equipment should
be checked. Even a moderate surf can knock equip-
ment out of adjustment or tear it away.
Sand may have entered the mask, regulator, or fins
after the diver has passed through the surf. Divers
should take time to remove the sand before continuing
the dive. Sand in the exhaust valve of a regulator can
cause it to seal improperly, permitting water, as well as
air, to enter the mouthpiece when inhaling. Sand in the
fins, though only mildly irritating at first, may cause a
painful abrasion by the end of a dive.
Exiting the water through the surf involves performing
the same procedures used to enter, except in reverse
order. The diver should wait just seaward of the surf
for a small set of waves. When a set has been selected,
the diver should begin swimming shoreward (while
keeping an eye on the incoming waves) immediately
after the passage of the last of the larger waves. The
smaller waves breaking behind will assist the diver's
progress toward the beach. Using this assisting wave
action, the diver should swim toward the beach until
reaching waist-deep water. At this point, while there
is still enough water for support and balance, divers
should pivot around, face the waves, and plant their
feet firmly. The diver should then stand up, and, bend-
ing at the knees and hips enough to maintain balance,
back out of the water. When exiting with a float, divers
should position it down current or push it ahead of
them to avoid becoming entangled in the towline. As
soon as the divers are out of the water, they should
turn; only then should they remove their fins.
If knocked over by surf action after standing up,
divers should not try to stand again but should let the
waves carry them onto the beach. Hands and fins should
be dug into the bottom to prevent being swept seaward
by the backwash. On reaching shore, the divers should
crawl out of the surf on their hands and knees.
10.2.2 Through Surf on a Rocky Shore
Before entering surf from a rocky shore, divers should
evaluate wave conditions and should not attempt to
stand or walk on rocks located in the surf zone. Instead,
divers should select the deepest backwash of the last
large wave of a series and enter the water; the back-
wash should carry the diver between the larger rocks.
Every effort should be made to swim around the rocks
rather than over them. Divers should stay in the small
deeper channels between rocks and maintain a prone
swimming position facing the next oncoming wave.
They should kick or grasp a rock to keep from being
carried back toward the shore and then kick seaward
after the wave passes.
When exiting on a rocky shore, divers should stop
outside the surf zone to evaluate the wave conditions
and should then exit toward the beach on the backside
of the last large wave of a series. As momentum from
the wave is lost, divers should kick or grasp a rock to
avoid being carried seaward by the backwash. Divers
should maintain their position, catch the next wave,
and thus move shoreward, exercising caution over slip-
pery rocks.
10.2.3 Through Shore Currents
In and adjacent to the surf zone, currents are gener-
ated by 1) approaching waves (and surf); 2) bottom
contours and irregularities; 3) shoreline geography;
and 4) tides. When waves approach the shore at an
angle, a longshore current is generated that flows par-
allel to the beach within the surf zone. Longshore
currents are most common along straight beaches. The
current velocity increases with 1) breaker height;
2) increasing angle of the breaker to the shore;
3) increasing beach slope; and 4) decreasing wave period.
The velocity of longshore currents seldom exceeds 1 knot
(0.5 m/s). Wave fronts advancing over non-parallel
bottom contours are refracted to cause convergence or
divergence of the energy of the waves. In areas of
convergence, energy concentrations form barriers to
the returning backwash, which is deflected along the
beach to areas of less resistance. These currents turn
seaward in concentrations at locations where there are
'weak points,' extremely large water accumulations,
gaps in the bar or reef, or submarine depressions per-
pendicular to shore, and form a rip current through the
surf (Figure 10-2).
The large volume of returning water has a retarding
effect on the incoming waves. Waves adjacent to the
rip current, having greater energy and nothing to retard
them, advance faster and farther up the beach. Rip
currents may transport large amounts of suspended
material. A knowledgeable and experienced diver can
use rip currents as an aid to swimming offshore. A
swimmer caught unsuspectingly in a rip should ride
the current and swim to the side, rather than swimming
against the current. Outside the surf zone the current
widens and slackens, which permits the diver to enter
the beach at another location. Rip currents usually
dissipate a short distance seaward of the surf zone.
Most shorelines are not straight. Irregularities in
the form of coves, bays, and points affect the incom-
ing waves, tidal movements, and current patterns. When
preparing for beach entries and exits, a diver should
October 1991 — NOAA Diving Manual
10-9
Section 10
Figure 10-2
Near-shore Current System
o
CD
o
03
-£ O'l
\ 4 <f \ MassTranspo
\ \ \
Neck
\ I »
III *
sS?W
-*► -»- •*" "\Feeder ^>*~ Longshore
Current Current
Shore Line
Source: Baker et al. (1966)
take wave approach, shoreline configuration, and cur-
rents into account. Entries and exits should be planned
to avoid high waves and to take advantage of current
movements. Divers should avoid dives that require
swimming against the current and should never under-
take a dive from an ocean beach without considering
these factors. Hypothetical beach configurations, wave
approaches, and current diagrams are shown in
Figure 10-3 to aid divers in planning beach-entry dives.
10.2.4 From a Coral Reef
Diving operations from a reef should be planned, if
possible, to take place at high tide when water covers
the reef. For a diver wearing equipment, walking on a
reef is hazardous. Footing is uncertain, reefs are gen-
erally pocked with holes, and areas that look solid may
break under a diver's weight.
NOTE
Coral shoes or hard-sole neoprene boots
should be worn around coral.
In some instances, there may be an area on the shore
side of the reef where the water is deep enough for
swimming. In this case, the outer side of the reef will
10-10
break up the wave action sufficiently to allow passage
over the inside calm area without difficulty. If a chan-
nel can be located that will allow passage through the
reef, the diver should follow it, submerged if possible,
into deep water. If a satisfactory passage cannot be
located, the diver should approach the edge of the reef,
wait for a wave to pass, and slip over.
10.3 DIVING FROM A STATIONARY
PLATFORM
Diving from a pier or platform rather than directly
from the shore offers many advantages. Deep water
can be entered without having to traverse a surf line,
rocks, or other obstacles. Also, if the dive site is under
or close to a pier, surface-supplied diving equipment
can be used. In addition, all required equipment can be
transported by vehicle directly to the dive site.
Ladders should be used to get as close to the water as
possible before entry. Any approved entry technique,
such as stepping, can be used safely for heights up to
10 feet (3.0 m). The roll-in method shown in Figure 10-4
is not recommended for heights greater than 3 or 4 feet
(0.9 to 1.2 m) above the water. Immediately prior to
entering, the diver should carefully check for floating
debris or submerged obstructions. Floating debris is
common around a pier, and pilings often rot or break
off just below the waterline. Divers should not jump
into an area that has not been examined beforehand or
where the water is not clear enough to see to the depth
of the intended dive.
If the dive is to be conducted from an ocean pier or
other high platform and no ladder is available, heavy
gear can be lowered into the water and divers can make
a shore entry with a snorkel, equipping themselves
with scuba at pierside. If conditions make a shore entry
impossible, using a small boat is advisable. When swim-
ming under a pier or platform, divers should be sub-
merged whenever possible to avoid contact with pil-
ings, cross-supports, and other potentially hazardous
objects.
When exiting the water onto a pier or platform, the
diver should stop at the ladder to remove his or her fins.
(The ladder should extend 3 to 4 feet (0.9 to 1.2 m) into
the water.) Climbing a ladder with fins is awkward and
dangerous and should be avoided unless the ladder is
designed specifically for use with fins (see Figure 10-5).
Tanks and other cumbersome equipment should also
be removed and tied securely to a line and be hauled up
after the diver reaches the top of the pier. Piers and
docks often contain fishing lines, and care must be
taken to avoid being hooked or becoming entangled in
these lines.
NOAA Diving Manual — October 1991
Diving Under Special Conditions
Figure 10-3
Shore Types and Currents
R ' ' '/
is } J
Xy
Small Deep Coves
Points
Rip Currents
Rocky Cove - Reefs
Sand Bar - Sandy Beach - Rip Current
E = entry; X — exit.
Heavy arrows indicate direction of wave approach; dashed lines represent path of currents, while direction is shown by light arrows.
Source: NOAA (1979)
10.4 DIVING FROM A SMALL BOAT
A small boat is probably the most common surface-
support platform used by divers with self-contained
equipment. Configurations and types of small boats
vary greatly and range from small inflatable boats to
larger solid-hulled vessels. A boat used as a platform
should:
• Be equipped with a means for divers to enter and
leave the water easily and safely
• Be seaworthy and loaded within the capacity
recommended by the manufacturer for the expected
water conditions
• Be large enough to accommodate all members of
the dive party, the diver's life-support equipment,
and any special equipment being used in support
of the dive
October 1991 — NOAA Diving Manual
• Provide some shelter in cold or inclement weather
for the dive party en route to the dive site and,
after the dive, back to shore
• Be maintained properly and in good repair
• Carry a diver's flag (see Table 14-2).
Small boats used to tend divers can be either anchored
or unanchored. When anchored, the boat should be
positioned downstream of the site for easy access when
divers surface, and a surface float should be streamed
off the stern. Even anchored boats need to be able to
move immediately in case an incapacitated diver must
be recovered; a buoyed anchor line facilitates a quick
getaway. The operator in the boat should keep a con-
stant watch on the diver's bubbles, and great care
should be taken to stay clear of divers if an engine is in
gear. When tending without an anchor, the operator
10-11
Section 10
Figure 10-4
Entering the Water Using the Roll-In Method
Source: NOAA (1979)
Figure 10-5
Transom-Mounted Diver Platform
Source: NOAA (1979)
should drop the divers off upstream of the site. The
boat should then remain downstream of the site during
operations. Drift-diving with a surface float provides
an effective method for keeping the boat in position for
pickup.
10.4.1 Entering the Water
Entering the water from a small boat can be accom-
plished safely by several methods. Sitting on the gun-
10-12
wale and rolling into the water is considered best if the
distance is not greater than 3 to 4 feet (0.9 to 1.2 m)
(Figure 10-4). The diver should examine the area to be
entered to ensure that it is clear, sit on the gunwale
facing the center of the boat with both feet inside, and
lean forward to counterbalance the weight of the equip-
ment. When ready to enter, the diver should simply sit
up, lean backward, and let the weight of the diving
equipment carry him or her over the side. A second
method of entry is the 'step-in' method, which is gen-
erally used when entering the water from a larger boat.
The diver should step onto the gunwale, bend slightly
forward at the waist, and step off into the water.
When entering the water using these methods, the
diver should always hold the face mask firmly in place.
Also, any required equipment that cannot be carried
conveniently and safely should be secured to a piece of
line, hung over the side, and retrieved after entry.
As a general rule, the diver should always enter the
water slowly, using the method that will result in the
least physical discomfort and disturbance to equip-
ment. Each diver should determine the method best
suited to various water conditions.
10.4.2 Exiting the Water
When exiting the water into a boat, there are two
general rules to remember and follow. First, exiting
actually begins while the divers are still submerged.
While ascending, divers should look upward continuously
to ensure that the boat is not directly overhead and
NOAA Diving Manual — October 1991
Diving Under Special Conditions
Figure 10-6
Side-Mounted Diver Platform
that they will not strike it when surfacing. Holding an
arm over the head during ascent is also a good practice.
Exhaling during the ascent will produce bubbles, which
will alert surface personnel that the diver is ascending.
Second, after surfacing, the diver should not attempt
to enter the boat wearing tanks or other heavy equip-
ment unless the ladder is strong enough to handle the
combined weight of diver and equipment. The diver
should remove the tanks and obtain assistance from
someone in the boat or from another diver in the water
before climbing aboard. Rails extending above the
sides of the boat are useful as handrails to support the
diver as he or she climbs into the boat.
Probably the most widely used method of returning
to a small boat is via a diver's ladder. Ladders also
provide a secure point for divers to grasp while they are
still in the water. A ladder may be built in many con-
figurations but should have these general characteristics:
• It should extend below the surface of the water 3 to
4 feet (0.9 to 1.2 m), providing a place for the diver
to stand and hold on while removing equipment.
• It should be strong, well built, and capable of
being securely fastened to the side so it will not
shift when subjected to the action of the seas and
the diver's weight.
• It should be wide enough to accommodate the
diver comfortably.
• It should be angled away from the boat to permit
easier ascent.
• It should have rungs that are flat and wide.
Modifying conventional ladders to fit small boats is
unsatisfactory because these ladders are closed on both
sides by rung support shafts, are difficult to climb
with equipment, and hang too close to the boat to provide
sufficient toe space.
Figure 10-5 shows a ladder that is designed to allow
a fully equipped diver to re-enter a small boat with
safety and ease even in strong currents. The most impor-
tant features of the ladder are lack of side supports
('open step' design), its slope, and its ability to be
positioned on the transom of the boat. With a ladder of
the open step type, divers can use the inner sides of
their feet to locate the ladder rungs and can then step
onto the rung from the side. The angle between the
shaft and the transom should be 35 to 40 degrees.
Positioning the ladder on the transom (the strongest
part of the boat) is particularly important in rivers
because the boat partially protects the diver from the
force of the current and because the diver can climb
out of the water parallel to the current. If conventional
ladders positioned on the side of the boat are used, the
current may push the diver sideways.
October 1991 — NOAA Diving Manual
Source: NOAA (1979)
The ladder should extend about 30 inches (77 cm)
below the water's surface to allow diver access. The
ladder should have a handle only on the side next to the
motor, so the diver can pass unhampered on the other
side.
Another method of assisting a diver into a small boat
is the use of a platform rigged to the stern or the side of
the boat and suspended just below the surface of the
water. A diver can swim onto the platform, sit securely
while removing equipment, and then stand up and step
safely into the boat. A hand- or arm-hold should
be provided. A portable, easily stored platform
(Figure 10-6) can be constructed from either wood or
metal.
10.5 FRESH WATER DIVING
There are thousands of square miles of fresh water in
the United States. The five Great Lakes alone have a
total area of 95,000 square miles (2,460,500 sq km),
and the two-thirds of these lakes that lie within U.S.
boundaries represent almost half of the fresh water
acreage in the country.
Basic techniques for diving in lakes, rivers, and quar-
ries are much like those used in ocean waters. Howev-
er, some differences should be noted. For example,
depth gauges are calibrated for seawater density, and
adjustments must be made to achieve accuracy in fresh
water (see Section 10.12. 5). Buoyancy requirements
also are somewhat different for fresh and salt water.
10.5.1 Great Lakes
Great Lakes divers need to be aware of the tempera-
ture changes that occur with changes in depth and
10-13
Section 10
season. In a typical fresh water lake, the upper layer
(epilimnion) temperature generally ranges between
55 and 75 °F (13 and 24 °C) in late summer. However, the
waters below the thermocline (hypolimnion) approach
the temperature of maximum density for fresh water,
39.2 °F (4°C). Consequently, divers working below the
thermocline, which averages 60 feet (18.3 m) in these
lakes in late summer, must plan to use buoyancy con-
trol and thermal protection.
During the winter months, the water temperature in
the Great Lakes ranges between 32 °F (0°C) near the
surface and 39.2 °F (4°C) on the bottom; during this
period, a significant portion of the Great Lakes is ice
covered. Occasionally, divers are required to work under
2 to 16 inches (5.1 to 40.6 cm) of ice to make observa-
tions, collect samples, or maintain scientific equipment.
Diving under ice is particularly hazardous, requires
special techniques and equipment, and should be under-
taken only when absolutely necessary (see Section 10.9).
Divers and surface support personnel operating in the
lakes may be subjected to atmospheric temperatures
of -30 °F (-34 °C), with wind chill factors approaching
-100°F(-73°C).
Underwater visibility in the Great Lakes ranges from
about 100 feet (30.5 m) in Lake Superior to less than
1 foot (0.3 m) in Lake Erie. Visibility is influenced by
local precipitation and runoff, nutrient enrichment,
biological activity, local bottom conditions, and diver
activity. Significant seasonal variations also occur in
these waters.
From September to December, storms and severe
wave conditions can be expected in the Great Lakes.
Divers working offshore at these times must use sturdy
vessels and monitor weather forecasts. Because swift
currents may be encountered in rivers and straits
connecting with the lakes, Great Lakes divers must use
considerable caution and be properly trained in the
techniques of diving in currents (see Section 10.15).
10.5.2 Inland Lakes
Other lakes in the United States vary from clear
mountain lakes with low sediment input to reservoirs,
sediment-laden rivers, and glacial lakes, which usu-
ally have a milky appearance. When planning a lake
dive, bottom terrain is as important a consideration as
underwater visibility. Lakes may have vertical rocky
sides, rocky outcrops, ledges, and talus slopes, or they
may be sedimentary and composed primarily of old
farm land. Algal blooms often occur in lakes during
the warmer months and may completely block the light,
even at shallow depths. Thermoclines also occur, and
temperature and underwater visibility may vary greatly.
10-14
Old cables, heavy equipment, electric cables, rope,
fishline, fishing lures, and even old cars are often found on
lake bottoms. Many lakes have never been cleared of
trees, barns, houses, water towers, and other objects.
The bottom sediment of lakes is easily stirred up, as is
sediment that has settled on lake-bottom trees or brush.
Divers should stay off the bottom as much as possible
and move slowly when forced to work on the bottom.
10.5.3 Quarries
Artificial water systems such as reservoirs and flooded
strip mines, gravel pits, or stone quarries are popular
spots for diving. In some areas, they represent the only
place for diving, and in other regions they are used
primarily for diver training. Quarries usually are deep;
their water originates from seepage in the surrounding
water table. For this reason, the water usually is low in
nutrients and significantly colder than water in areas
primarily fed by runoff. As the water near the surface
warms up during the summer months, a sharp thermo-
cline is created that must be taken into account when
dressing for a quarry dive. Quarries are used frequently as
dump sites for old cars and a variety of junk, and
quarry divers must beware of becoming snagged on
sharp metal or monofilament line, especially when the
sediment is stirred up and visibility is reduced.
10.6 OPEN-OCEAN DIVING
Researchers have recently become interested in observing
and sampling pelagic organisms directly in the open
ocean instead of collecting specimens using such con-
ventional techniques as Niskin® bottles, grabs, or nets.
However, because open-ocean (also termed blue-water)
diving does not provide a fixed frame of reference,
divers performing open-ocean dives may become
disoriented because they have a reduced awareness of
depth, buoyancy, current, surge, other divers, marine
organisms, or, occasionally, even of the direction of the
surface (Heine 1985). Special techniques have there-
fore been developed to aid the diver operating in the
open ocean to carry out scientific tasks safely.
Blue-water diving is usually done from a small boat
to facilitate diver entry, exit, and maneuverability and
to minimize the 'sail' area, which reduces drift and the
consequent dragging of divers through the water. Even
when operations are being conducted from a large
vessel, a small boat should be used to tend the divers
because wind and surface currents often carry a larger
boat away from the actual dive site.
Open-ocean dive teams generally consist of a boat
operator (who remains in the boat), a safety diver, and
as many as four or five working divers. After reaching
NOAA Diving Manual — October 1991
Diving Under Special Conditions
Figure 10-7
Down-line Array for Open-Ocean Diving
the dive site, a downline about 100 feet (30 m) long,
loaded with 5 to 10 pounds (2.3 to 4.5 kg) of weight and
knotted at specific depths, is passed from the boat
through a surface float and lowered to serve as a safety
line for the divers (Figure 10-7). This line is then
secured to the surface float and to the small boat. A
4-foot (1.2 m) sea anchor is frequently used to reduce
drift caused by wind; the anchor can be attached to a
loop in the downline at the surface float or to a separate
float to keep it from collapsing and sinking if the wind
dies. To mark the dive site, it is useful to drop a small
open jar of fluorescein dye into the water. The vertical
column of dye emitted as the jar descends will be
distorted by currents, giving a visual display of the
current pattern in the water column (see Section 9.8.2).
Because of the absence of any visible reference and
the inherent danger of drifting away or down, all open-
ocean divers are tethered at all times to the safety line
via an underwater trapeze. The trapeze can be configured
from any bar or ring that accepts clips and shackles
easily. Figure 10-8 shows examples of three types of
trapezes that have been used for this type of diving.
In conventional diving, buddy divers swim together;
in open-ocean diving, however, the safety diver serves
as the buddy diver for all of the divers on the team. As
shown in Figure 10-7, all divers are tethered to the
trapeze by means of lines approximately 30 to 50 feet
(9.1 to 15.2 m) long; the length of the line depends on
underwater visibility and the task being undertaken.
To avoid kinking, tethers should be braided lines. A
good rule of thumb is to restrict the length of the tether
to about 50 to 75 percent of the nominal underwater
visibility distance (Heine 1985). The exception to this
rule is the safety diver's tether, which should only be
about 3 feet (0.9 m) long.
Because tethers of a fixed length tend to droop and
become tangled, they should be designed to remain
taut at all times, which also facilitates line-pull signal-
ling. This can be achieved by weighting the end nearest
the safety diver with a 4 to 8 ounce (113 to 227 gm)
fishing weight. The tether then passes freely through
the metal loop on the end of a swivel clip (Figure 10-8);
these clips are attached to the trapeze, which is located
near the safety diver. Thus, as the working diver swims
away from the safety diver, the tether pays out smoothly,
and, when the diver returns, the tether retracts as the
weight sinks. In conditions of low visibility, tether
lines can be shortened by tying a knot on the weight
side of the tether, thus shortening the length available
to pay out. The other end of the tether should be con-
nected to the diver's buoyancy compensator or to a
separate harness. If the quick-release shackle is attached
to the diver's buoyancy compensator or harness (rather
October 1991 — NOAA Diving Manual
Adapted from Hamner (1975)
than to the tether), it can be released by pulling it away
from the diver's body, which ensures that it will release.
WARNING
Tethers Should Not Be Attached to a Diver's
Weight Belt, Because Ditching or Losing the
Belt Would Add Excessive Weight to the Tra-
peze Array
Before starting a blue-water dive, all equipment
must be checked and the divers must all be sure that
they understand the diving signals, especially the line-
tug signals, that will be used. The safety diver enters
the water first, but all of the divers usually descend
down the line together to connect the pivot ring to the
vertical line and to prepare the tethers. During the
dive, the safety diver monitors the tethers, keeps a
lookout for hazards, and supervises the dive. The safety
diver maintains visual contact with the other divers
and can attract their attention by tugging at their
tethers. The boat operator can signal the safety diver
by pulling on the vertical line. In this way, the entire
team can communicate and be alerted to ascend at any
time during the dive. A good practice is to have each
diver run the tether through the palm of one hand so
that the line-tugs can be detected easily. The safety
diver can move the pivot ring up and down the vertical
line to any of the knotted stops, as required, and can
thus control the maximum depth of all of the divers.
The safety diver can also terminate the dive or send
10-15
Section 10
Figure 10-8
Three Multiple Tether Systems (Trapezes)
Used for Open-Ocean Diving
Brass Snaps
Working Diver's Tether
Bottom Weight
Running
Counterweight
Source: Rioux, as cited in Heine (1985)
Swivel Snaps
Running Counterweight
Knot in Line
Source: Hamner (1975)
Stainless Steel
Attachment Ring
Working Diver
Tether Line
Polypropylene Washer
Safety Diver Tether Line
( )) Small Coated Weight
Source: Coale and Pinto, as cited in Heine (1985)
10-16
NOAA Diving Manual — October 1991
Diving Under Special Conditions
any diver up if the situation warrants such action.
Divers can ascend at will by signalling their intent to
the safety diver, unclipping their tethers at the pivot
ring, and ascending the vertical line to the boat. It is
important that the divers hold the downline when ascend-
ing so that they do not drift away from the boat.
If scientific or diving equipment is hung on the
downline, it can be attached to the line at the appropriate
depth as the line is deployed, which makes it unneces-
sary for the divers to carry the equipment. Any equip-
ment hung on the downline should be positioned above
the trapeze and safety diver, and the weight of the
equipment must not be so great that it overweights the
downline. Divers working below the trapeze must be
careful to avoid entanglement in the weighted tethers,
which would envelop the safety diver in a cloud of
bubbles and reduce his or her ability to see. If a second
line is deployed for equipment, it must be separated
clearly from the safety line and should not be used as
an attachment for tethers.
In addition to diving, safety, and scientific equip-
ment, most open-ocean divers carry a shark billy (see
Section 5.7). According to experienced blue-water divers
at the University of California at Santa Cruz:
Twenty percent of all the blue water dives
performed by our group in the central north
and south Pacific gyre systems and the eastern
tropical Pacific were aborted due to the
persistent presence of sharks, specifically
oceanic white tip sharks. In all cases they
were spotted first by the safety diver. This
underscores the value of the safety diver
and a routine abort plan and the utility of
the shark billy (Heine 1985).
Divers generally work in an area upstream of the
trapeze, which allows them to collect fresh, undisturbed
samples and to stay in a single area in sight of the
safety diver. As they perform their tasks, the divers
scan their surroundings and make visual contact with
the safety diver. The safety diver constantly monitors
the surroundings, checks for sharks, keeps an eye on
the divers and the downline, and generally monitors
the progress of the dive. During the course of the dive,
the safety diver maintains contact with the divers by
periodically tugging on the divers' tethers to ensure
that they are comfortable, their air supply is adequate,
and they are responding to pull signals appropriately.
If a diver requires minor assistance, the safety diver
signals another diver to go to his or her aid. Before the
safety diver becomes involved in helping another diver, he
or she must first signal another diver to act as the
temporary safety diver. There must always be someone
acting as safety diver (Heine 1985).
As with any specialized diving, open-ocean diving
requires individualized training and practice. Readers
should consult a specialized open-ocean diving man-
ual for further details about this type of diving.
10.7 CAVE DIVING
Cave diving is a specialized form of diving that can be
performed in both inland fresh waters and ocean 'blue
holes.' To scientists, caves offer new laboratories for
research. In cave diving, the emphasis should be placed on
developing the proper psychological attitude, training
in specialized techniques and life support systems,
dive planning, and the selection of an appropriately
trained buddy diver.
WARNING
Only Experienced and Specially Trained
Divers Should Undertake Cave Diving. Open-
water Experience Is No Substitute for Cave
Diving Training
The cave diving environment is alien to humans,
because it involves both the underwater environment
and the limited-access, limited visibility, confined space
environment typical of caves. Examples of the special
hazards that may be encountered in cave diving are:
the absence of a direct and immediate ascent route to
the surface, the sometimes instantaneous loss of visi-
bility because of silting or failure of the diver's light,
and the entanglement and impact hazards associated
with being in a confined, enclosed area. These and
other factors all have an effect on the psychological
composure of divers and their ability to cope with
stressful situations. Improperly trained divers, unaware
of the hazards unique to cave diving, often panic and
drown when they encounter situations that are in fact
normal for the cave diving environment. It is impera-
tive that divers develop the proper psychological atti-
tude before they consider conducting a cave dive. Com-
pletion of a standard scuba diving course does not
prepare a diver for the special perils faced in cave
diving.
Before taking a course in cave diving, the diver-
student must have enough open-water experience to
feel psychologically and physically comfortable under
water. Because their lives may one day depend on the
October 1991 — NOAA Diving Manual
10-17
Section 10
Figure 10-9
Safety Reel Used in Cave Diving
quality of instruction received, persons contemplating
taking a course should select one taught by a mature
and nationally certified cave diving instructor. A good
cave diving course should include prescreening of poten-
tial divers, at least 100 hours of training in underwater
work, and instruction in line safety, the elements of
buoyancy control, buddymanship, dive planning, equip-
ment handling, and dive theory. Three. basic rules of
safe cave diving that must be adhered to by every diver
are:
(1) Always use a continuous guideline to the surface.
(2) Save two-thirds of the total air supply for returning
to the surface.
(3) Carry at least three lights during the dive.
A common hazard in cave diving is the presence of
silt. To minimize silting, cave divers must be specially
trained to swim horizontally and to maintain proper
buoyancy at all times.
A safety reel and line are the cave diver's link to the
surface and survival. Several kinds of lines are used for
safety and navigation. Temporary lines are the most
commonly used and consist of a safety reel and line. A
suitable safety reel should feature a line guide, drum,
buoyancy chamber, a good turns ratio, and be capable
of carrying approximately 400 feet (122 m) of
1/16 inch (1.6 mm), 160-pound (72.6 kg) test to 1/8 inch
(3.2 mm), 440-pound (199.6 kg) test braided nylon
line. The reel should be neutrally buoyant, compact,
and rugged (Figure 10-9). Large reels and lines create
extra drag for the diver and require extra exertion.
When running a safety line, the diver with the reel
should maintain tension. The line should be tied within
surface light, and safety wraps should be made approxi-
mately every 25 feet (8.3 m). The line should be cen-
tered in the cave as much as possible. The reel-diver is
first in and last out. The buddy is responsible for
unwrapping the safety wraps on leaving the cave and
for providing light for the diver tying or untying the
line. Physical contact with the line should be avoided
except when visibility decreases. In some cases, cave
divers will use permanent lines for mapping or to per-
mit a more complete exploration of a cave. Novices
should use temporary lines and should not attempt to
follow permanent lines unless they have a thorough
knowledge of the cave. The technique for laying and
retrieving a safety line is unique to cave diving and
should be practiced until it becomes second nature,
because it could save one's life in a total silt-out,
where there is a complete loss of visibility. It is impor-
tant to remember that in cave diving the safety line is
not a tow line and should not be used for support.
Source: NOAA (1979)
Standard cave diving life-support systems should
include:
double tanks
double manifolds
two regulators
submersible pressure gauge
buoyancy compensator with automatic inflator hose
depth gauge
watch
decompression tables
wet or dry suit
safety reel with line
lights
compass
slate
pencil.
The larger capacity double-tank arrangement recom-
mended for cave diving has an 'ideal' or double-orifice
manifold. This system manifolds two tanks together
with a common gas supply and uses two regulator
adaptors. If one regulator fails, that regulator may be
shut off while the second regulator continues to func-
tion without interruption and with access to both gas
cylinders. One of the regulators also should have a
5-foot (1.5 m) hose so that divers may share their gas
supply when maneuvering out of tight situations.
Although the need for lighting in cave diving is
obvious, the lighting taken on cave dives is often not
adequate for safety. Each diver must carry at least 3
lights, with the brightest being at least 30 watts. Backup
lights can be of lower wattage, but they must also be
dependable and of high quality.
All cave diving equipment must be checked and
rechecked by each member of the dive team before
10-18
NOAA Diving Manual — October 1991
Diving Under Special Conditions
submersion to ensure proper functioning, ease of oper-
ation, and diver familiarity. During this time, the smooth
operation of backup equipment should also be verified
and the dive plan should be reviewed for the last time.
The maximum recommended number of cave divers
per team is three. Larger groups cannot handle the
integrated 'buddymanship' necessary to maintain the
constant contact so essential in cave diving. For fur-
ther information about cave diving, readers should
write to the National Association for Cave Diving, Box
14492, Gainesville, Florida 32604, or the National
Speleological Society's Cave Diving Section, 3508 Hol-
low Oak Place, Brandon, Florida 3351 1.
10.8 COLD-WATER DIVING
Diving in cold water is associated with several equip-
ment problems not found in warmer waters; the major
difficulty involves the regulator. Most single-hose
regulators have a tendency to freeze in the free-flow
position after approximately 20-30 minutes of extreme
cold-water exposure. However, several models are avail-
able that are designed to resist freezing and that use a
special antifreeze-filled housing system. The standard
double-hose regulator rarely develops this freezing
problem. If a regulator begins to freeze up, the dive
should be aborted immediately. An early sign that
freeze-up is about to occur is the presence of ice crys-
tals on the tongue. Second-stage freeze-up is gener-
ally caused by moisture in the exhaled breath, which
then condenses and freezes on the metal parts.
Another cold-water diving problem is that the diver's
mask is more likely to fog or freeze in cold water, which
means that a non-irritating defogging agent should be
applied to the mask before diving. Partially flooding
the mask and flushing seawater over the faceplate will
relieve this condition temporarily. Divers must be careful
to avoid inhaling cold seawater through their noses,
because introducing very cold water into the mask
often causes divers to inhale involuntarily.
Keeping the diver's body warm is the most impor-
tant requirement in cold-water diving (Figure 10-10).
The standard foamed-neoprene wet suit has been used
in 29 °F (2°C) water for dives lasting longer than an
hour, but it is doubtful whether the divers on these
dives were comfortable or thermally safe. A major
drawback of wet suits is that, by the time the dive is
over, the diver is wet and will therefore probably con-
tinue to lose body heat even after leaving the water.
Further, the loss of foam thickness with depth drasti-
cally reduces the efficiency of any wet suit for cold
water diving much below 60 feet (18.3 m).
October 1991 — NOAA Diving Manual
Two types of diving dress have been used with suc-
cess under severe thermal conditions: the hot-water
wet suit, which provides a continuous flow of preheated
water to the diver, and the variable-volume dry suit,
which allows the diver to control the amount of air in
the suit and thus its insulating capability. (A more
detailed description of these suits is presented in Sec-
tion 5.4.) Except for the hot-water wet suit, no dry or
wet suit provides complete protection of the diver's
hands for long periods. As the extremities become cold
and dexterity is lost, the diver becomes less efficient
and should terminate the dive. The use of heavy insu-
lating socks under the boots of a wet or dry suit will
help to keep the feet warm. Hands should be protected
with gloves or mittens having the fewest possible dig-
its; the loss of manual dexterity associated with the use
of gloves or mittens is overridden by the added warmth
they provide. Filling the gloves or mittens with warm
water just before the dive begins is also recommended.
Heat loss from the head can be reduced by wearing a
second well-fitted neoprene hood over the regular suit
hood. Wearing a knitted watchcap under the hood of a
dry suit is especially effective in conserving body heat.
If the cap is pushed back far enough to permit the
suit's face seal to seat properly, the diver's head will be
kept relatively dry and comfortable. With a properly
fitting suit and all seals in place, a diver can usually be
kept warm and dry, even in cold water, for short periods.
If divers and members of the surface-support crew
follow certain procedures, the adverse effects of cold-
water exposure can be greatly reduced. Suits should be
maintained in the best possible condition, dry suit
underwear should be kept clean and dry, and all seals
and zippers should be inspected and repaired (if neces-
sary) before the dive. During the dive, divers should
exercise as much as possible to generate body heat.
Dives should be terminated immediately if the diver
begins to shiver involuntarily or experiences a serious
loss of manual dexterity. Once involuntary shivering
begins, the loss of dexterity, strength, and ability to
function decreases rapidly (see Section 3.4). After leaving
the water, cold-water divers are often fatigued, and,
because heat loss from the body continues even after
removal from cold water, such divers are susceptible to
hypothermia. Flushing the wet suit with warm water as
soon as the diver surfaces has a comforting, heat-
replacing effect, although such flushing can cause addi-
tional body heat loss unless it is done cautiously. Facilities
must be provided that allow the diver to dry off in
a comfortable, dry, and relatively warm environment,
so that he or she can regain lost body heat (see
Section 3.4.4). Divers should remove any wet clothes
or suits, dry off, and then don warm protective clothing
10-19
Figure 10-10
Water Temperature Protection Chart
Section 10
/7=\\
*"tVpl£ Normal Body Temperature 98°F (3rC) ►
Unprotected Diver
Average Skin Temperature 93°F (34°C) ^
Unprotected Diver
Uncomfortably Cold 88°F (31 °C) ^
Shivering 86°F (30 C) ^
Unprotected
Diver
Comfortable
During
Moderate
Work
Wet or Dry Suit
Diver's
Underwear
Or Wet Suit
Required
Pain 60°F (15°C)^
Dry Suit
Required
Over 60'; Wet
Suit For Short
Duration Dives
Less Than 60'
' Unprotected Diver
f. Death Within One Hour 40°F(5°C)^
Hot Water Suit
Or Variable
Volume Dry
Suit Required
Protection Usually Needed
Heated Suit
35—
30—
25 —
20 —
15-
10 —
5 —
5 —
^| Rest
— 90
— 70
°F
80
60
50
— 40
30
mg
Working
Diver Will
Overheat
Unprotected
Diver At
Rest Chills In
1-2 Hours
Fresh
^ Water Freezing
<4 Sea Point
Water
10-20
Source: US Navy (1985)
NOAA Diving Manual — October 1991
Diving Under Special Conditions
Figure 10-11
Diver Tender and Standby
Diver in Surface Shelter
as soon as possible. In cold-water diving situations
that require repetitive dives, it is even more important
to conserve the diver's body heat, to maintain an
adequate fluid balance, and to select the diving dress
carefully.
Adequate rest and nutrition are essential to provid-
ing cold-water divers with the energy necessary for
this type of diving. A diver should have a minimum of
6-8 hours of sleep before the dive. Care must be taken
to avoid dehydration, which can interfere with the
body's thermal regulatory mechanism. Careful plan-
ning is thus of the utmost importance in all cold-water
diving.
WARNING
If a Diver Is Extremely Cold, the Decompres-
sion Schedule Should Be Adjusted to the
Next Longer Time
10.9 DIVING UNDER ICE
In addition to the problems and limitations of diving
in cold water (see Section 10.8), there are specific
precautions that must be taken when diving under ice.
Diving under ice is extremely hazardous and should be
done only by experienced divers who have been care-
fully trained.
Most ice diving is done from large and relatively flat
surface ice sheets that are stationary and firmly frozen
to the shore. Even at locations many miles from the
nearest land, these ice caps often offer a stable work-
ing platform. However, diving from drifting or broken
ice is dangerous and should only be done as a last
resort. When the ice cap is solid, there is no wave
action to the water; however, divers must constantly be
on guard because the current beneath the entry hole
can change quickly and dramatically without produc-
ing any noticeable effect on the surface. In most cases,
the absence of wave action produces good underwater
visibility, although under-ice diving operations con-
ducted in areas characterized by river runoff or heavy
plankton may be associated with conditions of reduced
visibility.
To enter the water through ice, divers should first
drill a small hole through the ice at the site to deter-
mine ice thickness and water depth. If conditions are
satisfactory, the area around the site should be cleared
of snow and the size of the entry determined. A hole of
approximately 3 by 5 feet (0.9 by 1.5 m) allows three
fully dressed divers to be accommodated at one time.
If no shelter is used, a triangle-shaped entry hole
works best.
October 1991 — NOAA Diving Manual
Photo Doug Eiser
In all diving operations under ice, there should be
one surface tender for each diver and at least one
standby diver (Figure 10-11). While the diver is in
the water, the tender must be attentive both to the
diver and surface conditions, such as deteriorating
weather or moving ice. Tenders should be briefed on
the diver's tasks, so that they will understand the diver's
movements and be able to respond quickly in an emer-
gency. A safety line should be tied to the diver (not to
the equipment) and the other end should be tied firmly
to a large fixed object on the surface. Excursions under
the ice should be well planned, and the distance to be
traveled under the ice away from the entry hole should
be kept to a minimum; under normal circumstances,
this distance should be limited to 90 feet (27.4 m) and
should be extended to as much as 250 feet (45.7 m)
only in unusual circumstances. Longer under-ice excur-
sions make it difficult for the diver to get back to the
entry hole in an emergency and increase the difficulty
of searching for a lost diver. If divers must travel long
distances under the ice, additional holes should be cut
for emergency exits. Divers lost under the ice should
ascend to the overhead ice cover immediately, main-
tain positive buoyancy, relax as much as possible to
conserve air, and wait for assistance.
10-21
Section 10
WARNING
Divers Lost Under the Ice Should Ascend to
the Ice Cover and Wait Calmly to Conserve
Air. They Should Not Search for the Entry
Hole
To aid the diver to return to the entry hole, a bright
light should be hung just beneath the surface. For
night diving under ice, this light is a necessity; it is
usually the only item required beyond those used in
day-time operations. However, since cold water short-
ens the life of batteries, homing beacons and strobes
should be checked before use. Because direct ascent to
the surface is impossible when under the ice, a rapid
means of determining direction often is critical. In
shallow water, detours are often necessary to circum-
vent the 'keels' (thickened areas) built up beneath the
ice. Also, because of the absence of waves, there are no
ripple patterns on the bottom to aid in orientation. For
these reasons, the use of a tether is absolutely essential
in under-ice diving.
If there is a failure in an ice diver's primary breath-
ing system, the diver should switch to the backup sys-
tem, notify the buddy diver, and exit to the surface
with the buddy diver. Because buddy breathing is dif-
ficult in cold water, all divers should practice buddy
breathing before making excursions under the ice. Octo-
pus regulators should not be used in cold water as
substitutes for buddy breathing because the first stage
of these regulators tends to freeze up. If a diver's
exposure suit tears or floods, the diver should surface
immediately, regardless of the degree of flooding,
because the chilling effects of frigid water can cause
thermal shock within minutes. Surface-supplied tethered
diving is becoming more popular in under-ice opera-
tions because it eliminates the need for safety lines and
navigation lights and provides unlimited air. The full-
face masks or helmets of most surface-supplied diving
systems provide additional protection for the diver's
face and provide the capability for diver-to-diver and
diver-to-surface communication. These added features
must be weighed carefully against the burden of the
added logistic support required to conduct surface-
supplied diving. If the advanced dry suits now availa-
ble (see Section 5.4.5) are used, the surface-supplied
diver can spend long periods under the ice in relative
safety and comfort.
If an under-ice dive operation is scheduled to last
for more than 1 or 2 days, a tent or shed should be
constructed over the entry hole (Figure 10-11). Such a
shelter will protect both surface support personnel and
divers from the wind and, together with a small porta-
ble heater, can provide relative comfort in these severest
of diving conditions.
10.10 KELP DIVING
Kelp is found in dense beds along many of the colder
and temperate coasts of the world. In the United States,
these plants are found along the shore regions of the
west coast. Kelp beds or forests are widely diversified
both geographically and as a function of depth and
temperature. Different varieties grow in different zones
and support an incredible variety of sea life. Kelp will
attach itself to practically any substrate (i.e., rock,
concrete, steel, wreckage, etc.) and will often form a
treelike structure, the base of which is a rootlike hold-
fast that provides a secure anchor and a home for many
organisms. There is generally an area of open water
between the stipes originating from one holdfast. A
diver can swim between the stipe columns just as a
hiker can walk between the trunks of trees in a forest
on the land. Hollow floats or pneumatocysts are found
at the base of the blades or fronds on many of the
larger, longer kelp plants. These floats cause the fronds to
float up and keep the stipes relatively upright. The
floating fronds form a canopy when they have grown
sufficiently to reach the surface. In many instances,
this rapidly growing canopy becomes very dense and
can be several feet thick on and near the surface. The
canopy will usually have thin spots or openings located
randomly throughout the area, and these thin spots or
openings provide entry and exit points for divers. These
thinner areas are easily seen from below the surface
because the light penetration in these areas is much
better; in addition, as a diver positioned under such a
light area exhales, the rising bubbles usually float the
kelp outward to form an opening that is sufficiently
large to enable the diver to surface. Care should be
exercised when the diver's head is out of the water,
because the kelp may float back and fill in the hole and
surround the diver. Although the kelp will not actually
wrap itself around the diver, divers who twist around
and struggle may become entangled. Training in kelp
diving is necessary to master the skills to make entries
and exits easily.
Equipment that is not relatively streamlined can
snag and tangle in the kelp and cause problems. If the
diver becomes entangled, it is important to remember
that kelp is designed to withstand the pulling force of
wind, waves, and currents and consequently that the
tensile or stretching strength of the plant is very great.
Divers wishing to break a strand of kelp should fold it
to develop a sharp angle in the stipe. Pulling on the
10-22
NOAA Diving Manual — October 1991
Diving Under Special Conditions
kelp will result in frustration and may cause panic.
Nicking the kelp with a sharp object will separate the
kelp easily, but using sharp objects such as knives
needs to be done with care because of the proximity of
regulator hoses and other critical paraphenalia. The
easiest way to get free is to remain calm and to pull the
strands away carefully with a minimum of movement.
When working from a boat, it is best to anchor in an
opening so that the wind or current will drift the boat
back on the anchor line to a second opening in the kelp.
Divers may also anchor outside the kelp and swim in to
do their work. If the boat is anchored in the kelp, the
anchor will be full of kelp that must later be removed
surgically.
Entry through the kelp is best accomplished by finding
a thin area and making a feet-first, feet-together entry
rather than a headfirst or backroll entry that could
easily lead to entanglement. It is important to get
through the canopy and into the open water between
the stipes. Once through the surface canopy, the diver
can swim with comfort in the forestlike environment.
As the diver swims along, it is important to watch for
the light areas that signal the thinner areas in the kelp
bed. Surfacing slowly permits a diver's exhaust bub-
bles to assist in making an opening. When the diver
approaches the surface, the arms should be raised over
the head so that any kelp that may be encountered can
be moved to the side easily as the diver moves upward
into the hole that has been opened. Once on the sur-
face, the diver should stay in the vertical position and
should not turn around; this helps to avoid entangle-
ment. Submerging can be accomplished easily by either
exhaling and sinking or raising the arms overhead,
which forces the body deeper down into the water.
Smooth and slow movements make this maneuver easy
and safe.
The diver who wishes to travel on the surface of a
kelp bed to get back to the shore or boat has several
choices. If the diver is sufficiently skilled, it is easy to
use a series of breath-hold dives to move in steps to the
desired location. Each step requires the diver to sur-
face through an opening in the kelp and to take a
breath or two in preparation for the next step. Another
useful technique, often called the Kelp Crawl, resem-
bles the 'dog paddle' and involves keeping the body on
the surface above the kelp canopy and using the arms
to pull the diver across the top of the kelp as the diver's
fins make a narrow flutter kick to slide the body across
the top of the floating kelp canopy. The arms should
reach across the kelp in an extended position and then
the hands should grasp the kelp and press down as the
body is pulled over the kelp. It is important to present a
streamlined surface to the kelp, since anything that
extends out from the body will probably snag. Swim
fins with adjustable heel straps should have the loose
end of the strap on the inside rather than the outside of
the buckle. Taping the loose end of a strap to the main
portion of the strap is also a good solution. Wearing the
diving knife on the inside of the calf rather than any-
where on the outside of the body is also a snag reducer.
Kelp divers should remember that they want to move
through the kelp or over the kelp in a streamlined
fashion and that inflated buoyancy compensators, game
bags, and tools of all kinds should be organized to
present minimal problems.
Divers should also remember that kelp floats and that,
in a pinch, it is possible to achieve flotation by using
the kelp for support. Under windy conditions, divers
should approach the stern of a small boat to avoid
being pressed by the boat's movement into the kelp and
becoming entangled.
The various forms of kelp may grow so that the taller
kelps such as Macrocystis may be found growing over a
forest of Pelagophycus (or elk kelp). This second lower
canopy of kelp will further reduce the light level but
will be easier to swim through than the surface canopy.
All kelp beds are influenced by wind, currents, and
surge, and major beds may disappear from surface
view in a swift current because they are held down at a
45-degree angle. This has its advantages because the
kelp will stream with the current and thus may be used
as a navigational aid during the dive.
Achieving comfort and efficiency in kelp diving is
the result of training and practice. Having a buddy
diver along who is equally well trained is also extremely
important.
10.11 WRECK DIVING
Wreck diving subjects the diver to many of the same
hazards that are found in cave or ice diving. In the past
20 years, wreck diving has evolved into an activity
requiring both specialized equipment and training, par-
ticularly in the case of deep wreck diving. Regardless
of purpose (lobstering, artifact collecting, photogra-
phy, or exploring), true wreck diving involves the diver
entering the wreck. It is the act of penetrating the
enclosed space of the wreck that necessitates the addi-
tional equipment and training.
Most intact wrecks are at depths in excess of 80 feet
(24.4 m), because those in shallower water have been
destroyed either by storms or because they were
navigational hazards. After arriving on the bottom at
the wreck site, the first team of divers must check the
anchor of the boat for security and to ensure that the
October 1991 — NOAA Diving Manual
10-23
Section 10
anchor line will not chafe. The path into a wreck usu-
ally has fair to good visibility. On the return trip,
however, visibility may be reduced dramatically because
the divers have stirred up the silt and ferrous oxide
(rust) from the walls and exposed steel plates of the
wreck. The reduced visibility and the confusion and
anxiety caused by the many passageways, entrances,
chambers, bulkheads, and tight spaces require that
wreck divers use a penetration line such as a braided
1/8-inch (3.2 mm) nylon line on a reel. The line should
be tied off at the wreck's entrance, payed out during
entry, and reeled in during return. If the line is lost or
cut, the diver should pause, allow the silt to settle, and
regain his or her composure before attempting to return to
the entrance. Placing the faceplate of the underwater
light into the silt will reduce the ambient light level
and allow the diver's eyes to adapt partially to the
darkness. This will facilitate the detection of any sur-
face light coming into the passageways and thus aid in
the identification of possible exit paths.
Because of depth, the use of twin scuba cylinders,
together with a pony bottle with a separate regulator,
is recommended as standard wreck diving equipment.
In some instances, a spare air supply and regulator
should be placed outside the wreck. These precautions
are necessary in case the diver becomes entangled or
decompression is needed unexpectedly. During wreck
diving, entanglement may be caused by objects such as
monofilament fishing line, fish nets, collapsed bulk-
heads, or narrow spaces. A bag containing appropriate
tools for artifacts, liftbags, and an upline should be
carried to reduce the risk of entanglement that pre-
vails if this equipment is carried by or attached to the
diver. Most instrumentation can be strapped to the
underwater light; a set of decompression tables may be
attached to the light housing, reducing the amount of
equipment carried by the diver but still permitting
ready access to the tables if decompression is required.
Although a diver inside a wreck may be tempted to
breathe in the air pockets produced by previous divers,
this practice should be avoided because the partial
pressure of oxygen in these pockets is usually quite low
and hydrogen sulfide may be present.
The water temperature around a wreck is usually
low, and divers must therefore dress properly. Variable-
volume dry suits or 1/4- to 3/8-inch (6.4 to 9.5 mm)
wet suits should be used in water temperatures of 50 °F
(10°C) or less (see Section 5.4). Extreme caution must
be taken not to snag the suit or equipment on the sharp
objects commonly found in wrecks, such as decayed
wooden decks or corroded metal bulkheads, because
these hazards are frequently overgrown by algae, sea
polyps, or other marine growth.
10-24
10.12 DIVING AT HIGH ELEVATIONS
The U.S. Navy Standard Decompression Tables,
No-Decompression Table, and Repetitive Dive Tables
were calculated and validated on the assumption that
the diver started from and returned to an ambient
atmospheric pressure of 1 atmosphere absolute (ATA).
Consequently, these tables do not account accurately
for dives conducted from ambient environments hav-
ing pressures less than 1 ATA. Two sets of tables or
corrections are now in use for calculating diving sched-
ules for altitude diving: the Boni/Buehlmann tables
and the Cross corrections, as modified by Bell and
Borgwardt. These are described below, and represent-
ative dive profiles based on these tables are compared.
10.12.1 Altitude Diving Tables
Currently in Use
The Boni/Buehlmann tables were developed by Boni
and his colleagues (1976) and include no-decompres-
sion, decompression, surface interval, and residual
nitrogen (called the 'repetitive timetable') tables for
each 1,640 feet (500 m) of altitude up to 10,496 feet
(3,200 m). The tables to 6,561 feet (2,000 m) have
been tested on humans in wet dives (Boni et al. 1976).
The results of 94 non-repetitive dives to depths between
52 and 98 feet (15.8 and 9.1 m) and for bottom times as
long as 40 minutes were reported. The results of 184 dives
under approximately the same conditions were also
reported by these authors. No symptoms of decompres-
sion sickness of any kind were observed during these
278 dives. These tables require a routine decompres-
sion stop for 3 minutes at 6.6 feet (2 m) for dives
within the no-decompression limits. Consequently, all
dives used for testing the tables included a decom-
pression stop for 3 minutes or longer.
The Cross corrections to the U.S. Navy tables were
developed to convert the standard U.S. Navy decom-
pression tables to tables that could be used in altitude
diving. This adjustment method was first developed in
1965 by Dr. Jon Pegg but was never published. A
similar set of corrections was later developed by H. J.
Smith, Jr. (Cross 1967) and was subsequently published
in greater detail (Cross 1970). The Cross method involves
determining a theoretical ocean depth (TOD) by mul-
tiplying the dive depth by the ratio of the atmospheric
pressure at sea level to that at the altitude at which the
dive will be made. The TOD and the actual bottom
time in the U.S. Navy tables are then used to deter-
mine the altitude diving schedule.
The theory of the Cross corrections has been exam-
ined in detail (Bell and Borgwardt 1976); the correc-
tion factors used in the Cross tables do not apply to the
NOAA Diving Manual — October 1991
Diving Under Special Conditions
Table 10-1
Comparison of Differences in
Time Limits (in Minutes of
Bottom Time) for No-Decompression Dives
critical tissue pressures used in the Navy tables as
safety criteria. On the other hand, in the cases studied,
the Cross corrections always 'failed' on the conserva-
tive, i.e., safe, side. University of California underwa-
ter research teams have used the Cross corrections as a
guide to diving in California lakes and in Lake Tahoe,
Nevada (elevation 6200 feet (1890 m)). Diving sched-
ules used have included procedures for up to three
repetitive dives per day to depths of 130 feet (39.6 m).
Both no-decompression and decompression dives have
been conducted; no reported cases of decompression
sickness have occurred in several hundred dives.
10.12.2 Comparison of Existing Tables
A comparison of the no-decompression limits given
by the two altitude correction methods and the U.S.
Navy tables is shown in Table 10-1. As this table
shows, both the Cross corrections and the Navy tables
yield no-decompression limits that are longer than
those predicted by the Boni/Buehlmann tables, although
in both cases the no-decompression limits are less than
those that apply to sea level.
There have been no reported cases of decompression
sickness in divers using the Cross corrections on dives
from an altitude of 6200 feet (1890 m). The Cross
corrections therefore appear to be safe. Several labo-
ratories are continuing to study this problem, but at
this time the true bends threshold for these tables has
not been established. Consequently, altitude diving,
and particularly decompression altitude diving, should be
performed using conservative assumptions and special
precautions to ensure access to emergency treatment.
10.12.3 Recommendations for Altitude Diving
The Cross corrections are recommended for general
use within the no-decompression limits. Although
decompression dives have been conducted using the
Cross corrections, they have been relatively few and
have not involved depths greater than 130 feet (39.6 m)
from an elevation of 6200 feet (1890 m). In general,
decompression dives at altitude should be avoided.
10.12.4 Calculations for Diving at Altitude
The Cross correction tables, as modified by Bell and
Borgwardt, are shown in Table 10-2. This table is
identical to that presented by Cross ( 1 970), except
that it has been modified to account for fresh water
and rate of ascent. The table is used as follows:
1. The depth of the planned dive is found in the
column on the left marked "Measured Depth."
October 1991 — NOAA Diving Manual
Measured
USN
Cross
Boni/Buehlmann
Depth
Tables
Tables
Tables
(ft)
(min)
(min)
(min)
60
60
40
15 ( + 3 at 2 m)
80
40
25
6 (+ 3 at 2 m)
100
25
10
4 ( + 3 at 2 m)
120
15
5
Decompression
In this example, dives are assumed to take place at an elevation of
6000 feet (1829 m).
Adapted from NOAA (1979)
2. The altitude of the dive site or the next greater
altitude is found in the top row of the table.
3. The entry corresponding to the intersection point
of the depth row and the altitude column marks
the "theoretical ocean depth" (TOD), which,
according to the assumptions of the Cross theory,
yields a probability of decompression sickness
equivalent to that for the altitude and measured
depth of the dive.
4. The TOD and the total bottom time, including any
residual nitrogen time accrued from repetitive
dives, are then used with the U.S. Navy tables.
The dive schedule is calculated exactly as it would
be for a sea-level exposure. Each time a dive is
planned, the TOD equivalent is substituted for
that measured depth.
5. The ascent rate at altitude must be reduced, as
shown in Table 10-2.
6. If a decompression dive is conducted (which is not
recommended), the depth of the decompression
stops must also be corrected, as shown in Table 10-2.
Example:
Two dives are to be conducted at an altitude of
6000 feet (1829 m) on a no-decompression schedule.
The first is to be to 80 feet of fresh water (ffw) (24.4 mfw)
for 20 minutes; the second to 60 ffw (18.3 mfw) for
25 minutes. Find the surface interval required to com-
plete the dive schedule in minimum time.
Solution:
From Table 10-2, the theoretical ocean depth in fsw
that corresponds to a depth of 80 feet of fresh water
(ffw) (24.4 mfw) in a lake whose surface altitude is
6000 feet is 97 fsw (29.6 msw) and that for a depth of
60 feet of fresh water (18.3 mfw) is 73 fsw (22.2 msw).
The sea-level decompression table (Appendix B) must
therefore be entered at 100 fsw (30.1 msw) and 80 fsw
(24.4 msw), respectively. A 20-minute dive to a TOD
10-25
Section 10
Table 10-2
Theoretical Ocean Depth (TOD)
(in fsw) at Altitude for a
Given Measured Diving Depth
Measured
Altitude in
feet
Depth*
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
TOD in fsw at Altitude
0
0
0
0
0
0
0
0
0
0
0
0
10
10
10
10
11
11
12
12
13
13
14
14
20
20
20
21
22
23
23
24
25
26
27
28
30
29
30
31
33
34
35
36
38
39
41
43
40
39
40
42
44
45
47
49
51
52
55
57
50
49
51
52
54
56
59
61
63
66
68
71
60
59
61
63
65
68
70
73
76
79
82
85
70
68
71
73
76
79
82
85
88
92
95
99
80
78
81
84
87
90
94
97
101
105
109
113
90
88
91
94
98
102
105
109
114
118
123
128
100
98
101
105
109
113
117
122
126
131
136
142
110
107
111
115
120
124
129
134
139
144
150
156
120
117
121
126
131
135
141
146
152
157
164
170
130
127
131
136
141
147
152
158
164
171
177
184
140
137
142
147
152
158
164
170
177
184
191
199
150
146
152
157
163
169
176
182
190
197
205
213
160
156
162
168
174
181
187
195
202
210
218
227
170
166
172
178
185
192
199
207
215
223
232
241
180
176
182
189
196
203
211
219
227
236
245
255
190
185
192
199
207
214
223
231
240
249
259
270
200
195
202
210
218
226
234
243
253
262
273
284
210
205
212
220
228
237
246
255
265
276
286
298
220
215
222
231
239
248
258
268
278
289
300
312
230
224
233
241
250
260
270
280
291
302
314
326
240
234
243
252
261
271
281
292
303
315
327
340
250
244
253
262
272
282
293
304
316
328
341
355
Stops
0
0
0
0
0
0
0
0
0
0
0
0
10
10
10
10
9
9
9
8
8
8
7
7
20
21
20
19
18
18
17
16
16
15
15
14
30
31
30
29
28
27
26
25
24
23
22
21
40
41
40
38
37
35
34
33
32
30
29
28
50
51
49
48
46
44
43
41
40
38
37
35
Ascent Rate
60
62
59
57
55
53
51
49
47
46
44
42
* Measured depth is not gauge depth. Table takes into account the effect of water density. The zero feet altitude column is for
diving in a freshwater lake at sea level. According to Bell and Borgwardt (1976), these tables are theoretically correct (although
they do not account for seasonal or daily barometric changes) but are still untested. Adapted from Bell and Borgwardt (1976)
i
«
of 100 fsw (30.1 msw) places the diver in the F repeti-
tive group (Appendix B). The no-decompression limit
for a TOD of 80 fsw (24.4 msw) is 40 minutes (Appen-
dix B). Therefore, the diver can have no more than
15 minutes of residual nitrogen time when starting the
second dive; the diver is in the C repetitive group. To
move from the F group to the C group requires 2 hours
and 29 minutes.
A dive schedule for an altitude dive at 6000 feet
(1829 m) would therefore be 80 fsw (24.4 msw) for
20 minutes, 2 hours and 29 minutes of surface interval
time, followed by a 60-fsw (18.3 msw) dive for
25 minutes. In high-altitude diving, the last dive is often
followed by a trip through mountain passes at an elevation
higher than that used in the calculation. In this event,
it is good practice to calculate the last dive as though it
10-26
had taken place at the maximum elevation the diver
will be passing through on the trip out.
10.12.5 Correction off Depth Gauges
Neither oil-filled nor capillary depth gauges pro-
vide accurate depth indications when used at altitude.
Oil-filled depth gauges are designed to read 0 feet at a
pressure of 1 ATA. At reduced atmospheric pressure,
the gauge will read less than zero (unless there is a pin
that stops the needle at zero); in the water, such a
gauge will give a reading that is shallower than the
actual depth. The depth readings can be corrected by
adding a depth that is equal to the difference between
the atmospheric pressure at the altitude site and
1 ATA. Table 10-3 shows mean atmospheric pressures
NOAA Diving Manual — October 1991
4
Diving Under Special Conditions
Table 10-3
Pressure Variations with Altitude
Altitude,
Pressure,
Pressure,
Pressure,
Oil-filled
ft
mmHg
psl
atm*
gauge
correction, ft
0
760.0
14.70
1.000
0
1000
732.9
14.17
0.964
1.22
2000
706.7
13.67
0.930
2.37
3000
681.2
13.17
0.896
3.53
4000
656.4
12.70
0.864
4.61
5000
632.4
12.23
0.832
5.70
6000
609.1
11.78
0.801
6.75
7000
586.5
11.35
0.772
7.73
8000
564.6
10.92
0.743
8.72
9000
543.3
10.51
0.715
9.67
10000
522.8
10.11
0.688
10.58
11000
502.8
9.73
0.662
11.47
12000
483.5
9.35
0.636
12.35
13000
464.8
8.99
0.612
13.16
14000
446.6
8.64
0.588
13.98
15000
429.1
8.31
0.565
14.76
16000
412.1
7.97
0.542
15.54
17000
395.7
7.66
0.521
16.25
18000
379.8
7.35
0.500
16.96
19000
364.4
7.04
0.479
17.67
20000
349.5
6.76
0.461
18.28
* U.S. standard atmosphere-
Source: NOAA (1979)
at various altitudes and the corrections necessary for
oil-filled gauges.
Because of the reduced density of the air trapped in
the capillary gauge at altitude, less water pressure is
required than at sea level to compress the air to a given
volume. As a result, the capillary gauge will indicate a
depth greater than the actual depth. Because of the
question about the accuracy of these gauges, a meas-
ured downline should be used.
10.12.6 Hypoxia During Altitude Diving
A diver surfacing from an altitude dive is moving
from a breathing gas in which the oxygen partial pres-
sure is relatively high to an atmosphere in which it is
low. As a result, the diver may experience symptoms of
hypoxia and breathing difficulty for a period after the
dive (see Section 3.1.3.1).
10.13 NIGHT DIVING
Night diving exposes the diver to an entirely different
aspect of the underwater world. Marine life may be
more or less abundant and appear to be of different
colors than is the case during the day. Areas that are
familiar to the diver during the day may appear changed
to the extent that orientation and locating familiar
landmarks may be difficult even with good artificial
light. Accordingly, special precautions and extra plan-
ning are required for night dives.
Anchoring is especially critical at night. The boat
must be secure before the diver enters the water (except
when liveboating, in which case other steps are appro-
priate (see Section 8.10.1)). It is also important at
night to have correct marking lights that are clearly
visible to other vessels in addition to a light the divers
can see under water. A chemical light or small strobe
light attached to the anchor line or downline is recom-
mended.
Predive checks are particularly important at night,
because the limited visibility precludes even a cursory
inspection of equipment once in the water. Night div-
ing in fog or heavy rain should be avoided because it is
easy for the diver to lose sight of the lights on the dive
boat or those carried by other divers.
Each diver should carry a reliable diving light with a
charge sufficient to last longer than the time antici-
pated for the dive. A second light is advisable, because
failure of lights is common. The light should be secured to
the diver in a manner that permits the illumination of
watches, gauges, or navigational aids. A chemical light
should be taped to the snorkel or tank valve for under-
water and surface visibility in case the dive lights fail.
The entire night dive team should be careful to main-
tain dark adaptation before and during the dive (see
Section 2.8.2). Every effort should be made to avoid
shining diving lights directly into the eyes of crew
members, both before and during the dive. Once in the
water, it is easy to keep track of a buddy's light at
night; however, one diver may occasionally lose another
because the glare of the light being held prevents seeing
the buddy's light. In this case, the divers should turn
off or otherwise shield their lights momentarily, adjust
their eyes, locate the buddy's light, and then immedi-
ately turn their lights back on.
If a team is left with only one light, the dive should
be terminated. Lights may also be used to signal the
surface; sweeping the light in a wide arc over the head
is the standard 'pick me up' signal. At night, a whistle
or chemical flare should also be carried in case of light
failure.
Shore entries are more hazardous at night because
such features as rocks, algae, holes, waves, and rip
currents are not easily seen. Entries from boats, piers,
and other surface platforms require special caution so
that the diver avoids hitting objects on or below the
surface.
If a shore exit requires a particular approach because of
in-water obstacles, two shore lights in a line can serve
as a navigational aid for divers. When possible, experi-
enced night divers should be buddied with novice night
October 1991 — NOAA Diving Manual
10-27
Section 10
divers. Making the entry at dusk rather than at night
reduces some of the problems of night diving. When-
ever possible, the area to be dived by night should first
be dived by day to provide the divers with entry and
exit experience.
NOTE
Decompression diving is more hazardous at
night than during the day and should be
avoided if possible. To be conducted safely,
night decompression dives need considera-
ble advance planning.
In night decompression diving, lights marking the
decompression line are necessary to ensure that the
divers conduct their in-water decompression near the
dive boat or other platform. Divers operating in a
decompression mode should not swim out of sight of
lines or lights that will guide them back to the decom-
pression line and dive platform.
10.14 DIVING IN DAMS AND RESERVOIRS
Hydroelectric dams across rivers in the northwest United
States incorporate bypass and collection systems for
the protection of migrating fish species such as salmon
and steelhead trout (Figure 10-12). Because fish pas-
sage research is conducted at many of these dams,
NOAA and other scientist/divers are often required to
inspect, maintain, install, or retrieve research gear
such as flow meters and fish guidance and passage
devices. If time and circumstances permit, a shutdown
and de-watering of turbine intakes, gatewells, and fish
ladders is the safest and most efficient manner for
performing work on dam bypass and collection facili-
ties. However, safe and efficient diving operations can
be performed within and on the upstream and down-
stream faces of dams even when these are still operat-
ing. The agency operating the dam supplies a diving
inspector who coordinates such dives, because strict
cooperation between the divers and the powerhouse
operations staff is mandatory to ensure proper clear-
ances for turbine shutdown and flow gate closures.
10.14.1 Diving at Dams
The safety aspects of diving at dams are comparable
to those prevailing in cave, wreck, and over-bottom
diving, and many of the same procedures are used in
dam diving. Predive planning by the dive team with
dam personnel will help to ensure a safe diving opera-
10-28
tion. If such operations are undertaken at altitudes in
excess of 1000 feet, divers should take special precau-
tions (see Section 10.12).
Three major conditions must be considered when
planning dives at dams in the northwest (or any other)
region:
(1) Water temperature
(2) Visibility
(3) Flow velocities.
Water temperatures may vary from slightly above freez-
ing in winter to almost 80 °F (27 °C) in summer. Divers
should be protected from the elements before diving
and during surface intervals in both warm and cold
seasons, because of the potential for heat exhaustion or
hypothermia (see Section 10.8). Most research diving
at dams occurs during the spring freshet, when rivers
swell from rains and melting snow and fish migrations
occur. The spring runoff produces low underwater vis-
ibility (e.g., 0-2 feet [0-0.6 m] in the Snake River)
from silt carried by flooding waters. In warmer months,
algae blooms may cause low underwater visibility. Even
in clear water, the sediment disturbed by divers reduces
visibility so that the small amount of natural light
penetrating the gatewells is reduced. Although diving
lights are only minimally effective, the problems
associated with low visibility at dams can be overcome
by careful planning, studies of the blueprints and plans
of the dam, and familiarization with the research devices
to be used during the dive. Objects can be recognized
by touch and orientation maintained, even in zero under-
water visibility, if the diver is familiar both with the
gear and the dam's structures. The velocity of the flow
and the force of the suction through screens or orifices
at dams can be eliminated or controlled by coordinat-
ing the diver's actions carefully with dam operations
personnel before the dive.
When bypass systems become fouled or clogged by
river debris, divers sometimes are required to enter
dam gatewells to clear the system's orifices. The haz-
ards of gatewell diving can be reduced by taking ade-
quate precautions to ensure that the influence of suc-
tion, caused by the large hydrostatic head, is avoided
at the orifice. Variable-volume suits, which eliminate
the need for buoyancy compensators, should be worn to
avoid the danger of loose equipment becoming caught
(see Section 5.4). Procedures are much the same as
those for umbilical diving, whether the diver is using
surface-supplied air or scuba cylinders. At a mini-
mum, a tender line to the diver should be used for
contact and signals, although hard wire communica-
tion is preferred. A diver cage should be provided to
transport the diver to and from the orifice level and the
NOAA Diving Manual — October 1991
Diving Under Special Conditions
Figure 10-12
Cross Section of a Typical Hydroelectric
Dam in the Northwestern United States
Courtesy George Swan
intake deck of the dam, and a safety diver is required.
Figure 10-13 shows a diver ready to be lowered into a
dam gatewell. Procedures to shut down the bypass
system immediately in the event of an emergency should
be coordinated with the dam operations controller before
the dive.
Work on fish ladders (Figure 10-14) should be
performed during off-season when the number of
upstream adult fish runs is low and water flows can be
cut off for a period of time, which permits the task to
be completed in the open air. On rare occasions this is
impractical, and diving is then the only way to com-
plete the task. Flows in fish ladders appear quite turbulent
when viewed from above; however, baffles or weir walls
are regularly spaced perpendicularly to the flow, and
the water flows either over the top of each weir or
through large rectangular orifices located at the base
of the baffle wall. When diving in pools between baffle
walls, flows as high as 8.0 feet per second (fps)
(2.4 mps) may be encountered in areas directly in line
with the orifices but may be as low as 1.0 fps (0.3 mps)
to either side or above the line of the orifice. By using
safety lines and exercising caution, diving tasks may
October 1991 — NOAA Diving Manual
be performed in much the same manner as they are
conducted when diving amid pools and boulders in
rivers with relatively fast currents (see Section 10.15).
When diving tasks must be performed on the upstream
face of a dam, turbines and/or spillway gates must be
shut down. Adjacent units should also be shut down for
safety and to reduce flows near the work station. Divers
can be transported to and from the level of work and to
the intake deck of the dam by means of a diver cage
and crane. A boat or floating platform also is useful for
the safety (standby) diver and equipment. Diving on
the downstream face of a dam is handled similarly;
flows are shut off to avoid sweeping the diver off station.
Divers should avoid water contaminants, such as
spilled petroleum or lubrication products used in the
routine operation and maintenance of dams or gaseous
byproducts generated by underwater cutting and welding.
These contaminants can become concentrated in con-
fined areas such as gatewells, where the water level
may be 1 5 to 20 feet (4.6 to 6. 1 m) below the deck of the
dam. Before starting or continuing a dive, any contam-
inant discovered should be eliminated from the dive
site.
10-29
Section 10
Figure 10-13
Diver Protected by Cage and Ready to
be Lowered Into Dam Gatewell
Figure 10-14
A Fish Ladder at a Hydroelectric
Dam in the Northwest
Courtesy George Swan
10.14.2 Diving at Water Withdrawal and
Pumping Sites
The impact of water withdrawal on populations of
juvenile fish in the Columbia Basin of the northwest
United States is a major concern to fisheries agencies.
Water is withdrawn from the Columbia and Snake
Rivers via pumps and siphons and is then used for
irrigation, industrial applications, drinking water, ther-
mal cooling, fish and wildlife propagation, and other
domestic needs. Before water can be withdrawn from
these rivers, the U.S. Army Corps of Engineers requires
those seeking permits to install and operate water with-
drawals to install fish protective facilities. Periodical-
ly, divers are required to inspect fish screens at water
withdrawal sites to monitor the condition of the screening
and the status of compliance with established fish
screening criteria.
Several basic types of water withdrawal sites are
common: (1) a vaultlike structure with a screened under-
10-30
Courtesy George Swan
water opening; (2) a pierlike structure set out from the
shoreline that supports turbine pumps; (3) a combina-
tion pier/vault created by closing in the area under a
pier with driven sheet piling or other material; and
(4) a simple arrangement of a pump or siphon with a
single intake line extending to a depth below the low
water elevation. Some vaultlike structures may have
trash rack bars in front of the fish screening.
A good and stable work boat serves as the best diving
platform for accessing most withdrawal sites and expe-
dites diver travel between sites, but divers should be
careful when entering the water from a small boat.
Some sites with enclosed fish screens must be accessed
by ladder or small crane. For such a diving task, tanks,
weight belts, masks, and fins are lowered by lines to the
divers once they are in the water; this procedure is
reversed after the dive.
Diving in and around pump intakes can be performed
safely if certain hazards are recognized and the neces-
sary precautions are taken. In general, intake veloci-
ties are not high enough to present a suction hazard,
although pumps should be shut down, if possible. To
perform an inspection during the pumping season,
NOAA Diving Manual — October 1991
Diving Under Special Conditions
however, the approach velocities may have to be meas-
ured while the pumps are operating. Surface air supply
hoses and safety lines should never be used when div-
ing on sites with operating pumps unless the tender or
another diver can tend the umbilical line to keep it
away from the pump. Loose lines, hoses, straps, cylin-
der pressure gauges, and other gear should not be used
or should be well secured to avoid being sucked into
unscreened pumps or wound around impeller shafts.
Because of the need for mobility in and around a pump
site, a buddy team with scuba gear is the preferred
method of diving at pump intakes. Low underwater
visibility, ranging from 0-6 feet (0-1.8 m), is found in
the lower Columbia and Snake Rivers, and this distance
increases to 15 feet (4.6 m) in the upper Columbia
River. If large pumps are operating and the visibility is
exceptionally low, the dive should not be performed.
Divers should enter the water carefully with their
feet first, because pump sites are notorious for the
presence of debris, rocks, snags, and pieces of sharp
metal, all of which present a hazard to divers, their
suits, and any loose equipment. In addition, because
there is less scuba diving activity in inland waters than
in salt water areas, inland boaters tend to be less familiar
with 'diver down' signal flags and their meaning. Pump
site divers should descend and ascend close to the
pump site structure or the shoreline. Surface personnel
should watch for boating traffic and hail it with a
loudspeaker to inform boaters that divers are operat-
ing under water. During the summer months, any activity
conducted on or near the shoreline should be conducted
cautiously because of the presence of rattlesnakes.
10.15 RIVER DIVING
Rivers throughout the world vary in size, turbidity,
and in the terrain through which they flow; diving
conditions vary with the river. Any river should be
studied thoroughly and conditions known before the
dive is planned. Log jams may be a hazard, as are
submerged objects such as sharp rocks, trees, limbs,
old cars, barbed wire, and the ever-present monofila-
ment fishing lines, nets, and lures. Rapids or steep
profiles are hazardous because a diver may be slammed
against a rock or other submerged object and sustain
serious injury or be held by the current.
River diving has a number of special aspects for
which a diver should be prepared. For example, divers
who grab the bottom to stop and look at an object
should hold their face masks to prevent them from
being torn off by the current. Divers should be aware
that more weights are required when diving in currents
than in quiet water, and they should plan their dives
October 1991 — NOAA Diving Manual
accordingly. Where there is considerable surface cur-
rent, diving in large holes may be done by dropping
directly to the bottom. At some distance below the
surface, the diver may be surprised to find either no
current or one flowing slightly toward the head of the
hole. Divers should also remember when working with
lines, tethers, or umbilicals in any type of current that
the drag on these lines greatly hampers a diver's ability
to travel and that the lines also create an entanglement
hazard.
In a swift river current, entering the water can be
difficult. One technique is to attach a line about 20
feet (6.1 m) long to the anchor with a handle (similar to
those used by water skiers) on the other end. The diver
can grasp the handle and descend by making appropri-
ate changes in body position, which lets the current do
most of the work. Descent can also be made by using
the anchor line, but this requires considerably more
effort. Divers always need something to hold onto because
of the difficulty of moving across the bottom in fast
currents. One helpful device is shown in Figure 10-15
(Gale 1977). This device, referred to as a creeper, is
used by lifting and moving the corners forward in
alternate turns, as shown; it can also serve as a diver's
anchor when not in use. Large rocks or sharp drop-offs
along river bottoms may create enough turbulence down-
stream to disorient a diver. In such a situation, the
diver should move hand-over-hand along the bottom
or use a creeper, because the current is less on the
bottom. This technique can be used even on sand or
gravel bottoms.
Another difficulty sometimes encountered in a fast-
flowing stream or river is the blocking of light by
bubbles. In or under white water, it may be almost
dark. Rivers carrying large amounts of sediment, either
normally or as a result of recent rains, are also extremely
dark. Using underwater lights is not much help in
turbid waters because the light is reflected or blocked
by the particles suspended in the water. When working
in rivers where the waters are reasonably clear but the
bottom is easily stirred up, divers should work upstream
against the flow. Any sediment that is disturbed will
flow downstream, away from the direction of travel,
which allows the diver to work in much greater visibility.
River diving near low-head dams presents additional
hazards because the hydraulic acrion created by such
dams creates currents with the potential to pull boats
and swimmers back toward the dam from downstream
(see Section 10.14.1). River divers required to work
without lines in waters near low-head dams, water-
falls, or rapids with significant dropoffs should work
on the bottom and as far clear of the affected area as
possible.
10-31
Section 10
Figure 10-15
Creeper— A Device Used to Move Across
Rocky Substrates in Strong Currents
A. Closeup view
Photo William Gale
B. Creeper in use
Source: NOAA (1979)
10.16 DIVING FROM A SHIP
As in all diving operations, diving from a large ship
requires comprehensive planning before the dive or
series of dives. Because operating a ship represents a
significant investment, all logistical factors involving
personnel, equipment (diving and scientific), weather,
etc., should be thoroughly considered in dive planning.
10.16.1 Personnel
When a ship is being used as a surface-support
diving platform, the ship's captain has the final deci-
sion in any matter pertaining to the vessel. However,
the dive master or senior diver has the final decision in
any matter involving the divers. It is imperative that
close communication between the dive master and the
captain be initiated and maintained so that the intent
of the diving operations is well understood and opera-
tions can be carried out as safely as possible.
It is highly desirable for the captain to have prior
knowledge of diving techniques and procedures. Al-
though this may not always be the case, a captain with
such a background can add immeasurably to a diving
operation's success. When diving from a ship, the fol-
lowing personnel requirements should be considered
before beginning a cruise.
Dive master. Dive masters are responsible for all
diving portions of the operation. These supervisors
schedule all dives and designate divers and dive teams.
They discuss the operational necessities of the dive
with the captain and, as required, assist in carrying out
these requirements (see Section 14.1.2.1).
Science coordinator. In conjunction with the dive
master and the captain, the science coordinator formu-
lates and ensures that the scientific goals of the diving
mission are achieved. On a regular basis throughout
the cruise, these goals are re-evaluated and, when
necessary, re-directed (see Section 14.1.2.3).
10.16.2 Use and Storage of Diving and
Related Equipment
A suitable diving locker should be designated and
used for storing diving equipment. The designated area
should be well ventilated, adequate in size, and equipped
so that diving equipment can be hung up to dry. The
diving locker should be kept locked when not in use,
and the key should be kept by the dive master.
During predive planning, the stock of backup diving
gear should be assessed. Equipment easily lost, such as
knives, weight belts, etc., should be stocked in excess
so that divers can be re-equipped quickly. Spare parts
and replacements for critical life-support items such
as regulators should be available on board.
Air compressors play an important role in a ship-
board diving operation. The compressor should be
positioned with intake toward the bow of the ship (the
ship will swing into the wind while at anchor), away
from the exhausts of main, auxiliary, or any other
engines, and free of fume contamination from paint
lockers, gasoline, and other solvents (or preservatives
being used by diver/scientists). Cool running of the
compressor requires good ventilation; in hot climates,
the compressor should be run at night. When filling air
cylinders, salt water from the ship's seawater system
may be flushed over the tanks as a coolant. Oil-lubricated
compressors should have some type of oil/water sepa-
rator built into the system. It is also desirable to have a
filtration column that eliminates CO, C02, hydro-
carbons, oil, water, and other contaminants, in accor-
dance with breathing air specifications (see Sec-
tion 4.2).
10-32
NOAA Diving Manual — October 1991
Diving Under Special Conditions
10.16.3 Safety Considerations
When a large ship is selected for a diving platform, it
is generally because the diving must be conducted a
considerable distance from shore or in a remote region.
When the distance is beyond the range of rapid emer-
gency assistance or transport, the dive master should
have preplanned procedures for prompt, adequate treat-
ment on board ship and, when necessary, evacuation to
a destination where further treatment can be obtained
(see Section 19.7).
The dive master should contact all sources of emer-
gency assistance and rapid transport close to the dive
site and should determine the round-trip range of emer-
gency transport vehicles, including the distances and
times from shore to the dive site and back to the nearest
recompression chamber.
On cruises out of the rapid emergency assistance or
transport range, especially where decompression or
repetitive diving is scheduled, a recompression cham-
ber and a trained, qualified chamber operator should
be on board ship. The possibility of decompression
sickness, gas embolism, or an emergency free ascent
requiring immediate surface recompression cannot be
discounted. A portable double-lock chamber should
be provided (see Section 6.1).
Safe execution of the dive also depends upon the
proper handling of the mother ship before, during, and
after the dive (Coale, Michaels, and Pinto, as cited in
Heine 1985). Typically, any object remaining in one
place for a period of time, such as sediment trap arrays,
productivity arrays, or ships, will attract sharks. For
this reason, open-ocean diving near such objects is not
recommended. The bridge and the mess deck personnel
should be told that no garbage can be dumped and no
bilges can be pumped in the vicinity of the dive; fishing
is also not permitted near the site. If the ship has been
on station for some time before initiation of a dive, the
ship should steam away from the station for a distance
of at least 5 miles (8.0 km) so that the boat can be
launched in cleaner water. To minimize the sonic attrac-
tion of sharks to the divers, the dive boat motor should
be shut off and the mother vessel should be instructed
not to come closer than 1/2 mile (0.8 km) to the dive
location.
10.16.4 Using Surface-Supplied Equipment
All personnel, divers, and surface tenders should
perform a thorough check of equipment. The ship's
captain must be notified that divers are about to enter
the water, and clearance should be obtained before the
diving operation commences. The air supply system,
helmet or mask, and communications should be checked
to ensure they are functioning properly. If not, correc-
tions must be made before the diver enters the water.
The water should be entered using a ladder. Jump
entries are discouraged from heights more than
3 to 4 feet (about l.O m) above the water. A descent
line should be used. Descent rate will depend on the
diver; generally, however, it should not exceed 75 feet
(22.9 m) per minute. If descending in a tideway or
current, divers should keep their backs to the current
so that they will be forced against the descent line
(see Section 14.1.3.2).
Divers and surface tenders should review the line
pull signals described in Section 8.1.4 thoroughly.
Although voice is the primary means of communica-
tion between divers and surface tenders when surface-
supplied equipment is used, pull line signals are the
backup form of communication if the voice system
fails.
When the bottom is reached, the surface tender should
be notified and the diver should proceed to the work
site. The surface tender also should keep the diver
constantly informed of bottom time. The diver should
always be notified a few minutes in advance of termi-
nation time so that there is time to complete the task
and prepare for ascent.
When work is completed, the diver should return to
the ascent line and signal the surface tender that he or
she is ready for ascent. The surface tender should pull
in the excess umbilical line slowly and steadily. The
diver should not release the ascent line but may assist
the tender by climbing the line. The surface tender or
dive master must inform the diver of his or her decom-
pression requirements well in advance of dive termina-
tion. A diving stage may be required for long decom-
pressions. When decompression is completed, the diver
should return on board ship via the ladder or diving
stage, receiving assistance from the surface tenders as
required.
10.16.5 While Underway
Diving while underway is not widely practiced and
can clearly be dangerous. However, divers may occa-
sionally be required to dive from a ship that is under-
way to perform work or to make underwater observa-
tions that cannot be made from a stationary platform
or surface. Because this type of operation is inherently
more dangerous than other diving operations, it should
be done only when no safer alternative exists. Strict
compliance with certain rules is mandatory.
Only self-contained diving equipment should be used
when entering the water from a moving ship. Although
special requirements may dictate higher speeds, the
October 1991 — NOAA Diving Manual
10-33
Section 10
ship should proceed if possible at speeds under 3 knots
(1.6 m/s). The use of a small boat, manned continuously
while divers are in the water, is required.
It is essential that great care be taken when entering
the water from a moving ship. A spot should be selected on
the side of the ship well aft and, if possible, aft of the
ship's propeller(s). The diver should never enter the
water directly off the stern, because propellers and the
ship's movement through the water cause turbulence
that could buffet a diver severely or damage or tear off
equipment.
The step-in method (see Section 10.4.1) is recom-
mended for entry from a moving ship. This allows
maximum distance between the side of the ship and the
point of entry. Caution should be exercised in using the
step-in method when the deck of the ship is high off the
water surface.
Most dives from a ship underway require the ship to
tow equipment (trawls, sleds, etc.) that the diver will
use during the dive. This equipment may be on the
surface, partially submerged, or submerged. The small
boat should maintain position behind and just to the
side of the towed equipment. Divers should enter the
water in succession; the interval between entries should be
long enough to avoid having the divers collide with
each other but short enough to prevent the divers from
being too widely separated in the water.
Divers should drift back and maintain visual or hand
contact with the cable being used by the ship to tow the
equipment. They should work their way back along the
cable until the equipment is reached, descending as
required.
Hazards and diver difficulties increase if active nets
or their components are moving at great speed. During
the early retrieval of purse seines, the net components
(web, purse rings, and purseline) move slowly. Toward
the end of the pursing and net-retrieving sequence,
however, these components move through the water
quickly. Since divers usually lack communication with
surface winch and line hauler operators, the divers
must stay out of the bight of the line or the immediate
path of the gear.
Diving within the influence of a trawl or other device
towed from vessels under way is hazardous. The haz-
ards include entrapment within the net, fouling, and
being forced against bottom obstructions. If the device
is moving slowly (under 1.5 knots; 0.8 m/s), the diver
may be able to swim alongside for short periods. At
speeds up to about 2.5 knots (1.3 m/s), divers may hold
onto large nets without seriously distorting them. Both
of these methods require the diver to be in excellent
physical condition and to be trained in this special
form of research diving. Scientists who plan to dive
near capturing systems should undertake special training
dives that simulate conditions likely to be encountered.
High (1967) and Wickham and Watson (1976)
described methods used by divers to observe trawls.
Fishing gear researchers operating in relatively deep
waters off the northwestern coast of the United States
on large midwater or bottom trawls generally descend
to the trawl by entering the water from the towing
vessel and moving down the towing cables. Care must
be exercised to avoid jamming broken cable strands
into the diver's hand. This descent technique provides
a direct route to the net and expends a minimum of
energy and compressed air. Caution must be observed
as the divers approach the turbulent water behind the
otterboards, especially when the boards are in contact
with the bottom. Clouds of sediment stirred up by the
otterboard obscure portions of the bridles between the
otterboard and the net, so divers must feel their way
along the bridle. As an alternative, when horizontal
visibility is as much as 25 feet (7.6 m), experienced
divers may swim inboard of the otterboard just within
the path of the oncoming trawl and wait for the bridles
to clear the mud cloud or for the net to appear.
When this type of trawl diving is conducted, a safety
pickup boat is required. The boat is operated on a
parallel course adjacent to the estimated position of
the trawl and divers. At the termination of the dive, the
buddy team makes a normal ascent and is picked up by
the boat.
In the shallow waters available for fishing gear
research in the southeastern United States, a two-place
diver sled is used to transport divers to and from the
trawl. The dive sled, which is towed behind the vessel
towing the trawl, is positioned above and slightly behind
the trawl's headrope. The divers are transported in a
small support boat and are positioned well ahead of the
sled close to the downwind side of the sled towrope.
When the divers are ready to enter the water, the
support boat is turned away from the towrope, and the
motor is taken out of gear. Once the divers are in the
water and clear of the propeller, the support boat motor is
placed in gear, and the support boat moves to a position
slightly behind and to the downwind side of the sled.
The divers position themselves 20 to 30 feet (about 6 m)
apart along opposite sides of the towline. The pilot
takes the lead position facing the port side of the sled.
When the sled reaches the pilot, he or she grabs the
passing control surface or sled frame and trails back to
a parallel position with the sled. From this position, the
pilot slides aboard the sled and assumes a prone posi-
tion at the controls. The observer boards the sled in the
same manner but from the opposite side. When the
10-34
NOAA Diving Manual — October 1991
Diving Under Special Conditions
Figure 10-16
Support Ship, Trawl, Diver Sled,
and Support Boat
Adapted from Wickham and Watson (1976)
divers are positioned, the pilot releases the dive control
restraints and takes control of the sled. The divers
descend to the trawl and, depending on the size of the
trawl or the purpose of the dive, observe it from the
sled or land the sled on the trawl and tie it to the trawl
webbing (Figure 10-16). With the sled tied off, both
divers can leave the sled to conduct their work on the
trawl. At the end of the dive, the divers reboard the
sled, release the tie downs, and ascend to the surface.
The support boat then moves to the sled, and, on a
signal from the pilot, the motor is taken out of gear.
The divers kick free of the sled and swim over to board
the support boat.
When using a dive sled, divers must be particularly
careful to maintain proper breathing rhythms to pre-
vent an embolism from occurring if the dive sled rises
suddenly on a wave. The pilot should have a depth
gauge mounted so that it can be read easily at all times
and should continually monitor the gauge, maintaining a
constant depth or making any necessary depth changes
slowly. A dive sled also facilitates the use of a hardwire
communications system between divers and the sur-
October 1991 — NOAA Diving Manual
face, which increases the safety and efficiency of trawl
diving operations.
Divers making observations while hanging directly
onto the trawl can move to different parts of the trawl
by pulling themselves hand-over-hand. However, trawls
having a stretched mesh size of less than 2 inches
(about 5 cm) (i.e., each side of the aperture about
1 inch long) are difficult to hang onto and may necessi-
tate the use of hand-held hooks to enable the divers to
move about.
By using a separate towline for the divers, small
trawls and other moving gear can be observed without
direct contact, which might affect the system. A dive
sled can also be used for this purpose and, with the
addition of a current-deflecting shield, will provide
more protection for divers than is possible for divers
hanging directly onto the gear.
Trawl divers must be alert to possible dangers in the
bottom trawl's path. Some underwater obstructions
may cause the trawl to stop momentarily and then to
surge ahead with great force. Large objects may be
lifted and carried into or over the net. Turbulence
10-35
Section 10
behind the otterboards may lift sharp-spined animals
up off the bottom and into the path of the divers. If any
of the diver's extremities get ahead of the bottom
trawl, the diver is in imminent danger, because severe
injury would result from being pinned between parts of
the net and an obstruction.
Jellyfish present a hazard to trawl divers and can
seriously reduce their ability to function safely under
water. When jellyfish are abundant, it is impossible for
towed divers to avoid contact with them. The problem
increases when jellyfish are strained through the trawl's
webbing, which causes the divers to be showered with
hundreds of jellyfish pieces. To avoid being stung,
trawl divers must dress in full-length wet suits (1/8 in.
(0.3 cm) thick in warm water), hoods, gloves, boots,
and full-face masks whenever large numbers of jelly-
fish are in the vicinity.
In the event divers are carried into a trawl from
which they cannot readily extricate themselves, they
must cut an exit through the web. Since trawls usually
have heavier web in the aft portion (cod end), an escape
should be cut forward in the top of the trawl body and a
3 foot (0.9 m) long diagonal slit should be made in the
trawl. Another similar slit should be made at 90 degrees
to and beginning at the upstream end of the first slit.
The water current should then fold a triangular flap of
webbing back out of the way, leaving a triangular
escape hole. The diver's buddy should assist the trapped
diver through the opening to free any gear that snags
on meshes. Often an additional small single-blade knife is
carried in an accessible place such as the forearm.
WARNING
Divers Working Around Trawls Must Carry a
Sharp Knife Strapped to the Inside of the
Calf or Forearm to Prevent Its Catching on
the Web
Vessel course or speed changes normally pose no
hazard to working divers. Often, changing speed can
be used as a simple signal between divers and vessel
personnel. As speeds rise above 2.5 knots (1.3 m/s),
divers will have difficulty holding their mouthpieces
in and keeping their face masks on. At higher speeds
they may lose their grip and be forced off the net.
When stopped, the net settles slowly, becoming slack
gradually rather than suddenly. In this situation, the
divers should be cautious of a sudden start, which may
tangle them in a line or web. Divers working from a sea
sled adjacent to a trawl may be forced against the trawl
during a turn. Trawl divers should be well-trained so
that they will know where they are in relation to any
part of the trawl at all times, even when only a small
portion of the net is visible in turbid waters.
To determine gear efficiency, it is necessary to measure
trawls under tow. A number of measuring tools have
been adapted or designed specifically for measuring
trawls. The measuring tools selected to use when stud-
ying a trawl will depend on the size of the trawl and the
degree of accuracy required. An estimate of the dis-
tance between two points on a trawl can be made by
pulling low-stretch polypropylene twine taut between
the points and then cutting the line. The tied end will
remain with the trawl until retrieval, when the line can
be removed and measured. To measure more accurately
the horizontal spread of a trawl (the distance from
wing to wing across the mouth of a trawl), a 1/8 inch
(0.3 cm) in diameter stainless steel cable marked in
1 foot (0.3 m) increments is used. The cable is stretched
across the mouth of the trawl, with one end attached to
the first hanging on one wing and the other cable end
pulled through a small pulley attached to the first
hanging on the opposite wing. The cable is pulled taut
across the net by one diver, while the other diver records
the spread reading. The vertical opening (the distance
between the trawl headrope and footrope) on small
trawls is measured with a fiberglass measuring rod
marked in 6 inch (15.2 cm) increments. On larger
trawls, the vertical opening is measured with a cali-
brated depth gauge. Short distance measurements can
be made accurately with a fiberglass tape measure.
Trawl door measurements are made with an inclinometer
for door tilt and a door angle measuring device for door
angle of attack.
Equipment for Diving While Under Way. Special
attention must be given to diving equipment used dur-
ing dives on moving gear. Single-hose regulators with
large-diameter purge buttons occasionally free flow
when used during underway diving because of the strong
water current being exerted against the face of the
button.
Reserve valve pull rods are the single greatest source
of diver entanglement in webbing. K-valves in combi-
nation with submersible pressure gauges are generally
safer for use in trawl diving; however, if J-valves are
used, the following information is important. When a
pull rod is used, the pull-ring should be brazed shut or
taped to prevent webbing from slipping into the loop.
Submersible pressure gauges permit team members to
monitor each other's air supply and depart the net
while ample air reserve remains. The strap on the
pressure gauge hose should be fastened to a strap of the
backpack only. If the gauge is left dangling at the
diver's side, it may become caught in the net.
10-36
NOAA Diving Manual — October 1991
Diving Under Special Conditions
Adjustable straps on face masks and fins are an
occasional source of difficulty for trawl divers. The
loose ends of the fin straps should be on the inside of
the strap next to the ankle to prevent the flopping strap
or buckle from entangling in the net. Straps should be
adjusted until comfortable and then securely taped in
place to prevent pulling out.
Towed divers must have exposure suits with warmth
qualities superior to those necessary during regular
dives. Rapid movement through cold waters will quickly
chill divers, reducing their effectiveness and exposing
them to the dangers of hypothermia (see Section 3.4).
Variable-volume dry suits are excellent for use in water
temperatures below 60° F (16°C); however, additional
drag on a towed diver may preclude the use of these
suits when high mobility is desired.
Snorkels should not be attached to a towed diver's
mask. Generally, snorkels are omitted from the gear
complement because of their tendency to catch on
webbing. They are not normally needed because the
diver is on the surface only for a short period before
being picked up by a safety boat. Divers are advised to
carry signal flares under conditions where it may be
difficult for the boat to locate the diver after surfacing.
October 1991 — NOAA Diving Manual
10-37
4
<
Page
SECTION 11 11.0 General 11-1
POLLUTED- 11.1 Microbial Hazards 1 1-1
WATER 11.1.1 Health Effects of Exposure to Microbial Hazards 11-1
DIVING 11.1.2 Factors Affecting Microbial Pathogenicity 11-2
11.2 Chemical Hazards 1 1-2
11.3 Thermal Hazards 1 1-3
11.4 Equipment for Polluted-Water Diving 1 1-3
11.4.1 Self-Contained Underwater Breathing Apparatus 11-3
11.4.2 Surface-Supplied Diving Equipment 11-4
1 1.4.3 Polluted-Water Diving Procedures and Precautions 1 1-5
11.4.3.1 Decontamination Procedures 11-5
11.4.3.2 Medical Precautions 11-6
♦
i
POLLUTED-
WATER
DIVING
11.0 GENERAL
NOAA divers, commercial divers, and scientific divers
have all been called on in recent years to perform
working dives in waters contaminated by a variety of
pollutants, including pathogenic micro-organisms, toxic
chemicals, and nuclear reactor effluents. Research is
continuing on the specific hazards and effects on diver
safety and health of these occupational exposures and
on the development of equipment and methods of pro-
tecting divers from such hazards.
Because water pollution is so widespread, all divers
should be aware of the hazards of polluted-water div-
ing. They should also be familiar with the pre- and
post-dive procedures, equipment requirements, and
medical surveillance activities appropriate for polluted-
water diving.
11.1 MICROBIAL HAZARDS
Microbial pathogens — bacteria, viruses, parasites,
protozoa, fungi, and algae — may occur as part of the
natural environment or be introduced into the aquatic
environment through an external source, such as sew-
age or chemical wastes from industrial sources, com-
mercial ships, or agricultural run-off. These wastes
are often carried into the ocean by rivers and streams;
although contaminants are diluted by the ocean, they
can continue to have a powerful effect on water quality
and the diver's environment. In addition, pollutants
may "clump" together to form discrete and highly
toxic parcels of contaminated water. Divers may be
exposed to waters polluted by microbes in a variety of
occupational settings: when they clean or paint ship
hulls in polluted rivers or harbors, monitor ocean sew-
age dump sites, or perform scientific dives to observe
the behavior of marine life in lakes, rivers, or coastal
waters. NOAA divers are most likely to be exposed to
hazardous contaminants during dives near or on the
soft bottom sediments, which provide ideal environ-
ments for accumulating contaminants and encourag-
ing microbial growth (Phoel 1981).
11.1.1 Health Effects of Exposure to
Microbial Hazards
The number and kinds of pathogenic organisms that
may be present in polluted water are many. To date,
October 1991 — NOAA Diving Manual
the following organisms have been implicated as potential
hazards to the health of divers swimming in polluted
water: several bacterial species, including Vibrio,
Escherichia, Legionella, Actinomycetes, Aeromonas,
Salmonella, Shigella, Enterobacter, Klebsiella, Pseudo-
monas, and Staphylococcus; viruses; protozoa; molds;
fungi; algae; and parasites belonging to other families
(Colwell and Grimes 1983).
WARNING
Before Diving in Potentially Polluted Waters,
Divers Should Sample the Water for the Pre-
sence of Pathogens or Other Contaminants
or Obtain Such Information From Reliable
Sources
Divers working in waters contaminated or infested
with these organisms may be subject to a variety of
maladies, including:
• ear infections
• eye infections
• respiratory tract infections
• inflammation of the intestinal tract
• warts
• skin infections
• parasitic infections
• central nervous system effects
• systemic or pulmonary fungus infections.
Because the signs and symptoms of many of these
conditions do not manifest themselves for a period of
hours to weeks after the dive, it is often difficult to
associate the polluted-water exposure with the resulting
symptoms. Although personal hygiene and specific pre-
ventive measures can counteract some of these effects,
the surest methods of protecting divers operating in
microbially contaminated waters are to isolate them
completely from contact with these organisms and to
ensure that divers are adequately decontaminated after
completion of the dive. Section 11.4 describes pro-
tective equipment and procedures designed to achieve
these goals.
11-1
Section 1 1
Figure 11-1
Diver Working in Contaminated Water
11.1.2 Factors Affecting Microbial
Pathogenicity
Recent research efforts have identified several fac-
tors that affect the pathogenicity and virulence of the
microbes found in polluted water (Colwell 1982). Con-
centrations of heavy metals, such as those associated
with waste petroleum products, may reduce species
diversity in a manner that favors pathogenic species;
changes in water temperature or salinity may also have
similar effects. Altering the levels of certain nutrients
in the water may operate to select out non-pathogenic
species and thus permit pathogens to thrive. The abil-
ity of some organisms to stick or attach themselves to
surfaces, including a diver's skin and mucosa or his
equipment, makes them persistent threats. Seasonality
also affects the distribution of many species of microbes,
and divers are generally at greater risk of incurring
microbial infections during the summer months or when
diving in warm water.
11.2 CHEMICAL HAZARDS
As many as 15,000 chemical spills are estimated to
occur in U.S. waterways every year, and countless
other chemical-laden discharges take place regularly
as industrial and municipal facilities expel their wastes
into lakes, rivers, and coastal waters (McClellan 1982).
Divers operating in waters contaminated by chemi-
cals, many of which are toxic, have experienced upper
respiratory tract infections, difficulty in breathing,
skin reactions, nausea, burns, severe allergic reactions,
and tingling of the limbs. As in the case of microbial
hazards, it may be difficult to relate cause and effect.
Industrial chemicals commonly found in polluted
water include:
• phosphates
• chlorates
• peroxides
• acids
• solvents (benzene, xylene, toluene).
Petroleum and petroleum products are the most com-
mon chemical hazards encountered by divers, because
these substances are frequently spilled in incidents
involving commercial vessels or in other marine acci-
dents, such as oilwell blowouts and spills from storage
facilities. Divers may be called on to help with spill
cleanup and must wear carefully selected gear during
such operations because oil destroys neoprene and rubber
(Figure 11-1). In addition, the solvents and other chemi-
cal substances used to clean up spills permeate many
types of protective clothing and can cause either grad-
ual or catastrophic deterioration of other materials. It
Photo: Steven M. Barsky, Courtesy Diving Systems International
is important not to wear the same equipment in succes-
sive dives involving incompatible chemicals, because
diving equipment may absorb enough of the first chemi-
cal or chemicals to cause a reaction on subsequent
contact with an incompatible substance.
Chemical and petroleum-product spills occur as a
result of vessel collisions and groundings, oilwell blow-
outs, major storage facility releases, and illegal dumping
of toxic or hazardous wastes. The Environmental Pro-
tection Agency (EPA), the U.S. Coast Guard, and
NOAA all have important roles to play in emergency
response and environmental assessment.
The steps involved in protecting the health and safety
of divers and other personnel (and the health of the
public and the environment) responding to a spill emer-
gency include:
• identifying the hazardous substance(s) present
• evaluating the hazard associated with these
substances
• ameliorating the effects of the release.
Field samplers are used to take grab samples of the
contaminated water as close to the source of the con-
11-2
NOAA Diving Manual — October 1991
Polluted-Water Diving
tamination as possible. On-site portable "laboratories"
can often be used to analyze these samples. Results of
sampling are useful in selecting the appropriate level
of protective equipment and clothing needed by response
personnel, measuring the extent of the potential envi-
ronmental impact of the spill, and determining the
necessary cleanup procedures.
11.3 THERMAL HAZARDS
Overheating of the diver, or hyperthermia, may be a
critical factor for divers working in tropical waters or
in the heated environment typical of cooling water
outfalls or nuclear reactor pools. The temperature of
the water in the cooling pools surrounding nuclear
reactors and in the canals at facilities that generate
nuclear power may reach H0-l20°F (43~49°C). Divers
performing maintenance and repair tasks in these
superheated waters must be specially trained in safety
and emergency procedures and be protected from
hyperthermic stress; in addition, since biological sam-
pling has shown that pathogenic organisms are often
present in these waters, divers must also be isolated
from microbial hazards.
Overheating can become acute even when divers are
working in polluted-water environments at moderate
temperatures (82 °F or 28 °C), because the divers are
in effect encapsulated in their diving suits. In addition,
the need to remain suited-up during the often-lengthy
decontamination period after a polluted-water dive
adds to the overheating problem, because divers' body
temperatures will continue to rise throughout this post-
dive period (Wells 1986).
The threat posed by hyperthermia is increased by
the fact that divers are generally unaware of the extent
of their own overheating. For example, many divers do
not exhibit the signs or symptoms of hyperthermia
until after their core temperatures have risen to a level
that is considered medically unsafe. Thermal monitoring
is thus highly recommended for divers working in warm
polluted waters.
11.4 EQUIPMENT FOR POLLUTED-
WATER DIVING
Divers who must dive or work in contaminated waters
should choose their equipment with a view toward
maximum protection. When selecting equipment, divers
must consider such factors as the degree and extent of
the contamination, the duration of the exposure, and
the type of contamination they will be dealing with —
biological, chemical, or thermal. Other factors to be
considered when selecting equipment include the geo-
graphic area in which the dive will take place, the
October 1991 — NOAA Diving Manual
space available for set-up operations, and the cost-
effectiveness of various types of equipment. This latter
consideration may be particularly important if the
contaminated equipment will have to be disposed of
after use.
11.4.1 Self-Contained Underwater
Breathing Apparatus
Standard scuba gear offers inadequate protection to
divers operating in contaminated water environments.
When scuba is used, the diver's mouth is directly exposed
to the water, and the process of inhalation introduces
droplets of water into a diver's respiratory tract. Scuba
divers who are wearing a dry suit and full-face mask
mated to a second-stage regulator can be exposed via
inhalation, ingestion, and skin contact (at the neck,
hands, etc.). Thus, even hybrid scuba equipment
arrangements often provide grossly inadequate protec-
tion. However, an extended series of tests performed
by NOAA has succeeded in identifying a suit-and-
mask system that can be used by scuba divers required
to dive in biologically (and in some cases chemically)
contaminated waters. NOAA considers this scuba system
the best protection currently available, but research to
identify and develop a better system continues.
The recommended system consists of a "smooth-skin"
dry suit with an attached hood and boots. Because
neoprene material acts as a sponge and degrades when
in contact with chemicals, suits of this substance can-
not be used in contaminated water. The seams of the
suit selected should be sealed by vulcanization or a
similar procedure. The number of openings in the suit
should be minimized to reduce the number of potential
failure points. Requiring boots to be attached to the
suit permits the number of openings to be reduced to 3
or 4, depending on whether or not the suit is of the
neck-entry or shoulder-entry type. Because many neck-
entry suits are not compatible with the types of helmet
appropriate in this kind of diving, most polluted-water
suits will be of the shoulder-entry type. The gloves and
helmet should be attached to the suit via positive locking
mechanisms, and heavy-duty zippers should be used
for the shoulder opening. Because gloves are the weakest
point in the suit systems used in polluted-water diving,
they should be selected carefully, with consideration
given to compatibility of material with the chemicals
encountered and resistance of the glove material to
puncture and stress. The boots chosen for the scuba
suit system should be made of a thick, smooth material
that is resistant to abrasion and punctures, have a
nonslip sole, and be designed to accommodate fins
(Pegnato 1986).
11-3
Section 1 1
Figure 11-2
Diver in Dry Suit
The suit must be inflatable either by means of the
diver's air tanks or a pony bottle. The suit must also
have a diver-controllable exhaust valve to keep water
out of the suit. The hood must have an installed relief
valve that automatically vents any air that accumu-
lates in the hood, and the skirt surrounding the face
must have a smooth outer surface. Figure 11-2 shows a
diver wearing a Viking dry suit, with a Draeger hood
attached via a neck ring.
The mask to be used with this suit system must be
internally pressurized to prevent the inward leaking of
the contaminated water. Such a mask offers polluted-
water divers a considerable increase in protection over
other masks, because it provides full face coverage,
separate air intake and exhaust ports, and a positive
interior pressure that seats and seals the mask skirt
against the diver's hood (Pegnato 1986). The mask can
be coupled with any top-rated standard first-stage
regulator; the regulator's secondary output pressure
must be freeze-protected and provide an intermediate
pressure that is compatible with the second stage. Before
attempting a dive in polluted water with this system,
divers should make a test dive in clean water to ensure
that the diver remains completely dry. Because many
of these systems use more air than the standard scuba
system, predive planning must take this need for addi-
tional air into account (Pegnato 1986).
WARNING
Divers Operating on Compressed Air Near
Spill Sites Should Use Bottled Air Compressed
in a Clean Atmosphere To Avoid the Danger
Of Contaminated Compressor Air
11.4.2 Surface-Supplied Diving Equipment
To achieve the degree of protection necessary for
surface-supplied diving in polluted water, several mod-
ifications to existing surface-supported diving systems
are necessary. For example, a series exhaust valve
(SEV) that consists of two exhaust valves aligned in
series has been designed to overcome the problem of
"splashback" through the exhaust valve of a demand
regulator. Several commercially available helmets and
masks now incorporate this NOAA-designed SEV
feature.
The "suit-under-suit" (SUS) concept was developed
by NOAA, in conjunction with the Environmental Pro-
tection Agency, the Coast Guard, and the Department
of Energy, to solve two of the most significant prob-
lems of polluted-water diving: thermoregulation and
suit leakage. The SUS has two layers: a thin, foam,
11-4
Photo: NOAA Diving Program
neck-entry inner dry suit layer with attached booties,
and an outer layer that consists of a dry suit with ankle
exhaust valves. An adjustable-pressure, arm-mounted
exhaust valve is worn over the inner suit, and a "neck
dam" installed in the outer suit is clamped to the
entrance yoke of the inner suit and thus creates a
closed cavity between the two suits. Figure 11-3 shows
a drawing of the SUS.
Clean water is pumped into the cavity between the
two layers of the SUS; the water can be hot or cold,
depending on whether the diver will need cooling or
heating during the dive. The working temperature
range for the SUS appears to be from 30 to 130°F
(-1.1 to 54.4 °C), allowing divers to perform rescues in
freezing waters or to work in the cooling pools of nuclear
power facilities. Since the entire volume of the SUS is
filled with water under a pressure slightly greater than
the pressure of the ambient water, any leak in the suit
will result in clean water from the suit leaking out into
the polluted water, rather than polluted water entering
NOAA Diving Manual — October 1991
Polluted-Water Diving
Figure 11-3
NOAA-Developed Suit-Under-Suit (SUS) System
Figure 11-4
Dressing a Diver for Contaminated-Water Diving
Drager ankle
exhaust valve
Photo: NOAA Diving Program
the suit. The SUS thus provides protection against
microbial, thermal, petrochemical, and chemical div-
ing hazards (Pegnato 1986).
Another system that is appropriate for polluted-water
diving is the traditional hard-hat diving rig, consisting
of built-in or attachable gloves and a suit mated to a
breastplate or to a breach ring mated to the helmet.
The entire hard-hat unit is waterproof and provides
complete protection unless the suit develops a tear or
leak.
11.4.3 Polluted-Water Diving Procedures
and Precautions
Divers required to work in polluted waters must
rigorously observe a series of procedures designed to
provide maximum protection of the diver and the sup-
port crew. In addition to the careful selection of suits
and helmets, divers and support crew members must
be specially trained in the hazards of polluted-water
diving. Figure ll -4 shows NOAA support personnel
preparing a diver for a polluted-water dive. Careful
records must also be maintained of the types of con-
taminants divers are exposed to, e.g., names of chemi-
cals, types of pathogens, etc. Equipment used in con-
taminated water must be maintained, repaired, and
October 1991 — NOAA Diving Manual
Photo: Steven M. Barsky, Courtesy Diving Systems International
replaced more frequently than equipment used in
unpolluted environments.
11.4.3.1 Decontamination Procedures
Both divers and tenders must go through a de-
contamination process after completing a dive in con-
taminated water, because evidence shows that divers
infected with microbes can contaminate their suits and
thus spread infection or reinfect themselves unless the
suit is adequately decontaminated. Suits badly con-
taminated with radiation from reactor pool diving must
be discarded and disposed of properly. Figure ll-5
shows a polluted-water decontamination team decon-
taminating a diver after a polluted-water dive. Team
members are wearing decontamination protective equip-
ment, and the diver is wearing a MK.12 helmet and
polluted-water diving suit. After each dive, the diver
is sprayed with a high-pressure sprayer; three separate
spraying solutions are often used. The first involves a
11-5
Section 1 1
Figure 11-5
Decontamination Team at Work
Source: NOAA Diving Program
neutralizing agent or disinfectant appropriate for the
particular contaminant, the second consists of a deter-
gent washdown, and the third and final spray is a
fresh-water rinse. If contamination is severe, heavy-
duty brushes can be used to scrub the zippers, helmet
locking mechanism, boots, boot soles, and seams of the
suit system. The entire decontamination process should
be as thorough as possible, but it is important to remem-
ber that time is important because the diver remains
effectively encapsulated throughout the procedure and is
thus subject to hyperthermia (Wells 1986).
11.4.3.2 Medical Precautions
Divers who work in polluted waters should be given
baseline and annual physical examinations. Physicians
administering these examinations should pay particu-
lar attention to the respiratory and gastrointestinal
systems and to the ears and skin. Any polluted-water
diving guidelines recommended by NOAA, the Envi-
ronmental Protection Agency, the National Institute
for Occupational Safety and Health, or the Occupa-
tional Safety and Health Administration should be
observed. Individuals with open cuts should not dive in
microbially polluted waters. In addition, divers must
maintain current immunizations for diphtheria, teta-
nus, smallpox, and typhoid fever, and they should clean
their ears carefully with otic solution immediately after
any dive in polluted water. This ear-cleaning proce-
dure has proven to be dramatically effective in reduc-
ing the incidence of otitis externa associated with
polluted-water diving.
11-6
NOAA Diving Manual — October 1991
SECTION 12
HAZARDOUS
AQUATIC
ANIMALS
12.0
12.1
12.2
12.3
12.4
12.5
Page
General 12-1
Animals That Abrade, Lacerate, or Puncture 12-1
Animals That Sting — Venomous Marine Animals 12-1
12.2.1 Hydroids, Jellyfishes, Sea Anemones, and Corals 12-1
12.2.2 Marine Worms 12-3
12.2.3 Cone Shells 12-4
12.2.4 Octopuses 12-5
12.2.5 Sea Urchins 12-5
12.2.6 Fishes 12-5
12.2.7 Reptiles 12-7
Animals That Bite 12-8
12.3.1 Fishes 12-8
12.3.2 Reptiles 12-10
12.3.3 Aquatic Mammals 12-1 1
Animals That Shock 12-1 1
Animals Poisonous to Eat 12-1 1
4
(
HAZARDOUS
AQUATIC
ANIMALS
12.0 GENERAL
Many aquatic animals are potentially hazardous to
divers. Although only a few present serious physical
threats, the damage inflicted by others can seriously
impair a diver's effectiveness. The material that fol-
lows discusses some of these animals. For convenience,
hazardous aquatic animals have been classified as:
• those that abrade, lacerate, or puncture
• those that sting
• those that bite
• those that shock
• those that are poisonous to eat.
This classification has limitations: the categories overlap,
and, although most hazardous species fall neatly into
one or another, some of the classifications are arbitrary.
For a discussion of the treatment of injuries inflicted
by hazardous aquatic organisms, see Section 18.
12.1 ANIMALS THAT ABRADE,
LACERATE, OR PUNCTURE
The bodies of many aquatic animals are enclosed in
sharp, pointed, or abrasive armor that can wound the
exposed areas of a diver's body that come into forceful
contact with these creatures. Included in this group of
animals are such forms as mussels, barnacles, sea urchins,
and stony corals (Figure 12-1). The wounding effect of
contact between these animals and humans is intensi-
fied in aquatic habitats because human skin is softened by
water. Although single encounters of this sort are unlikely
to produce serious injury, repeated encounters during
extended diving operations can produce multiple inju-
ries that may become problems. Wounds continuously
exposed to water resist healing, and careless divers
may in time be incapacitated by an accumulation of
ulcerated sores. Wounds are especially likely to be aggra-
vated when working in the tropics. To compound the
problem, secondary infections in such wounds are not
uncommon. Thus, long-term diving projects can be
crippled if participants fail to avoid these injuries,
minor though they may initially seem.
12.2 ANIMALS THAT STING— VENOMOUS
MARINE ANIMALS
A diverse array of otherwise unrelated animals is con-
sidered together in this section because their ability to
October 1991 — NOAA Diving Manual
Figure 12-1
Sea Urchin Echinothrix diadema on a Hawaiian Reef
Photo Tony Chess
inject venom into other organisms poses a threat to
divers in the water. The instrument of injection varies
from the stinging cells of the coelenterates (hydroids,
corals, anemones, and jellyfishes) to the spines on the
bodies of crown-of-thorns starfish, sea urchins and
fishes, radular teeth of cone shells, beaks of octopuses,
bristles of annelid worms, and the fangs of snakes.
Mere contact with the surface of some sponges can
produce a severe dermatitis. The toxicity of the venom,
as well as the amount of venom introduced, varies from
one species to another and sometimes among individu-
als of the same species. Furthermore, humans may
differ in their sensitivity to a given venom. The reac-
tions of humans to marine animal stings may range
from no noticeable reaction to mild irritation to sud-
den death. It is wise to become informed about and to
avoid all marine organisms known to be venomous;
occasional contact is inevitable, however, for even the
most experienced divers.
12.2.1 Hydroids, Jellyfishes, Sea
Anemones, and Corals
Grouped here are a variety of organisms that drift or
swim slowly at the water's surface or at mid-depths.
12-1
Section 12
Figure 12-2
Stinging Hydroid
They have gelatinous, semi-transparent, and often bell-
shaped bodies from which trail tentacles armed with
stinging cells, called nematocysts. In large specimens,
these stinging tentacles may trail down as much as
100 feet into the water.
Nematocysts are characteristic of a large group of
related, though superficially very diverse, marine ani-
mals known as coelenterates. In addition to the jelly-
fishes, the coelenterates also include the hydroids and
stinging corals, considered below. Different coelenterates
have different types of nematocysts, but all function
similarly. When the animal is disturbed, the nemato-
cyst forcefully discharges a venomous thread that, in
some species, can penetrate human skin. The reactions
of humans to the stings of hazardous coelenterates
range from mild irritation to death.
Stinging hydroids occur on many reefs in tropical
and temperate-zone seas. Typically, they are featherlike
colonies of coelenterates (Figure 12-2) armed, like
jellyfish, with nematocysts. Because colonies of these
animals may be inconspicuous (they are often only a
few inches high), they may go unnoticed. Except to the
occasional person who is hypersensitive to their stings,
hydroids generally are more of a nuisance than a haz-
ard. Divers are most likely to be affected on the more
sensitive parts of their bodies, such as the inner sur-
faces of their arms. Although clothing protects most of
the body from the stings of hydroids, it will not protect
against stings on the hands and face.
Stinging corals (Figure 12-3), often called fire coral,
belong to a group of colonial coelenterates known as
millepores. They are widespread on tropical reefs among
the more familiar stony corals, which they superfi-
cially resemble. Contact with the nematocysts of mil-
lepores affects humans in about the same way as con-
tact with the nematocysts of stinging hydroids. Common
Florida and Bahama species have a characteristic tan-
colored blade-type growth, with lighter (almost white)
upper portions. Millepora may appear in the bladed or
encrusting form over rock surfaces or on the branches
of soft corals such as alcyonarians. The Millepora zone
of the outer Florida Keys ranges from 10 to 25 feet
deep.
Portuguese Men-o-War (Figure 12-4), which are
grouped together in the genus Physalia, are colonial
hydroids known as siphonophores. Siphonophores dif-
fer from the other forms considered here as jellyfish in
that each organism is actually a colony of diverse
individuals, each performing for the entire colony a
specialized function such as swimming or capturing
prey. A gelatinous, gas-filled float, which may be
6 inches or more in diameter, buoys the man-o-war at
the surface, and from this float trail tentacles as long
Photo Tony Chess
Figure 12-3
Stinging or Fire Coral
Photo Morgan Wells
as 30 feet that bristle with nematocysts. Man-o-war
stings can be dangerous to humans, so divers should
stay well clear of these animals. Unfortunately, even
the most careful diver can become entangled in a man-
o-war tentacle, because these nearly transparent struc-
tures trail so far below the more visible float. It is
i
12-2
NOAA Diving Manual — October 1991
Hazardous Aquatic Animals
Figure 12-4
Portuguese Man-of-War
Figure 12-5
Large Jellyfish of Genus Cyanea
Photo Morgan Wells
especially difficult to detect fragments of tentacles
that have been torn from the colony and are drifting
free. The nematocysts on these essentially invisible
fragments can be as potent as those on an intact organ-
ism, and chances are good that divers who repeatedly
enter tropical waters will sooner or later be stung by
one.
More properly regarded as jellyfish are a group of
coelenterates known as scyphozoans, each individual
of which is an independent animal. These include the
common jellyfishes encountered by divers in all oceans.
Although many can sting, relatively few are dangerous.
One large jellyfish of the genus Cyanea (Figure 12-5)
is often encountered by divers in temperate coastal
waters of both the Atlantic and Pacific oceans. Divers
should be aware that there is a chance of being stung
even after they leave the water, because segments of
the tentacles of these animals may adhere to the diver's
October 1991 — NOAA Diving Manual
Photo Tony Chess
gloves, and touching the glove to bare skin, especially
on the face, will produce a sting as painful as any
received from the intact animal.
The most dangerous of the jellyfish belongs to a
tropical subgroup of scyphozoans known as cubomedusae.
or sea wasps. Sea wasps have an extremely virulent
sting; one species in the southwest Pacific has caused
death in humans. Fortunately, the more dangerous sea
wasps are rarely encountered by divers.
Sea anemones of various species are capable of
inflicting painful stings with their nematocysts. These
animals frequently look like beautiful flowers, which
may deceive people into touching them. The Hell's
Fire sea anemone (Actinodendron), which is found in
the Indo-Pacific region, is an example of such an
anemone.
True corals are capable of inflicting serious wounds
with their razor-sharp calcarious outer skeletons. Coral
cuts are one of the most common hazards facing divers
in tropical waters, and contact with corals should be
carefully avoided. Divers should be equipped with leather
gloves and be fully clothed when working among cor-
als, because coral cuts, if not promptly and properly
treated, can lead to serious skin infections.
12.2.2 Marine Worms
Marine worms that can be troublesome to divers are
classified in a group known as polychaetes. Two types
12-3
Section 12
Figure 12-6
Bristleworm
Figure 12-7
Cone Shell
Photo Richard Rosenthall
reportedly inflict venomous wounds: bristle worms and
blood worms.
Bristle worms (Figure 12-6), which divers often
encounter when overturning rocks, have tufts of sharp
bristles along their segmented bodies that, in many
species, can be extended when the animal is irritated.
It has not been established that these bristles are ven-
omous, but there is evidence for at least some species
that this is so.
Blood worms burrow in mud or sand and some spe-
cies can be a problem to divers who handle them. Their
jaws contain venomous fangs, and their bite is compa-
rable to a bee sting.
12.2.3 Cone Shells
Of the many diverse kinds of shelled mollusks in the
sea, only some of the tropical cone shells are hazardous
to divers (Figures 12-7 and 12-8). Cone shells, char-
acterized by their conical shape, are an especially attrac-
tive hazard because collectors are drawn to the color-
ful shells of the most dangerous species. There are
more than 400 kinds of cone shells, each with a highly
developed venom apparatus used to stun the small
animals that are its prey. The weapon of cone shells is
thus an offensive rather than defensive one, a fact that
helps to reduce the number of times people handling
these shells are stung. Although only a relatively few
Source: NOAA (1979)
of the cone shells are dangerous to divers, the stings of
some can reportedly be deadly. Because cone shells
inject their venom with a harpoonlike structure located at
the narrow end of their shells, persons handling these
animals should grasp them at the wide end.
i
12-4
NOAA Diving Manual — October 1991
Hazardous Aquatic Animals
Figure 12-8
Anatomy of a Cone Shell
Figure 12-9
Rare Australian Blue-Ring Octopus
Rodular Sheath
Radular
'Teeth
Proboscis
Tentacles Foot
Venom Dl
Venom
Bulb
Photo Bruce W. Halstead
12.2.4 Octopuses
Octopuses are timid creatures that will take any
opportunity to retreat from divers. Some species, how-
ever, can be hazardous to divers who attempt to handle
them. When an octopus bites into prey with its parrotlike
beak, venom enters the wound and subdues the prey.
This venom normally is not toxic to humans, however.
Although there have been relatively few cases of octo-
pus bites in humans, one diver in Australia who allowed a
rare blue-ring octopus to crawl over his bare skin was
bitten on the neck and died within 2 hours. Because the
bite of this species can be lethal, the Australian blue-
ring octopus (Figure 12-9) should be carefully handled.
12.2.5 Sea Urchins
Among the more troublesome animals for divers
working near tropical reefs are venomous sea urchins.
This is especially true after dark, when visibility is
reduced and many of the noxious sea urchins are more
exposed than in daylight. Sea urchins may also be a
problem in temperate waters, but the species in these
regions lack the venom of the tropical species and
therefore present a puncture rather than poisoning
hazard.
Most difficulties with venomous sea urchins result
from accidental contact with certain long-spined spe-
cies. The smaller secondary spines that lie among the
larger primary spines do the most damage; apart from
Photo Bruce W. Halstead
their venom, these spines invariably break off in the
wound and, being brittle, frequently cannot be completely
removed. Gloves and protective clothing afford some
protection against minor brushes with these animals
but do not help much when a diver strikes forcefully
against them. To avoid painful injury when working
close to venomous sea urchins, divers should avoid
contact.
Some of the short-spined tropical urchins are reported
to be hazardous because they have tiny pincerlike organs,
called pedicellariae, that occur among their spines.
Although some pedicellariae contain a potent venom,
they are very small structures that probably do not
threaten divers who incidentally come into contact
with the urchins that carry them. When wearing gloves,
one can handle these urchins without concern for their
pedicellariae.
12.2.6 Fishes
Many fishes inflict venomous wounds. Most do so
with their fin spines, but some wound with the spines
located on their heads or elsewhere on their bodies.
Generally these fishes injure only divers who deliber-
ately handle or provoke them; however, some wound
divers who unintentionally touch them or come too
close.
Stingrays. Stingrays carry one or more spikelike
spines near the base of their flexible tails, which they
can use effectively against those who come in contact
with them. Although these spines can inflict venomous
puncture wounds similar to those of the fishes discussed
above, they more often inflict a slashing laceration.
Humans are most threatened when they are wading on
sandy bottom in shallow water or swimming close to
the bottom. Walking with a shuffling motion tends to
frighten stingrays away. Stingrays are responsible for
October 1991 — NOAA Diving Manual
12-5
Section 12
Figure 12-10
Dasyatid Stingray
more fish stings than any other group of fishes. Species
of the family Dasyatidae present the greatest danger,
combining as they do large size, the habit of lying
immobile on the seafloor covered with sand, and a
large spine that is carried relatively far back (com-
pared to those of other stingrays) on a whiplike tail
(Figure 12-10). Large rays of this type can drive their
spines through the planks of a small boat or through a
human arm or leg. Swimmers coming into contact with
the bottom have been mortally wounded when struck
in the abdomen by a dasyatid stingray lying unseen in
the sand.
The urolophid, or round, stingrays have a short mus-
cular caudal appendage to which the sting is attached;
they are thus able to deliver severe stings with a whip
of their tail. Many of the most common stingray
envenomations are caused by round stingrays.
Less dangerous are stingrays of the family My-
liobatidae, which includes the bat rays and eagle rays
(Figure 12-11), even though these animals can be large
and have long venomous spines on their tails. The
spines of these species are at the bases of their tails
rather than farther back and so are far less effective
weapons than the spines of the dasyatid or urolophid
rays. The myliobatid rays are also less cryptic than the
dasyatids or urolophids: rather than lying immobile on
the bottom most of the time, they more often swim
through the midwaters, their greatly expanded pecto-
ral fins flapping gracefully like the wings of a large
bird. When on the seafloor, myliobatid rays usually
root actively in the sand for their shelled prey, and thus
are readily seen.
Scorpionfishes. Scorpionfishes are among the most
widespread and numerous family of venomous fishes.
The family, which numbers several hundred near-shore
species, has representatives in all of the world's seas,
but the most dangerous forms occur in the tropics.
Scorpionfishes usually inject their venom with their
dorsal fin spines and less often do so with the spines of
their anal and pelvic fins.
Many scorpionfishes are sedentary creatures that lie
immobile and unseen on the seafloor. An example is
the sculpin, a common near-shore scorpionfish species
of southern California. Another example, the stone-
fish, is common in the shallow, tropical waters of the
western Pacific and Indian Oceans; this species has the
most potent sting of all scorpionfishes and has caused
deaths among humans. Although stonefish are not
aggressive toward divers, their camouflage makes it
easy to step on them unless special care is taken.
In contrast to the cryptic sculpin and stonefish, another
group of scorpionfishes, the brilliantly hued lionfishes
12-6
Photo Morgan Wells
Figure 12-11
Myliobatid Stingray
Photo Edmund Hobson
i
NOAA Diving Manual — October 1991
Hazardous Aquatic Animals
Figure 12-12
Lionfish
Figure 12-13
Surgeonfish
Photo Al Giddings
(Figure 12-12), stand out strikingly against their sur-
roundings. Because lionfishes are beautiful animals
that make little effort to avoid humans, inexperienced
divers may be tempted to grasp hold of one. This could
prove a painful mistake, because lionfish venom is
especially potent.
Other fishes similarly armed with venomous fin-spines
include: the spiny dogfish, family Squalidae; weever
fishes, family Trachinidae: toadfishes, family Batrac-
hoididae; stargazers, family Uranoscopidae; freshwa-
ter and marine catfishes, family Ariidae; rabbitfishes,
family Siganidae; and surgeonfishes. family Acanthur-
idae. These fishes do not usually generate sufficient
force to drive their venom apparatus into their victims;
instead, the force is supplied by the victims themselves,
who handle or otherwise come into contact with these
fishes. A number of fishes, however, do actively thrust
their venom apparatus into their victims, an action
that often produces a deep laceration; fishes of this
type are discussed next.
Surgeonfishes. As noted above, some surgeonfishes
(Figure 12-13) can inflict venomous puncture wounds
with their fin spines; these wounds are much like those
produced by scorpionfishes and other similarly armed
fishes. Many surgeonfishes can also inflict deep lacer-
ations with knifelike spines they carry on either side of
October 1991 — NO A A Diving Manual
Photo Edmund Hobson
their bodies, just forward of their tails. Although not
conclusive, there is evidence that these spines are ven-
omous in at least some species. The more dangerous
surgeonfishes, which belong to the genus Acanthurus,
usually carry these spines flat against their bodies in
integumentary sheaths; however, when threatened, these
fish erect these spines at right angles to their bodies
and attack their adversaries with quick, lashing move-
ments of their tails. Divers injured by surgeonfishes
have usually been hurt while trying to spear or other-
wise molest them.
12.2.7 Reptiles
Venomous snakes are a more widespread hazard in
fresh water than in the sea. The cottonmouth water
snake, which has an aquatic bite known to have been
fatal to humans, may be the most dangerous animal
hazard that divers face in fresh water. This species,
which is difficult to identify because of its highly
variable coloration, does not show the fear of humans
that is characteristic of most aquatic snakes. In regions
inhabited by the cottonmouth, divers should avoid any
snake that does not retreat from them. The best defense is
a noiseless, deliberate retreat. Wet suits afford reason-
ably good protection but can be penetrated by the
teeth of larger specimens. The diver should not attempt
to strike back, since this practice may result in multiple
bites. Although the evidence is not conclusive, the
snake is believed not to dive deeper than about 6 feet.
Another species to avoid is the timber rattlesnake, an
excellent swimmer at the surface. Venomous sea snakes
occur only in tropical regions of the Pacific and Indian
12-7
Section 12
Figure 12-14
Sea Snake
oceans. These reptiles have a highly virulent venom,
but fortunately for divers they generally do not bite
humans unless roughly handled. Sometimes a sea snake
that is caught amid a netload of fishes will bite a
fisherman, but generally they are not aggressive toward
divers who meet them under water. Sea snakes are
especially numerous in the waters near the East Indies.
Sea snakes are the most numerous of all reptiles and
are sometimes seen in large numbers in the open ocean.
Divers most often see them amid rocks and coral, where
they prey on small fishes (Figure 12-14). They are
agile underwater swimmers, and divers should not lose
respect for their deadly bite simply because they are
reportedly docile.
12.3 ANIMALS THAT BITE
Serious injuries caused by the bites of non-venomous
marine animals are rare. However, the possibility of
such injury is psychologically threatening, partly because
this hazard has been so widely publicized that many
divers are distracted by it. It is important that working
divers view this hazard realistically.
12.3.1 Fishes
Sharks have been given more sensational publicity
as a threat to divers than any other animal, even though
shark bites are among the most infrequent of all inju-
ries that divers sustain in the sea. This notoriety is
understandable; injuries from shark bites generally
are massive and are sometimes fatal. Nevertheless,
only a very few of the many species of sharks in the sea
threaten humans.
The vast majority of sharks are inoffensive animals
that threaten only small creatures like crabs and shell-
fish. However, some sharks that are usually inoffen-
sive will bite divers who are molesting them; included
here are such common forms as nurse sharks (family
Orectolobidae) and swell sharks (family Scyliorhinidae).
These animals appear docile largely because they are
so sluggish, but large specimens can seriously injure a
diver. Although any large animal with sharp teeth
should be left alone, the sharks discussed below may
initiate unprovoked attacks on divers.
Most sharks known to attack humans without apparent
provocation belong to one of four families: the Car-
charhinidae, which include the gray shark, white-tip
shark, blue shark, and tiger shark; the Carchariidae,
which include the sand shark (including the species
called grey nurse shark in Australia, not to be confused
with the animals called nurse sharks in American waters);
the Lamnidae, which include the mako shark and great
Photo John Sneed
Figure 12-15
Great White Shark
Photo Ron and Valerie Taylor
white shark (Figure 12-15); and the Sphyrnidae, which
include the hammerheads. All of these are relatively
large, active animals whose feeding apparatus and
behavior give them the potential to injure divers seri-
ously. Except for the hammerheads, whose name well
characterizes their appearance, these sharks all look
much alike to the untrained eye. The characteristics
distinguishing them would certainly not impress most
divers encountering them under water.
I
12-8
NOAA Diving Manual — October 1991
Hazardous Aquatic Animals
Figure 12-16
Gray Reef Shark
Photo Edmund Hobson
The great white shark is reputed to be the most dan-
gerous of all sharks. This shark is credited with more
attacks on humans than any other shark species. It
attains a length of 20 feet or more.
The gray reef shark (Figure 12-16), numerous on
tropical Pacific reefs, is typical of these potentially
dangerous species. These sharks have repeatedly been
incriminated in human attacks. Any creature over about
3 feet long that generally resembles this animal should
be regarded cautiously, and if over about 8 feet long, it
should be avoided — even if this requires the diver to
leave the water. Sharks of these species that range
between 3 and 7 feet in length are numerous in shallow
tropical waters, and diving operations often cannot be
performed unless the presence of sharks in the area is
tolerated. When such sharks are in the vicinity, divers
should avoid making sudden or erratic movements.
Common sense dictates that no injured or distressed
animals should be in the water, because these are known
to precipitate shark attacks. When operations are
conducted in the presence of sharks, each group of
divers should include one person who keeps the sharks
in view and is alert for changes in their behavior. The
chances of trouble are minimal as long as the sharks
swim slowly and move naturally. However, the situa-
tion becomes dangerous as soon as the sharks assume
unnatural postures, such as pointing their pectoral fins
downward, arching their backs, and elevating their
heads. The moment sharks show such behavior, divers
should leave the water. Gray reef sharks are sometimes
encountered in large numbers, and when in large groups
they may become very aggressive if food is in the
water.
Moray eels (Figure 12-17) are a potential hazard on
tropical reefs, and a few species occur in the warmer
temperate regions of California and Europe. They are
secretive animals, with body forms highly specialized
for life within reef crevices; they are only rarely exposed
on the reef top. Although relatively few grow large
enough to threaten divers seriously, some attain a size
greater than 5 feet. The moray's powerful jaws, with
long needlelike teeth, can grievously wound humans.
Divers injured by morays have usually been bitten
when they are reaching into a reef crevice for some
object; they were struck by a moray that probably felt
threatened or perhaps mistook the diver's hand for
prey. The moray will usually release its grip when it
recognizes that it has taken hold of something unfamiliar.
and if divers can resist the impulse to pull free, they
may escape with no more than a series of puncture
wounds. But such presence of mind is rare in such a
situation, and divers often receive severe lacerations
when wrenching their hands from between the backward-
pointing teeth of the eel.
October 1991 — NOAA Diving Manual
12-9
Section 12
Figure 12-17
Moray Eel
Photo Edmund Hobson
Barracudas (Figure 12-18) are potentially danger-
ous fishes that occur widely in the coastal waters of
tropical and subtropical seas. Often exceeding 4 feet in
length and with long canine teeth in a large mouth,
these fishes have the size and equipment to injure
humans severely. Large barracuda often follow divers
about, apparently to get a good look at the divers; it is
important to remember that even the smallest diver is
much larger than anything the barracuda is accustomed
to eating. The barracuda's teeth are adapted for seiz-
ing the fish that are its prey; however, these teeth are
ill-suited to tearing pieces from an animal as large as a
human. Attacks on divers are most likely to occur
where the barracuda has not had a good look at its
victim. Where visibility is limited, for example, the
barracuda may see only a moving hand or foot, which
may be mistaken for prey. An attack may also occur
when a diver jumps into the water, as when entering
the sea from a boat. To a nearby barracuda, the diver's
splash may simulate the splash of an animal in diffi-
culty— and hence vulnerable — and the barracuda may
strike without realizing what made the splash. Thus
one should be especially alert in murky water to avoid
unnecessary splashing when large barracudas may be
present.
Other fishes that bite. Any large fish with sharp
teeth or powerful jaws can inflict a damaging bite.
12-10
Generally, however, such fish are hazardous to divers
only when they are handled. The pufferfishes, wolffishes,
and triggerfishes can be especially troublesome in
this respect. These fishes have teeth and jaws adapted
to feeding on heavily armored prey, and large speci-
mens are quite capable of biting off a human finger.
In the tropics, some of the larger sea basses can grow
to more than 7 feet. These giant fish, including certain
groupers and jewfishes, are potential hazards. Their
mouths can engulf a diver, and there are reports that
they have done so.
12.3.2 Reptiles
Reptiles that bite, including turtles, alligators, and
crocodiles, are potential hazards to divers, both in
freshwater and in the sea.
Turtles are frequently encountered by divers; how-
ever, although the larger individuals of some species
can injure divers with their bites, these animals are not
generally threatening. Although the larger marine turtles
have occasionally inflicted minor injuries, several
freshwater species are far more vicious and aggressive;
these include the alligator snapping turtle and com-
mon snapping turtle of American fresh waters. The
softshell turtle also may inflict a serious wound.
NOAA Diving Manual — October 1991
Hazardous Aquatic Animals
Figure 12-18
Barracuda
Photo Dick Clarke
Alligators that have been encountered by divers,
including the American alligator, have not proved
threatening. Nevertheless, the potential for serious
injury exists, and divers should be cautious.
Crocodiles are more dangerous than alligators. A
species in the tropical western Pacific that enters coastal
marine waters is feared far more than sharks by the
natives, and with good reason: it is known to have
attacked and eaten at least one diver.
12.3.3 Aquatic Mammals
Juvenile and female seals and sea lions frequently
frolic in the water near divers. Underwater encounters
with sea lions can be expected if the animals are nearby
during a dive. Their activity can be distracting or even
October 1991 — NOAA Diving Manual
frightening, but it is rarely dangerous. Large bull seals
and sea lions, although aggressive on the above-water
rocks of their breeding rookery, apparently do not
constitute a serious threat under water. A potentially
greater danger when swimming with seals is being shot
by a person hunting illegally. Some divers wear bright
markings on their hoods for this reason. If bitten by a
seal or sea lion, the diver should consult a physician,
because some species may transmit diseases that are
infectious among humans.
Common sense dictates that divers avoid large whales
under water. Usually whales stay clear of divers, so
that most incidents occur when divers put themselves
in jeopardy by provoking the whales. Whales may be
startled when a diver approaches too close and may
strike a diver senseless in their sudden surge of evasive
action.
Muskrats are potential hazards in fresh water. Usu-
ally they attack only if they believe themselves to be
threatened; their bites produce only minor wounds.
However, there is a serious danger that rabies can be
contracted from muskrat bites, so in addition to seek-
ing immediate medical advice, divers who are bitten
should make every effort to capture or kill the animal
for later examination.
12.4 ANIMALS THAT SHOCK
Among marine animals that produce an electric shock,
the only one significantly hazardous to divers is the
electric ray, which has representatives in all the oceans of
the world. The torpedo ray of California (Figure 12-19),
which can grow to 6 feet in length and weigh up to
200 pounds, is an example. These rays are shaped
somewhat like a stingray, except that their "wings"
are thick and heavy and their tails are flattened for
swimming. Electric rays are slow-moving animals, and
alert divers should have little trouble avoiding them.
As is true of so many undersea hazards, these animals
generally threaten only those divers who molest them.
The electric ray's shock, which can be as large as
200 volts, is generated by modified muscles in the
forward part of the animal's disc-shaped body. The
shock, which is enough to electrocute a large fish, can
jolt a diver severely.
12.5 ANIMALS POISONOUS TO EAT
Most seafoods are edible and nourishing; however,
several of the most toxic substances known are some-
times found in marine organisms. Mollusk shellfish,
such as clams, mussels, and oysters, are sometimes
poisonous to eat. These shellfish become poisonous
because they feed on toxic dinoflagellates, which are
12-11
Section 12
Figure 12-19
Torpedo Ray
Figure 12-20
Examples of Pufferfish
Photo Tony Chess
microscopic plankton. Most of these episodes of poi-
soning have occurred along the Pacific coast from
California to Alaska; the northeast coast from Massa-
chusetts to Nova Scotia, New Brunswick and Quebec;
and in the North Sea countries of Britain and West
Germany. It is advisable to check with local authori-
ties to determine what periods are safe for eating mol-
lusk shellfish. Violent intoxications and fatalities have
also been reported from eating tropical reef crabs;
these should not be eaten without first checking with
the local inhabitants. Numerous species of tropical
reef fishes are known to be poisonous to eat because
they cause a disease known as ciguatera (see Section 18
for a discussion of ciguatera poisoning treatment).
An edible fish in one locality may be deadly in another.
Photo Bruce W. Halstead
In addition, most pufferfish (Figure 12-20) contain a
deadly poison known as tetrodotoxin, and puffers and
related species should be carefully avoided.
i
12-12
NOAA Diving Manual — October 1991
SECTION 13
WOMEN
AND
DIVING
Page
13.0 General 13-1
13.1 Physiological Considerations 1 3-1
13.1.1 Anatomical Differences 13-1
13.1.2 Diving During the Menstrual Period 13-1
13.1.3 Birth Control Methods 13-2
13.1.4 Temperature Regulation 13-2
13.1.5 Aging and Diving 13-2
13.2 Women Divers and Decompression Sickness 13-2
13.3 Diving During Pregnancy 13-3
13.3.1 Effects of Diving on the Fetus 13-3
13.3.1.1 Direct Pressure 13-3
13.3.1.2 Effects of Changes in Oxygen Pressure 13-3
13.3.1.3 Effects of Increased Nitrogen Pressure 13-3
13.3.1.4 Pregnancy and Diving 13-4
13.4 Training Considerations 13-4
13.5 Equipment for the Smaller Diver 13-4
<
WOMEN
AND
DIVING
13.0 GENERAL
Women have played significant roles as divers for many
years, beginning with their work as Hae-Nyu and Ama
divers in Korea and Japan. The number of certified
female sport divers, instructors, research, and com-
mercial divers in America has increased significantly
since the early I970's, and national certification agen-
cies report that approximately 25 percent of newly
certified divers are women. This increase in the female
diving population has raised many issues not formerly
addressed. Some of these questions are asked by women
divers themselves, and others are raised by researchers
in hyperbaric medicine and physiology. This section
discusses several of these topics.
13.1 PHYSIOLOGICAL CONSIDERATIONS
Women have proven themselves to be safe and compe-
tent divers. They are capable of participating in the
same training and withstanding most of the same stresses
as their male colleagues. However, the anatomical and
physiological differences between men and women have
some implications for women divers.
13.1.1 Anatomical Differences
Some of the anatomical differences between women
and men are obvious, but others are more subtle. Even
an athletic woman in good physical condition has less
muscle mass than a man in comparable condition,
because the male hormone, testosterone, which is needed
for the development of large muscles, is present only in
reduced quantities in women. However, all divers ben-
efit from being in good physical condition, and female
divers can improve their strength and aerobic capabil-
ities with specially designed exercise programs.
Women generally have a lower center of gravity than
men, and have relatively longer trunks and shorter
legs, which means that most of a woman's weight is
distributed at a lower point than a man's. Moreover,
the shape of several joints, such as those at the hip and
elbow, differ in women, because the bones at these
joints meet at slightly different angles than is the case
for men. In addition, a greater percentage of total body
weight is composed of fatty tissue in women than men.
Another anatomical difference between men and
women occurs in the cardiovascular and respiratory
October 1991 — NOAA Diving Manual
systems (heart, lungs, and circulation). Even when
relative weight is taken into consideration, a woman's
heart and lungs are smaller than a man's. Women tend
to breathe more shallowly, although their breathing is
equally efficient. Consequently, in comparison to male
divers, a female diver takes less air into her lungs and
her heart rate is slightly higher. These facts have implica-
tions for diving. For example, a female diver may use
less air than her male buddy for the same dive. Women
also have increased pulse and respiration rates and
may tend to work closer to their maximum exertion
level when diving. It is important for all divers to pace
themselves carefully under water and to avoid maxi-
mum or near-maximum exertion as much as possible.
13.1.2 Diving During the Menstrual Period
One of the most common questions asked by female
divers is, "Should I dive during my period?" Before
answering that question, it is important to understand
certain hormonal changes that occur in a woman's
body in the course of her normal 20-45 day cycle.
Several hormones are involved in this cycle: hypotha-
lamic and pituitary hormones, which are secreted by
glands in the brain, adrenal hormones, and the two
ovarian hormones, estrogen and progesterone. A wom-
an's estrogen level increases up to ovulation and then
drops slightly, while the level of progesterone increases
rapidly after ovulation and then decreases during men-
struation. The female sexual cycle is thus regulated by
various hormones. The levels of hormones are highest
before menstruation and lowest during menstruation.
The drop in estrogen and progesterone levels triggers
menstruation.
Based on current knowledge, there is no reason for
women to refrain from diving during their periods if
they feel well. As in all diving, however, it is important
not to dive to the point of fatigue. Fluid retention,
which can occur during the premenstrual period, may
be a problem for some women divers. Although the
effect of fluid retention on the susceptibility of divers
to decompression sickness has not yet been established,
women divers should use common sense and plan their
dives so that they are well within the no-decompression
limits during the premenstrual and menstrual portions
of their cycles.
13-1
Section 13
Some women have asked whether there is a greater
likelihood of shark attack during their periods. According
to some recent Australian research, there is no evi-
dence that sharks are attracted to menstruating women
(Edmonds, Lowry, and Pennefather 1981). Sharks thus
may not pose a greater threat to women divers during
menstruation than at any other time.
13.1.3 Birth Control Methods
Women divers should select a method of birth con-
trol on the basis of their physician's advice and their
own preference. The physician should be informed that
the patient is a diver, which may be an important
consideration if either an intrauterine device or birth
control pills are selected. In general, however, women
who have no adverse responses to the method of birth
control they are using on land should have no difficulty
with the same method when diving.
13.1.4 Temperature Regulation
Staying thermally comfortable during a dive is impor-
tant both for enjoyment and to accomplish the work
planned for a dive. Despite the fact that women have a
layer of subcutaneous fat that is a good insulator,
many women become chilled quickly when they dive.
By studying the responses of women in cool water,
two factors involved in the sensitivity to cold have
emerged: percentage of body fat and ratio of surface
area to body mass (Kollias et al. 1974). Lean women
with 27 percent or less body fat have a larger ratio of
surface area to body mass than fatter women; women
with such a low percentage of body fat chill more
rapidly than women or men with a higher body fat
percentage. Both men and women who have 30 percent
or more body fat will experience the same amount of
heat loss in water.
Suitable exposure suits, properly fitted, are re-
commended to ensure thermal protection (see Sec-
tion 5.4). Although wearing an exposure suit on the
surface on a warm day will make any diver hot, the
problem may be exacerbated in women because they
have fewer sweat glands than men and do not begin to
sweat until their body temperature is 2-3 °F higher
than the temperature that causes sweating in men
(Kollias et al. 1974). (See Sections 3.4 and 3.5 for a
more detailed discussion of thermal regulation.)
13.1.5 Aging and Diving
Many middle-aged divers, both male and female,
continue to enjoy the sport of scuba diving. In fact,
13-2
many middle-aged and older men and women learn to
dive for the first time at this stage of life. Although
advancing age may lessen people's interest in competi-
tive or strenuous sports, scuba diving can be a lifelong
recreational activity. Older divers should have an annual
diving physical examination, and they should swim
several times a month with mask, fins, and snorkel to
stay in good diving condition. In addition, older divers
should watch their weight, avoid fatigue, ascend and
descend at a reasonable rate, and consider the poten-
tial interactions between pressure and any prescribed
medication before diving.
Usually between the ages of 45 and 50, women undergo
a series of hormonal changes called menopause. Ovu-
lation fails to occur during the monthly cycle and
estrogen production by the ovaries decreases. Abrupt
changes in hormonal levels of estrogen and progester-
one may cause a variety of symptoms, including hot
flashes, irritability, fatigue, and anxiety. A woman
suffering from any of these symptoms should not dive
if these symptoms are sufficiently acute to make her
feel uncomfortable.
Older divers, both male and female, may be more
susceptible to decompression sickness. Therefore,
middle-aged and older divers should use conservative
judgment in dive planning and should remain at a
particular depth for less time than the maximum
no-decompression tables permit.
13.2 WOMEN DIVERS AND
DECOMPRESSION SICKNESS
Many factors are believed to increase an individual's
susceptibility to decompression sickness, including age,
degree of body fat, and general vascular condition.
Because the U.S. Navy dive tables were developed for
young, physically fit males, their applicability to other
groups of divers, especially to women, has been
questioned. Women usually have a relatively greater
amount of subcutaneous fat than men. They also expe-
rience hormonal changes during their menstrual cycles
that can cause fluid retention, and some women use
birth control pills that may affect their circulation. All
of these factors suggest that the risk of decompression
sickness may be higher for women than for men.
In one study, a 3.3-fold increase in the incidence of
decompression sickness was reported among women
divers, as compared with divers in the male control
group (Bangasser 1978). In this study, other distin-
guishing factors, such as age and weight/height fac-
tors, were not significantly different for the female
and male groups. These results are too tentative to use
NOAA Diving Manual — October 1991
Women and Diving
as the basis for any conclusion concerning the relative
bends susceptibility between males and females. How-
ever, women divers should be conservative in their use
of the Navy tables and should make 3- to 5-minute
safety stops at 10 feet (3 meters) after deeper dives.
breathes pure oxygen under pressure, as might occur
during hyperbaric treatment for decompression sick-
ness or gas embolism. To date, even under such cir-
cumstances, fetal effects have not been reported; how-
ever, experience is not sufficiently extensive to be
conclusive.
13.3 DIVING DURING PREGNANCY
As more women enter sport and professional diving,
the chance that dives will inadvertently take place
during pregnancy increases. Women who would not
knowingly dive during pregnancy may dive unwittingly
during the first few weeks of pregnancy, before they
discover that they are pregnant. Several factors that
could affect both the mother and the fetus indicate
that women should take care to avoid diving when
there is any chance that they are pregnant.
13.3.1 Effects of Diving on the Fetus
The health and safety of the developing fetus are of
primary importance to expectant mothers. Since scuba
divers are exposed to increased hydrostatic pressure
and to increased partial pressures of oxygen and nitro-
gen, the effects of these pressures on the fetus have
been investigated.
13.3.1.1 Direct Pressure
Since the fetus is completely enclosed in amniotic
fluid and no air spaces are present, there is no direct
effect of increased pressure on the fetus. During a dive,
a fetus will not experience squeeze, e.g., pressure on
the ear drums.
13.3.1.2 Effects of Changes in Oxygen Pressure
Oxygen is essential to maintaining life, and either a
lack or an excess of oxygen can have harmful effects.
To some extent, the fetus is protected from either
extreme, but circumstances affecting the mother's oxy-
genation must be considered in terms of their potential
effects on the fetus. As long as the diver has an ade-
quate compressed-air supply, too little oxygen (hypoxia)
is unlikely. (Hypoxia is thus a potentially greater problem
in breath-hold than in scuba diving.)
At any depth below sea level, the oxygen pressure,
even when air is the breathing medium, is higher than
it is at sea level. For example, breathing compressed
air at 132 fsw (40.2 msw) produces an inspired oxygen
pressure of 4 ATA. However, a fetus is most likely to be
exposed to too much oxygen (hyperoxia) if the mother
October 1991 — NOAA Diving Manual
13.3.1.3 Effects of Increased Nitrogen Pressure
As a diver descends, the body absorbs increasing
amounts of nitrogen. If the nitrogen is eliminated too
quickly (which could happen during a rapid ascent),
decompression sickness may occur, either during ascent,
at the surface, or after surfacing. Decompression sick-
ness occurs when the nitrogen in solution in a diver's
tissues comes out of solution in the form of bubbles
(see Section 3.2.3.2).
Any bubbles that form in the fetus could obstruct
blood flow and cause major developmental anomalies
or death. Research has been conducted on bubble for-
mation in the fetus using laboratory studies of animals
or retrospective surveys of women divers (Lanphier
1983, Bolton 1980, Bangasser 1978). The questions
addressed were: Does diving cause birth defects? Are
bubbles more or less likely to form in the fetus than in
the mother? If the mother develops decompression
sickness, what happens to the fetus?
Scuba diving and birth defects. The results of one
survey (Bolton 1980) showed a birth defect rate of
5.5 percent among women who had dived to depths of
100 fsw (30 msw) or greater during pregnancy; this
incidence is statistically greater than the rate ob-
served in infants born to a control group of non-diving
women. Although this finding was significant, the rate
of birth defects among all U.S. women (approximately
3-3.5 percent) is not much lower than that found in the
divers. Results from another survey of women who had
dived during pregnancy failed to demonstrate a rela-
tionship between diving while pregnant and birth defects
(Bangasser 1978).
Data gathered from animal studies thus far show no
conclusive evidence of a connection between increased
pressure and fetal abnormalities. For example, rats
exposed to high pressures during peak embryonic devel-
opment had no increase in birth defects (Bolton and
Alamo 1981). In a similar experiment, pregnant sheep
were exposed to a pressure of 4.6 atmospheres early in
pregnancy, that is, during peak embryonic develop-
ment (Bolton-Klug et al. 1983). Toward the end of
pregnancy, the fetuses were examined anatomically
and were found to have no detectable abnormalities.
Bubble formation in the fetus during a dive. Research
on the likelihood of bubble formation in the fetus of a
13-3
Section 13
pregnant woman during a dive has resulted in contro-
versial findings (Bangasser 1979). Early experiments
on dogs and rats showed a resistance to bubble forma-
tion in the fetus. More recent experiments using sheep
and goats as experimental models have produced some-
what conflicting results. When sheep were put under a
pressure of 165 fsw (50 msw) for 20 minutes, a Doppler
bubble monitor detected bubbles in the mothers but
not in the fetuses. The lambs developed normally after
birth (Nemiroff et al. 1981). In another hyperbaric
experiment, bubbles were detected both in the dams
and fetuses of sheep and goats; however, these lambs
and kids were also normal on delivery (Powell and
Smith 1985).
These experiments show that, although the fetus is
probably less susceptible to bubble formation during
decompression than the mother, there is a real poten-
tial danger of fetal bubble formation during decom-
pression.
Effect of maternal decompression sickness on the
fetus. Although evidence pointing to the potentially
adverse consequences of maternal decompression sick-
ness on the developing fetus is not definitive, it rein-
forces the view that pregnant women should not dive.
Although early studies on dogs and rats (Mclver 1968,
Chen 1974) indicated that the fetus would suffer no
harm even if the mother had decompression sickness,
more recent studies (Nemiroff et al. 1981, Lehner et
al. 1982) on sheep report different results. If sheep
dived late in gestation and did not incur decompression
sickness, the lambs were born healthy (Nemiroff et al.
1981); however, if pregnant sheep developed decom-
pression sickness immediately before delivery, their
lambs were stillborn (Lehner et al. 1982). Decompres-
sion sickness in a pregnant woman thus might also be
associated with fetal morbidity and mortality.
13.3.1.4 Pregnancy and Diving
Although obstetricians encourage patients to con-
tinue their favorite sports during pregnancy as long as
they are comfortable and use common sense, hyperbaric
pnysicians take the most conservative position and
recommend that their patients discontinue diving while
they are pregnant, since so much is still unknown about
the effects of diving on the fetus. Considering the
evidence to date, the conflicting results of animal as
well as human studies, and the seriousness of the potential
consequences, NOAA recommends that women in the
agency not dive during pregnancy. Women divers who
personally elect to continue diving during pregnancy
despite this recommendation should do so only on
the advice of a trained hyperbaric physician.
13-4
WARNING
Women Should Not Dive While Pregnant
13.4 TRAINING CONSIDERATIONS
Scuba instructors have observed several tendencies
common among women divers. For example, many
women prefer to learn new skills in small steps rather
than to master complex tasks in one step. Women also
tend to over-learn a skill before having confidence in
their mastery, and they may also be more conservative
than men when planning their dives (S. Bangasser,
personal communication). Because some women have
not had much experience in handling mechanical equip-
ment, they may need additional training to learn how
to assemble and maintain their equipment.
Psychological studies of experienced male and female
divers have not demonstrated any important basic dif-
ferences in the psychology of men and women divers
(Lanphier, personal communication). It is important
that women divers, like men divers, develop the inde-
pendent competence and confidence they need to dive
safely and to assist other divers in an emergency.
13.5 EQUIPMENT FOR THE
SMALLER DIVER
In the past few years, the diving industry has made
great advances in manufacturing equipment to fit the
smaller diver. (This development has also helped small
men and younger divers of both sexes.) Properly sized
diving equipment is now readily available.
Smaller divers should pay extra attention to equip-
ment selection and fit. Masks should seal completely,
leave the hair free, and be comfortable. A snorkel with
a smaller mouthpiece is recommended for anyone with
a narrow mouth. If need be, the mouthpiece on a standard
regulator can be replaced with a more comfortable
model. Buoyancy devices are available in many lengths
and chest sizes and should be selected for size, com-
fort, and their ability to float the diver in a safe posi-
tion on the surface (see Section 5.3.2). Tanks that
are smaller and lighter in weight are also available.
Hoods, boots, and gloves are made in smaller sizes and
are available at many dive shops. Figure 13-1 shows a
scientist on an underwater mission wearing properly
fitted clothing and equipment.
WARNING
Equipment Fit and Comfort Are Essential to
Dive Safety
NOAA Diving Manual — October 1991
Women and Diving
Figure 13-1
Scientist on Research Mission
Photo Ronald Bangasser
Selecting a proper fitting wet suit takes more time
and effort than locating other types of properly fitted
equipment. Although suits are manufactured for women,
many women cannot be properly fitted in a standard
off-the-shelf suit. A diver renting a wet suit may need
to wear a top of one size and a bottom of a different
size. Since splitting sizes can be a problem for the
owner of the dive shop, active female divers should
invest in a custom wet suit. Zippers make donning and
doffing easier and provide a snug fit. With properly
fitted gear, small divers — whether male or female — can
enjoy the dive, concentrate on the task at hand — not
the gear — and feel comfortable and confident about
diving.
October 1991 — NOAA Diving Manual
13-5
i
SECTION 14
AIR DIVING
AND
DECOMPRESSION
14.0
14.1
14.2
14.3
14.4
14.5
14.6
14.7
14.8
14.9
Page
General 14-1
Dive Planning 14-1
14.1.1 Selection of Diving Equipment 14-1
14.1.2 Dive Team Organization 14-2
14.1.2.1 Dive Master 14-2
14.1.2.2 Diving Medical Officer/ Diving Medical
Technician 14-3
14.1.2.3 Science Coordinator 14-3
14.1.2.4 Divers 14-3
14.1.2.5 Tender for Surface-Supplied Diving 14-3
14.1.2.6 Support Divers and Other Support Personnel 14-3
14.1.3 Environmental Conditions 14-4
14.1.3.1 Surface Environmental Conditions 14-4
14.1.3.2 Underwater Environmental Conditions 14-4
Diving Signals 14-8
14.2.1 Hand Signals 14-8
14.2.2 Surface-to-Diver Recall Signals 14-8
14.2.3 Line Signals 14-8
14.2.4 Surface Signals 14-8
Air Consumption Rates 14-8
14.3.1 Determining Individual Air Utilization Rates 14-12
Self-Contained Diving 14-13
14.4.1 Scuba Duration 14-13
14.4.2 Scuba Air Requirements 14-16
High-Pressure Air Storage Systems 14-18
Decompression Aspects of Air Diving 14-19
14.6.1 Definitions 14-20
14.6.2 Air Decompression Tables and Their Applications 14-20
14.6.2.1 No-Decompression Limits and Repetitive Group
Designation Tables for No-Decompression
Air Dives 14-21
14.6.2.2 Standard Air Decompression Table 14-23
14.6.2.3 Residual Nitrogen Timetable for Repetitive
Air Dives 14-23
14.6.2.4 Recordkeeping and Table Use 14-24
Surface Decompression 14-25
14.7.1 Surface Decompression Using Oxygen After an Air Dive 14-26
14.7.2 Surface Decompression Using Air After an Air Dive 14-26
Omitted Decompression 14-26
Flying After Diving at Sea Level 14-28
(
AIR DIVING
AND
DECOMPRESSION
14.0 GENERAL
Diving with air as the breathing medium may be
conducted using a variety of life-support equipment.
The most frequently used mode is open-circuit scuba,
where the diver carries the compressed air supply, but
divers can also use umbilical-supplied air with a scuba
regulator, a full-face mask, a lightweight diving hel-
met, or deep-sea diving equipment. This section deals
with planning for air dives, methods of calculating
air supply requirements, and the decompression aspects
of air diving.
14.1 DIVE PLANNING
Careful and thorough planning are the keys to conducting
an efficient diving operation and are also imperative
for diver safety. The nature of each dive operation
determines the scope of the planning required. The
dive plan should be devised to take into account the
ability of the least qualified diver on the team and be
flexible enough to allow for delays and unforeseen
problems. It should include at least the following items.
Definition of Objectives:
• A clear statement of the purpose and goals of the
operation.
Analysis of Pertinent Data:
• Surface conditions, such as sea state, air tempera-
ture, and wind chill factor;
• Underwater conditions, including water tempera-
ture, depth, type of bottom, tides and currents,
visibility, extent of pollution, and hazards; and
• Assistance and emergency information, including
location, status, and contact procedures for the
nearest decompression chamber, air evacuation
team. Coast Guard, and hospital.
Schedule of Operational Tasks for All Phases:
• Transit to the site;
• Assembling dive gear and support equipment;
• Predive briefing;
• Calculating allowable/required bottom time;
• Recovery;
• Cleaning, inspection, repair, and storage of gear; and
• Debriefing of divers and support personnel.
Diving Mode Selection:
• Open-circuit scuba;
• Surface-supplied;
October 1991 — NOAA Diving Manual
• Mixed gas; or
• Saturation.
Equipment and Supplies Selection:
• Breathing gas, including a backup supply;
• Dive platform and support equipment, including
diver/crew shelter;
• Oxygen resuscitator;
• Dive flag; and
• Diving gear, tools, etc.
Diving Team Selection:
• Dive master;
• Medical personnel;
• Tenders/timekeeper; and
• Coxswain/surface-support personnel.
Briefing/Debriefing the Diving Team:
• The objective and scope of the operation;
• Conditions in the operating area;
• Diving techniques and equipment to be used;
• Personnel assignments;
• Particular assignments for each diver;
• Anticipated hazards;
• Normal safety precautions;
• Any special considerations; and
• Group discussion period to answer questions from
members of the diving team.
Final Preparations and Safety Checks:
• Review of dive plan, its impact on the operation,
and all safety precautions;
• Outline diving assignments and explain their
sequence;
• Complete and post on-site emergency checklist;
• Review diver qualifications and conditions; and
• Secure permission from command or boat captain
for dive.
14.1.1 Selection of Diving Equipment
The selection of the proper diving equipment depends
on environmental conditions, qualifications of diving
personnel, objectives of the operation, and diving
procedures to be used. Although most diving is performed
at depths less than 130 fsw (39.3 msw) and often uses
open-circuit scuba, some missions can be accomplished
using only skin diving equipment. Other more complex
assignments require surface-supplied or closed-circuit
breathing equipment. Depth and duration of the dive,
14-1
Section 14
type of work to be accomplished (heavy work, light
work, silent work), temperature of the water, velocity
and nature of current, visibility, logistics, and the diver's
experience and capabilities all influence the selection
of diving equipment. Detailed descriptions of the vari-
ous types of diving equipment are presented in Section 5.
For planning purposes, the following guidelines may
be used in selecting diving equipment.
Breath-Hold Diving Equipment
Generally Used For:
• Scientific observation and specimen collection in
shallow water in areas where more complex equip-
ment is a disadvantage or is not available
• Shallow-water photography
• Scouting for diving sites
Major Advantages:
• Less physical work required to cover large surface
areas
• Simplified logistics
• Fewer medical complications
Major Disadvantages:
• Extremely limited in depth and duration
• Requires diver to develop breath-holding techniques
• Can only be used in good sea conditions
Open-Circuit Scuba
Generally Used For:
• Scientific observation
• Light underwater work and recovery
• Sample collection
• Shallow-water research
• Ship inspection and light repair
Major Advantages:
• Minimum support requirements
• Mobility
• Accessibility and economy of equipment and breath-
ing medium
• Portability
• Reliability
Major Disadvantages:
• Lack of efficient voice communication
• Limited depth and duration
Umbilical-Supplied Systems
Generally Used For:
• Scientific investigation
• Ship repair and inspection
• Salvage
• Long-duration scientific observation and data
gathering
• Harsh environments (low visibility, strong currents,
polluted water)
Major Advantages:
• Ease of supplying heat
• Long duration
• Voice communication
• Protection of diver from environment
Major Disadvantages:
• Limited mobility
• Significant support requirements
Closed-Circuit Scuba
Generally Used For:
• Observations of long duration
Major Advantages:
• Mixed-gas capability
• No noise or bubbles
• Conservation of breathing medium
• Long duration
Major Disadvantages:
• Complicated maintenance
• Extensive training requirements
• Lack of efficient voice communication.
14.1.2 Dive Team Organization
14.1.2.1 Dive Master
Dive masters have complete responsibility for the
safe and efficient conduct of diving operations. They
must be experienced divers who are qualified to handle
the requirements of the proposed dive. When no dive
master is present, diving should not be conducted. The
dive master's responsibilities are many, and include
but are not necessarily limited to:
• Overall responsibility for the diving operation
• Safe execution of all diving
• Preparation of a basic plan of operation, including
evacuation and accident plans
• Liaison with other organizations
• Selection of equipment
• Proper maintenance, repair, and stowage of
equipment
• Selection, evaluation, and briefing of divers and
other personnel
• Monitoring progress of the operation and updating
requirements as necessary
• Maintaining the diving log
• Monitoring of decompression (when required)
• Coordination of boat operations when divers are in
the water.
The dive master is responsible for assigning all divers
to an operation and for ensuring that their qualifications
are adequate for the requirements of the dive. The dive
14-2
NOAA Diving Manual — October 1991
Air Diving and Decompression
master must ensure that all divers are briefed thoroughly
about the mission and goals of the operation. Individ-
ual responsibilities are assigned to each diver by the
dive master. Where special tools or techniques are to
be used, the dive master must ensure that each diver is
familiar with their application.
Enough training and proficiency dives should be
made to ensure safe and efficient operations. During
especially complex operations or those involving a large
number of divers, dive masters should perform no actual
diving but should instead devote their efforts entirely
to directing the operation.
The dive master is in charge when divers are in the
water during liveboating operations. Before any change is
made to the boat's propulsion system (e.g., change in
speed, direction, etc.), the boat captain must clear the
change with the dive master.
14.1.2.2 Diving Medical Officer/Diving
Medical Technician
When it not practical to have a qualified diving
medical officer on site, a Diving Medical Technician
trained in the care of diving casualties may be assigned.
An individual so trained is able both to respond to
emergency medical situations and to communicate
effectively with a physician located at a distance from
the diving site. There are specialized courses available
to train Diving Medical Technicians in the care of
diving casualties (see Section 7.3).
In the event that neither a physician nor a trained
technician is available, the dive master should obtain
the names and phone numbers of at least three diving
medical specialists who can be reached for advice in
an emergency. Emergency consultation is available
from the service centers listed below. Referred to as a
"Bends Watch," each of these services is available
to provide advice on the treatment of diving casualties:
• Navy Experimental Diving Unit, Panama City,
FL 32407, telephone (904) 234-4351, 4353;
• National Naval Medical Center, Naval Medical
Research Institute, Bethesda, MD 20814, telephone
(202)295-1839;
• Brooks Air Force Base, San Antonio, TX 78235,
telephone (512) 536-3278 (between 7:30 a.m. and
4:15 p.m. CST, emergency calls are also received
on (512) 536-3281); and
• Diver's Alert Network, Duke University Medical
Center, Durham, NC 27710, telephone (919) 684-8111
(ask for the Diving Accident Physician).
Diving personnel should obtain and keep the phone
numbers of these facilities, especially if they will be
diving in remote areas.
October 1991 — NOAA Diving Manual
14.1.2.3 Science Coordinator
On missions where diving is performed in support of
scientific programs, a science coordinator may be needed.
The science coordinator is the prime point of contact
for all scientific aspects of the program, including
scientific equipment, its use, calibration, and mainte-
nance. Working with the dive master, the science coordi-
nator briefs divers on upcoming missions and super-
vises the debriefing and sample or data accumulation
after a dive.
14.1.2.4 Divers
Although the dive master is responsible for the overall
diving operation, each diver is responsible for being in
proper physical condition, for checking out personal
equipment before the dive, and for thoroughly under-
standing the purpose and the procedures to be used for
the dive. Divers also are responsible for using safe
diving procedures and for knowing all emergency
procedures.
14.1.2.5 Tender for Surface-Supplied Diving
The tender must be qualified to tend divers in-
dependently and to operate all surface-support equip-
ment. To use manpower efficiently, the tender may be
a qualified diver used in a diver-tender rotation sys-
tem. Although there is no specific requirement that
tenders be qualified divers, they should be trained in
theory and operational procedures by the divers and
diving supervisors (see Section 7.2). Ideally, tenders
should be trained by instructors and be assigned to diving
operations by the diving supervisors. A tender-assistant
may assume the tender's responsibilities when the assis-
tant is working under the direct supervision of fully
qualified diving and tending personnel. Another ten-
der, diver, or qualified person should be assigned as
communications person, console operator, timekeeper,
recordkeeper, and diver's assistant.
It is recommended that one qualified person be des-
ignated as standby diver, ready to enter the water
promptly in an emergency. The standby diver may
accept tender responsibilities in routine operations; in
more complex diving operations, however, the standby
diver must be free of all other duties. A tender must be
available and ready to tend the standby diver during an
emergency.
14.1.2.6 Support Divers and Other Support
Personnel
In most diving operations, the number and types of
support divers depend on the size of the operation and
14-3
Section 14
the type of diving equipment used. As a general rule,
those surface-support personnel working directly with
the diver also should be qualified divers. Using unquali-
fied personnel who do not understand diving techniques
and terminology may cause confusion and be danger-
ous. Persons not qualified as divers can be used when
the need arises only after they have demonstrated to
the satisfaction of the dive master that they under-
stand procedures adequately.
14.1.3 Environmental Conditions
Environmental conditions at a dive site should be
considered when planning a diving operation. Envi-
ronmental conditions can be divided into surface envi-
ronmental conditions and underwater environmental
conditions. Surface conditions include weather, sea
state, and amount of ship traffic. Underwater condi-
tions include depth, bottom type, currents, water tem-
peratures, and visibility. Regional and special diving
conditions are discussed in Section 10.
14.1.3.1 Surface Environmental Conditions
Weather conditions are an important factor to con-
sider when planning a dive. Whenever possible, diving
operations should be cancelled or delayed during bad
weather. Current and historical weather data should
be reviewed to determine if conditions are acceptable
or are predicted to continue for a sufficient amount of
time to complete the mission. Personnel should avail
themselves of the continuous marine weather broad-
casts provided by NOAA on the following frequencies:
162.40 MHz, 162.475 MHz, or 162.55 MHz, depending
on the local area. These broadcasts can be heard in
most areas of the United States and require only the
purchase of a VHF radio receiver. Weather radios are
designed to pick up NOAA radio broadcasts only. A
boater with such a set will hear regular weather fore-
casts and special marine warnings any time of the day
or night. Although all three receivers pick up weather
signals from approximately the same distance, the two-
way systems have the advantage of transmission
capability.
NOTE
The flag system for weather warnings is no
longer in general use; all weather reports are
now transmitted by radio.
In some cases, surface weather conditions may influ-
ence the selection of diving equipment. For instance,
14-4
even though water temperature may permit the use of
standard wet suits, cold air temperature and wind may
dictate that a variable-volume dry suit (or equivalent)
be worn when diving from an open or unheated platform.
Whenever possible, avoid or limit diving in moderate
seas (see Table 14-1). Sea state limitations depend to a
large degree on the type and size of the diving platform.
Diving operations may be conducted in rougher seas
from properly moored larger platforms such as diving
barges, ocean-going ships, or fixed structures. Divers
using self-contained equipment should avoid entering
the ocean in heavy seas or surf, as well as high, short-
period swell. If bad weather sets in after a diving
operation has commenced, appropriate recall signals
should be employed. Except in an emergency, divers
should not attempt scuba or surface-supplied diving
in rough seas (see Figure 14-1).
Because many diving operations are conducted in
harbors, rivers, or major shipping channels, the presence
of ship traffic often presents serious problems. At times, it
may be necessary to close off the area around the dive
site or to limit the movement of ships in the dive site's
vicinity. Ship traffic should be taken into considera-
tion during dive planning, and a local "Notice to
Mariners" should be issued. Any time that diving
operations are to be conducted in the vicinity of other
ships, these other vessels should be notified by message
or signal that diving is taking place. Signal flags, shapes,
and lights are shown in Table 14-2.
If the dive operation is to be carried on in the middle
of an active fishing ground, it is necessary to anticipate
that people with various levels of experience and com-
petence will be operating small boats in the vicinity.
The diving team should assume that these operators
are not acquainted with the meaning of diving signals
and should take the necessary precautions to ensure
that they remain clear of the area.
The degree of surface visibility is important. Reduced
visibility may seriously hinder or force postponement
of diving operations. If operations are to be conducted
in a known fog-belt, the diving schedule should allow
for probable delays caused by low visibility. The safety
of the diver and support crew is the prime considera-
tion in determining whether surface visibility is ade-
quate. For example, in low surface visibility condi-
tions, a surfacing scuba diver might not be able to find
the support craft or might be in danger of being run
down by surface traffic.
14.1.3.2 Underwater Environmental Conditions
Dive depth is a basic consideration in the selection
of personnel, equipment, and techniques. Depth should be
determined as accurately as possible in the planning
NOAA Diving Manual — October 1991
Air Diving and Decompression
Figure 14-1
Sea States
ft «
(1)
0)
28
* 20
SS6 Waves Start to Roll
SS5 Spindrift Forms
SS3 White Caps Form
2 3 4
Source: Bunker Ramo Corp
phases, and dive duration, air requirements, and decom-
pression schedules (when required) should be planned
accordingly.
Type of bottom affects a diver's ability to see and
work. Mud (silt and clay) bottoms generally are the
most limiting because the slightest movement will stir
sediment into suspension, restricting visibility. Divers
must orient themselves so that any current will carry
the suspended sediment away from the work area, and
they also should develop a mental picture of their
surroundings so that an ascent to the surface is possible
even in conditions of zero visibility.
Sand bottoms usually present little problem for divers
because visibility restrictions caused by suspended sedi-
ment are less severe than is the case for mud bottoms.
In addition, sandy bottoms provide firm footing.
Coral reefs are solid but contain many sharp pro-
trusions. Divers should wear gloves and coveralls or a
wet suit for protection if the mission requires contact
with the coral. Divers should learn to identify and
avoid corals and other marine organisms that might
inflict injury (see Section 12).
Currents must be taken into account when planning
and executing a dive, particularly when using scuba.
When a boat is anchored in a current, a buoyed safety
line at least 100 feet (30.3 m) in length should be
trailed over the stern during diving operations. If, on
entering the water, a diver is swept away from the boat
by the current, he or she can use this safety line to keep
from being carried down current.
Free-swimming descents should be avoided in cur-
rents unless provisions have been made to reach safety.
Descent from an anchored or fixed platform into water
with currents should be made along a weighted line. A
line also should be used unless adequate provisions are
made for a pickup boat to operate down current so that
surfacing some distance from the entry point will not
be dangerous. A knowledge of changing tidal currents
may allow divers to drift down current and to return to
the starting point on the return current.
Tidal changes often alter the direction of current
and sometimes carry sediment-laden water and cause
low visibility within a matter of minutes. Tidal cur-
rents may prevent diving at some locations except dur-
ing slack tides. Because a slack tide may be followed
by strong currents, divers should know the tides in the
diving area and their effects.
Currents generally decrease in velocity with depth,
and it may therefore be easier to swim close to the
bottom when there are swift surface currents. Howev-
er, current direction may change with depth. When
there are bottom currents, it is useful to swim into the
current rather than with the current; this facilitates
return to the entry point at the end of the dive. Divers
should stay close to the bottom and use rocks (if present)
to pull themselves along.
Water temperature is a major factor to consider in
planning a diving operation because it has a significant
effect on the type of equipment selected and, in some
cases, determines the practical duration of the dive. A
thermocline is a boundary layer between waters of
different temperatures. Although thermoclines do not
pose a direct hazard to divers, their presence may
affect the selection of diving dress, dive duration, or
equipment. Thermoclines occur at various water lev-
els, including levels close to the surface and in deep
water. Temperature may vary from layer to layer. As
much as a 20° F (a range of 1 1 "C) variation has been
recorded between the mixed layer (epilimnion) above
the thermocline and the deeper waters (hypolimnion)
beneath it.
Underwater visibility depends on time of day, locality,
water conditions, season, bottom type, weather, and
currents. Divers frequently are required to dive in
water where visibility is minimal and sometimes at the
zero level. Special precautions are appropriate in either of
October 1991 — NOAA Diving Manual
14-5
Section 14
Table 14-1
Sea State Chart
Sea-General
Wind
Sea
Sea
State Description
5
u
0
u-
"D
C
5
i
O
a>
ca
c
0
a.
"C
u
U)
0
a
0
c
0
en
c
a
OS
>.
"o
_o
«
> V
II
3 *
Wave
Fe
0
CO
D
a
>
<
Height
et
M
Significant
Range of
Periods
(Seconds)
■o
o
0
a.
0
CO
D
O
>
<
1—
.c
ffi CO
en c
o o
| ~t>
< 5
-C 'in
u ffi
0 =
u. 5
E"5
.i'-s
C D
c
0
o
3
a
E
I!
c o
S5
Sea like a mirror.
o
U
Calm
Less
than 1
0
0
0
-
-
-
-
-
Ripples with the
1
Light
1-3
2
0.05
0 10
up to
0.5
10 in.
5
18
appearance of scales are
Airs
1.2 sec.
min.
formed, but without foam
crests.
Small wavelets, still short
2
Light
4-6
5
0 18
0.37
0.4-2 8
1.4
6.7 ft.
8
39
but more pronounced; crests
Breeze
min.
have a glassy appearance, but
do not break.
1
1
Large wavelets, crests
3
Gentle
7-10
8.5
0.6
1.2
0.8-5.0
2.4
20
9.8
1.7
begin to break. Foam of glassy
Breeze
10
0.88
1.8
1.0-6.0
2.9
27
10
2.4
appearance. Perhaps
scattered white horses.
) Small waves, becoming
4
Moderate
1 1-16
12
1.4
2.8
1.0-7.0
3.4
40
18
3.8
larger; fairly frequent white
Breeze
13.5
1.8
3.7
1.4-7.6
3.9
52
24
4.8
horses.
14
2.0
4.2
1.5-7.8
4.0
59
28
5.2
^
16
2.9
5.8
2.0-8.8
4.6
71
40
6.6
Moderate waves, taking a
5
Fresh
17-21
18
3.8
7.8
2.5-10.0
5.1
90
55
8.3
. more pronounced long form;
jLL many white horses are
formed. (Chance of some
Breeze
19
4.3
8.7
2.8-10.6
5.4
99
65
9.2
20
5.0
10
3.0-1 1.1
5.7
1 1 1
75
10
spray).
Large waves begin to form;
6
Strong
22-27
22
6.4
13
3.4-12.2
6.3
134
100
12
£" the white foam crests are
Breeze
24
7.9
16
3.7-13.5
6.8
160
130
14
v_J more extensive everywhere.
24.5
8.2
17
3.8-13.6
7.0
164
140
15
(Probably some spray).
26
9.6
20
4.0-14.5
7.4
188
180
17
Sea heaps up and white
7
Moderate
28-33
28
1 1
23
4.5-15.5
7.9
212
230
20
foam from breaking waves
Gale
30
14
28
4.7-16.7
8.6
250
280
23
/ begins to be blown in streaks
30.5
14
29
4.8-17.0
8.7
258
290
24
(j along the direction of the
32
16
33
5.0-17.5
9.1
285
340
27
wind. (Spindrift begins to be
seen).
these situations. If scuba is used, a buddy line or other
reference system and float are recommended. A con-
venient way to attach a buddy line is to use a rubber
loop that can be slipped on and off the wrist easily,
which is preferable to tying a line that cannot be removed
rapidly. However, the line should not slip off so easily
that it can be lost inadvertently.
Heavy concentrations of plankton often accumulate
at the thermocline, especially during the summer and
offshore of the mid-Atlantic states. Divers may find
that plankton absorb most of the light at the thermocline
and that even though the water below the thermocline
is clear, a light is still necessary to see adequately.
Thermoclines in clear water diffuse light within the
area of greatest temperature change, causing a signifi-
cant decrease in visibility.
14-6
NOAA Diving Manual — October 1991
Air Diving and Decompression
Table 14-1
(Continued)
Sea-General
Wind
Sea
'
1
i
i
o
u.
Wave
Height
TJ
c
0
-o
c
_
Feet
•°
-C ~*
a
>.
a>
u O
5
c
o
0
c
_o
_
a.
■
u. 2
3
a
0
a
tt
0
■
n
01 -£,
S O M ■?
n
a
0 o
E "5
3 u
E
3 ^
Sea
State
Description
3
o
o
u
•
n
c
o
DC
11
a
■
>
■ x
> °
Signifi
Range
Period
(Secor
0
>
<
< o
I?
c a
IS
c o
CD
D
2 *
<
< -S
►-
rs
s^
s£
Moderately high waves of
8
Fresh
34-40
34
19
38
5.5-18 5
9.7
322
420
30
7
greater length; edges of crests
Gale
36
21
44
5 8-19 7
10.3
363
500
34
break into spindrift. The foam
37
23
46.7
6-20 5
10.5
376
530
37
is blown in well marked
38
25
50
6 2-20.8
10 7
392
600
38
streaks along the direction of
40
28
58
6 5-21 7
1 1 4
444
710
42
the wind Spray affects
visibility.
Q
High waves. Dense streaks
9
Strong
41-47
42
31
64
7-23
12 0
492
830
47
O
of foam along the direction of
Gale
44
36
73
7-24.2
12.5
534
960
52
the wind Sea begins to roll.
46
40
81
7 25
13 1
590
1 1 10
57
Visibility affected-
Very high waves with long
10
Whole
48-55
48
44
90
7 5-26
13 8
650
1250
63
overhanging crests. The
Gale
50
49
99
7.5-27
14.3
700
1420
69
resulting foam is in great
51.5
52
106
8-28.2
14.7
736
1560
73
patches and is blown in dense
52
54
1 10
8-28.5
14.8
750
1610
75
white streaks along the
54
59
121
8-29 5
15 4
810
1800
81
direction of the wind. On the
whole the surface of the sea
takes a white appearance.
The rolling of the sea becomes
heavy and shocklike. Visibility
/-V
is affected.
9
Exceptionally high waves
1 1
Storm
56-63
56
64
130
8 5-31
16.3
910
2100
88
(Small and medium-sized
59 5
73
148
10-32
17 0
985
2500
101
ships might for a long time be
lost to view behind the waves.)
The sea is completely covered
with long white patches of
foam lying along the direction
of the wind. Everywhere the
edges of the wave crests are
blown into froth. Visibility
affected.
Air filled with foam and
12
Hurricane
64-71
>64
>80
>164
10(35)
,181
spray Sea completely white
with driving spray visibility
very seriously affected
Source: US Navy (1985)
WARNING
Divers Should Be Extremely Cautious Around
Wrecks or Other Structures in Low Visibility
to Avoid Swimming Inadvertently Into an Area
With Overhangs
A well-developed sense of touch is extremely impor-
tant to divers or scientists working in low or zero
October 1991 — NOAA Diving Manual
underwater visibility. The ability to use touch cues
when handling tools or instruments in a strange work
environment is valuable to a diver in the dark. Rehearsing
work functions on the surface while blindfolded will
increase proficiency in underwater tasks.
Underwater low-light-level closed-circuit television
has been used successfully when light levels are reduced,
because a television camera "sees" more in these
14-7
Section 14
conditions than does the human eye. This is true mainly
when the reduced visibility is caused by the absence of
light; in cases where the problem is caused by high
turbidity, a TV camera does not offer a significant
advantage. When the purpose of the dive is inspection
or observation and a closed-circuit television system is
used, the diver serves essentially as a mobile under-
water platform. The monitor is watched by surface
support personnel who, in turn, direct the movements
of the diver. Underwater television cameras are avail-
able that are either hand held or mounted on a helmet
(see Section 8.14).
Divers are often required to dive in contaminated
water that contains either waterborne or sediment-
contained contaminants. The health hazards associated
with polluted-water diving and the equipment to be
used on such dives are described in Section 11.
14.2 DIVING SIGNALS
14.2.1 Hand Signals
Hand signals are used by divers to convey basic
information. There are various hand signalling systems
presently in use. Divers in different parts of the coun-
try and the world use different signals or variations of
signals to transmit the same message. A set of signals
used by NOAA is shown in Figure 14-2 and explained
in Table 14-3. The signals consist of hand instead of
finger motions so that divers wearing mittens can also
use them. To the extent possible, the signals were derived
from those having similar meanings on land. Before
the dive, the dive master should review the signals
shown in Figure 14-2 with all of the divers. This review
is particularly important when divers from different
geographical areas constitute a dive team or when
divers from several organizations are cooperating in a
dive. Signal systems other than hand signals have not
been standardized; whistle blasts, light flashes, tank
taps, and hand squeezes generally are used for attracting
attention and should be reserved for that purpose.
14.2.2 Surface-to-Diver Recall Signals
Unexpected situations often arise that require divers to
be called from the water. When voice communication
is not available, the following methods should be
considered:
• Acoustic Detonator (Firecracker) — a small device
ignited by a flame and thrown into the water
• Hammer — rapping four times on a steel hull or
metal plate
• Bell — held under water and struck four times
• Hydrophone — underwater speaker or sound beacon
• Strobe — used at night, flashed four times.
14.2.3 Line Signals
Divers using surface-supplied equipment use line
signals either as a backup to voice communications to
the surface or as a primary form of communication.
Line signals also may be used by divers using self-
contained equipment to communicate with the surface
or, in conditions of restricted visibility, for diver-to-
diver communications. Table 14-4 describes line sig-
nals commonly employed.
NOTE
Hand or line signals may vary by geographi-
cal area or among organizations. Divers should
review signals before diving with new buddies
or support personnel.
14.2.4 Surface Signals
If a diver needs to attract attention after surfacing
and is beyond voice range, the following signaling devices
may be used:
• Police whistle
• Flare
• Flashing strobe
• Flags (see Table 14-2).
14.3 AIR CONSUMPTION RATES
When considering diver air consumption rates, three
terms need definition:
• Respiratory minute volume (RMV), the total vol-
ume of air moved in and out of the lungs in
1 minute;
• Actual cubic feet (acf) — the unit of measure that
expresses actual gas volume in accordance with
the General Gas Law; and
• Standard cubic feet (scf), the unit of measure
expressing surface equivalent volume, under stand-
ard conditions,* for any given actual gas volume.
In computing a diver's air consumption rate, the basic
determinant is the respiratory minute volume, which is
directly related to the diver's exertion level and which,
because of individual variation in physiological response,
differs among divers (Cardone 1982). Physiological
research has yielded useful estimates of respiratory
*Standard conditions for gases are defined as 32 °F (0°C), 1 ATA
pressure, and dry gas.
14-8
NOAA Diving Manual — October 1991
Air Diving and Decompression
Table 14-2
Signal Flags, Shapes,
and Lights
Signal
Use
Meaning
White
Red
Displayed by civilian divers in the United
States. May be used with code flag alpha
(flag A), but cannot be used in lieu of flag A.
The Coast Guard recommends that the red-
and-white diver's flag be exhibited on a float
marking the location of the divers.
Divers are below. Boats should not
operate within 100 feet.
(Varies in accordance with
individual state laws)
Sport Diver Flag
White
Blue
International Code Flag
"A"
Must be displayed by all vessels operating
either in international waters or on the
navigable waters of the United States that
are unable to exhibit three shapes (see last
row of this table). Flag A means that the
maneuverability of the vessel is restricted.
"My maneuverability is restricted
because I have a driver down; keep well
clear at slow speed."
Yellow
Black Displayed by all vessels in international
and foreign waters.
Yellow
Red
International Code Flags
R"1
"I am engaged in submarine survey
work (under water operations). Keep
clear of me and go slow."
"I D"i
International Day
Shapes and Lights
Shapes/Day
Lights/Night
Displayed by all vessels in international
and foreign waters engaged in under-
♦
Black
Ball
Red water operations.
This vessel is engaged in underwater
operations and is unable to get out of
the way of approaching vessels.
Black
Diamond
Black
Ball
r~^) White
Red
Derived from USCG Navigation Rules: International/Inland 1983. and
International Code ot Signals, United States Edition. 1981. published by
the Defense Mapping Agency
October 1991 — NOAA Diving Manual
14-9
Figure 14-2A
Hand Signals
Section 14
Go Down/Going Down Go Up/Going Up Ok! Ok?
Something is Wrong
Distress
Low on Air
Out of Air
Let's Buddy Breathe
Danger
14-10
NOAA Diving Manual — October 1991
Air Diving and Decompression
Figure 14-2B
Additional Hand Signals
Me, or watch me
Come here
Go that way
am cold
Which direction?
Yes
No
Take it easy, slow down
Ears not clearing
Hold hands
Get with your buddy
Look
You lead, I'll follow
What time? What depth?
don't understand
Developed by American National Standards Institute Z86 Committee (1976)
in cooperation with the Council for National Cooperation in Aquatics
October 1991 — NOAA Diving Manual
14-11
Section 14
Table 14-3
Hand Signals
No.
Signal
Meaning
Comment
1.
Hand raised, fingers pointed up, palm
to receiver
STOP
Transmitted in the same way as a Traffic
Policeman's STOP
2.
Thumb extended downward from
clenched fist
GO DOWN or
GOING DOWN
3.
Thumb extended upward from clenched
fist
GO UP or
GOING UP
4.
Thumb and forefinger making a circle
with 3 remaining fingers extended (if
possible)
OK! or OK?
Divers wearing mittens may not be able to extend
3 remaining fingers distinctly (see both drawings
of signal)
5.
Two arms extended overhead with
fingertips touching above head to make
a large 0 shape
OK! or OK?
A diver with only one free arm may make this
signal by extending that arm overhead with
fingertips touching top of head to make the 0
shape. Signal is for long-range use
6.
Hand flat, fingers together, palm down,
thumb sticking out, then hand rocking
back and forth on axis of forearm
SOMETHING IS
WRONG
This is the opposite of OK! The signal does not
indicate an emergency
7.
Hand waving over head (may also
thrash hand on water)
DISTRESS
Indicates immediate aid required
8.
Fist pounding on chest
LOW ON AIR
Indicates signaller's air supply is reduced to the
quantity agreed upon in predive planning or air
pressure is low and has activated reserve valve
9.
Hand slashing or chopping throat
OUT OF AIR
Indicates that signaller cannot breathe
10.
Fingers pointing to mouth
LET'S BUDDY
BREATHE
The regulator may be either in or out of the
mouth
11.
Clenched fist on arm extended in
direction of danger
DANGER
and
All signals are to be answered by the receiver's repeating the signal as sent. When answering signals 7, 9,
10, the receiver should approach and offer aid to the signaller.
i
i
Source: NOAA (1979)
minute volumes for typical underwater situations likely
to be encountered by most divers (US Navy 1985).
Table 14-5 shows these estimates. These estimates of
respiratory minute volumes apply to any depth and are
expressed in terms of actual cubic feet, or liters, per
minute (acfm or alpm, respectively).
The consumption rate at depth can be estimated by
determining the appropriate respiratory minute vol-
ume for the anticipated exertion level and the absolute
pressure of the anticipated dive depth. This estimate,
expressed in standard cubic feet per minute (scfm), is
given by the equation:
Cd = RMV (Pa)
where Cd = consumption rate at depth in scfm; RMV
= respiratory minute volume in acfm; and Pa = abso-
lute pressure (ATA) at dive depth.
Problem:
Compute a diver's air consumption rate for a 50 fsw
(15.2 m) dive requiring moderate work.
14-12
Solution:
Cd = RMV (Pa)
RMV =1.1 acfm (from Table 14-5); Pa = 50/33 + 1 =
2.51 ATA; and Cd = (1.1)(2.51) = 2.76 scfm.
14.3.1 Determining Individual Air Utilization
Rates
An alternative approach that can be used by indi-
vidual divers expresses air utilization rates in terms of
pressure drop in pounds per square inch (psi) rather
than respiratory minute volume, keeping in mind that
usable tank pressure is defined as the beginning tank
pressure minus recommended air reserve (see
Table 14-8). This technique allows divers to make a timed
swim at one particular depth once they have deter-
mined their individual air utilization rate. To deter-
mine their rate, divers must read their submersible
pressure gauges at the beginning and end of a dive to a
NOAA Diving Manual — October 1991
I
Air Diving and Decompression
Table 14-4
Line Pull Signals for
Surface-to-Diver Communication
Emergency Signals
2-2-2 Pulls "I am fouled and need the assistance of
another diver"
3-3-3 Pulls "I am fouled but can clear
myself"
4-4-4 Pulls "Haul me up immediately'
All signals will be answered as given
except for
emergency signal 4-4-4
From tender to diver
1 Pull "Are you all right?"
When diver is descending,
one pull means
"stop"
2 Pulls "Going down"
During ascent, 2 pulls mear
i "You have come
up too far, go back down until we stop you"
3 Pulls "Stand by to come up"
4 Pulls "Come up"
2-1 Pulls "I understand," or "Answer
the telephone"
From diver to tender
1 Pull "I am all right" or "I am on
the bottom"
2 Pulls "Lower" or "Give me slack
■
3 Pulls "Take up my slack"
4 Pulls "Haul me up"
2-1 Pulls "I understand" or "Answer
the telephone"
3-2 Pulls "More air"
4-3 Pulls "Less air"
Special signals from the diver to the tender should be
devised as required by the situation
Searching Without
With
Signals circling line
circling line
7 Pulls "Go on (or off)
Same
searching signals"
1 Pull "Stop and search
Same
where you are"
2 Pulls "Move directly
"Move away
away from the
from the
tender if given
weight"
slack, move toward
the tender if strain
is taken on the life-
line"
3 Pulls "Go to your right"
"Face the
weight and
go right"
4 Pulls "Go to your left"
"Face the
weight and
go left"
determine the amount of air used during the timed
dive (A psi);
(2) Using the following formula, estimate air utilization
rate on the surface:
A psi/time (min)
(depth in ft + 33)/33
psi per minute on the surface;
(3) Find the psi per minute on the surface on the left
side of the Air Utilization Table (Table 14-6)
that is closest to your estimated psi per minute.
Read across until you come to the desired depth,
which will give you your estimated air utilization
rate;
(4) To estimate how many minutes your tank of air
will last at that depth, divide the number of usa-
ble psi in the tank (as shown on your submersible
pressure gauge) by the psi per minute used at
that depth.
Problem:
A diver swims a distance at 30 fsw (9 m) in 10 minutes;
the submersible pressure gauge reads 2350 psi at the
start and 2050 at the end of the timed dive, showing
that a total of 300 psi was consumed. What is the
diver's air utilization?
The basic equation is:
A psi/time (min)
(depth in ft + 33)/33
Solution:
300 (psi)
10 (minutes)
30 (depth) + 33
33
30
63
33
30
1.9
5.7 psi/min.
Source: NOAA (1979)
The diver would consume 15.7 psi per minute at the
surface. Knowing your utilization rate at the surface
allows you to use Table 14-6 to find your rate at any
depth.
Air utilization rates determined by this method are
valid only for air coming from the same type of tank as
that used on the timed swim. Further, individuals vary
somewhat from day to day in their air utilization rates,
and these calculations should thus be considered esti-
mates only (Cardone 1982).
constant depth. These readings give them the informa-
tion needed to use the simple 4-step procedure shown
below.
(1) Subtract ending psi (as read from the submersi-
ble pressure gauge) from the beginning psi to
October 1991 — NOAA Diving Manual
14.4 SELF-CONTAINED DIVING
14.4.1 Scuba Duration
Knowing the probable duration of the scuba air sup-
ply is vital to proper dive planning. With scuba, the
duration of the available air supply is directly depend-
14-13
Section 14
Table 14-5
Respiratory Minute Volume (RMV)
at Different Work Rates
Respiratory Minute Volume
Activity
Actual liters/min Actual cubic ft/min
(STP) (STP)
REST
Bed rest (basal)
Sitting quietly
5 0.18
6 0.21
8 0.28
Standing still
LIGHT
WORK
SLOW WALKING ON HARD BOTTOM
12 0.42
14 0.49
16 0.60
Walking, 2 mph
SWIMMING, 0.5 KNOT (SLOW)
MODERATE
WORK
SLOW WALKING ON MUD BOTTOM
20 0.71
24 0.85
26 0.92
30 1.1
Walking, 4 mph
SWIMMING, 0.85 knot (av. speed)
MAX. WALKING SPEED, HARD BOTTOM
HEAVY
WORK
SWIMMING, 1.0 KNOT
35 1.2
35 1.2
44 1.5
MAX. WALKING SPEED, MUD BOTTOM
Running, 8 mph
SEVERE
WORK
SWIMMING, 1.2 KNOTS
53 1.9
84 2.9
Uphill running
Underwater activities are in capitals.
Adapted from US Navy (1985)
ent on the diver's consumption rate. Scuba air supply
duration can be estimated using the equation:
r* Va
Da = —
Cd
where Da = duration in min; Va = available volume in
scf; and Cd = consumption at depth in scfm.
The available volume depends on the type (rated
volume and rated pressure) and number of cylinders
used, the gauge pressure measured, and the recom-
mended minimum cylinder pressure. The diver's air
consumption rate depends on the depth and the exer-
tion level of the dive.
The "standard 72" steel scuba cylinder has an inter-
nal volume of 0.423 ft3 (1 1.98 L) at 1 ATA. At its rated
pressure (2475 psig), the cylinder contains a delivera-
ble volume of 71.2 ft3 (2016 L).
For a given scuba cylinder, the ratio of rated volume
to rated pressure is a constant, meaning that a constant
volume of air is delivered for each unit of cylinder
pressure drop. Mathematically, this results in a linear
relationship between gauge pressure and deliverable
volume. Figure 14-3 shows this relationship for a
71.2 ft3 (2016 L) steel cylinder and an 80 ft3 (2266 L)
aluminum cylinder. Deliverable volumes at any gauge
14-14
pressure for these two cylinder types can be read
directly from Figure 14-3, or they can be individually
computed using the equation
Vd = Pgk
where Vd = deliverable volume in scf; Pg = gauge
pressure in psig; and k = cylinder constant. This
equation can be used for any type of cylinder; see
Table 14-7 for the appropriate cylinder constant.
For planning purposes, the available volume of air is
the difference between the deliverable volume at a
given cylinder pressure and the recommended minimum
cylinder pressure. The recommended minimum cylin-
der pressures for the two most commonly used scuba
cylinder types are shown in Table 14-8. The available
volume of air in a diver's supply is given by the equation
Va = N(Pg - Pm)k
where Va = available volume in scf; N = number of
cylinders; Pg = gauge pressure in psig; Pm ^ recom-
mended minimum pressure in psig; and k = cylinder
constant. For planning purposes, estimates of cylinder
duration are based on available air volumes rather
than deliverable air volumes.
NOAA Diving Manual — October 1991
Air Diving and Decompression
Table 14-6
Air Utilization Table at Depth
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October 1991 — N0AA Diving Manual
14-15
Section 14
Figure 14-3
Deliverable Volumes
at Various Gauge Pressures
3000-
2500
CO
CO
£ g>
0_ 'co
a) Q-
CO
C5
1500
1000
500
10 20 30 40 50 60 70
Deliverable Volume
Cubic Feet
80
Source: NOAA (1979)
Problem:
Estimate the duration of a set of twin 80 ft3 (2266 L)
aluminum cylinders charged to 2400 psig for a 70 fsw
(21.3 m) dive requiring the diver to swim at 0.5 knot
(0.25 m/s).
Solution:
The basic equation for duration is
Da=^
Cd
where Da = duration in minutes; Va = available
volume in scf; and Cd = consumption rate at depth in
scfm.
Step 1
Determine Va using
Va = N(Pg - Pm)k
Va = 2(2400 psig - 600 psig) (0.0266 scf/ psig)
= 2(1800 psig) (0.0266 scf/psig)
= 95.76 scf.
Step 2
Determine Cd using
Cd = RMV (Pa)
Table 14-7
Cylinder Constants
Rated
Working
Rated
Volume
Pressure
Pressure
Cylinder
(scO
(Psig)
(psig)
Constant
Aluminum
90
3000
3000
0.0300
80
3000
3000
0.0266
71.2
3000
3000
0.0237
50.0
3000
Steel
3000
0.0166
100
2400
2640
0.0378
71.2
2250
2475
0.0288
52.8
1800
1980
0.0267
50.0
2250
2475
0.0202
42.0
1880
2068
0.0203
38.0
1800
1980
0.0192
Adapted from NOAA (1979)
where RMV = respiratory minute volume in acfm; Pa
= absolute pressure at dive depth.
Cd = 0.6 acfm
= 1.87 scfm.
Step 3
Solve the basic equation for Da
n Va
Da = —
(1+0
14-16
Cd
_ 95.76 scf
" 1.87 scfm
= 51.2 minutes.
Table 14-9 shows estimates of the duration of a
single steel 71.2 ft3 (2016 L) cylinder at five exertion
levels for various depths. These estimated durations
are computed on the basis of an available air volume of
58.9 ft3 (Va = 2475 psig - 430 psig) (0.0288 ft3/psig).
14.4.2 Scuba Air Requirements
Total air requirements should be estimated when
planning scuba operations. Factors that influence the
total air requirement are depth of the dive, antici-
pated bottom time, normal ascent time at 60 ft/min
(18.3 m/min), any required stage decompression time,
and consumption rate at depth. For dives in which direct
ascent to the surface at 60 ft/min (18.3 m/min) is
allowable, the total air requirement can be estimated
using the equation
TAR = tdt (Cd)
where TAR = total air requirement in scf; tdt = total
dive time in minutes (bottom time plus ascent time at
NOAA Diving Manual — October 1991
Air Diving and Decompression
Table 14-8
Scuba Cylinder
Pressure Data
Cylinder
Type
Rated
Pressure (psig)
Working
Pressure (psig)
Reserve
Pressure (psig)
Recommended
Minimum
Pressure (psig)
Steel 72
Aluminum
80
2475
3000
2250
3000
500
500
430
600
Source: NOAA (1979)
Table 14-9
Estimated Duration of
71.2 ft3 Steel Cylinder
RMV
0.25 acfm
0.7 acfm
1.1 acfm
1.5 acfm
2.2 acfm
At
Light
Moderate
Heavy
Severe
Depth
ATA
Rest
Work
Work
Work
Work
0
1.0
235.6
84.1
53.5
39.3
26.8
33
2.0
117.9
42.1
26.8
19.6
13.4
66
3.0
78.5
28.0
17.8
13.1
8.9
99
4.0
58.9
21.0
13.4
9.8
6.7
132
5.0
47.1
16.8
10.7
7.8
5.4
165
6.0
39.3
14.0
8.9
6.5
4.4
Values are minutes.
60 ft/min); and Cd = consumption rate at depth in
scfm.
Problem:
Estimate the total air requirements for a 30-minute
dive to 60 fsw (18.3 m) involving swimming at
0.85 knot (0.43 m/s).
Solution:
Step 1
Determine tdt. Toial dive time is defined as the sum of
the bottom time and normal ascent time at 60 ft/min
(18.3 m/min):
tdt = 30 + 1 = 31 minutes.
Step 2
Determine Cd using the equation
Cd = RMV (Pa)
RMV = 0.92 acfm (from Table 14-5)
Pa = —+ l = 2.81 ATA
33
Cd = (0.92 acfm) (2.81 ATA)
= 2.59 scfm.
Source: NOAA (1979)
Step 3
Determine TAR using the equation
TAR = tdt (Cd)
= (31 min) (2.59 acfm)
= 80.37 scf.
For dives in which stage decompression will be
necessary, the total air requirement can be estimated
using the equation
TAR = Cd (BT + AT) + Cd,T, + Cd2T2 + Cd3T3 (etc.)
where Cd,T,, Cd2T2, and Cd3T3 are the air consump-
tion rates and times at the respective decompression
stops.
Problem:
Estimate the total air requirement for a 60-minute
dive to 70 fsw (21.3 m) requiring the diver to swim at
0.5 knot (0.25 m/s).
Solution:
Step 1
Determine Cd and Cd, using the equation
Cd = RMV (Pa)
= (0.6 acfm) (3.12 ATA)
= 1.87 scfm.
October 1991 — NOAA Diving Manual
14-17
Section 14
Figure 14-4
Typical High Pressure Cylinder
Bank Air Supply
Step 2
Determine the total time for the dive, ascent, and
decompression stops. For the dive and ascent to the
first decompression stop, add the bottom time and the
ascent time (to the nearest whole minute) to the first
decompression stop at 60 ft/min (18.3 m/min).
BT + AT = 60 + 1 =61 minutes.
This dive requires a 10-foot decompression stop. At an
ascent rate of 60 ft/min, it will take 1 minute to ascend
from 70 feet (21.3 m) to 10 feet (3 m).
The time required for decompression at 10 feet (3 m) is
8 minutes, according to the Air Decompression Table
(US Navy 1985) for a dive to 70 feet for 60 minutes.
Cd, = 0.6 (— + 1 j = 0.78 scfm
(Assume light work (0.6 acfm) on decompression stop.)
Step 3
Determine TAR using the equation for this case
TAR = Cd (BT + AT) + CdjT,
= (1.87 scfm) (61 min) + (0.78 scfm) (8 min)
= 114.1 + 6.2 = 120.3 scf.
Computation of these estimates during predive planning
is useful to decide whether changes in assigned tasks,
task planning, etc. are necessary to ensure that the dive
can be conducted with the available air supply. However,
positioning an auxiliary tank at the decompression
stop is considered a safer practice than relying on
calculations of the available air supply.
14.5 HIGH-PRESSURE AIR STORAGE
SYSTEMS
For most scientific surface-supplied diving operations, a
high-pressure air storage system is better than a low-
pressure compressor system. In some cases, the size of
the surface support platform dictates the use of the
simpler and more compact low-pressure compressor
system. A high-pressure system can be tailored con-
ven-'ently to the requirements of a particular operation,
is easier to handle than the other type of system, and
offers the additional advantage of reduced noise and
improved communication. The planning factors that
influence the configuration of a high-pressure air storage
system include:
• Depth of the planned dive
• Number of divers to be supplied and the anticipated
exertion level
• Type of breathing apparatus (free flow or demand)
• Size of the surface support platform.
FROM
SECONDARY
SUPPLY
AIR SUPPLY TO DIVERS
1
oo-
PRESSURE REGULATOR
Source: US Navy (1985)
A complete system includes high-pressure cylinders
(200-350 standard ft3 size), the necessary piping and
manifolds, a pressure reduction regulator, and a vol-
ume cylinder (at least 1 ft3 volume) (Figure 14-4). A
high-pressure filter should always be incorporated into or
be located just upstream of each pressure regulator.
Filter elements should be of the woven-metal cloth
type and should have a collapse pressure rating greater
than the maximum possible pressure differential. A
high-pressure gauge must be located ahead of the
pressure reduction regulator, and a low-pressure gauge
must be connected to the volume cylinder. The volume
cylinder must be fitted with an overpressure relief
valve. A manually controlled regulator by-pass valve
or a redundant regulator with its own filter also should
be included in the system.
NOTE
If cylinder banks are used to back up a com-
pressor supply, the bank must be manifolded
with the primary source so that an immedi-
ate switch from primary to secondary air is
possible.
System Capacity and Air Supply Requirements
Estimations of air supply requirements and duration
of air supplies for surface-supplied divers are the same
as those of scuba divers (Section 14.4.2) except when
free-flow or free-flow/demand breathing systems are
14-18
NOAA Diving Manual — October 1991
Air Diving and Decompression
used; in these cases, the How, in acfm, is used (in all
calculations) instead of RMV (see Table 14-5 and
Table 14-10). Also, the minimum bank pressure must
be calculated to be equal to 220 psig plus the absolute
pressure of the dive (expressed in psia).
Problem:
Estimate the air requirements for a 90 fsw (27 m) dive
for 70 min with a free-flow helmet. This dive requires
decompression stops of 7 minutes at 20 feet (6.1 m)
and 30 minutes at 10 feet (3 m).
TAR = Cd (BT + AT) + Cd,T, + Cd2T2.
Step 1
Determine Cd, Cd,, Cd2
Cd = flow x Pa
= (6 acfm)(3.73 ATA) = 22.4 scfm
Cd, = (6 acfm)(1.61 ATA) = 9.7 scfm
Cd: = (6 acfm)(1.30 ATA) = 7.8 scfm.
Step 2
TAR = 22.4 (70 + 1.2) + 9.7 (7) + 7.8 (30)
= 1595 + 67.9 + 234
= 1897 scf.
Cylinder constants for large high-pressure air stor-
age systems are determined in the same fashion as
those for scuba cylinders, i.e., rated volume/rated
pressure = k.
The procedure for determining available volume of
air is also the same as for scuba. For example,
Va = N(Pg - Pm) k.
Problem:
Determine the number of high-pressure air cylin-
ders required to supply the air for the above dive
(1897 scf) if the rated volume equals 240 scf, rated
pressure equals 2400 psi, and beginning pressure equals
2000 psi.
Step 1
How much air could be delivered from each cylinder?
Va = N(Pg - Pm) k
240 scf „ , .
k - = 0. 1 scf/ psi
2400 psi
Pm = 220
psi + I
90 + 33
33
X 14.7
)
Va = 1(2000 - 275) X 0.1
Va = 172.5 scf/cylinder.
October 1991 — NOAA Diving Manual
Table 14-10
Flow-Rate Requirements
for Surface-Supplied Equipment
Equipment Type
Flow Rate
Free flow/demand
Free flow
1.5 acfm
6.0 acfm
NOTE: Significant variations in
on the flow-valve set by the
minimum estimates.
these values can
diver. Therefore,
occur, depending
these values are
Source: Morgan Wells
Step 2
How many cylinders would be required in the bank
to supply the required amount of gas?
N =
vol. required
vol/cyl
1 897 scf
172.5 scf/cyl
= 10.9 or 1 1 cylinders.
14.6 DECOMPRESSION ASPECTS OF AIR
DIVING
The principal inert gas in air is nitrogen. The role of
nitrogen in the physiological processes of inert gas
absorption and elimination and its role in decompres-
sion sickness are discussed in detail in Sections 3 and
20. When air is breathed under pressure, the inert
nitrogen diffuses into the various tissues of the body.
Nitrogen uptake by the body continues, at different
rates for the various tissues, as long as the partial
pressure of the inspired nitrogen is higher than the
partial pressure of the gas absorbed in the tissues.
Consequently, the amount of nitrogen absorbed increases
as the partial pressure of the inspired nitrogen (depth)
and the duration of the exposure (time) increases.
When the diver begins to ascend, the process is reversed
because the nitrogen partial pressure in the tissues
exceeds that in the circulatory and respiratory sys-
tems. If the partial pressure of nitrogen in the blood
significantly exceeds ambient pressure, bubbles can
form in the tissues and blood, causing decompression
sickness.
To prevent the development of decompression sick-
ness, several decompression tables have been developed.
These tables take into consideration the amount of
nitrogen absorbed by the body at various depths for
given time periods. They also consider allowable pressure
gradients that can exist without excessive bubble for-
14-19
Section 14
mation and the different gas elimination rates associated
with various body tissues.
Stage decompression, which involves stops of spe-
cific durations at given depths, is used for air diving
because of its operational simplicity. The decompres-
sion tables require longer stops at more frequent inter-
vals as the surface is approached because of the higher
gas expansion ratios at shallow depths.
A basic understanding of the use of these decom-
pression tables is essential to the safety of a diving
operation. The constraints these tables and procedures
impose on the conduct of air diving operations must
always be a factor in dive planning.
14.6.1 Definitions
The definitions of some terms used frequently in
discussing the decompression aspects of air diving (which
are defined in the glossary) are:
Depth — The maximum depth attained during the
dive, measured in feet of seawater (fsw)
Total bottom time — The total elapsed time starting
when the diver leaves the surface to the time (next
whole minute) that ascent begins (in minutes)
Decompression stop — The designated depth and time
at which a diver must stop and wait during ascent from
a decompression dive; the depth and time are specified
by the decompression schedule used
Decompression schedule — A set of depth-time re-
lationships and instructions for controlling pressure
reduction
Normal ascent rate — 60 feet per minute (18.3 m/min)
No-decompression dive — A dive from which a diver
can return directly to the surface at a controlled rate
without spending time at shallower depths to allow
inert gas to be eliminated from the body
Decompression dive — Any dive involving a depth
deep enough or a duration long enough to require con-
trolled decompression; any dive in which ascent to the
surface must be carried out through decompression
stops
Single dive — Any dive conducted no less than
1 2 hours or more after a previous dive by the same diver
Residual nitrogen — A theoretical concept that de-
scribes the amount of nitrogen remaining in a diver's
tissues after a hyperbaric exposure
Surface interval — The elapsed time between surfacing
from the dive and the time when the diver leaves the
surface for the next dive
Repetitive dive — Any dive conducted within 12 hours
of a previous dive
14-20
Repetitive group designation — A letter that is used
in decompression tables to designate the amount of
residual nitrogen in a diver's body for a 12-hour period
after a dive
Residual nitrogen time — Time (in minutes) added
to actual bottom time for calculating the decompres-
sion schedule for a repetitive dive, based on the con-
cept of residual nitrogen
Equivalent single dive bottom time — A dive for which
the bottom time used to select the decompression sched-
ule is the sum of the residual nitrogen time and the
actual bottom time of the dive
Exceptional exposure dives — Any dive in which the
diver is exposed to oxygen partial pressures, environ-
mental conditions, or bottom times considered to be
extreme.
14.6.2 Air Decompression Tables and Their
Applications
In the conduct of normal operations, two dive tables
are commonly used. These tables are:
• U.S. Navy No-Decompression Limits and Repeti-
tive Group Designation Table for No-Decompres-
sion Air Dives (also called the No-Decompression
Table) (see Table 14-11).
• U.S. Navy Standard Air Decompression Table
(also called the Standard Air Table) (see
Appendix B).
For non-saturation air dives, these two tables cover
every possible decompression schedule required in rou-
tine diving. Except under the guidance of qualified
diving medical personnel in emergency situations, these
tables must be followed to ensure maximum diving
safety. In repetitive diving situations, these tables are
supplemented by the U.S. Navy Residual Nitrogen
Timetable for Repetitive Air Dives (also called the
Repetitive Dive Table) (see Table 14-12), which is a
planning aid, not a decompression table.
Whether a dive is a decompression or a no-decom-
pression dive, the use of these decompression tables
involves observing the following instructions.
• All dives that are not separately listed are covered
in the tables by the next deeper and next longer
schedule; DO NOT INTERPOLATE
• Enter the tables at the listed depth that is exactly
equal to, or is the next greater depth than, the
maximum depth attained during the dive
• Select the bottom time of the bottom times listed
for the selected depth that is exactly equal to, or is
next greater than, the bottom time of the dive
NOAA Diving Manual — October 1991
Air Diving and Decompression
Table 14-11
No-Decompression Limits and Repetitive Group
Designation Table for No-Decompression
Air Dives
Depth
(feet)
No decom-
pression
limits
(mm)
Repetitive Group Designation
B
D
60
35
25
20
15
120 210 300
70 110 160 225 350
50 75 100 135 180 240 325
Uhi 1,") 11,0 195
30 45 60 75 95 120 145
245
170
mm
80
40
5
10
15
20
25
30
35
90
30
5
10
I?
15
<?0
25
30
100
25
5
7
10
15
20
22
25
1 10
20
5
10
13
15
20
Hi
120
15
5
10
12
15
130
10
5
3
10
■i
140
10
5
7
10
150
5
5
■1
160
5
5
170
5
5
■1
180
5
5
190
5
5
40
315
205
250 310
.35
310
5
15
25
40
50
60
80
100
120
140
mm
5
15
25
30
40
50
70
80
100
110
50
100
10
15
<55
30
40
50
60
70
80
60
60
10
15
20
25
30
40
50
55
60
70
50
5
10
15
20
30
35
40
45
50
160
130
90
190
150
100
220
170
270 310
200
Source: US Navy (1985)
• Use the decompression stops listed on the line for
the selected bottom time
• Ensure that the level of the diver's chest is kept as
close as possible to each decompression depth for
the number of minutes listed
• Commence timing each stop on arrival and resume
ascent when specified time has elapsed. Do not
include ascent time as part of stop time
• Observe all special table instructions
• Always fill out a Repetitive Dive Worksheet or a
similar systematic guideline.
When using the decompression tables, a normal ascent
rate is necessary. If for some reason the normal ascent
rate cannot be maintained, the decompression sched-
ule must be modified as follows:
• If the delay was at a depth greater than 50 feet
(15.2 m), increase the bottom time of the dive by
the difference between the time used in ascent and
the time that should have been used at a rate of
60 feet/minute (18.3 m/min); decompress according
to the requirements of the new total bottom time
• If the delay was at a depth less than 50 feet
(15.2 m), increase the first stop by the difference
between the time used in ascent and the time
that should have been used at the rate of
60 feet/minute (18.3 m/min).
14.6.2.1 No-Decompression Limits and Repetitive
Group Designation Tables for
No-Decompression Air Dives
The No-Decompression Table (Table 14-11) serves
two purposes. First, it summarizes all the depth and
bottom time combinations for which no decompression
is required. Second, it provides the repetitive group
designation for each no-decompression dive. Although
decompression is not required, an amount of nitrogen
remains in the diver's tissues after every dive. For
additional dives within a 12-hour period, the diver
must consider this residual nitrogen when calculating
his or her decompression requirements.
Each depth listed in the No-Decompression Table
has a corresponding no-decompression limit given in
minutes. This limit is the maximum bottom time that a
diver may spend at that depth without requiring decom-
pression. The columns to the right of the no-decom-
pression limits column are used to determine the
repetitive group designation that must be assigned to a
diver after every dive. Dives to depths shallower than
35 feet (10 meters) do not have a specific no-decom-
pression limit. However, such dives are restricted in
that they provide repetitive group designations only
for bottom times of between 5 and 6 hours. These
bottom times are considered the limitations of the
October 1991 — NOAA Diving Manual
14-21
Section 14
Table 14-12
Residual Nitrogen Timetable
for Repetitive Air Dives
*Dives after surface intervals of more than 12 hours are not repetitive
dives. Use actual bottom times in the Standard Air Decompression
Tables to compute decompression for such dives. See section 14.6.2.3
for instructions in the use of this table.
c
B
0:10
1:39
A
0:10
210
1:40
2 49
010
12:00
2:11
1 2 00
2:50
1 2:00
a
y
D
0 10
1:09
1 10
2:38
2:39
548
5:49
1 2 00
+*
E
0:10
0:54
0:55
1 57
1 58
3:22
3:23
6:32
6:33
1 2:00
v H
F
0:10
0:45
046
1:29
1 30
2:28
229
3:57
3:58
7:05
7:06
12 00
\
G
010
0:40
0:41
1 15
1 16
1:59
2:00
2:58
2:59
4:25
4:26
7:35
736
1 2 00
0:10
0:36
0:37
1:06
1 07
1:41
1:42
2:23
2:24
3:20
321
4 49
4-50
7:59
8:00
1 2:00
s
1 0:10
0:33
0 34
0:59
1:00
1 29
1 30
2:02
203
2:44
2:45
3:43
3:44
5:12
5:13
8:21
8:22
1 2:00
,#e
J 0:10 0:32
0:31 0:54
0:55
1 19
1:20
1 47
1:48
2:20
221
3 04
3:05
4 02
403
5 40
5:41
8:40
8:41
12:00
It*
K
0:10 0:29 0:50
0:28 0:49 1:11
1 12
1:35
1:36
2:03
2:04
2:38
2.39
3:21
322
4:19
420
5:48
5:49
8:58
8:59
1 2.00'
L
0:10
0:26
0:27 0:46 1 05
0:45 1:04 1:25
1
1
26
49
1:50
2:19
2:20
253
2.54
336
3 37
4:35
4:36
6:02
6:03
9:12
9:13
1 2:00
M
0:10
0:25
0:26
0:42
0:43 1:00 1:19
0:59 1:18 1:39
1
2
40
05
2:06
2:34
2:35
308
3:09
3:52
3:53
4:49
4:50
618
6:19
928
9:29
1 2:00 ;
N
0:10
0:24
0:25
0:39
0:40
0:54
0:55 1:12 1:31
1:11 1:30 1:53
1:54
2:18
2:19
2:47
248
3:22
3:23
404
4:05
5:03
5:04
632
6 33
9:43
9:44
12:00
0
0:10
0:23
0:24
0:36
0:37
0:51
0:52
1:07
1:08 1:25 1:44
1 :24 1 43 2:04
2:05
2:29
2:30
259
3:00
333
3.34
4:17
4:18
5:16
5:17
6:44
6:45
9:54
9:55
1 2:00
0:10
0:22
0:23
0:34
0:35
0:48
0:49
1:02
1:03
1:18
1:19 1:37 1:56
1:36 1:55 2 17
2:18
2:42
2:43
3:10
3:11
3:45
3.46
4:29
430
5:27
5:28
6 56
6:57
1005
10:06
1 2:00*
NEW-*- Z
GROUP
DESIGNATION
0
N
M
L
K J 1
H
G
F
E
D
C
B
A
REPETITIVE
DIVE
DEPTH
40 257
241
213
187
161
138 116 101
87
73
61
49
37
25
17
7
50 169
160
142
124
111
99 87 76
66
56
47
38
29
21
13
6
60 122
117
107
97
88
79 70 61
52
44
36
30
24
17
11
5
70 100
96
87
80
72
64 57 50
43
37
31
26
20
15
9
4
80 84
80
73
68
61
54 48 43
38
32
28
23
18
13
8
4
90 73
70
64
58
53
47 43 38
33
29
24
20
16
11
7
3
100 64
62
57
52
48
43 38 34
30
26
22
18
14
10
7
3
110 57
55
51
47
42
38 34 31
27
24
20
16
13
10
6
3
120 52
50
46
43
39
35 32 28
25
21
18
15
12
9
6
3
130 46
44
40
38
35
31 28 25
22
19
16
13
11
8
6
3
140 42
40
38
35
32
29 26 23
2
1
0
18
15
12
10
7
5
2
150 40
38
35
32
30
27 24 22
9
17
14
12
9
7
5
2
160 37
36
33
31
28
26 23 20
18
16
13
11
9
6
4
2
170 35
34
31
29
26
24 22 19
17
15
13
10
8
6
4
2
180 32
31
29
27
25
22 20 18
16
14
12
10
a
6
4
2
190 31
30
28
26
24
21 19 17
15
13
11
10
8
6
4
2
RESIDUAL NITROGEN TIMES (MINUTES)
14-22
Adapted from US Navy (1985)
NOAA Diving Manual — October 1991
Air Diving and Decompression
No-Decompression Table, and no field requirement
for diving should extend beyond them.
Any dive to depths below 35 feet (10 meters) that
has a bottom time greater than the no-decompression
limit given in this table is a decompression dive and
should be conducted in accordance with the Standard
Air Table.
NOTE
If field requirements for dives in the depth
range 0-21 feet (0 - 6.5 m) exceed the
no-decompression limits specified in the No-
Decompression Table (Table 14-11), they may
be conducted in this range without decom-
pression, regardless of bottom time. Consult
the Standard Decompression Schedule Fol-
lowing Normoxic Nitrogen-Oxygen Saturation
Exposures (see Section 16) for details.
No-Decompression Limits and Repetitive Croup
Designation Table for No-Decompression Air Dives
(Table 14-11)
Special Instructions
• No-decompression limits column: allowable maximum
bottom time that permits surfacing directly at
60 feet/minute (18.3 m/min) with no decompression
stops
• For longer bottom times, use the Standard Air Table
• Repetitive group designation table: time periods in
each vertical column are the maximum exposures at
various depths during which a diver will remain within
the group listed at the head of the column
• Repetitive group designation: enter table on exact or
next greater depth than exposure and select the expo-
sure time that is exactly the same as or next greater
than the actual exposure time. Read the group des-
ignation (letter) at the top of the column for the next
dive
• Exposure times beyond 5 hours and to depths less
than 40 feet (12.2 meters) are beyond the field
requirements of this table.
Decompression from most routine air diving operations
will be in accordance with the Standard Air Decom-
pression Table (Appendix B). Special instructions for
the use of this table are listed below.
14.6.2.2 Standard Air Decompression Table
The Standard Air Decompression Table (Appen-
dix B) combines the Standard Air Table and the Excep-
October 1991 — NOAA Diving Manual
tional Exposure Air Table into one table. To delineate
clearly the standard and exceptional exposure decom-
pression schedules, the exceptional exposure schedules
have been printed in blue.
If the bottom time of a dive is less than the first
bottom time listed for its depth, decompression is not
required. The diver may ascend directly to the surface
at a rate of 60 feet per minute (18.3 m/min). The
repetitive group designation for no-decompression
dives is given in the No-Decompression Table.
There are no repetitive group designations for
exceptional exposure dives. Repetitive dives are not
permitted after an exceptional exposure.
Standard Air Decompression Table
Special Instructions
• Rate of ascent between stops is not critical for stops
of 50 feet (15.2 meters) or less
• If the dive was particularly cold or strenuous, use the
next longer bottom time listed for the schedule used.
14.6.2.3 Residual Nitrogen Timetable for
Repetitive Air Dives
If additional dives are conducted within a 1 2-hour
period after any air dive, it is necessary to determine
the level of residual nitrogen in the diver's body at the
time each additional dive is begun.
During the 12-hour period after an air dive, the
quantity of residual nitrogen gradually returns to its
normal level. The quantity of residual nitrogen imme-
diately after a dive is designated by the repetitive
group letter assigned by either the Standard Air Decom-
pression Table (Appendix B) or the No-Decompression
Table (Table 14-11). This designation relates directly
to the residual nitrogen level on surfacing. As nitrogen
passes out of the tissues and blood, the repetitive group
designation changes. The Residual Nitrogen Timeta-
ble (Table 14-12) permits this designation to be
determined at any time during the surface interval.
Just before beginning a repetitive dive, the residual
nitrogen time should be determined by using the Residual
Nitrogen Timetable. This time is then added to the
actual bottom time to give the bottom time of the
equivalent single dive to be used to select the appro-
priate decompression schedule. Equivalent single dives
that require the use of exceptional exposure decom-
pression schedules should be avoided whenever possible.
The upper portion of the Residual Nitrogen Timeta-
ble is composed of various intervals between 10 minutes
and 12 hours, expressed in hours:minutes (2:21 =
2 hours 21 minutes). Each interval has two limits, a
14-23
Section 14
minimum time (top limit) and a maximum time (bot-
tom limit). Residual nitrogen times corresponding to
the depth of the repetitive dive are given in the body of
the lower portion of the table.
To use the Residual Nitrogen Timetable, the special
instructions listed below should be followed for each
portion of the Timetable.
NOTE
There is one exception to the Residual Ni-
trogen Timetable for Repetitive Air Dives:
when the repetitive dive is to the same or a
greater depth than the previous dive, the
residual nitrogen time may be longer than
the actual bottom time of the previous dive.
In this event, add the actual bottom time of
the previous dive to the actual bottom time
of the repetitive dive to obtain the equiva-
lent single dive time.
Surface Interval Credit for Air Dives
Special Instructions
• Surface interval time in the schedule is in hours and
minutes
• Surface interval must be at least 10 minutes
• Repetitive group designation after surface interval:
enter the schedule on the diagonal slope using the
group designation from previous dive. Read hori-
zontally until the actual surface interval is equal to
or between the interval shown in the schedule. Read
the new group designation at the bottom of the column.
• Dives after surface intervals of more than 12 hours
are not repetitive dives. Use actual bottom times and
the appropriate decompression table to compute the
decompression needed for such dives.
Residual Nitrogen Timetable for Repetitive Dives
Special Instructions
• Bottom times listed in this timetable are called residual
nitrogen times.
• Residual nitrogen time is the time a diver is to con-
sider that he or she has already spent on the bottom
when a repetitive dive to a specific depth is started.
• Residual nitrogen time: enter the timetable vertically
with the repetitive group from the surface interval
credit table. Read directly the bottom time to be added
to the repetitive dive in the depth column for that dive.
14-24
• If the surface interval is less than 10 minutes, the
residual nitrogen time is the bottom time of the previous
dive.
14.6.2.4 Recordkeeping and Table Use
To verify that decompression requirements have been
determined accurately, carefully follow the steps outlined
in the Repetitive Dive Flowchart (Figure 14-5). A
systematic means of recording the steps in the Repetitive
Dive Flowchart is the Repetitive Dive Worksheet
(Figure 14-6).
To demonstrate the correct application of the air
decompression tables and the proper use of the Repetitive
Dive Flowchart and Worksheet, examples of several
situations are presented with the appropriate flowchart
sequence and worksheet solution. These examples cover
most single and repetitive dive situations likely to be
encountered during field operations. For correct decom-
pression table and schedule selection, reference should
be made to the instructions in Section 14.6.2, any
special instructions for the table selected, and instruc-
tions for the Residual Nitrogen Timetable.
It is frequently necessary to determine the minimum
permissible surface interval for a no-decompression
repetitive dive. In this situation, the planned depth and
probable duration of the repetitive dive should be evalu-
ated carefully.
To determine the minimum permissible surface inter-
val for a no-decompression repetitive dive, the follow-
ing sequence of steps should be observed:
• Determine the repetitive group designation from
the previous dive.
• Subtract the probable bottom time of the repetitive
dive from the applicable no-decompression time
limit for the depth of the repetitive dive. The result is
the maximum allowable residual nitrogen time
after the surface interval.
• Enter the Residual Nitrogen Timetable horizontally
with the appropriate depth for the repetitive dive
and find the residual nitrogen time that is exactly
equal to or less than the maximum allowable residual
nitrogen time determined in Step 2.
• Once the appropriate residual nitrogen time is
located, move vertically up the column and find the
repetitive group designation that corresponds to this
residual nitrogen time at the repetitive dive depth.
• From the surface interval credit table portion of
the Residual Nitrogen Timetable, enter the table
with the repetitive group designation after the
previous dive and move horizontally to find the
minimum permissible surface interval that corre-
sponds to the necessary new repetitive group des-
ignation determined in Step 1.
NOAA Diving Manual — October 1991
Air Diving and Decompression
Figure 14-5
Repetitive Dive
Flowchart
Conduct
single
dive
<■
Surface interval greater
than 12 hours
A
k
Decompress according
to Standard Air Table
— fc.
or No-Decompression
Table. Obtain repetitive
group designation
Surface interval greater
than 10 minutes and
less than 12 hours
I
i
Obtain residual nitrogen
time using Residual
Nitrogen Timetable
Surface interval less
1
f
than 10 minutes
Add residual nitrogen
time to bottom time of
repetitive dive to obtain
equivalent single dive
bottom time
Add bottom time of
previous dive to that of
IF
repetitive dive
Decompress using
schedule for repetitive
dive depth and equi-
valent single dive
bottom time
Decompress from
repetitive dive using
schedule for deeper of
two dives and combined
bottom times
Source US Navy (1985)
October 1991 — NOAA Diving Manual
Example:
A diver wishes to make a 35-minute repetitive dive
to 60 fsw (18.3 m) after a 12-minute dive to 92 fsw (27.6 m).
How long must the surface interval be to make the
repetitive dive without decompression?
Solution:
1. The repetitive group designation after the 92/12
dive is given by the 100/15 schedule: E.
2. The no-decompression time limit at 60 fsw (18.3 m)
is 60 minutes. The maximum allowable residual nitrogen
time is 60 — 35 = 25 minutes.
3. For a 60-fsw repetitive dive, the Residual Nitrogen
Timetable indicates a residual nitrogen time of
24 minutes, which is equal to or less than the maximum
allowable residual nitrogen time of 25 minutes.
4. This corresponds to a repetitive group designation
of D, as found at the head of the column.
5. To drop from one repetitive group designation,
e.g., E to D, requires a minimum surface interval of
55 minutes, as shown in Table 14-11.
Many of the national sport diving agencies, as well
as other organizations, have developed easy-to-use
repetitive dive table formats based on the U.S. Navy
tables. Most of these modified formats are pocket-sized,
color-coded, and printed on durable plastic cards for
field use. They are inexpensive, can aid the diver to
calculate repetitive dive times quickly, and fit readily
into dive bags or buoyancy compensator pockets. Divers
interested in a review of these diving aids should refer
to a series of articles published in the January to August
1982 issues of Skin Diver magazine.
14.7 SURFACE DECOMPRESSION
Surface decompression is a technique for discharging
all or a portion of the diver's decompression obligation
in a recompression chamber rather than the water.
Using this technique significantly reduces the time a
diver must spend in the water, and when oxygen is
breathed in the recompression chamber, the diver's
total decompression time is reduced even further.
Surface decompression offers many advantages, most
of which enhance the diver's safety: (I) shorter expo-
sure to the water prevents chilling; (2) the pressure
that can be maintained inside the recompression chamber
is constant, unlike the pressure while the diver is
decompressing in the water; and (3) the diver can be
observed constantly by the chamber operator and
monitored intermittently by medical personnel, which
means that any signs of decompression sickness can be
detected and treated immediately.
14-25
Section 14
Figure 14-6
Repetitive Dive
Worksheet
Example #1 — Single No-Decompression Dive
A diver has made a 43-minute dive to 58 fsw. Determine the diver's repetitive group designation.
I. PREVIOUS DIVE:
43 (50) minutes g| No-Decompression Table
□ Standard Air Table
58 (60) feet fj Previous Repetitive Drive
H repetitive group designation
II. SURFACE INTERVAL:
ho u rs
-minutes on surface.
Repetitive group from I
New repetitive group, from Surface
Interval Credit Table
III. RESIDUAL NITROGEN TIME:
_feet (depth of repetitive dive)
New repetitive group from ll._
Residual nitrogen time, from
Residual Nitrogen Timetable.
IV. EQUIVALENT SINGLE DIVE TIME:
minutes, residual nitrogen time from III.
+ minutes, actual bottom time of repetitive dive.
= . — minutes, equivalent single dive time.
V. DECOMPRESSION FOR REPETITIVE DIVE:
.minutes, equivalent single dive time from IV.
.feet, depth of repetitive dive
Decompression from (check one):
□ No-Decompression Table fj Standard Air Table
□ Surface Table Using Oxygen
□ Surface Table Using Air
Decompression
Stops:
feet
minutes
feet
feet
minutes
minutes
Schedule used
feet
minutes
Repetitive group
feet
minutes
If an oxygen breathing system is installed in the
recompression chamber, surface decompression should
be conducted according to the Surface Decompression
Table Using Oxygen. If air is the only breathing medium
available, the Surface Decompression Table Using Air
(see Appendix B) must be used. There is no surface
decompression table for use after an exceptional expo-
sure dive. In addition, no repetitive diving tables have
been developed for dives after surface decompression.
14.7.1 Surface Decompression Using Oxygen
After an Air Dive
The Surface Decompression Table Using Oxygen
(Appendix B) is used for surface decompression from
an air dive. It is essential that only pure oxygen be
breathed during this procedure. If the oxygen supply is
interrupted or symptoms of oxygen toxicity are experi-
enced, the decompression may be completed on air. If
either of these events occurs, the Surface Decompres-
sion Table Using Air should be used (the time spent on
oxygen should be disregarded). The notes on the Sur-
face Decompression Table Using Oxygen and the Sur-
face Decompression Table Using Air are self-explana-
tory and should be followed.
14.7.2 Surface Decompression Using Air
After an Air Dive
The Surface Decompression Table Using Air (Appen-
dix B) may be used after an air dive. When surface
14-26
decompressing on air, the standard air tables should
not be used; the Surface Decompression Table Using
Air should be used instead.
14.8 OMITTED DECOMPRESSION
Certain emergencies may interrupt or prevent a diver
from taking his or her specified decompression stops.
Blowup, exhausted air supply, bodily injury, and the
like constitute such emergencies. If a diver shows any
signs or symptoms of decompression sickness or gas
embolism after surfacing, immediate treatment using
the appropriate oxygen or air recompression treatment
table is essential. Even if the diver shows no signs or ill
effects, omitted decompression must be made up in
some manner to avoid later difficulty.
Use of Surface Decompression Tables
The Surface Decompression Table Using Oxygen or
the Surface Decompression Table Using Air may be
used to make up omitted decompression only if the
emergency surface interval occurs at such a time that
water stops are not required by these tables or, if
required, have already been completed.
Surface Decompression Tables Not Applicable
When the conditions that permit the use of the sur-
face decompression tables are not fulfilled, the diver's
decompression has been compromised. Special care
must be taken in such situations to detect signs of
NOAA Diving Manual — October 1991
Air Diving and Decompression
Figure 14-6
(Continued)
Example #2 — Single Decompression Dive
A diver has made a dive to 110 fsw for 25 minutes. Determine the diver's required decompression and
repetitive group designation.
I. PREVIOUS DIVE:
25 minutes
IV. EQUIVALENT SINGLE DIVE TIME:
110
□ No-Decompression Table
R Standard Air Table
feet □ Previous Repetitive Dive
repetitive group designation
II. SURFACE INTERVAL:
hours
.minutes on surface.
Repetitive group from I .
New repetitive group, from Surface
Interval Credit Table
III. RESIDUAL NITROGEN TIME:
feet (depth of repetitive dive)
New repetitive group from II
Residual nitrogen time, from
Residual Nitrogen Timetable.
+
.minutes, residual nitrogen time from III.
.minutes, actual bottom time of repetitive dive.
.minutes, equivalent single dive time.
V. DECOMPRESSION FOR REPETITIVE DIVE:
25 minutes, equivalent single dive time from IV.
110 feet, depth of repetitive dive
Decompression from (check one):
□ No-Decompression Table rA Standard Air Table
□ Surface Table Using Oxygen
□ Surface Table Using Air
Decompression Stops
Schedule used 110/25
Repetitive groupJH
: 10 feet
3
minutes
feet
minutes
feet
minutes
feet
minutes
feet
minutes
Example #3 — Repetitive No-Decompression Dive; surface interval greater than 10 minutes but less than 12 hours
A diver has made a 31-minute dive to 55 fsw, takes a 3-hour surface interval, and then makes a 48-fsw dive
for 18 minutes. Determine the diver's repetitive group designation.
I. PREVIOUS DIVE:
31 minutes
55
^ No-Decompression Table
□ Standard Air Table
_feet □ Previous Repetitive Dive
repetitive group designation
IV. EQUIVALENT SINGLE DIVE TIME:
21 minutes, residual nitrogen time from III.
II. SURFACE INTERVAL:
3 hours 0_minut.es on surface.
Repetitive group from I. G
New repetitive group, from Surface
Interval Credit Table C
III. RESIDUAL NITROGEN TIME:
48 feet (depth of repetitive dive)
New repetitive group from II. C
Residual nitrogen time, from
Residual Nitrogen Timetable 21
+ 1i
39
minutes, actual bottom time of repetitive dive,
minutes, equivalent single dive time.
V. DECOMPRESSION FOR REPETITIVE DIVE:
39 minutes, equivalent single dive time from IV.
48 feet, depth of repetitive dive
Decompression from (check one):
IS No-Decompression Table □ Standard Air Table
□ Surface Table Using Air
□ Surface Table Using Oxygen
Decompression
Stops:
feet
feet
minutes
minutes
feet
minutes
Schedule used 50/40
feet
minutes
Repetitive group F
feet
minutes
decompression sickness, regardless of what action is
initiated. The diver must be returned to pressure as
soon as possible. The use of a recompression chamber
is strongly preferred to the use of in-water recompression.
ate. If the diver shows no ill effects, he or she should be
decompressed in accordance with the treatment table.
Any decompression sickness developing during or after
this procedure should be considered a recurrence.
When a Recompression Chamber is Available
Even if the diver shows no ill effects from omitted
decompression, he or she needs immediate recompression
and should be taken to depth for treatment on
Recompression Treatment Table 5 or 1A, as appropri-
When No Chamber is Available
When no recompression facility is available, use the
following in-water procedure to make up omitted decom-
pression in asymptomatic divers for ascents from depths
below 20 feet (6.1 meters):
October 1991 — NOAA Diving Manual
14-27
Section 14
Figure 14-6
(Continued)
Example #4 — Repetitive Decompression Dive; surface interval greater than 10 minutes but less than 12 hours
A diver has made a decompression dive to 80 fsw for 50 minutes, takes a 4-hour, 20-minute surface interval,
and then makes a 70-fsw dive for 46 minutes. Determine the diver's decompression and final repetitive group
designation.
I. PREVIOUS DIVE:
50 minutes
80
□ No-Decompression Table
EI Standard Air Table
feet □ Previous Repetitive Dive
repetitive group designation
II. SURFACE INTERVAL:
4 hours 20 minutes on surface.
Repetitive group from I. K
New repetitive group, from Surface
Interval Credit Table _C
III. RESIDUAL NITROGEN TIME:
70 feet (depth of repetitive dive)
New repetitive group from II. _C
Residual nitrogen time, from
Residual Nitrogen Timetable 15
IV. EQUIVALENT SINGLE DIVE TIME:
15
minutes, residual nitrogen time from III.
; 46 minutes, actual bottom time of repetitive dive.
=■ 61 minutes, equivalent single dive time.
V. DECOMPRESSION FOR REPETITIVE DIVE:
61 minutes, equivalent single dive time from IV.
70 feet, depth of repetitive dive
Decompression from (check one):
□ No Decompression Table E Standard Air Table
□ Surface Table Using Oxygen
□ Surface Table Using Air
Decompression
Stops:
10
feet
feet
14
minutes
minutes
feet_
minutes
sed 70/70
feet_
minutes
iroup L
feet_
minutes
Example #5 — Repetitive No-Decompression Dives; surface interval less than 10 minutes
A diver makes a 60-fsw dive for 15 minutes, takes a 5-minute surface interval, and then makes a dive to
50 fsw for 25 minutes. Determine his repetitive group designation.
I. PREVIOUS DIVE:
15 minutes
IV. EQUIVALENT SINGLE DIVE TIME:
60
E No-Decompression Table
□ Standard Air Table
feet □ Previous Repetitive Dive
repetitive group designation
II. SURFACE INTERVAL:
_hours_
_5 minutes on surface.
Repetitive group from I. N/A
New repetitive group, from Surface
Interval Credit Table N/A
III. RESIDUAL NITROGEN TIME:
50 feet (depth of repetitive dive)
New repetitive group from II. N/A
Residual nitrogen time, from
Residual Nitrogen Timetable 15
15
minutes, residual nitrogen time from III.
| 25 minutes, actual bottom time of repetitive dive.
_ 40 minutes, equivalent single dive time.
V. DECOMPRESSION FOR REPETITIVE DIVE:
40 minutes, equivalent single dive time from IV.
60 feet, depth of repetitive dive
Decompression from (check one):
El No-Decompression Table □ Standard Air Table
□ Surface Table Using Oxygen
□ Surface Table Using Air
Decompression Stops:_
Schedule used 60/40
Repetitive group G
_feet_
_feet_
-feet_
_feet_
Jeet_
.minutes
_minutes
.minutes
.minutes
.minutes
Recompress the diver in the water as sewn as possible
(preferably less than a 5-min surface interval). Keep
the diver at rest, provide a standby diver, and maintain
good communication and depth control. Use the fol-
lowing procedure with 1 minute between stops:
• Repeat any stops deeper than 40 feet (12.2 meters)
• At 40 feet (12.2 meters), remain for one-fourth of
the 10-foot stop time
• At 30 feet (9 meters), remain for one-third of the
10-foot stop time
14-28
• At 20 feet (6. 1 meters), remain for one-half of the
10-foot stop time
• At 10 feet (3 meters), remain for 1.5 times the
scheduled 10-foot stop time.
14.9 FLYING AFTER DIVING AT SEA LEVEL
The elimination of inert gas from body tissues after an
exposure to pressure continues for a period of 24 hours
or more after the dive before equilibration with the
NOAA Diving Manual — October 1991
Air Diving and Decompression
Figure 14-6
(Continued)
Example - 6 — Multiple No-Decompression Repetitive Dives; surface intervals greater than 10 minutes but less
than 12 hours
A diver makes a 55-fsw dive for 20 minutes, takes a 2-hour surface interval, makes a second dive to 45 fsw
for 56 minutes, takes a surface interval of 1 hour 56 minutes, and then makes a third dive to 70 fsw for 12 minutes.
Determine the diver's final repetitive group designation.
I. PREVIOUS DIVE:
20 (20) minutes
55 (60) feet
D repetitive group designation
T-] No-Decompression Table
□ Standard Air Table
□ Previous Repetitive Dive
IV. EQUIVALENT SINGLE DIVE TIME:
21
II. SURFACE INTERVAL:
2 hours
0 minutes on surface
Repetitive group from I. D_
New repetitive group, from Surface
Interval Credit Table C
III. RESIDUAL NITROGEN TIME:
45 feet (depth of repetitive dive)
New repetitive group from II. C
Residual nitrogen time, from
Residual Nitrogen Timetable 21
_±_
minutes, residual nitrogen time from III.
56 minutes, actual bottom time of repetitive dive.
= 77 minutes, equivalent single dive time.
V. DECOMPRESSION FOR REPETITIVE DIVE:
77 minutes, equivalent single dive time from IV.
45 feet, depth of repetitive dive
Decompression from (check one):
M No-Decompression Table □ Standard Air Table
□ Surface Table Using Oxygen
□ Surface Table Using Air
Decompression Stops:
Schedule used 50/80
Repetitive group J
feet
minutes
fpet
minutes
feet
minutes
feet
minutes
feet
minutes
I. PREVIOUS DIVE:
77 minutes ^
□
feet □
repetitive group
45
No-Decompression Table
Standard Air Table
Previous Repetitive Dive
designation
IV. EQUIVALENT SINGLE DIVE TIME:
31
II. SURFACE INTERVAL:
1 hour
56 minutes on surface.
Repetitive group from I
New repetitive group, from Surface
Interval Credit Table F
II. RESIDUAL NITROGEN TIME:
70 feet (depth of repetitive dive)
New repetitive group from II. F
Residual nitrogen time, from
Residual Nitrogen Timetable 31
minutes, residual nitrogen time from III.
12 minutes, actual bottom time of repetitive dive.
= 43 minutes, equivalent single dive time.
V. DECOMPRESSION FOR REPETITIVE DIVE:
43 minutes, equivalent single dive time from IV.
70 feet, depth of repetitive dive
Decompression from (check one):
S No-Decompression Table □ Standard Air Table
□ Surface Table Using Oxygen
□ Surface Table Using Air
Decompression Stops:
Schedule used 70/45
Repetitive group I
feet
minutes
ffiet
minutes
feet
minutes
feet_
feet
minutes
minutes
ambient partial pressure of nitrogen in the air at the
surface is completed. During this period, reducing the
ambient pressure further will create a condition iden-
tical to the situation that occurs during decompression
after a dive. After diving, divers should exercise cau-
tion when travelling in mountainous terrain as well as
when flying. The cabin atmosphere in a modern,
pressurized airplane usually is maintained at an alti-
tude of 8000 feet (2438 meters), and this reduction in
pressure may be sufficient to cause inert gas dissolved
in a diver's tissues to come out of solution in the form of
bubbles, causing decompression sickness. This has
occurred, with severe symptoms, in divers who fly after
diving. Flying after diving is a recognized hazard that
should be avoided. Termination of the flight, which
increases the ambient pressure to l atmosphere, does
not necessarily cause the gas bubbles to decrease
sufficiently in size to stop causing symptoms, and
recompression treatment may be required to relieve
symptoms. Any delay in starting recompression may
cause permanent tissue damage and extend treatment
time.
October 1991 — NOAA Diving Manual
14-29
Section 14
Figure 14-6
(Continued)
Example #7 — Repetitive No-Decompression Dives; surface interval greater than 10 minutes but less than 12
hours; residual nitrogen time greater than actual bottom time of first dive. (This is the exception situation.)
A diver has made a 31 -minute dive to 80 fsw, takes a 20-minute surface interval, and then makes another dive
to 80 fsw for 6 minutes. Determine the diver's repetitive group destination.
I. PREVIOUS DIVE:
31 (35) minutes £3 No-Decompression Table
□ Standard Air Table
80 (80) feet □ Previous Repetitive Dive
H repetitive group designation
II. SURFACE INTERVAL:
hours
20
minutes on surface.
Repetitive group from l._H
New repetitive group, from Surface
Interval Credit Table JH
III. RESIDUAL NITROGEN TIME:
80 feet (depth of repetitive dive)
New repetitive group from II. _H
Residual nitrogen time, from
Residual Nitrogen Timetable 31*
IV. EQUIVALENT SINGLE DIVE TIME:
31 minutes, residual nitrogen time from III.
+ 6 minutes, actual bottom time of repetitive dive.
= 37 minutes, equivalent single dive time.
V. DECOMPRESSION FOR REPETITIVE DIVE:
37
minutes, equivalent single dive time from IV.
80 feet, depth of repetitive dive
Decompression from (check one):
IEl No-Decompression Table □ Standard Air Table
□ Surface Table Using Oxygen
□ Surface Table Using Air
Decompression
Stops:
feet
feet
minutes
minntfis
ffifit
minutes
Schedule used 80/40
fpfit
minutes
Repetitive group I
ffifit
minutes
*ln this example, the residual nitrogen time for the second dive from the Residual Nitrogen Timetable would be 38
minutes. This residual nitrogen time exceeds the actual bottom time of the first dive, 31 minutes, and thus the
exception rule is called for. In following the steps on the Flowchart and Worksheet, the "residual nitrogen time" is
the bottom time of the first dive. If the normal application of the rules were used, the repetitive dive would
become a decompression dive requiring decompression on the 80/50 schedule.
Adapted from NOAA (1979)
If it is necessary to fly immediately after a decom-
pression dive, after a series of repetitive dives, or after
recompression treatment (as might occur in the case of
an injury that requires medical capability beyond that
available at the dive site), the diver should be trans-
ported at low altitude by helicopter or aircraft or in a
plane having a cabin pressure of not more than 800 feet
(244 meters) of altitude. The same rules should be
followed if a diver experiencing decompression sickness
must be transported by air, except that the victim
should also breathe pure oxygen until arrival at a
recompression chamber.
WARNING
The Following Procedures Do Not Apply to
Flying After Saturation Diving (see Sec-
tion 16.6.2)
Before flying in an aircraft in which the cabin atmo-
sphere is less than 8000 feet (2438 meters) (usually
the case in most flights), a diver who has completed
any number of dives on air and been decompressed
14-30
according to the U.S. Navy Standard Air Decompres-
sion Table should wait at sea level, breathing air, for
the computed surface interval that allows him or her to
be classified as a Group D diver, in accordance with
the U.S. Navy No-Decompression Limits and Repetitive
Group Designation Table for No-Decompression Dives
(Table 14-11). This procedure is illustrated by the
following example:
0800 Dive to 50 feet (15.2 meters) on air for
60 minutes.
0900 Surface. (The U.S. Navy No-Decompression
Limits and Repetitive Group Designation Table
for No-Decompression Dives (Table 14-11)
indicates that the diver is in repetitive Group H.)
Remain at sea level for 5 hours.
1400 U.S. Navy Residual Nitrogen Timetable for
Repetitive Air Dives (Table 14-12) indicates that
the diver has moved to Group B (dive to 60 feet
(18.3 meters) on air for maximum no-decom-
pression time of 49 minutes). This is found
by subtracting the residual nitrogen time of
11 minutes for Group B at 60 feet (18.3 meters)
(Table 14-12) from the maximum no-decom-
NOAA Diving Manual — October 1991
Air Diving and Decompression
pression time of 60 minutes at 60 feet
(18.3 meters) (Table 14-11).
1449 Surface. (Table 14-11 indicates that the diver is
in Group J.) Diver must wait 3 hours and 5 minutes
to move into Group D.
1754 Diver can now fly at a maximum cabin altitude
of 8000 feet (2438 meters).
Before flying, the diver should check with the flight
engineer to ascertain the maximum planned cabin
altitude and to inform the engineer that divers will be
aboard.
To shorten the necessary surface interval before flying,
oxygen may be breathed instead of air. Table 14-13 lists.
Table 14-13
Optional Oxygen-Breathing
Times Before Flying After Diving
Repetitive Dive Groups
Groups M through Z
Groups H through L
Groups E through G
Groups A through D
Oxygen Time
Before Flying
(Hr:Min)
1:30
1:00
0:30
0:00
Source: NOAA (1979)
for the various Repetitive Dive Group classifications,
the length of oxygen breathing time necessary before
flying is allowed.
October 1991 — NOAA Diving Manual
14-31
4
i
Page
SECTION 15
MIXED GAS
AND OXYGEN
DIVING
15.0
15.1
15.2
15.3
15.4
15.5
General 15-1
Mixed Gas Composition 15-1
15.1.1 Limitations of Diluent Gases 1 5-1
15.1.2 Nitrogen-Oxygen Mixtures 15-2
15.1.3 Helium-Oxygen Mixtures 15-4
15.1.4 Oxygen Concentrations in Breathing Mixtures 15-5
1 5. 1 .4. 1 General Safety Precautions for Oxygen 1 5-5
Diving With Mixed Gas and Mixed Gas Diving Equipment 15-7
15.2.1 Scuba 15-7
15.2.1.1 Open-Circuit Systems 15-7
15.2.1.2 Semi-Closed-Circuit Systems 15-8
15.2.1.3 Closed-Circuit Systems (Rebreathers) 15-10
15.2.2 Surface-Supplied Mixed Gas Equipment 15-12
Breathing Gas Purity 15-12
15.3.1 Compressed Air Purity 15-12
15.3.2 Diluent Gas Purity 15-12
15.3.3 Oxygen Purity 15-13
Breathing Gas Analysis 15-13
Gas Mixing 15-14
15.5.1 Continuous-Flow Mixing 15-15
15.5.2 Mixing by Partial Pressure 15-15
i
(
MIXED
GAS AND
OXYGEN
DIVING
15.0 GENERAL
The term mixed gas diving refers to diving operations
in which the diver breathes a medium other than air.
Mixed gas may be composed of nitrogen and oxygen in
proportions other than those found in the atmosphere,
or it may be a mixture of other inert gases and oxygen.
The breathing gas can also be 100 percent oxygen,
which, although technically not a mixed gas, is used
under specialized circumstances; the use of oxygen
requires knowledge and training similar to that needed
for mixed gas diving. During some phases of a mixed
gas dive, air may be used as the breathing mixture.
Mixed gas diving operations require detailed plan-
ning, specialized and sophisticated equipment, and
extensive surface-support personnel and facilities. The
very nature of mixed gas operations, and the fact that
such dives are often conducted at great depths and for
extended periods of time, increases the risks associated
with such dives. For these reasons, there is no such
thing as a casual mixed gas or oxygen dive.
15.1 MIXED GAS COMPOSITION
Oxygen must be a component of any breathing mix-
ture; the commonly used inert components are nitro-
gen and helium. Other gases, such as neon and hydro-
gen, are being studied as replacements for helium.
Still others, including argon, sulfur hexafluoride, and
carbon tetrafluoride, have been used experimentally
to vary the properties of breathing mixtures. The advan-
tages and limitations of these gases are discussed below,
in Section 15.1.1.
As is true for any breathing mixture, the quality of
the breathing gas is vitally important. (Gas purity
standards, including Federal specifications, are cov-
ered in Section 14.) In general, few purity problems
are associated with gases obtained in cylinders from
commercial vendors. The problems that do occur are
usually caused by factors such as improper mixing,
analysis, labeling, or color coding, contamination
resulting from improper handling or a poorly maintained
compressor, or solvent residue left in storage contain-
ers or hoses. The importance of ensuring that any mix-
ture used for breathing is correct cannot be over-
emphasized.
October 1991 — NOAA Diving Manual
The manner in which oxygen and inert gases are
combined and used as a breathing mixture depends on
both the type of breathing apparatus and the depth of
the planned operation. General considerations regard-
ing mixtures based on nitrogen and/or helium are
discussed in Sections 15.1.2 and 15.1.3. Mixing tech-
niques are covered in Section 15.5, and the equipment
used for mixed gas diving is discussed in Section 15.2.
The physiological effects of each component of a gas
mixture are a function both of the partial pressure of
that component at the pressure involved and the per-
centage of that component in the mixture. An under-
standing of the concept of partial pressure is essential
to the safe management of mixed gas diving. The par-
tial pressure (Pp) of a component (Y) in a gas mixture
is the product of the total absolute pressure (Pat,s) of
the mixed gas times the fraction constituted by the
component
Pp = PabsxY%/100.
(See Section 2.2.5 for additional information on the
physics of diving.)
15.1.1 Limitations of Diluent Gases
The use of nitrogen, the most commonly used dilu-
ent, is limited because of its tendency to produce nar-
cosis (see Section 3.2.3.5), in addition to the fact that
adding it to an air mixture affects the amount of allow-
able bottom time for a given decompression obligation.
The density of nitrogen is also a detrimental characteris-
tic. When mixtures containing increased nitrogen par-
tial pressures are used with the air decompression tables,
the air-equivalent depths must be calculated before
diving (see Section l 5. 1 . 1 ).
Helium has not produced narcotic effects on divers
at any depth at which it has been used, but its use is
limited by its high cost, relative scarcity, high thermal
conductivity, and the difficulty of communicating by
voice when breathing a helium-oxygen mixture because
helium distorts human speech. The communication
limitation can be largely eliminated by using a special
helium unscrambler that utilizes electronic filtering
and special frequency modulation techniques. Helium
15-1
Section 15
also has a high diffusivity that allows it to leak
through penetrators and into equipment easily, with
occasionally disastrous effects.
The thermal conductivity of helium is six times that
of nitrogen, which causes heat to be lost from the body
very rapidly in a bell or saturation chamber. During a
short dive (15 minutes or less) even in very cold water,
the amount of heat loss may not be significant, but on a
prolonged dive, it can reduce diver efficiency substan-
tially. It is current diving practice on dives to depths
greater than 326 fsw (100 msw) to heat helium-oxygen
breathing mixtures to reduce the loss of body heat.
Neon is sometimes used as a component of diver's
breathing gas, but it is far too expensive to use in the
pure state. Neon offers some advantages over helium.
Most notably, it has lower thermal conductivity and
distorts speech less. A mixture of neon and helium
(about 75 percent neon and 25 percent helium) is a
by-product of the cryogenic production of oxygen and
nitrogen. This mixture is available commercially and
is suitable for use as a diluent in diver's breathing gas.
Neon does not appear to have narcotic effects, and
tests indicate that its decompression requirements are
similar to those of helium. However, neon does create
more breathing resistance than helium at greater depths.
Hydrogen is not used as often as a diver's breathing
gas because of its explosive qualities. By keeping the
oxygen concentration in the mixture below the limit of
combustion, however, non-explosive hydrogen-oxygen
mixtures can be made. Hydrogen causes more speech
distortion than helium and its thermal capacity is higher,
which causes an even greater rate of body heat loss
with hydrogen than with helium. However, the advan-
tage of hydrogen is that it is easier to breathe at great
depths because of its low density. The effects of hydro-
gen on body tissues at high pressure have not yet been
fully explored. However, hydrogen or hydrogen-helium
mixtures have recently been used on a series of deep
dives by French, Swedish, and Norwegian divers. New
technology is available that removes the hydrogen in
the hydrogen-helium mixture at the beginning of decom-
pression; this decreases the risk of handling hydrogen
considerably.
15.1.2 Nitrogen-Oxygen Mixtures
Nitrogen-oxygen breathing gas mixtures are gener-
ally used for relatively shallow dives. The most com-
mon nitrogen-oxygen mixture is air, which can be used
effectively from sea level to depths in the range of
130-150 fsw (40-46 msw). Experience with air as a
breathing mixture serves as a starting point for work
15-2
with other nitrogen-oxygen mixtures. Nitrogen narcosis,
covered in detail in Section 3.2.3.5, is the limiting
factor in the use of nitrogen-oxygen breathing mix-
tures. The pressure (depth) at which narcosis symp-
toms first appear varies considerably among individu-
als and may vary from day to day in the same person.
Experience has shown that individuals may become
partially acclimated to higher nitrogen partial pressures
after several days of saturation in a hyperbaric nitrogen-
oxygen environment; repeated daily exposure to nitro-
gen-oxygen also may facilitate partial acclimation.
When diving on an air breathing mixture, the first
observable symptoms of nitrogen narcosis are likely to
occur at a depth of about 100 fsw (31 msw), and they
usually worsen rapidly in the depth range between
100 and about 200 fsw (31 and 61 msw). Beyond this
depth, the performance of most individuals is signifi-
cantly compromised.
The fraction of the inert gas (in this case nitrogen) in
a breathing mixture is an important factor in deter-
mining a diver's decompression requirements. Breath-
ing a nitrogen-oxygen mixture that contains a higher
fraction of oxygen than air (which is approximately 79
percent nitrogen and 21 percent oxygen) may reduce
the need for decompression stops and may also reduce
the narcosis problem. A commonly used breathing gas
mixture in NOAA diving is one containing 68 percent
nitrogen and 32 percent oxygen. With this enriched air
nitrogen-oxygen (nitrox) mixture, the nitrogen partial
pressures at 63 and 122 fsw (19 and 37 msw) would be
2.0 and 3.2 ATA, respectively, pressures which are
equivalent to those that would occur at depths of
50 and 100 fsw (15 and 31 msw), respectively, if air were
being breathed.
Although it has been possible to delay the onset of
nitrogen narcosis symptoms and to reduce decompres-
sion requirements by using enriched oxygen mixtures,
another limitation, oxygen toxicity, must be consid-
ered when using such enriched breathing mixtures.
Table 15-1 shows, for example, that 180 minutes is the
longest recommended exposure to an oxygen partial
pressure of 1.3 ATA. In the case of an air dive,
this oxygen partial pressure is achieved at 172 fsw
(53 msw); however, if an enriched mixture of 68 percent
nitrogen-32 percent oxygen is used, this partial pres-
sure is reached at a depth of 102 fsw (31 msw). Thus
both nitrogen narcosis and oxygen toxicity must be
considered carefully when planning a dive that will use
enriched nitrogen-oxygen breathing gas mixtures.
Table 15-1 takes into account the results of new
experiments with human subjects, as reported by But-
ler and Thalmann (1986) and by researchers at the
Institute for Environmental Medicine, which are con-
NOAA Diving Manual — October 1991
Mixed Gas and Oxygen Diving
Table 15-1
Oxygen Partial Pressure and Exposure
Time Limits for Nitrogen-Oxygen
Mixed Gas Working Dives
NORMAL EXPOSURE OXYGEN PARTIAL PRESSURE LIMITS
Oxygen Partial
Pressure (P02)
in ATA
Maximum Duration for
a Single Exposure
(min) (hr)
Maximum Total Duration
for Any 24-Hour Day
(min) (hr)
Normal exposures are those involved in standard diving operations, e.g., dives for research, sampling, inspection and observation,
and repair. A series of repetitive dives may be conducted without a normoxic interval between dives if the sum total of the oxygen
partial pressure duration limit for all of the dives does not exceed the Maximum Single Exposure Limits.
If one or more dives within a 24-hour period have reached or exceeded the limits for a normal single exposure, the diver must spend a
minimum of 2 hours at a normoxic P02 before diving again. If one or more dives within a 24-hour period have reached the Maximum
Total 24-Hour Day Limits, the diver must spend a minimum of 12 hours at a normoxic P02 before diving again.
Exceptional exposures are for use only in lifesavmg operations.
Adapted from Butler and Thalmann (1986) and derived from data
in the International Diving and Aerospace Data System.
Institute for Environmental Medicine. University of Pennsylvania
by C. J. Lambertsen and R. E. Peterson
sistent with general industry experience. These results
indicate that single exposures somewhat longer than
those shown in Table 15-1 can be conducted without
episodes of central nervous system (CNS) oxygen tox-
icity. However, the more conservative exposure times
shown in Table 15-1 take operational safety into
consideration and are sufficient in duration for antici-
pated NOAA dives. At the same time, the limits shown
in Table 15-1 extend the limits published in the second
edition of the NOAA Diving Manual.
The values shown in Table 15-1 take pulmonary
oxygen toxicity as well as CNS toxicity into considera-
tion. Prolonged and repetitive exposure to high oxygen
pressures can cause lung damage, which is initially
reversible. In addition, at lower oxygen pressures, pulmo-
nary oxygen toxicity can limit exposures even when
CNS oxygen toxicity is not a limiting factor. At the
higher PO-> levels shown in Table 15-1, however, CNS
oxygen toxicity is considered the constraint. A simpler
way to manage the long-duration aspects of oxygen
exposure that takes whole-body toxicity into consid-
eration can be found in the Repex procedures and
tables (Hamilton, Kenyon, Peterson et al. (1988a):
Hamilton, Kenyon, and Peterson (1988b)).
Recent research reported by Butler and Thalmann
(1986) indicates that oxygen tolerance testing does not
screen satisfactorily for susceptibility to CNS oxygen
convulsions during working dives. Thus, continuation
October 1991 — NOAA Diving Manual
15-3
Section 15
of NOAA's policy, which is not to conduct oxygen
tolerance testing, appears appropriate. Butler and
Thalmann's experiments did demonstrate a direct cor-
relation between rapid cooling of core temperature
and the onset of oxygen toxicity.
Another use for nitrogen-oxygen gas mixtures occurs
in shallow saturation and saturation-excursion diving.
These dives have traditionally been performed by NOAA
divers breathing air during the dive and breathing
normoxic nitrox in the habitat. (Saturation diving is
discussed further in Section 16.)
15.1.3 Helium-Oxygen Mixtures
For diving to depths greater than 150 to 200 fsw
(46 to 61 msw), helium-oxygen mixtures are commonly
used; such mixtures often contain some nitrogen as
well. The substitution of helium for nitrogen elimi-
nates the nitrogen narcosis problem and makes the gas
easier to breathe, but the use of helium is associated
with other problems.
One of these is speech distortion, the so-called Donald
Duck effect. This distortion has to do with differences
in the impedance match between air spaces and the
surrounding tissues and the speed of sound in helium.
The effect becomes progressively more pronounced
with increasing depth. With experience, divers and
tenders learn to overcome some of the communication
interference imposed by this distorted speech. The
problem can be ameliorated further by using pressure-
insensitive microphones and one of the commercially
available electronic helium speech unscramblers. Such
devices are commonly used for mixed gas dives to
depths beyond about 300 fsw (92 msw).
Another problem associated with the use of helium
is body heat loss, which is caused in part by the fact
that the thermal conductivity of helium is approxi-
mately six times that of air. Heat loss occurs both from
the skin because of thermal conductivity and from the
respiratory tract because of the heat capacity of com-
pressed gas. In deep saturation dives that use helium-
oxygen mixtures, there is a significant and continuous
insensible heat loss even if the divers are thermally
comfortable. The most obvious reflection of this effect
is an increased dietary caloric intake, but it also means
that special effort needs to be made to ensure that
helium-saturated divers are properly rewarmed between
dives. Respiratory heat loss increases with depth (with
any gas, not just helium) to the point where, at about
800 fsw (246 msw), it is as great as an individual's
entire metabolic heat production. For dives of suffi-
cient depth and duration, heating the breathing gas is
essential, because without supplemental heating, the
temperature of a diver's breathing gas will approach
the ambient water temperature, which can be un-
acceptable if the water is cold. The minimum inspired
gas temperatures recommended for a dive of any dura-
tion are presented in Figure 15-1.
Divers who are being compressed to deep depths
while breathing helium-oxygen mixtures may experi-
ence other physiological phenomena. Hyperbaric
arthralgia (pain in the joints) may occur during com-
pression and after arrival at the maximum depth. These
pains tend to improve with time and can be controlled
by compressing slowly. Another problem is the high
pressure nervous syndrome (HPNS), which manifests
itself in tremors of the hands and jerky movements of
the limbs, dizziness, nausea, decreased alertness, and
the desire to sleep when not active. Divers have experi-
enced HPNS during heliox and hydrogen-oxygen dives.
These symptoms are accompanied by changes in the
electrical activity of the brain (as shown by an electro-
encephalogram). Although the cause of HPNS is not
really understood, experience has shown that it can be
controlled by using a slow rate of compression, or, for
very deep dives, a staged compression profile.
During decompression from a dive using a helium-
oxygen breathing gas mixture, the divers may be shifted
to an air mixture, both to increase the rate of helium
offgassing from the body and, in 'bounce' dives (short,
deep dives), to conserve the amount of helium used
during the dive. At depths greater than 100 fsw
(31 msw), if the body is surrounded by a helium-oxygen
mixture (as in a diving bell or chamber) and the diver is
breathing a nitrogen-oxygen mixture by mask, gas
gradients can develop through the skin, causing a severe
itching that is similar to the itching of skin bends and
predisposing the diver to vestibular decompression sick-
ness. This phenomenon, in which one inert gas is inhaled
while another inert gas surrounds the body, is referred
to as isobaric counterdiffusion (see Section 3.2.3.3).
Counterdiffusion can be avoided by shifting to air
gradually or doing so at a shallow depth and by preventing
the divers from breathing air at depths deeper than
100 fsw (31 msw) when their tissues are equilibrated
with a helium atmosphere.
Pure oxygen is commonly used for breathing during
the later stages of decompression from mixed gas dives.
Since oxygen is consumed by the body, it does not
contribute to the tissue's gas loading, which must be
reduced to provide safe decompression. Oxygen breath-
ing, however, can be used only during the shallower
portions of the decompression profile because of the
danger of oxygen poisoning (see Sections 3.3 and 20.4.3).
15-4
NOAA Diving Manual — October 1991
Mixed Gas and Oxygen Diving
Figure 15-1
Minimum Safe Inspired
Gas Temperature Limits
Inspired
Gas
Temp (*C)
Inspired
Gas
Temp (°F)
25
20
15
10
5
0
-5
s^ Minimum Temperature
nf <Zanvuatnr
1 1
68
59
50
41
32
23
600
I
700 800 900 1000
(Fsw)
I I
F
&
6
7
7
a
MM
30
50
DO
50
DO
20
°C
-1.0
1.7
4.0
6.0
7.8
25 30
Absolute Pressure (ATA)
°F Fsw °C °
30.1 850 9.4 48
35.0 900 10.8 51
39.2 950 12.1 53
42.9 1000 13.3 55
46.1
F
.9
.5
.8
.9
Source: NOAA (1979)
15.1.4 Oxygen Concentrations in Breathing
Mixtures
The partial pressure of oxygen that is considered
normal and to which humans are adapted is 0.21 ATA.
A healthy person can maintain the oxygen level of
blood at a tolerable level even if the inspired oxygen
pressure drops to about 0.16 ATA (16 percent oxygen
at atmospheric pressure). Below this level, performance
is distinctly impaired; unconsciousness occurs when the
level drops acutely below about 0.10 ATA. Levels much
below this will cause brain damage or death if main-
tained for more than brief periods.
Demonstrable pulmonary oxygen toxicity is likely to
occur when the inspired oxygen partial pressure exceeds
0.6 ATA for prolonged periods (several days), and
acute toxicity may result from much shorter exposures
to higher levels. The oxygen partial pressures that can
be tolerated for limited periods of time during normal
exposures on a regular repetitive basis are shown in
Table 15-1. Most people can tolerate partial pressures
greater than 2.0 ATA for many minutes while at rest;
these levels are used in both routine decompressions
and in the treatment of decompression sickness. The
partial pressure at which the onset of symptoms of
CNS oxygen poisoning occurs varies inversely with
activity level and differs significantly among individ-
uals. Symptoms of acute oxygen poisoning that may
signal an incipient convulsion are facial twitching,
dizziness, nausea, lightheadedness or confusion, eupho-
ria, and dilation of the pupils. At oxygen partial pres-
sures of 1.3 ATA and lower, CNS oxygen toxicity is not
likely. Section 20.4.3 provides a further discussion of
oxygen poisoning and the appropriate corrective actions.
For long-term exposures in a hyperbaric chamber or a
habitat, the oxygen partial pressure of the breathing
gas should be maintained between 0.3 and 0.4 ATA.
NOTE
The likelihood of CNS oxygen poisoning is
directly related to work level.
The physiological and toxic boundaries of oxygen
partial pressures as a function of depth and percentage
of oxygen are shown in Figure 15-2, which shows that,
for any fixed depth, it is feasible to breathe a wide
range of oxygen mixtures without ill effects. Fig-
ure 15-2 and Table 15-1 may be used together to deter-
mine the usable depth range and dive duration for a
fixed oxygen fraction or percentage. For example, at
10 percent oxygen by volume, a depth range between
21 and 495 fsw (0.16 and 1.6 ATA oxygen) is permissi-
ble, provided exposure time at maximum depth does
not exceed 45 minutes (Table 15-1).
Certain research investigations and military appli-
cations call for the use of a pure oxygen 'rebreather'
apparatus. Use of this equipment requires a thorough
understanding of the principles and hazards involved;
a major problem with these devices is oxygen toxicity.
The most recent research results on pure oxygen diving
in exercising human volunteers are reported by Butler
and Thalmann (1986). Table 15-2 shows depth-time
limits for pure oxygen working dives. As noted earlier,
exposure times somewhat greater than those shown at
the highest pressures in Tables 15-1 and 15-2 are
possible without the occurrence of oxygen convulsions;
however, NOAA finds that the conservative limits
established in Table 15-2 (as well as in Table 15-1)
are satisfactory for NOAA diving operations. (Note
that the exposure times in Table 15-2 are different
from those presented for pure oxygen breathing in the
second edition of the NOAA Diving Manual.)
15.1.4.1 General Safety Precautions for Oxygen
Oxygen is the most hazardous gas divers handle
because it lowers the ignition temperature of flamma-
ble substances and greatly accelerates combustion.
Hydrocarbons ignite almost spontaneously in the pres-
ence of oxygen, and oxygen fires instantly create intense
October 1991 — NOAA Diving Manual
15-5
Section 15
Figure 15-2
Percentage of Oxygen in Breathing Mixtures
as a Function of Depth and Oxygen Partial Pressure
Relative to Ranges for Hypoxia and CNS Toxicity
80
^>X
^X
XX
60
40
30
^
^
X,
X
V
1
^x
\
Ni
iXVsNV
20
^~"~~---^
\ XX
Time-Dependent
' CNS Toxicity
QJ ^v
Range
en N
c
10
8
|\
^
\\\\
■^
I \
v
V \
Si
N>
s
b
N
v^
i
^
6
\ Depth Range
^ *
N
X
N
XSJ
X
4
3
2
K
x \
\ \
X
X
Nx
3
f s
NX
\
^n
Hyp
oxia L
imits i
Y/
N
\v
\ X
\
N
1 1 /
First Symptoms' J
v
s
Helpless J
f
1.0
0.8
U
1 . /
nconscious
\N
s
x N
\
0.6
0.4
X\
0.3
0.2
W N
o
O
O
a.
o
E
■*-
<
6
D
(/>
U)
0
a.
"5
2.0
1.8
1.6
1.5
1.4
1.3
1.2
1.0
0.6
0.3
0.21
0.16
0.12
0.10
10
20
30 40 60 80 100 200 300 400 600 800 1000 2000
Depth, Feet of Sea Water
A wide range of oxygen mixtures can be used without the diver experiencing ill effects during the dive. For example, near 200 fsw (61 msw) ,
the mixture may contain as little as 3 percent oxygen (0.21 atmosphere partial pressure) in extreme duration exposures. However, at
18 percent oxygen (1.3 atmosphere partial pressure) at the same depth, the diver can remain only for 3 hours (Table 15-1) without
deleterious effects.
15-6
Adapted from NOAA (1979)
NOAA Diving Manual — October 1991
Mixed Gas and Oxygen Diving
Table 15-2
Depth-Time Limits for
Breathing Pure Oxygen
During Working Dives
Oxygen
Maximum Single
Maximum Daily
Depth
Pressure
Dive
Exposure
(few)
(atm)
(min)
(min)
5
1.15
180
240
10
1.30
180
210
15
1.45
180
210
20
1.61
150
180
25
1.76
80
150
30
1.91
40
120
35
2.06
20
80
Repetitive dives to the maximum single dive limit must be separated by
a 2-hour surface interval. If the maximum daily exposure is reached,
these additional dives must be separated by a 12-hour surface
interval.
Derived from data in the International Diving and
Aerospace Data System, Institute for Environmental Medicine,
University of Pennsylvania by C. J. Lambertsen and
R. E. Peterson
heat. When materials burn in oxygen, the flame tem-
peratures are higher than they are in air.
Oxygen cylinders should never be completely emp-
tied, but should be maintained with a minimum of
25 psi cylinder pressure to prevent contamination from
entering the cylinder. Oxygen systems must be cleaned
and kept free of organic contaminants and loose parti-
cles; the process used to ensure that oxygen systems
are safe to use is called 'cleaning for oxygen service/
Oxygen of the purity required for diving is generally
refined by cryogenic separation from air. In the United
States, oxygen is shipped in gas cylinders that are
color-coded green. The label on the cylinder, also color-
coded green, provides exact data as to the grade of
oxygen in the cylinder.
15.2 DIVING WITH MIXED GAS AND MIXED
GAS DIVING EQUIPMENT
Mixed gas diving can be performed with a variety of
equipment, the most common of which can be divided
into two general categories: scuba and surface-supplied.
Included within the scuba category are the open-circuit,
semi-closed-circuit, and closed-circuit systems. The
surface-supplied category includes the standard Navy
MK 12 heavyweight dress and a variety of lightweight
surface-supplied helmets and masks (see Section 5).
Equipment supplied by different manufacturers
requires the use of different operating procedures. There-
fore, operating manuals for each type of equipment
should be obtained from the manufacturer before any
of the equipment described below is used.
October 1991 — NOAA Diving Manual
15.2.1 Scuba
The scuba mode is generally associated with com-
plete autonomy of diver operation. The semi-closed
and closed types of scuba systems, however, include
variations that utilize a gas umbilical either as a pri-
mary or backup source of breathing gas.
15.2.1.1 Open-Circuit Systems
Open-circuit mixed gas systems are identical to com-
mon scuba systems in terms of equipment and opera-
tion. The only difference is that the gas cylinders are
filled with a mixed gas (nitrogen-oxygen or helium-
oxygen) rather than air. Since mixed gas is more expen-
sive than air, its use usually is limited to those diving
operations where the advantages gained by using a
special gas mixture outweigh the cost. These advan-
tages are an increase in allowable diving depth, an
increase in possible bottom times for initial or repetitive
dives, and (for longer dives) a decrease in decompression
time. The most common gases used in open-circuit
systems are mixtures of nitrogen-oxygen, helium-
oxygen, and helium-nitrogen-oxygen. Although the
lack of publicly available decompression tables limits
the general use of these mixtures, they are used widely
in commercial and scientific diving.
Within a limited range, the air decompression tables
can be used to determine a diver's decompression
requirements after a nitrogen-oxygen dive. The advan-
tages and limitations of nitrogen-oxygen mixtures other
than air are described in Section 15. 1.2. These advan-
tages are illustrated further by the no-decompression
limits given in Table 15-3 for a 68 percent nitrogen, 32
percent oxygen breathing mixture, a mixture that has
been utilized in several NOAA diving operations and
is designated NOAA Nitrox-I. The limits shown in
Table 15-3 are based on extensive diving experience
within NOAA, and the breathing mixtures shown fall
in about the mid-range of mixtures used by the U.S.
Navy for semi-closed systems. To utilize the standard
air decompression tables with an enriched air nitrogen-
oxygen breathing mixture, it is first necessary' to calculate
an equivalent air depth (EAD). This is the depth at
which air will have the same nitrogen partial pressure
as the enriched mix has at the depth of the dive. The
EAD and the bottom time are then used to enter the
standard air decompression tables.
EAD is determined as follows:
EAD (fsw) = [(1 - F02)(D + 33)/0.79] - 33
where F02 = fraction of 0: = percent/ 100 of O^ in
the gas mixture; D = deepest depth achieved during
15-7
Section 15
Table 15-3
NOAA NITROX-I (68% N,,, 32% 02) No-Decom-
pression Limits and Repetitive Group Designation
Table for No-Decompression Dives
Depth,
No-decompression
fsw
15
Limits, min
A
60
B
120
C
210
D
E
F
G
H
I
J
K
L
M
N O
300
20
35
70
110
160
225
350
25
25
50
75
100
135
180
240
325
30
20
35
55
75
100
125
160
195
245
315
40
15
30
45
60
75
95
120
145
170
205
250
310
45
310
5
15
25
40
50
60
80
100
120
140
160
190
220
270 310
50
200
5
15
25
30
40
50
70
80
100
110
130
150
170
200
60
100
10
15
25
30
40
50
60
70
80
90
100
70
60
10
15
20
25
30
40
50
55
60
80
50
5
10
15
20
30
35
40
45
50
90
40
5
10
15
20
25
30
35
40
100
30
5
10
12
15
20
25
30
110
25
5
7
10
15
20
22
25
120
25
5
7
10
15
20
22
25
130
20
5
10
13
15
20
140
15
5
10
12
15
150
10
5
8
10
See Section 15.2.1.1 for an explanation of this table.
Source: NOAA (1979)
the dive (expressed in fsw), and 0.79 is the percentage
of nitrogen in air, expressed as a decimal.
Since oxygen partial pressure also may be a limiting
factor in nitrogen-oxygen dives, it is calculated as
follows:
P02 (ATA) = F02 (D + 33)/33
where D = deepest depth achieved during dive (expressed
in fsw). For NOAA Nitrox-I dives, F02 = 0.32.
Using these equations, Table 15-4 has been calcu-
lated for NOAA Nitrox-I (68 percent N2, 32 percent
02) mixtures and gives the EAD associated with actual
dive depth, the standard air table that would be used
based on the EAD, the oxygen partial pressure at the
actual depth of the dive, and, for reference purposes,
the maximum allowable normal oxygen exposure time
associated with the calculated oxygen partial pressure, as
depicted in Table 15-1. As a further aid to users of
NOAA Nitrox-I in open-circuit scuba, Appendix D
contains nitrox decompression tables that may be
entered directly without calculation, using actual depth
and bottom time.
WARNING
The Decompression Tables Contained In
Appendix D Are Applicable Only to Dives
Using NOAA Nitrox-I (68 Percent N2, 32 Per-
cent 02) as the Breathing Gas In Open-Circuit
Scuba. These Tables Must Not Be Used When
Breathing Air or Any Other Nitrogen-Oxygen
Mixture
15-8
15.2.1.2 Semi-Closed-Circuit Systems
A semi-closed-circuit system is one in which only a
portion of the exhaled gas is vented into the sea; the
remainder is recirculated within the system and re-
breathed. The obvious advantage of this system over
the open-circuit system is more efficient utilization
of the diver's gas supply, since only a small portion of
the inhaled oxygen is used by the body. This in turn
means that, for a given gas supply, the diver can spend
a longer time under water. Other advantages of semi-
closed-circuit systems are:
• Increased depth, because of these systems' ability
to use a variety of inert gases and their flexibility
to vary the oxygen content;
• Reduction of decompression time and of the like-
lihood of decompression sickness because the oxy-
gen concentration is increased;
• Possible reduction in the effects of nitrogen narcosis
because higher concentrations of oxygen may be
used.
The penalty for this increased efficiency is increased
complexity of diving equipment and procedures. Because
a major portion of the exhaled gas is recirculated, a
means must be provided for the removal of exhaled
carbon dioxide. Failure to remove the carbon dioxide
would result in hypercapnia, discussed in Section 3.1.3.2.
The most common method of removing carbon dioxide
(C02) is by means of a scrubber containing a C02
absorbent. As the exhaled gas passes through the packet
bed of absorbent, the carbon dioxide is removed.
Sodasorb® is the most commonly used absorbent; another
NOAA Diving Manual — October 1991
Mixed Gas and Oxygen Diving
Table 15-4
Equivalent Air Depths (EAD) and Maximum Oxygen
Exposure for Open-Circuit Scuba Using a Breathing
Mixture of 68% Nitrogen and 32% Oxygen (NOAA Nitrox-I)
Oxygen Partial
Actual Dive
Equivalent
Pressure at Actual
Maximum Oxygen
Depth.
Air Depth,
USN Air Table
Diving Depth,
Exposure,
fsw
fsw
fsw
ATA
min
15
8.3
0.47
„
20
12.6
0.51
720
25
16.9
0.56
720
30
21.2
0.61
570
35
25.5
0.66
570
40
29.8
0.71
450
45
34.1
0.76
450
50
38.4
40
0.80
450
60
47.1
50
0.90
360
70
55.7
60
1.00
300
80
64.3
70
1.10
240
90
72.9
80
1.19
210
100
81.5
90
1.29
180
110
90.1
100
1.39
150
120
98.7
100
1.48
120
130
107.3
110
1.58
45
*
Maximum oxygen
(O,)
exposure = maximum
time to be spent at the
indicated P02 as per NOAA Oxygen
Partial Pressure Limits
Table for Normal Exposure
(Table
15-1). * =
Exceptional
exposure as per
NOAA 0>
(ygen Partial Pressure
Limits Table (Table 15-1).
Adapted from NOAA (1979)
material is Baralyme®. The effectiveness of these absorb-
ents is reduced at low temperatures.
NOTE
Semi-closed-circuit scubas are manufactured
by several U.S. and European companies.
Because of the complexity of this equipment
and related safety considerations, operating
manuals and training should be obtained from
the equipment manufacturer before using it.
Because only a portion of the exhaled gas is vented into
the water, the remainder must be stored in a reservoir
(breathing bag) until it is used for the next inhalation.
Furthermore, the vented gas must be replaced by the
addition of a like amount of gas from a gas supply (gas
cylinder). Finally, the oxygen deficiency in the exhaled
gas caused by the body's metabolic uptake must be
corrected for by injecting more oxygen. In most semi-
closed systems, the latter two functions, gas addition
and oxygen enrichment, are accomplished by a con-
stant mass flow of oxygen-rich gas from a high-pressure
gas cylinder into the breathing bag.
Because most semi-closed-circuit systems use a preset
flow principle, they are subject to certain operational
limitations. The breathing bag oxygen percentage or
'bag level' (average 02 level in the system) must be
predetermined, based on the anticipated work rate of
the diver and the maximum allowable oxygen partial
pressure at depth. These considerations establish the
flow rate setting and oxygen percentage in the supply
mixture. The oxygen percentage in the mixture is
governed by the maximum partial pressure at depth
that may be breathed safely if the recirculation system
must be bypassed and the supply gas used for direct
breathing. Flow rate setting is based on the percentage
of oxygen in the supply mixture and the diver's antici-
pated work rate or oxygen utilization rate.
The use of a system with preset limits means that
these limits cannot be altered during the dive if the
underwater situation changes. As an example, depth
cannot be increased without the danger of oxygen poi-
soning, which would occur if the premixed gas was
used at a higher pressure. A flow rate set for minimum
exertion may be insufficient for a strenuous swim and
might also produce hypoxia because of overconsumption
of the available oxygen. The depth range over which a
October 1991 — NOAA Diving Manual
15-9
Section 15
semi-closed-circuit system can be employed also is
limited by injection gas considerations. A free diver
deploying from the surface must have a minimum bag
oxygen level of 16 percent at 1.0 ATA to avoid hypox-
ia. The oxygen concentration in the supply mix and
flow rate considerations for the surface condition obvi-
ously will govern the maximum depth of the dive because
of partial pressure limits. In practice, the maximum
depth at which the highest oxygen percentage can be
breathed is the depth at which the partial pressure of
oxygen equals 1.6 ATA. Common mixtures with this
partial pressure are:
• 60 percent oxygen-40 percent nitrogen; maximum
depth 55 fsw(17 m).
• 40 percent oxygen-60 percent nitrogen; maximum
depth 99 fsw (31 m).
• 32.5 percent oxygen-67.5 percent nitrogen;
maximum depth 129 fsw (40 m).
Mixtures that are richer in oxygen decrease decom-
pression requirements but are limited to shallower depths
because of concerns for oxygen poisoning.
A number of factors directly affect the duration of
the breathing gas supply:
• Flow rate (dependent on work loads and resulting
C02 production);
• C02 absorbent characteristics and canister capacity;
• Changes in depth (duration is decreased because
of loss of gas from the breathing bag each time an
ascent is made);
• Tank capacity (and the pressure to which it can be
filled).
15.2.1.3 Closed-Circuit Systems (Rebreathers)
The closed-circuit (rebreather) system is a further
advance in the efficiency of scuba systems that has
been achieved at the price of increased complexity.
Like the semi-closed-circuit system, the rebreather
employs breathing bags and a carbon dioxide scrub-
ber; however, unlike the semi-closed-circuit systems,
rebreathers recirculate all of the exhaled gas within
the system. Furthermore, the rebreather operates with
a constant oxygen partial pressure, regardless of working
depth. Oxygen metabolically consumed by the body
is replaced from a bottle of 100 percent oxygen.
When using any closed-circuit scuba, the utilization
of the available oxygen is nearly 100 percent, because
the only gas that is expelled into the surrounding water
is the amount that is purged intentionally from the
system or vented automatically as the gas expands
during ascent. This means that the gas supply will last
longer and the quantity of breathing gas that must be
carried is smaller. Oxygen consumption will vary,
depending on the diver's exertion level (see Table 14-5).
Mixed Gas Rebreathers
Mixed gas rebreathers utilize two distinctly different
and separate gas supply cylinders, one of which contains
100 percent oxygen and the other a diluent gas. The
diluent gas may be air, nitrogen/oxygen, or helium/
oxygen. The choice of nitrogen or helium in the diluent
depends on the depth of the dive. The inclusion of
oxygen in the diluent provides a source of oxygen in the
event of failure of the oxygen control system. Diluent
gas is added automatically and breathing gas is vented
automatically from the breathing bags to keep the
pressure in the breathing circuit equal to the pressure
of the surrounding water. Oxygen is added automati-
cally to the breathing circuit to maintain a fixed,
preselected oxygen partial pressure in the circuit. Manual
bypass systems are included for both oxygen and dilu-
ent gases.
The added complexity of mixed gas rebreathers
(see Figure 15-3) is a result of the oxygen control
system. Sensors that measure oxygen partial pressure
are installed in the breathing circuit. More than one
sensor is used to provide redundancy in the event of
sensor failure during a dive. The output of these
sensors is fed to a display that is monitored by the
diver and that reads out the oxygen partial pressure
in the breathing circuit. Sensor output also is fed to
an electronic control circuit that compares the sensor
output to a preset value that represents the desired
oxygen partial pressure. If the sensor output indicates
that the oxygen partial pressure in the breathing circuit
is within the preset limits, no oxygen is added to the
circuit. However, should the oxygen partial pressure
be less than the preset limit, power is provided to
pulse open a solenoid that permits a fixed amount of
oxygen to flow from the oxygen bottle into the breath-
ing circuit. Power to operate the oxygen control system
is provided by batteries that must either be recharged
or replaced after each dive. The rebreather's operating
duration is relatively independent of depth and is usu-
ally limited by the capacity of the carbon dioxide
scrubber.
Oxygen Rebreathers
An oxygen rebreather is a special type of rebreather
requiring no diluent gas, which means that the diver
breathes 100 percent oxygen. The oxygen rebreather
utilizes breathing bags and a carbon dioxide scrubber,
as in the case of mixed-gas rebreathers; however, since
15-10
NOAA Diving Manual — October 1991
Mixed Gas and Oxygen Diving
Table 15-5
Air Purity Standards
Component
Purity
— Oxygen concentration
— Carbon dioxide
— Carbon monoxide
— Total hydrocarbons
other than methane
— Particulates and oil mist
— Odor and taste
20-22% by volume
1000 ppm maximum
20 ppm maximum
25 ppm maximum
o
5 mg rrr maximum
Not objectionable
Measured at standard temperature and pressure.
Source: US Navy (1988)
the diver breathes 100 percent oxygen, there is no
requirement for an oxygen control system or batteries.
Most units have a mouthpiece breathing valve assem-
bly, breathing hoses, inhalation and exhalation breathing
bags, a COi absorption canister, an oxygen supply
cylinder, and an adjustable gas-flow regulating assembly
(Figure 15-4). This simplification in the equipment,
however, does impose severe restrictions on the man-
ner in which the oxygen rebreather may be used. The
most significant of these restrictions is the limitation
on operating depth.
When using a closed-circuit oxygen rebreather, it is
necessary to purge both the apparatus and the lungs
with oxygen before entering the water to eliminate
nitrogen and air from the breathing system. If the
excess air is not eliminated from the breathing bags
and lungs before the initiation of oxygen breathing,
sufficient nitrogen may remain in the system to provide
a breathable volume of a hypoxic gas mixture. During
a prolonged dive, the nitrogen eliminated from the
body can cause a measurable increase of nitrogen in
the breathing medium. The danger of excess nitrogen
in a closed-circuit system is that hypoxia (see Sec-
tion 3.1.3.1) may occur if the volume of nitrogen is
enough to dilute or replace the oxygen. Unconsciousness
or death may result from hypoxia (see Figure 15-2).
WARNING
Divers May Not Be Able to Sense the Onset of
Hypoxia
Advantages and Limitations
The advantages of closed-circuit oxygen scuba include
freedom from bubbles, almost completely silent opera-
tion, and maximum utilization of the breathing medium
carried by the diver. A small oxygen supply lasts a long
time, and the duration of the supply is not decreased by
depth. Divers are not subject to decompression sick-
ness or nitrogen narcosis while using closed-circuit
October 1991 — NOAA Diving Manual
Figure 15-3
Closed-Circuit
Mixed-Gas
Scuba (Rebreather)
Courtesy Biomarme. Inc.
Figure 15-4
Closed-Circuit Oxygen
Scuba (Rebreather)
BYPASS VALVE
Courtesy Biomanne. Inc.
15-11
Section 15
oxygen scuba because there is no inert gas in their
breathing gas.
The major limitations of oxygen rebreathers are related
to the toxic effects of oxygen on the body, which sharply
limit the depths at which rebreathers can be used
safely. The oxygen system must be thoroughly purged
at the beginning of each dive, after 1 hour of submer-
gence, and again immediately before ascent. An excess
of carbon dioxide can build up in the system as a result
of absorbent exhaustion, wetting of absorbent, improper
canister filling, or over-breathing of the system.
Because of the chance of oxygen poisoning, NOAA
rarely uses oxygen rebreathers at depths in excess of
25 fsw (8 msw) (Table 15-2). Dives deeper than this
depth will result in a much shorter allowable bottom
time; for example, the maximum permissible dive
using this apparatus for a period of 20 minutes is 35 fsw
(11 msw, Table 15-2). The use of rebreathers beyond
these limits can result in serious or fatal accidents
involving oxygen convulsions. The amount of training
required and the extensive maintenance requirements
further restrict the use of this equipment.
NOTE
Oxygen rebreathers are manufactured by sev-
eral U.S. and European companies. Operat-
ing manuals and training must be obtained
from the manufacturer before attempting to
use any rebreather.
15.2.2 Surface-Supplied Mixed Gas Equipment
Surface-supplied mixed gas diving includes those
forms of diving in which a breathing mixture other
than air is supplied to the diver through a hose from the
surface. Either nitrogen-oxygen or helium-oxygen gas
mixtures may be employed, depending on the depth of
the dive. In addition to the U.S. Navy MK 12 surface-
supported diving system, there are a wide variety of
masks and helmets manufactured worldwide that may
be employed (see Section 5). Most military surface-
supplied equipment utilizes a constant flow of breath-
ing gas through the mask or helmet. Although this
results in a very high gas usage rate, equipment of this
type is simple to use. To reduce gas consumption, some
surface-supplied equipment incorporates a recirculation
feature that permits a portion of the gas leaving the
helmet to be recirculated through a carbon dioxide
scrubber and back through the mask. The most popu-
lar surface-supplied equipment in commercial use
employs a demand mechanism similar to that of scuba
(except that it is supplied by an umbilical). Because of
the complexity of the equipment required on the sur-
face, including large supplies of gas, various quantities
of different gas mixtures, compressors, special decom-
pression tables, and so forth, surface-supplied diving
generally is limited to military, commercial, or scien-
tific applications.
15.3 BREATHING GAS PURITY
Whatever the breathing gas or gases used, it is essen-
tial that the necessary standards of purity be met.
Standards are set by the Federal government and by
private organizations.
15.3.1 Compressed Air Purity
There are several specifications for the purity of
breathing air. The requirements most applicable to
divers' breathing air are discussed in:
• U.S. Navy Diving Manual (1988)
• Occupational Safety and Health Administration,
Standard for Commercial Diving Operations (29
CFR 1910, Subpart T)
• Compressed Gas Association Grade F standard
• American National Standards Institute, Z86.1
standard.
The most commonly used air standards for safe diving
practice are summarized and shown in Table 15-5.
15.3.2 Diluent Gas Purity
Mixed gases are used with mixed gas scuba or with
equipment using helmets designed specifically for
mixed gas. Various grades of the different gases are
produced for different uses.
Helium is produced in several quality verification
levels (QVL); QVLG is approximately 99.999 percent
pure, is free of oil and moisture, and is suitable for
use in diving. Several private manufacturers and the
Federal government produce helium.
Nitrogen, oxygen, and neon are produced by the
cryogenic fractioning of air. Hydrogen is produced
as a by-product of a number of chemical processes
or by the electrolysis of water.
Nitrogen purity is defined in Federal Specification
BB-N-4HC. This specification describes three grades
of Type I (gaseous), Class 1 (oil free) nitrogen:
• Grade A is 99.95 percent pure, low moisture con-
tent, no solids;
• Grade B is 99.5 percent pure, low moisture content; and
• Grade C is 99.5 percent pure, no moisture con-
tent specified (US Navy 1987).
15-12
NOAA Diving Manual — October 1991
Mixed Gas and Oxygen Diving
Nitrogen of Class 1 in Grades A, B, or C may be used
for diving operations if the trace contaminants in the
gas, which may not constitute more than 0.5 percent by
volume, consist only of oxygen and carbon dioxide. A
high percentage of CO-, contamination in Grades B or
C nitrogen may preclude its use as breathing gas. The
label on the cylinder may provide data about class and
grade.
The individual gases used in preparing various breath-
ing mixtures are available in a highly pure state. Any
trace contaminants are usually the result of cleaning
agents used to prepare the gas containers. (For addi-
tional information, see the most recent Compressed
Gas Association Handbook of Compressed Gases.)
15.3.3 Oxygen Purity
The purity standards for oxygen are detailed in Mili-
tary Specification MIL-0-27210 (US Navy 1988).
This specification categorizes oxygen in the following
three grades:
• Grade A Aviator's oxygen
• Grade B Industrial, medical oxygen
• Grade C Technical oxygen.
Grades A and B differ in moisture content. Grade A,
used by aviators, must be extremely dry to prevent
freezing at the low temperatures associated with high
altitudes. Grade B is allowed to contain a maximum of
5 ml of free water per cylinder. Grades A and B oxygen
are suitable for use in a breathing medium for divers.
Both Grades A and B are required to be 99.5 percent
pure oxygen and must pass tests for acidity and alkalinity,
carbon dioxide, carbon monoxide, halogens, and other
oxidizing substances, as specified in the current edi-
tion of the U.S. Pharmacopoeia. Grade C, technical
oxygen, is safe to breathe, but it may have an objection-
able odor and, for that reason, should not be used in
diving.
15.4 BREATHING GAS ANALYSIS
The type and concentration of the constituents of breath-
ing gas are vitally important because adverse physio-
logical reactions can occur whenever exposure dura-
tions and concentrations of various components in the
breathing atmosphere vary from prescribed limits. The
quality of the breathing gas is important in both air and
mixed gas diving. Because the basic composition of the
gas is fixed in air diving, primary attention is directed
toward the identification of impurities (carbon monoxide,
hydrocarbons) that may be present in the air supply
October 1991 — NOAA Diving Manual
and the effects of inadequate ventilation (carbon
dioxide).
The use of gas analysis is essential in mixed gas
diving. Because both hypoxia (oxygen partial pressures
below the normal range) and oxygen poisoning are real
hazards in mixed gas diving, it is essential that the
oxygen content of the gas supply be known before a
dive. Oxygen analysis is the most common but not
the only type of analytical measurement performed in
mixed gas diving. When selecting an instrument to
analyze one or more constituents of a gaseous atmo-
sphere, two instrument characteristics are particularly
important: accuracy and response time. Both accuracy
and sensitivity within the range of the expected con-
centration must be adequate to determine the true
value of the constituent being studied; this can be a
problem when samples must be taken at elevated pres-
sure. It is also important that the response time of the
instrument be adequate for the situation. Other factors
that may be important in the selection of analytical
instruments are accuracy, reliability, sampling range,
portability, and cost.
Instruments for testing the composition and purity
of gases fall into two categories: those for laboratory
use and those for field use. Laboratory instruments are
complex and highly accurate and include the mass
spectrometer, the gas chromatograph, and other chemical
analysis devices. These instruments generally are not
available at dive sites because they require specialists
trained in their use, operation, calibration, and inter-
pretation of the data and are expensive.
Some private and state agency health laboratories
provide air analysis services. Several private laborato-
ries provide diver air analysis services and will supply
diving firms or organizations with air sampling kits
designed to meet the requirements specific to the air
supply system being used (Figure 15-5). Using this
equipment and the directions supplied with such kits,
air samples can be collected from the compressor,
particulate samples for oil mist and solid particles can
be collected from the compressor's filter system, and
samples of the ambient air can be obtained to provide
background levels of contamination. The kit and sam-
ples are returned to the laboratory for immediate analy-
sis. Using modern gas chromatography equipment and
other appropriate techniques, the samples are analyzed
for carbon monoxide, carbon dioxide, methane, total
gaseous hydrocarbons, oxygen, nitrogen, oil mist, and
other particulates. U.S. Navy standards are generally
used as an air purity guideline.
Instruments also are available for field use that pro-
vide sufficiently accurate data to determine whether a gas
15-13
Section 15
Figure 15-5
Air Analysis Kit
for On-Site Use
Courtesy Texas Research Institute
is safe to use as a breathing medium. Field instruments
that operate on the colorimetric principle are available
to measure a large number of gases (e.g., oxygen, hydro-
carbons, carbon monoxide, carbon dioxide, etc.). These
devices come with several different tubes, each spe-
cific for a particular gas or group of gases. When the
material in the tube comes into contact with a specific
gas, it changes color. Portable instrumentation is used
to determine the percentage of oxygen in the gas, the
gross percentage of carbon dioxide, and the amount of
carbon monoxide present; however, field instruments
are not capable of precise analysis of the total gas
composition. A brief description of portable gas analysis
equipment follows.
Oxygen analyzers. Several portable oxygen analyzers
are available for measuring the percentage of oxygen
in a gas. Calibration of these instruments is important,
and calibration instructions are usually included with
the equipment. Oxygen content can be determined by
using a fuel cell or paramagnetic analyzer, a gas chro-
matograph, a standard volumetric gas analyzer, an
electrometric analyzer, a thermal conductivity analyzer,
or color-indicating tubes.
Carbon dioxide analyzers. Analysis conducted in
the field can detect only gross amounts of carbon diox-
ide (C02) in a breathing medium. Field-use C02
analyzers are capable of detecting C02 in quantities of
less than 1 percent. Any diver's gas that contains a
gross amount of C02 is not safe to use. Carbon dioxide
content can be determined by using a gas chromato-
graph, titrimetric analysis, a standard volumetric gas
analyzer, an infrared analyzer, or color-indicating tubes.
Carbon monoxide analyzers. Equipment also is
available for the laboratory or on-site determination
of carbon monoxide in ambient air. Field equipment
works either on the potentiometric or colorimetric
(Figure 15-6) principle. Potentiometric analyzers are
generally more costly than colorimetric devices, and
color-indicating analyzers are therefore used more
frequently.
It is commonly assumed that unpolluted air com-
pressed in a well-maintained compressor designed for
compressing breathing gas will meet oxygen and car-
bon dioxide requirements without testing. However, a
simple test for water, oil, or particulate matter in the
gas can be performed. The gas cylinder is inverted for
at least 5 minutes in the valve-down position. The
valve is then opened slightly, and air is allowed to flow
into a clean glass container. If the gas is contaminated,
oil, water, or particulate matter can be observed on the
glass. Laboratory methods for testing for water in breath-
ing gas include the electrolyte monitor, the piezoelec-
tric hydrometer, the standard dew point apparatus, or
an electrical conductivity test. Ultraviolet spectros-
copy is used to test for oil contamination.
The total hydrocarbon content in air can be deter-
mined in a laboratory using a total hydrocarbon analyzer.
For further information on gas analysis equipment, see
the US Navy Diving Manual (1988).
Compressed air sources should be tested at least
semi-annually. Compressed air from an untested source
should not be used except in unusual or emergency
conditions; under these conditions, it is recommended
that the diver breathe the air for a few minutes at
the surface before diving.
15.5 GAS MIXING
Two or more pure gases or gas mixtures may be com-
bined by a variety of techniques to form a final mixture
of predetermined composition. The techniques for mixing
gases, in the order of their frequency of use, are:
(1) Continuous-flow mixing, in which a precalibrated
mixing system proportions the amount of each
gas in a mixture as it is delivered to a common
mixing chamber.
(2) Mixing by partial pressure, which is based on the
fact that the proportion by volume of each gas in
a mixture is directly related to its partial pres-
sure (to the extent that the gases behave as 'ideal'
gases).
Aboard ship, where space is limited and motion might
affect the accuracy of precision scales, gases normally
15-14
NOAA Diving Manual — October 1991
Mixed Gas and Oxygen Diving
Figure 15-6
Direct-Reading Colorimetric
Air Sampler
A. Sampling Tube
B. Complete Kit
Courtesy Draegerwerk AG
are mixed by partial pressure or by continuous-flow
mixing systems.
15.5.1 Continuous-Flow Mixing
Continuous-flow gas mixing systems perform a series
of functions that ensure extremely accurate mixtures.
Constituent gases are regulated to the same pressure
and temperature before they are metered through pre-
cision micrometering valves. The valve settings are
precalibrated and displayed on curves that are pro-
vided with every system and that relate final mixture
percentages to valve settings. After mixing, the mix-
ture is analyzed on-line to provide a continuous his-
tory of the oxygen percentage. Many systems have
feedback controls that automatically adjust the valve
settings when the oxygen percentage of the mixture
varies from preset tolerance limits. The final mixture
may be supplied directly to a diver or chamber or be
compressed into storage tanks for later use.
15.5.2 Mixing by Partial Pressure
This method frequently is used in filling cylinders
aboard ship or in the field. It employs high-pressure
gas sources from which gases are mixed according to
the final partial pressure desired. The basic principles
behind this method are the ideal gas laws, such as
Dalton's Law of Partial Pressures, which states that
the total pressure of a mixture is equal to the sum of the
partial pressures of all the gases in the mixture.
Two methods are available to calculate the partial
pressure of a gas in a mixture: the ideal-gas method
and the real-gas method. The ideal-gas method assumes
that pressure is directly proportional to the temperature
and inversely proportional to the volume of a contained
gas. The real-gas method additionally accounts for the
fact that certain gases will compress more or less than
other gases.
Compressibility is a physical property of every gas:
oxygen compresses more than helium. Therefore, if
two cylinders with the same internal volume are filled
to the same pressure, one with oxygen and the other
with helium, the oxygen cylinder will hold more cubic
feet of gas than the helium cylinder. As pressure is
increased or as temperature is decreased, the differ-
ence in the amount of gas in each cylinder will increase.
The same phenomenon occurs when any two gases are
mixed together in one cylinder. In the case of oxygen
and helium, if an empty cylinder is filled to 1000 psia
with oxygen and then topped off to 2000 psia with
helium, the resulting mixture will contain more oxygen
than helium.
An awareness of the differences in the compressibil-
ity of various gases usually is sufficient to avoid many
of the problems encountered when mixing gases. When
using ideal-gas procedures, knowledgeable divers add
less oxygen than is called for, analyze the resulting
mixture, and compensate as necessary. As an alterna-
tive when mixing certain specific mixtures, the US
Navy Diving Gas Manual (1971) may be consulted for
procedures to calculate the partial pressures of each
gas in the final mixture. These procedures take into
account the compressibility of the gases being mixed.
Regardless of the basis of the calculations used to
determine the final partial pressures of the constituent
gases, the mixture always must be analyzed for oxygen
content before use.
October 1991 — NOAA Diving Manual
15-15
i
SECTION 16
SATURATION
DIVING
16.0
16.1
16.2
16.3
16.4
16.5
16.6
Page
General 16-1
Principles of Saturation Diving 16-1
Breathing Gases 16-7
Life Support Considerations 16-8
Operational Considerations 16-9
16.4.1 General Procedures 16-9
16.4.2 Emergency Procedures (Habitats) 16-10
16.4.3 General Health Practices 16-12
16.4.4 Hazardous Materials 16-12
Excursion Diving 16-13
Decompression After an Air or Nitrogen-Oxygen
Saturation Dive 16-13
16.6.1 Diving After Decompression From Saturation Exposure.... 16-13
16.6.2 Flying After a Saturation Decompression 16-14
i
SATURATION
DIVING
16.0 GENERAL
As interest in the oceans and man's ability to work
there increase, techniques and facilities are needed
that will enable the scientist or working diver to remain at
depth for longer periods of time. An approach that has
proved useful in underwater scientific research is
nitrogen-oxygen and air saturation-excursion diving
from habitats positioned on the seabed. Habitat-based
diving is relatively new, and techniques for this type of
diving are still developing. To improve the safety and
effectiveness of nitrogen-oxygen saturation techniques
further, organizations using these procedures are re-
quested to report their experience to the NOAA Diving
Program.
Saturation is the term used to describe the state that
occurs when a diver's tissues have absorbed all the
nitrogen or other inert gas they can hold at any given
depth. Once tissue saturation has occurred, the length
of the decompression that will be required at the end of
the dive will not increase with additional time spent at
that depth.
Under saturation conditions, the diver works out of
a pressure facility whose atmosphere is maintained at
approximately the same pressure as that of the sur-
rounding water or, in a chamber, of the working depth.
The saturation facility may be an ocean floor instal-
lation, a pressurized chamber on board a surface vessel,
or a diver lockout submersible.
The term habitat usually is applied to a pressure- or
ambient-pressure vessel that is placed on the floor of
the ocean and that provides basic life support, comfort,
and a base of operation for the diver and the necessary
support equipment. Habitats are maintained at a pressure
that is equivalent to the pressure of the seawater at the
habitat's entrance hatch. (See Section 17 for more
information on habitats.)
A surface-based saturation diving system consists of
a deck decompression chamber (DDC) that is located
on a surface support platform and a pressurized diving
bell that the saturation diver uses to commute to and
from the underwater worksite. The DDC. which provides
facilities for the life support and comfort of the saturated
diver, may be maintained at a pressure that is close to
that of the working depth. The personnel transfer capsule
(PTC) (which can be either a diving bell or a lockout
submersible) also is maintained at a pressure close to
October 1991 — NOAA Diving Manual
that of the working depth. During transfer from one
chamber to another, the PTC is mated to the DDC to
enable the diver to remain at pressure at all times.
A diver lockout submersible is a vehicle designed
with at least two separate compartments; these compart-
ments enable the divers to enter and exit the water
while submerged. Regardless of the system used, the
saturation diver undergoes decompression only on
completion of the total dive sequence rather than at
the end of each dive (unless an excursion dive requiring
decompression has been made).
Saturation diving is an essential technique for the
scientist who needs to spend long periods on the bottom
and for the working diver who wishes to extend the
working portion of the dive. Since 1958, when Captain
George Bond, USN, conducted the laboratory experi-
ments that led to the development of saturation diving
(Bond 1964), saturation diving programs have been
carried out by a variety of organizations from many-
nations, using both land-based hyperbaric chambers
(simulated dives) and habitats or bells in the open sea.
The saturation depths employed in these programs
have ranged from 26 to 2250 fsw (8 to 686 m). Although
the military and commercial diving industries have
devoted substantial effort to developing practical
saturation diving techniques involving helium-oxygen
gas mixtures for use at depths to 1000 fsw (307 m) and
deeper, NOAA has concentrated on saturation diving
in shallower waters (40 to 300 fsw; 12 to 92 m) utilizing
more readily available and less costly nitrogen-based
gases, particularly air. This section discusses various
aspects of saturation diving and provides, for historical
interest, summaries of some air and nitrogen-oxygen
exposures (Table 16-1).
16.1 PRINCIPLES OF SATURATION DIVING
The tissues of a diver's body absorb inert gases as a
function of the depth and duration of the dive, the type
of breathing mixture used, the characteristics of the
individual diver's tissues, and factors affecting the
diver's condition at the time of the dive, such as
temperature and work rate. In long-duration dives,
the diver's body tissues become saturated with the
inert gases in the breathing mixture at the partial
pressure of each inert gas component in the mixture.
16-1
Section 16
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N0AA Diving Manual — October 1991
Saturation Diving
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Saturation Diving
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16-5
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16 6
NOAA Diving Manual — October 1991
Saturation Diving
For practical purposes, the state of saturation is reached
in less than 24 hours. The techniques of saturation
diving make use of the fact that, once the body's
tissues have reached this equilibrium, they can safely
remain saturated for long periods without increasing
the diver' s decompression obligation.
From an operational standpoint, there are two principal
factors in saturation diving, i.e., the depth at which
the diver's tissues become saturated (called the storage
depth), and the vertical range of depths over which the
diver can move (termed the excursion depths). The
storage depth determines the breathing mixtures that
can be used, the possible range of vertical excursions
the diver can undertake, and the decompression schedule
to be followed; the storage depth should be selected to
maximize the diver's effectiveness in the working
depth range. When selecting a storage depth, both
ascending and descending excursions should be kept in
mind, although descending excursions have several
safety and operational advantages.
16.2 BREATHING GASES
Several different breathing mixtures have been used
successfully in saturation diving, e.g., air, nitrogen-
oxygen, and helium-oxygen. These mixtures may be
used singly or in combination, both as the habitat gas
at storage depth and as the breathing gas for excursions
from the habitat.
Air has been used extensively as a breathing gas in
saturation diving. Its use as a habitat gas is limited to
relatively shallow depths (50 fsw; 15 m) because of
oxygen toxicity (Adams et al. 1978). Short excursion
dives from the storage depth have been conducted
successfully to depths as great as 250 fsw (76 m) using
air as the breathing medium. Because oxygen toxicity
and nitrogen narcosis are both concerns on air dives to
such depths, excursions using this breathing medium
must be planned carefully.
NOTE
Because of the gas exchange characteristics
of nitrogen and helium, saturation and satura-
tion-excursion diving involving switches
from one inert gas to another should not be
attempted without the advice of a qualified
person who has a thorough knowledge of the
factors involved.
Several successful laboratory and at-sea saturation
programs have been carried out at storage depths of
October 1991 — NOAA Diving Manual
60 fsw (18 m) using air as the breathing medium. These
dives have revealed physiological responses that,
although apparently normal and reversible adaptations,
suggest that operational air-saturations should be limited
to 50 fsw (15 m; see Table 15-1). There is also some
indication that habitation at this oxygen partial pressure
(PO;) level (i.e., that of air at 60 fsw (18 m); P02 = 0.59)
may predispose divers to central nervous system (CNS)
oxygen toxicity (Miller 1976) and that such an oxygen
partial pressure may reduce a diver's tolerance for
oxygen during any subsequent treatment for decom-
pression sickness (Adams et al. 1978). Because the use
of air has obvious advantages, research on its use as a
breathing medium at depth will continue.
Shallow-water saturation diving also has been
conducted using nitrogen-oxygen (nitrox) mixtures.
The proportions of oxygen and nitrogen in nitrox mixtures
are selected to provide a partial pressure of oxygen
within a range from 0.21 ATA (close to the normal
atmospheric value) to 0.50 ATA. Such mixtures can be
used for habitat depths equal to or shallower than
50 fsw (15 m) and should be used for habitat depths
greater than 50 fsw (15 m). Based on extensive military'
and commercial saturation diving experience with
helium-oxygen gas mixtures, the optimal saturation
oxygen partial pressure range is 0.30 to 0.40 ATA,
with a nominal value of 0.35 ATA considered accepta-
ble for all applications.
If the oxygen partial pressure of air at the saturation
depth is too high, it can be adjusted by adding either
nitrogen or low-oxygen nitrox mixtures or by allowing
the oxygen in the habitat to be "breathed down" by the
divers. If the oxygen partial pressure is above the
recommended maximum level, care must be taken to
ensure that the divers do not experience oxygen toxicity as
a result of breathing hyperoxic gas in the habitat and
during their air excursion dives. Consequently, breathing
down the oxygen concentration is not acceptable in
most situations and can only be used in very small
habitats.
Divers engaged in excursion diving using air as the
breathing medium must continuously be aware of the
danger of oxygen toxicity (see Section 3.3). They must
know the maximum amount of time that can be spent
safely at various depths without incurring problems
related to oxygen exposure. As with other toxicities,
oxygen poisoning is a function of both dose and dura-
tion of exposure.
Although neurological symptoms, such as convulsions,
are the most serious consequence of oxygen poisoning,
the symptoms most likely to be associated with over-
exposure in saturation-excursion diving are pulmonary.
Accordingly, pulmonary tolerance limits that are safe
16-7
Section 16
for repeated daily exposures have been incorporated
into the limits shown in Table 15-1 and have also been
applied (where appropriate) to the tables in this section on
saturation diving.
The degree of oxygen exposure can be quantified by
using a system that permits pulmonary oxygen toxicity
to be correlated with reduced vital capacity. The oxygen
dose that causes a 10 percent reduction in vital capacity
is considered the maximum safe cumulative oxygen dose,
and diving operations should be planned so that every
diver has a safety margin that will allow him or her
to be treated for decompression sickness with oxygen
without exceeding this 10 percent level.
Nitrox breathing mixtures have been used to depths
of 198 fsw (60 m) in the laboratory, but the safe limit
for such exposures has not been established, and nitrox
saturation dives have been conducted in the open sea to
depths as great as 111.5 fsw (34 m). To date, open-sea
saturation dives that have used nitrogen-oxygen mixtures
as the storage gas have employed air as the breathing
gas for excursion dives. A review of the data gathered
during these exposures reveals that
• The limiting factor when air is used as the saturation
storage gas is oxygen partial pressure.
• The limiting factor when a nitrogen-oxygen mixture
is used as the storage gas is nitrogen narcosis.
• Extended exposure (for as long as 1 1 days) to air at
50 fsw (15 m; 0.5 ATA P02) has not produced
irreversible or deleterious effects on human vol-
unteers (Adams et al. 1978).
• Extended exposure (27 days) to air at 60 fsw
(18 m; 0.589 ATA P02) has caused significant
decreases in red blood cell mass and, in some but
not all individuals, a significant decrease in lung
vital capacity, which indicates pulmonary oxygen
toxicity (Miller 1976).
• The degree of nitrogen narcosis varies among
individuals.
• Partial adaptation to narcosis may occur in some
individuals after continued exposure.
• Prolonged exposure to normoxic nitrogen at depths
to 120 fsw (37 m) has not produced a significant
decrement in diver performance.
Based on this information, the following recommen-
dations can be made for air and nitrox saturation dives:
• Air saturation should be limited to a depth of
50 fsw (15 m).
• The oxygen partial pressure of nitrogen-oxygen
mixtures used in saturation storage gases should
be kept within the range of 0.3 to 0.5 ATA.
• The operational use of nitrogen-oxygen as a storage
gas should be limited to a depth of 120 fsw (37 m).
16-8
Helium-oxygen has been used widely as a breathing
medium by the U.S. Navy and the commercial diving
industry for saturation and excursion diving. (Readers
should refer to the U.S. Navy Diving Manual (1987),
the diving physiology literature, and Section 15.1.3 for
information on this type of diving.) In general, helium-
oxygen is selected as a breathing gas in surface-oriented
diving when the job to be done requires that work be
performed at a depth of 150 fsw (45 m) or more. The
principal reason for using a helium-oxygen mixture is
the avoidance of nitrogen narcosis (see Section 3.2.3.5).
Helium mixtures have rarely been used as breathing
gases for excursions from nitrogen saturation exposures;
under some circumstances, isobaric bubble disease (the
counterdiffusion phenomenon) could occur when these
two gases are used (D' Aoust 1977; see Section 3.2.3.3).
16.3 LIFE SUPPORT CONSIDERATIONS
Excursion diving from a saturation system or habitat
usually is performed with standard diving equipment,
e.g., scuba, umbilical, or closed-circuit rebreathers.
Because this equipment is described elsewhere in this
manual, the following discussion describes the life
support features of the saturation system itself.
Life support equipment and techniques vary greatly
from one system to another. Some systems require
complicated gas mixing and monitoring equipment on
a surface support vessel, while others can be supported
by equipment that supplies compressed gas, power,
and environmental control from an unmanned buoy.
Other systems, such as the mobile lockout submersibles
commonly used by the offshore oil and gas industry,
require a self-contained life support system.
The characteristics that a particular saturation diving
life support system must have depend on the depth,
mission duration, water temperature, sea surface
condition, requirements for mobility, type of equipment
to be used for excursions, rescue potential, and, in many
cases, the nature of the work or scientific program to be
carried out. Regardless of the system and its peculiari-
ties, all divers must become familiar with the function
of each system component, the system's maintenance
requirements, and all emergency procedures. Training
programs usually provide this information and offer an
opportunity for such familiarization. However, all
saturation systems have some features in common that
relate directly to the health and safety of divers.
In saturation diving, the oxygen pressure for storage
should be maintained between 0.30 and 0.50 ATA.
Carbon dioxide levels should not exceed a sea level
equivalent of 0.5 percent (0.005 ATA) (US Navy 1987).
Carbon monoxide should not exceed a partial pressure
NOAA Diving Manual — October 1991
Saturation Diving
that is equivalent to 0.002 percent by volume (20 ppm)
at sea level. If air is the breathing gas, safe partial
pressures of carbon dioxide can be maintained by
constantly venting the interior atmosphere at a rate of
2 cfm for each diver at rest and 4 cfm for each diver not
at rest (U.S. Navy 1988). Control of the oxygen partial
pressure usually is not a problem at shallow depths
when air is used as both the storage and excursion
diving gas.
In closed-circuit life support systems and diver-
carried rebreathers, which usually use mixed gases,
carbon dioxide buildup is a significant problem, and a
carbon dioxide scrubbing system is therefore necessary.
The active ingredient in scrubbing systems is a chemical,
usually composed predominantly of barium hydroxide
(Baralyme5). lithium hydroxide, or soda lime (Sodasorb® or
other trade name), that will absorb the carbon dioxide.
The length of the absorbent's active life depends on the
CO-, output of the divers, the ambient temperature,
and the relative humidity. The man-hour rating of a
particular absorbent is provided by the manufacturer.
Table 16-2 summarizes the characteristics of barium
hydroxide, lithium hydroxide, and soda lime. Because
carbon dioxide absorption is influenced by tempera-
ture, less C02 is absorbed at 40aF (4.4°C) than at
70°F (21.1 *C). Some scrubbers sized for adequate
performance at 70°F (21.1 X) may have only one-third
of their absorbing capacity at 40° F (4.4°C).
Providing external insulation and heating scrubbers
that are to be used in cold water are ways of minimizing
the size of the canister that must be carried and ensuring
that the absorbent achieves its design efficiency.
Insulation and heating also minimize moisture con-
densation.
The efficiency of C02 absorbents also is influenced
by relative humidity. Barium hydroxide and soda lime
absorbents can only achieve their rated capacity when
the relative humidity is above 70 percent. Lower humidity
levels reduce absorbent capacity. Under conditions of
high gas humidity and low scrubber surface tempera-
ture, water may condense on the walls of the canister or
in the absorbent, which reduces absorptive capacity
and increases pressure drop through the canister.
An auxiliary habitat scrubbing system frequently is
used as a backup in case the primary system fails. If no
backup scrubber system is available, the chamber should
be vented as described above. Divers must remain alert
for symptoms of carbon dioxide poisoning (changes in
breathing rate or shortness of breath, headache, sweating,
nausea, or weakness); the onset of such symptoms is
sometimes difficult to detect over a long period. Divers
also may not be aware of CO-, buildup because they
associate minor breathing difficulties with the greater
density typical of breathing gases under pressure.
In addition to atmospheric control, a satisfactory
life support system must have adequate controls for
temperature and humidity. At shallow depths, com-
fortable temperature and humidity ranges are 78 to 83 " F
(25.6 to 28.3 °C) and 50 to 75 percent, respectively, in
air or nitrogen/oxygen environments. At deeper depths
or in helium-oxygen saturation atmospheres, temper-
atures as high as 92 °F (33.3 °C) and a relative humidity
between 40 and 60 percent may be necessary for comfort.
The atmosphere's relative humidity affects both the
comfort and safety of chamber inhabitants. Habitat
humidity is controlled by air conditioning and the use
of dehumidifiers or moisture absorbers. Excessive
humidity not only decreases scientific productivity but
encourages the growth of fungus or bacteria that cause
infections (see Section 3.2.1.1). On the other hand,
humidity that is too low can create a fire hazard.
16.4 OPERATIONAL CONSIDERATIONS
Saturation divers working from a habitat or PTC have
direct access to the work site. Use of the saturation
mode greatly extends a dive's bottom time or working
time because it reduces the relative amount of time
that divers must spend compressing and decompressing.
Saturation divers also find this mode psychologically
advantageous because they find it convenient and
reassuring to have a dry chamber close at hand.
16.4.1 General Procedures
A diver undergoing saturation on the seafloor for the
first time has much to learn. First and foremost, the
diver must learn that the surface is not a haven in an
emergency; instead, refuge must be found at the working
depth. Also, saturated divers must:
• Learn to rely on the surface support team for support;
• Be aware that the entire saturation, from predive
preparation to the long decompression at the end
of the mission, demands substantial commitment;
• Become familiar with the saturation system, its
operation, all emergency procedures, and all fire
safety rules;
• Become familiar with the diving equipment and its
limitations;
• Become familiar with the surrounding area of the
seafloor, the transect lines, and any other orienta-
tion markers;
• Learn the limits and procedures for making vertical
excursions;
October 1991 — NOAA Diving Manual
16-9
Table 16-2
Characteristics of Three
Carbon Dioxide Absorbents
Absorbent
Section 16
Characteristic
Barium
Lithium
Soda
Hydroxide
Hydroxide
Lime
Absorbent density, lb/ft3
65.4
28.0
55.4
Theoretical C02absorption, lb CO^'lb
0.39
0.92
0.49
Theoretical water generated, lb/lb CO2
0.41
0.41
0.41
Theoretical heat of absorption, BTU/lb CO2
6701
8751
6702
Useful CC>2absorption, lb CO2/ID
0.195
0.46
0.245
(based on 50 percent efficiency)
Absorbent weight, lb per diver hr
3.65
1.55
2.90
(0.71 lbC02)
Absorbent volume, ft3 per diver hr
0.0558
0.0552
0.0533
'Based on calcium hydroxide reaction only.
2Based on generating gaseous H2O.
Source: NOAA (1979)
• Plan all missions and excursions in advance, taking
into account the equipment, saturation system,
depth, excursion profiles, and the saturation experi-
ence of other team members; and
• Assume responsibility both for their own and their
buddy's safety during excursions.
16.4.2 Emergency Procedures (Habitats)
All well-conceived saturation operations should have
contingency plans that chart a course of action in case
a primary life support system fails or another emergency
arises. Any contingency plan should give first priority
to diver safety. In a habitat or PTC, any emergency,
however minor, threatens diver safety. The following
emergency procedures are intended to serve as general
guidelines that apply to all habitats and personnel
transfer capsules. However, because most habitats and
PTC's are one-of-a-kind systems, certain differences
in hardware and design will dictate specific procedures
that should be followed for each.
WARNING
Complete Emergency Procedures Should Be
Developed for Each System, and All Surface
Support Personnel and Divers Should Become
Familiar With Them
Fire Safety
Fire probably is the most critical emergency that
can threaten divers using a saturation system. Habitats
using air as the storage medium are susceptible to fire
because air supports combustion more readily under
increased pressure. Burning rates under hyperbaric
conditions are primarily a function of the percentage
16-10
of oxygen present (Shilling et al. 1976). Atmospheres
that have less than 6 percent oxygen will not support
combustion. A normoxic nitrogen-oxygen habitat
atmosphere contains a lower percentage of oxygen than
an air-filled habitat and therefore presents a lesser
fire hazard. When helium is used at great depths, the
potential for fire is even further reduced. Care must be
taken, however, when oxygen is used during decompres-
sion or treatment for decompression sickness.
For diving operations conducted outside the zone of
no combustion (see Section 6.5.2), materials that are
highly combustible should not be placed in the habitat.
In the event of fire, divers should follow the general
procedures below, although their order may vary:
• Make a quick assessment of the source of the smoke
or flame. (If the source is a movable item, eject it
from the habitat immediately, if possible.)
• Don emergency breathing masks.
• Shut off all power except lights and emergency
communications.
• Notify surface personnel.
• Attempt to extinguish the fire with water.
• Attempt to remove all flammable materials from
the immediate area of the flames. Also attempt to
discharge smoldering material from the chamber.
• Leave the chamber after donning diving gear unless
you are directly involved in fighting the fire.
• If the fire goes out of control, abandon the chamber,
notifying surface personnel of this action if condi-
tions permit. Proceed to available underwater
stations and await surface support.
Loss of Power
Most shallow water habitat systems have a primary
power source and an emergency or standby power source.
Primary power is usually 110 volts a.c; emergency
NOAA Diving Manual — October 1991
Saturation Diving
power is usually 12 volts d.c. In some systems, the
emergency power is designed to activate automatically
if the primary source fails.
In a power emergency, divers should perform the
following procedures:
• Activate the emergency power source, if this system
is not automatically activated;
• Notify surface support personnel and stand by to
assist in isolating and remedying the cause of the
failure.
Loss of Communication
Most saturation systems have a backup communication
system. Sound-powered phones that require no external
power often are used. In some cases, communication
over diver communication circuits may be possible.
When a communication failure occurs, communication
should be established immediately on a secondary system,
the surface should be notified of primary system failure,
and attempts should be made to reactivate the primary
system.
Blowup
Inadvertent surfacing, commonly called blowup, is
a serious hazard facing saturated divers, especially
when they are using self-contained equipment and are
not physically attached to a habitat or PTC by an
umbilical or tether. Saturated divers who are away
from the habitat must be careful to avoid any cir-
cumstance that would require them to make an emer-
gency ascent to the surface or that might result in
accidental surfacing.
If a diver does surface accidentally, however, the
buddy diver must:
• Immediately return the diver to the saturation
depth. If the accidental surfacing was caused by
equipment failure, the diver's buddy should swim
immediately to the surface and bring the surfaced
diver down, using the emergency octopus regulator,
and should then proceed to the habitat. If the
saturation depth is greater than 100 fsw (30 m),
the surfaced diver should be rescued by the surface
support team, because a saturated buddy who
surfaces to help the diver will also be endangered.
• Notify surface support personnel immediately.
• At depths of 60 fsw (18 m) or less, have the diver
begin breathing pure oxygen while awaiting instruc-
tions from surface support; if deeper, an enriched
oxygen mixture should be used to provide an oxygen
partial pressure of between 1.5 and 2.5 ATA.
• Make preparation for emergency recompression,
if directed to do so by surface support personnel.
NOTE
A diver who accidentally surfaces or becomes
lost is in great danger. The best assurance
against such emergencies is strict adherence
to carefully planned preventive measures.
Lost Diver
A saturated diver working away from a habitat or
PTC should be aware continuously of his or her
dependence on that facility for life support. Any excursion
should be planned carefully so that the way back to the
chamber is known and assured. As in all diving, buddy
divers are a necessity. In the saturated condition, it is
especially necessary for diving buddies to stay close
together and to be aware at all times of their location,
significant landmarks, and the distance and direction
back to the habitat or PTC. Many habitats, particularly
those permanently fixed and continually used, have
navigation lines extending to various underwater areas.
Divers should become familiar with these navigation
patterns and use them as reference points during
excursions.
WARNING
Saturation Divers Should Place Primary
Reliance for Orientation on Established Navi-
gation Lines. A Compass Should Be Used
Only to Provide a Backup Orientation System
If a diver becomes lost, he or she should take the
following actions:
• Begin signaling by banging on his or her scuba
cylinder with a knife, rock, or other hard object;
• To conserve breathing gas, ascend to the maximum
upward excursion depth limit that still permits the
bottom to be seen clearly (in murky water or at
night, this will not be possible);
• If lost at night, switch his or her light off momen-
tarily to look for the habitat or buddy's light;
• Begin making slow circular search patterns, looking
for familiar landmarks or transect lines.
Divers hopelessly lost at saturation depths shallower
than 100 fsw (30 m) should ascend slowly to the surface
while they still have sufficient air. On reaching the
surface, the diver should take a quick (less than
30 seconds) compass sighting on the support system or
buoy over the habitat and should then return to the
October 1991 — NOAA Diving Manual
16-11
Section 16
bottom, rejoin his or her buddy, and proceed directly to
the habitat.
WARNING
Divers Should Start Their Return to the Habitat
From Excursion Dives Before the Pressure in
Their Cylinder Falls Below the Amount That
Will Support Them During Their Return
Night Diving
Night excursions from habitats are common, particu-
larly for scientific divers wishing to observe marine
life. Divers must take special care not to become lost
during these excursions. Every diver must be equipped
with two well-maintained lights that are in good working
condition and are equipped with fresh batteries. Every
diver should also have an emergency light, preferably
a flashing strobe. In emergencies, the strobe can be
used for navigation if the diver shields his or her eyes
from the flash. To assist divers back to the habitat if
their lights have failed, a flashing strobe should be
located on the habitat or PTC.
Decompression Sickness After Excursions
Although excursions from a habitat are not likely to
cause decompression sickness, habitat operational plans
should include procedures for treating decompression
sickness. Specific procedures will vary from one habitat
program to another, but the following general guidelines
can be used if decompression sickness occurs after an
excursion dive.
Therapy should be carried out in the habitat. The
treatment of choice, as always, is recompression and
the breathing of enriched oxygen mixtures (P02 1.5 to
2.5 ATA). If recompression is not possible, treatment
using oxygen breathing and the administration of fluids
and drugs should be attempted under medical super-
vision. Recompression in the water should be used only
as a last resort. Decompression from saturation should
be delayed for at least 36 hours after a diver has been
treated for decompression sickness.
to maintain a proper balance among the indigenous
microflora. To maintain this balance, certain health
practices should be followed. Although different
underwater programs may require different practices,
depending on the habitat and local conditions, obser-
vance of the general procedures that follow will help to
maintain the health of saturation divers.
• Do not allow a person with a cold, ear infection,
severe skin problem, or contagious disease to go
into the habitat or to have contact with any diver
who is to go into the habitat.
• Do not allow any medicines into the habitat that
have not been approved by the responsible physician.
• Maintain the habitat's humidity and temperature
at proper levels.
• Ensure that divers wash thoroughly with soap and
fresh water after the last excursion of the day.
• Have the divers wash the inside of their wet suits
daily with soap and water.
• Treat divers' ears daily, in accordance with the
instructions in Section 3.2.1.1.
• Treat any cut, abrasion, etc., no matter how small.
• Have divers remove wet equipment before entering
the habitat's living quarters and store it away from
the living quarters.
• Ensure that any food that has fallen into crevices,
where it might decay, is cleaned up.
• Remove garbage from the habitat daily, because it
is both a health and a fire hazard.
• Change bed linens and towels in the habitat at
least twice a week.
• Prevent divers from staying in the water without
proper thermal protection, because body temperatures
can drop significantly even in tropical waters.
• When inside the habitat, ensure that divers wear
warm, clean, and dry clothing (including footwear).
• Wash the interior of the habitat thoroughly after
each mission with a solution of benzalkonium
chloride (Zephiran®) or other comparable disin-
fectant.
• Wash the habitat's sanitary facilities and sur-
rounding walls and floor thoroughly every day with
a suitable disinfectant solution.
16.4.3 General Health Practices
The health and welfare of aquanauts living in an
open, semi-closed, or closed environmental system are
of prime importance to maintaining high performance
in an underwater program. The micro-organisms that
are associated with habitat living may impair the per-
formance of divers to the point where the divers must
be removed from the program; it is therefore essential
16-12
16.44 Hazardous Materials
To avoid atmospheric contamination, fires, and diver
disability, equipment and materials that could be
hazardous must be excluded from the habitat. Such
hazardous materials fall into five general categories:
• Volatile materials, both liquids and solids;
• Flammables;
NOAA Diving Manual — October 1991
Saturation Diving
• Medications whose pharmacologic effects may be
altered by pressure;
• Objects that cannot withstand increased pressure;
and
• Ungrounded or otherwise hazardous electrical
equipment.
Before beginning a habitat mission, all personal diving
and scientific equipment should be submitted to the
operations director for review and logging. To avoid
difficulties, aquanauts should provide documentation
for any equipment or materials whose safety is likely to
be questioned. Table 16-3 presents a list of materials
that are hazardous in habitat operations. This list is
not exhaustive, and any doubtful materials should be
screened carefully by qualified personnel before being
allowed inside a habitat; factors such as mission dura-
tion and the habitat's scrubbing capability should be
taken into account during this process. If substances
that are necessary also have the potential to affect
divers in the habitat adversely, safe levels, control
methods, and monitoring procedures for the use of
these materials should be established. In addition, all
divers and topside staff should be made aware of the
signs and symptoms of any exposure-related effects
potentially associated with the use of these substances.
16.5 EXCURSION DIVING
Excursion diving from saturation in a habitat or
DDC/PTC system requires special preparation and
strict adherence to excursion diving tables. A diver
who is saturated at one atmosphere (i.e., at surface
pressure) can make dives (excursions) to depth and
return directly to the surface without decompression
as long as his or her body has not absorbed more gas
during the dive than it can safely tolerate at surface
pressure. Similarly, a diver who is saturated at a pressure
greater than one atmosphere (i.e., at the habitat's
pressure) can make excursions either to greater depths
(downward) or lesser depths (upward) by following the
depth/time limits of excursion tables. Many factors
change the conditions of excursions (e.g., temperature,
work load, equipment, the diver's experience); these
factors must be considered when planning any excursion
dive or decompression.
Specific procedures for both ascending and descending
excursions from air or nitrox saturation can be found in
Hamilton et al. (1988b), and the methods used to develop
these procedures have been published in Hamilton et
al. (1988a). Information on other procedures that have
been used in the past to conduct excursions from air or
nitrox saturation is available in earlier editions of the
NOAA Diving Manual and in Miller (1976).
October 1991 — NOAA Diving Manual
16.6 DECOMPRESSION AFTER AN AIR OR
NITROGEN-OXYGEN SATURATION DIVE
The operational procedures for decompression after a
saturation dive vary with different dive systems. In
systems located at depths of 50 fsw (15 m) or less,
the divers can swim to the surface, immediately enter
a recompression chamber, recompress to the saturation
depth, and begin decompression. This method is possible
if the interval the diver spends on the surface before
recompressing is less than 5 minutes and the storage
depth is less than 50 fsw (15 m) (Edel 1969, Weeks
1972, Walden and Rainnie 1971). Other systems are
designed to decompress divers in the habitat on the
bottom, after which the divers swim to the surface
(Wicklund et al. 1973). In other cases, the habitat can be
raised to the surface and towed to a base on the shore,
where decompression is completed and standby facilities
are available (Koblick et al. 1974).
For decompressions after saturation in deep diving
systems, divers usually are transferred to a surface
decompression chamber in a personnel transfer capsule
that is pressurized at the pressure of the storage depth.
Decompression is then accomplished in accordance
with standard procedures for that depth and the
saturation breathing medium. Specific procedures for
saturation decompression can be found in previous
editions of the NOAA Diving Manual and in Hamilton
etal. (1988b).
16.6.1 Diving After Decompression From
Saturation Exposure
Divers who have completed a saturation decompression
may be resaturated immediately. However, if a diver
wishes to make non-saturation dives soon after com-
pletion of a saturation decompression, he or she must
wait 240 minutes before qualifying in repetitive Group Z
of the Residual Nitrogen Timetable for Repetitive
Air Dives (see Appendix B). The Residual Nitrogen
Timetable for Repetitive Air Dives should then be
followed as directed, with the diver moving to suc-
cessively lower repetitive groups after the intervals
specified in the tables. Any dives undertaken within
36 hours after an air or nitrox saturation dive should
be limited to a depth of 50 fsw (15 m) or shallower
for a maximum exposure of 1 hour.
Example:
Time
0800 A diver surfaces from a completed saturation
decompression; however, more coral specimens
16-13
Section 16
Table 16-3
Hazardous Materials
for Habitat Operations
Flammables
(Volatile)
Explosion/
Implosion
Hazards
Volatile
Poisons
Metals,
Metalloids
And 1 "heir
Salts
Mood-Altering
Drugs
Miscellaneous
Materials
Acetones
Pressurized
aerosol cans
Mercury
Mercury
Ethanol
Tobacco smoking materials of
any kind
Gasoline
Flares of any kind
or ignitables
Ammonia
Fluorides
Marijuana
Matches or lighters
Ethers
Signaling devices
Chlorine
Selenium
Sedatives
Newly made (un-aired) vinyl or
styrofoam materials (their
solvents, vinyl chloride and
isocyanate, respectively, are
very toxic)
Naphtha
Sulfur dioxide
Hallucinogens
Cosmetics or perfumed
materials (deodorants)
Alcohols
Hydrogen sulfide
Halogenated
hydrocarbons
Aromatic
hydrocarbons
Formalin
Tranquilizers
Ataractics
Hypnotics
Anti-depressants
Stimulants
Concentrated acids or bases
Adhesives, including
wet suit cement
i
Derived from NO A A (1979)
located at 50 fsw (15 m) are needed. How long
must the diver wait before he or she may go to
50 fsw (15 m) for 30 minutes without incurring
a decompression obligation?
,200 After waiting 240 minutes, the diver is in
repetitive Group Z. The Residual Nitrogen Time-
table for Repetitive Air Dives specifies that
2 hours and 18 minutes must be spent at the sur-
face for the tissues to have released sufficient
nitrogen to permit a 34-minute dive to 50 fsw
1418
(15 m) (which will place the diver in repetitive
Group H).
The diver dives to 50 fsw (15 m) for 30 minutes
and surfaces without decompressing.
(
16.6.2 Flying After a Saturation Decompression
After a saturation decompression, divers should wait
for at least 48 hours before flying. Observance of this
rule greatly reduces the likelihood that such divers will
experience decompression sickness.
(
16-14
NOAA Diving Manual — October 1991
SECTION 17
UNDERWATER
SUPPORT
PLATFORMS
17.0
17.1
17.2
17.3
17.4
17.5
17.6
17.7
17.8
Page
General 17-1
Pressurized Diving Bell Systems 17-1
Open Bell Systems 17-1
17.2.1 Description 17-1
17.2.2 Operational Parameters 17-2
17.2.3 Operational Procedures 17-3
Diver- Lockout Submersibles 17-3
Free-Flooded Submersibles 17-5
Underwater Habitats 17-6
17.5.1 Saturation Diving Habitats 17-10
17.5.2 Non-Saturation Habitats 17-17
Diver Propulsion Vehicles 17-18
Atmospheric Diving Systems 17-18
Remotely Operated Vehicles 17-20
(
UNDERWATER
SUPPORT
PLATFORMS
17.0 GENERAL
During the last two decades, new technology and a
better understanding of the physiology of diving have
made saturation diving available as a method of
accomplishing extensive work under water. With the
development of this new method of diving, underwater
support platforms have become common in commer-
cial diving and are becoming increasingly valuable in
scientific studies and underwater archaeology. Underwa-
ter support platforms include manned habitats, work
shelters, diving bells, lockout submersibles, flooded
submersibles, remotely operated vehicles, and one-
atmosphere diving systems.
17.1 PRESSURIZED DIVING
BELL SYSTEMS
Although most underwater habitats are fixed on the
seabed and cannot be transported with divers inside,
semi-mobile underwater support platforms, which are
known as diving bells, have proven their worth in sev-
eral types of undersea tasks. A diving bell usually is
only one part of an integrated system (Figure 17-1)
designed to provide divers with a dry, safe living envi-
ronment that can be maintained for long periods at or
near the pressure prevailing at the dive site itself. A
diving bell functions as a dry, pressurized, and some-
times heated elevator to transport divers between sur-
face living quarters and underwater work sites. While
the divers are on the bottom, the nearby diving bell
functions as a tool storehouse and ready refuge. Most
diving bells are capable of carrying and supporting 2 to
4 working divers.
On board the support ship or barge are the deck
decompression chamber(s), control van, and other
supporting machinery, such as electric generators,
hydraulic power systems, and hot water generators.
Normal living operations and decompression are car-
ried out in the deck decompression chamber.
When beginning a job, divers enter the bell and are
lowered to the work site. After reaching the required
depth, the divers equalize the bell pressure with the
outside seawater pressure, open the lower hatch, and
exit to start work. If necessary, the bell can be moved
closer to the job site by maneuvering the ship. Upon
completion of the task, the divers re-enter the bell and
October 1991 — NOAA Diving Manual
are raised to the surface, where the bell is mated to the
deck decompression chamber. In the deck decompres-
sion chamber, the divers remain at depth and prepare
for their next trip to the work site. With one or more
teams, this cycle can continue for days or weeks if
necessary. Decompression is carried out after comple-
tion of the mission. Bell diving systems offer advan-
tages over a fixed habitat if a large bottom area is to be
covered or if heavy tools and substantial surface sup-
port are required. Under saturated conditions, one or
more teams of divers can live in relative comfort in the
deck chamber. Hot meals can be passed in, and surface
personnel can maintain direct contact with the divers.
Commercial bell diving systems are designed to
be operated between 200 and 1500 fsw (61 and
457.3 msw).
Today, most work done from diving bells is in sup-
port of the offshore oil industry. Additionally, the var-
ious navies of the world use bell diving systems for
salvage, search and recovery, and instrument implanta-
tion.
17.2 OPEN BELL SYSTEMS
17.2.1 Description
The open bottom bell, referred to as a Class II or
non-pressurized bell, was developed as an in-water
work platform and emergency way station. Unlike a
diving stage, which serves only as an elevator between
the surface and the work site, the open bottom bell
provides a semi-dry refuge, emergency breathing gases,
and communications capability.
The bell consists of a rigid frame with an open grat-
ing on which the diver stands and an acrylic hemispheric
dome that is open on the bottom. By adding suitable
breathing gases to the inside of the dome, water is
forced out, creating a dry gas bubble for the diver's
head and shoulders. The acrylic dome is transparent,
which affords the divers a full field of vision. Ballast is
added to the bottom of the bell to make it negatively
buoyant in the water (Figure 17-2).
Emergency breathing gases are supplied to the bell
from two separate sources: one from a topside umbili-
cal and another from high-pressure gas cylinders
mounted on the outside of the bell. Both gases are
routed to a manifold inside the dome and used for
17-1
Section 17
Figure 17-1
Saturation Diving Complex
Courtesy Saturation Systems
dewatering the bell dome and emergency breathing via
built-in-breathing (BIB) masks or scuba regulators.
A speaker mounted in the dome allows two-way voice
communication with topside personnel.
The bell is raised and lowered by a wire cable from a
crane, davit, or A-frame on the support vessel. A life
support umbilical consists of a hardwire communica-
tion cable, gas supply hose routed from a surface con-
trol manifold, pneumofathometer hose providing con-
tinuous depth readouts at the surface, a strength member
in case the primary lift cable breaks, and additional
specialty components as required (Figure 17-3).
17.2.2 Operational Parameters
Although typically used in support of surface-supplied
diving, the open bell may be used in conjunction with
many types of diving operations. When supporting
surface-supplied diving operations, the diver's umbil-
17-2
ical is routed from the surface rather than from the
bell. Most open bells can support two divers in normal
operations and three divers in an emergency; however,
they are often designed and built for specific purposes
in various sizes and weights. Safe operation of an open
bell requires a stable support platform capable of holding
its position in a variety of sea conditions.
OSHA and United States Coast Guard (USCG) regu-
lations require the use of an open bell on all dives
deeper than 200 fsw (61 msw) or those involving more
than 120 minutes of in-water decompression, except
when a heavy-weight diving outfit (full helmet with a
constant-volume dry suit) is used or when dives are
being performed in a physically confining space. These
regulations also allow open bell use to a depth of
300 fsw (91 msw) in helium-oxygen diving operations;
in actual practice, however, the use of open bells is
usually restricted to 225-250 fsw (70-75 msw) because
of limited emergency support capabilities. Longer and
NOAA Diving Manual — October 1991
Underwater Support Platforms
Figure 17-2
Open Diving Bell on Deck of Seahawk
Courtesy NURC-UNCW
deeper dives are more safely performed using a closed
and pressurized diving bell.
17.2.3 Operational Procedures
Operation of an open bell requires completion of a
rigorous predive checklist of all major support sys-
tems, including the bell-handling, life-support, and
communications systems. Positive control of the bell is
essential during deployment and retrieval and requires
the use of control lines (Figure 17-4). The bell is
lowered into the water, shackled into a separate downline
to prevent the bell from turning during ascent and
descent, and all control lines are removed. Divers enter
the water, secure themselves on the outside of the bell,
and prepare to descend. Riding the bell in this position
rather than being transported inside the bell prevents
the divers from being trapped inside if the lift cable
breaks.
During ascent and descent, the bell and diver's depth
and rate of travel are monitored and controlled by
October 1991 — NOAA Diving Manual
topside personnel via a control panel. Compressed gases
are added to the bell dome during ascent to exclude
water. Descent is stopped when the bell is 10-15 feet
(3-4.5 meters) from the bottom, and the bell remains
suspended in the water column while the divers are on
the bottom. Whenever they leave the bell, the divers
vent the dome to reduce the buildup of carbon dioxide,
because an emergency return to the bell may require
the divers to breathe the gas inside the dome while they
don their emergency breathing equipment. The divers
pass their umbilicals through the legs of the bell to
help them to relocate the bell at the conclusion of the
dive.
During ascent, the bell is raised at the appropriate
rate of speed and is stopped at predetermined depths in
accordance with the appropriate decompression schedule.
After the last in-water decompression stop, the bell is
brought to the surface, the divers climb aboard the
support platform, and any further decompression is
completed on board.
Retrieval of the bell reverses the steps in the deploy-
ment procedure, except that a surface swimmer must
enter the water to attach the control lines and unshackle
the bell from its downline. The bell is lifted aboard and
secured to the deck. All systems are rechecked for
proper operation, gas supplies are inventoried, gas banks
are charged, and maintenance is performed in prepa-
ration for the next dive (Figure 17-5).
17.3 DIVER-LOCKOUT SUBMERSIBLES
Most research submersibles have one or two compart-
ments designed to maintain the crew at a pressure of
one atmosphere. All allow direct observation through
viewing ports or acrylic spheres. Many research sub-
mersibles have manipulators that permit the occupants to
collect samples and place equipment on the seafloor.
Others have lockout capabilities that permit divers to
leave the submersible. Lockout submersibles have a
separate chamber that can be pressurized to ambient
pressure so that the divers may enter and exit while the
pilot and other personnel remain at atmospheric pres-
sure within the submersible (Figure 1 7-6). When locking
out, the diver is usually tethered to the submersible by
an umbilical that provides hardwire communication to
the submersible and a gas supply that can be either a
primary or backup breathing source. With lockout capa-
bility, scientists have the choice of directing collec-
tions from the observation compartment or locking out
from the dive chamber and collecting the samples. A
diver-lockout submersible also affords great mobility,
reduces unnecessary in-water time for the divers, al-
lows decompression to be initiated soon after the di-
17-3
Section 17
Figure 17-3
Bell System
ri ?t I /A compressor
""Lru G____Dair rec
Y MANIFOLD
|PremixhX] I I <j I jj ' * I'l frCXH.^
Manifold (OBB)
1 1 Premix
AIR SUPPLY TO MANIFOLD
!±J
COMMUNICATIONS
SYSTEM
f-\ OOO
q oo o oo
OPEN BOTTOM
BELL
WATER
LINE
17-4
Courtesy David A. Dinsmore
NOAA Diving Manual — October 1991
Underwater Support Platforms
Figure 17-4
Open Bell Showing Control Lines
Courtesy NURC-UNCW
ver returns to the vehicle, and permits the divers to
be transported from site to site under pressure. Gener-
ally, decompression is managed and controlled by a
dive controller positioned in the one-atmosphere com-
partment of the submersible. Some lockout submersi-
bles can be mated to deck decompression chambers.
This allows the diving team to saturate in the chamber
on deck and to be transported to the work site via the
submersible. Also, in the case of deep, long exposures,
most of the decompression can be carried out in a
larger, more comfortable environment.
The value of the lockout submersible to the scientist
lies in its high maneuverability in three planes, its
mobility, and its ability to provide shelter for long
periods at depth. Lockout submersibles can cruise at
atmospheric pressure until they arrive at the dive site.
The pilot can station the submersible so that the work
site is directly in front of the pilot compartment before
locking the diver out. During the lockout, both the
pilot and dive controller can observe the activities of
the diver. If there is a need to investigate an area where
the depth prohibits diver lockout, the lockout submersible
can serve as an observation vehicle. Remotely oper-
ated collection tools, manipulators, and cameras can
be used to enhance observation in this mode.
Although diver/scientists normally do not pilot the
submersible themselves, they must be familiar with its
October 1991 — NOAA Diving Manual
capabilities and operating procedures. A detailed ori-
entation schedule must be developed prior to any oper-
ation, and training must include at least one shallow-
water excursion so that the diver/scientist can learn to
operate all high- and low-pressure systems and become
familiar with decompression and emergency procedures.
Lockout submersibles always have space in the diving
chamber for at least two divers. A general practice is to
pair a member of the submersible's crew with a scien-
tist so that a well-trained crew member can act as a
tender when the scientist is in the water. Using the
submersible in this manner allows a scientist with a
good diving background but little or no previous lock-
out experience to use the facility to best advantage,
without actually becoming a full member of the sub-
mersible's crew. The scientist performing work in the
water is in most cases monitored visually and via voice
communication by the submersible pilot or dive con-
troller. In-situ ecological observations can be made
concurrently with the lockout dive, using external still
or movie cameras and videotape systems.
17.4 FREE-FLOODED SUBMERSIBLES
Although conventional one-atmosphere and diver-lockout
submersibles require a pressure-resistant hull, a free-
flooded submersible (wet sub) can be thought of as an
underwater convertible. When in use, these vehicles
are full of water and the divers breathe by using scuba
equipment. This equipment can be open-circuit, semi-
closed, or closed-circuit and may be worn on the back
or mounted in the vehicle, depending on the nature of
the mission and the design of the submersible.
There are several configurations of wet subs. In some,
as many as four divers sit one behind the other, while
others are designed to have divers side by side, either
sitting or in the prone position. These vehicles are used
primarily for transporting divers at speeds of up to
4 knots (2 m/s) to conserve time and air and to assist
diver/scientists in conducting ocean floor surveys. They
also can be used as small underwater pickup vehicles.
Wet subs are excellent vehicles for all kinds of survey
work because they can cover large areas carrying still
and television cameras as well as divers. However, most
wet subs require extensive maintenance.
In planning for operations involving wet subs, cer-
tain factors must be considered:
• Training in general operating procedures, especially
in obstacle avoidance, is essential.
• When making long excursions with a wet sub under
normal diving conditions, a buoy should be used to
permit easy tracking by a surface support boat.
17-5
Section 17
Figure 17-5
Open Bell Emergency Flow-Chart
i
Diver Loses
Primary Gas
Supply
Diver Loses
Communication
Diver Uses Bailout;
Returns to Bell
Notes: #1 Gas supplied to diver from secondary supply through diver umbilical.
#2 Gas supplied to bell from topside source through bell umbilical.
#3 Diver may breathe gas trapped in bell dome or BIB masks.
#4 Standby diver may transport additional gas to diver if necessary.
#5 Standby diver may be deployed to assist if necessary.
Activate Gas
Supply From
Topside Source
(See Note #2)
Establish
Communication
With Topside
Activate
Onboard Gas
Supply
Breathe Gas
Supply From
Bell
(See Note #3)
Terminate
Dive
Remain on
Bailout Supply
(See Note #4)
L
Continue Using
Line-Pull
Signals
(See Note #5)
Terminate J^^»
Dive * ^*
7-
Courtesy David A. Dinsmore
Because a diver can be lulled easily into a false
sense of security, bottom time and depth must be
monitored carefully.
A good compass mounted on the sub is essential
for navigation.
Wet sub divers will get cold faster because they
are essentially motionless in the water and thus
generate little body heat.
Wet sub use under saturated conditions requires
careful consideration of current velocity, direction,
and reserve air supply to ensure that a diver could
swim back to the habitat should the sub's propulsion
system fail.
17-6
WARNING
When Using Either a Wet Sub or Swimmer
Propulsion Unit Under Saturated Conditions,
Precautions Must Be Taken To Avoid Acci-
dental Ascent
17.5 UNDERWATER HABITATS
Early underwater habitats were designed primarily to
evaluate engineering feasibility or to demonstrate human
capability to survive in the undersea environment. They
NOAA Diving Manual — October 1991
Underwater Support Platforms
Figure 17-6
Cutaway Showing Mating Position
With Deck Decompression Chamber
Forward Sphere
• Hatch Cover
Diver Compartment
Lock-In Hatch (Open)
Helium Sphere
Horrz Thruster
I>
Lights
Vert. Thruster
Horiz. Thruster
Manipulator
Deck Decompression Chamber
Medical Lock v Main Lock •— Entrance Lock
Hatch
INBOARD PROFILE
Johnson-Sea— Link I & II Submersible & Ship Decompression Chamber
Scale In Feet
Source: NOAA (1979)
were not designed to accommodate the average scien-
tific diver, nor could they be emplaced or moved easily.
Since 1962, over 65 habitats have been utilized in 17
countries throughout the world (Figure 17-7) (Miller
and Koblick 1984). They have been used for observa-
tion stations, seafloor laboratories, and as operational
bases for working divers.
Underwater habitats provide diving scientists with
unlimited access to defined areas of the marine envi-
ronment, enabling them to make observations and to
conduct experiments over long periods of time in the
saturation mode. Because habitats are open to ambient
pressure, the blood and tissues of the aquanauts become
saturated with the gas they are breathing, and decom-
pression is required only at the end of a mission.
Habitats come in many shapes and sizes; the degree
of comfort of these underwater quarters varies from
spartan to luxurious. Habitats have consisted of an
arrangement as simple as a rubberized tent with a
single cot; in contrast, some have been four-room apart-
ments. A University of New Hampshire survey (1972)
describes those features of an underwater habitat that
users consider desirable (Table 17-1).
When designing and selecting habitats for marine
science programs, technical, logistic, and habitability
criteria must be applied if systems are to facilitate
mission objectives. Important considerations include
simplicity, functionality, and comfort. An aquanaut-
scientist who is constantly wet, cold, crowded, and
miserable for days at a time cannot be expected to
October 1991 — NOAA Diving Manual
17-7
Section 17
Figure 17-7
Undersea Habitat Specifications and Operational
Data
(
Depth
Name Country Date Location (m) Crew
Duration
Size
Weight
Habitat
Surface
(Days)
(m)
(Tons)
Cas
Support
Mobility
pression
(Hours)
Remarks
Adelaide Australia 1967-
1968
,QiQ»n_, Aegir
U.S.A.
1969-
1971
Hawaii
24-157
4-6
14
2cyl.,
2.7 • 4.6
plus 3m
sphere
Italy
1971
Lake
Garda
50
Italy
1969
Lake
Cavazzo
12
4
L = 7
W=2
BAH-I
Federal 1968- Baltic
Republic 1969
of Germany
10
^r3
Balanus USSR
Bentos-300 USSR 1966 Sevastopol 300
1968 lapanese
Sea
Bubble U.K. 1966
Caribe-I Cuba-Czech 1966
1969-
1974
Aui
LDT-nnrr
Chernomor-I USSR
Chernomor-ll USSR
Conshelf-I France
Diogenes
Conshelf-I I France
Starfish
House
Conshelf-I I France
Deep Cabin
Conshelf-I 1 1 France
Malta 10 2-3
Rincon de 20 2
Guanabo
near
Havana
Black Sea 5-14 4-5
Black Sea 5-31 4-5
Marseilles, 10
Mediterra-
nean Sea
11
Edalhab
Ere bos
Czech
Galathee France
1968
1972
1967-
1968
1977
Shaab
Rumi
Reef,
Red Sea
Shaab 27.4
Rumi
Reef,
Red Sea
Mediterra- 100
nean Sea
Alton's 12.2
Bay, N.H.; 13.7
Miami,
Fla.
Olsany
11.5
Approx.
18
Ceonur Poland 1975-
1976
Gdynia 50
Glaucus U.K.
1965 Plymouth 10.7
/ 0~
Hebros-I Bulgaria 1967
(Khebros)
Hebros-ll Bulgaria 1968
Helgoland-I Federal 1969
Republic
of Germany
Helgoland-I I Federal 1971
Republic 1977
of Germany
Lake 7
Varna
North Sea 23 2-4
North Sea 22-31 4
Baltic,
USA
14-52
L = 6
D = 2
H = 5.5
D=1.2
L = 21
W = 5.5
H = 11 2
D = 2.1
Sphere
L = 3.5
D = 1.5
L=7.9
D = 29
L = 8
D = 3
L = 5.2
D = 2.4
104
4 legs
1.2-24
22 D = 5.5
sphere
3-5 L = 3.6
D=2.4
L=2.7
W=1 3
H = 1.8
L = 7
W = 66
H = 48
H = 76
W = 4.2
W = 2.1
L = 3.6
L = 5.5
D = 2.0
W = 2.5
L = 6.7
L = 9.0
D = 6.0
L=13.8
W = 60
44
Displ.
Each
20
6
Bal
62
Displ
74
Displ
100
Bal
15
Bal
Ship raft
N2/02 Ship
He/O,
Air
He/O,,
Air Shore
N2/02 Ship
Shore
Air
He/O,
Air
N,/0,
Ship
buoy
Shore
Ship
Ship
Ship
Ship
Shore
Ship
50% He Ship
50% Air
2.5% 02 Ship
97.5% He
Air Shore
ship
Shore
Air Ship
Towable
Readily
movable
Self-
propelled
Readily
movable
Readily
movable
Towable
Towable
Readily
movable
Readily
movable
Towable
Towable
Readily
movable
Readily
movable
From pontoons
Can ascend and
descend by internal
control
Diver training,
instrument testing
3 separate habitats
Primary compressor
located on seafloor
Observation
chamber
Only self-
propelled habitat
0 Decompression
experiments
First Eastern Bloc
habitat
Modified
Chernomor-I
(
3.5 from
27.4 m to
11 m
84 Mounted on
8 5 • 14.6 m barge
Deployed in quarry
Ship
Towable
For geology
Air
Shore
Readily
movable
3.0-
3.5
Decompression
experiments
Air
Shore
Shore
Towable
Made from a
locomotive boiler
Not known if usee
N/02
Buoy
Readily
movable
Varied
N/02
Buoy
Towable
Varied
Modified
Helgoland-I
(
17-8
NOAA Diving Manual — October 1991
Underwater Support Platforms
Figure 17-7
(Continued)
Decom-
Depth
Duration
Size
Weight
Habitat
Surface
pression
Name
Country
Date
Location
(m)
Crew
(Days)
(m)
(Tons)
Gas
Support
Mobility
(Hours)
Remarks
H
G
HUNUC South 1972
Africa
Durban
N/A
Hydrolab
U S A
66-70
70-74
75-84
Florida
Bahamas
Virgin
Islands
12-1
Ikhtiandr
USSR
1966
Crimean
Coast
Black Sea
12
Ikhtiandr
USSR
1967
Crimean
Coast
Black Sea
12.2
Ikhtiandr
USSR
19b8
Crimean
Coast
Black Sea
10
Karnola
Czech
19fa8
8
15
Kitjesch
USSR
1965
Crimean
15
(Kitezh)
Coast
Klobouk
Czech
1965
Koza-
6
(Hat)
rovice
Kockelbockel
Nether
ands 1967
Sloterplas
15
LaChalupa U.S.A. 1971-
1974
Lakelab USA. 1972
LORA Canada 1973-
1975
LS-I Rumania 1967
Malter-I German 1968-
Democratic 1983
Republic
Man-m-Sea I USA 1962
Meduza-I Poland 1967
Meduza-ll Poland
Mmitat USA 1970
Nentica Federal 1977
Republic
of Germany/
Israel
Permon-ll/lll Czech 1966
1967
Portalab U SA. 1972
Robinsub-I Italy
Sadko-I
Puerto 15-30 4-5
Rico
Grand 15 2 2
Traverse
Bay.
Michigan
New- 7.9 2
foundland
Lake 12-14 3-4
Bicaz
Malter 8 2-4
Dam
Mediterra- 61
nean
Lake 24
Klodno
Gdansk, 26
Baltic Sea
Virgin
Islands
Eilat.
Red Sea
Sadko-I I
USSR
runtanya 10
Rhode 11 3
Island
Ustica
Island
Black Sea. 12
Sukumi
Bav
Black Sea. 25
Sukumi
Bay
3-7
Daily
visits
Short
period
6hrs/
team
L = 5.9
W = 1 5
L = 4.9 40
W=2.4
L = 2.i
W=1.6
H = 2.0
3 cubes
L=8.6
H = 7.0
L = 20
W = 20
L = 2 4
W = 1 8
H = 2 1
D = 3
sphere
10
Bal
L = 63 25
W = 2.2
L=1.2
H = 1 0
D = 1 9 9.5 +
H = 4b
2cyl. 150
2.4>6.0
1 rm (6
D = 3.0 24
H = 2 1 Bal
L = 2.4
24
D = 4 9
Bal
L=7.2
20
D = 24
Bal
L=4.2
14
D = 2.0
L = 3 2 2.1 incl
D = 09 Bal
L = 2 2 3.0
W = 1 8
H = 2.1
L = 36
W = 2 .2
H=1 8
H= 1.4
D=24
L=3 4
W=2.0
13 5
displ.
7.2
Bal
L=2 5 7 5
VV = 1 5 Displ
H = 20
13.5
D=i 28.5
2 spheres Bal
Air
Air
3% 02
97% He
37% 02
63% N2
Air
Shore
Buoy
Air Shore
Air Shore
Air Shore
Shore
Auton-
omous
Nj/Oj Buoy
Air Shore
Air Shore
Ship
Shore
Ship
Shore
Ship
N. O, Ship
Air Shore
N, O, Shore
Air Shore
Air Shore
Air Ship
shore
N^O; Ship
shore
Movable
Sank during
emplacement —
never occupied
Towable 1 3-20 Most utilized
habitat in the
world
Readily
movable
Readily
2 female
movable
aquanauts
Readily
towable
Readily
movable
Readily
movable
Readily
movable
Readily
movable
Readily
movable
Fixed
Readily-
movable
Readily
movable
Readily
movable
Readily
movable
Readily
movable
Towable
Readily
movable
Readily
movable
Readily
movable
Readily
movable
Readily
movable
Readily
movable
Made from a
converted railroad
tankcar
Farthest operation
from shore
N/A
0
Under ice
48
Still used for
observation
Under ice
35.5
World's first open
sea saturation
53.5
Entire habitat
raised tor
decompression
22
Excursions to
50m
N/A Never operational
Wire fage
plastic tent
Stationed in
midwater
70 Stationed in
midwater
October 1991 — NOAA Diving Manual
17-9
Section 17
Figure 17-7
(Continued)
Namv
Country
Date
Location
Depth
(m)
Crew
Duration
(Days)
Size
(m)
Weight
(Tons)
Habitat
Gas
Surface
Support
Mobility
Decom-
press/on
(Hours)
Remarks
f
Sadko-lll
USSR
1969
Black Sea,
Sukumi
Bay
25
3'
14
D = 3.0
H = 15.0
30
Bal.
He/N2/
Ship
Readily
movable
Stationed in
midwater
SD-M
UK
1969
Malta
6-9
2
1-7
L = 29
W = 1.8
H = 1.8
Air
Auton-
omous
Rubber tent with
steel frame
. JT"3t il-JL
Sealab-I
USA
(Navy)
1964
Argus
Island
Bermuda
58.8
4
11
L = 122
D = 2.7
H=4.5
20
Bal.
4%02
17%N2
79% He
Ship
Movable
56
%f>
Sealah-ll
USA
(Navy)
1965
La lolla,
California
62.5
10
15-30
L=17 5
D = 36
H = 3.6
200
4% O
25% N2
71% He
Ship
Movable
30
lePU-XMl
Sealab-I 1 1
U.S.A.
(Navy)
1969
San
Clemente,
California
1829
5-12
N/A
L = 17.5
D = 36
H = 36
2% O;
6% N2
92% He
Ship
Movable
N/A
Death of aquanaut
I ooi"^ooi
caused
cancellation
ti±M
Seatopia
Japan
1968-
1973
Yokosuka
30
4
2
L = 10.5
W = 2.3
H = 6.5
65
4.8% 02
16.0% N2
79.2% He
Ship
Movable
66
Only used for one
open-sea mission
ft
Selena-I
Shelf-I
USSR
Bulgaria
1972
1970
Beloye
Lake
Burgas
Culf
11.5
20
1
3
15 hrs.
4-5
D = 2.0
H = 3.0
L = 6.0
D = 2.5
5
30
Air
Air
Ship
Readily
movable
Readily
movable
33.5
Semipermeable
membrane
u . J
u »
ftp
SPID
(Man-in-Sea
M)
US. A.
1964
1974
Bahamas
Canadian
Arctic
131.7
4.3
2
1
L = 2.4
W = 1.2
3.6% 02
5.6% N2
90.8% He
Ship
shore
Readily
movable
92
0
Inflatable
habitat
^
DCQ
Sprut
(Octopus)
USSR
1966
Black Sea
10.5
3
14
D^5.0
sphere
Air
Shore
Readily
movable
Inflatable
habitat
Sprut-M
USSR
1968
Black Sea
14
2
D = 2.4
Air
Shore
Readily
movable
Inflatable
habitat
Sprut-U
USSR
1969-
1970
Black Sea
12-34
1-4
Air
Shore
Readily
movable
Inflatable
habitat
y^\.
Sub-Igloo
Canada
1972-
1975
Cornwallis
Island
12.2
2-4
1
D = 2.5
sphere
8
Bal
Air
Shore
Readily
movable
0
Under ice
A
Sublimnos
Canada
1969-
Georgian
Bay.
Ontario
10.1
2-4
Up to
24 hrs.
H = 2.7
D = 24
9
Air
Ship
shore
Readily
movable
Designed for day-
long occupation
Suny-lab
Tektite l-ll
USA
USA.
1976-
1969-
1970
New York
US
Virgin
Islands
12.2
13 1
2-3
4-5
1
6-59
1.5
D = 3.8
H = 5.5
6
79
Air
92% N2
8%02
Ship
Ship
shore
Readily
movable
Fixed
19.5
Made from cement
mixer
World's longest
open-sea
saturation
Xenie
Czech
1967
Adriatic
6
1
3
L = 3.3
H=1.0
W = 1.0
0.13
Air
Shore
Readily
movable
Note Bal = ballast, displ = displacement
From Miller and Koblick (1984) , with permission
from Jones and Bartlett Publishers
perform efficiently or to produce scientific results of
high quality. For a description of specific scientific
projects accomplished to date using underwater habi-
tats, consult Pauli and Cole (1970), Miller et al. (1971),
Miller et al. (1976), Wicklund et al. (1972, 1973, 1975),
Beaumariage (1976), or Miller and Koblick (1984).
17.5.1 Saturation Diving Habitats
More than 65 underwater habitats have been con-
structed throughout the world since 1962. Their level
of sophistication ranges from the simple shelters
described in Section 17.5.2 to large systems designed
for extended seafloor habitation. The habitats used
most extensively were Chernomor (Soviet Union),
Helgoland (West Germany), and Tektite, Hydrolab,
and La Chalupa (USA). The habitats described in this
section were selected because they represent a cross-
section of those built to date, and the programs in
which they were utilized include most U.S. marine
scientific saturation programs. Saturation diving hab-
itats differ from work shelters in that they allow divers
to stay on the seafloor long enough to become satu-
rated (see Section 16.1). Decompression may be ac-
complished either inside the habitat or in a surface
decompression chamber after an ascent made with or
without a diving bell.
Edalhab (Figure 17-8) was designed and built by
students from the University of New Hampshire as an
17-10
NOAA Diving Manual — October 1991
Underwater Support Platforms
Table 17-1
Desirable Features of Underwater Habitats
Overall Size About 8 Feet x 38 Feet
(2.4 Meters x 11.6 Meters)
Separate Wet Room:
Large entry trunk
Wet suit rack
Hot shower
Hookah and built-in-
breathing system
Scuba charging
Wet lab bench
Specimen freezer
Clothes dryer
Diving equipment storage
Rebreathers
Living Room:
Bunks
Microwave
Food freezer and refrigerator
Water heater
Toilet
Individual desk and storage
Dry lab bench
Compactor
Library
Tapes, TV, radio
Emergency breathing system
Computer terminal
GENERAL:
Hemispheric windows
Temperature and humidity
control
Separate double chambers
On-bottom and surface
decompression capability
Suitable entry height off
bottom
Submersible decompression
chamber for
emergency escape
External survival shelter
External lights at trunk and
viewports
External cylinder storage and
charging
Habitat-to-diver
communication
Diver-to-diver
communication
Adjustable legs
Mobility
External or protected internal
chemical hood
Adapted from NO A A (1979)
engineering project. The habitat was constructed mainly
of salvaged and donated materials. The living quarters
were enclosed in an 8 x 12 foot (2.4 x 3.7 meter)
cylinder with a small viewing port at each end. The
interior was insulated with 1.5 inch (3.8 centimeter)
thick unicellular foam. Entry was made through a
hatch centrally located in the floor. The interior had
two permanent bunks (which folded to form a large
seat) and a collapsible canvas cot. Communications,
air, and power were provided from the support ship to
the habitat through umbilicals. Decompression was
accomplished by having the divers swim to the surface
and immediately enter a deck decompression cham-
ber. Edalhab had no specific facilities for scientific
investigation, required a manned support ship, and
was not easily moved from site to site.
Hydrolab (Figure 17-9) was designed to be simple
and inexpensive to operate. The main structure was an
8x16 foot (2.4 x 4.9 meter) cylinder supported on four
short legs and positioned 3 feet (0.9 meter) above a
concrete base. It was submerged by venting and flooding
ballast tanks and could be towed short distances for
relocation in depths up to 100 feet (30.5 meters). Entry
into the habitat took place through a hatch at one end
that also functioned as a lock when the chamber pres-
sure was below ambient pressure. The single room was
furnished with three bunks, folding chairs, a dehumid-
ifier, an air conditioner, a sink, and a table surface.
A self-contained, unmanned, 23 foot long (7 meter)
life-support barge floated at the surface above the
habitat and supplied, via an umbilical, all life support,
including electrical power, high- and low-pressure
air, and water. A small stand-up shelter was provided
nearby for emergencies and to serve as an air filling
station. More than 700 scientist-aquanauts have lived
in Hydrolab since 1972. After almost 20 years of serv-
ice, Hydrolab was decommissioned by NOAA in 1985,
and the habitat is now on view in the Smithsonian's
Museum of Natural History.
Tektite (Figure 17-10) was a four-person habitat
consisting of two hulls attached to a base and con-
nected by a cross-over tunnel. The two cylinders were
each divided into two compartments, containing the
control center, living quarters, equipment room, and
wet room. The control center also served as a dry
laboratory for scientists. The living quarters contained
four bunks, a small galley, and storage and entertain-
ment facilities. The equipment room contained the
environmental control system, frozen food, and toilet
facilities.
Air, water, electrical power, and communications
were provided from the shore by means of umbilicals.
The wet room was intended for scientific work; howev-
er, participants had difficulty entering with specimens
in hand and found that most of the work space had been
taken up with diving equipment and carbon dioxide
absorbent. The dry lab in the control compartment
served as an instrument room.
One or more hemispherical windows in each com-
partment and a cupola on the top of one cylinder allowed
scientists to view the midwater and bottom areas adja-
cent to the habitat. Decompression was accomplished
by having the divers enter a personnel transfer capsule
on the bottom, raising them to the surface, and locking
them into a deck decompression chamber.
La Chalupa (Figure 17-11) was a four-person habi-
tat built as an underwater marine laboratory. Instead
of a typical entrance tube, there was a 5 x 10 foot (1.5 x
3.0 meter) door in the wet room floor that allowed
divers to enter and exit easily.
Large stainless-steel tables were provided in the wet
room for sorting specimens; additional instrumenta-
tion space was provided next to a 42 inch (107 centi-
meter) window where scientific equipment could be
used. The laboratory had a computer for data analysis.
A special waterproof connector in the wet room
October 1991 — NOAA Diving Manual
17-11
Section 17
Figure 17-8
Edalhab
17-12
Source: NOAA (1979)
NOAA Diving Manual — October 1991
Underwater Support Platforms
Figure 17-9
Hydrolab
*
October 1991— NOA A Diving Manual
Photo Dick Clarke
17-13
Section 17
Figure 17-10
Tektite
Courtesy General Electric Company
allowed instruments outside the habitat to have readouts
for current, salinity, and water temperature in the
control room. The habitat structure consisted of two
8 x 20 foot (2.4 x 6.1 meter) chambers within a barge;
between the chambers was the 10 x 20 foot (3.0 x 6.1 meter)
wet room.
La Chalupa was used at depths of 40 to 100 feet
(12.1 x 30.5 meters) and could be moved easily from
one location to another and emplaced in about 1 hour.
Surface support was provided by a self-contained
unmanned utility buoy that supplied power, water,
high- and low-pressure gas, and communications. A
pair of two-man submersible decompression chambers
was attached to the habitat for emergency use; these
could be entered, pressurized to gain buoyancy, and
released from the main habitat. Once on the surface,
the pressurized chambers could be transported by hel-
icopter and mated to a shore-based decompression
chamber. At completion of a mission, the habitat was
brought to the surface and towed to shore while the
aquanauts began decompression in the pressurized living
compartment.
The Aegir habitat (Figure 17-12) was capable of
supporting six divers at depths of up to 580 feet
(176.8 meters) for as long as 14 days. The personnel
chamber consisted of three compartments: living, control,
and laboratory. The living and laboratory compartments
were identical in size and shape, cylindrical with
dished heads and an inside dimension of 9 x 15 feet
(2.7 x 4.6 meters). The control compartment, located
17-14
NOAA Diving Manual — October 1991
Underwater Support Platforms
Figure 17-11
La Chalupa
Living compartment (LC), control compartment (CC) and subport (SP) within the barge structure. On deck the high-
pressure air (A), reserve water (W) and battery power (B), and two personnel transfer capsules (PTC) take up the
remaining deck space. The whole structure is supported by four adjustable pneumatic legs.
October 1991 — NOAA Diving Manual
Courtesy Marine Resources Development Foundation
17-15
Section 17
Figure 17-12
Aegir
EATING/WORKING CYLINDER
Wall Shelving
Passageway Passageway
DIVING/ENTRY SPHERE
330 Surface
Entry Hatch
s 36
Passagewoy '
Dehumidifier
ECS Wall
-30 Escape Port-(
'Lavatory Wall
Lavatory & Water
Closet
SLEEPING/STORAGE CYLINDER
o
6 Sight Port
SsJtooI H
Lock
Galley Sink T— r
Cabinet Floor Plate
'6 Sight Po
rtO
Jr Beam Floor Structure
bi
30 Surface Entry Hatch
36
Passageway
EATING/WORKING CYLINDER
Golley Wall Elevation
&
Environmental
Control System
|\*2 x36 Diving
48 Diving Skirt Entry Port
30 Escape Port
DIVING/ENTRY SPHERE
Shower Wall Elevation
SLEEPING/STORAGE CYLINDER
ECS Wall Elevation
17-16
Photo Courtesy Makai Range
NOAA Diving Manual — October 1991
Underwater Support Platforms
Figure 17-13
Underwater Classroom
between the two cylinders, was spherical, with an inside
diameter of 10 feet (3 meters). The three compartments
were connected by two 36 inch (91.4 centimeter) in diam-
eter necks. The support platform (twin 70 foot (21.3 meter)
long pontoons, each 9 feet (2.7 meters) in diameter)
was capable of controlling the ascent and descent of
Aegir independent of surface control.
A support ship tended the habitat when it was sub-
merged. At the completion of a mission, the habitat
was brought to the surface while the aquanauts remained
in the pressurized compartment. The habitat was then
towed to shore for completion of decompression.
Of the 65 habitats built since 1962, only one currently
is used regularly. This is a small underwater classroom
located on Key Largo in the Florida Keys (Figure 17-13).
Designed and constructed as an engineering project at
the United States Naval Academy in 1974, this 8 x 16 foot
(2.4 x 4.9 meter) habitat, now privately owned, is
located in a mangrove lagoon at a depth of 20 feet
(6.1 meters) and is used by students and researchers
for missions lasting from 1 to 3 days. Normally occu-
pied by 3 to 4 persons, the habitat has housed over 200
persons in the first 1 1/2 years of operation. Because of
the shallow depth, decompression is not required after
missions are carried out.
NOAA has recently constructed a new habitat named
the Aquarius (Figure 17-14) for use at research sites
throughout the Caribbean. This latest addition in the
long line of habitats will operate at depths of up to
120 feet (36.6 meters) and will accommodate 6 scientist-
aquanauts. Because of its mobility, the Aquarius can
be moved to selected sites in response to the needs of
scientific research.
17.5.2 Non-Saturation Habitats
Many diving projects require long periods of work or
observation to be carried out in relatively shallow water.
Simple underwater work shelters are useful on such
projects; the primary function of these shelters is to
allow divers to work for longer periods without surfac-
ing, to protect them from the cold, and to serve as an
emergency refuge and an underwater communication
station. To be most effective, the shelter should be
close to the diver's work site.
Underwater shelters vary in size and complexity,
depending on the nature of the work and the funds
available to provide support equipment and facilities.
They can be made of materials such as steel, rubber,
plastic, or fiberglass. Most of the shelters constructed
to date consist of a shell designed to contain an air
pocket, although some have been supplied with air
from the surface or have used auxiliary air cylinders.
Photo ®Robert Holland, 1987
Figure 17-14
Aquarius
Photo R. Rounds
Hardwire or acoustic communication systems have been
used with some shelters. The decision to use work
shelters should be based on considerations of ease of
emplacement, operational preparation time, bottom
working time, and cost-effectiveness.
The following are examples of four shelters that
have been used successfully for scientific observation
October 1991 — NOAA Diving Manual
17-17
Section 17
Figure 17-15A
Sublimnos
and studies. Sublimnos (Figure 17-15A) is a Cana-
dian shallow-water shelter that was built for scientists
operating on a tight budget. The shelter provided day-
long underwater work capability for as many as four
divers. The upper chamber was 9 feet (2.7 meters) tall
and 8 feet (2.4 meters) in diameter. Entry was made
through a 35 inch (88.9 centimeter) hatch in the floor
of the living chamber.
Subigloo (Figure 17-15B), also Canadian, was used
with great success in Arctic exploration programs in
1972 and 1974 and in the Caribbean in 1975. It con-
sists of two 8 foot (2.4 meter) acrylic hemispheres on
aluminum legs and permits an unrestricted view, mak-
ing it an excellent observational platform. Subigloo is
now used daily by divers as a part of 'The Living Seas'
exhibit at Walt Disney's Epcot Center in Orlando,
Florida.
Lake Lab (Figure 17-15C) was designed to be oper-
ated continuously for 48 hours by two people and to be
emplaced at depths of up to 30 feet (9.1 meters). As
with the other shelters, decompression was accomplished
by having the divers swim to the surface and immedi-
ately enter a deck decompression chamber. Another
type of support platform that is used on undersea research
projects is shown in Figure 17-1 5D. This Undersea
Instrument Chamber (USIC) houses instruments that
record temperature, oxygen content, pH, light level,
redox potential, conductivity, and sounds.
17.6 DIVER PROPULSION VEHICLES
Diver propulsion vehicles (DPV's) are useful for scuba
divers who must make long-distance underwater sur-
veys or travel long distances from a boat or shore base
to an underwater work site (Figure 17-16). Basically,
a DPV is a small hand-held cylinder with a propeller
on one end that usually is constructed of aluminum
alloy. The propeller is driven by an electric motor
supplied with power from rechargeable batteries. The
amount of thrust varies among models; however, one
popular model delivers 30-35 pounds of thrust at full
power. On some models, the thrust may be varied from
5 to 35 pounds. Two 12-volt batteries (in series) pro-
vide about 1 hour of operation at full power. The DPV
is held by pistol-grip handles in front of and below the
diver's body so that the thrust pushes the water under,
and not in the face of, the diver.
17.7 ATMOSPHERIC DIVING SYSTEMS
The operational problems associated with work at great
depths and biomedical considerations (decompression
sickness and the high pressure nervous syndrome) have
17-18
VIEW DOME
VIEW PORT-
- LIGHT
BALLAST-
SUBLIMNOS
SERVICE CABLE
Illustration copyright 1969, Great Lakes Foundation
revived interest in atmospheric diving systems, which
allow the operator to remain at one atmosphere regardless
of the operational depth.
In 1969, the British developed the atmospheric div-
ing system now referred to as JIM (Figure 17-17),
which has undergone modification to achieve greater
flexibility and depth capability. The new modified sys-
tem is called SAM.
The advantages of one-atmosphere diving systems
are largely biomedical, i.e., the elimination of decom-
pression sickness and the risks associated with the high
pressure nervous syndrome. The operational advantages
of these systems include long bottom times at depth,
greater repetitive dive capability, security, and pro-
tection from the cold at depth. Such advantages have
been demonstrated in many open-sea operations over
the last few years. One, and perhaps the most dramat-
ic, was a dive in 1976 to 905 fsw (275.8 msw) in the
Canadian Arctic through 16 feet (4.9 meters) of ice
into 25 °C seawater. An operator worked successfully
for 5 hours and 59 minutes below the ice and experi-
enced only minimal discomfort. To accomplish the
NOAA Diving Manual — October 1991
Underwater Support Platforms
Figure 17-15B
Subigloo
Figure 17-15D
Undersea Instrument Chamber
Courtesy National Geographic Society
Figure 17-15C
Lake Lab
mm
Photo Lee Somers
October 1991 — NOAA Diving Manual
Photo Morgan Wells
same task using conventional diving methods (only the
saturation mode could have been used) would have
incurred a decompression obligation of more than 8
days; with JIM, however, no decompression was neces-
sary, because the operator remained at a pressure of
one atmosphere. The present JIM system has a magne-
sium alloy cast body; a new development is a JIM
system constructed of carbon fiber steel. Equipping
JIM systems with the aluminum articulated arms of
the SAM systems has improved performance signi-
ficantly. The record dive for JIM to date has been
a working dive in the Gulf of Mexico to 1780 fsw
(542.7 msw),where the JIM system worked in tandem
with WASP (Figure 17-18), a manned diving system that
allows the operator to perform midwater tasks. Like
JIM, the WASP system can be used to perform motor
tasks, such as shackling and threading nuts.
Compensating joints developed for the JIM system
provide the flexibility for performing tasks that was
lacking in earlier one-atmosphere systems. Future devel-
opments in atmospheric diving systems and other manned
17-19
Section 17
Figure 17-16
Diver Propulsion Vehicle
Photo Dick Clarke
submersibles will include advances in manipulator tech-
nology, which will enhance human performance under
water. Although these advances are not likely to permit
divers to be replaced, they will augment the underwater
performance of divers and allow them to concentrate
on underwater tasks that require judgment, flexibility,
and the ability to deal with the unexpected.
17.8 REMOTELY OPERATED VEHICLES
Remotely operated vehicles (ROV's) have become valua-
ble adjuncts to divers in several ways: they allow the
diver's bottom time to be increased and thus enhance
productivity; they provide tools and instruments for
underwater work assistance; and they can be helpful in
an emergency.
Although very few ROV systems are identical, the
major components that comprise such systems are gener-
ally the same and are shown in Figure 17-19. There are
over 106 different types of ROV's. They range in cost
from about $27,000 (Figure 17-20) to well over $1 million,
from the size of a basketball to that of a compact
automobile, and in depth of operation from 98.4 feet
17-20
(30 meters) to more than 9840 feet (3000 meters).
In their simplest form, they provide free-ranging, mobile
TV capability. In their more sophisticated form, ROV's
provide complete assemblages of tools and instruments
to conduct detailed bottom surveys, non-destructive
testing (NDT) and cleaning of offshore structures,
maintenance and repair of structures, and a variety
of specialized tasks related to the offshore petroleum
industry and the military. More recently, interest in
using ROV's in scientific and other types of diving
has increased.
The offshore oil industry has been the major user of
ROV's for diver assistance. Virtually all of this use has
been in connection with saturation diving operations,
but the same methods can be applied to non-saturation
diving. The following is a tabulation and brief descrip-
tion of the various support tasks ROV's have conducted.
Diving Support Ship Positioning Assistance
With a pinger or acoustic beacon attached to the
ROV and a receiving hydrophone deployed from the
surface ship, the ROV is launched to locate the exact
position of the dive site. When the site is located, the
NOAA Diving Manual — October 1991
Underwater Support Platforms
Figure 17-17
JIM System
Figure 17-18
WASP System
Courtesy Oceaneering International, Inc. and U.S. Navy
support ship is positioned directly over the vehicle and
is anchored or holds station dynamically while the dive
is conducted. This procedure offers two advantages:
1) the diver does not need to consume bottom time looking
for the work site; and 2) the support ship can remain
close to the diver in case an unscheduled return to the
surface is required. In many instances, it is the prac-
tice to station the ROV at the work site with its lights
on. The diver can then use the lights to home in on the
job.
Evaluate Diving Conditions Related to Safety
Before deploying divers, the ROV is sent to the dive
site to ascertain such aspects of the environment as
visibility, currents, and man-made or natural hazards
that might influence diver safety. This use of ROV's
greatly enhances subsequent dive safety.
Evaluate Dive Site With Respect to Tooling
During predive reconnaissance, the ROV can be
used to assess the work site and identify the tools that
will be needed to conduct the job. The ROV can also
help the diver to map out a technique to use when
conducting the task. This procedure can save many
trips back and forth to the surface and can also reduce
the bottom time that is spent appraising the job.
October 1991 — NOAA Diving Manual
Courtesy Oceaneering International, Inc.
Continuous Monitoring of the Diver for Safety
Industrial diving may be carried out at depths of up
to 1000 fsw (304.9 msw). The knowledge that an ROV
is positioned outside of the bell can be reassuring to
divers. An ROV can be used to check the diver's gear
for leaks and can then accompany the diver during the
dive to provide immediate on-scene appraisal if the
diver runs into trouble. In several instances, ROV's
have been used to assist during the retrieval of dive
bells that have been parted from their umbilicals.
Monitor, Inspect, and Document Diver's Work
In the past, it has been difficult if not impossible for
surface personnel to understand precisely what the
diver is describing, what difficulties he or she is hav-
ing, or, in the worst case, whether the work was performed
properly. An ROV can be used to monitor the diver
during work and to record task performance on video
tape in real-time. This reduces communication prob-
lems and provides a permanent visual record that can
be used to orient subsequent divers who may have to
perform similar tasks. Many ROV's also carry still
cameras that can be used to obtain high-resolution
photographs.
WARNING
ROV's Used by Divers Must Be Safe Electri-
cally and Mechanically— Propellers May Need
Guarding and Some Form of Communication
Should Be Established Between the ROV
Operator and the Diver
17-21
Section 17
Figure 17-19
ROV System Components
Umbilical
Power Pack
Control
Console
17-22
Courtesy Hydro Products, San Diego, CA
NOAA Diving Manual — October 1991
Underwater Support Platforms
Figure 17-20
Mitsui Engineering and Shipbuilding RTV-100
Courtesy Busby Associates, Inc.
Provide Lighting and Tooling Assistance
All ROV's have lights that can be used to provide
additional illumination for divers. Although divers can
Figure 17-21
Examples of ROV David Work Tasks
carry flashlights, this practice leaves them with only a
single hand free for work; if the light is head mounted,
it may not adequately illuminate some angles that
would make the task easier. The maneuverability of
the smaller ROV's provides a variety of angles of attack.
The foregoing tasks have been performed by ROV's
that were not specifically designed to provide for diver
assistance. In 1984, the ROV David (Diver Assistance
Vehicle for Inspection Duty) (Figure 17-21) completed
sea trials and became available for work in underwater
inspection, maintenance, and repair tasks. David is a
large ROV that weighs more than 4 tons in air and
measures 12.5 feet x 6.5 feet x 5.2 feet (3.8 meters x
2.0 meters x 1.6 meters). It can be controlled remotely
from the surface or by the diver under water. The
vehicle is equipped with a power winch, a diver's work
platform, standard tools that include a grinder, cut-
off saw, impact wrench, chipping hammer, hammer
drill, and suction pump. It also carries three adjustable
TV cameras and can provide the capability for water
jetting and pumping equipment.
WELD CLEANING
ROUGH CLEANING
NDT
TRANSPORT
LIFTING
PUMPING -r
October 1991 — NOAA Diving Manual
Courtesy ZF-Herion-Systemtechnik GmbH, Fellbach, West Germany
17-23
i
SECTION 18
EMERGENCY
MEDICAL
CARE
Page
18.0 General 18-1
18.1 Basic Principles of First Aid 18-1
18.1.1 Primary Survey 18-1
18.1.1.1 Airway Maintenance and Cervical
Spine Control Survey 18-1
18.1.1.2 Breathing Survey 18-1
18.1.1.3 Circulation and Hemorrhage Control Survey 18-3
Airway Maintenance and Cervical Spine Control 1 8-3
18.2.1 Establishing the Airway 18-3
18.2.2 Cervical Spine Control 18-5
Breathing (Mouth-to-Mouth or Bag- Valve-Mask Resuscitation) 18-5
18.3.1 Mouth-to-Mouth Resuscitation 18-5
18.3.2 Bag-Valve-Mask Resuscitation 18-5
Circulation 18-6
18.4.1 Treatment by One Person 18-6
18.4.2 Treatment by Two People 18-6
Bleeding 18-7
Shock 18-7
Near-Drowning 18-8
Heat and Cold Casualties 18-8
18.8.1 Heat Exhaustion 18-8
18.8.2 Heatstroke 18-8
18.8.3 Hypothermia 18-9
Injuries and Infections 18-9
18.9.1 Injuries to the Spine 18-9
18.9.2 Injuries to the Head and Neck 18-9
18.9.3 Wounds 18-10
18.9.4 Burns 18-10
18.10 Fractures 18-11
18.11 Electrocution 18-11
18.12 Seasickness (Motion Sickness) 18-11
18.13 Poisoning Caused by Marine Animal Envenomation 18-12
18.13.1 Envenomation Caused by Fish 18-12
18.13.2 Envenomation Caused by Jellyfish 18-12
18.13.3 Envenomation Caused by Cone Shells 18-12
18.13.4 Envenomation Caused by Sea Snakes 18-13
18.13.5 Envenomation Caused by Coral 18-13
18.13.6 Envenomation Caused by Sea Urchins 18-13
18.14 Poisoning Caused by Eating Fish or Shellfish 18-13
18.14.1 Ciguatera 18-13
18.14.2 Scrombroid Poisoning 18-14
18.14.3 Paralytic Shellfish Poisoning 18-14
18.2
18.3
18.4
18.5
18.6
18.7
18.8
18.9
i
EMERGENCY
MEDICAL
CARE
18.0 GENERAL
First aid is the immediate, temporary assistance pro-
vided to a victim of injury or illness before the services
of a qualified physician-paramedical team can be
obtained. The purpose of first aid is to save the victim's
life and to prevent further injury or worsening of the
victim's condition. When an accident occurs, the proper
response can mean the difference between life or death,
temporary or permanent disability, and short- or long-
term hospitalization. Because diving is often conducted in
isolated areas, all individuals involved in diving opera-
tions should have a thorough understanding of the
basics of first aid and should complete, as a minimum,
both the Advanced First Aid and Emergency Care and
the Cardiopulmonary Resuscitation (CPR) courses
offered or certified by the American Red Cross and the
American Heart Association.
18.1 BASIC PRINCIPLES OF FIRST AID
The first step in administering first aid is to evaluate
the victim's condition quickly and accurately and to
elect an appropriate course of action. This evaluation
must be done systematically, speedily, and compre-
hensively. Four phases are involved in the initial care
of accident victims or victims of sudden medical prob-
lems; only the first three of these are considered first
aid:
• Primary survey. This is a quick examination whose
purpose is to identify and assess any life- or limb-
threatening problems.
• Resuscitation phase. In this phase, life-threatening
conditions are treated. This phase and the primary
survey can sometimes, depending on the situation,
be accomplished simultaneously.
• Secondary survey. This is a head-to-toe evalua-
tion of the patient and includes x ray and other
laboratory studies. Although best performed in an
emergency room, the secondary survey phase of
first aid should include the identification of less
serious injuries, because treatment may be neces-
sary to prevent further injury.
• Definitive care. During this phase, the patient's
major problems are corrected and less threatening
problems are dealt with. Because this phase is not
October 1991 — NOAA Diving Manual
part of first aid, it will not be discussed further in
this section.
The following paragraphs provide more detailed dis-
cussions of the three first aid phases.
18.1.1 Primary Survey
The first priority in any first aid situation is to make
sure that the patient can breathe, has a heart beat, and
is not obviously hemorrhaging to death. The primary
survey covers the ABC's of initial first aid, which are:
A. Airway maintenance and cervical spine control
B. Breathing
C. Circulation and hemorrhage control.
A decision tree depicting the sequence for this survey
is shown in Figure 18-1.
18.1.1.1 Airway Maintenance and Cervical Spine
Control Survey
The first step is to make sure that the patient's
airway is open. This can be done by applying the chin
lift or jaw thrust maneuver or by clearing the airway of
debris with the fingers (see Section 18.2.1 for tech-
niques). It is important to remember when establishing
an airway that the patient may have a cervical spine
injury that may be made worse during maneuvers to
establish an airway. The patient's head and neck should
never be hyperextended to establish or maintain an
airway.
WARNING
If There Is Any Obvious Injury Above the Clavi-
cles, the Person Administering First Aid
Should Assume That a Cervical Spine Frac-
ture Exists
18.1.1.2 Breathing Survey
The establishment of an adequate airway does not
ensure that the victim has adequate respiration. The
victim's chest should be exposed to observe if there are
any obvious injuries and to see whether both sides of
the chest rise and fall together. If the victim is not
breathing, cardiopulmonary resuscitation must be
instituted.
18-1
Section 18
Figure 18-1
Life-Support Decision Tree
i
ENTER
Recognize
unconsciousness
Call for help
and position
victim
Maintain
open airway
Transport to
Life Support
Unit
Readjust
head tilt
6-10 manual
thrusts
Clear throat
Breathe
Open
airway
yes
Give 2
full breaths
yes
(
Transport to
Life Support
Unit
Continue rescue
breathing 12
times per minute
yes
±
^^ Air ^n.
C^ entering ^
^s^ ? ^r
no
yes
Transport to
Life Support
Unit
i
i
Continue
attempts to
open airway
18-2
(
Source: JAMA (1986)
NOAA Diving Manual — October 1991
Emergency Medical Care
18.1.1.3 Circulation and Hemorrhage Control Survey
The person administering first aid should feel for a
pulse to determine if cardiac arrest has occurred. The
easiest place to find a pulse is over the carotid artery in
the neck. If there is no pulse, CPR must be instituted.
Rapid blood loss should be identified during the initial
survey and managed by the direct pressure method
(see Section 18.5).
18.2 AIRWAY MAINTENANCE AND
CERVICAL SPINE CONTROL
The first step in determining whether a victim has an
airway obstruction is to:
LOOK for breathing movements;
LISTEN for airflow at the mouth and nose; and
FEEL for air exchange.
The person administering first aid should not be mis-
led into thinking that a victim is breathing adequately
because his or her chest is rising and falling in the
usual manner, because involuntary muscle action may
cause the chest to continue to move even when the
airway is completely obstructed. It is important to
remove any gear and to open the wet suit jacket or cut
it away so that the victim's chest can be seen and felt.
Unless the exchange of air through the mouth and
nose can be heard or felt and it is possible to see that
the victim's chest is rising and falling, the person
administering first aid should not assume that the
victim is breathing adequately. To hear and feel the
exchange of air, the person conducting the survey should
place his or her ear close to the patient's mouth and
nose; in cases of complete obstruction, there will be no
detectable movement of air. However, partial obstruc-
tion is easier to detect and can be identified by listen-
ing. Noisy breathing is a sign of partial obstruction of
the air passages. 'Snoring' usually indicates obstruc-
tion by the tongue, which occurs, for example, when
the neck is flexed. 'Crowing' can indicate spasms of the
larynx, while gurgling sounds can indicate that foreign
matter has lodged in the larynx or trachea. Under no
circumstances should noisy breathing go untreated.
Cyanosis, or a noticeable dusky bluish coloration of
the lips, nailbeds, or skin, is not a reliable sign of
airway obstruction, particularly in a diver who is cold.
The presence or absence of cyanosis should not be used
to judge the adequacy of the victim's airway or of his or
her breathing.
18.2.1 Establishing the Airway
If the patient is unconscious, one of two maneuvers
can be used to open the airway and maintain it. The
October 1991 — NOAA Diving Manual
first, called the chin lift, is done by placing the fingers
of one hand under the front of the chin and gently
lifting the chin upward. The thumb of the same hand is
used to depress the lower lip and open the mouth. The
thumb may also be placed behind the lower teeth to lift
the chin gently. This maneuver should not hyperextend
the head, and it is the method of choice if a cervical
spine injury is suspected because it does not risk com-
promising a possible cervical spine fracture and
converting a fracture without cord injury into one with
cord injury. The second maneuver is performed by
grasping the angles of the lower jaw and pulling the
jaw upward and forward. The lower lip may be pulled
down with the thumbs (Figure 18-2).
After performing either of these maneuvers, the person
administering first aid should check the mouth to see if
any foreign matter, blood, or vomitus is blocking the
airway. Any foreign matter should be removed by
inserting the index finger of one hand down alongside
the cheek, moving it to the base of the tongue, and
sweeping the finger across the back of the base of the
tongue to the other side and out, bringing the obstructing
material with it.
If the victim does not begin to breathe on his or her
own immediately after this maneuver, it may be because
an obstruction continues to exist lower in the respiratory
tract. The rescuer should attempt to inflate the vic-
tim's chest by beginning cardiopulmonary resuscita-
tion. If the rescuer cannot force air into the lungs, the
following methods can be used to dislodge an obstruction.
Manual Thrusts
Manual thrusts consist of a rapid series of 6 to 10
thrusts to the upper abdomen (abdominal thrust) or
lower chest (chest thrust) that are designed to force air
out of the victim's lungs.
Abdominal Thrusts (Heimlich Maneuver)
Victim Standing or Sitting
• The rescuer should stand behind the victim and
wrap his or her arms around the victim's waist.
• The rescuer should grasp his or her fist with the
other hand and then place the thumb side of the fist
against the victim's abdomen, between the lower
end of the victim's breastbone and the victim's
navel.
• The rescuer should press his or her fist 6 to 10
times into the victim's abdomen with a quick upward
thrust.
Victim Lying
• The rescuer should position the victim on his or
her back, with the rescuer's knees close to the
18-3
Section 18
Figure 18-2
Jaw-Lift Method
victim's hips, and should then open the victim's
airway and turn the victim's head to one side.
• The rescuer should place the heel of one hand
against the victim's abdomen, between the lower
end of the victim's breastbone and the victim's
navel, and should then place the second hand on
top of the first hand.
• The rescuer should move sharply forward until his
or her shoulders are directly over the victim's abdo-
men, which puts pressure on the victim's abdo-
men. This should be repeated 6 to 10 times.
Chest Thrusts
This technique is an alternative to the abdominal
thrust. It is particularly useful when the victim's abdomi-
nal girth is so large that the rescuer cannot fully wrap
his or her arms around the victim's abdomen, or when
pressure applied directly to the victim's abdomen is
likely to cause complications, as would occur, for exam-
ple, if the victim were in advanced pregnancy.
Victim Standing or Sitting
• The rescuer should stand behind the victim, place
his or her arms directly under the victim's armpits,
and encircle the victim's chest.
18-4
Source: NOAA (1979)
• The rescuer should place the thumb side of his or
her fist on the victim's breastbone, but not on the
lower end of it or on the margins of the victim's rib
cage.
• The rescuer should then grasp his or her fist with
the other hand and exert 6 to 10 quick backward
thrusts.
Victim Lying
• The rescuer should place the victim on his or her
back and kneel close to the side of the victim's
body. The rescuer should open the victim's airway
and turn the victim's head to one side.
• The rescuer's hand position for and application of
chest thrusts are the same as those for applying
closed-chest heart compression (heel of rescuer's
hand on lower half of victim's breastbone).
• The rescuer should then exert 6 to 10 quick down-
ward thrusts that will compress the victim's chest
cavity.
Conscious Victim
If the victim has good air exchange, only partial
obstruction, and is still able to speak or cough effectively,
the rescuer should not interfere with the victim's attempts
NOAA Diving Manual — October 1991
Emergency Medical Care
to expel a foreign body. The following sequence of
maneuvers (described in detail below) should be
performed by the rescuer if there is airway obstruction:
• Determine if the airway obstruction is complete
by asking the victim to speak.
• Deliver 6 to 10 manual thrusts.
• Repeat 6 to 10 manual thrusts until they are effec-
tive or until the victim loses consciousness.
18.2.2 Cervical Spine Control
Cervical spine injury should be suspected if there is
evidence of any injury above the clavicles. The absence
of neurological signs or the presence of reflexes should
not be considered evidence that no cervical spine injury
exists; only an x ray can rule out such an injury.
The management of a suspected cervical spine injury is
immobilization of the head and neck. This can be done
with sand or sandbags, weights, rocks, or anything that
is heavy enough to keep the head from moving. If
another person is present, immobilization can be accom-
plished by having the other person hold the victim's
head on both sides and apply slight traction to the
head. If a patient must be rolled on the side because of
vomiting or severe bleeding that is obstructing the
airway, this can be done if no back board or cervical
brace is available by moving the body and head together
while maintaining their relative positions. This is
extremely difficult to do because of the weight of the
head, which must be held and rolled with the body
while the helper continues to apply traction. As empha-
sized in the previous section, the cervical spine should
not be extended during the establishment of an airway
if cervical spine injury is suspected.
18.3 BREATHING (MOUTH-TO-MOUTH
OR BAG-VALVE-MASK
RESUSCITATION)
If, after establishing an airway, the victim does not
begin breathing on his or her own, the rescuer should
begin resuscitation efforts, which may require both
cardiac and respiratory resuscitation. This section deals
with the procedure for providing respiration to a victim.
18.3.1 Mouth-to-Mouth Resuscitation
If the airway is being maintained by using the chin
lift method, the rescuer should pinch the victim's nos-
trils closed with the hand that is not holding the vic-
tim's chin, make a seal with his or her mouth over the
victim's mouth, and exhale into the victim's mouth.
The rescuer then removes his or her mouth and turns
October 1991 — NOAA Diving Manual
the face away while the victim exhales. When exhaling
into the victim, the rescuer should make sure that the
victim's chest rises, which is proof that the victim's
airway is open. If it is not, the rescuer should recheck
whether the victim's jaw is lifted fully, the tongue is
held out of the way, etc. The rescuer should give the
victim two full breaths and check for a carotid pulse. If
a pulse is present, the rescuer should continue with
mouth-to-mouth breathing at the rate of 10-12 breaths
per minute until the victim begins breathing on his or
her own or until the rescuer is relieved by someone else
or is too exhausted to continue. If a pulse is not present,
the rescuer should begin combined cardiopulmonary
and respiratory resuscitation, which is described in
Section 18.4.
If a rescuer is using the two-hand jaw-lift method to
maintain the victim's airway, the rescuer can seal the
victim's nostrils by pressing his or her cheek against
them. In some cases, the victim's jaw may be badly
damaged or the victim's mouth cannot be forced open.
If this happens, a rescuer can perform resuscitation by
sealing the victim's mouth and exhaling into the vic-
tim's nose.
18.3.2 Bag-Valve-Mask Resuscitation
If a bag-valve-mask resuscitator (BVMR) (Figure 18-3)
and a trained user are available, this device should be
used to treat cardiac arrest. The self-inflating bag-
valve-mask forms an airtight seal around the victim's
mouth and nose. It can deliver a higher partial pres-
sure of oxygen than is possible with mouth-to-mouth
resuscitation, and the resuscitator can be used in atmo-
spheric air, which contains 21 percent oxygen com-
pared with the 16-17 percent in the exhaled air of a
rescuer. A BVMR can also be supplied with 100 per-
cent oxygen. In addition, rescuers using a BVMR can
ensure that the victim is ventilating adequately and
can detect and correct airway obstruction.
NOTE
A bag-valve-mask resuscitator should be
used only by those who are trained and pro-
ficient in its use.
Precautions
• An oropharyngeal airway should be inserted in an
unconscious victim only if the rescuer is trained in
this procedure.
• Bag-valve-mask resuscitators should not be used
on children younger than 2 years.
18-5
Section 18
Figure 18-3
Bag-Valve-Mask Resuscitator
A. Complete System
B. Operating Position
Source: NOAA (1979)
• Rescuers should ensure that the face mask is
completely sealed about the victim's nose and
mouth.
• Rescuers should never use oxygen flow rates that
are in excess of 10 liters per minute.
• Rescuers should always release the bag quickly
and completely.
While maintaining the victim's airway, the rescuer
should apply the mask firmly to the victim's face, with
the rounded cushion between the victim's lower lip and
chin and the narrow cushion as high on the bridge of
the victim's nose as possible. The rescuer should hold
the mask firmly against the victim's face with the
thumb and index finger while keeping the victim's chin
18-6
and head tilted back with the other three fingers. The
rescuer should ensure that there is an airtight seal
between the mask and the victim's face. The rescuer
should then squeeze the bag firmly while observing the
victim's chest for rise. When administering air to a
child, the rescuer should exercise care not to overexpand
the child's lungs. The rescuer should release the bag
sharply and completely to allow the victim to exhale
(observe for chest fall) and then repeat this squeeze-
and-release pattern approximately every 3 to 4 sec-
onds (about 1 second for chest rise and 2 seconds for
chest fall). The rescuer should continue resuscitation
until he or she is too exhausted to continue or until
additional qualified help comes.
If oxygen is available, the rescuer can use the proce-
dures described above, except that an oxygen bottle
should be connected to the bag-mask system and the
oxygen should be allowed to flow at a rate of 8-10 liters
per minute.
When using this method, the rescuer should be alert
for signs of vomiting. If vomiting occurs, quickly remove
the mask, turn the victim's head to one side, and clean
out the victim's mouth. After the vomiting has stopped
and the mouth has been cleared, the rescuer should
resume resuscitation.
18.4 CIRCULATION
This section describes the procedure for performing
CPR if no pulse is found in a non-breathing victim.
18.4.1 Treatment by One Person
The rescuer should give the victim two full rapid
mouth-to-mouth ventilations; then, with the heel of
one hand on the lower third of the victim's breastbone
and the other hand directly on top of that hand,
the rescuer should press vertically downward about
1.5 inches (3.8 centimeters). The rescuer should then
release the pressure contact with the victim's chest.
This downward pressure should be applied 15 times, at
the rate of 80 per minute, after which the victim should
be ventilated twice. This two-ventilation procedure
should be repeated after every 15 heart compressions,
until the pulse or spontaneous respiration (or both)
returns, the victim is pronounced dead by a physician,
or the rescuer cannot continue because of exhaustion.
18.4.2 Treatment by Two People
With the heel of one hand on the lower third of the
victim's breastbone and the other hand directly on top,
the rescuer should press vertically downward, using
NOAA Diving Manual — October 1991
Emergency Medical Care
some body weight, until the victim's breastbone depresses
about 1.5 to 2 inches (3.8 to 5.1 centimeters). While
maintaining contact with the victim's chest, the res-
cuer should then release the pressure by lifting his or
her hands. This pressure should be applied at the rate
of 60 times per minute. Simultaneously, a second per-
son should apply mouth-to-mouth resuscitation at the
rate of one ventilation for each five pressure applica-
tions to the heart, without a pause in the pressure
applications. To determine whether the pulse has
returned, it should be checked every four cycles.
This routine should be continued until a pulse or spon-
taneous respiration returns, the rescuer(s) is exhausted, or
the victim is pronounced dead by a physician. If the
victim's heart begins beating and the victim breathes
on his or her own, close observation must be continued
until medical help arrives because respiratory or car-
diac arrest may suddenly recur.
18.5 BLEEDING
If a diver suffers an injury under water, the rescuer's
first action should be to remove him or her from the
water. The first step in stopping severe hemorrhaging
is for the rescuer to apply direct pressure on the wound,
which can be done using the hand, finger, or a sterile
dressing. The most sterile material available should be
used, although time should not be wasted looking for
something sterile. The victim should be lying down
and, unless the injury prevents this, the injured area
should be elevated higher than the heart. Pressure
should be maintained for no less than 10 minutes. The
rescuer should cover the entire wound, if possible, with
the fingers or palm of the hand. If blood seeps through
the covering, the rescuer should not remove it but
should add more material and continue to apply pres-
sure. This method of controlling bleeding is much more
effective than using either pressure points (places where
major arteries lie close to the skin) or tourniquets.
A tourniquet is a constricting band used as a last
resort to stop serious bleeding in a limb. A traumatic
amputation, crushed limb, or cases in which direct
pressure fails to stop the bleeding are instances in
which a tourniquet should be used. In these situations,
a wide belt or strong piece of cloth not less than
2 inches (5.1 centimeters) wide should be tied around
the victim's injured limb above the wound, using an
overhand knot. A short stick is tied to the band at the
overhand knot, and the tourniquet is tightened by rotating
the stick. The tourniquet should only be as tight as
necessary to stop the bleeding. Once in place, the tour-
niquet should be loosened only on the advice of a qualified
physician. A tag should be placed on the tourniquet
October 1991 — NOAA Diving Manual
indicating at what time it was applied. Before applying
it, one last effort should be made to stop the bleeding
by using direct pressure.
18.6 SHOCK
Shock may occur after any trauma and will almost
always be present to some degree when a serious injury
occurs. Shock is caused by the loss of circulating blood,
which causes a drop in blood pressure and decreased
circulation. The resulting tissue hypoxia or anoxia can
have permanent effects or may cause death.
Symptoms and Signs
• Feeling 'faint,' weak
• Agitation, mental confusion
• Unconsciousness
• Pale, wet, clammy, cold skin (not a reliable sign
in a diver who has been in the water)
• Nausea, vomiting
• Thirst
• Rapid pulse; absence of peripheral pulses
• Systolic blood pressure 90 mmHg or less.
Treatment
The treatment of shock takes priority over all other
emergency care measures except for the correction of
breathing problems, the re-establishment of circula-
tion, and the control of profuse bleeding. After respi-
ration and cardiac output have been established and
the control of bleeding has been instituted, the follow-
ing procedures should be performed to treat shock.
• Administer 100 percent oxygen (if available) either
by mask or, if the patient does not tolerate the
mask, by allowing oxygen to free flow across the
victim's nose from the end of the connector tubing.
• Elevate the lower extremities. Since blood flow to
the heart and brain may have been diminished,
circulation can be improved by raising the legs
slightly (10-15 degrees). The entire body should
not be tilted down at the head because the abdom-
inal organs pressing against the diaphragm may
interfere with respiration. If the legs are severely
injured or fractures are suspected, the rescuer should
not attempt leg elevation.
• Avoid rough handling. The victim should be han-
dled as gently and as little as possible. Moving a
victim has a tendency to aggravate shock conditions.
• Prevent loss of body heat. Keep the victim warm
but guard against overheating, which can aggra-
vate shock. The rescuer should remember to place
18-7
Section 18
a blanket under the patient as well as on top, to
prevent loss of body heat into the ground.
• Keep the victim lying down. This practice avoids
taxing the victim's circulatory system at a time
when it should be at rest.
• Give nothing by mouth.
18.7 NEAR-DROWNING
Near-drowning refers to an accident in which an
apparently drowned and lifeless victim is pulled from
the water and resuscitated. The causes of near-drowning
are many but a frequent cause is diver panic, which
incapacitates the victim and prevents him or her from
surfacing or staying on the surface. As a result, the
near-drowning victim inhales water or experiences a
laryngeal spasm, which, in turn, causes severe hypoxia.
Symptoms and Signs
• Unconsciousness
• Lack of respiration
• Lack of heart beat.
Treatment
Immediate institution of cardiopulmonary resusci-
tation (see Section 18.4) is required in cases of near-
drowning, even if the victim has been in the water for a
long time. Cases of successful resuscitation have been
reported even after 40 minutes of submersion, presuma-
bly because the rapid hypothermia associated with
immersion in cold water protects the brain and other
vital organs from permanent injury. If hypothermia is
suspected, see Section 18.8.3 for other procedures that
should be performed in addition to CPR.
WARNING
Do Not Withhold CPR Because a Drowning
Victim Appears to be Dead. The Victim May
Only Appear to be Dead Because of Severe
Hypothermia
18.8 HEAT AND COLD CASUALTIES
18.8.1 Heat Exhaustion
Heat exhaustion occurs when cardiac output and
vasomotor control cannot meet the increased circula-
tory demands of the skin in addition to those of the
brain and muscles. It is caused by simultaneous expo-
sure to heat and very hard work in a hot, humid envi-
ronment. Where heat exhaustion is likely, periodic rest
18-8
breaks should be taken in the shade or other cool place.
Fluid intake should be forced, even when not thirsty,
because thirstiness is a poor indicator of dehydration.
Symptoms and Signs
• Rapid weak pulse
• Nausea, vomiting
• Fainting
• Restlessness
• Headache
• Dizziness
• Rapid, usually shallow, breathing
• Cold, clammy skin, continuous sweating.
Treatment
The victim of heat exhaustion should be placed in a
shaded, cool place in a comfortable position, either
lying down or semi-reclining, and should be protected
from chilling. The victim should be forced to drink a
quart of any non-alcoholic fluid as soon as possible;
this drink does not need to be iced. The victim should
recover fairly rapidly, but symptoms such as headache
and exhaustion may linger. Further heat exposure should
not be allowed until all symptoms are gone.
18.8.2 Heatstroke
Heatstroke is a result of excessive physical exertion
in a hot environment and is caused by failure of the
body's thermoregulatory mechanism. It can be avoided
by limiting exertion, wearing protective clothing, and
preventing dehydration. Heatstroke is a serious emer-
gency, and the body temperature of a heat stroke vic-
tim must be lowered quickly to prevent permanent
brain damage or even death.
Symptoms and Signs
• Rise in body temperature
• Sudden collapse
• Skin extremely dry and hot, no sweating
• Dizziness
• Mental confusion
• Convulsions
• Coma.
Treatment
The major factor in treating heatstroke is to lower
the body temperature to a safe level as quickly as
possible. The victim's body should be bathed in tepid
water or, if possible, completely immersed. The head
and neck of the victim should be sponged with the same
tepid water. If conscious, the victim should drink large
amounts of any non-alcoholic fluid. Transfer to a medical
NOAA Diving Manual — October 1991
Emergency Medical Care
facility should be accomplished immediately; without
proper medical care, serious complications are possible.
18.8.3 Hypothermia
Strictly defined, hypothermia is a decrease in the
body's core temperature to a level below 98.6 °F (37 °C).
However, many people can stand a drop in core tem-
perature of 0.9 °F (0.5 °C) without significant prob-
lems. If the temperature continues to drop, shivering
begins and becomes uncontrollable. A core tempera-
ture of 91.4°F (33 °C) is lethal for about 50 percent
of all victims of such hypothermic exposure. The symp-
toms and signs of hypothermia are many and are listed
below in the order of their appearance with decreasing
core temperature.
Symptoms and Signs
• Cold skin and vasoconstriction
• Sporadic shivering
• Uncontrollable shivering
• Mental confusion, impairment of rational thought
• Loss of shivering response
• Sensory and motor degradation
• Hallucinations, decreasing consciousness
• Cardiac abnormalities
• Loss of consciousness
• Loss of reflexes
• Ventricular fibrillation and death.
If a hypothermic victim is conscious and can help
himself or herself, no vigorous rewarming procedures
should be attempted. Warm dry clothing, hot soup,
tea, or coffee, and the avoidance of further cold expo-
sure are recommended. If spontaneous respiration is
present but the victim is still unconscious or extremely
lethargic, active rewarming should be instituted.
Active rewarming should be done at a medical facil-
ity, but simple steps, such as body-to-body rewarming,
can be taken at the dive site while waiting for medical
evacuation. If a supply of hot water is available, run
warm water, 102 to 109°F (39 to 43 °C) into the vic-
tim's diving suit with a hose. Further heat loss should
be prevented by shielding the victim from the wind to
block the evaporative cooling of wet skin and clothes.
Mouth-to-mouth resuscitation also reduces respiratory
heat loss but should be administered only if the victim
is not breathing spontaneously. Providing warmed, satu-
rated air or oxygen at 104 to 113°F (40 to 45 °C)
prevents respiratory heat loss and adds a little heat to
the body core.
The major means of rewarming involves immersion
of the victim's body in warm water at 104 to 109°F
(40 to 43 °C) until his or her rectal temperature has
October 1991 — NOAA Diving Manual
climbed to 96.8°F (36°C) and the patient is again
alert. Rewarming is best done in a medical facility,
where the process can be closely monitored, because of
the serious cardiac and metabolic problems that can
occur during this process. However, rewarming in a
habitat or a saturation chamber may be necessary if,
for example, the victim cannot be taken to a hospital
until he or she has been decompressed. Hot water
should be introduced into the diving suit unless a hot
tub is available in the chamber. Pulse rate and blood
pressure should be taken frequently to guard against
rewarming shock, which can occur as the patient
rewarms. As peripheral blood vessels reopen, periph-
eral resistance is lowered and, if the cardiac output is
low, hypotension can occur. Hydrostatic support, such
as that provided by keeping the suit full of water or
keeping the diver in the tub, can also be helpful.
18.9 INJURIES AND INFECTIONS
18.9.1 Injuries to the Spine
Symptoms and Signs
• Local pain or tenderness over the vertebrae
• Painful movement of back or neck
• Deformity or an obvious hump (both are rare signs)
• Severe trauma to rest of body
• Paralysis or lack of sensation in a body part.
To check a conscious patient for spinal cord injury,
rescuers should observe the following procedures:
• Ask the victim what happened, where it hurts,
whether hands or feet can move, whether sensation
is present in hands and feet
• Look for bruises, cuts, deformities
• Avoid moving the injured patient if the neck and
spine cannot be immobilized.
For an unconscious patient, the rescue procedures to
be observed are:
• Look for trauma or deformities
• Ask others what happened
• Avoid moving the patient if spinal injury is suspected
• Provide resuscitation as required
• Report any symptoms or signs observed to the
physician or rescue team.
18.9.2 Injuries to the Head and Neck
Symptoms and Signs
• Injury to the skull (including face)
• Blood or clear fluid (cerebrospinal fluid) draining
from ears or nose
18-9
Section 18
• Black eyes
• Unconsciousness
• Paralysis or loss of sensation
• Uneven dilation of pupils (one dilated more than
the other)
• Airway obstruction.
Treatment
• Assume that a cervical spine injury is present
• Maintain respiration and circulation
• Control active bleeding.
The face and scalp are richly supplied with arteries
and veins, and wounds of these areas bleed heavily.
Bleeding should be controlled by direct pressure. For
cheek wounds, it may be necessary to hold a gauze pad
inside the cheek as well as outside. The main danger of
facial fractures is that they can cause airway problems
if bone fragments or blood obstructs the airway. If a
neck wound is present, a neck fracture should be sus-
pected and the victim's head and neck should be im-
mobilized to prevent injury to the spinal cord.
18.9.3 Wounds
Divers can experience a wide variety of wounds. The
majority, such as coral wounds or wounds from sharp
edges of metal, are minor and require a minimum of
first aid. However, there is always the chance that a
diver will sustain massive injuries, such as might be
inflicted by a shark or a boat propeller. In such cases,
the right response, promptly applied, may be necessary
to stop bleeding and prevent shock.
Minor wounds, abrasions, scratches, small lacera-
tions, etc., may be noticed by a diver at the time
they occur under water. When such wounds are noticed
after the diver leaves the water, they should be washed
gently with soap and water and covered with a sterile
dressing.
If the wound is deep, gaping, or has a large flap of
skin, the diver should immediately leave the water,
rinse the wound with plain water, and cover it with a
sterile dressing. Medical attention should be sought
because wounds occurring under water are more liable
to become infected than those occurring on the sur-
face. Antibiotic ointments or other medications should
not be introduced into open wounds because they will
have to be removed from the wound before definitive
care can be administered.
A rescuer's most immediate concern when confronted
with a major wound is to stop the bleeding and prevent
the onset of shock. Bleeding should be controlled with
18-10
a pressure dressing (see Section 18.5). Steps should be
taken to prevent shock until medical aid is obtained
(see Section 18.6).
Objects that are impaled in the body or eye should
not be removed except under direct medical supervi-
sion; instead, they should be stabilized for transport to
medical care. The only exception to this rule occurs in
the case of an object that penetrates the cheek. Such an
object can be removed, after which the wound should
be packed inside the mouth to prevent the victim from
choking on blood.
18.9.4 Burns
Burns are classified into three general categories,
according to severity. The least serious is the first-
degree burn, which is a reddening of the skin. With
second-degree burns, the skin is blistered. The most
serious is the third-degree burn, in which the skin (and
possibly the underlying tissue) is charred beyond repair.
Burns can result from either heat or chemical action.
Treatment
The treatment that can be administered to a burn
victim other than by a physician is extremely limited.
The immediate treatment for all burns, however, is
immersion in cool or tepid water to reduce tissue tem-
peratures rapidly to levels below those that cause damage.
If the skin is broken or burned through, the burned
area itself should be covered with a sterile or clean
dressing, using a material that will not adhere to the
burn, to exclude air from the area. (Blisters should not
be opened.)
In minor burn cases, the victim may be given aspirin
to reduce the pain. To assist in replacing lost fluids, the
victim may be given liquids, except alcohol. All burns
of more than a minor degree may be accompanied by
shock, and the victim must be observed carefully and
treated accordingly. For all burns except minor reddening
of the skin, the victim should be examined by a doctor.
Burn ointment, grease, baking soda, or other substances
should not be applied to burns that involve opened
blisters or other wounds.
Sunburn is common for anyone who spends time
near the water. Avoiding prolonged, direct exposure to
sunlight and wearing protective clothing and sunshield
ointment are the best sunburn prevention. A sunshield
with a protection factor of 15 should provide good
protection if used properly. Sunshields with lower pro-
tection factors provide correspondingly lower shielding
capabilities. Sunburns can cause skin damage severe
enough to keep the sunburned individual from working.
NOAA Diving Manual — October 1991
Emergency Medical Care
Symptoms and Signs
• Prickly sensation on skin in affected area
• Pain and tenderness to the touch
• Extreme redness
• Blisters
• A desire to avoid having the affected area come into
contact with clothing
• Fever.
Treatment
Many sunburn ointments that provide partial relief
are commercially available. If no special ointment is
available, bandages soaked in cool water will provide
some relief. The victim should avoid further exposure
until the condition has passed. Sunburn blisters should
not be opened.
18.10 FRACTURES
It is unusual for a diver to suffer a fracture while
diving. Diving-related fractures usually occur on the
surface. If divers suffer fractures while submerged,
they should immediately terminate the dive.
Fractures can be classed into two general types. A
closed fracture consists of a broken bone that has not
penetrated the skin. In an open (compound) fracture,
the broken bone has caused an open wound, from which
the bone frequently protrudes. This type of wound is
complicated by the likelihood of infection.
Symptoms and Signs
• Area of fracture painful and tender
• Inability to move affected limb
• Limb bent at unusual angle
• Swelling in area of fracture
• Abnormal movement occurring at a location other
than a joint.
Treatment
The only first aid required for closed fractures is to
immobilize the affected limb with a splint. Flat pieces
of wood, plastic, metal, or any firm substance may be
used. Inflatable splints are excellent. The splint serves
to prevent movement and consequent complication of
the injury. To prevent movement, the splint should be
bound to the limb at a minimum of three places: at the
wound, and above and below the joints closest to the
fracture.
When treating an open fracture, the limb should not
be moved to its natural position. The open wound should
be covered with a sterile dressing and splinted to pre-
vent movement. With any fracture, shock should be
anticipated and its symptoms treated (see Section 18.6).
Regardless of the type of fracture, the rescuer should
not try to set the bone; this should be done only by
qualified medical personnel. In joint injuries (shoul-
der, elbow, wrist, knee, or ankle), the injury should be
immobilized just as it was found; moving the joint may
damage nerves or major blood vessels.
18.11 ELECTROCUTION
Electrocution may result from the careless handling,
poor design, or poor maintenance of power equipment,
such as welding and cutting equipment or electric under-
water lights. All electrical equipment used under water
should be well insulated. In addition, divers should be
properly insulated from any possible source of electri-
cal current.
When leaving the water to enter a boat or habitat,
divers should not carry a connected light or electric
tool. Victims may not be able to separate themselves
from the source of the shock.
Signs
• Unconsciousness
• Cessation of breathing
• Cardiac arrest
• Localized burns.
Treatment
The first step in treatment is to neutralize the source
of electricity to protect the rescuer and the victim. If
this cannot be done immediately, a non-conductive
substance (such as a piece of lumber) should be used to
break the contact between the source and the victim.
The victim must then be treated for cardiac arrest
and given artificial resuscitation, if necessary (see
Section 18.4). Regardless of how complete the recovery
may seem, the victim should be examined by a physician
immediately because of the possibility of delayed car-
diac or kidney complications.
18.12 SEASICKNESS (MOTION SICKNESS)
Seasickness can be a distinct hazard to a diver using
small craft as a surface-support platform. Diving should
not be attempted when a diver is seasick: vomiting
while submerged can cause respiratory obstruction and
death.
Symptoms and Signs
• Nausea
• Dizziness
• Feelings of withdrawal, fatigue
• Pallid or sickly complexion
• Slurred speech
• Vomiting.
October 1991 — NOAA Diving Manual
18-11
Section 18
Prevention
There is no effective treatment for seasickness except
to return the stricken diver to a stable platform. All
efforts are therefore directed at prevention. Some peo-
ple are more susceptible than others, but repeated
exposures tend to decrease sensitivity. Suggestion ther-
apy by a trained mental health specialist has been
helpful in some cases. The susceptible person should
eat lightly just before exposure and avoid diving with
an alcohol hangover. Seasick individuals should be
isolated to avoid affecting others on board adversely.
Drug therapy is of questionable value and must be used
with caution because most motion sickness prepara-
tions contain antihistamines that make the diver drowsy
and could affect a diver's judgment. The administra-
tion of scopolamine by means of a skin patch has been
shown to be useful in preventing seasickness, but this
drug may cause psychotic behavior in sensitive per-
sons. Drugs should be used only under the direction of
a physician who understands diving, and then only
after a test dose on non-diving days has been shown not
to affect the individual adversely.
18.13 POISONING CAUSED BY MARINE
ANIMAL ENVENOMATION
18.13.1 Envenomation Caused by Fish
Divers are in contact with a variety of marine life
that can inflict poisonous wounds if handled carelessly.
Some of the most frequently encountered wounds are
inflicted by stingrays, stonefish, scorpionfish, catfish,
and sea urchins. (For more detailed information on the
identification of poisonous marine animals, see Sec-
tion 12.) The poisoning caused by these animals ranges
from mild to fatal, depending on the animal, wound
site, amount of poison injected, and individual sus-
ceptibility.
Symptoms and Signs
• Severe, localized pain at the wound site
• Localized swelling, which may be accompanied by
an ashy appearance
• Fainting, weakness, nausea, or shock
• Respiratory distress
• Cardiac arrhythmias, cardiac arrest.
Treatment
Because fainting is common after a poisonous wound,
the victim should be removed from the water as soon as
possible. The wound should be washed with a sterile
saline solution or cold salt water. The wound should be
soaked in water as hot as the victim can stand (not
more than 120°F (50 °C)) for a period of at least
18-12
30 minutes because this may neutralize the venom. The
patient should be observed for signs of cardiac or
respiratory arrest. Medical assistance should be obtained
as quickly as possible.
18.13.2 Envenomation Caused by Jellyfish
Jellyfish poisoning ranges in severity from minor to
fatal.
Symptoms and Signs
(These vary depending on species and extent of sting.)
• Pain ranging from a mild prickly sensation to an
intense throbbing, shooting pain
• Reddening of the area (welts, blisters, swelling)
• Pieces of tentacle on affected area
• Cramps, nausea, vomiting
• Decreased touch and temperature sensation
• Severe backache
• Loss of speech
• Frothing at the mouth
• Constriction of the throat
• Respiratory difficulty
• Paralysis
• Delirium
• Convulsions
• Shock.
Treatment
A diver who has been stung by jellyfish should be
removed from the water as quickly as possible. The
rescuer should remove any tentacles, taking care not to
come into contact with them himself or herself. The
wound area should be rinsed with vinegar, sodium
bicarbonate solution, or boric acid solution to prevent
untriggered nematocysts from discharging. The area
should not be rinsed with fresh water or rubbed with
sand to remove any tentacles, because this will cause
increased stinging. The victim should be kept lying
down with feet elevated, and CPR should be administered
if required. In serious cases, medical support may be
required.
18.13.3 Envenomation Caused by Cone Shells
These animals have a very toxic poison that has
caused death in as many as 25 percent of cases.
Symptoms and Signs
• Stinging or burning at wound site
• Numbness or tingling at wound that spreads to the
rest of the body
• Muscular paralysis
• Difficulty in swallowing and speaking
• Respiratory distress.
NOAA Diving Manual — October 1991
Emergency Medical Care
Treatment
The patient should be removed from the water immedi-
ately and laid down. A loose constricting band such as
an ace wrap or belt should be placed above the sting to
prevent venous drainage from the wound but should
not be tight enough to stop arterial flow. Loosen for
90 seconds every 10 minutes. Immediate medical atten-
tion should be sought. Careful observation is required
in case of cardiac or respiratory failure. Be prepared to
administer CPR.
18.134 Envenomation Caused by Sea Snakes
The most serious poisonous bite is that of the sea
snake. These reptiles are closely allied to the cobra and
have a highly toxic venom. A sea snake bite usually is
small and may not even be noticed, and the onset of
symptoms is often delayed for 1 hour or more.
Symptoms and Signs
• Generalized malaise, anxiety, or, possibly, a feel-
ing of well-being
Difficulty with speech and swallowing
Vomiting
Aching or pain on movement
Weakness, progressing within 1 to 2 hours to an
inability to move, beginning in the legs
Muscle spasm
Droopy eyelids
Thirst, burning dryness of throat
Shock
Respiratory distress
Fang marks (two small punctures approximately
1/2 inch (1.3 centimeters) apart) and, possibly, a
fang left in the wound.
Treatment
The victim must remain quiet. If bitten on the arm or
leg, a constricting bandage should be placed above the
wound but should not be drawn so tightly as to inter-
rupt arterial flow. The band should be periodically
loosened, as described in Section 18.13.3. The victim
should be transported immediately to the nearest medical
facility for the antivenom treatments necessary to combat
the poison. If possible, capture or kill the snake for
identification purposes.
18.13.5 Envenomation Caused by Coral
Coral is common in most tropical waters. These tiny
animals leave behind a hard, calcium-like skeleton,
which is frequently razor sharp and capable of inflicting
painful wounds. The wounds tend to be slow in healing,
easily infected, and, if not treated, may become ulcer-
October 1991 — NOAA Diving Manual
ous. Some corals have stinging cells similar to those in
a jellyfish and produce a sting that rapidly disappears
but may leave red itchy welts.
Symptoms and Signs
• Itchy, red, swollen area or wound
• Lingering, infected wound
• Lacerations, bleeding.
Treatment
The wound should be washed with soap and water to
remove bacteria and foreign matter. An antiseptic should
then be used and the wound covered with a sterile
dressing. Aspirin or other mild analgesics may be used
if the wound is painful; if severe, medical attention
should be sought.
18.13.6 Envenomation Caused by Sea Urchins
Most divers in marine waters are familiar with the
sea urchin. The spines of these creatures can penetrate
wet suits, and, being very brittle, can break off at the
slightest touch.
Symptoms and Signs
• Immediate sharp, burning pain
• Redness and swelling
• Spines sticking out of skin or black dots where
they have broken off
• Purpling of skin around place spines entered
• Numbness.
Treatment
Spines that can be grasped should be removed with
tweezers. Spines that have broken off flush with the
skin are nearly impossible to remove, and probing around
with a needle will only break the spines into little
pieces. Most of the spines will be dissolved by the body
within a week; others may fester and can then be pushed
out to the point where they can be removed with
tweezers. Alternately immersing the affected area in
hot and cold water may help dissolve the imbedded
fragments.
18.14 POISONING CAUSED BY EATING
FISH OR SHELLFISH
18.14.1 Ciguatera
Ciguatera poisoning is caused by eating fish containing
a poison (ciguatoxin) whose origin is unknown but
which is believed to come from a certain species of
algae eaten by the fish. There is no way to distinguish
18-13
Section 18
fish with ciguatera from harmless fish except by labo-
ratory analysis or by feeding the suspected fish to
animals and watching for a reaction. The occurrence
of fish containing ciguatoxin is unpredictable and can
occur in a fish species that was harmless the day before.
About 800 species of fish have been known to produce
ciguatera, and common types that have been known to
carry ciguatera include barracuda, grouper, snappers,
jack, wrasse (Labridae), parrotfish (Scaridae), and
surgeonfish (Acanthuridae). Toxic fish seem more preva-
lent in tropical areas and, because the concentration
builds up over time, large fish of a given species are
more likely to be toxic than smaller ones. The internal
organs and roe of diseased fish are particularly toxic.
Severe ciguatera poisoning may end in death, which is
caused by respiratory paralysis. The toxin is not destroyed
by cooking.
Symptoms and Signs
• Numbness of lips, tongue, throat
• Abdominal cramps
• Nausea, vomiting
• Diarrhea
• Weakness, prostration
• Reversal of thermal sensitivity (hot feels cold and
cold feels hot)
• Muscle and joint aching
• Nervousness
• Metallic taste in mouth
• Visual disturbances
• Extreme fatigue
• Muscle paralysis
• Convulsions.
Treatment
There is no definitive first aid available for ciguatera
poisoning. If symptoms occur within 4 hours of eating
fish, vomiting should be induced. Medical attention
should be sought as soon as possible, and the treatment
team should be told that fish has been consumed within
the last 30 hours. In some cases death occurs within
10 minutes, but a period of days is more common. If
untreated, death may be caused by paralysis of the
respiratory system. Careful observation for respiratory
failure should be continued until medical help is reached,
and CPR should be started if required.
18.14.2 Scrombroid Poisoning
Some scrombroid fish (tuna, bonito, mackeral, skip-
jack, etc.) that have been exposed to sunlight or been
left standing at room temperature for several hours
may develop a toxin and have a peppery or sharp taste.
18-14
Within a few minutes of consumption, symptoms of
this type of poisoning, which resemble a severe allergy,
will develop. The symptoms usually clear within
8-12 hours.
Symptoms and Signs
• Nausea, vomiting
• Diarrhea
• Abdominal pain
• Severe headache
• Dizziness
• Massive red welts
• Severe itching
• Severe dehydration
• Shock.
Treatment
The victim should seek medical aid as soon as possi-
ble. Vomiting should be induced if it does not occur
spontaneously.
18.14.3 Paralytic Shellfish Poisoning
During the summer months, many shellfish that
inhabit the Pacific coast and Gulf of Mexico may
become poisonous. This poison is caused by the inges-
tion of poisonous plankton and algae, which contain
different types of toxins that do not affect the shellfish
but can be poisonous to humans. Mussels and clams
carry this poison, but abalone and crabs, which do not
feed on plankton, are not affected. In most cases, cooking
will not neutralize the toxin. The poison works directly
on the central nervous system and the usual signs, such
as nausea and vomiting, are not generally present. The
poison impairs respiration and affects the circulation
of the blood. Death, which occurs in severe cases,
results from respiratory paralysis. Onset is variable
but may occur within 20 minutes of ingestion.
Symptoms and Signs
• Tingling or burning of lips, mouth, tongue, or face,
which spreads to other parts of the body
• Numbness
• Muscle weakness and paralysis
• Respiratory failure
• Infrequently, nausea, vomiting, and other gastrointes-
tinal ailments.
Treatment
Vomiting should be induced as quickly as possible,
and immediate medical attention should be sought.
Rescuers should be prepared to provide mouth-to-mouth
resuscitation or CPR.
NOAA Diving Manual — October 1991
SECTION 19
ACCIDENT
MANAGEMENT
AND EMERGENCY
PROCEDURES
19.0
19.1
19.2
19.3
19.4
19.5
19.6
19.7
19.8
19.9
Page
General 19-1
Anticipating a Problem 19-1
19.1.1 During Training 19-2
19.1.2 During Dive Preparation 19-2
19.1.3 During Entry and Descent 19-3
19.1.4 During the Dive 19-3
19.1.5 During Ascent and Exit 19-3
Causes of Emergencies 19-4
19.2.1 Loss of Air Supply 19-4
19.2.2 Loss or Flooding of Equipment 19-7
19.2.3 Fouling and Entanglement 19-7
19.2.4 Near Drowning 19-8
Assessing a Problem 19-8
Approaching a Victim 19-9
Rescue Procedures 19-10
19.5.1 Victim Submerged and Unconscious 19-10
19.5.2 Victim Submerged and Conscious 19-14
19.5.3 Victim on the Surface and Unconscious 19-16
19.5.4 Victim on the Surface and Conscious 19-16
19.5.5 Towing a Victim in the Water 19-17
19.5.6 Leaving the Water with a Victim 19-18
Accident Management 19-19
19.6.1 Summoning Aid 19-20
19.6.2 On-Site Care of the Diving Casualty 19-22
Evacuation by Air 19-27
Guidelines for Emergency Evacuation 19-27
Accident Reporting Procedures 19-28
4
<
ACCIDENT
MANAGEMENT
AND EMERGENCY
PROCEDURES
19.0 GENERAL
Accident management has a broader meaning than the
term implies; it includes many activities, ranging from
accident prevention to selection of personnel, equip-
ment, and procedures and the emergency care of victims
after an accident. Preventing accidents through proper
training, forward planning, and the on-scene manage-
ment of casualties is emphasized in this section, which
applies only to open-water accidents. The reader should
consult Sections 18 and 20 of this manual for first aid
and treatment procedures.
Statistics on fatal scuba accidents show that acci-
dents occur in clusters, particularly in areas where
diving activity is concentrated, such as California,
Florida, the Great Lakes, and off the Northwest coast.
Although the number of dives undertaken per year has
risen markedly, it seems likely that the actual inci-
dence of accidents (i.e., number of accidents per unit
time, or rate of accidents) has decreased on an annual
basis. Reports of scuba fatalities indicate that proper
accident management procedures frequently could have
prevented the accident or saved a life once an accident
occurred (McAniff 1986). Divers killed accidentally
are usually found with intact equipment, weight belts
on, functioning regulators, tanks containing some air,
and uninflated buoyancy control devices. Instances in
which equipment failure led to the death of the diver
are extremely rare. Human error and inadequate diver
performance seem to be the major contributing factors
in many fatal accidents, and panic is probably the
initiating cause in most instances. In some cases, a
feeling of apprehension may precede panic and itself
produce problems leading to a diving accident. Many
divers are apprehensive, and even the experienced ones
may be disturbed by certain kinds of water conditions
or other circumstances associated with a particular
dive. The competent diver is one who gains as much
information as possible about the dive site, boat, equip-
ment, and other important features of the dive. Plan-
ning prepares the diver to meet unexpected eventuali-
ties; a thorough knowledge of the dive site, including
currents, marine hazards, and sea states, is essential to
proper planning (see Section 10).
Panic
Panic is different from apprehension. One kind of
panic involves the belief that an individual is losing
October 1991 — NOAA Diving Manual
control of his or her own performance and the situa-
tion. Panic is accompanied by severe physiological
changes that may in turn facilitate loss of control. For
example, an individual breathing rapidly and shallowly
because of panic causes a buildup of carbon dioxide as
a result of inadequate ventilatory exchange (see Sec-
tion 3.1.3.9). Lowered air intake also can result in a
loss of buoyancy and lead to inefficient swimming
movements, which further contribute to a loss of control.
Stereotypical behavior also can result from panic.
For example, a diver discovering that the air valve
reserve mechanism has been tripped accidentally, leaving
no reserve air, could respond properly either by releas-
ing the weight belt and slowly ascending to the surface
or by asking a buddy for assistance. On the other hand,
the stereotypical response would be to continue pulling
the reserve mechanism lever, causing greater panic
and loss of control. The basic problem in many cases is
that the diver delays releasing the weight belt or asking
for assistance until the onset of panic, by which time he
or she has probably lost the necessary degree of motor
coordination to act effectively.
Before a diver reaches the point of panic, warning
signs appear that should alert dive masters and dive
partners to the presence of impending problems. Among
the warning signs of panic in the water are indications
of anxiety (primarily a change in breathing rate and
pattern from smooth and regular to rapid and shallow)
and changes in swimming movements (generally a shift
from smooth and regular movements to jerky and irregu-
lar motions). A detailed discussion of the problem of
panic appears in Bachrach and Egstrom (1986). The
panicking diver frequently goes through desperate
motions, such as "clawing" the surface, trying to hold
the head above the water, and spitting out the mouth-
piece, which only create further problems.
The best means of preventing panic is to make sure
that a diver is well trained, especially in emergency
procedures such as ditching the weight belt and oper-
ating the buoyancy compensator, well equipped, in
good physical condition, and well informed about dive
conditions and the purpose of the dive. The following
paragraphs describe these aspects of dive planning.
19.1 ANTICIPATING A PROBLEM
Every diver should develop skill in recognizing the
warning signs, either in himself, another diver, or the
19-1
Section 19
dive situation, that foreshadow a diving accident. This
ability can significantly increase the chance of averting a
fatality and thus can enhance the safety of both victim
and rescuer. Danger signs exhibited by divers are both
varied and subtle and may be apparent before or dur-
ing the dive. A diver's ego may cause him or her to
mask incompetence, anxiety, illness, or other distress
before the dive, and features of the environment, such
as difficulty in communication, may make it nearly
impossible to observe such signs once the dive has
begun.
19.1.1 During Training
The management of scuba accidents should begin
when a candidate expresses an interest in learning to
dive. The process of screening applicants before admit-
ting students to a scuba training program should include
obtaining medical releases from physicians and evalu-
ating swimming and watermanship. (Most sport certi-
fication agencies require a physician's release only if
something unusual is reported on the medical form.)
During the in-water evaluation, the candidate should
be required to demonstrate endurance and confidence
in the water so that the instructor can assess whether
the candidate is comfortable in the aquatic environ-
ment. Students should be encouraged to obtain breath-
hold diving experience before beginning scuba lessons
to enhance their ability and confidence in the use of
mask, snorkel, fins, and other equipment and to main-
tain these skills throughout their diving career. Points
for the instructor to observe include such things as
breathing through the snorkel with the face (without a
mask) in the water, surface diving to pick up an object
in about 20 feet (6 meters) of water, and clearing the
snorkel easily. Another good test of aquatic ability is
having an unequipped swimmer catch his or her breath
and rest while unsupported in deep water after a stren-
uous swim.
Throughout the preliminary training and evaluation,
the instructor should estimate how the diver-candidate is
likely to handle an emergency or react under stress and
should identify the areas in which the student needs
special attention and extra training. An area of train-
ing often neglected is learning the proper procedures
for dressing and attachment of gear such as weight
belts, buoyancy compensators, gauges, etc. These
procedures should be overlearned to the extent that
they become second nature, which ensures that equip-
ment will be properly positioned in the event of an
emergency.
Because panic is frequently involved in diving acci-
dents, it is important that the student learn to feel
confident and at ease in the water at the outset of
19-2
training. Signs that indicate anxiety or a lack of confi-
dence in the water are:
Evidence of claustrophobia
Expressed fear of and difficulty with underwater
swimming
Difficulty in adapting to mouth breathing
Difficulty in adapting to underwater breathing
using scuba apparatus
Poor watermanship without swim or flotation aids
Complaints about the regulator's breathing re-
sistance
Constant fidgeting with dive equipment
Obvious overweighting
Constant interest in swimming to the surface
Rapid and/or shallow breathing
Stiff and uncoordinated movements
Reluctance to exhale fully when requested to do
so by the instructor
Hanging onto the instructor's hand too tightly
when being escorted
Becoming anxious when minor equipment pro-
blems occur on the bottom
Lack of acknowledgment when the instructor looks
directly into the eyes
Constantly being "wide-eyed"
Complaints of inability to clear the ears, especially
during early open-water training.
Many other signs that reveal anxiety, fear, or incompe-
tence can be observed. Although in most instances these
problems can be overcome by proper training, some
individuals, even with excellent training, are better
advised not to pursue scuba diving.
Experienced divers sometimes can anticipate another
diver's problems during open-water training. In such
cases the experienced diver should observe the extent
of the other diver's familiarity with equipment, ease in
donning it, and ability to correct a leaky mask or put a
regulator in the mouth under water. The experienced
diver also should note whether the inexperienced diver
swims off alone, oblivious to the buddy, and whether
there is difficulty in breathing from the regulator with
the mask off. Each of these occurrences may be a clue
indicating that the student in question may subsequently
panic easily or become overconfident. Even the best
divers are concerned about becoming overconfident
and seek advanced training when necessary.
19.1.2 During Dive Preparation
Although individuals suffering from serious illnesses or
injuries usually make no attempt to dive, many divers
enter the water with minor discomforts that may have
NOAA Diving Manual — October 1991
Accident Management and Emergency Procedures
adverse consequences, particularly if an emergency
develops. Examples of such minor maladies are ear or
sinus infections, headaches, lung congestion, seasick-
ness, cramps, and the side effects of medication. Divers
should assess not only their own condition but also that
of other divers in the group.
Before entering the water, each diver should note
the configuration, condition, and completeness of the
buddy diver's equipment. The overequipped diver
encumbered with more equipment than can be handled
safely in the water should be advised to leave non-
essential items on the shore or in the boat. During
predive preparations, every diver should be alert to
signs of diver ineptness or error, such as lack of knowl-
edge of procedures, nervousness, or mistakes made
while assembling equipment.
Other signs of potential problems are more subtle
and psychological in nature; included in this category
are changes in personal characteristics, such as an
increase in the pitch of the voice, incessant chattering,
procrastinating before actually entering the water, and
withdrawal. Signs of overheating or chilling, such as
excessive sweating or shivering, also should be noted.
These signs should be responded to before entering the
water, either by providing direct assistance (if the
problem is mechanical), by giving reassurance, by prac-
ticing a particular skill, or by suggesting that the indi-
vidual not dive (if circumstances warrant). Although
some divers might be embarrassed by the latter sug-
gestion, others might welcome it with relief.
19.1.3 During Entry and Descent
Failure to use proper entry techniques or forgetting
essential equipment such as fins or mask may be signs
that the diver requires watching. Other hints that the
diver may be under stress or uncomfortable in the
water are failure to surface properly or to check with
the buddy before descent and excessive "high tread-
ing." High treading means that the diver treads and
fins with vigor sufficient to lift the major portion of the
body out of the water without using buoyancy compen-
sation. When this activity is accompanied by dog pad-
dling and using the arms excessively, it is a sign that a
potentially serious problem may be in the making.
Rejecting the mask or other essential equipment in the
water is also a portent of problems, as is the tendency
to cling to or clamber onto objects above the surface
(not to be confused with the normal practice of using a
float or some other object for temporary support).
Once the descent begins, there may be other signs
that a problem is developing. Although anyone can
have occasional difficulty with ear clearing or buoy-
October 1991 — NO A A Diving Manual
ancy control, chronic problems or overconcern may
indicate an uneasy diver who needs watching. Ear equali-
zation problems at depths below 50 feet (15.2 meters)
are particularly indicative of a potential problem. Sudden
changes in descent rate also should be noted because
they may indicate either overconfidence or a desire to
return to the surface. Throughout the descent and
initial phase of the dive, every diver should observe his
or her buddy for signs of erratic behavior, such as abrupt
changes in swimming speed, fiddling with equipment,
lack of stability, or difficulty with buoyancy control.
Sudden or unnecessary use of the hands and arms for
propulsion or buoyancy often is a sign of anxiety and
impending difficulty. The diver exhibiting any or all of
these signs may be unaware that anything is out of the
ordinary, but experienced divers should be sensitive to
such behavior before a problem develops.
19.1.4 During the Dive
Once entry and descent have been achieved, the
alert diver continues to watch for signs that suggest an
approaching problem. The things to watch for are bas-
ically the same as those during descent, i.e., general
uneasiness, fast breathing, straying from the buddy,
erratic behavior, or equipment problems. Any devia-
tion from good diving practice, such as failure to check
the air supply, depth, and time, should be mentally
noted. Diving accidents are particularly likely to hap-
pen either in the first 3 minutes of a dive (because of
lack of preparedness) or in the final 5 minutes (because
the dive has been extended too long). Photographer-
divers should be watched especially carefully because
it is easy to become preoccupied with the task at hand
and to forget to keep track of time, depth, and air
supply. It is also important to keep track of significant
changes in surface conditions or currents that might
affect ascent or exit from the water. In conditions of
poor visibility or during night dives, extra care must be
taken to ensure that lights are functioning properly
and that divers stay close together. In addition, at least
one diver should watch for potentially dangerous marine
animals if they are known to exist in the area.
At the end of the dive, divers should surface in
buddy pairs. Prior arrangements about when and where
the dive will be terminated should have been made
before beginning the dive.
19.1.5 During Ascent and Exit
It is especially important to maintain a continual
awareness of potential problems at the end of a dive.
19-3
Section 19
Several factors can contribute to carelessness and acci-
dents, such as fatigue, cold, equipment malfunction,
and overconfidence. In observing a buddy diver during
ascent, it is essential to note whether the no-decom-
pression time has been exceeded, the rate of ascent is
too rapid (especially during the last 10 feet (3 meters)),
the distance between divers is too great, or that surfacing
will take place either where there are obstacles (kelp,
active boat channels, rip current, breaking waves) or
down current from the support platform. Proper atten-
tion also must be given to ensuring an adequate air
supply and that the buddy is breathing properly during
ascent.
Each diver should ensure that the buddy does not
exit from the wrong place in the surf line, exit to an
unsafe surface in a heavy surge, get too close to a dive
platform in a heavy swell, or hang on tightly to a line
attached to the bottom during a heavy swell. Because
divers are often fatigued at the end of a dive, extra
caution must be paid to the routine handling of equipment
while climbing up a ladder or into a boat. In particular,
divers should avoid coming up the ladder under the
tank or the falling zone of another diver.
WARNING
Unless the Diver is Exhaling When the Trough
of the Wave Passes Overhead, Hanging onto
a Line Attached to the Bottom in Heavy Swells
is Dangerous Because the Change in Pres-
sure May Cause an Embolism
19.2 CAUSES OF EMERGENCIES
Diving emergencies can arise from an almost infi-
nite number of causes, including exhaustion, embo-
lism, decompression sickness, nitrogen narcosis, heart
attacks, high currents, entanglement, heavy surf, out-
of-air emergencies, equipment failure, and panic. In
general, diving accidents are overwhelmingly caused
by human error rather than equipment failure. The
probable causes of non-occupational diving fatalities
are summarized in Table 19-1, which shows that only
12 percent of fatalities occurring over a 9-year period
were attributable directly to equipment malfunction.
Readers interested in more details about the causes of
diving fatalities should consult McAniff (1986).
In the planning stages of a dive, contingency plans
should be made, and all divers should be briefed and
familiarized with those plans. New or unfamiliar equip-
ment should be understood thoroughly by all divers,
and practice sessions should be held before the dive.
19-4
Before initiating a dive, experienced dive masters
visualize the worst accident scenarios and mentally
rehearse the management of these hypothetical acci-
dents. It is even more effective to sketch an accident
management flow diagram (Somers 1986). In planning, it
is essential to assess the capabilities of the dive team to
ensure that, in the event of an accident, novice divers
are not unnecessarily exposed to risks.
No matter how well planned the dive or how well
trained the diver, however, emergency situations occa-
sionally arise, usually as a result of failure to observe
some safety precaution. In most instances, taking a
few seconds to assess the situation accurately and deter-
mine the actions necessary can keep the emergency
from becoming an accident. Instinctive reactions sel-
dom are correct and may prove to be blind impulses
brought on by panic. Adequate training should prepare
the diver for most emergencies, provided that panic
does not intervene.
The following paragraphs describe some of the more
common causes of diving emergencies and methods of
avoiding and managing emergencies if they do occur.
19.2.1 Loss of Air Supply
The first step in evaluating an out-of-air situation
should be to confirm that the apparent air loss is real.
Before reacting precipitously, the diver should stop,
think, attempt to breathe, and, if it is possible to do so,
proceed with a normal ascent. Students should be taught
that many out-of-air situations are related to the diver
or the situation rather than to the equipment or actual
loss of air supply. If considered before resorting to
emergency procedures, the human aspects of apparent
air loss situations often can be corrected (Kent 1979).
If a diver determines that his or her air supply is
depleted, experts recommend that the diver initiate an
independent action such as a controlled emergency
ascent or use of an alternative personal breathing appara-
tus (when feasible) (Egstrom 1984). If it is not possible
to institute an independent response, a dependent action
(e.g., buddy breathing, alternate stage breathing, breath-
ing from an inflated buoyancy compensator (BC), use
of an auxiliary scuba cylinder) should be considered.
As a last resort, an emergency buoyant ascent may be
necessary.
It has been found that breathing from an inflated or
partially inflated BC is a safe practice in an emergency
situation if proper procedures are followed (Pierce
1983, Bove 1985). If this technique is used, it is essen-
tial that the bag be flexible and be prevented from
becoming overinflated as the diver ascends. If the bag
loses its flexibility as a result of overinflation, it can
NOAA Diving Manual — October 1991
Accident Management and Emergency Procedures
Table 19-1
Summary of Probable Causes of Non-Occupational
Diving Fatalities from 1976-1984
Probable Cause
of Accident
1976
1977
1978
1979
1980
1981
1982
1983
1984
Total
Medical condition
or injury
Environmental
condition
Equipment
Unknown
49 (33)
45(31)
14(10)
39 (26)
51 (50)
19(19)
19(19)
13(12)
45 (39)
26 (22)
22(19)
23 (20)
62 (44)
29(21)
19(14)
29(21)
54 (49)
28 (26)
14(13)
13(12)
27 (26)
43 (42)
9(9)
24 (23)
33 (44)
16(22)
8(11)
17(23)
47 (43)
33 (30)
6(5)
24 (22)
25 (36)
16 (23)
3(4)
26 (37)
393(41)
255 (26)
114(12)
208(21)
Total
147
102
116
139
109
103
74
110
70
970
Values in parentheses are
percentage of all scuba fatalities reported for the year.
Derived from McAniff (1986)
cause a lung overpressure accident by forcing too much
air into the lungs on inhalation or by causing an exces-
sive rate of ascent. Inhaling water while using the BC
mouthpiece can be avoided by proper purging. Divers
can rebreathe exhaled air safely for as long as one full
minute without incurring any adverse physiological
effects (Bove 1985).
Many divers choose to equip their scuba cylinders
with two second-stage hoses with regulators (octopus)
to use for emergency buddy breathing or in case the
primary regulator fails. The use of an octopus is con-
sidered one of the more desirable options in out-of-air
situations and is recommended by the major sport div-
ing training agencies (Graver 1985). If this technique
is used, the octopus hose should be at least 12 inches
(30.5 centimeters) longer than the primary hose, be
marked for easy identification, and be oriented so that
it will always be right side up when used. When using
an octopus system, the distressed diver should notify
the buddy that air is needed and should then proceed to
breathe from the extra regulator. Since the air supply
of the buddy also is likely to be low, ascent should
begin immediately after a brief stabilization period.
Two persons breathing from a tank with a low air
volume through a single first stage can quickly deplete
the air supply. Also, in cold water, the extra flow may
cause the regulator to freeze. The divers should main-
tain physical contact by holding onto each other's straps.
Auxiliary scuba cylinders attached to the primary
cylinder can be used as an emergency air source, and
their use is recommended in some cases (Graver 1987).
Such cylinders can be obtained in sizes ranging from
1.7 to 15 cubic feet (0.05 to 0.4 cubic meter) and
normally are used with a separate regulator. They are
designed as an emergency system only. For example, a
October 1991 — NOAA Diving Manual
4 cubic foot (0.11 cubic meter) cylinder provides about
14 to 16 breaths at a depth of 100 feet (30.5 meters)
and about 80 breaths in shallow water (Anonymous
1984).
If loss of air is sudden and unexpected and no auxil-
iary air sources are available, buddy breathing utiliz-
ing a single regulator may be necessary. Often, the
distressed diver will begin to cough or choke. Until the
diver's condition has stabilized, both the diver and
buddy should maintain their depth while continuing to
buddy breathe. Air donors should allow the victim to
use their air supply as much as is possible without
jeopardizing their own supply. When the distressed
diver's condition has stabilized, a safer ascent can be
made.
If it is necessary to remove the distressed diver's
equipment, the ascent should be stopped while the
equipment is removed. Because equipment removal
will distract the diver and interrupt the breathing pat-
tern, increasing the possibility of gas embolism, this
step should only be undertaken when absolutely essen-
tial. Every effort should be made to maintain an ascent
rate no greater than 60 feet (18.3 meters) per minute.
The most efficient method of buddy breathing is for
the two divers to face each other, each alternately
breathing from the same mouthpiece while ascending
(Figure 19-1). During the exchange of the mouthpiece,
the exhaust valve on single-hose regulators must be
positioned below the mouthpiece so that water can be
eliminated from the second stage; this position can be
achieved conveniently if the divers are side by side,
with the diver in distress on the left. The donor controls
the air, and both divers must exhale between exchanges.
Contact should be maintained by having each diver
hold the straps or belt of the other diver.
19-5
Section 19
Figure 19-1
Buddy Breathing
Source: NO A A (1979)
WARNING
During Buddy Breathing, One Diver Should
Be Breathing From the Regulator While the
Other Diver Is Exhaling
When using constant-volume dry suits or large buoy-
ancy compensators, extra precautions should be taken
to prevent uncontrolled ascent caused by air expansion
of the suit as the diver rises in the water column. For
example, the normal procedure of dropping the weight
belt should not be followed when a constant-volume
dry suit is used unless the suit is flooded. During ascent,
the amount of air in the dry suit or partially inflated
19-6
buoyancy compensator should be controlled by the
exhaust valves or use of another venting method such
as opening a cuff.
If it is necessary to cover a horizontal distance while
buddy breathing, a number of different methods can
be used. The two most common are for the divers to
swim side by side (about halfway on their sides), facing
each other, or to swim one above the other, the diver
with the good air supply on the bottom. In this manner,
the mouthpiece can easily be passed back and forth
between divers.
WARNING
When One Diver Runs Out of Air, the Buddy's
Supply Is Also Usually Very Low. With Dou-
ble Consumption, the Available Air Can Be
Depleted in Seconds. Buddy Breathing Ascent
Should Therefore Be Prompt
If buddy breathing is not possible, the diver can
make an emergency buoyant ascent to the surface while
venting air continuously. Unless the breathing apparatus
is entangled, however, a diver should not abandon it.
The reduction of ambient pressure as the diver rises to
the surface increases the pressure differential, provid-
ing additional air for breathing from the scuba and
allowing the diver to make a controlled ascent. Trying
to breathe by sucking on the regulator or swallowing
may decrease the urge to breathe during ascent, but
divers should remember not to hold their breaths while
employing these tactics.
WARNING
Emergency Buoyant Ascents Are Difficult and
Hazardous and Should Be Used Only as a
Last Resort to Resolve an Emergency Situation
When using constant-volume dry suits or large buoy-
ancy compensators, extra caution should be taken to
prevent uncontrolled ascent. Spreading the arms and
legs increases drag and stability and slows the rate of
ascent. The diver must continue to exhale throughout
the ascent. The head should be extended back, allowing
maximal opening of the throat and a good overhead
view. The diver should swim to the surface, staying
constantly aware of possible entanglements or obstruc-
tions and the consequences of breath-holding. The
mouthpiece should be left in place.
NOAA Diving Manual — October 1991
Accident Management and Emergency Procedures
WARNING
If the Diver Is Having Difficulty Ascending,
the Weight Belt Should Be Released Imme-
diately. Make Sure No Divers Are Below Before
Dropping the Belt
At night or when visibility is low, the diver should
exert extra care to hold his or her hand over the head
during ascent to prevent it from hitting a boat or some
other object on the way up.
WARNING
Discarding Self-Contained Equipment and
Making a Free Ascent Should Be Considered
Only as a Last Resort. When This Procedure
Must Be Used, Exhale All the Way to the
Surface (see Section 3.2.2)
Regardless of the out-of-air emergency response
system used, certain criteria should be met. Egstrom
(1984) has listed the essential ones:
• the procedure should be standardized;
• it should be simple;
• it should require only a minimal amount of skill to
implement;
• it should be reliable and effective;
• it should involve a minimum amount of retraining;
• it should not be expensive.
All of these emergency techniques require learning of
skills and must be practiced to the point of overlearning.
For example, a study conducted by the staff of the
University of California, Los Angeles, Diving Safety
Research Project found that students who had prac-
ticed buddy breathing on 17-21 successful trials were
able to perform without errors (Egstrom 1984). Prac-
tice while swimming was more effective than practic-
ing while sitting on the bottom of the pool. When
diving with a familiar partner and equipment, buddy
breathing should be practiced periodically. This is even
more important when either the partner or the equip-
ment is unfamiliar. (For additional information on
ascents, see Section 19.5.2.)
19.2.2 Loss or Flooding of Equipment
Flooding of a face mask may be caused by another
diver inadvertently kicking the mask loose with a fin,
by high currents, or by turning the head into a rock,
October 1991 — NO A A Diving Manual
net, or other obstruction. The mask can be cleared by
tilting the head back, pressing the top of the mask
against the forehead, and blowing into the mask through
the nose (Figure 19-2). The air will displace the water,
forcing it out the bottom of the mask. When the mask is
equipped with a purge valve, the diver should position
his or her head so that the purge valve is in the lowest
position relative to the mask, hold the mask against the
face, and then exhale through his or her nose. If the
mask is lost, divers should fix their position, wave one
hand over their heads, and have their partner come to
them.
When the second stage of the regulator is lost, the
hose generally remains lying over the diver's right
shoulder. If it is not, it can be located by reaching back
over the right shoulder with the right hand, grasping
the first stage of the regulator at the tank's valve to
locate the hose where it joins the first stage, and then
following the hose out to the mouthpiece. The mouth-
piece probably will be flooded, but it can be cleared by
a sharp exhalation or by pushing the purge button.
With a double-hose regulator, the mouthpiece and
hose will float above the diver's head. One method of
recovery is for the diver to roll onto his or her back. The
hose and mouthpiece will then float above the diver's
face. When the mouthpiece of a double-hose regulator
is above the level of the regulator, it will free flow. The
hose and mouthpiece can be cleared of water by hold-
ing the mouthpiece above the head. If the exhaust hose
is flooded, it can be cleared after the mouthpiece is
back in the mouth by exhaling or rolling over on the
left side, which allows the water to flow the length of
the exhaust hose and be forced out the air exhaust
valve. If a double-hose regulator is to be used, the
diver should practice clearing it.
19.2.3 Fouling and Entanglement
When a diver becomes trapped, entangled, or fouled, it
is important to make a calm assessment of the situa-
tion. Struggling generally results in even deeper entan-
glement and damage to, or loss of, diving equipment.
Scuba divers should be more concerned about entan-
glement than other types of divers, because their air
supply is limited and communication with the surface
usually is not possible. Maintaining a cool head, using
common sense, the presence of a nearby buddy diver,
and use of a diving knife usually suffice to gain free-
dom from entanglement. Emergency free ascent should
be used only as a last resort. When the dive is in the
surface-supplied mode, the diver should notify sur-
face personnel as soon as the entanglement occurs. If
the diver cannot become untangled promptly, the assis-
tance of a standby diver should be requested.
19-7
Section 19
Figure 19-2
Clearing a Face Mask
Source: NOAA Office of Undersea Research
19.2.4 Near Drowning
The most common antecedent to drowning is panic,
which occurs when divers find themselves in a position
for which they are mentally or physically unprepared.
The majority of drownings can be avoided if the diver
is trained properly, is in good physical condition, and is
using reliable, well-maintained equipment.
The most important step in the immediate treatment
of a near-drowning victim is to restore breathing (see
Section 18.1.5). The most effective means of artifi-
cial resuscitation (when used by trained personnel) is a
mechanical resuscitator. If one is not available, artifi-
cial resuscitation is required; the most effective form
is mouth-to-mouth resuscitation. This method is sim-
ple and can be administered to a victim still in the
water (see Section 19.5.1). Victims of near drowning
in water at a temperature of less than 70 °F (21 °C)
may appear to be dead and yet have a significant
chance of survival if cardiopulmonary resuscitation is
started immediately. Recovery has occurred even after
submersion in cold water for periods of up to 40 min-
utes (see Section 18.1.5). The chances of recovering
increase if the victim is young and the water is cold.
19.3 ASSESSING A PROBLEM
Obvious indicators of diver distress that most swimmers
and rescuers recognize easily include cries for help,
arm or whistle signals (see Section 14.2), an actively
struggling diver, or one who appears ill or unconscious.
Because scuba divers should always dive in pairs, find-
19-8
ing one drowned or distressed diver may mean that the
buddy has also succumbed or is in distress. In some
cases, there is no forewarning of serious trouble. For
example, an exhausted diver may simply slip quietly
and suddenly beneath the surface without a sound.
Indications of anxiety or difficulty may be suppressed
either because of ego (unwillingness to admit having a
problem) or may actually be hidden by the face mask
or other diving equipment. As discussed earlier, high
treading, clinging, clambering, and removing equip-
ment are all signs of impending trouble.
Regardless of how the rescuer becomes aware that a
diver is in distress or whether the emergency occurs on
the surface or under water, the first step is a rapid but
thorough assessment of the situation. Factors that should
be considered at the outset are location and distance to
the victim, ability to establish and maintain visual
contact, and the availability of additional assistance
(personnel and equipment). It is not advisable even for
a trained rescuer to attempt to rescue a diver without
taking the appropriate equipment. For example, res-
cue in the surf should not be made without fins. Dive
boats usually have readily accessible life-saving floats,
seat cushions, and ring-buoys that can be thrown.
There may also be surf boards, floats, buoys, and res-
cue boards on the beach. Rescuers should assess their
own ability to carry out a rescue. The rescue hierarchy
is reach-throw-row-go, i.e., the first choice of strat-
egy should be to reach the victim by boat or other
means, followed by throwing a lifeline or ring buoy,
and so on to the last step, which involves a rescuer
NOAA Diving Manual — October 1991
Accident Management and Emergency Procedures
going to the aid of the victim in the water. If more than
one person is in a group, the individual or individuals
most suited to perform a rescue should be selected
immediately, while others are assigned to stay with the
boat, use the radio, obtain flotation equipment, and
perform other necessary tasks, which are particularly
important if there are adverse environmental condi-
tions, such as poor visibility, high currents, or poor
surface conditions. If the victim is under water, over-
head obstructions may further complicate the situation.
As the victim is approached, the rescuer should try
to determine the nature of the problem — whether the
problem is caused by entanglement, a strong current, a
rough sea, or some other environmental factor. Other
possible causes of distress include nausea, decompres-
sion sickness, embolism, contact with a poisonous marine
animal, or equipment problems. Being familiar with
the victim's equipment is an important part of the
overall assessment. If the weight belt is to be released,
care must be taken to ensure that it falls clear of both
the victim and the rescuer and that the waist strap of
the backpack is not confused with the weight belt.
shore. For example, returning the victim to the starting
point of the dive may not be the best procedure because
other locations may be more accessible, have essential
lifesaving equipment, or be more suitable for ad-
ministering first aid.
19.4 APPROACHING A VICTIM
The approach is defined as those events taking place
between the time the rescuer initiates action and phys-
ical contact is established with the victim. One of the
first decisions to be made is whether or not a swimming
rescue is necessary. An extension rescue, one involving
lines, poles, ring buoys, or rescue throw bags, is usually
safer and more desirable. Rescue throw bags, which
provide a 60 to 70 foot (18.3 to 21.3 meter) 'extension'
of the rescuer's arm, are now accepted pieces of rescue
equipment. If two rescuers are involved, one can attempt
an extension rescue while the other initiates a swim-
ming rescue. Situations requiring a swimming rescue
include those involving a submerged victim, a victim
unable to respond adequately to verbal instructions, or
a victim losing the battle to stay afloat.
WARNING
Divers Experiencing Stress at the Surface
Should Drop the Weight Belt Immediately to
Ensure That They Will Float Sufficiently High
in the Water
NOTE
Water safety authorities strongly advocate
that the rescuer avoid coming into phys-
ical contact with an unstabilized victim,
if possible.
The rescuer should note immediately the location of
the C02 inflator for the buoyancy compensator and
activate the appropriate mechanism or begin oral infla-
tion. Many BC's available on the market do not have
C02 inflators, although these can be purchased separately
and installed. If it is necessary to ditch the backpack,
most systems require the release of both the waist belt
and at least one shoulder strap.
Of primary importance is the state of the victim. If
unconscious and under water, the victim must be brought
to the surface quickly. If unconscious and on the sur-
face, the method of handling will differ from that of a
conscious victim. If the victim is conscious, the rescuer
must assess the victim's mental state and then proceed
in a manner that does not increase the victim's pain,
induce panic, or complicate existing injuries or the
rescue process. Finally, the rescuer must assess the
victim's state of buoyancy. If the victim is not positive,
the rescuer should take immediate action to establish
positive buoyancy. An additional factor that must be
assessed is the method of transporting the victim to
In all cases of a swimming rescue, the rescuer should
continue trying to enlist help as long as possible. The
victim should be observed continuously at all times
because the victim may sink, become unconscious,
become panicky, or stop breathing. When a rescuer is
approaching a submerged victim, especially in water
with poor visibility, two observers stationed at fixed
points (boat or shore) pointing at the place of the
victim's submergence provide a bearing for the rescuer.
If the victim is conscious and on the surface, the
rescuer should explain what is going to happen and
make every effort to calm the victim. If the victim is
submerged and conscious, conventional hand signals
should be used and the rescuer should demonstrate
exactly what the victim is expected to do. Positive
buoyancy should be established for the victim imme-
diately. If the victim's equipment is to be ditched, it is
recommended that it be handed to the rescuer rather
than dropped, because this makes it more likely that it
will fall clear of the body. Depending on the situation,
rescuers also may have to remove their own equipment,
October 1991 — NOAA Diving Manual
19-9
Section 19
such as the tank or weight belt, to facilitate the rescue.
Upon reaching the victim, the rescuer should pause
momentarily to reasses the situation and to rest briefly
before establishing physical contact.
19.5 RESCUE PROCEDURES
Although certain rescue procedures should be consid-
ered standard, the trained rescuer must still use com-
mon sense because no two emergencies are identical.
The following procedures are not intended to be an
exhaustive treatment of scuba lifesaving techniques
but rather to alert the reader to these rescue proce-
dures. (For further information, the reader is referred
to Seiff 1985, Pierce 1985, Somers 1986, Anonymous
1986.)
When attempting any of the rescue procedures
described in the following paragraphs, the diver should be
careful not to become entrapped by the victim or the
result may be a double casualty. The first concern of
rescuers when they are seized by a struggling victim
must be for their own safety. One way to escape from a
victim's grasp is to inflate the victim's or the rescuer's
buoyancy system, which will push the divers apart.
19.5.1 Victim Submerged and Unconscious
An unconscious, unbreathing victim, whether sub-
merged or at the surface, is in imminent danger of
death. Virtually all of the rescuer's efforts must be
directed at initiating and maintaining artificial resus-
citation. Since resuscitation cannot be administered
under water, the first consideration of the rescuer should
be to get the victim to the surface.
WARNING
No Resuscitative Efforts Should Be Attempted
While Submerged
The rescuer should establish positive buoyancy as
soon as possible and bring the victim to the surface in a
controlled buoyant ascent. The rescuer should approach
the victim and remove the weight belt. If this is not
possible, the BC should be inflated to achieve a slight
positive buoyancy. Rescuers may need to remove their
own weight belts and adjust their BC's to ensure that
they are not more buoyant than the victim. As described
in Seiff (1985), the victim should then be placed in a
left-sided do-si-do position with the head tilted back
and be brought to the surface at a normal rate of ascent.
In this position, expanding gases in the victim's lungs
should escape without difficulty. The do-si-do is a
swimming carry that affords the rescuer maximum
mobility while controlling the victim (see Figure 19-3).
The left upper arms are interlocked so that the rescuer
can increase his or her control over the victim by
squeezing the victim's arm between the rescuer's arm
and chest. The rescuer always should be on the left side
of the victim to facilitate control of the power inflator
hoses on both the victim's and rescuer's BC's.
WARNING
Rescuers Should Be Careful Not to Risk Embo-
lism or Decompression Sickness by Ascend-
ing Too Fast With An Unconscious Victim
Once the unconscious diver is on the surface (weight
belt already removed, buoyancy compensator inflated,
and mask off) and it has been determined that there is
no breathing, the rescuer should be positioned for mouth-
to-mouth artificial resuscitation. Based on in-water
tests, it is recommended that the rescuer's mask be left
on to retain optimal visual capabilities (Orr 1981).
Removal of the victim's mask may be enough to start
the victim breathing again. The best method for con-
trolling the victim's position in the water while per-
forming mouth-to-mouth resuscitation is the do-si-
do position, shown in Figure 19-3.
The procedure for in-water mouth-to-mouth arti-
ficial resuscitation is:
• With the victim in a face-up position, slide your
arm between the body and the same arm of the
victim (see Figure 19-3). Remain on the victim's
left side for ease of controlling BC power inflators.
• Reach back, grasp the victim's hair, hood, or buoy-
ancy compensator, and pull back to place the vic-
tim in a level position and to drop his or her head to
open the airway.
• Place the heel of your other hand on the victim's
forehead and seal the nose with your thumb and
forefinger (see Figure 19-4).
• Seal your mouth over the victim's mouth and give
two slow, deep inflations to re-establish an ade-
quate oxygen level. Do not pull yourself up over
the victim to start resuscitation; this will tend to
force the victim's head under water. Instead, sim-
ply roll the victim's head over to a position that
allows you to seal the victim's mouth with yours
19-10
NOAA Diving Manual — October 1991
Accident Management and Emergency Procedures
Figure 19-3
Do-Si-Do Position for Administering In-Water
Mouth-to-Mouth Artificial Resuscitation
Source: NOAA Office of Undersea Research
with a minimum amount of kicking effort on your
part.
• If there is resistance to lung inflation, pull the
victim's head back further and try again. If this
does not work, check the airway for blockage. If a
foreign object or vomit is present, remove the
obstruction quickly with your fingers before continu-
ing attempts to inflate the victim's lungs.
• After successfully completing the two inflations,
continue ventilating the victim's lungs at approx-
imately 12 breaths per minute. The ventilation
rate is not as important as filling the victim's lungs
with each breath.
Sea conditions may override a controlled ventilation
rate and require that the rate be modified to meet the
October 1991 — NOAA Diving Manual
sea's rhythm. This is accomplished by timing the ventila-
tions to occur when the waves are washing over the
victim's face. While continuing to resuscitate the vic-
tim, the rescuer should start swimming toward the
beach or boat at a comfortable pace. The rescuer should
be careful not to overexert during the rescue attempt.
If it is necessary to use one arm for swimming, the
rescuer can achieve a nose seal by pressing his or her
cheek against the victim's nose. If two rescuers are
present, one should be stationed at the head and one at
the feet. The rescuer at the head is in charge. If three
rescuers are available, two should be at the head and
one at the feet (to push). The tank, BC, and weight belt
(if still attached) should be removed from both victim
and rescuers prior to bringing the victim on board a
vessel or on shore.
19-11
Section 19
Figure 19-4
Mouth-to-Mouth In-Water Artificial Resuscitation
Derived from photo by Dan Orr, Wright State University
NOTE
A single rescuer should angle the kick down-
ward and toward the victim's feet, which not
only provides some momentum toward shore
or a boat but also tends to keep the faces of
both rescuer and victim out of the water.
Care must be taken not to overinflate the
buoyancy compensators because the bulk
created may prevent the rescuer from get-
ting close enough to permit good mouth-to-
mouth contact.
Mouth-to-mouth resuscitation requires no equipment
and can be started immediately but is difficult to sus-
tain for any period, especially in rough water. In addi-
tion, because the victim's mouth is open during exhala-
tion, water may enter the victim's mouth.
A somewhat more energy-conserving method of per-
forming artificial resuscitation in the water is mouth-
to-snorkel artificial resuscitation (Figure 19-5). Using
the snorkel to resuscitate the victim allows the rescuer
to be positioned lower in the water, reducing the amount
of kicking effort required to keep the head above water.
To perform mouth-to-snorkel artificial resuscitation
effectively, training is essential and continued prac-
tice is recommended. General procedures for admin-
istering mouth-to-snorkel artificial resuscitation are
as follows:
• After the victim has been brought to the surface,
administer two slow inflations, using mouth-to-
mouth artificial resuscitation.
• Bend the snorkel and place it in the victim's mouth,
keeping it between the middle and ring fingers as
shown in Figure 19-5 A. Make sure it is pressed
down tightly around the flange. Seal the nose with
the thumb and forefinger of the same hand, as
shown in Figure 19-5B. It is not necessary to pinch
the victim's nose, since the side of the rescuer's
index finger will make the seal if pushed against
the victim's nostrils. The best mouth seal can be
made if the snorkel is inserted between the vic-
tim's lips and teeth. This may not be easy to do and
time should not be wasted in the attempt because
an adequate seal may be made by pressing the
flange tightly over the outside of the lips.
• Place the victim in the standard chin-pull position
with the head against the rescuer's chest, as shown
in Figure 19-6.
• Place the tube end of the snorkel in your mouth
and blow. It is necessary to blow longer than with
19-12
NOAA Diving Manual — October 1991
Accident Management and Emergency Procedures
Figure 19-5
Mouth-to-Snorkel Artificial Resuscitation
A. Bending the snorkel and placing it in the victim's mouth
B. Getting a seal
October 1991 — NOAA Diving Manual
Reprinted from Scuba Life Saving, pub. Royal Life Saving Society,
Canada, 1987
19-13
Section 19
Figure 19-6
Towing Position for
Mouth-to-Snorkel Artificial Resuscitation
Source: NOAA Office of Undersea Research
mouth-to-mouth resuscitation to overcome the
dead air space in the snorkel.
• After filling the victim's lungs, remove the tube
end from your mouth and allow the victim's air to
escape through the tube. Although the chest cannot
be seen to rise and fall, the rescuer can hear the air
passing through the tube or feel it on the cheek.
• Continue to check to ensure that an adequate seal
is maintained. A perfect seal is not essential, but
an effort should be made to minimize escaping air.
• The victim should be checked continually to ensure
that there is no choking or vomiting.
• Continue to ventilate the victim's lungs during the
tow to the beach or boat. The victim's lungs should
be filled with each breath to ensure that fresh air,
rather than stale, is being provided. If the rescuer
begins to feel dizzy because of hyperventilation,
the rate can be slowed down.
Some snorkels work better than others because of
shape, corrugations, or flexibility. Divers should check
their snorkels and practice the procedures described
above. Further details of in-water artificial resuscita-
tion are described elsewhere (Smith and Allen 1978;
Pierce 1977, 1985).
If the submerged victim is unconscious but still breath-
ing, the rescuer should hold the victim's mouthpiece in
19-14
place to ensure a good seal, achieve positive buoyancy,
and proceed with a controlled buoyant ascent to the
surface. The victim should be kept in a vertical posi-
tion with the head in a normal, straight forward, but
not hyperextended attitude.
19.5.2 Victim Submerged and Conscious
An assessment of the condition of a submerged vic-
tim may reveal any one of a variety of situations, each
requiring a different form of contact and handling.
When approaching a conscious submerged victim, eye
contact should be established immediately and the
victim should be signaled to stop swimming and hold
onto a solid object, if one is available.
If both the victim and the rescuer are suspended in
the water column, the rescuer should immediately neu-
tralize the victim's buoyancy and drop the victim's
weight belt or neutralize the buoyancy by appropriate
means if the victim is wearing a dry suit or variable-
volume wet suit. The rescuer should then neutralize his
or her own buoyancy. When making physical contact
with the victim, the rescuer should be alert for sudden
grasping motions or rapid ascents; initially the rescuer
should offer a hand only. If at all possible, only highly
trained divers should attempt a mid-water rescue.
NOAA Diving Manual — October 1991
Accident Management and Emergency Procedures
Stabilizing the victim may be enough to rectify the
problem, assuming that the anxiety or distress was not
caused by a problem such as entanglement or injury.
Attempts to ascend with the victim before stabiliza-
tion are not advised because the situation may con-
tinue to deteriorate uncontrollably. After stabilization,
the rescuer should, in almost all cases, signal and initi-
ate a controlled ascent while maintaining both eye and
physical contact with the distressed diver. If, after
reaching the surface, the victim still shows signs of
anxiety or stress, the dive should be terminated. If the
submerged victim is entangled, the first action of the
rescuer is to provide a source of air (if needed), calm
the victim, and tell the victim what will be done next.
Knives or other tools should be used with great caution
and the rescuer should remain alert for renewed strug-
gling on the part of the victim during disentanglement.
Except in cases of a minor snag, the victim and buddy
should return to the surface and at least temporarily
terminate the dive. Reassessment of both victim and
equipment should be made on shore or support vessel.
An injured or ill diver should be taken to the surface
at a reasonable rate of ascent, with care taken to main-
tain breathing. Depending on the severity of the injury
or illness, the victim may have to be assisted by buoy-
ancy control or propulsion during ascent. The ascent
should be interrupted only if breathing is impaired by
vomiting or other aspects of the injury or illness and
should be continued as soon as breathing has been
restored. Limited first aid or treatment of a particu-
larly serious injury, e.g., hand pressure on a severe
laceration, can be performed during ascent, but should
not be allowed to interfere with the victim's breathing
or with continuing ascent. In an injury involving seri-
ous bleeding, the rescuer should stay alert for preda-
tors in the water both during the ascent and after
surfacing.
An uncontrolled descent caused by loss of buoyancy
can create problems for the diver and rescuer even in
relatively shallow waters, because of the danger of
barotrauma or impact with bottom features. Uncon-
trolled descents in deep water may be complicated by
nitrogen narcosis and can involve very serious prob-
lems of oxygen poisoning, rapid air consumption, and
subsequent drowning. In this situation, a rescuer must
quickly assess the risk and make a decision. In shallow
water, for example, it may not seem prudent to risk ear
squeeze to rescue a diver who is certain to come to rest
on a shallow bottom and who will almost certainly be
able to be rescued by a conservative rescue procedure.
A diver descending uncontrollably in very deep water,
however, presents a serious dilemma for the would-be
rescuer. Variables to be quickly assessed include not
only the victim's situation, but the potential rescuer's
capabilities, air supply, susceptibility to narcosis, and
so forth. Only a rescuer can make this personal deci-
sion. A wrong decision can mean the loss of two divers
instead of one.
In such situations, the possibility of a rescue without
physical contact should not be overlooked. An attempt
should be made to get the descending diver's attention
by banging on a tank or possibly even dropping an
object past the descending diver's line of vision. Then,
the diver can be motioned to the surface if the problem
has simply been a lack of attention or concern. Visual
contact serves at least to arrest the victim's descent
long enough for a pursuing rescuer to reach that depth.
If pursuit of a descending diver is successful, the
first contact should almost always be made from behind
the victim. This permits grasping the tank valve of a
diver dropping in a vertical feet-first position or in a
horizontal plane. A diver dropping in a head-first position
should first be grasped by the fin(s) to retard descent
and to arrest any propulsive action. In such cases, the
rescuer should quickly "climb" down the descending
diver to grasp the tank valve. In situations where nar-
cosis may be a factor for either party, the rescuer
should remain behind the victim while arresting the
descent and initiating ascent. Before establishing con-
tact with the victim and inflating the victim's buoy-
ancy device, the rescuer should establish his or her own
buoyancy. This ensures the safety of the rescuer and
permits the rescuer to use his or her own oral inflator
to add additional buoyancy rather than attempting to
use the victim's inflation device.
If a descending victim is struggling or appears oth-
erwise to be irrational, a rescuer should remain above
and behind the victim to ensure his or her own safety.
Divers not directly involved in handling the victim of
uncontrolled descent should be sensitive to both the
decompression and air supply needs of the victim and
rescuer. They can pre-position additional scuba equip-
ment or obtain other resources that might be necessary.
An uncontrolled ascent may be caused by a loss of
buoyancy control or panic. Although rescue of such a
victim requires an extremely rapid response, rescuers
must first ensure that their own ventilation will be
adequate during the rescue. The rescuer also should be
aware of the fact that a rapidly ascending individual
may be making a calculated emergency swimming ascent.
"Rescuing" such a diver may create more problems
than it solves.
Where obvious breath-holding is a factor, the main
rescue objective is to arrest the ascent quickly. The
rescuer should grab the most accessible part of the
victim, which, on a rapidly ascending individual, may
October 1991 — NOAA Diving Manual
19-15
Section 19
be the fins. This will serve not only to maintain contact
but also will arrest the propulsive motion. The rescuer
should shift the grasp immediately to the victim's ankle or
leg because the victim could easily swim right out of
his or her fins.
Victims not overly buoyant may be stopped simply
by physical contact with a slightly negatively buoyant
rescuer. As soon as possible in a rescue procedure, the
rescuer should establish a position above the ascend-
ing victim. The most effective position is face to face,
maintained by keeping a grip on the victim's buoyancy
compensator. Eye contact can be established and the
rescuer's other hand should be used to vent the victim's
buoyancy compensator. Panicky ascending victims often
claw desperately, and a rescuer must be alert to the
possibility of losing his or her own mask or regulator
during contact with a desperate victim.
During attempts to arrest uncontrolled ascent in
deep water, the rescuer also must recognize that an
ascent that initially is non-buoyant may become buoyant
near the surface because of expanding air in the buoy-
ancy compensators of both the victim and the rescuer.
Attempts to use signals, demonstrations, and if neces-
sary squeezes, pushes, or other, more vigorous thoracic
pressures directed at the diaphragm should be made to
make the victim exhale during uncontrolled ascent.
Applying steady pressure may be safer and more effective
than using a jab or punch.
19.5.3 Victim on the Surface and Unconscious
When confronted with an unconscious victim on the
surface, speed is of the utmost importance. A surface
approach is recommended because it affords continu-
ous eye contact with the victim. Although some degree
of positive buoyancy on the part of the victim may be
assumed, many buoyancy compensators currently in
use do not ensure that the face of a helpless victim will
be maintained out of the water.
When approaching the victim, the rescuer should
have positive buoyancy and the BC should be inflated
as needed. The victim should be pulled to the face-up
position and the weights and scuba tank dropped. It
may be necessary for the rescuer to drop his or her
weights and tank, also. If the equipment is not dropped
at the outset, the rescuer may forget to do so, thus
making the rescue much more hazardous. While
maintaining contact, the victim should be placed in a
left-sided do-si-do position (see Figure 19-3). Mouth-
to-mouth resuscitation should be started as soon as
possible and continued at the rate of one breath every
5 seconds while the victim is being transported to the
dive platform or shore.
NOTE
At the present time, the administration of
in-water cardiopulmonary resuscitation is
not recommended (Kizer 1984). Its effective-
ness, even in swimming pool conditions, has
not been demonstrated successfully and to
attempt it in the open water will delay get-
ting the victim to a place where it could be
administered properly.
19.5.4 Victim on the Surface and Conscious
When approaching a conscious victim on the sur-
face, every effort should be made to utilize an exten-
sion rescue technique and to obtain help, as described
in Section 19.4. The rescuer also must carefully assess
the victim's mental state. If the victim is rational
and coherent and no alternative rescue technique is
available, the approach should probably be made from
the front and on the surface, because this approach
allows continuous eye contact and reassures the victim
because it allows him or her to observe the rescuer's
actions.
NOTE
If possible, get the victim to initiate self-
rescue by weight belt ditching or inflating
the buoyancy compensator. Use guile if nec-
essary, e.g., say "Hand me your weights."
If the victim is panicky or struggling, a different
approach is required. One technique requires the res-
cuer to approach the victim from the front and while
submerged. This is generally a safe method because
the victim will be extremely reluctant to go under
water. Another technique involves a surface approach
from the rear of the victim. Some prefer this approach
because an unexpected wave or rescuer buoyancy prob-
lem is unlikely to bring the rescuer within the grasp of
the victim. An approach from the rear facilitates the
rescuer's grabbing the victim's tank valve, permits the
rescuer to reach and activate the buoyancy device, to
release the weight belt, and to disconnect the low-
pressure inflator hose going to the buoyancy compen-
sator. The rescuer also is in good towing position and
can release the tank from the backpack, if necessary.
However, it is better not to surprise a victim and in
most instances the rescuer will be seen or heard even
when approaching from the rear. Thus, the rear approach
frequently will become a frontal approach because the
victim will turn to face the rescuer.
19-16
NOAA Diving Manual — October 1991
Accident Management and Emergency Procedures
Once physical contact has been made between the
victim and the rescuer, the first action of the rescuer
should be establishing victim buoyancy by releasing
the victim's weight belt and inflating the buoyancy
compensator. When releasing the weight belt, care
must be taken not to mistake the tank strap for the belt
release mechanism and to ensure that the weight belt
does not become entangled with other equipment in the
drop path.
It is important for the rescuer to be aware of the
head position of the victim. It is natural for an anxious
or frightened diver to lift his or her head from the
water. Because the head is heavy (it weighs about
17 pounds (7.7 kilograms)), it takes a significant effort
on the part of the diver to raise it and keep it out of the
water. Therefore, if the rescuer can induce the victim
to keep the head in the water, the rescue effort will be
simplified. Even without using a snorkel or regulator,
the rescuer should keep the victim in a head-back
position with the nose and mouth clear of the water,
because most people can float with little effort if the
head is partially or completely submerged.
Once buoyancy and contact have been established,
the rescuer may consider removing the victim's mask.
This will facilitate breathing, ease some of the psycho-
logical stress, and improve eye contact. If the victim is
calm, however, the mask can be left on to keep water
out of the nose. Generally, it is desirable to remove the
backpack and tank to facilitate towing; it is essential
to do so when an unassisted long tow is anticipated, if
the tow will require passing through kelp, or if exit
from the water must be made through surf or rocks.
Throughout the process of equipment removal, the
procedures followed should be explained and the assis-
tance of the victim obtained, if possible.
19.5.5 Towing a Victim in the Water
After the victim has been stabilized at the surface,
the cause of the original incident may still be present.
The victim should be checked immediately to see that
the face is not in the water, the mask is not pulled down
over the mouth, and the airway is clear. The regulator
(if functioning properly) may need to be restored to the
victim's mouth. In calm water, it may be useful to
leave a snorkel in the victim's mouth; however, if the
victim is being towed on his or her back, water may
enter the snorkel and mouth. The victim is then ready
to be transported to a boat, to shore, or to some other
type of stable platform.
Towing a victim should not be attempted if the vic-
tim is panicky or struggling, or if the safety of the
rescuer is otherwise jeopardized. If the victim is con-
scious and breathing and help is on the way, the res-
cuer should wait until it arrives before beginning to
tow. Distance, chop, swells, current, surf, kelp, and the
strength of the rescuer all should be considered.
To tow a victim effectively, the rescuer must remain
mobile, which may require the removal of equipment
such as the tank or weight belt. The victim's body
should be in a position (usually on the back) that will
not impede the tow. If the victim does not have a
functioning regulator, the face must be out of water,
which can best be accomplished by having the buoy-
ancy compensator inflated enough to keep the face out
of water.
The rescuer should use a towing technique that allows
the victim to be observed. If possible, the rescuer
should maintain eye contact with a conscious victim.
Towing with a Line
Whenever possible, a towline or rescue throw bag
(see Section 19.4) should be used because it is less
fatiguing for the rescuer, reduces the need to ditch
equipment, and may permit the rescuer to minimize
physical contact with a struggling victim.
A conscious victim should grasp the line, which
may have a buoyant object attached to it. After grasp-
ing the line, the conscious victim should be told to roll
over on his or her back to avoid being pulled under
during tow. Once the victim has the line and is in
position, the tow can be started slowly, because haste
could result in pulling the line loose or swamping the
victim. If the victim is unconscious, the line should
be attached by the rescuer so that it can be detached
easily. The line also may be attached to the rescuer as
long as it can be released easily. As with a conscious
victim, the tow must be slow so as not to swamp the
victim. This technique is particularly useful because it
permits the rescuer to administer artificial resuscita-
tion easily or to otherwise tend the victim, if necessary.
Tank-Tow Method
Although many towing techniques require physi-
cal contact between the victim and rescuer, it is gener-
ally recommended that divers learn the tank-tow method.
Using this technique, the rescuer grasps the victim's
tank with his or her right hand from his or her position
at the victim's left side, being sure to maintain visual
and verbal contact (see Figure 19-7). This method
allows the rescuer to commence mouth-to-mouth
resuscitation in the do-si-do position described earlier
(see Figure 19-3). It should be kept in mind, however,
that although the victim's tank provides a convenient
October 1991 — NOAA Diving Manual
19-17
Section 19
Figure 19-7
Tank-Tow Method
Reprinted from Scuba Life Saving, pub. Royal Life Saving Society,
Canada, 1987
handle, towing is faster if the tank is removed. Cir-
cumstances such as surface conditions, towing distance,
and relative size of rescuer and victim dictate whether
equipment should be left intact or dropped. Regardless
of these circumstances, both the victim's and the rescuer's
tanks must be removed if the tow is through kelp or
heavy surf.
Towing with Two Rescuers
Two rescuers may efficiently tow a victim on the
surface. After the victim has been placed on his or her
back and the weight belt has been removed, buoyancy
compensator inflated, and mask and mouthpiece
removed, one rescuer is positioned on each side. The
rescuer on the victim's right supports the victim's head
with the left hand and grasps the victim's elbow or
upper arm, using the right hand in a palm-down posi-
tion. The second rescuer grasps the victim's upper and
lower left arm firmly. The tow is made with the rescu-
ers swimming on their backs.
Another method that may be used by two rescuers is
to place the victim on the back with a rescuer on each
side. Each rescuer grasps a wrist of the victim with the
outside hand and places the inside hand on the victim's
upper arm or in the armpit. When using this tow, the
rescuers swim in a snorkel position.
19.5.6 Leaving the Water with a Victim
Removing the victim from the water may be the
most difficult part of a rescue. It can be exceedingly
difficult to transport a victim through heavy surf, coral
formations, or mud,. or to lift a victim onto a pier, dock,
or boat. The situation may be complicated further if
the victim is in continued need of artificial resuscita-
tion. Regardless of the point of exit, any encumbering
equipment belonging to either the victim or the rescuer
should be removed before leaving the water. Victims
requiring artificial resuscitation should be placed on a
flat hard surface as quickly as possible, because CPR
cannot be administered in the water.
If the victim is unconscious, the head and chest
should be tilted downward during removal from the
water; this position will help water drain from the
airways. In cases where a back or neck fracture is
suspected, care should be taken to avoid any twisting,
bending, flexing, or extending of these parts. In such
cases the victim should be fastened securely to a back
board, with many ties or straps, before being removed
from the water. These special precautions should not
delay removal of victims from the water if they are not
breathing, because CPR must be started as soon as
possible. Further details of the techniques for removing
a victim from the water may be found in Smith and
Allen (1978).
NOTE
When attempting to remove a victim from
the water, every effort should be made to
obtain help by shouting, lighting flares, using a
radio, or any other means at hand.
Into Small Boats. A single rescuer will have consid-
erable difficulty getting an incapacitated diver into a
19-18
NOAA Diving Manual — October 1991
Accident Management and Emergency Procedures
small boat, particularly if the victim is unconscious. If
the boat is properly equipped with a ladder (see Sec-
tion 10.4.2), the rescuer should climb in first and
then assist the victim. If there is no ladder, the hands of
the victim may have to be secured to the anchor line or
some part of the boat to keep the face out of the water
while the rescuer climbs in. Once aboard, the rescuer
can then untie the victim's hands and pull the victim
aboard. If the victim can climb aboard a boat with no
ladder, the rescuer's shoulders may be used as a step-
ping stone. It is important during efforts to get into
small boats to keep the victim between the rescuer and
the boat, in order to maintain control.
Onto Larger Boats, Piers, and Cliffs. Lifting an
incapacitated victim into a boat, onto a high dock, or
up a wall or cliff presents a serious problem to a res-
cuer even if assistants are available. If the boat's gun-
wale is too high to reach over, a line with a bowline in it
may be slipped under the victim's arms, with the knot
in the middle of the back. If assistants are available,
one or more light lines can be attached to the loop so
that the weight of the victim can be divided among
the members of the rescue team.
Through Surf. Exiting through the surf with an injured
diver is very difficult and exposes both the victim and
the rescuer to the possibility of serious injury. As the
surf zone is approached from open water, the rescuer
must continually watch the approaching waves. Large
waves generally come in "sets" or groups of 3 to 6 waves
about 10 to 15 seconds apart, with 2 to 3 minutes
of smaller waves between sets. It is advisable to leave
the surf zone during the lull between sets of larger
waves, waiting outside the surf zone for a lull. If the
victim is apprehensive or panicky, it may be necessary
to pause seaward of the surf zone to calm him or her
down.
WARNING
Never Attempt to Tow a Panicky Victim
Through Surf to Shore
To permit continued observation of the surf, the
rescuer should tow the victim from the back toward
shore. If it appears that large breaking waves may catch
them, it is advisable to move seaward again to wait for
the next lull. As a breaking wave approaches, the res-
cuer should turn toward shore, hold the victim firmly,
cover the victim's mouth and nose, and let the wave
strike from behind. Surf often is accompanied by rip
currents, and the rescuer must be cautious to avoid
October 1991 — NOAA Diving Manual
being swept seaward (see Section 10.2.3). The use
of more than one rescuer is highly desirable when
exiting through surf. If two rescuers are available, the
victim should be transported with one rescuer on each
side towing the victim by the arms. Once ashore, the
victim should be treated in accordance with the injuries
sustained. A non-breathing victim should be placed on
shore as soon as possible and CPR should be started
(see Section 18.1.4).
Onto a Rocky Shore. When going from deep water
onto an adjacent rock or reef, the rescuer should tow
the victim as close to the rocks as possible, then attempt to
ride a swell up onto the rock with the buoyant victim
turned sideways and held in front of the prone rescuer.
The wave may serve as a kind of cushion because the
leading edge precedes the body and rebounds back off
the rocks, which helps prevent the victim from striking
the rocks. The rescuer must brace on the rocks as soon
as contact is made and hold on until the water from the
swell has receded. The victim then can be rolled higher
on the rocks. Once on solid ground, a standard fire-
man's or shoulder carry can be used to move the victim
further inshore. As with other resuscitation techniques,
CPR, if needed, should be started as soon as possible.
19.6 ACCIDENT MANAGEMENT
Once the victim has been removed from the water and
is on a solid platform such as a boat, pier, or beach, a
reassessment of the situation must be made immedi-
ately. The first things to check for are life-threatening
conditions such as airway obstruction, cessation of
breathing, reduced circulation, bleeding, and shock.
The examination procedures for each of these are
described in detail in Section 18. An unconscious diver
should be suspected of suffering from gas embolism
and be treated accordingly, unless embolism definitely
can be ruled out. Concurrently, every effort should be
made to summon outside help, using the telephone,
radio, runners, flags, or any means available.
Although cost should not be a factor in the manage-
ment of a diving accident, it is an important element to
keep in mind during planning. Statistics show that
costs incurred for treatment of a diving injury can
exceed $l,400/day. When added to an expense as great as
$10,000 for a jet air ambulance, costs can easily reach
$33,000 for a 14-day recompression treatment/hospital
stay (Wachholz 1986). For example, the cost for chamber
treatment ranges from $100 to more than $300 per
hour, depending on the type of chamber, its geographical
location, and supporting medical services. The charge
for a non-hospital-based chamber will be less than
that for a hospital-based chamber. Most chambers
19-19
Section 19
charge about $225 per hour (Wachholz 1986). Thus,
good planning and accident management practices make
sense from a financial point of view.
19.6.1 Summoning Aid
Because many divers and boaters are not familiar
with the procedures for summoning aid in emergen-
cies, critical time is lost, causing needless suffering
and perhaps even loss of life. The nature of the aid and
the procedures to obtain it obviously vary with the
situation, e.g., on land in a populated area, on land in a
remote area, or at sea. When on land in a populated
area, local police, fire, and rescue services should be
notified, as in any kind of accident. When on a boat,
the best procedure is to seek assistance from the U.S.
Coast Guard.
Many signals have been devised over the years to
signal distress or other emergency status. The most
common, which have been accepted by international
agreement or national custom or may be used occa-
sionally by Coast Guard Search and Rescue Units
(U.S. Coast Guard 1973), are shown below.
INTERNATIONAL DISTRESS SIGNALS
A gun or other explosive signal fired at intervals of
about a minute.
A continuous sounding with any fog-signaling ap-
paratus.
Rockets or shells throwing red stars fired one at a
time at short intervals.
A signal made by radiotelegraphy or by any other
signaling method consisting of the group S-O-S in
the Morse code.
A voice signal consisting of the spoken word "May-
day."
The International Code Signal of distress indicated
by the code group NC.
A signal consisting of a square flag having above or
below it a ball or anything resembling a ball.
Flames on a vessel (as from a burning tar barrel,
oil barrel, etc.).
A rocket parachute flare or a hand flare showing
a red light.
A smoke signal giving off a volume of orange-
colored smoke.
Slowly and repeatedly raising and lowering arms out-
stretched to each side.
The radiotelegraph alarm signal, which is design-
ed to actuate the radiotelegraph auto alarms of vessels
so fitted, consisting of a series of 12 dashes, sent
in 1 minute, the duration of the interval between 2
consecutive dashes being 1 second.
• The radiotelephone alarm signal consisting of 2 tones
transmitted alternately over periods of from 30 seconds
to 1 minute.
Table 19-2 summarizes the procedures for obtaining
emergency aid, evacuation of casualties, and diving
medical advice. Only national information has been
included because local numbers and procedures vary
from location to location and radio call numbers and
telephone numbers are changed frequently.
When contact is made by radio or telephone, the
caller should declare that the situation is an emer-
gency and state the nature of the emergency. For exam-
ple, "This is an emergency. I have a diving accident
victim needing treatment in a recompression cham-
ber." The caller should be prepared to provide infor-
mation on the location, including direction and dis-
tance from prominent land marks, environmental
conditions relating to sea state, roads, wind, etc., and
the status of the victim. Unusual circumstances should
be described and the number of victims identified. If
the victim's location changes, all individuals involved
in the rescue should be advised of the new location and
of any planned moves or changes.
In 1980, a national Divers Alert Network (DAN)
was established at Duke University Medical Center,
Durham, North Carolina, as the country's medical
advisory service for divers. For administrative purposes,
the system is divided into seven regions (see Figure 19-8).
Medical help for victims of diving accidents is now
available 24 hours a day (Mebane and Dick 1985).
To use DAN, a diver or physician dials (919) 684-8111
and asks for DAN (collect calls are accepted in an
emergency). The call is answered by an operator at the
Duke University Medical Center. If the call is in regard to
an injured diver, the caller is put in contact with a dive
physician (one is available 24 hours a day). This physi-
cian may advise the caller directly or refer the caller to
a local diving physician. If needed, the physician will
work with a DAN Regional Coordinator to arrange
referral and transport to an appropriate treatment facili-
ty. DAN regional coordinators are qualified in diving
medicine and know what treatment facilities are availa-
ble in their regions. In addition, each region has trained
medical staff and suitable chambers available con-
tinuously (Dick 1982).
Although the Coast Guard does monitor Citizens
Band (CB) Channel 9, this is a very unreliable means
of communication, for many reasons. If unable to raise
the Coast Guard via CB, contact someone else to relay
19-20
NOAA Diving Manual — October 1991
Accident Management and Emergency Procedures
Table 19-2
Sources of Emergency Assistance
Medical Advice — Nearest Operable Chamber Location
U.S. Navy Experimental Diving Unit Divers Alert Network
Panama City, Florida (904) 234-4355 Box 3823 - DAN - 215
Duke University Medical Center
Durham, North Carolina 27710
(919)684-8111
Search, Rescue and Casualty Evacuation
Atlantic SAR Coordinator — Commander, Atlantic Area
U.S. Coast Guard Rescue Coordination Center
Governor's Island, NY (212) 668-7055
Pacific SAR Coordinator — Commander, Pacific Area
U.S. Coast Guard Rescue Coordination Center
San Francisco, CA (415) 556-5500
Inland SAR Coordinator — Commander, Aerospace Rescue and Recovery Service
U.S. Air Force
Rescue Coordination Center
Scott Air Force Base, IL (618) 256-4815
Emergency Communications Frequencies
500 kHz International CW/MCW distress and calling
2182 kHz International voice distress, safety and calling (particularly
useful for communications between aircraft and vessels)
156.8 MHz FM, U.S. voice distress and international voice safety and
(ch 16) calling
Continuous Broadcast NOAA Weather Frequencies
(When weather affects emergency operations)
162.550 MHz
162.400 MHz
162.475 MHz
Derived from NOAA (1979)
messages. If there is no radio on the boat, hail a boat
that has a marine band radio and give it the informa-
tion to relay to the Coast Guard. Keep the boat with
you for further contacts. The International Conven-
tion for the safety of life at sea requires that assistance
be provided to vessels in distress.
If other boats are not immediately available, pro-
ceed to the nearest inhabited dock and telephone local
paramedic or USCG services. Advise them of a diving
accident, state the need for transportation, and give
your exact location. Have someone remain at the tele-
phone for further assistance. Ensure that the person on
the line is aware that a recompression chamber will be
needed.
If symptoms occur on land after diving, contact
local paramedics or the USCG. These individuals should
be able to assist or give the location of the nearest
recompression chamber. If the accident has occurred
in a remote area and radio communication is not avail-
able, any means at hand should be used to signal the
emergency, e.g., smoke, fire, flares, etc. If, under such
conditions, help arrives by air but cannot land, the
signals shown in Table 19-3 should be used to convey
information to the rescuers.
When the rescue aircraft arrives, you should wave
and fire flares or smokes, if possible. Let them know
you are the one who needs assistance. Do not assume
the pilot will recognize you, because valuable time
may be wasted searching unnecessarily. In addition to
the signals described in Table 19-3, there are a num-
ber of miscellaneous signals used for signaling dis-
tress; these are shown below.
October 1991 — NOAA Diving Manual
19-21
Section 19
Figure 19-8
Divers Alert Network (DAN)
919-684-8111
MISCELLANEOUS EMERGENCY
VISUAL SIGNALS
• Inverted U.S. flag. Used as a distress signal by marine
craft in the United States.
• The following are used as a surface-to-air distress
recognition signal. When spread horizontally or waved,
they indicate that this is the unit in need of assistance:
— A cloth of international orange color (United States).
— A cloth of international orange color with a black
square and ball inscribed thereon (United States
and Canada).
— A cloth of red color (Caribbean territories).
— Green fluorescent dye marker.
— Flashes (as from a signal mirror).
— Smoke from signal fires. Note: Three signal fires
arranged in a triangular pattern are a positive
signal of distress.
Occasionally, divers in a small boat may be called on
to render assistance in an emergency situation. If the
emergency call is by radio or telephone, the procedures
will be obvious. If, however, a rescue aircraft is seek-
ing assistance from a boat in the area of an emergency,
it is important that those in the boat understand some
simple air-to-surface signals. The maneuvers used in
this situation by the U.S. Coast Guard Search and
Rescue system are described below.
INTERNATIONAL AIRCRAFT TO
SURFACE CRAFT SIGNALS
The following maneuvers performed in sequence by
an aircraft means that the aircraft wishes to direct a
surface craft toward an aircraft or a surface craft in
distress:
• Circling the surface craft at least once
• Crossing the projected course of the surface craft
close ahead at low altitude and:
— rocking the wings
— opening and closing the throttle
— changing the propeller pitch
• Heading in the direction in which the surface craft is
to be directed.
The following maneuver by an aircraft means that
the assistance of the surface craft is no longer required:
• Crossing the wake of the surface craft close astern at
a low altitude and:
— rocking the wings
— opening and closing the throttle
— changing the propeller pitch.
NOTE
Opening and closing the throttle and changing
the propeller pitch are alternative signals to
rocking the wings.
19.6.2 On-Site Care of the Diving Casualty
A major problem with divers is that they tend to
ignore mild symptoms of decompression sickness that
may develop into a more serious problem later on.
Detailed descriptions of the symptoms of decompres-
sion sickness are provided in Section 3.2.3.2. Sec-
tion 20.10.1 gives treatment procedures. If there is
no hyperbaric chamber on site, divers suspected of
having serious decompression sickness and who are not
having breathing problems should be administered
oxygen immediately and be placed on the left side in a
head downward position (modified Trendelenberg Posi-
tion) with the head at least 19 inches (48.3 centimeters)
lower than the feet, as shown in Figure 19-9. This
position is not recommended for victims requiring CPR or
those with breathing problems. In these cases, it is
recommended that a flat supine position be used (Mebane
and Dick 1985). The patient should then be transferred
immmediately to the nearest hyperbaric chamber. If
the symptoms are relieved within 10 minutes, the patient
should be kept on oxygen for a total of 30 minutes. If
the symptoms get worse, follow the recommendations
of the flowchart shown in Figure 19-10. An excellent
source of accident management and on-site patient
care is the DAN Underwater Diving Accident Manual
(Mebane and Dick 1985).
19-22
NOAA Diving Manual — October 1991
Accident Management and Emergency Procedures
Table 19-3
Ground-to-Air Visual Signal Code
No.
Message
Code
Symbol
No.
Message
Code
Symbol
1
Require doctor — serious injuries
I
10
Will attempt take-off
l>
2
Require medical supplies
I I
11
Aircraft seriously damaged
□
3
Unable to proceed
X
12
Probably safe to land here
<^
4
Require food and water
F
13
14
Require fuel and oil
All well
i_
L_l_
5
Require firearms and ammunition
V
6
7
Require map and compass
Require signal lamp with
battery and radio
□
I
I
15
No
N
16
17
Yes
Not understood
Y
JL
8
9
Indicate direction to proceed
Am proceeding inthis direction
K
T
18
Require engineer
W
Source: U.S. Coast Guard (1973)
WARNING
The Trendelenberg Position Should Not Be
Used if Airway Is Blocked or CPR Is Needed
A common problem in the management of diving
cases is that such cases are often misdiagnosed initial-
ly, either by divers at the scene or by a physician
untrained in diving medicine. To minimize the likeli-
hood of overlooking serious symptoms of decompres-
sion sickness or gas embolism, an attending physician
should give a neurological examination before, during,
and after treatment. Such an examination usually takes
about 30 minutes and requires certain diagnostic equip-
ment and training to interpret the results.
Since a physician is rarely at the scene of a diving
accident, however, a preliminary 4-minute neurologi-
cal evaluation has been developed that requires no
equipment and can be administered by non-medical
persons. This examination is shown below, and a checklist
for recording examination results is shown in Table 194.
October 1991 — NOAA Diving Manual
INITIAL NEUROLOGICAL EXAMINATION
TO BE ADMINISTERED BY
NON-MEDICAL PERSONNEL
NOTE
When interpreting the results of this exami-
nation, be sure that abnormalities are a result
of the diving disorder and not the result of a
previous disorder, e.g., some divers may have
a hearing impairment caused by working
around loud equipment.
Mental Condition or Status
Since less interference is required to impair functioning
of the higher mental faculties, test for subtle signs of
serious decompression sickness by observing:
• Orientation
— Time (the first function to go). Example: "What
day is this?"
— Place (the next to go). Example: "Where are
youi
19-23
Section 19
Figure 19-9
Modified Trendelenberg Position
19-Inch
Lift Affords
Minimum
Effective
Distance
Best Angle
Strap victim in place but do not interfere with respiration
Administer 100 percent oxygen if available
Derived from Rutkowski (1985) and Mebane and Dick (1985)
— Person (severe impairment). Example: "What is
your name?"
• Memory
— Immediate (test with a number series).
— Recent (happenings within last 24 hours).
— Remote (background).
• Mental function
— Test by using serial 7's. (Subtract 7 from 100,
then 7 from the answer, and so on. If an error
is repeated, like "93, 90, 83, 80, 73, 70," a
condition called perseveration exists, which
usually indicates impairment.
• Level of consciousness
— Watch for any fluctuation.
• Seizures
— These are readily apparent.
Cranial Nerves
What to check and how to test 12 cranial nerves,
if possible. Test one side vs. the other side.
19-24
• Sense of smell (Olfactory nerves)
— Test with coffee, one nostril at a time. Do not
delay for this test if appropriate testing material
is not available.
• Sight (Optic nerves)
— Hold up fingers for the patient to count; test
one eye at a time.
• Eye movement (Oculomotor, Trochlear, and Ab-
ducens nerves)
— Have the patient's eyes follow your finger as you
move it up and down, left and right.
• Chewing (Trigeminal nerves)
— Can the teeth be clenched? Feel jaw muscles on
both sides simultaneously.
• Mouth (Facial nerves)
— Can the patient smile?
— Can both corners of the mouth be lifted simul-
taneously?
• Hearing (Acoustic nerves)
— Test one ear at a time by whispering or rubbing
your fingers together approximately 1 inch away
from the ear.
• Talking (Glossopharyngeal, Vagus nerves)
— Check for gagging and proper enunciation.
• Shoulder muscles (Spinal Accessory nerves)
— Have patient shrug the shoulders while you press
down on them. Note any unilateral weakness.
• Tongue (Hypoglossal nerves)
— Can the patient stick the tongue out (not to
one side)?
Sensory Nerves
• Sharp vs. dull (check one hand vs. other)
— Using sharp and dull objects, see if patient can
distinguish between them by testing:
1 . Back of hand
2. Base of thumb
3. Base of little finger
Motor Nerves
• Muscle strength
— Have patient grip two of your fingers with each
hand. Is the strength the same in each hand?
— With patient sitting or lying down, place your
hands on the legs just above the ankle and press
down lightly. Have the patient try to lift the
legs. Is the strength e'qual in both?
• Range of motion
— Check normal movement of both arms and legs.
NOAA Diving Manual — October 1991
Accident Management and Emergency Procedures
Figure 19-10
Diving Accident Management Flow Chart
Mild Signs/Symptoms
Immediate Evacuation
Not Necessary
First Aid
1. Fatigue
2. Skin rash
3. Indifference
4. Personality change
Yes
No
More
Severe Signs/Symptoms
Immediate Evacuation
To Recompression Chamber
1. Administer 100% oxygen by demand for
30 minutes.
2. Head and chest inclined downward on left
side.
3. Observe for onset of more serious
symptoms.
4. Administer oral fluids.
5. Administer two aspirins.
Relief
Symptoms
No
1. Joint pains
2. Dizziness or weakness
3. Paralysis of face
4. Visual disturbances
5. Feeling of blow on chest
6. Chest pain
7. Severe hacking cough
8. Shortness of breath
9. Bloody, frothy mouth
10. Staggering
11. Difficulty telling direction
12. Paralysis or weakness of extremities
13. Collapse or unconsciousness
14. Convulsions
15. Cessation of breathing
INSERT INFORMATION FOR YOUR
DIVE AREA:
Chamber .
Rescue _
Coast Guard .
Diving Doctor .
Yes
Relief
Keep patient under prolonged
observation and have him
consult diving physician as
soon as possible.
Relief
Did patient take a breath underwater,
regardless of depth (2 ft. or deeper)
from a scuba tank, hose, bucket,
submerged car, etc.
| No
Yes
If patient was not under the water for
the past 24 hours:
1. Begin CPR, if needed.
2. Administer oxygen.
3. Evacuate to nearest physician or
medical facility.
1. CPR is necessary to restore breathing
and/or heart function.
2. Modified TRENDELENBERG
POSITION
a. Head and chest inclined downward
and lying on left side 19".
b. Place patient on oxygen and
ensure that he remains on oxygen
until taken off by diving physician
even if breathing normally.
c. Alert evacuation system.
3. Intravenous fluids
(lactated Ringers solution).
U.S.C.G. (at sea)
VHF16
HF2182
Evacuate directly to a recompression
facility and a diving physician.
1. Keep head down, 19" lower than feet,
left side.
2. Transport below 1,000 ft. elevation.
3. Forward complete history of all events
leading up to accident.
Duke University
Divers Alert
Network
(919)684-8111
Source: Rutkowski (1985)
• Muscle tone
— Check if muscles are spastic (in state of con-
traction) or flaccid (totally relaxed).
Coordination (Cerebellar function)
• Point in space
— Can patient touch your finger held in front of
his or her nose?
• Finger to nose
— Can the patient touch the tip of his or her nose
after touching the tip of your finger?
Gait
— Walking gait — check for rubber legs, staggering,
and unsteadiness.
— Tandem gait — walking heel to toe.
Balance (sharpened Romberg)
— Have patient stand straight, feet together, arms
folded in front and eyes closed.
Basic reflexes (check both sides with blunt instru-
ment)
— Biceps
— Triceps
October 1991 — NOAA Diving Manual
19-25
Section 19
Table 19-4
Diving Casualty Examination Checklist
(
Patient
Date
LIFE-THREATENING CONDITIONS
1. Airway
2. Breathing .
3. Circulation
MENTAL CONDITION OR STATUS
1. Orientation:
2. Memory:
Time.
Place .
Person .
Immediate.
Recent .
Remote .
3.
4.
5.
Mental function
Level of consciousness
Seizures
CRANIAL NERVES
1. Sense of smell (Olfactory)
2. Sight (Opiic)
3. Eye movement
(Oculomotor, Trochlear, Abducens)
4. Chewing (Trigeminal)
5. Mouth, smile (Facial)
6. Hearing (Acoustic)
7. Talking (Glossopharyngeal, Vagus)
8. Shoulders (Spinal Accessory)
9. Tongue (Hypoglossal)
Comments or conclusions
4. Hemorrhage
5. Shock
SENSORY NERVES
1. Sharp vs. Dull
MOTOR NERVES
Muscle strength
Range of motion
Muscle tone
R
1
R
1
R
1
R
L
R
1
R
1.
R
I
R
1
R
1
COORDINATION
1. Point in space
2. Finger to nose
3. Gait:
4. Balance
REFLEXES
1. Basic:
2. Babinski reflex
LANGUAGE
1. Aphasia
Walking
Tandem
Biceps R .
Triceps R .
Forearm R .
Knee R .
Ankle R.
R.
R L
R L
R L
(
Examiner
Source: NOAA (1979)
— Forearm
— Knee
— Ankle
Reflexes
• Babinski reflex
— Run a blunt object up the sole of the foot. If the
toes curl down toward the sole of the foot, a
normal Babinski is present. If nothing happens,
no conclusion can be drawn, but if the toes flex
19-26
backward, upward, and spread, this is a reliable
sign of probable spinal involvement.
Language Problem
• Aphasia (Speech impairment)
— Check for language foulups like misplaced words
and incorrect word order.
The results of this examination should be communi-
cated to a consulting physician if a physician is not on
NOAA Diving Manual — October 1991
(
Accident Management and Emergency Procedures
Figure 19-11
Evacuation by Helicopter
site or should be given directly to an attending physi-
cian at the first opportunity.
19.7 EVACUATION BY AIR
Each helicopter evacuation presents unique problems.
Knowing what to expect and the procedures to follow,
however, can save time, effort, and perhaps a life. The
following information is applicable to U.S. Coast Guard
(USCG) helicopter evacuation by sea, but the same
rules also apply to most helicopter evacuations.
• Try to establish communications with the helicop-
ter. If your boat does not have the necessary fre-
quency, try to work through another boat.
• Maintain speed of 10 to 15 knots (5 to 7.5 m/s);
do not slow down or stop.
• Maintain course into wind about 20 degrees on
port bow.
• Put all antennas down, if possible without losing
communications.
• Secure all loose objects on or around the decks,
because the helicopter will create strong winds.
• Make sure the patient is ready in advance of the
transfer, because time is critical both to the victim
and the hovering aircraft.
• Signal the helicopter pilot when all is ready, using
hand signals by day and flashlight at night (see
Figure 19-11).
• If a trail line is dropped by the aircraft, guide the
basket to the deck with the line.
• To prevent electric shock, allow the lifting device
(stretcher) to touch the boat before handling it.
• Do not secure any lines/wires from the boat to the
basket.
• Place a personal flotation device on the patient.
• Tie the patient in the basket, face up.
• If the patient cannot communicate, attach per-
sonal information such as name, age, address, what
happened, and what medication has been ad-
ministered.
• If the patient is a diving accident victim, ensure
that the flight crew has a copy of, or is instructed
in, medical procedures for diving accidents.
• If the patient is a diving accident victim, ensure
that the flight crew delivers the patient to a
hyperbaric trauma center (recompression cham-
ber complex).
• If the patient dies, inform members of the flight crew
so they do not take unnecessary risks.
• Helicopter transfers should not be made if the
victim is being given cardiopulmonary resuscita-
tion, because the chest compression should not be
October 1991 — NOAA Diving Manual
V||
Photo Wayne Marshall
stopped for the time needed to lift the victim. In
addition, the helicopter crew may not include an
individual trained in CPR.
WARNING
Do Not Secure a Trail Line, Basket, or Cable
from the Aircraft to the Boat. To Prevent Elec-
tric Shock, Always Allow the Lifting Device
(Stretcher) To Touch the Boat Before Han-
dling It
19.8 GUIDELINES FOR EMERGENCY
EVACUATION
Regardless of the means of evacuation, certain factors
must be followed to minimize additional injury to the
patient. These factors include providing the maximum
amount of advance information to the rescuing organiza-
tion and the emergency receiving facility and advising
the rescue crew in the proper procedures for transporting
a diving casualty.
The following medical evacuation information should
be forwarded with the patient. If possible, take time to
explain the following steps to the physician or para-
medic. Do not assume that they understand the reasons
why oxygen should be administered to a diving accident
victim. If a patient is breathing normally, a physician
may stop the oxygen breathing because he or she does
not realize that the patient must continue to breathe
oxygen to off-load bubbles. The following steps should
be taken:
• Maintain breathing and heart functions; ensure air-
way remains open.
19-27
Section 19
• Keep patient on 100 percent oxygen delivered by
demand valve and incline head downward, left side
down, during transportation (see Figure 19-8).
• Ensure paramedics/physicians understand why head
down, left side, on 100 percent oxygen by demand
is required until patient arrives at chamber.
• Ensure that paramedics and physicians understand
why the patient needs to be taken to a recompression
chamber instead of a hospital.
• Do not stop giving oxygen to a diving accident
patient even if patient is breathing normally, unless
there is a need to reopen the airway or the patient
shows signs of oxygen convulsions (see Section 3.3).
Without oxygen, bubbles will reload with nitrogen
and cause increasing symptoms.
• Keep patient out of the hot sun and watch for
shock.
• Do not give any pain-killing drugs (including aspi-
rin); intravenous injections can be given to prevent
vascular collapse or dehydration.
• Instruct flight crews to fly or pressurize aircraft
below 800 feet (244 meters) (see Section 14.8).
• Provided the aircraft can handle the extra weight,
the diving buddy should be transported with the
patient, because he or she also may need recom-
pression or can provide information, comfort, and
contact with patient's relatives.
• A complete history of all events leading up to
the accident and evacuation must be forwarded
with the patient.
• Depth gauges, tanks, regulators, and other diving
equipment should be forwarded with patient if
weight limitations allow, especially if the accident
was fatal. If this is not possible, they should be
maintained in the condition in which they were
found, pending any accident investigation.
Once the patient arrives at the emergency treatment
facility, the procedures described in Section 20 should be
followed.
19.9 ACCIDENT REPORTING PROCEDURES
All diving accidents involving NOAA personnel, whether
fatal or non-fatal, must be reported promptly. The
procedures for reporting accidents are contained in
the NOAA Diving Regulations. In addition, all diving
accidents should be reported to the National Under-
water Accident Data Center, University of Rhode Island,
P.O. Box 68, Kingston, RI 02881. The telephone number
is (401) 792-2980.
Accidents, both fatal and non-fatal, also should be
reported to DAN (see Section 19.6.1). In addition
to providing medical advice in diving emergencies, DAN
serves as a clearinghouse for information on diving
accidents and their treatment. Information (without
identifying data) is collected on the victims to be studied
on a national level. It is then made available to those
participating groups, such as certifying agencies and
equipment manufacturers, who are responsible for train-
ing and equipping divers (Dick 1982).
Reporting accidents is more than a legal responsibility;
it permits an investigation and compilation of accident
statistics. From this information, all concerned can
learn to improve diving techniques, which will result in
fewer diving accidents in the future.
19-28
NOAA Diving Manual — October 1991
SECTION 20
DIAGNOSIS
AND TREATMENT
OF DIVING
CASUALTIES
Page
20.0 General 20-1
20. 1 Physiologic and Pathologic Effects of Diving Gases 20-1
20.1.1 Carbon Dioxide Poisoning 20-1
20.1.2 Hypoxia 20-1
20.1.3 Carbon Monoxide Poisoning 20-2
20.1.4 Asphyxia 20-2
20.1.5 High Pressure Oxygen Poisoning 20-2
20.1.6 Inert Gas Narcosis 20-3
20.2 Ear Problems in Diving 20-3
20.2.1 Ear Fullness 20-3
20.2.2 Hearing Loss 20-4
20.2.3 Tinnitus 20-4
20.2.4 True Vertigo 20-4
20.2.5 Alternobaric Vertigo 20-4
20.2.6 Damage to Inner Ear 20-4
20.2.7 Otitis Externa (Swimmer's Ear) 20-5
20.3 Squeeze or Barotrauma 20-6
20.3.1 Face Mask Squeeze 20-6
20.3.2 Middle Ear Squeeze 20-6
20.3.3 Round Window Rupture 20-7
20.3.4 Sinus Squeeze 20-7
20.3.5 Lung Squeeze (Thoracic Squeeze) 20-8
20.3.6 External Ear Squeeze 20-8
20.4 Decompression Sickness and Gas Embolism 20-8
20.4.1 Decompression Sickness 20-9
20.4.1.1 Decompression Sickness — Pain Only 20-9
20.4. 1 . 2 Decompression Sickness — Serious Symptoms 20-9
20.4.2 Gas (Air) Embolism 20-9
20.4.3 Omitted Decompression 20-13
20.4.4 Pretreatment Procedures 20-13
20.4.5 Tending the Patient 20-14
20.4.6 Treatment Tables 20-15
20.4.7 Failures of Treatment 20-15
Other Lung Overpressurization Accidents 20-17
20.5.1 Pneumothorax 20-17
20.5.2 Mediastinal Emphysema 20-17
20.5.3 Subcutaneous Emphysema 20-17
Management of the Unconscious Diver 20-18
Personnel Requirements for Chamber Operations 20-18
20.7.1 Diving Supervisor 20-18
20.7.2 Inside Tender 20-18
20.7.3 Outside Tender 20-18
20.7.4 Diving Physician 20-18
20.8 Pressure and Oxygen Tolerance Tests 20-19
20.8.1 Procedures for Pressure and Oxygen Tolerance Tests 20-19
20.9 Emergency Medical Response 20-19
20.9.1 Medical Equipment and Supplies 20-20
20.9.2 Diving Operations Medical Kit (First Aid) 20-20
20.9.3 Primary Medical Treatment Kit 20-20
20.9.4 Secondary Medical Treatment Kit 20-21
20.9.5 Use of the Kits 20-21
20.5
20.6
20.7
i
DIAGNOSIS
AND
TREATMENT
OF DIVING
CASUALTIES
20.0 GENERAL
This chapter covers the diagnosis and treatment of a
variety of diving- and pressure-related conditions that
may occur during diving operations. These conditions
range from relatively minor (otitis externa) to life-
threatening (Type II decompression sickness, arterial
gas embolism). The on-site treatment of injuries is
addressed in Section 18, Emergency Medical Care.
20.1 PHYSIOLOGIC AND PATHOLOGIC
EFFECTS OF DIVING GASES
The presence or use of air and other gases under pressure
is accompanied by a variety of adverse physiological
effects, ranging from carbon dioxide poisoning to
nitrogen narcosis. This section describes the symptoms
and signs associated with these effects, the conditions
under which they are likely to occur, and the appropri-
ate forms of treatment.
20.1.1 Carbon Dioxide Poisoning
Carbon dioxide (C02) buildup (or excess) often occurs
when divers work hard and their lung ventilation does
not increase enough to vent off the C02 produced by
their exertion. Scuba divers who skip-breathe often
experience C02 buildup. Carbon dioxide poisoning
may also occur when a faulty rebreather causes a buildup
of C02 in the diving mask or helmet.
Symptoms and Signs
Occasionally, C02 poisoning produces no symptoms,
although it is usually accompanied by an overwhelming
urge to breathe and noticeable air starvation. There
may be headache, dizziness, weakness, perspiration,
nausea, a slowing of responses, confusion, clumsiness,
flushed skin, and unconsciousness. In extreme cases,
muscle twitching and convulsions may occur.
Treatment
Divers who are aware that they are experiencing
carbon dioxide buildup should stop, rest, breathe, and
ventilate themselves and their apparatus. Fresh breathing
October 1991 — NOAA Diving Manual
gas usually relieves all symptoms quickly, although
any headache caused by the buildup may persist even
after surfacing. If a diver becomes unconscious, he or
she should be treated in accordance with the procedures
described in Section 20.6.
20.1.2 Hypoxia
When the tissues do not have enough oxygen to
maintain normal function, the condition is called hyp-
oxia. Hypoxia usually reflects inadequate oxygen in
the gases in the lungs (but see Section 20.1.3 on carbon
monoxide). Because an increase in total pressure also
increases the partial pressure of the oxygen in the
breathing mixture (see Section 2.5.1), a diver breath-
ing a gas mixture with less than 20 percent oxygen can
often continue to function normally at depth. Howev-
er, when the diver begins to ascend, the oxygen partial
pressure drops as depth decreases, and the diver may
lose consciousness before reaching the surface. Breath-
hold divers are particularly at risk, especially if they
hyperventilate before diving, because hyperventilation
reduces the level of C02 in the blood, and it is the blood
C02 level that provides the principal impetus to take
another breath. As a consequence, a diver with a low
C02 blood level can stay under water longer without
discomfort and without experiencing the urge to breathe
again. This situation can produce a vicious cycle: in
the time it takes for the diver's C02 blood level to build
up sufficiently to make him or her aware of the need to
take another breath, the tissues have used up addi-
tional oxygen and the C02 tension in the diver's blood
has dropped. If the oxygen partial pressure drops below
the level necessary to maintain consciousness, the diver
loses consciousness.
A similar danger exists when artificial breathing
mixtures and rebreathing scuba are being used, because
heavy exertion or low gas flow may diminish the con-
centration of oxygen in the breathing bag. This may
continue until a pressure is reached that renders the
diver unconscious at depth or until the oxygen partial
pressure drops to an inadequate level during ascent.
The victims of hypoxia do not usually understand
what is occurring, and they may even experience a
20-1
Section 20
feeling of well-being. Hypoxia may be accompanied
by an excess of carbon dioxide in the blood (see
Section 20.1.1).
Symptoms and Signs
• Frequently none (the diver may simply lapse into
sudden unconsciousness)
• Mental changes similar to those of alcohol intoxi-
cation
• Confusion, clumsiness, slowing of response
• Foolish behavior
• Cyanosis (bluish discoloration of the lips, nailbeds,
and skin)
• In severe cases, cessation of breathing.
Prevention
• Avoid excessive hyperventilation before a breath-
hold dive.
• When diving with rebreathing scuba, flush the
breathing bag with fresh gas mixture before
ascending.
Treatment
• Get the victim to the surface and into fresh air.
• If under water and using a rebreather, manually
add oxygen to the breathing circuit.
• If the victim is still breathing, supplying a breath-
ing gas with sufficient oxygen usually causes a
rapid reversal of symptoms.
• An unconscious victim should be treated as if
he or she is suffering from gas embolism (see
Section 20.4.2).
• Cardiopulmonary resuscitation should be admin-
istered if necessary and should be continued after
the victim is in the recompression chamber.
20.1.3 Carbon Monoxide Poisoning
When carbon monoxide (CO) is absorbed, it prevents
the blood from transporting oxygen, causing tissue
hypoxia even when there is adequate oxygen in the
lungs. During treatment, this tissue hypoxia must be
overcome by administering higher concentrations of
oxygen, and the toxic CO must be eliminated by sup-
plying the diver with CO-free breathing gas. The most
frequent cause of carbon monoxide in a diver's air
supply is that exhaust fumes from the compressor have
entered the compressor's air intake. As the total pressure
increases with depth (see Section 3.1.3.4), very slight
amounts of carbon monoxide in the diver's breathing
gas can have toxic effects.
20-2
Symptoms and Signs
Carbon monoxide poisoning usually produces no symp-
toms until the victim loses consciousness. Some vic-
tims experience headache, nausea, dizziness, weakness, a
feeling of tightness in the head, confusion, or clumsi-
ness, while others may be unresponsive or display poor
judgment. Rapid deep breathing may progress to ces-
sation of breathing. There may be abnormal redness or
blueness of lips, nailbeds, or skin. The classic sign of
CO poisoning, "cherry-red" lips, may or may not occur
and is therefore not a reliable diagnostic aid.
Treatment
The victim should be given fresh air and, if availa-
ble, oxygen. Some effects, such as headache or nausea,
may persist after the exposure has ended. An uncon-
scious victim should be treated in accordance with the
procedures outlined in Section 20.6. If a recompression
chamber is available, the victim should be treated using
U.S. Navy Treatment Table 5 or 6 (see Appendix C).
20.1.4 Asphyxia
Asphyxia (or suffocation) occurs when the lung is
unable to carry out the function of ventilation. In
diving, this situation could be the result of blockage of
the windpipe or gas supply hose or the breathing of an
irrespirable gas mixture (too little oxygen or too much
carbon dioxide). Drowning is a special case of asphyxi-
ation.
The signs and symptoms of asphyxia and the treat-
ment for it are the same as those for hypoxia and
carbon dioxide poisoning. For instructions on the treat-
ment of blocked airway, see Section 18.2.
20.1.5 High Pressure Oxygen Poisoning
Oxygen poisoning is the direct result of breathing
pure oxygen or excessive oxygen under pressure. It is
most likely to occur when closed-circuit scuba is being
used and the depth for which the gas was mixed has
been exceeded. If not treated promptly, oxygen poisoning
can cause death.
Symptoms and Signs
• Restlessness
• Tingling sensation of the finger tips, lips, and nose
• Tunnel vision
• Ringing in the ears
• Twitching of the face
• Nausea
• Dizziness
NOAA Diving Manual — October 1991
Diagnosis and Treatment of Diving Casualties
• Difficult breathing
• Anxiety and confusion
• Unusual fatigue
• Clumsiness
• Grand mal seizure.
Before the onset of a seizure, the only sign likely to
be noticed is twitching of the facial muscles. Conscious-
ness is lost at the onset of the seizure. Shortly thereaf-
ter, breathing usually stops. Violent seizures generally
continue for a minute or two; biting the tongue and
various physical injuries may occur during seizures.
Breathing generally resumes spontaneously after a sei-
zure, but the victim may remain unconscious for sev-
eral minutes afterward and may be drowsy or confused
after consciousness is regained.
Treatment
In dives where the oxygen level is high, oxygen
poisoning should be suspected if any of the symptoms
or signs listed above is noticed. Steps to decrease the
oxygen partial pressure should be taken as soon as one
or more of these signs or symptoms occurs. If a diver
exhibits one of the signs or symptoms while in a dry
chamber, the oxygen breathing mask should be removed
and the diver should breathe chamber air. Because an
increase in C02 can trigger oxygen toxicity, the diver
should breathe deeply to ventilate C02 from the lungs.
If a diver using rebreathing circuit scuba shows signs
of incipient oxygen poisoning, he or she should flush
the breathing bag with fresh breathing gas.
Oxygen-induced seizures generally stop before any
treatment can begin. Those treating the victim should
concentrate on preventing the victim from injuring
himself or herself or from drowning. Because of the
risk of breath-holding and air embolism, the pressure
(depth) should not be changed while a diver is convuls-
ing. If normal breathing does not resume, cardiopul-
monary resuscitation should be administered. If a con-
vulsing diver surfaces, there is reason to suspect an air
embolism; the diver should be recompressed and treated
immediately (see Section 20.4.6).
20.1.6 Inert Gas Narcosis
Narcosis is a state of stupor or unconsciousness that
is caused in diving by breathing inert gases at pressure.
Inert gases vary in their narcotic potency, and they
may interact with each other to produce effects greater
than those produced individually. Nitrogen narcosis,
which is caused by breathing compressed air at depth,
is the most common form of narcosis encountered in
diving. The effects of narcosis may be noticed even at
October 1991 — NOAA Diving Manual
depths barely exceeding 100 fsw (30.5 m), but the
symptoms become more pronounced at depths greater
than 150 fsw (47 m). Inert gas narcosis produces a
sensation of apprehension, confusion, impaired judgment,
and a false sense of well-being. The ability to concentrate
or even to perform simple tasks is difficult. Divers may
do things they normally would not attempt (removing
their regulator, swimming to unsafe depths without
regard for decompression sickness or the duration of
their air supply). By forcing themselves to concentrate
on the task at hand, experienced divers can keep narcotic
effects under some control, but even they may be unaware
of the decrement in their performance under these
conditions.
Symptoms and Signs
• Loss of judgment and skill
• A false feeling of well-being
• Lack of concern for job or safety
• Apparent stupidity
• Inappropriate laughter.
Treatment
There is no specific treatment for nitrogen narcosis.
A diver experiencing narcosis must be brought to a
shallower depth, where the effects will gradually wear
off.
20.2 EAR PROBLEMS IN DIVING
The common signs and symptoms of ear injury are a
sensation of ear fullness, pain, hearing loss, noise in the
ear (tinnitus), or vertigo. The conditions leading to ear
problems and the consequences of these problems are
described below.
20.2.1 Ear Fullness
Ear fullness, or a sensation that the ears are blocked,
is usually the result of a condition that causes a decrease
in the transmission of sound to the inner ear. On the
surface, ear fullness occurs when the external ear canal is
completely blocked with wax or other material. With
upper respiratory tract illnesses, ear fullness may be
the result of fluid that has been secreted into the cavity
of the middle ear and that has not been able to drain
out through the eustachian tube. In diving, failing to
keep the pressure in the middle ear equalized when the
external pressure increases during descent may cause
middle ear squeeze and be accompanied by fluid or
blood in the middle ear and a consequent feeling of ear
fullness (see Section 20.3.2). Divers may find it diffi-
cult or impossible to equalize the pressure in their ears
20-3
Section 20
during an episode of upper respiratory tract infection
or hay fever because of the swelling of the throat
tissues, which blocks the opening of the eustachian
tubes.
The best way to avoid ear fullness in diving is to
maintain the ear canal in a clean and open condition.
In addition, divers should not dive when they have an
upper respiratory tract infection or are suffering from
hay fever or other allergic symptoms.
20.2.2 Hearing Loss
Hearing loss is classified in three categories:
(1) Conductive hearing loss, which is caused by dys-
function of any component of the sound conduction
system, such as complete occlusion of the external
auditory canal by wax, inflammation, swelling of the
ear drum or lining of the middle ear, fluids in the
middle ear, changes in middle ear gas densities, pressure
gradients across the ear drum, fixation of the ear bones, or
loss of elasticity of the ear drum caused by scarring,
large perforations, or interruption of the ear bones.
(2) Neurosensory or nerve hearing loss, which is
caused by occlusion of the blood supply to the inner
ear, head injury, stroke, bubbles, leakage of inner ear
fluids from a round or oval window rupture, excessive
noise exposure, or various other inner ear diseases or
conditions.
(3) Mixed or combined conductive and neurosensory
hearing losses, which are caused by simultaneous dys-
function of the middle and inner ear.
20.2.3 Tinnitus
Tinnitus (spontaneous noise or ringing in the ear)
can occur with the type of middle ear disease that
causes a conductive hearing loss. However, this condi-
tion is usually associated with inner ear or brain disease.
20.2.4 True Vertigo
True vertigo is a disorder of spatial orientation that
is characterized by a sense that either the individual or
his or her surroundings are rotating. Injury to the
vestibular system that results in vertigo is frequently
associated with nausea, vomiting, visual disturbance,
fainting, and generalized sweating. Vertigo is the most
hazardous ear symptom in diving. When it is caused by
inner ear dysfunction, it may be accompanied by ear
pain, hearing loss, or tinnitus. Vertigo can result from
cold water entering the external ear canal, unequal ear
clearing during ascent or descent, inner ear barotrau-
ma, ear drum rupture, or injury to the central nervous
system. Once a diver has experienced dizziness during
20-4
diving, he or she should be examined by a specialist in
diving medicine before attempting further diving.
20.2.5 Alternobaric Vertigo
Unequal or asymmetrical clearing of the middle ear
during descent or ascent, and particularly during ascent,
can cause vertigo. Regardless of the cause, vertigo and
its accompanying spatial disorientation are hazardous
if they occur during a dive.
Treatment
The best treatment for alternobaric vertigo is pre-
vention. First, individuals should not dive if they have
difficulty clearing their ears or if a Valsalva maneuver
on the surface produces vertigo. Second, if a diver
notices any vertigo, ear blockage, or ear fullness dur-
ing compression, he or she should stop any further
descent and should ascend until the ears can be cleared.
Third, if such symptoms are noted during ascent, the
diver should stop and descend until the symptoms dis-
appear (if breathing gas and other conditions permit).
20.2.6 Damage to Inner Ear
The inner ear may be damaged permanently by inade-
quate pressure equilibration of the middle ear during
descent. It is therefore critical that divers equalize the
pressure in the middle ear with the external pressure.
Symptoms and Signs
Inner ear injuries are accompanied by vertigo, nerve
deafness, and a loud roaring in the involved ear. One or
all of these symptoms may be present. Deafness may be
total or partial and may occur concurrently with or
several days after middle ear barotrauma. Many of
these injuries have been associated with forceful
attempts, against closed mouth and nose, to clear the
ears at depth. This force results in an increase in cere-
brospinal fluid pressure, which is transmitted to the
fluid in the inner ear spaces, causing an increase in the
already negative pressure in the middle ear. The oval
window or the thin round window membranes may then
bulge into the middle ear and rupture, causing a leak of
inner ear fluids into the middle ear. The signs and
symptoms of inner ear barotrauma can easily be con-
fused with those of inner ear decompression sickness.
Table 20-1 differentiates between these two conditions.
Prevention
Divers should not perform a forceful exhalation against
a closed nose and mouth (Valsalva maneuver) to attempt
to clear their ears at depth. If ear-clearing cannot be
NOAA Diving Manual — October 1991
Diagnosis and Treatment of Diving Casualties
Table 20-1
Characteristics of Inner Ear
Barotrauma and Inner Ear
Decompression Sickness
Inner ear barotrauma
Inner ear decompression sickness
1. Time of symptom onset
During compression (associated with
middle ear barotrauma) .
During or shortly after decompression.
2. Dive characteristics
Dives not requiring staged
decompression.
Dives requiring staged decompression.
Can occur during compression phase
Dives without proper, staged ascents.
of deeper dives.
Dives with rapid descents.
Reported cases associated with air
More common during decompression
diving — can probably occur with
from helium dives — can occur with air
helium diving.
diving.
3. Possible associated symptoms
Difficulty with ear clearing and/or ear
None or other symptoms of
pain or drainage — frequent. May have
decompression sickness.
history of preexisting nasal, sinus, or
middle ear disease.
4. Possible associated physical findings
Signs of middle ear barotrauma —
None or other signs of decompression
frequent.
sickness.
Source: Bennett and Elliott (1982) .
with the permission of Bailliere Tindall Ltd.
performed easily at depth, the diver should ascend
until the ears can be cleared, even if this means that
the dive must be aborted.
Treatment
Any diver who experiences persistent vertigo, hear-
ing loss, or noise in the ear after a dive should consider
the possibility of inner ear barotrauma. Any diver with
these symptoms should be placed immediately on bed
rest, with the head elevated, and should avoid coughing,
nose blowing, or straining. If the dive involved a
no-decompression schedule or if the diver noted that
symptoms began when he or she had difficulty clearing
the ears during compression, inner ear barotrauma of
compression is the most likely cause. Recompression
therapy should be avoided in these cases, because it
would expose the diver to the same pressure change
that initially caused the injury. Immediate referral of
the patient to a medical specialist in ear, nose, and
throat problems is a matter of urgency.
20.2.7 Otitis Externa (Swimmer's Ear)
Exposure to water or humid atmospheres can produce
maceration, or softening and wasting, of the skin of the
ear canal. The canals itch or feel sore, and, if cleaned or
scratched with implements like Q-tips, paper clips, or
pencils, the macerated skin is further irritated and
may become infected. The resulting condition is called
October 1991 — NOAA Diving Manual
otitis externa. Divers who are exposed to water with a
high bacterial count, i.e., polluted water, are at spe-
cial risk for this infection (see Section 11). Divers
who have skin allergies or seborrheic dermatitis are
particularly vulnerable and may develop otitis externa
from showering or shampooing even when they are not
diving or swimming.
Symptoms and Signs
Symptoms include pain, irritation, itching, and burn-
ing of the ear canal, sometimes accompanied by thin or
serous discharge. Examination shows an inflamed, swol-
len, and tender external ear canal. As the condition
worsens, the surrounding ear and skin become red and
the lymph nodes in the neck may also become tender
and enlarged. The condition may progress to complete
obstruction of the ear canal, abcess, and/or spread of
infection into the surrounding tissues.
Prevention
Special ear drops (Domeboro® otic solution) are
useful for general prophylaxis in humid and aqueous
environments, and they should be used after each expo-
sure (1-2 drops in each ear). If a diver is continuously
exposed, as occurs in saturation diving, these ear drops
should be used four times a day. Particular attention
should be paid to keeping the ear canal dry and to
maintaining a slightly acid pH in the secretions on the
skin surface. An easy and effective formulation is to
20-5
Section 20
add a dropper full of household vinegar to one ounce of
rubbing alcohol in a dropper bottle. The alcohol absorbs
water in the ear, while the vinegar restores its normal
acid pH. Another useful measure is to blow warm dry
air from a hair dryer into the ear canal gently after
each dive or before putting in ear drops.
WARNING
Do Not Put Otic Solutions Into the Ear if There
Is Any Possibility of Ruptured Ear Drum
Treatment
The treatment of otitis externa consists of cleansing
the canal, applying specific antibiotic therapy, restoring a
more normal acid-base balance to the canal, and
relieving the victim's pain. The pain is frequently severe
and may require analgesics for relief. Cases with severe
pain, significant swelling of the ear canal, and redness
or inflammation of the external ear should be referred
to a physician for treatment. Less severe cases can be
managed by irrigating the auditory canal, using
lukewarm tap water, and carefully drying the canal
after irrigation. After drying, a mild acid solution,
such as Domeboro® otic solution, should be applied.
This process should be repeated several times daily.
Swimming and diving should cease until the symptoms
have cleared completely.
of water makes diving possible, but these compressed
gases must infiltrate into all the rigid bony cavities
(the middle ear, sinuses, and chest cavity) to equalize
the pressure inside, or the resulting deformations will
lead to squeeze of these areas.
20.3.1 Face Mask Squeeze
Face mask squeeze is generally caused by failure to
admit air into the face mask during descent. It can also
occur if surface air pressure is lost and the diver is
wearing a surface-supplied mask without a non-return
valve. The resulting pressure differential between the
air pocket in the semi-rigid mask and the flexible
tissues of the face can result in serious tissue damage.
The most tender tissues are those covering and sur-
rounding the eyeball and the lining of the eyelids. In
serious cases of face mask squeeze, damage to the optic
nerve and blindness may occur. This type of squeeze
can be avoided entirely by exhaling into the mask
during descent or by having a non-return valve on the
gas supply line of a surface-supplied full-face mask.
Symptoms and Signs
• Sensation of suction on the face, or of mask being
forced into face
• Pain or a squeezing sensation
• Face swollen or bruised
• Whites of eyes bright red.
20.3 SQUEEZE OR BAROTRAUMA
The human body automatically adjusts to any change
in the pressure of the surrounding environment; it usu-
ally does so without the person involved noticing the
change. Most of the body is composed of watery tissue
that can transmit imposed pressure without deforma-
tion, but there are a few areas where this is not true. If
the gas pressure within some air-filled cavities of the
body, such as the middle ear or the bony sinuses of the
skull, is not easily equalized with the surrounding
pressure, an individual undergoing even mild pressure
changes (such as those that occur when riding an ele-
vator, driving in the mountains, or flying in an air-
plane) may be aware of the pressure difference. In
more severe cases, pain, accompanied by fluid and
blood in the middle ears or sinuses, may be the result of
a "squeeze" in these areas. Such effects are exagger-
ated in divers because the water that surrounds them is
much denser and heavier than air. The ability of diving
equipment automatically to deliver breathing gases
that are at the same pressure as the surrounding depth
20-6
Treatment
Ice packs should be applied to the damaged tissues
and pain relievers should be administered if required.
In serious cases, the services of a physician should be
obtained.
20.3.2 Middle Ear Squeeze
The most common transient ear problem associated
with diving is middle ear squeeze or barotrauma, which is
caused by inadequate pressure equalization between
the middle ear and the external environment. Most
divers have experienced middle ear squeeze at one
time or another.
Symptoms and Signs
The symptoms of middle ear squeeze consist initially of
pain and a sensation of ear blockage (see Section 20.2.1).
Conductive hearing loss is always present but may not
be the afflicted diver's primary complaint because of
the intense ear pain. Mild tinnitus and vertigo may also
NOAA Diving Manual — October 1991
Diagnosis and Treatment of Diving Casualties
occur. If the ear drum ruptures, the pain is usually
severe; vertigo may also occur, especially if cold water
has entered the ear.
Nasal conditions such as congestion and discharge
increase the likelihood of poor eustachian tube func-
tion during the dive. However, the absence of predive
symptoms does not guarantee that a diver will not
develop middle ear barotrauma. Divers who develop
symptoms of middle ear barotrauma should discon-
tinue diving immediately and should have their ears
examined by a physician.
Treatment
Divers who have difficulty clearing their ears and
who are not able to resolve this difficulty quickly (for
example by ascending a little way and then gently
trying to clear their ears again) should stop diving for
the moment. After returning to the surface, they should
be examined by a qualified person to determine whether
there is fluid or blood in the middle ear behind the
eardrum.
Often, returning to the surface is all that is necessary to
relieve the symptoms of mild ear squeeze, but it may
take a few days for the fluid or blood to drain from or
be absorbed from the middle ear cavity. A nasal decon-
gestant spray, nose drops, a mild vasoconstrictor
medication, or an antihistamine taken by mouth may
help to alleviate eustachian tube blockage and facili-
tate drainage from the middle ear. Chewing gum,
yawning, or swallowing may also help.
If examination reveals that the diver has a rupture of
the ear drum, the diver should stay out of the water
until the tear has healed, which usually occurs quickly
(unless an infection in the ear delays the repair process).
To monitor the healing process and take steps to con-
trol infection in the damaged ear, any diver with a
ruptured ear drum should be seen by a physician.
20.3.3 Round Window Rupture
Round window rupture is most often a result of very
forceful attempts to equalize ear pressures. Examina-
tion and treatment by an ear, nose, and throat special-
ist is important to prevent permanent injury in these
cases.
Symptoms and Signs
If hearing loss, tinnitus, or vertigo occur in associa-
tion with a no-decompression dive, barotrauma with
round window rupture and inner ear damage should be
suspected. These symptoms and signs may indicate a
serious condition.
Treatment
Divers who have developed deafness, ringing in the
ears, or vertigo during a difficult descent or in a
no-decompression dive may have suffered a rupture of
the round window in the inner ear and should be referred
immediately to an ear, nose, and throat specialist as a
medical emergency. If inner ear barotrauma is suspected,
recompression therapy should not be attempted, because
this therapy exposes the diver to the same pressure
differentials that resulted in the initial injury and could
thus exacerbate round window and inner ear damage.
Figure 20-1 illustrates the structure of the external,
middle, and inner ear.
20.3.4 Sinus Squeeze
The sinus cavities are air pockets located within the
skull bones that have openings into the nasal passages
(see Figure 3-7). These cavities are lined with a mucous
membrane. As in middle ear squeeze, sinus squeeze
normally is the result of diving with a cold or head
congestion. Adequate ventilation and pressure equali-
zation in the paranasal sinuses are important in diving,
both in descent and ascent, and depend to a large
degree on adequate nasal function. Inflammation and
congestion of the nasal mucosa caused by allergies,
smoking, chronic irritation from prolonged or exces-
sive use of nose drops, upper respiratory tract infec-
tions, or structural deformities of the nose can result in
blockage of the paranasal sinus openings. The inability
to equalize pressure on descent creates negative relative
pressure within the sinus cavity, deforming the mucous
membrane and causing swelling, fluid exudation, hemor-
rhage, and pain. Paranasal sinus barotrauma also may
occur during ascent. In this case, the key mechanism is
thought to be one-way blockage of the sinus opening
by cysts or polyps located within the sinus that allow
pressure equalization during descent but not during
ascent.
Symptoms and Signs
• Sensation of fullness or pain over the involved
sinus or in the upper teeth
• Numbness of the front of the face
• Bleeding from the nose.
i
Treatment
The treatment of sinus squeeze may involve the use
of nose drops, vasoconstrictors, and antihistamines taken
by mouth. These medications will promote nasal mucosal
shrinkage and opening of the sinus. Most of the symp-
toms of paranasal sinus barotrauma disappear within
5 to 10 days without serious complications. Divers who
October 1991 — NOAA Diving Manual
20-7
Section 20
Figure 20-1
Structure of External,
Middle, and Inner Ear
Semicircular canals
Endolymphatic
duct and sac
EXTERNAL EAR
MIDDLE I
1 EAR '
The air-containing external auditory canal, middle ear and eustachian tube are noted.
The fluid-filled inner ear is subdivided into the perilymphatic and endolymphatic
spaces, which connect to the subarachnoid space by the cochlear duct and
endolymphatic duct, respectively. Source: Bennett and Elliott (1982) ,
with the permission of Bailliere Tindall Ltd.
have symptoms for longer periods should see a special-
ist. If severe pain and nasal bleeding are present or if
there is a yellow or greenish nasal discharge, with or
without fever, a specialist should be seen promptly.
Individuals with a history of nasal problems or sinus
disease should have a complete otolaryngologic evalu-
ation before beginning to dive.
20.3.5 Lung Squeeze (Thoracic Squeeze)
Lung squeeze is a hazard for the breath-hold diver.
It occurs when the ambient pressure rises but there is
no corresponding intake of air into the lungs. Tissue
damage can result when the size of the lungs has been
reduced below the residual volume.
Symptoms and Signs
• Feeling of chest compression during descent
• Pain in the chest
• Difficulty in breathing on return to the surface
• Bloody sputum.
Treatment
In severe cases of lung squeeze, the diver requires
assistance to the surface. The diver should be placed
face down, and blood should be cleared from the mouth. If
20-8
breathing has ceased, cardiopulmonary resuscitation
with oxygen (if available) should be administered. Atten-
dants should be alert for symptoms of shock, and treat-
ment for shock should be instituted, if necessary. A
physician should be summoned as quickly as possible.
20.3.6 External Ear Squeeze
External ear squeeze is related to blockage of the
external ear canal during descent or ascent. Such block-
age causes ear canal pressure to be negative relative to
both ambient and middle ear pressure, which causes
damage to the tympanic membrane (ear drum) and
some swelling of the lining of the external auditory
canal. The common causes of external ear canal ob-
struction are wax or other foreign bodies, mechanical
ear plugs, or a tight-fitting diving hood.
Symptoms and Signs
• Fullness or pressure in region of the external ear
canals
• Pain
• Blood or fluid from external ear
• Rupture of ear drum.
Prevention
• Use of solid ear plugs should be prohibited in
diving
• Fit of diving hoods and earphones should be adjusted
so that they do not completely cover or seal the
external ear canal during ascent or descent
• Accumulated wax that can obstruct the ear canal
should be removed by gently irrigating the canal
with a lukewarm water solution, using a rubber
bulb syringe. Care should be taken before irriga-
tion to guarantee that there is no ear drum per-
foration behind the obstructing wax.
Treatment
Ear drum rupture should be treated according to the
procedures for treating middle ear barotrauma. These
procedures are described above, in Section 20.3.2.
20.4 DECOMPRESSION SICKNESS AND
GAS EMBOLISM
The only adequate treatment for decompression sick-
ness or gas embolism in divers is recompression in a
recompression chamber. However, all of the pain a
diver experiences after a dive may not be the result of
decompression sickness, and other causes should be
kept in mind. Generally, however, if symptoms of decom-
pression sickness or gas embolism are observed, it is
NOAA Diving Manual — October 1991
Diagnosis and Treatment of Diving Casualties
prudent to initiate recompression treatment rather than
to delay. If it cannot be determined whether the diver
has serious decompression sickness or gas embolism,
the treatment for gas embolism should be chosen; the
correct diagnosis is often not made until after the
events of the dive have been reviewed with the patient.
(See Figure 20-2 for a comparison of the symptoms
and signs of decompression sickness and gas embo-
lism.) Although immediate recompression is not a matter
of life and death with pain-only bends (as it is in
central nervous system decompression sickness or gas
embolism), there is a relationship between the speed
with which the patient is recompressed and the rate of
recovery and avoidance of permanent damage.
Divers can help to reduce the incidence of decom-
pression sickness by knowing and following established
limits for depth and time at depth. The hazard of flying
at altitudes as low as 1220 meters (4000 feet) even
after safe depth-time dives should also be recognized
(see Section 14.8).
20.4.1 Decompression Sickness
Decompression sickness, also known as caisson dis-
ease or compressed air illness, is the result of inade-
quate decompression after an exposure to increased
pressures. (See Section 3.2.3.2 for a detailed descrip-
tion of decompression sickness symptoms.) The condi-
tion is classified in two categories: Type I or pain-only
bends, and Type II or central nervous system bends.
20.4.1.1 Decompression Sickness— Pain Only
Type I decompression sickness usually occurs within
6 hours after a dive but may occasionally be diagnosed
as long as 24 to 48 hours after surfacing. The signs and
symptoms of pain-only decompression sickness are
described below.
Symptoms and Signs
• Local pain, usually in joints of arms or legs
• Pain made worse by exercise
• Itching
• Blotchy skin rash.
Immediate Action
• Perform quick neurological examination before
recompression to ensure that case is pain only
• Put patient on oxygen (if possible)
• Enter chamber, put patient on oxygen, initiate
recompression on appropriate treatment table
• Examine patient thoroughly.
October 1991 — NOAA Diving Manual
Treatment
Directions for the treatment of pain-only decom-
pression sickness are presented in Section 20.4.5, the
list of U.S. Navy Treatment Tables in Table 20-2, the
decompression sickness treatment flowchart (Fig-
ure 20-3), and in Appendix C.
20.4.1.2 Decompression Sickness — Serious
Symptoms
The onset of Type II or central nervous system (CNS)
decompression sickness usually occurs within 6 hours
of surfacing. The signs and symptoms and treatment
of this condition are described below.
Symptoms and Signs
• Dizziness
• Ringing in ears
• Difficulty in seeing
• Shortness of breath
• Rapid breathing
• Choking
• Severe pain
• Pain in abdomen
• Extreme fatigue
• Loss of sensation (numbness)
• Weakness of extremities
• Staggering
• Paralysis
• Collapse or unconsciousness.
Immediate Action
• Institute cardiopulmonary resuscitation, if necessary
• Administer oxygen
• Start immediate recompression on appropriate
treatment table
• Perform physical examination, including a neuro-
logical examination, as soon as patient's situation
permits
• Provide additional life support measures
• Repeat, and complete, physical examination when
patient is at treatment depth in recompression
chamber.
Treatment
For treatment procedures, see Section 20.4.6, the
list of U.S. Navy Treatment Tables in Table 20-2, the
decompression sickness treatment flowchart (Fig-
ure 20-3), and in Appendix C.
20.4.2 Gas (Air) Embolism
A gas embolism occurs when a bubble of gas (or air)
causes a blockage of the blood supply to the heart,
20-9
Section 20
Figure 20-2
Summary of Decompression Sickness
and Gas Embolism Symptoms and Signs
DIAGNOSIS OF DECOMPRESSION SICKNESS AND GAS EMBOLISM
DECOMPRESSION SICKNESS GAS EMBOLISM
SERIOUS CNS SYMPTOMS
SYMPTOMS AND
SIGNS
Skin
Pain-
Only
CNS
Chokes
Brain
Damage
Spinal
Cord
Damage
Pneumo-
thorax
Mediastinal
Emphysema
Pain-head
Pain-back
□
Pain-neck
■ Probable
□ Possible
CONFIRMING INFORMATION
Diving History
Decompression obligation?
Decompression adequate?
Blow-up?
Breath-hold?
Non-pressure-cause?
Previous exposure?
Yes No
□ □
□ □
□ □
□ □
D □
□ □
Patient examination
Does diver feel well?
Does diver look and act normal?
Does diver have normal strength?
Are diver's sensations normal?
Are diver's eyes normal?
Are diver's reflexes normal?
Is diver's pulse rate normal?
Is diver's gait normal?
Is diver's hearing normal?
Is diver's coordination normal?
Is diver's balance normal?
Does the diver feel nauseated?
Pain-chest
D
■
□
■
□
Pain-stomach
■
□
Pain-arms/ legs
■
□
Pain-shoulders
■
D
Pain-hips
■
"'□
Unconsciousness
□
□
□
Shock
D
□
□
Vertigo ■
Visual difficulty ■ ■
Nausea/vomiting ■ ■
Hearing difficulty ■ ■
Speech difficulty ■ ■
Balance lack ■ ■
Numbness
□
□
□
Weakness
□
□
Strange sensations
□
□
Swollen neck
■
Short of breath
□
■
□
□
□
D
Cyanosis
□
□
D
□
□
Skin changes
■
Yes No
□ □
□ D
□ □
D D
D D
□ □
□ D
□ □
□ □
a □
D D
□ □
20-10
Source: US Navy (1985)
NOAA Diving Manual — October 1991
Diagnosis and Treatment of Diving Casualties
Table 20-2
List of U.S. Navy
Recompression Treatment Tables
TABLE USE
TABLES USED WHEN OXYGEN AVAILABLE
4 Air/Oxygen Treatment of
Type II Decompression Sickness
or Gas Embolism
Treatment of worsening symptoms during the first
20-min oxygen breathing period at 60 feet on Table 6
or unresolved arterial gas embolism symptoms after 30 min
at 165 feet.
5 Oxygen Treatment of Type 1
Decompression Sickness
Treatment of Type I decompression sickness when
symptoms are relieved within 10 minutes at 60 feet and a
complete neurological exam was done and is normal.
6 Oxygen Treatment of Type II
Decompression Sickness
Treatment of Type II decompression sickness or Type I
decompression sickness when symptoms are not relieved
within 10 minutes at 60 feet.
6A Air and Oxygen Treatment of
Gas Embolism
Treatment of gas embolism symptoms relieved within 30 min
at 165 feet. Use also when unable to determine whether
symptoms are caused by gas embolism or severe decom-
pression sickness.
7 Air and Oxygen Treatment of Life
Threatening or Extremely Serious
Symptoms
Treatment of unresolved severe symptoms at 60 feet
after initial treatment on Table 6, 6A or 4. Used only in
consultation with a Diving Medical Officer.
TABLES USED WHEN OXYGEN NOT AVAILABLE
1A Air Treatment of Type I Decom-
pression Sickness— 1 00-foot
Treatment
Treatment of Type I decompression sickness when oxygen
unavailable and pain is relieved at a depth greater than
66 feet.
2A Air Treatment of Type I Decom-
pression Sickness— 165-foot
Treatment
Treatment of Type I decompression sickness when oxygen
unavailable and pain is relieved at a depth greater than
66 feet.
3 Air Treatment of Type II Decom-
pression Sickness or Gas Embolism
Treatment of Type II symptoms or gas embolism when
oxygen unavailable and symptoms are relieved within 30 min
at 165 feet.
4 Air Treatment of Type II Decom-
pression Sickness or Gas Embolism
Treatment of symptoms which are not relieved within
30 min at 165 feet using Air Treatment Table 3.
NOTE: 1 Always use Oxygen Treatment Tables when oxygen available.
2 Helium-oxygen may be used in lieu of air on these treatment tables upon the recommendation of a
Diving Medical Officer.
Source: US Navy (1985)
brain, or other vital tissue. The bubble tends to increase in
size as the pressure decreases (Boyle's Law), which
makes the blockage worse. (A more complete discus-
sion of gas embolism is given in Section 3.2.2.4.) When
divers hold their breath or have local air trapped in
their lungs during ascent, the pressure-volume re-
lationships discussed above can occur. Alveoli can rup-
ture or air can be forced across apparently intact alveoli.
If air bubbles enter the pulmonary veins, they are
October 1991 — NOAA Diving Manual
swept to the left side of the heart and pumped out into
the aorta. Bubbles can enter the coronary arteries sup-
plying the heart muscle, but they are more commonly
swept up the carotid arteries to embolize the brain. As
the bubbles pass into smaller arteries, they reach a
point where they can move no further, and here they
stop circulation. Symptoms of gas embolism usually
occur immediately or within 5 minutes after surfacing.
One, a few, or all of the symptoms listed below may be
20-11
Figure 20-3
Decompression Sickness
Treatment From Diving
or Altitude Exposures
Section 20
Diagnosis:
Decompression
Sickness
w
Diver on Oxygen
Compress to
60 Feet
1
'
Complete First
20 Min Oxygen
Breathing Period
No
Remain at
60 Feet at
Least 12 Hrs
Decompress
on
Table 7
Note 3
Decompress
on
Table 4
Note 2
n
/ Type II >.
' Symptoms ^v
N. Note 1 /
Decompress to
60 Feet on
Table 4
Note 2
JL Ves
i
I
^r Worsening >w
^ Symptoms and ^\
Need for Deeper
v Recompression J
N. Note 2 >^
. Yes
Compression on Air
to 165 Feet
and Remain
30 to 120 Min
Complete Two
More Oxygen
Breathing Periods
on Table 6
NOTES:
1 — If a complete neurological exam was not completed before
recompression, treat as a Type II symptom.
2 — A Diving Medical Officer should be consulted if at all possible before
committing to a Treatment Table 4.
3 — Commit to a Treatment Table 7 only in consultation with a Diving
Medical Officer.
4 — Treatment Table 6 may be extended up to two additional oxygen
breathing periods at 60 feet.
5 — Treatment Table 6 may be extended up to two additional oxygen
breathing periods at 30 feet.
(
i
20-12
Source: US Navy (1985)
NOAA Diving Manual — October 1991
Diagnosis and Treatment of Diving Casualties
present. Prompt recompression is the only treatment
for gas embolism. Patients should be treated in ac-
cordance with appropriate U.S. Navy Treatment Tables
(see Figure 20-4), or the tables in Appendix C.
WARNING
Gas Embolism Is An Absolute Medical Emer-
gency and Requires Immediate Treatment
Symptoms and Signs
• Chest pain
• Cough or shortness of breath
• Bloody, frothy sputum
• Headache
• Visual disturbances such as blurring
• Blindness, partial or complete
• Numbness and tingling
• Weakness or paralysis
• Loss of sensation over part of body
• Dizziness
• Confusion
• Sudden unconsciousness (usually immediately after
surfacing but sometimes before surfacing)
• Cessation of breathing.
Immediate Action
• Institute cardiopulmonary resuscitation, if necessary
• Administer oxygen
• Start immediate recompression
• Perform physical examination, including a neuro-
logical examination, as soon as situation permits
• Provide additional life support measures
• Repeat, and complete, physical examination when
patient is at treatment depth in recompression.
Treatment
Rescuers and attendants must be aware that most
embolism victims are also near-drowning victims.
Positioning the patient with the head low, in the left
side position, is recommended, but trying to position
the patient should not be allowed to interfere with the
immediate administration of CPR. If available, 100 per-
cent oxygen should be administered, and the patient
should be moved as rapidly as possible to a recompression
chamber that has a 6-ATA pressure capability. A gas
embolism case is a minute-to-minute emergency
transfer. The chances of full recovery decrease with
each minute lost in returning the patient to pressure. If
air transportation is required, the patient must not be
exposed to decreased cabin pressure during transit;
consequently, aircraft capable of being pressurized to
sea level must be used. If a helicopter or unpressurized
October 1991 — NOAA Diving Manual
aircraft is used, the cabin pressure must not be allowed to
exceed a few hundred feet of altitude (see Section 14.9).
The patient should be transported as rapidly as possible
to the nearest adequate recompression facility. Despite
the decreased chance of recovery if therapy is delayed,
patients have responded even after several hours'
delay. Victims should not be taken back into the
water for treatment.
20.4.3 Omitted Decompression
In situations such as blow-up, loss of air supply,
bodily injury, or other emergencies, a diver may be
required to surface prematurely, without taking the
required decompression. If a diver has omitted the
required decompression and shows any symptom of gas
embolism or decompression sickness after surfacing,
immediate treatment using the appropriate treatment
table should be instituted. Treatment in a recompression
chamber is essential for these omitted decompression
accidents.
Even if the diver shows no ill effects from omitted
decompression, immediate recompression is essential.
The diver should be compressed to the depth appropri-
ate for the table selected (USN Table 5 or 1 A or
any other appropriate Appendix C recompression table).
If no ill effects are evident, the diver should then be
decompressed in accordance with the appropriate
treatment table. Any decompression sickness developing
during or after this procedure should be considered a
recurrence (see Section 20.4.7).
NOTE
The procedure for in-water treatment for
omitted, asymptomatic decompression is
described in Appendix B and Section 14.8.
This procedure should be used only if no
recompression chamber is available.
20.4.4 Pretreatment Procedures
Patients may arrive at a chamber in almost any condi-
tion: they may have only a mild ache in a joint or they
may be comatose. In the best of circumstances, the
patient will arrive at the treatment chamber in a
pressurized, transportable chamber that is capable of
being mated to the treatment chamber. (For a sum-
mary of patient handling procedures, see Table 20-3.)
In all instances, a rapid examination must be made to
determine the condition of the patient. To establish a
baseline, the patient is examined at ground level, before
the chamber is pressurized. When signs of gas embo-
20-13
Section 20
Figure 20-4
Treatment of Arterial
Gas Embolism
Diagnosis:
Arterial Gas
Embolism
Compress on
Air to 165 Feet
Complete 30 Minute
Period Breathing Air
on Table 6A
Remain at
165 Feet an
No
Additional
90 Min.
'
'
Decompress
on Table 4
to 60 Feet
Decompress to
60 Feet at 26
Feet Per Minute
Complete
Treatment
Table 6A
Note 3
NOTES:
1 — A Diving Medical Officer should be consulted if at all possible before
committing to a Treatment Table 4.
2 — Commit to a Treatment Table 7 only in consultation with a Diving Medical Officer.
3 — Treatment Table 6A may be extended if necessary at 60 and/or 30 feet.
yS Symptoms \.
Still Present and
More Time Needed
. at 60 Feet? .,
\. Note 2 yS
\ No /
Complete /
> 1
Table 4 /
Note 1 /
|Yes
Remain at
60 Feet at
Least 12 Hours
J
Decompress /
on /
7
Table 7 /
Note 2 /
Source: US Navy (1985)
lism are present, the patient must immediately be
pressurized to 165 fsw (see Figure 20-4). To determine
which treatment table to use and to gauge the success
of the treatment, this examination is repeated on reaching
treatment depth and thereafter. The minimum exami-
nation must include:
• A discussion with the patient to determine the
cause of the accident, how the patient feels, and
his or her level of alertness
• Testing of the patient's:
— Blood pressure
— Pulse and respiration rates
— Eyesight
— Hearing
— Reflexes
— Muscular coordination
— Strength
20-14
— Balance
— Response to pinprick.
For further information on the preliminary examina-
tion of victims suffering from hyperbaric-related acci-
dents, see Section 19.6.2.
20.4.5 Tending the Patient
When a recompression treatment is conducted for
pain-only decompression sickness, an experienced
physician or diving medical technician should tend the
patient inside the chamber. The inside tender must be
familiar with all treatment procedures and with the
signs, symptoms, and treatment of diving-related injuries
and illnesses. If it is known before the treatment begins
that specialized medical aid must be administered to
the patient, or if a gas embolism is suspected, a physician
should accompany the patient inside the chamber. If
NOAA Diving Manual — October 1991
Diagnosis and Treatment of Diving Casualties
Table 20-3
General Patient
Handling Procedures
Patient
Walking
Medical/Recent
Diving History
+
Brief Medical
Examination
*
Patient Not
Walking
Prepare For
Entering
Chamber
+
Patient In
Pressurized
Transportable
Chamber
Put In
Chamber
+
Begin
Recompression
♦
Examination
*
Begin Treatment
According To
Appropriate Table
+
Completion Of
Treatment
+
Post-Treatment
Examination And
Observation
the chamber is sufficiently large, a second tender may
also enter the chamber to assist during treatment. Inside
the chamber, the tender ensures that the patient is
lying down and positioned to permit free blood circulation
to all limbs. During any treatment, the inside tender
must remain alert for symptoms of oxygen toxicity.
These symptoms can be remembered with the aid of
the acronym V-E-N-T-I-D, which derives from:
• VISION, which may include any abnormality, such
as tunnel vision (a contraction of the normal field of
vision, as if looking through a tube)
• EARS, which may include any abnormality of
hearing
• NAUSEA, which may be intermittent
October 1991 — NOAA Diving Manual
• TWITCHING, which usually appears first in the
lips or other facial muscles but may affect any
muscle. (This is the most frequent and clearest
warning of oxygen poisoning.)
• IRRITABILITY, which includes any change in
behavior, such as anxiety, confusion, and unu-
sual fatigue
• DIZZINESS, which may additionally include
symptoms such as difficulty in taking a full breath,
an apparent increase in breathing resistance,
noticeable clumsiness, or lack of coordination.
20.4.6 Treatment Tables
The primary treatment for decompression sickness
is recompression. Recompression tables developed by
many different agencies and organizations are availa-
ble. These include USN Treatment Tables 1A, 2 A, 3,
4, 5, 6, 6A, and 7; Figure 20-3 summarizes the use of
these tables. The NOAA Diving Safety Board recom-
mends a number of recompression procedures for treating
diving accidents; these tables are shown in Appendix
C, along with an Accident Treatment Flowchart to be
followed when selecting a treatment strategy. The first
step in any treatment involves diagnosing the condi-
tion properly. Figure 20-2 is a diagnostic aid designed
to ensure the selection of an appropriate table. Once a
treatment table has been chosen, treatment is conducted
by carrying out the recompression procedures speci-
fied for that table (see Figures 20-3, 20-4, and Appendix
C). If complications occur during or after treatment,
the procedures shown in Figure 20-5 and Appendix C
apply.
20.4.7 Failures of Treatment
Four major complications may affect the recom-
pression treatment of a patient. These are:
• Worsening of the patient's condition during
treatment
• Recurrence of the patient's original symptoms or
development of new symptoms during treatment
• Recurrence of the patient's original symptoms or
development of new symptoms after treatment
• Failure of symptoms of decompression sickness or
gas embolism to resolve despite all efforts using
standard treatment procedures.
When any of these complications occurs, the advice of
diving medicine experts should be sought immediate-
ly, because alternative treatment procedures have been
developed and used successfully when standard treat-
ment procedures have failed. These special procedures
may involve the use of saturation diving decompres-
sion schedules; cases of this type occur more frequently
20-15
Section 20
Figure 20-5
Treatment of Symptom Recurrence
Recurrence During Treatment
Recurrence Following Treatment
Recurrence
During
Treatment
Compress to
Depth of Relief
(165 Feet Maximum)
With Patient
Off 02
Remain at
Depth 30 to
120 Min.
to 60 Feet
on Table 4
NOTES:
1 —A Diving Medical Officer should be consulted if at all possible before
committing to a Treatment Table 4.
2 —Commit to a Treatment Table 7 only in consultation with a Diving Medical
Officer.
3 —Treatment Table 6 may be extended up to two additional oxygen breathing
periods at 60 feet.
Recurrence
Following
Treatment
No
Continue
and/or
Extend
Current Table
Yes
Diver on Oxygen
Compress to
60 Feet
Complete Three
20 Min. Oxygen
Breathing Periods
at 60 Feet
Symptoms
Relieved
7
No
Needed?
Note 1
No
Yes
Treat According
to Rgure 20-3
Decompress
-**/ on
Table 6
v No
./
Decompress /
on /
Table 6 /
^More Time Needed^1
Table 6
May be
Extended at
30 Feet
w at 60 Feet .
N. 7 /
7
Extended /
>v Note 3 /
[Yes
./
1
Remain at
60 Feet at
Least 12 Hours
Decompress /
on /
v N°
1
Table 7 /
Note 2 /
/
I Y8S
J
^^symptomsN.
^/'still Present and^
More Time Needed
V at 60 Feet /
/
Complete /
Table 4 /
7
Note 1 /
.Note
20-16
Source: US Navy (1985)
NOAA Diving Manual — October 1991
Diagnosis and Treatment of Diving Casualties
when a significant period of time has elapsed between
the onset of symptoms and the initial recompression.
Although it is important to know that alternative
procedures are available, it is equally important to
note that they have not been standardized. It is there-
fore essential that the advice of experts in the field of
hyperbaric medicine be obtained as soon as there are
indications that the standard treatment procedures are
not alleviating the symptoms. The use of an oxygen-
nitrogen saturation therapy may be the only course of
action when the situation involves a paralyzed diver
already at depth whose condition is deteriorating.
20.5 OTHER LUNG OYERPRESSURIZATION
ACCIDENTS
In addition to gas embolism, several other types of
lung overpressurization accidents may occur under
diving conditions. These accidents include pneumo-
thorax, mediastinal emphysema, and subcutaneous
emphysema.
20.5.1 Pneumothorax
Pneumothorax is the result of air escaping from
within the lung into the space between the lungs and
the inner wall of the chest cavity. As the air continues
to expand, there is partial or total collapse of the lung.
In serious cases, the heart may be displaced and the
blood circulation may be diminished or stopped.
Symptoms and Signs
• Sudden onset of cough
• Shortness of breath
• Sharp pain in the chest, usually made worse by
breathing
• Swelling of neck veins
• Blueness (cyanosis) of skin, lips, and nailbeds
• Pain in chest, evidenced by grimacing or clutching
of chest
• A tendency to bend the chest toward the side involved
• Rapid, shallow breathing
• Irregular pulse.
Treatment
First aid treatment of pneumothorax consists of
administering oxygen. Unless air embolism is present,
recompression is not indicated. If breathing is impaired
seriously and no physician is available to vent the
pleural cavity with a chest tube or large needle, the
victim should be recompressed to the point of relief. A
qualified individual must then be locked into the chamber
to insert a chest tube before decompression is possible.
October 1991 — NOAA Diving Manual
20.5.2 Mediastinal Emphysema
Mediastinal emphysema (air within the chest in the
tissues between the lungs and the heart) may result
from rupture of a pleural bleb or injury to the lung,
esophagus, trachea, or mainstem of the bronchus.
Although not in itself serious, mediastinal emphysema
demonstrates that the lung has been overpressurized,
and close examination for the symptoms or signs of gas
embolism is therefore required.
Symptoms and Signs
• Pain under the breastbone that may radiate to the
neck, collarbone, or shoulder
• Shortness of breath
• Faintness
• Blueness (cyanosis) of the skin, lips, or nailbeds
• Difficulty in breathing
• Shock
• Swelling around the neck
• A brassy quality to the voice
• A sensation of pressure on the windpipe
• Cough.
Treatment
Unless gas embolism is also present, recompression
is not necessary for mediastinal emphysema. Medical
assistance should be obtained and oxygen administered, if
necessary.
20.5.3 Subcutaneous Emphysema
Subcutaneous emphysema has the same cause as
other lung overpressurization accidents but is not nearly
so serious. This condition results when air escaping
from the lung migrates out of the thorax into the sub-
cutaneous tissues (just under the skin), usually in the
area of the neck, collarbone, and upper chest. The two
conditions of subcutaneous and mediastinal emphy-
sema are often associated with one another, and the
signs of the two conditions may overlap.
Symptoms and Signs
• Feeling of fullness in the neck area
• Swelling or inflation around the neck and upper
chest
• Crackling sensation when skin is moved
• Change in sound of voice
• Cough.
Treatment
Unless complicated by gas embolism, recompression
is not necessary. The services of a physician should be
20-17
Section 20
obtained and oxygen should be administered if breath-
ing is impaired.
that communication, logging, and all phases of treat-
ment are carried out according to prescribed procedures.
20.6 MANAGEMENT OF THE
UNCONSCIOUS DIVER
When divers retrieved from the water are unconscious
or collapse soon after surfacing, they should be treated
for gas embolism unless another cause is clearly indi-
cated (see Section 20.4.2). The many possible causes
of unconsciousness include: gas embolism, decompression
sickness, cardiac arrest, carbon monoxide poisoning,
head injury, near-drowning, convulsion, insulin reaction
(in a diabetic on insulin), or hyperventilation or
hypoventilation. Regardless of the cause, the immedi-
ate priority if the patient is not breathing is cardio-
pulmonary resuscitation. Clearing of the airway, mouth-
to-mouth ventilation, and closed-chest heart massage
may also be required (see Sections 18.3 and 18.4).
Because the unconsciousness must be assumed to have
been caused by an embolism, the diver must be trans-
ported immediately to a recompression chamber. Dur-
ing transportation, the diver should be positioned, if
possible, with the head low and the body lying on the
left side. Cardiopulmonary resuscitation should be con-
tinued if necessary, and supplemental oxygen should
be administered if it is available. Resuscitation should
continue until the victim recovers or is pronounced
dead by a physician. Prompt recompression is necessary
for an unconscious diver under all conditions except
these two:
• Gas embolism or decompression sickness has been
completely ruled out.
• Another lifesaving measure that makes recom-
pression impossible, such as a thoracotomy, is
essential.
20.7 PERSONNEL REQUIREMENTS FOR
CHAMBER OPERATIONS
The minimum team for conducting any recompression
operation consists of a diving supervisor, an inside
tender, an outside tender and, depending on the cir-
cumstances, a diving physician. The responsibilities of
each of these team members are described below.
20.7.1 Diving Supervisor
The diving supervisor is in charge of the operation
and must be familiar with all phases of chamber operation
and treatment procedures. The supervisor must ensure
20-18
20.7.2 Inside Tender
The inside tender, who must be familiar with the
diagnosis of diving-related injuries and illnesses,
monitors and cares for the patient during treatment.
Other responsibilities of the inside tender include:
• Releasing the door latches (dogs) after a seal is
made
• Communicating with outside personnel
• Providing first aid as required by the patient
• Administering oxygen or helium-oxygen to the
patient
• Providing normal assistance to the patient as
required
• Ensuring that ear protection sound attenuators
are worn during compression and ventilation
• Maintaining a clean chamber and transferring body
waste as required.
During the early phases of treatment, the inside tender
must constantly watch for signs of relief of the patient's
symptoms. The patient should not be given drugs that
will mask the signs of sickness. Observing these signs is
the principal method of diagnosing the patient's condi-
tion, and the depth and time of symptom relief deter-
mine the treatment table to be used. The final decision
as to which treatment table to use must be made by the
diving supervisor on the recommendation of the attending
physician.
20.7.3 Outside Tender
The outside tender is responsible for:
• Maintaining and controlling the air supply to the
chamber
• Maintaining the oxygen supply to the chamber
• Keeping times on all phases of the treatment
(descent, stops, ascent, overall treatment)
• Keeping the dive log
• Communicating with inside personnel
• Decompressing any inside tending personnel leav-
ing the chamber before patient treatment is complete
• Pressurization, ventilation, and exhaust of the
chamber
• Operating the medical lock.
20.7.4 Diving Physician
The diving physician is trained in the treatment of
diving accidents. Although it may not be possible to
NOAA Diving Manual — October 1991
Diagnosis and Treatment of Diving Casualties
have a diving physician present during all treatments,
it is essential that the diving supervisor be able to
consult by telephone or radio with a diving physician.
When a diver is being recompressed, all attending
personnel must work as a team for the benefit of the
patient. Whether the inside or the outside tender operates
the chamber will be dictated by the availability of
qualified personnel and the circumstances of the casu-
alty being treated. If the patient has symptoms of
serious decompression sickness or gas embolism, the
team will require additional personnel. If the treat-
ment is prolonged, a second team may have to relieve
the first. Whenever possible, patients with serious
decompression sickness or gas embolism should be
accompanied inside the chamber by a diving medical
technician or diving physician, but treatment should
not be delayed to comply with this recommendation.
Effective recompression treatment requires that all
members of the treatment team be thoroughly trained
and practiced in their particular duties. It is also advisa-
ble to cross-train members to carry out the duties of
their teammates.
20.8 PRESSURE AND OXYGEN
TOLERANCE TESTS
Some government agencies require their divers or diver-
candidates to pass pressure or oxygen tolerance tests,
or both, before they are eligible for diver training or
annual recertification. Procedures for pressure and
oxygen tolerance tests have proven safe in many years
of experience with them. The purpose of the oxygen test
is to keep those individuals who are susceptible to
oxygen poisoning from diving.
20.8.1 Procedures for Pressure and Oxygen
Tolerance Tests
Procedures for pressure and oxygen tolerance tests
are as follows:
• The candidate must undergo a physical examina-
tion by a Diving Medical Officer and be cleared to
undergo the tests.
• The candidate and tender enter the recompression
chamber and are pressurized to 112 fsw (50 psig)
at a rate that can be tolerated by the candidate.
• The chamber is ventilated for one minute at 112 fsw
(33 m) to reduce the temperature.
• The chamber is brought to 60 fsw (18 m) at
60 fsw/min (18 m/min).
October 1991 — NOAA Diving Manual
• Upon arrival at 60 fsw, a new inside tender is
locked in and the first tender is placed in the outer
lock and decompressed in accordance with the
standard air decompression table. If a new inside
tender is unavailable, decompress both the candi-
date and the tender in accordance with the stand-
ard air decompression table upon completion of the
30-minute oxygen test. During this time, the can-
didate remains idle, and the chamber is ventilated
at 12.5 acfm for each person on 100 percent oxygen.
The tender must constantly monitor the candidate
for oxygen toxicity.
• The tender instructs the candidate in the use of the
oxygen mask, and the candidate breathes 100 percent
oxygen for 30 minutes.
• After 30 minutes, the chamber is depressurized to
the surface at a rate of 60 fsw/min (18 m/min).
• All candidates must remain at the chamber site
for a minimum of 15 minutes and in the vicinity
for 1 hour. Candidates should not fly after this
procedure until 12 hours have elapsed.
During pressurization, the candidate must demon-
strate the ability to equalize pressure in his or her ears
effectively and must otherwise withstand the effects of
pressure. During the oxygen tolerance test, if the can-
didate convulses or exhibits definite preconvulsive signs,
i.e., twitching of the muscles of face or limbs, the test is
failed and the mask should be removed. In such a case,
the test is not to be repeated. If the candidate com-
plains of symptoms such as nausea, tingling, or dizzi-
ness during the test, the mask should be removed and
the test terminated, but in such a case the test may be
repeated at a later date, at the discretion of the diving
physician.
20.9 EMERGENCY MEDICAL RESPONSE
In anticipation both of the routine and unusual medical
problems that may arise in the course of diving, all
diving operations should have a medical emergency
response plan. Such a plan should cover assignment
of individual responsibilities in an emergency, the
location of equipment and supplies necessary for medical
treatment, the availability of a trained hyperbaric
physician, and procedures for ensuring adequate patient
transport to recompression or medical facilities, if
required. In addition, emergency kits should be avail-
able that can be used at the scene of a diving accident.
These kits should contain the equipment and supplies
necessary to treat victims of diving accidents and to
maintain life support measures until an emergency
medical team can arrive, or until transportation to a
definitive treatment facility can be arranged.
20-19
Section 20
20.9.1 Medical Equipment and Supplies
Before a diving operation begins, it is important to
consider what medical items would be needed in a
diving accident. These items should then be sorted into
those that can be used in a hyperbaric chamber and
those that will be kept at the surface. An excellent way
to handle this requirement is to establish medical kits
small enough to carry on a diving operation or to take
into the recompression facility. One suggestion, in
accordance with an emergency response plan, is to
place the necessary medical items into three kits, each
having a different purpose:
• Diving operations medical kit (first aid)
• Primary medical treatment kit, containing diag-
nostic and therapeutic equipment to be available
when required and to be inside the chamber during
all treatments.
• Secondary medical treatment kit, including equip-
ment and medical supplies that need not be imme-
diately available within the chamber but that could
be locked in separately when required.
20.9.2 Diving Operations Medical Kit
(First Aid)
The following items are recommended for a diving
operations medical kit that would be available at all
diving sites:
• General: Number
— Bandaids 50
— Tube of disinfectant (first aid cream) 1
— Aspirin tablets
— Dramamine®
• Diagnostic Equipment:
— Flashlight
— Stethoscope
— Otoscope-ophthalmoscope
— Sphygmomanometer (aneroid type only)
— Thermometer
— Reflex hammer
—Tuning fork (500, 1000, and 2000 Herz)
— Pin and brush for sensory testing
— Tongue depressors
— Bandage scissors
Bandages:
— Topper sponges
—Adhesive tape, 1/2", 1", 2" rolls
— Adhesive compress, 1"
— Bandage compress, 4"
6
2 each
2
2
20-20
— Eye dressing packet 2
— Gauze pads, sterile, 4" x 4" 10
— Curlex® roller bandage, 1" 4
— Curlex® roller bandage, 2" 4
— Curlex® roller bandage, 4" 2
— Triangular bandages, 40" 4
— Trauma dressing 2
Emergency treatment equipment:
— Oropharyngeal airway, large 1
— Oropharyngeal airway, medium 1
— Oropharyngeal airway, small 1
— Tongue depressor taped and padded
as a bite pad in case of seizures
— Oxygen resuscitator 1
— Resuscitator masks with water-
filled rim
— Flexible rubber suction catheter
— Plastic non-flexible suction tips
(Yankauer® Suction Tip)
— Asepto® syringe 1
— Tourniquet 1
— Tweezers 1
—Artery forceps (5" and 8") 2
—Splinting boards 4" wide x 12" 2
— Splinting boards 4" wide x 24" 2
— Wire ladder splints 2
— Liquid/crystal cold packs 3
—Blanket. 1
20.9.3 Primary Medical Treatment Kit
The suggested contents for a medical treatment kit
to be available in the recompression chamber during
every treatment:
• Diagnostic Equipment:
— Flashlight
— Stethoscope
— Otoscope-ophthalmoscope
— Sphygmomanometer (aneroid
type only)
— Thermometer
— Reflex hammer
—Tuning fork (500, 1000, and
2000 Herz)
— Pin and brush for sensory testing
— Tongue depressors
• Emergency Airway Equipment:
— Large-bore needle and catheter
(12 or 14 French) for cricothy-
roidotomy or relief of tension
pneumothorax
NOAA Diving Manual — October 1991
(
Diagnosis and Treatment of Diving Casualties
— Small Penrose® drain or Heimlich®
valve for adaption to a thoracentesis
needle to provide a one-way flow of
gas out of the chest
— Laryngoscope with extra batteries
and bulbs
— Laryngoscope blades
— Cuffed endotracheal tubes with
adaptors (8.0, 8.5, and 9.5 mm)
— Syringe and sterile water for cuff
inflation (10 ml)
— Malleable stylet (approx. 1 2" in
length)
— Sterile lubricant
— Soft rubber suction catheters
• Miscellaneous:
— Bandage scissors
— Tourniquet
— Adhesive tape
— Decongestant nasal spray
— Decongestant tablets
• Drugs:
— 5 percent dextrose in lactated
Ringers® solution
— 5 percent dextrose in normal saline
— 5 percent dextrose in water
— Dextran 70 in saline, 500 ml
— Normal saline, 500 ml
— Atropine for injection
— Sodium bicarbonate for injection
— Calcium chloride for injection
— Dexamethasone for injection
— Epinephrine for injection, 1 mg/ml
— Lidocaine® for injection
— Diphenhydramine hydrochloride
for injection
— Phenytoin sodium for injection
— Codeine tablets, 30 mg
— Aspirin tablets, 325 mg
— Sterile water for injection
— Injection methyl prednisolone
(40 mg/ml in 5 ml) or Decadron®
shock pack (dexamethasone)
— Injection Valium® (10 mg in 2 ml)
— Sterets® injection swabs.
When possible, preloaded syringes should be available
to avoid the need for venting the vial to prevent implo-
sion during pressure change within the chamber. If
necessary, vials can be vented with a needle inserted
through the rubber stopper for pressure equalization
during descent and ascent, but the sterility of such
vials should then be considered to have been violated
and the vial should be discarded and replaced.
20.9.4 Secondary Medical Treatment Kit
The following additional medical supplies are rec-
ommended for a kit to be kept somewhere near the
recompression chamber to ensure that the contents are
available to be locked into the chamber when they are
needed:
• Drugs:
— 5 percent dextrose in lactated
Ringers® solution
— 5 percent dextrose in normal saline
— 5 percent dextrose in water
— Dextran 70 in saline, 500 ml
— Normal saline, 500 ml
Intravenous infusion sets 2
Intravenous infusion extension sets 2
3-way stopcocks
Syringes (2, 5, 10, 30 ml)
Sterile needles (18, 20, 22 gauge)
Nasogastric tube
Catheterization set, urethral
Myringotomy knife
Wound closure instrument tray,
disposable
Sterile scalpel and blade assortment
Assorted suture material
Surgical soap
Sterile towels
Sterile gloves, surgical (sizes 6-8)
Gauze pads, sterile, 4" x 4"
Gauze roller bandage, 1" and 2",
sterile
Bandaids
Cotton balls
Splints
Eye patches
Medicut® cannula.
20.9.5 Use of the Kits
Because conditions on board ship, at land-based
diving operations, and at diver training sites differ,
the responsible physician should modify the contents
of the medical kits to suit the operation's needs. All
three kits should be taken to the recompression cham-
ber or scene of the accident. Sterile supplies should be
produced in duplicate. Any sterile supplies not sealed
adequately against changes in atmospheric pressure
should be resterilized after each pressure exposure or,
if not exposed in the interim, at 6-month intervals. All
October 1991 — NOAA Diving Manual
20-21
Section 20
drug ampules will not withstand pressure, and bottle
stoppers may be pushed in by increased pressure. Bot-
tles with stoppers may be vented with a needle during
pressurization and can then be discarded if not used.
The emergency kit should be sealed in such a way
that it can be opened readily when needed; the condition
of the seal should indicate that it has been opened.
Each kit should contain a list of contents, and each
time it is opened, the contents should be verified against
the inventory and the condition of all items checked.
Use of the primary or secondary medical treatment
kits should be restricted to the physician in charge or
to a diving medical technician. Concise instructions
for administration of each drug should be provided in
the kit. In untrained hands, many of these items can be
dangerous.
(
(
20-22
NOAA Diving Manual — October 1991
APPENDIX A
DIVING WITH
DISABILITIES
Page
Introduction A-l
Equipment A-l
Adapting Prostheses for Diving Use A-3
Training for Divers with Disabilities A-4
Basic Water Skills A-4
Diving Procedures A-4
Communication A-4
Equipment Preparation A-5
Equipment Donning A-5
Entries A-5
Drop Entries A-5
Beach Entries A-6
Snorkel and Regulator Use A-6
Ear Clearing A-6
Mask Clearing A-6
Buoyancy Control and Descents/ Ascents A-7
Trim A-7
Propulsion A-8
Buddy Breathing A-8
Use of Underwater Lines A-9
Exits A-9
Onto Boats or Piers A-9
Onto the Beach A-10
Assisted Exits A-10
Other Considerations A-10
Thermoregulation A-10
Catheters A-10
Protection of Paralyzed Tissue A-l 1
Decompression Sickness A-ll
Autonomic Dysreflexia A-ll
Summary A-ll
i
i
DIVING WITH
DISABILITIES
INTRODUCTION
Increasingly sophisticated scuba equipment and training
techniques have made diving accessible to more peo-
ple. Non-physical attributes such as good judgment, a
healthy respect for personal, environmental, and equip-
ment limitations, and constant attention to safety are
now considered as important, if not more important, to
safe recreational diving than physical strength. In
addition, the availability of tanks of various sizes and
of suits and equipment designed to fit divers with
different physical characteristics has enabled many
individuals to dive who do not fit the traditional
stereotype. Among these are divers with a variety of
disabilities; these divers must accomplish diving tasks
using a lesser amount of physical force than is the
case for able-bodied divers. The equipment and tech-
niques that these divers with disabilities use minimize
the amount of effort required to accomplish a given
task — a clear advantage for any diver. Thus all divers
can benefit from the techniques developed by divers
with disabilities.
There are many types of disabilities: vision, hearing,
and speech impairments; disabling conditions caused
by diseases such as cerebral palsy, multiple sclerosis,
diabetes, and arthritis; brain and other injuries caused
by accidents or illnesses; and emotional and learning
disabilities. This appendix is concerned with orthope-
dic disabilities, i.e., those that make standing, walk-
ing, climbing ladders, or negotiating sandy beaches in
dive gear difficult if not impossible.
Orthopedic disabilities include "bad" backs, paral-
ysis, and amputation. Divers with orthopedic disabili-
ties may have partial* or total paraplegia (loss of function
and, occasionally, of sensation in the lower body) or par-
tial or total quadriplegia (loss of function and sensa-
tion from the neck or chest down), or they may have
lost all or part of one or both legs and/or arms. Para-
plegia, quadriplegia, and amputation can occur as a
result of spinal cord injuries, polio, spina bifida, or
accidents. People with orthopedic disabilities use wheel-
chairs, braces and crutches, prosthetic limbs, and a
variety of other devices to achieve mobility.
* The medical community uses the terms "paraparesis" and
"quadriparesis," while the disability community uses "partial para-
plegia" or "partial quadriplegia."
October 1991 — NO A A Diving Manual
EQUIPMENT
It is essential that divers with disabilities use diving
equipment that accommodates their disability and
enhances dive safety. Divers with disabilities have found
the equipment listed below useful in the following
situations:
• Masks — a face mask that has a low volume and a
purge permits divers who have limited manual
dexterity or reduced lung capacity to clear their
mask easily;
• Snorkels — a snorkel that has a purge also permits
easy clearing by divers who have limited manual
dexterity or reduced lung capacity, and use of a
snorkel that has a flexible hose makes snorkel-to-
regulator exchange easier. Divers who have upper-
extremity prostheses, however, may find it easier
to use a fixed J-valve;
• Fins — even divers who have little or no control
over their legs find small fins an aid to stability.
Fins can also be modified to fit over an amputee's
stump or to attach to the hand or wrist to improve
the stroking efficiency of arm-stroking divers;
• Wet suits — divers who have paralyzed limbs or
who cannot flex their limbs find wet suits (prefer-
ably custom made) that have maximum flexibility
or zippers over gussets running the length of the
suit's arms and legs the easiest to don and doff
(Figure A-l). Mitts and boots that have Velcro® or
zipper closures are also available;
• Buoyancy compensators — the ideal buoyancy com-
pensator for divers with disabilities is a snug-fitting
jacket that has a full front, shoulder inflation, and
a "soft-touch" low-pressure inflator (Figure A-2).
Velcro® closure of the jacket facilitates donning
and doffing, and a pull dump mechanism operated
by an oversize knob, handle, or ring makes grasp-
ing easier. It is important that all controls be
mounted on the diver's functional or stronger side;
• Regulators — divers with disabilities find a low-
resistance regulator that has a lightweight second
stage most comfortable. The second stage must be
mounted on the diver's functional or stronger side.
It is important that divers who have upper-limb
prostheses or whose manual dexterity is limited
carry an octopus or other alternative air supply;
A-1
Appendix A
Figure A-1
Wet Suit with Zippers
Over Gussets
Figure A-2
Jacket-Type Buoyancy
Compensator
Courtesy Curt Barlow
Courtesy Curt Barlow
• Tanks — divers with disabilities prefer to use tanks
that are small and cause relatively little drag in
the water: 50 cubic-foot (1416 liter) aluminum
tanks or 63 cubic-foot (1784 liter) tanks are gen-
erally easier to manage than steel tanks, although
steel tanks may provide more desirable buoyancy
characteristics;
• Weights — traditional weight belts made of nylon
webbing that are used with lead "bullets" or blocks
provide divers with disabilities with maximum flexi-
bility in terms of weight placement. It is important
that the buckle be easy to manipulate and that the
belt be comfortable and secure;
• Gauges — to ensure that divers with disabilities
can view the necessary gauges (pressure, compass,
watch, etc.) at all times, it is possible to design a
holder (Figure A-3) for the console that is attached
to cross bars and is then secured to the buoyancy
compensator with Velcro® strips. Mounting a com-
pass with a side-view window on the console per-
mits the diver to take readings on the surface
(Figure A-4). To avoid magnetic interference with
the functioning of the compass caused by a metal
prosthesis, the compass can be mounted on a non-
metallic rod or be positioned at the head of the
console;
Lights — dive lights must be attached in a manner
that permits an arm-stroking diver to have free
use of his or her hands. In this situation, the light
can be mounted on the mask, wet suit hood, diving
helmet, or bicycle helmet with Velcro® fasteners
(Figure A-5). A lanyard or holster can be used to
attach a light to the waist strap of the buoyancy
compensator or to the inflator hose or weight belt.
For divers with an upper-extremity prosthesis, a
light in a holster can be strapped to the arm; and
Other equipment — divers with disabilities often
carry a compact camera on a strap around their
neck or in a zipper bag carried on the weight belt
and tank harness. In addition, lift bags that have
manual dumps are easier for divers with disabili-
ties to use than those without.
A-2
NOAA Diving Manual — October 1991
Diving with Disabilities
Figure A-3
Holder for Console
Figure A-5
Helmet-Mounted
Dive Light
Courtesy Curt Barlow
Figure A-4
Side-View Compass
Mounted on Console
Courtesy Curt Barlow
The use of equipment of the types described above
enables divers with orthopedic disabilities to perform
diving tasks safely and effectively. To ensure that the
equipment is easy and efficient to operate, divers should
practice using a variety of equipment in a supervised
pool environment before using it in the open water.
Practice is especially important with buoyancy com-
pensators because it is essential that these devices
support the diver at the surface in an upright position.
Adapting Prostheses for Diving Use
Some single- and double-leg amputee divers find
that they can get a powerful kick by attaching fins to
waterproof prosthetics. Figure A-6 shows a diver put-
ting fins over prosthetic feet that are attached to a leg
October 1991 — NOAA Diving Manual
Courtesy Curt Barlow
prosthesis by means of a long bar that can be slipped
into the prosthetic leg. The technology for adapting
prostheses is not standard, and divers must work with
their own prosthetists to develop an appropriate mod-
ification. Double amputees need prosthetic sockets
that will equalize the length of their legs to facilitate
walking on the boat or beach. Rubber pads glued to the
bottom of the prosthesis make a non-slip surface, and
removable feet can be aligned parallel to the body and
be attached to the socket with a long metal rod on top
and a Velcro®-closure strap on the foot that loops through
a ring on the back of the socket.
A single above-the-knee amputee might use a wooden
or otherwise waterproof 'peg leg' attached to a pros-
thetic socket. A fin could be attached directly to the
leg by means of Velcro® and other fasteners. A single
below-the-knee amputee might simply mount a fin
directly on the socket, since the difference in leg lengths is
not great enough to prevent a straight swim. A better
(and far more expensive) alternative is to use water-
proof prostheses that have drop-ankles that are held in
A-3
Appendix A
Figure A-6
Fins Being Placed
on Prosthetic Feet
Courtesy Curt Barlow
a walking position on the boat or beach. After entering
the water, the diver pulls a pin that releases the ankles,
and the foot flattens out to a swimming position.
Buoyancy must be considered when crafting pros-
theses for diving. If the buoyancy of the prostheses is
either too negative or too positive, the power the pros-
theses were designed to provide for propulsion will
instead be used just to maintain the diver's orientation
in the water.
TRAINING FOR DIVERS WITH DISABILITIES
In general, the training of divers with disabilities par-
allels that for able-bodied divers. An exception to this
rule occurs during the first pool or confined-water
training session, when it is important that the instructor-
to-student ratio be one-to-one. Limiting the size of
this first class to a single student allows the instructor
to assess the type and extent of the student's disability
and to determine what equipment and procedural modifi-
cations may be necessary. Once the student is com-
fortable and confident in the water, and the instructor
is assured that the student has the potential to manipulate
all of the necessary pieces of equipment and to perform
all emergency procedures safely, the student is ready
to join group training sessions and to learn those basic
water skills that are essential to the safety of all divers.
Basic Water Skills
Before divers enter the water, they must develop a
combination of basic water skills, a high level of com-
fort in the water, and sufficient fitness to enable them
to face unexpected stresses calmly and with confidence
and competence. The overwhelming majority of indi-
viduals who have orthopedic disabilities can develop
these skills and this level of physical fitness.
Although there is no consensus about what degree of
strength is needed for safe diving or how it can be
measured objectively, today's diving certification stand-
ards emphasize the diver's basic water skills, fitness,
and comfort in the water. These skills and levels of
fitness were historically measured by means of timed
distance surface swims and distance underwater
breathhold swims; however, these methods were
developed before it was common for people with disa-
bilities to dive.
Today, diving instructors would agree that all dive
training candidates must be able to maintain them-
selves comfortably on the surface of the water for
reasonable periods of time, both in a stationary posi-
tion and while moving through the water for a speci-
fied distance. These requirements emphasize stamina
rather than speed, skill, or physical force.
DIVING PROCEDURES
This section describes the steps involved in carrying
out a dive and emphasizes the techniques and proce-
dures divers with disabilities have developed to enable
them to dive. No diver should dive alone; this basic
rule of diving is even more critical for divers with
disabilities, who may encounter situations where help
is needed to continue the dive.
Communication
During dive planning, it is essential that all divers
with disabilities discuss methods of communication
that can appropriately be used with the diver's disabil-
ity. Divers with limited manual dexterity find it diffi-
cult to form most conventional hand signals used in
diving. They must therefore develop equivalent signals
and teach them to their buddies during dive planning.
A-4
NOAA Diving Manual — October 1991
Diving with Disabilities
Figure A-7
Transporting Gear
in the Lap and on
Footplates
Early in basic training, it is often a good idea for
divers who are forced to rely on buoyancy and weighting
for stability and orientation in the water to agree with
their instructors on a signal that means, 'I'm not in
trouble, but I could use some help.' In addition, because
divers with disabilities often tap, squeeze, or poke
their buddies to get their attention, divers must know
what parts of the body have sensation so that they will
know where to touch their buddies when they need help.
Equipment Preparation
The first task in diving is getting diving equipment
to the boat or beach. Not all dive sites are easily
accessible to individuals with a variety of mobility
impairments (wheelchairs, crutches, prostheses, or lim-
ited walking endurance). In such cases, assistance may
be needed to transport equipment and divers to the
site. When the paths between the stored equipment
and the dive site are easily negotiable, wheelchair users
may be able to carry their tanks on the foot plate
of their chair and their equipment bag on their lap
(Figure A-7). Others may need to make several trips,
carrying a reasonable load each time. In all cases,
however, it remains the diver's responsibility to in-
ventory his or her equipment and to ensure that all of it
gets to the site.
Equipment Donning
Divers who, for whatever reason, cannot stand while
supporting the weight of their diving gear don their
tank and jacket-type buoyancy control device (BCD)
while sitting down at the water entry point (Fig-
ure A-8). To save time in the staging area, all of the gear
that can be managed while mobile, including wet suit,
mask, and weight belt (assuming the BCD does not
have a crotch strap), is donned before moving to the
staging area. Once the diver is at the entry point,
someone passes the tank over and, if necessary, stabi-
lizes it as the diver puts it on.
When the staging area is a beach without surf, it is
easier to enter the water before donning the tank. The
tank and BCD are moved out into water deep enough to
make them float but not deep enough to present a
negative buoyancy problem for the weight belt; this
equipment is then donned there.
One of the most trying chores for any diver is getting
into a wet suit. A custom-made suit is preferred, but
any wet suit with maximum flexibility or with zippers
over gussets that extend the length of the suit's arms
and legs can be used. Wearing a lycra body suit or
Courtesy Curt Barlow
nylon stockings as a liner or using a dilute soap solution
as a lubricant greatly facilitates the donning of a wet
suit.
Entries
Drop Entries. Entries involving a drop (from a boat,
pier, or dock, for example) are the easiest, cleanest
entries for divers who gear up sitting down. There are
no standards for graceful seated entries as there are (at
least informally) for giant strides and other standing
entries. In the case of seated entries, any entry that
lands the diver and gear safely in the water is a good
entry.
Both forward and back roll entries are used by divers
who have limited lower body function. From the seated
position, the diver performs whatever version of a roll-
over is deemed most comfortable under the circumstances.
The forward roll, used for short drops (less than
2 feet (0.7 m)), is accomplished by leaning forward with
the chin tucked to the chest, which permits the diver to
October 1991 — NOAA Diving Manual
A-5
Appendix A
Figure A-8
Donning Gear
While Sitting
Courtesy Curt Barlow
fall straight into the water, landing face first. Some
divers prefer to add a sideways twist or to start out
sitting slightly sideways so that a shoulder hits the
water first.
When dropping into the water from a height of more
than 2 feet (0.7 m), such as from a boat with no plat-
form and a high gunwale, it is more comfortable to
have the water broken by the tank than the body.
Sitting backward on the edge of the gunwale with the
tank hanging out over the water, the diver simply falls
over backward. For those with lower body paralysis,
care should be taken to ensure that the legs are guided
over the side. As with any entry, the mask and regula-
tor are held in place by one hand, while the console and
any other loose items are held with the other.
Beach Entries. At beaches without surf, there is no
need for a fully geared entry, because the tank and
BCD are donned in water deep enough to cause them to
float. Divers using this technique should remember
that their weight belts become negatively buoyant in
the water and that they should don their BCD's quickly.
In a seated entry under surf conditions, mobility-
impaired divers must don their equipment near the
water's edge and move backward into the waves while
breathing with their regulator. When the water is deep
enough to swim, the diver rolls over and continues
beyond the surf zone, remaining either at the surface
or submerged.
With either of these beach entries, regulators are
likely to pick up an inordinate amount of particulate
matter. They should be checked carefully before begin-
ning a descent and will need to be taken in frequently
for periodic maintenance.
Snorkel and Regulator Use
Divers with limited manual dexterity, a limited range
of motion, or a prosthesis need to practice finding,
retrieving, and replacing a snorkel and regulator. A
snorkel that has the mouthpiece mounted on a flexible
hose is relatively easy to reposition in the mouth; some
divers prefer a fixed J-tube. The diver should experi-
ment with different methods of regulator retrieval to
find the one that is most effective and should then
practice it often. Divers with mildly reduced respiratory
strength benefit from selecting easy-breathing regu-
lators and large-volume, smooth-bore, self-draining
snorkels that are designed to minimize breathing resist-
ance. In addition, divers should take care not to adjust
their weight belts and BCD straps so tightly that their
breathing is impaired. A lanyard attaching the mouth-
piece to the buoyancy compensator may be useful when
the diver has an alternative breathing source. All equip-
ment (regulator, snorkel, BC inflator hose, etc.) must
be mounted on the diver's functional or stronger side,
in cases where this is an issue.
Ear Clearing
A diver who does not have finger control or who has a
prosthesis can accomplish a Valsalva maneuver by
various methods. If the diver cannot clear by swallowing
or wiggling his or her jaw, the back of the hand can be
pressed against the bottom of the mask, or a finger or
knuckle of each hand can be used to pinch the nostrils
closed.
Mask Clearing
Divers whose lung capacity is reduced generally
find the use of a low-volume mask more efficient.
Divers who have a limited range of motion in the neck
that prevents them from tilting the head upward might
consider using a mask with a purge valve.
A-6
NOAA Diving Manual — October 1991
Diving with Disabilities
Buoyancy Control and Descents/ Ascents
Because stability on the surface and descents and
ascents are accomplished by means of buoyancy con-
trol, such control is one of the first skills that must be
mastered by divers who do not kick. Divers who use
their arms to propel and position themselves in the
water cannot afford to use their hands to inflate their
BCD's. A power inflation system is thus an absolute
requirement for these divers. The system should be
capable of quick and easy operation; the best technol-
ogy now commercially available is the soft-touch power
inflator mechanism commonly found on modern BCD's.
Divers with limited manual dexterity generally oper-
ate the inflate button by pressing it with the right palm
against the left palm. There is a need for a technologi-
cal advance that would allow one-handed operation of
the inflation device by individuals who have limited
manual dexterity.
Deflation systems should also be quick and easy to
operate. For divers with limited manual dexterity or
limited sensation, dump cords with a plastic knob on
the end or hoses that dump when stretched are often
easier to operate than deflate buttons on the end of the
inflation/deflation device. Better technology is needed in
deflation systems as well.
Divers who use buoyancy control to effect a descent
weight themselves heavily enough so that releasing air
from the BCD will begin their descent; however, divers
must be careful not to overweight themselves. Divers
also must remain alert to their increasing negative
buoyancy and must constantly compensate by adding
the amount of air to the BCD that will slow the descent
enough to permit ear clearing and keeping pace with a
buddy.
Divers who use buoyancy to control their descent
must master a greater number of skills than divers who
use kicks to slow their descent. These divers benefit
even more than other divers from practicing descents
with a descent line before doing ascents to the surface
in open water. The descent line can be held in the inside
bend of the elbow so that when the arm is bent tight,
the descent is stopped and both hands are available to
perform other tasks.
Achieving buoyancy control by means of the lungs is
a very useful skill for divers and may be especially
helpful for students or inexperienced divers who are
still becoming accustomed to their inflation/deflation
systems. Exhaling and breathing shallowly at the begin-
ning of a descent helps to get the descent under way.
Inhaling and keeping the lungs full while taking small
breaths adds lift faster than fumbling for, finding, and
operating the inflation device. The importance of keep-
ing the airway open while using this technique should
be understood before the technique is put to use.
When first learning and practicing buoyancy con-
trol, students and inexperienced divers must make a
point of remembering that shifting from a horizontal
to vertical or vertical to horizontal position under water
changes their buoyancy. They should be prepared even
as they shift position to make alterations, either via
lung control or by manipulating the inflation/deflation
device, to maintain neutral buoyancy. Early in the
learning experience, divers must also be conscious of
the rather sudden compression or decompression of
their wet suits and the dramatic effect this can have on
buoyancy. With experience, divers make these adjust-
ments automatically, without noticing that they have
done so.
Ascents are begun by adding just enough air to the
BCD to get the ascent under way. Once initiated, the
speed of the ascent is maintained at 60 feet per minute
(18.3 m/min) by releasing air from the BCD as the air
in the BCD expands and the wet suit decompresses.
Practicing ascents along an ascent line should precede
making an ascent to the surface in open water. Because
it is even more work to maintain a surface position with
arms than it is with legs, it is important that divers who
do not kick be taught before their first water session to
inflate their BCD's before entering the water.
Trim
Maintaining proper trim (balance and position in
the water) is essential to the swimming efficiency and
control of any diver, whether able-bodied or not. Divers
who do not use their legs either to keep their heads
constant in relation to their feet or their bodies from
rolling from side to side use the careful placement of
weight to achieve an efficient position and balance.
On the surface, divers wearing a wet suit may find
that their legs float to the surface and push them over
onto their backs, a position that some divers find uncom-
fortable because water splashes into their faces and
makes it difficult to see. This situation can be avoided
by using a buoyancy compensator that has enough lift
to keep the head above the water, combined with the
use of leg weights, placed either above the knee or at
the ankle. Alternatively, divers needing additional buoy-
ancy in the lower limb region can use negatively buoyant
neoprene fins. The amount of weight needed will vary,
depending on the individual and the depth of the dive.
At deeper depths, divers need less leg weighting because
of wet suit compression.
October 1991 — NOAA Diving Manual
A-7
Appendix A
The tendency of a steel tank to pull divers onto their
backs can be avoided by adjusting the tank and buoy-
ancy compensator straps so that the tank is held securely
in place at the center of the back and by placing the
weights at strategic points around the body and hold-
ing them in place with Velcro® fasteners. Because it is
difficult to fasten the weight belt securely while sitting
down, divers must check and tighten the belt as soon as
they stretch out prone in the water.
WARNING
Only Jacket-Type BCD's That Hold the Diver
Vertical on the Surface Should Be Used by a
Diver Who Relies on Buoyancy to Maintain a
Comfortable and Safe Surface Posture
Maintaining a horizontal attitude (position) in the
water provides the greatest swimming efficiency. Atti-
tude can be controlled partially by the position of the
tank; placing the tank closer to the head lowers the
head and upper body, and the inherent buoyancy of
flaccid lower extremities may further accentuate this
problem. If the placement of the tank in the buoyancy
compensator does not adequately control the orienta-
tion of the diver, weight placement can be adjusted to
compensate.
Flaccid legs also tend to drop at the hips, leaving the
diver with knees dragging, which is an inefficient swim-
ming position. The most efficient position keeps the
shoulders, hips, knees, and feet on the same horizontal
plane. Keeping the shoulders, hips, and knees in the
same plane and allowing the feet to be in a higher plane
is a reasonable compromise and can be achieved by
placing weights or extra lift where needed. Wearing
wetsuit booties or tennis shoes may raise the feet enough
so that the knees are positioned evenly with the shoulders.
this stroke to work. The sculling stroke is slower than
the breast stroke and is appropriate for casual cruising
and sightseeing.
When the space needed for strokes with a large
sweep is not available, the dog paddle provides effec-
tive propulsion. This stroke also can be performed with
one hand only, which is useful when the other hand is
impaired or occupied with a line, a buddy, or equipment.
Under the right circumstances, pulling along the
bottom hand-over-hand can be the strongest method
of propulsion. This technique involves the diver grab-
bing on and pulling himself or herself along a rocky
bottom hand-over-hand. On a sandy bottom, the diver
can dig a finger or a long tool into the sand to achieve a
similar, although weaker, effect. Pulling along the bottom
is often the best way to deal with an unexpected current.
Divers with good finger strength can add power to
their strokes by wearing webbed gloves. With the
fingers spread and cupped, these gloves add up to
10 percent more power to the stroke; they are a good item
to keep in the buoyancy compensator's pocket to help
out if the current increases.
Buddy Breathing
Although the use of a second stage, or octopus, for
buddy breathing is not universal, it is common in div-
ing. Buddy breathing that involves sharing one regula-
tor requires the use of both hands and thus could leave
an arm-stroking diver unable to swim or to maintain
body position. If propulsion or adjustments in positioning
are needed, the buddy-breathing diver must first release
the buddy (NOT the regulator); use of this procedure
decreases the likelihood that the diver will become
separated from his or her air source. Although buddy
breathing should be mastered and practiced frequent-
ly, it should never be included as a routine part of a
dive plan.
Propulsion
Divers who swim with their arms use a variety of
strokes for propulsion. The breast stroke is the most
common because it is a strong stroke and can be used to
maintain head-to-toe orientation in the water and to
provide propulsion. Buddies of breast-stroking divers
need to swim somewhat above or below the diver to
avoid the large sweep of this stroke.
A sculling stroke, in which the arms are held at the
sides with the hands sweeping out from the body and
then back toward the hips, is a relaxing and graceful
stroke. Because it cannot be used to maintain head-to-
toe orientation, the diver's trim must be just right for
A-8
NOTE
Divers who swim and maintain their position
in the water with their arms should them-
selves be equipped with an octopus and
should dive only with buddies so equipped.
Divers who propel themselves with a wide arm stroke
may find octopus buddy breathing easier if they and
their buddies mount their octopuses on an extra long
hose. Figure A-9 shows an octopus positioned in a
readily visible, easily accessible location that makes it
NOAA Diving Manual — October 1991
Diving with Disabilities
Figure A-9
Octopus Mounted
for Ease of Use
Courtesy Curt Barlow
easy to find, free, and use. Other options include swim-
ming at a slightly sidewise angle or in a one-above-
the-other position, moving the stroke above or below
the buddy. Again, because divers want to minimize the
amount of time their hands are busy, the octopus should
be secured in such a way that it is easy to find, uncou-
ple, and pass to a buddy.
Use of Underwater Lines
Arm-stroking divers can use a variety of techniques
to follow underwater lines. There is an inverse rela-
tionship between the amount of propulsion derived
from the stroke and the security of the diver's contact
with the line. The most secure method for following a
line is to keep the line in the circle formed by the
thumb and forefinger when the hand is in the 'OK'
position. Using the hand circling the line for propul-
sion is ineffective, and a one-handed dog paddle is
thus the only workable stroke when a line is being held.
Opening the hand and keeping the line against the area
between the thumb and forefinger provides less secu-
rity but permits greater use of the hand. The hand can
be moved forward and backward along the line in a
shortened breast stroke. More propulsion but less security
can be achieved by swimming just a bit above the line,
which keeps the line in contact with the underside of
the arm as the arm moves up and back in a full breast
stroke. The circumstances of each dive determine how
much security is needed, i.e., an increase in the likeli-
hood of a silt-out indicates the need for greater security.
The easiest way to lay a line while swimming with
the arms is to use a line reel with a braking mechanism
and a long handle that can be tucked under the weight
belt or buoyancy compensating device's waist strap.
With the braking mechanism set to keep a constant,
moderate tension on the line, the diver tucks the line
reel under a belt or strap and swims along until a
tie-off is needed. After tying off, the reel is again
tucked under the belt or strap until the next tie-off.
Careful attention is paid to making sure that the reel
does not drop away unnoticed. Attaching the reel with
a snap hook makes dropping the line reel virtually
impossible.
A self-retracting or otherwise one-handed line reel
is not yet available, so reeling in a line is necessarily a
two-handed job. Consequently, divers who swim with
the arms pull themselves along the line as they reel it
in. The extra strain this puts on the line must be con-
sidered both when selecting line for the reel and when
tying off. Although anyone who dives in circumstances
necessitating the use of a line must be proficient at
laying and reeling in a line, it usually is wiser for a
kicking member of the dive team to work the line; only
if that diver becomes incapacitated should the arm-
stroking diver tend the line.
Exits
Exiting the water is often difficult for a diver who
does not walk up a beach or climb a ladder. At the end
of a dive, mobility-impaired divers usually remove
their equipment in the water. The weight belt is always
removed before the buoyancy compensator and tank to
avoid leaving the diver too negatively buoyed.
Onto Boats or Piers. The easiest exits for mobility-
impaired divers to negotiate are those onto boats that
have a water-level dive platform and a walk-through
transom. Divers who can do so hoist themselves onto
the platform and then, while seated, pull themselves
backward to the deck via the walk-through transom.
On a pier or dock that has steps (rather than a ladder)
leading out of the water, divers can sit and hoist them-
selves up one step at a time until they reach the dock.
October 1991 — NOAA Diving Manual
A-9
Appendix A
Figure A- 10
Diver Being
Assisted from
the Water
Onto the Beach. Beach exits in calm conditions can
be accomplished by having the diver drag himself or
herself backward out of the water while seated. If
there is surf, the diver keeps his or her equipment in
place, swims as far as possible, and then crawls on his
or her elbows until the surf zone is reached; the regula-
tor is kept in the mouth during the exit process.
Assisted Exits. In some cases, it is useful for the
mobility-impaired diver to get help from another diver. It
is often easiest for one or two buddies to grasp the diver
under the armpits (Figure A-10) or by the hands
(depending on the height from the water) and to pull
the diver up the beach or to the deck or platform level,
perhaps with one assistant in the water to help lift or
guide the legs. On some boats where the gunwale is so
high that a diver in the water cannot be reached by
buddies on the boat, a very strong buddy may be able to
carry the diver up the ladder. For any person lifting
another, care must be taken to ensure proper lifting
techniques so that the lifter is not injured. Davits or
other lifting devices can also be useful in such situations.
If the boat is a sailboat, a variety of lifting devices
can be fashioned. To remove a diver from the water,
the boom can be positioned over the diver in the water,
a bosun's chair can be attached to the boom, and the
diver can hoist himself or herself up by means of a
block and tackle. When the diver is at the level of the
deck, the boom is swung across to the cockpit, and
the diver then lowers himself or herself to the seat.
To lift a diver to a level higher than the deck, such as
onto a pier, the bosun's chair can be attached to the
main halyard, and the diver can then be lifted by means
of a winch.
The difficulty in removing a mobility-impaired diver
from the water is also a measure of how difficult it would
be to remove an unconscious or otherwise incapacitated
victim. By creating systems that make it easier for
mobility-impaired divers, a boat is made safer for any
diver who may, for emergency reasons, need to be lifted
from the water.
OTHER CONSIDERATIONS
Thermoregulation
Some disabilities are associated with an increased
sensitivity to extremes of temperature. Chilling can
occur much faster in individuals with decreased cir-
culation; in addition, individuals with paralyzed extremi-
ties may not develop or perceive the early symptoms of
hypothermia. Overheating can be a significant prob-
lem for people who, like some people with spinal cord
A-10
i
i
Courtesy Curt Barlow
injuries, do not sweat. Carrying a pocket-sized reflec-
tive emergency blanket is a good precaution for deal-
ing with an unexpectedly cold post-dive boat ride.
Pouring water over the skin acts like artificial sweat
and effectively cools the body. Finally, warm water
can be poured into the diver's suit after he or she exits
the dive, which will greatly aid in restoring warmth.
Because the effects of hypothermia or hyperthermia
can be serious, divers should plan ahead to stay as
warm as possible in cool conditions (especially under
water) and as cool as possible in warm conditions.
Catheters
Various types of catheters are worn by many indi-
viduals with disabilities. If an external catheter and a
leg bag are worn, the bag should be emptied before
NOAA Diving Manual — October 1991
i
Diving with Disabilities
the dive (and should perhaps be left open during the
dive), since immersion in the water tends to cause people
to urinate. A plug can be made for an indwelling catheter
using a cut-up leg bag (use only the top piece that has
the one-way valve). Such a plug enables urine to drain
during the dive and prevents salt water and impurities
from entering the catheter.
Protection of Paralyzed Tissue
Blankets or cushions should be used to prevent bruis-
ing or the development of pressure sores. In cooler
water, the wet suit will protect the skin; in warm water,
clothing such as a lycra body suit will protect against
coral scrapes and jellyfish stings.
Decompression Sickness
Divers with orthopedic disabilities are concerned
about the extent of their susceptibility to decompression
sickness. It has been speculated that unused tissues, such
as those in paralyzed limbs, may off-gas at a different
rate than is the case for active tissues. To date, there
have been no scientific studies exploring this issue.
It is known, however, that paralyzed limbs have some
degree of reduced circulation and that circulation is
important to the safe uptake and elimination of nitro-
gen. Any diver with reduced circulation (including
smokers, for example) needs to use the U.S. Navy dive
tables conservatively. Divers who have disabilities that
may affect the rate of off-gassing should add safety
factors when they use the tables. Some divers add
10 minutes to their bottom time and/or 10 feet (3 m) to
their depth. Others stay well under the no-decompression
limit on their first dive and then penalize themselves
one or two repetitive group designations when they
plan their subsequent dives. Finally, many divers
routinely do a stop between 10 and 20 fsw (3-6 m) for a
few minutes even when the dive was well within the
no-decompression limits.
Autonomic Dysreflexia
Divers who are susceptible to autonomic dysreflexia
are aware that conditions commonly encountered in
diving may trigger this condition. Just as hypothermia
or hyperthermia can be prevented by taking necessary
precautions, autonomic dysreflexia can be avoided
by divers who are aware that extra care is needed.
Autonomic dysreflexia can cause a medical emergency
for people with spinal cord injuries at or above the
T-5 level, and in some cases for people whose injury is
between T-6 and T-10. This condition can occur when
there is an irritating stimulus, such as a full bladder, a
pressure sore, or an ingrown toenail, below the level of
the injury. The stimulus sends nerve impulses to the
spinal cord, where they travel upward until they become
blocked at the level of the injury. The impulses never
reach the brain, but they do trigger increased sympa-
thetic autonomic nervous system activity. The resulting
spasms and narrowing of the blood vessels cause the
blood pressure to rise and, eventually, the heartbeat to
slow. Autonomic dysreflexia can lead to seizures,
unconsciousness, stroke, or, if untreated, death.
The signs and symptoms of autonomic dysreflexia
include a pounding headache, slow pulse, sweating
above the level of the injury, goose bumps, blotching of
the skin, and nasal congestion. The condition can be
caused by anything that would have been painful or
physically stimulating before the injury, but it is most
often caused by a full bladder. Emergency treatment
of the condition involves getting the victim into (or
maintaining him or her in) a sitting position to help
decrease the blood pressure, loosening anything that
may be pressing on the abdominal area, and finding
and correcting the cause (often a plugged catheter, a
full drainage bag, or the need for an intermittent
catheterization).
To avoid having a problem with autonomic dysreflexia,
divers with disabilities that can be associated with this
condition need to be told in detail about certain aspects of
the planned dive; for example, prolonged immersion in
cold water, which increases the rate of bladder filling,
or the absence of wheelchair-accessible toilet facili-
ties could both contribute to the development of auto-
nomic dysreflexia.
SUMMARY
The procedures, equipment, and specialized techniques
described above show that trained and experienced
divers with disabilities can dive safely and efficiently.
In addition, this section demonstrates the importance
of intensive training, thorough predive planning, effective
communication, and use of the buddy system for divers
with disabilities.
October 1991 — NOAA Diving Manual
A-11
♦
i
APPENDIX B
U.S.NAVYAIR
DECOMPRESSION
TABLES
Page
Introduction B-l
Definition of Terms B-l
Table Selection B-2
No-Decompression Limits and Repetitive Group Designation Table for
No-Decompression Air Dives B-2
Selection of the Appropriate Decompression Schedule B-3
Air Decompression Tables B-3
U.S. Navy Standard Air Decompression Table B-3
Repetitive Dives B-3
Residual Nitrogen Timetable for Repetitive Air Dives B-5
Surface Decompression B-5
Surface Decompression Table Using Oxygen B-10
Surface Decompression Table Using Air B-12
Exceptional Exposure Dives B-l 3
General Use of Decompression B-13
Rules During Ascent B-13
Variations in Rate of Ascent B-19
i
APPENDIX B
U.S. NAVY AIR
DECOMPRESSION
TABLES
INTRODUCTION
When air is breathed under pressure, inert nitrogen
diffuses into various tissues of the body. This nitrogen
uptake by the body continues, at different rates for the
various tissues, as long as the partial pressure of the
inspired nitrogen is higher than the partial pressure of
the gas absorbed in the tissues. Consequently, the amount
of nitrogen absorbed increases with the partial pres-
sure of the inspired nitrogen (depth) and the duration
of the exposure (time).*
When the diver begins to ascend, this process is
reversed: the nitrogen partial pressure in the tissues
exceeds that in the circulatory and respiratory sys-
tems. The pressure gradient from the tissues to the
blood and lungs must be carefully controlled to pre-
vent nitrogen from coming out of solution in the form
of bubbles. If the pressure gradient is uncontrolled,
bubbles of nitrogen gas can form in tissues and blood
and cause decompression sickness.
To prevent decompression sickness, several decom-
pression tables have been established. These tables
take into consideration the amount of nitrogen absorbed
by a diver's body at various depths for given time peri-
ods. They also consider both the allowable pressure
gradients that can exist without excessive bubble-
formation and the different gas elimination rates
associated with various body tissues. Stage decompres-
sion, which requires that the diver make stops of spe-
cific durations at given depths during ascent, is used in
air diving because of its operational simplicity.
The U.S. Navy decompression tables are the result
of years of scientific study, mathematical modeling,
human and animal studies, and extensive field experi-
ence. These tables thus contain the best overall infor-
mation available; however, as dive depth and time
increase, these tables become less accurate and thus
require careful application. To ensure maximum diver
safety, these tables also must be followed strictly. Devia-
tions from established decompression procedures should
be made only under emergency conditions and with the
consent of the NOAA Diving Coordinator.
Five different tables are discussed in this chapter,
and each has a unique application in air diving. Four of
* The material in this appendix has been adapted from the US Navy
Diving Manual (1988).
October 1991 — NOAA Diving Manual
these tables provide specific decompression data for
use under various operational conditions; the remaining
table is used to determine decompression requirements in
situations where a diver has conducted or will be
conducting more than one dive in a 12-hour period.
Before using any of these tables, divers should read
Sections 14.6 through 14.9 of this manual.
DEFINITION OF TERMS
Terms which are frequently used when discussing decom-
pression tables are defined below.
Bottom Time - The total amount of time that elapses
from the time a diver leaves the surface in descent to
the time (next whole minute) he or she begins ascent;
bottom time is measured in minutes.
Decompression Stops - Stops that a diver must make
for specified times and at specified depths during ascent
from a decompression dive. The depths at which
decompression stops must take place and the time that
the diver must remain at each stop are specified in the
decompression schedule being followed.
Decompression Schedule - A list of depths and times
that indicates the decompression stops that a diver
must make for dives having particular maximum depths
and bottom times; decompression schedules are indi-
cated as feet/minutes.
Decompression Table - A set of decompression sched-
ules, or limits, usually organized in order of increasing
bottom times and depths.
Depth - When used in connection with the depth of a
dive, the following terms are used:
1. Deepest Depth: The depth indicated by the deepest
pneumofathometer reading during a surface-
supplied dive or the depth shown by the deepest
depth gauge reading during a scuba dive.
2. Maximum (Max) Depth: In surface-supplied opera-
tions, the deepest depth plus 5 feet (1.5 m); the
max depth is used to select a decompression sched-
ule. In scuba operations, the max depth and the
deepest depth are the same.
3. Stage Depth: The depth indicated by a pneumo-
fathometer reading taken when the diver is on the
stage and ready to leave the bottom. The stage
depth is used to compute distance and travel time
to the first stop.
B-1
Appendix B
Equivalent Single Dive Bottom Time - The time in
minutes used to select a schedule for a single repetitive
dive; the equivalent single dive bottom time is equal to
the bottom time of the planned repetitive dive and the
diver's residual nitrogen time.
No-Decompression Time - The maximum amount of
time that a diver can spend at a given depth and still be
able to make a safe ascent directly to the surface at a
prescribed rate and without taking any decompression
stops.
Repetitive Dive - Any dive conducted within a 12-hour
period after a previous dive.
Repetitive Group Designation - A letter that desig-
nates the amount of nitrogen remaining in a diver's
body during the 12-hour period following a dive.
Residual Nitrogen - The amount of nitrogen gas that
remains in a diver's tissues after the completion of a
dive.
Residual Nitrogen Time - The time, in minutes, that
must be added to the bottom time of a repetitive dive to
compensate for the nitrogen remaining in the diver's
tissues from a previous dive.
Single Dive - Any dive conducted more than 12
hours after a previous dive.
Single Repetitive Dive - Any dive performed by a
diver whose tissues still contain residual nitrogen from
a previous dive; to select an appropriate decompres-
sion schedule for a repetitive dive, the actual bottom
time of the planned dive must be added to the diver's
residual nitrogen time.
Surface Interval - The period of time that a diver
spends on the surface after a dive; the interval begins
as soon as the diver surfaces and ends as soon as the
diver starts his or her next descent.
TABLE SELECTION
The following U.S. Navy air decompression tables are
available:
• Standard Air Decompression Table
• No-Decompression Limits and Repetitive Group
Designation Table
• Surface Decompression Table Using Oxygen
• Surface Decompression Table Using Air
These tables each contain a series of decompression
schedules that must be adhered to rigidly during ascent
from an air dive. Conditions surrounding the dive dic-
tate which decompression table and schedule are select-
ed. These conditions are status of the diver, depth and
duration of the dive, availability of an oxygen breath-
ing system within the chamber, and environmental
conditions such as sea state, water temperature, etc.
The Surface Decompression Table Using Oxygen or
the Surface Decompression Table Using Air may be
used to make up a diver's omitted decompression only
if the diver's emergency surfacing occurs at a point in
the decompression when water stops are not required
(or have already been taken) and all of the conditions
for use of this table have been met.
The Residual Nitrogen Timetable for Repetitive Air
Dives (hereafter called the Residual Nitrogen Timeta-
ble) is not a decompression table in the strictest sense;
its purpose is to provide the information needed to plan
repetitive dives.
No-Decompression Limits and Repetitive
Group Designation Table for No-Decompres-
sion Air Dives
The No-Decompression Limits and Repetitive Group
Designation Table for No-Decompression Air Dives
(hereafter called the No-Decompression Table) serves
two purposes. First, it summarizes all the depth and
bottom time combinations for which no decompression
is required. Second, it provides the repetitive group
designation for any no-decompression dive. (Even on
no-decompression dives, some nitrogen remains in the
diver's tissues after the dive; if a diver dives again
within a 12-hour period, he or she must consider this
residual nitrogen when calculating decompression
requirements.)
Every depth listed in the No-Decompression Table
has a corresponding no-decompression limit in min-
utes. This limit is the maximum bottom time that a
diver may spend at that depth without needing decom-
pression. The columns to the right of the no-decompres-
sion limits column are used to determine the repetitive
group designation that is assigned to the diver after
every dive. To find a diver's repetitive group designa-
tion, enter the table at the depth equal to or next
greater than the maximum depth of the dive and follow
that row until you reach the bottom time that is equal
to or just greater than the actual bottom time of the
dive; then follow that column upward to the repetitive
group designation.
In the No-Decompression Table, depths shallower
than 35 fsw (10 m) do not have a specific no-decom-
pression limit. Implied time limits do pertain to these
depths, however, because repetitive group designations
are not provided for bottom times of greater than
6 hours. A 6-hour bottom time is the maximum time
permitted by the No-Decompression Table, and div-
ing should not be conducted for times longer than this
limit.
B-2
NOAA Diving Manual — October 1991
USN Air Decompression Tables
Any dive deeper than 35 fsw (10 m) that has a
bottom time greater than the no-decompression limit
given in the No-Decompression Table is by definition
a decompression dive and must be conducted in accord-
ance with the Standard Air Decompression Table.
Selection of the Appropriate Decompression
Schedule
The decompression schedules for all decompression
tables are given in 10- or 20-foot (3 or 6.1 m) depth
increments and, usually, in 5- or 10-minute bottom
time increments. The depth and bottom time combina-
tions of actual dives, however, rarely match any decom-
pression schedule exactly. To ensure that the decom-
pression schedule selected is conservative (i.e., on the
safe side): (1) always select a schedule that has a depth
that is equal to or next greater than the maximum depth
of the actual dive, and (2) always select a schedule that
has a bottom time that is equal to or next longer than
the bottom time of the actual dive.
If the Standard Air Decompression Table, for example,
is being used to select a schedule for a dive to 97 fsw
(29 m) for 31 minutes, the following procedure is used.
First, add 5 fsw (1.5 m) to the depth of the dive (i.e.,
97 fsw + 5 fsw = 102 fsw). Then, select the schedule for a
102-fsw dive; this would be the 110-fsw schedule.
Finally, select the appropriate schedule for a 31 -minute
dive; this would be the 40-minute schedule. Thus, the
dive would be conducted in accordance with the
110/40 schedule.
WARNING
Never Attempt To Interpolate Between Decom-
pression Schedules
If a diver is exceptionally cold during a dive or the
work load is strenuous, the decompression schedule for
the next longer duration should be selected. For exam-
ple, the normal schedule for a dive to 90 fsw (27 m) for
34 minutes would be the 90/40 schedule. However, if
the divers are cold or fatigued, they should decompress
according to the 90/50 schedule.
AIR DECOMPRESSION TABLES
U.S. Navy Standard Air Decompression Table
The Standard Air Decompression Table combines
two former tables — the Standard Air Table and the
Exceptional Exposure Air Table — into a single table.
October 1991 — NOAA Diving Manual
To distinguish clearly between standard and excep-
tional exposure decompression schedules, exceptional
exposure schedules on this table are printed in Blue.
As shown on this table, no decompression is required
if the bottom time of the dive is less than the first
bottom time listed for the dive's depth; in such cases,
the divers may ascend directly to the surface at a rate
of 60 feet per minute (fpm) (18.3 m/min). The repeti-
tive group designations for no-decompression dives
are shown in the No-Decompression Table.
As noted in the Standard Air Decompression Table,
there are no repetitive group designations for excep-
tional exposure dives. Repetitive dives are not permit-
ted after an exceptional exposure dive.
Example: A diver has just completed a dive to a
depth of 143 fsw (43 m) for 37 minutes. The diver is not
unusually cold or fatigued. What is the diver's decom-
pression schedule and repetitive group designation?
Solution: To determine the appropriate decompres-
sion schedule and the diver's repetitive group designa-
tion at the end of the decompression, select the depth
equal to or next deeper than the depth of the dive and
the bottom time equal to or next longer than the bot-
tom time of the dive. In the example, this would be the
150/40 schedule.
Repetitive Dives
During the 1 2-hour period after an air dive, the quan-
tity of residual nitrogen in a diver's body gradually
returns to its normal level. If divers are to make a
second dive (repetitive dive) within this 12-hour interval,
they must consider the amount of residual nitrogen in
their tissues when planning for the dive.
The procedures for conducting a repetitive dive are
summarized in Figure B-l. When divers complete their
first dive, the Standard Air Decompression Table or
the No-Decompression Table assigns them a repeti-
tive group designation. The repetitive group designa-
tion assigned to a diver immediately after surfacing
applies only to the amount of nitrogen remaining in his
or her tissues at that time. As nitrogen leaves the
tissues and blood over time, a diver's repetitive group
designation changes. The Residual Nitrogen Timetable
permits the appropriate residual nitrogen designa-
tion to be determined at any time during the diver's
surface interval.
Just before a diver begins a repetitive dive, his or her
residual nitrogen time should be determined using the
Residual Nitrogen Timetable. The residual nitrogen
time is then added to the actual bottom time of the
planned repetitive dive, and the new bottom time, called
the equivalent single dive time, is used to select the
B-3
Appendix B
Figure B-1
Repetitive Dive Flowchart
i
Decompress according
to Standard Air Table
or No-Decompression
Table
Obtain repetitive
group designation
Surface interval greater
than 1 2 hours
Surface interval greater
than 10 minutes and less
than 1 2 hours
£
Surface interval less
than 10 minutes
Obtain residual nitrogen
time using Residual
Nitrogen Timetable
I
Add bottom time of
previous dive to that
of repetitive dive
Add residual nitrogen
time to bottom time of
repetitive dive giving
equivalent single dive
bottom time
(
Use depth and bottom
time of equivalent
single dive.
I
Decompress using schedule
for repetitive dive depth
and equivalent single dive
bottom time
Decompress from repetitive
dive using schedule for
deeper of two dives and
combined bottom times
B-4
Source: U.S. Navy (1988)
NOAA Diving Manual — October 1991
USN Air Decompression Tables
appropriate schedule to use for decompression after
the repetitive dive. Equivalent single dives that require
the use of exceptional exposure decompression sched-
ules should not be conducted. To assist in selecting the
decompression schedule for a repetitive dive, a sys-
tematic repetitive dive worksheet, shown in Figure
B-2, should always be used.
If a diver wishes to make a third dive after his or her
first repetitive dive, the depth and bottom time of the
first equivalent single dive should be inserted into part
one of the second repetitive dive worksheet.
Residual Nitrogen Timetable for Repetitive
Air Dives
The quantity of residual nitrogen in a diver's tissues
immediately after a dive is expressed by the repetitive
group designation assigned either by the Standard Air
Decompression Table or the No-Decompression Table.
The upper portion of the Residual Nitrogen Timetable
shows a range of times between 10 minutes and 12 hours,
expressed in hours:minutes (2:21 = 2 hours 21 minutes).
Each interval has two limits: a minimum time (top
limit) and a maximum time (bottom limit).
Residual nitrogen times (in minutes) corresponding
to the depths of various repetitive dives are shown in
the body of the lower portion of the Residual Nitrogen
Timetable. To determine the residual nitrogen time for
a repetitive dive, locate the diver's repetitive group
designation from the previous dive along the diagonal
line above the table. Read horizontally until you reach
the time interval that includes the diver's surface interval.
(The time the diver spends on the surface must be
equal to or lie between the time limits of this interval.)
Next, read vertically downward to obtain the diver's
new repetitive group designation, which reflects the
amount of residual nitrogen left in the diver's body at
the present time. Continue downward in this same
column until you reach the row that includes the depth
of the planned repetitive dive. The time, in minutes,
shown at the intersection is the residual nitrogen time
that must be added to the bottom time of the planned
repetitive dive.
If a diver's surface interval is less than 10 minutes,
the residual nitrogen time is simply the bottom time of
the previous dive. If the planned repetitive dive is to be
made to a depth that is equal to or greater than the
depth of the diver's previous dive, the residual nitro-
gen time may turn out to be longer than the bottom
time of the previous dive. In this event, the bottom
time of the previous dive should be added to the bottom
time of the planned repetitive dive to obtain the diver's
equivalent single dive time. Because all of the residual
October 1991 — NOAA Diving Manual
nitrogen in a diver's tissues has passed out of the diver's
body after 12 hours, a dive conducted more than 12 hours
after the diver surfaced from the first dive is not
considered a repetitive dive.
Example: A repetitive dive is to be made to 98 fsw
(27.3 m) for an estimated bottom time of 15 minutes.
The previous dive was to a depth of 102 fsw (30 m) and
had a 48-minute bottom time. The diver's surface
interval is 6 hours 28 minutes (6:28). What is the
correct decompression schedule for the repetitive dive?
Solution: Add the residual nitrogen time of the pre-
vious dive to the bottom time of the planned repetitive
dive to obtain the diver's equivalent single dive time.
The correct decompression schedule for the repetitive
dive would then be the 100/25 schedule. Figure B-3
depicts the dive profile for this situation.
Surface Decompression
Surface decompression is a technique for fulfilling
all or a portion of a diver's decompression obligation in
a recompression chamber. Use of this technique greatly
reduces the time that a diver must spend in the water;
moreover, breathing oxygen in a recompression cham-
ber reduces the amount of time a diver must spend in
decompression.
Surface decompression also significantly enhances
a diver's safety: the shorter in-water exposure time
made possible by surface decompression keeps divers
from chilling to a dangerous level, and the constant-
pressure recompression chamber environment means
that divers can be protected from surface conditions.
In a chamber, the diver can also be observed constantly by
the chamber operator and be monitored as necessary
by medical personnel; this kind of monitoring allows
any sign of decompression sickness to be detected readily
and treated immediately.
If the recompression chamber has an oxygen breathing
system, surface decompression should be conducted in
accordance with the Surface Decompression Table Using
Oxygen. If air is the only breathing medium available
in the chamber, the Surface Decompression Table Using
Air must be used. No surface decompression table is
available for decompression from an exceptional expo-
sure dive.
Residual nitrogen times have not been developed for
repetitive dives. However, repetitive dives can be made as
long as the sum of the bottom times of all the dives
made by a diver in the previous 12 hours and the
maximum depth ever attained by the diver do not
exceed the maximum time/depth combinations shown
in the Surface Decompression Table Using Oxygen
(170 fsw (51.8 m)/40 min) or the Surface Decompres-
sion Table Using Air (190 fsw (57 m)/60 min) limits.
B-5
Appendix B
Figure B-2
Repetitive Dive Worksheet
REPETITIVE DIVE WORKSHEET
DATE
I. PREVIOUS DIVE:
minutes Q Standard Air Table f~I] No-Decompression Table
+ = feet Q Surface Table Using Oxygen [^Surface Table Using Air
repetitive group letter designation
2. SURFACE INTERVAL:
hours minutes on surface
repetitive group from item I above
new repetitive group letter designation from Residual Nitrogen Timetable
3. RESIDUAL NITROGEN TIME:
+ = feet, depth of repetitive dive
new repetitive group letter designation from item 2 above
minutes, residual nitrogen time from Residual Nitrogen Timetable or
bottom time of previous Sur D dive
4. EQUIVALENT SINGLE DIVE TIME:
minutes, residual nitrogen time from item 3 above or bottom time of
previous Sur D dive
+ minutes, actual bottom time of repetitive dive
= minutes, equivalent single dive time
5. DECOMPRESSION FOR REPETITIVE DIVE:
minutes, equivalent single dive time from item 4 above
+ = feet, depth of repetitive dive
Decompression from (check one):
Q Standard Air Table Q No-Decompression Table
H] Surface Table Using Oxygen Q Surface Table Using Air
Decompression Stops:
Depth
feet
Water
minutes
minutes
minutes
minutes
minutes
Chamber
minutes
feet
minutes
feet
feet
minutes
minutes
feet
minutes
schedule used (depth/time)
repetitive group letter designation
B-6
Source: U.S. Navy (1988)
NOAA Diving Manual — October 1991
(
USN Air Decompression Tables
Figure B-3A
Repetitive Dive Chart
DIVING CHART - AIR
DIVING APPARATUS
TYPE DRESS
voer suit
dATe
02 MAy iQ8e
EGS (PSIG)
NAME OF DIVER I
HvbHfZS
DIVING APPARATUS
TYPE DRESS
ECS (PSIG)
%1-SO
NAME OT DIVER 2
&QVOMAA/
TENDERS (DIVER 2)
B\N(? HAAA
00 £T SOlT
TENDER5 (DIVER I)
M \TtHELLo C?(LpA/$EtK
f SURFACE (LS) I DEEiWifsw5
fsWT
-t 5 = toz
REACHED BOTTOM (RB)
AND
sr^v^Ns
DESCENT TIME
02
LEFT SURFACE (LS)
OQDO
TOTAL BOTTOM TIME (TBT)
oboz -
LEFT BoT Tom (LB)
TABLE & SCHEDULE USED
//p/$0 STD Mr
TOTAL TIME OF DIVE (TTD)
Ot ■' 23 :: 37
TIME TO FIRST STOP
(9/ •••• in
REACHED SURFACE (RS)
Q9 23 • ; 5>7
TOTAL DECOMPRESSION TIME
(TDT)
REPETITIVE GROUP
35 -: V7
M
DESCENT
ASCENT
DEPTH
OF
STOPS
DECOMPRESSION TIME
WATER CHAMBER
TIME
WATER
CHAMBER
\Zc*
L 07*23 ••27
*OS57 r-2t
20
■02
L0857 ••••I7
ROgY? ••/7
30
i\0
50
60
70
80
o
90
97
inn
L O0t| g
R PgOl
-44^-
_i?n
— I Ev
•430-
PURPOSE OF DIVE
\A)0H\L
REMARKS
OK ~T0 LEPETT
DIVER'S CONDITION
DIVING SUPERVISOR
A/D&aAAl-
ftAAC CLIME
Note: In this example, travel time is shown in seconds. For most
diving operations, however, recording the travel time in
minutes is sufficient.
Source: U.S. Navy (1988)
October 1991 — NOAA Diving Manual
B-7
Appendix B
Figure B-3B
(Continued)
REPETITIVE DIVE WORKSHEET
DATE
oaMAj 0%
I. PREVIOUS DIVE:
T » minutes
[•fStondord Air Table
\^2 No-Decompression Table
Q Surface Table Using Air
il + J =/0£. feet Q Surface Table Using Oxygen
/frt repetitive group letter designation
2. SURFACE INTERVAL:
69 hours o( ^ minutes on surface
/A. repetitive group from item I above
D new repetitive group letter designation from Residual Nitrogen Timetable
3. RESIDUAL NITROGEN TIME:
7^ + D =_T o feet, depth of repetitive dive
P new repetitive group letter designation from item 2 above
*7 minutes, residual nitrogen time from Residual Nitrogen Timetable or
bottom time of previous Sur D dive
4. EQUIVALENT SINGLE DIVE TIME:
I minutes, residual nitrogen time from item 3 above or bottom time of
— I previous Sur D dive
+ C 1-^j minutes, actual bottom time of repetitive dive
= <p?ol minutes, equivalent single dive time
5. DECOMPRESSION FOR REPETITIVE DIVE:
cxpl minutes, equivalent single dive time from item 4 above
^ 3 + 5 - to feet, depth of repetitive dive
Decompression from (check one): .
I | Standard Air Table [Tf No -Decompression Table
j~J Surface Table Using Oxygen Q Surface Table Using Air
Decompression Stops:
Depth
feet
Water
minutes
minutes
minutes
minutes
minutes
Chamber
minutes
feet
feet
minutes
minutes
feet
minutes
feet
minutes
\00/t%(& schedule used (depth/time)
6? repetitive group letter designation
Source: U.S. Navy (1988)
(
B-8
NOAA Diving Manual — October 1991
USN Air Decompression Tables
Figure B-3C
(Continued)
DIVING CHART - AIR
date : ~r~
NAME OF DIVER I
HMHE5
NAME OF DIVER 2
TEKIDER5 (DIVER I)
M(TCH£H
DIVING APPARATUS
/WK| MOO (9
blVIKlC APPARATUS
MK I MOD 0
Mi
LEFT SURFACE (LS)
\ssz
AND
6?£0A/6EC\<
LEFT BOTTOM (LB)
/6>07
REACHED SURFACE (RS)
?3V5 v*8
.OTAl^OTTOM TpSEI [tfit)
TOTAL DECOMI
(TDT)
0/
TON TIME
S3
TYPE DRESS
SU/T
TENDERS (DIVER 2)
TYPE DRE55
%
CS (PSIC)
zzso
ECS (PSIC)
22.6 0
REACHED BOTTOM (RB)
AND
ST£\/£"aJS
, SCHEDULE I
TABLE & SCHEDULE USED
(OO/Z-L A/o'b'
TOTAL TIME OF DIVE (TTD)
DESCENT TIME
: 02-
TIME TO FIRST STOP
Of ••33
REPETITIVE GROUP
DESCENT
5
ASCENT
DEPTH
OF
STOPS
10
20
30
kO
50
60
70
80
90
<?3
-we-
* 1 1 Cr
+20-
PURPOSE OF DIVE
DECOMPRESSION TIME
WATER CHAMBER
TIME
WATER
L IbOl
g /65V
CHAMBER
u;c£j<
DIVER'S CONDITION
N0&AK al
REMARKS
OK TO HgfgT
DlViNG^SJJP£BVJS OR
LCDR PftuiTf
Note: In this example, travel time is shown in seconds. For most
diving operations, however, recording the travel time in
minutes is sufficient.
Source: U.S. Navy (1988)
B-9
October 1991 — NOAA Diving Manual
Appendix B
If a diver has exceeded his or her allowable surface
interval or displays signs of decompression sickness,
the diver should be treated in accordance with the
procedures discussed below for surface decompression
using air or oxygen.
Surface Decompression Table Using Oxygen
To use the Surface Decompression Table Using Oxy-
gen, an approved recompression chamber with an oxy-
gen breathing system is required. The ascent rate to
the first decompression stop, or to the surface if no
water stops are required, is 25 fpm (7.5 mpm). The
ascent time between each stop, and from the 30-foot
(9 m) stop to the surface, is 1 minute.
Once the divers are on the surface, the tenders must
remove the diver's breathing apparatus and assist the
diver into the recompression chamber, all within a
3.5-minute period. The divers begin to breathe oxygen
as soon as they enter the chamber. Pressurization of
the chamber with air should take about 30 seconds,
which means that the total time that will have elapsed
from the time the diver left the 30-foot (9 m) water
stop to the time that he or she reaches the 40-foot
(12.2 m) recompression chamber stop has not exceeded
5 minutes. Five minutes is the maximum amount of
time that can elapse without endangering the diver.
If the prescribed surface interval has been exceeded
and the divers show no signs of decompression sick-
ness, they are treated as if they had Type I decompres-
sion sickness symptoms. If the divers are symptomatic,
they must be treated as if they had Type II decompres-
sion sickness symptoms. Symptoms occurring during
chamber stops are treated as if they were decompres-
sion sickness recurrences.
As soon as the divers enter the chamber, they must
begin to breathe pure oxygen. The divers must remain
on oxygen down to and throughout the designated 40-foot
(12.2 m) stop time (except for the 5-minute air break
described below). On completion of the designated
40-foot (12.2 m) chamber stop, the chamber should be
surfaced at a constant rate of 20 fpm (6.1 mpm) over a
2-minute period.
During chamber stops, the divers are to continue to
breathe oxygen, with the following exceptions:
- Interrupt oxygen breathing after every 25-minute
period for a 5-minute air break. Count the air breaks
as dead time (that is, do not count them as part of the
oxygen stop time). If the time of the air break occurs
during the time the chamber is moving, the divers
should be kept on oxygen and the chamber should
continue to travel. This procedure simplifies timekeeping
B-10
and should be used whenever the Surface Decompres-
sion Table Using Oxygen is in use. See Figure B-4 for
an example.
- If the oxygen breathing system fails, the divers
should be decompressed in accordance with the Sur-
face Decompression Table Using Air, and all time
spent breathing oxygen should be disregarded. Because
oxygen breathing systems occasionally fail, the cham-
ber operator should be familiar with the appropriate
schedule of the Surface Decompression Table Using
Air.
- If a diver exhibits signs of oxygen poisoning, he or
she should be taken off oxygen breathing and should
breathe air until 15 minutes has elapsed since the last
sign of poisoning. The diver can then be put back on
oxygen. If signs of oxygen poisoning develop again,
take the diver off oxygen and, after all signs and symp-
toms have subsided, travel the chamber to 20 fsw (6.1 m)
and shift straight across to the appropriate sched-
ule of the Surface Decompression Table Using Air.
When using this table, no credit is given for the time
the diver spent at 40 fsw (12.2 m). Stop at 20 fsw
(6.1 m) even if the appropriate Surface Decompression
Table Using Air has no 20-foot (6.1 m) stop. At 20 fsw
(6.1 m), place the diver back on oxygen for one half of
the total decompression time listed in the Total Decom-
pression Time column from the appropriate schedule
of the Surface Decompression Table Using Air. This
procedure will compensate for the shorter water stops
completed previously by the diver on the Surface Decom-
pression Table Using Oxygen. On completion of the
required time at 20 fsw (6.1 m) with the diver breath-
ing oxygen, follow the appropriate Surface Decompres-
sion Table Using Air schedule to the surface with the
diver breathing either oxygen or air.
Example: Divers make a planned dive to 160 fsw
(48 m) for 40 minutes using the Surface Decompression
Table Using Oxygen. The appropriate schedule shows
that there is a 3-minute water stop at 50 fsw (15.2 m),
a 5-minute water stop at 40 fsw (12.2 m), an 8-minute
water stop at 30 fsw (9 m), and a 3 2-minute chamber
stop at 40 fsw (12.2 m) breathing oxygen. After
12 minutes of oxygen breathing at the 40-foot (12.2 m)
chamber stop, one of the divers exhibits signs of oxy-
gen toxicity that subside completely within 5 minutes.
After an additional 15 minutes, the diver is placed
back on oxygen breathing, and the decompression sched-
ule is continued from the point of interruption. After
another 10 minutes on oxygen, the same diver has a
recurrence of oxygen poisoning, which again subsides
completely within 5 minutes. What procedures should
be followed in this situation?
NOAA Diving Manual — October 1991
USN Air Decompression Tables
Figure B-4
Surface Decompression Using Oxygen Flowchart
SURD
OXYGEN
SELECT
SCHEDULE
-"In-water"
SCHEDULE
SURFACE DECOMPRESSION
USING OXYGEN
^/treatment/
7__rABLEs/
- / TREATMENT /
FOLLOW SUR D
AIR TABLE
INTERRUPT OXYGEN
BREATHING. STAY ON
CHAMBER AIR FOR
15 MINUTES AFTER
SYMPTOMS SUBSIDE
INTERRUPT OXYGEN
BREATHING. WAIT
FOR CONVULSIVE
SYMPTOMS TO SUBSIDE
NOTES:
1. Ascent rate to first decompression
stop is 25 fpm.
2. Travel time between stops is I minute.
3. Travel time from 30-foot stop to the
surface is I minute.
4. Surface interval shall not exceed 3
minutes, 30 seconds.
5. Travel from the surface to the first
chamber stop is 30 seconds.
6. Begin breathing oxygen upon entering
chamber.
7. Travel time from the 40-foot chamber
stop to the surface is
2 minutes (20 fpm).
CONTINUE SUR O
OXYGEN SCHEDULE
INTERRUPT OXYGEN
BREATHING UNTIL
SYMPTOMS SUBSIDE
TRAVEL TO 20 FSW.
BREATHE OXYGEN FOR
ENTIRE 20-FOOT STOP.
STOP TIME EQUALS ONE
HALF TOTAL DECOMPRESSION
TIME LISTED IN SUR D
AIR TABLE FOR THE DIVE
CONTINUE ON SUR D
AIR TABLE TO THE
SURFACE USING AIR OR
OXYGEN
STAY AT 20 FSW
FOR ENTIRE SUR D
AIR TOTAL DECOM-
PRESSION ON AIR
TRAVEL TO 10 FSW
DOUBLE THE SUR D
AIR 10-FOOT STOP TIME
-t
COMPLETE THE
DIVE
7
October 1991 — NOAA Diving Manual
Source: U.S. Navy (1988)
B-11
Appendix B
Solution: Travel the chamber to 20 fsw (6.1 m) and
shift straight across to the 160/40 schedule of the
Surface Decompression Table Using Air. The total
decompression time on this schedule is 98 minutes and
50 seconds. The time the diver must spend at the 20-foot
(6.1 m) stop on oxygen is half of that time: 49 minutes
25 seconds. This time is then rounded up to 50 minutes.
After completing 50 minutes of oxygen breathing at
the 20-foot (6.1 m) stop, follow the 160/40 schedule of
the Surface Decompression Table Using Air to the
surface while the diver is breathing either oxygen or
air.
If the diver has another episode of oxygen poisoning
at the 20-foot (6.1 m) stop, or if the chamber's oxygen
system fails, stay at 20 fsw (6.1 m) for the full time
listed in the Total Decompression Time column of the
appropriate schedule of the Surface Decompression
Table Using Air, and then double the time required at
the 10-foot (3 m) stop and come up the rest of the way
with the diver breathing air.
Example: On the 160/40 schedule, a diver has a
third episode of oxygen poisoning after 15 minutes at
the 20-foot (6.1 m) stop. What procedures should be
followed?
Solution: The time the diver must now stay at the
20-foot (6.1 m) stop is 98 minutes 50 seconds, which is
rounded up to 99 minutes, and the time required at the
10-foot (3 m) stop is 39 minutes doubled, or 78 min-
utes. The time already spent by the diver at 20 fsw
(6. 1 m) on oxygen counts toward completion of the stop
time. If oxygen breathing at the 40-foot (12.2 m) stop
is interrupted and then resumed, the time the diver
spent off oxygen is counted as dead time.
If oxygen poisoning occurring at the 40-foot (12.2 m)
stop progresses to a convulsion, oxygen breathing
must not be restarted at 40 feet (12.2 m). In this case,
the chamber depth is held constant until the convul-
sion has subsided and the diver has regained conscious-
ness. The chamber is then brought to 20 fsw (6.1 m),
the diver is put back on oxygen breathing, and the
diver is then decompressed on the appropriate sched-
ule of the Surface Decompression Table Using Air, as
described above.
Example: A diver dives to 136 feet (41 m) for
62 minutes. What is the correct schedule to use from the
Surface Decompression Table Using Oxygen?
Solution: The correct decompression schedule is the
140/65 schedule. This decompression profile is illus-
trated in Figure B-5. Figure B-6 is an example of a
dive chart for this dive.
There are no repetitive diving tables or surface interval
tables for surface decompression dives. If another sur-
B-12
face decompression dive using oxygen is planned within a
12-hour period, the following procedures apply: sum
the bottom times of all dives made to get an adjusted
bottom time and use the adjusted bottom time and the
maximum depth attained in the previous 12 hours to
select the appropriate decompression schedule.
Example: A dive is conducted to 170 fsw (51 m) for
25 minutes, has a surface interval of 3 hours 42 min-
utes, and is followed by a repetitive dive to 138 fsw
(42 m) for 15 minutes. The Surface Decompression
Table Using Oxygen is followed for both dives. What is
the correct schedule?
Solution: The correct decompression schedule is
170/25 for the first dive and 170/40 for the second
dive. Even though the second dive was to a maximum
depth of 138 fsw (42 m) for 15 minutes, the diver must
be decompressed in accordance with the maximum
depth ever attained in the previous 12 hours, which
was 170 fsw (51 m), and with the sum of all bottom
times, which equals 40 minutes. Figure B-7 charts this
example.
This example shows that, even if the second dive is a
standard air dive: (1) all bottom times must be added
together to get an adjusted bottom time; and (2) the
decompression schedule must be selected in accord-
ance with the maximum depth attained in the previous
12 hours.
Surface Decompression Table Using Air
The Surface Decompression Table Using Air should
be used for surface decompressions after air dives when
no recompression chamber with an oxygen breathing
system is available.
The total ascent times of the schedules in the Sur-
face Decompression Table Using Air exceed those in
the Standard Air Decompression Table; the only advan-
tage of using the Surface Decompression Table Using
Air is that it permits a diver to be kept in a controlled,
closely observed environment during decompression.
When employing the Surface Decompression Table
Using Air, the divers should ascend from the last water
stop at 60 fpm (18.3 mpm). The total elapsed time for
these procedures must not exceed 5 minutes.
If the prescribed surface interval of 5 minutes has
been exceeded and the divers are asymptomatic, they
are treated as if they had Type I decompression sick-
ness symptoms. If the divers are symptomatic, they are
treated as if they had Type II decompression sickness
symptoms. Symptoms occurring during chamber stops
are treated as decompression sickness recurrences.
NOAA Diving Manual — October 1991
USN Air Decompression Tables
Figure B-5
Dive Profile for Surface Decompression Using Oxygen
140"|
120-
Ox/gen
V777.
T
120
Time, Min: Sec
Bottom Time
Total Decompression Time
140
Source: U.S. Navy (1988)
Example: What schedule would be appropriate for a
dive conducted to 128 fsw (39 m) for 48 minutes using
the Surface Decompression Table Using Air?
Solution: The correct decompression schedule for a
dive conducted to 128 feet (39 m) for 48 minutes is the
130/50 schedule. The decompression chart is shown in
Figure B-8. If a second surface decompression air dive
is planned within a 12-hour period, the same rule
applies for making a second surface decompression air
dive as for a second surface decompression oxygen
dive.
Example: A repetitive surface decompression air
dive is planned to 143 fsw (43 m) for 20 minutes. The
previous dive was to 172 fsw (52 m) for 30 minutes.
The surface interval was 4 hours 27 minutes. What is
the appropriate schedule?
Solution: The correct schedule for the first dive is
180/30; for the second dive it is 180/50. As explained
in the section on the Surface Decompression Table
Using Oxygen, the correct procedure is to decompress
the divers on a schedule that reflects the maximum
depth attained and the sum of the bottom times of all
dives made in the previous 12 hours. In this example,
the divers could make a third surface decompression
air dive as long as the maximum depth of such a dive
did not exceed 190 fsw (57 m) and the bottom time did
not exceed 10 minutes. They would then be decompressed
on the 190/60 schedule of the Surface Decompression
Table Using Air.
Exceptional Exposure Dives
Use of the exceptional exposure air decompression
schedules shown in the Standard Air Decompression
Table is discouraged because decompressions conducted
in accordance with these schedules are likely to result
in decompression sickness. Accordingly, exceptional
exposure dives should be conducted only in an emer-
gency and then only with the consent of the NOAA
Diving Coordinator.
GENERAL USE OF DECOMPRESSION
Rules During Ascent
After the correct decompression schedule has been
selected, it is imperative that it be followed exactly.
Decompression must be completed in accordance with
the selected schedule unless a deviation has been
approved by the NOAA Diving Coordinator.
Ascend at a rate of 60 fpm (18.3 m/min) when using
tables other than the Surface Decompression Table
Using Oxygen. (This table uses a rate of 25 fpm
(7.5 mpm).) Any variation in the rate of ascent must be
corrected in accordance with the procedures described
below in the Variations in Rate of Ascent section.
Decompression stop depths should be measured from
the level of the diver's chest. Decompression stop times
are counted from the time the diver reaches the stop
October 1991 — NOAA Diving Manual
B-13
Appendix B
Figure B-6
Dive Chart for Dive Involving Surface Decompression
Using Oxygen
DIVING CHART - AIR
date . ^ ^
02 MAV 8&
NAME OF DIVER I
OEV L I M
NAME OT DIVER 2
M0E&\\J*>
TENbERS (DIVER I)
COY
DIVING APPARATUS
MK \z
DIVING APPARATUS
MK Z
LEFT SURFACE (LS)
/ZOO
AND
A/^AL
LEFT Bottom (Lb)
REACHED SURFACE (RS)
/3f7--'3V/y/fe>---37
DEP
iy 5 = /3(*
OTTOM TIME (TBT)
: Q?Z.
TOTAL DECOMPRESSION TIME
(TDT) D/-7V •'■M
TYPE DRESS
Sui'-r-/^r)g(e^iUfar-
K
I EGS (PSIG)
TENDERS (DIVER 2)
TYP* bRE55
O^SviW Under wear
t ^ J * '-'— " JC
EGS (PSIG)
AND
\a//\&vLEa/
REACHED BOTTOM (RB)
TABLE & SCHEDULE USED
WO/bS_S\irb'Qi
TOTAL TIME OF DIVE (TTD)
01 '■ LbA131
DESCENT TIME
oz
TIME TO FIRST STOP
• 3 ■ -39
REPETITIVE GROUP
DESCENT
I
AJome.
ASCENT
DEPTH
OF
STOPS
60
70
80
90
100
110
120
-T30
DECOMPRESSION TIME
WATER CHAMBER
TIME
WATER
L 11,02.
(2.02.
CHAMBER
PURPOSE OF DIVE
[A)0\L\C
DIVER'S CONDITION
A/^MAL
REMARKS
OK- TO &£P£T
DIVING SUPERVISOR
HTcAK(Mtv) HUSS
Note: In this example, travel time is shown in seconds. For most
diving operations, however, recording the travel time in
minutes is sufficient.
Source: U.S. Navy (1988)
(
B-14
NOAA Diving Manual — October 1991
USN Air Decompression Tables
Figure B-7A
Dive Chart for Dive Involving Surface Decompression
Using Oxygen
DIVING CHART - AIR
DATE
NAME OF DIVER I ""
M/\CHA$\Ctf.
DIVING APPARATUS
f2-
diVINg Apparatus
TYPE dress
TYf>2 b&ESS
Sbt«« .'
DZ MA* \Q8d
dcrw
ECS (PSIC)
ECS (PSIG)
NAME OF DIVER 1
TENDERS (DIVER 2)
LE\AJ |S
TYPE DKtbb I
nr* r^
TENDERS (DIVER I)
STAdcK
AND
WrlTvcK
REACHED BOTTOM (RB)
AND
b&EENWZLL
DESCENT TIME
03
LEFT SURFACE (LS)
0800
DE£ItL»sw)
9-- 170
lUlALbOlluMTIME(TBt)
TABLE & SCHEDULE USED
[70/255ujrVgz
TIME TO FIRST STOP
LEFT BOTTOM (LB)
•-Z5
TOTAL TIME OF DIVE (TTD)
REPETITIVE GROUP
REACHED SURFACE (RS)
0S3I-- Wo?ib:
3<»
TOTAL DECOMPRESSION TIME
(TDT) : ?/:•' 3fc>
DESCENT
ASCENT
DEPTH
OF
STOPS
DECOMPRESSION TIME
WATER CHAMBER
TIME
WATER
CHAMBER
10
20
30
O:
40
l1
0?$H ..lb
Q?5$ ■■Z(*
%
50
60
70
80
90
100
110
120
I JU
0 8zr
R Og 03
PURPOSE OF DIVE
UVO&K
REMARKS
QIC -To RZPET
DIVER'S CONDITION
DIVING SUPERVISOR
No&mAl
amc<> CMbv) QrHlbCrS
Note: In this example, travel time is shown in seconds. For most
diving operations, however, recording the travel time in
minutes is sufficient.
Source: U.S. Navy (1988)
October 1991 — NOAA Diving Manual
B-15
Appendix B
Figure B-7B
(Continued)
REPETITIVE DIVE WORKSHEET
DATE"
OZMM g&
I. PREVIOUS DIVE:
CaO minutes
| | Standard Air Table
| | No-Decompression Table
l(of)+ S" = MQ feet Q Surface Table Using Oxygen (^Surface Table Using Air
hi I A repetitive group letter designation
2. SURFACE INTERVAL:
vJ hours ick minutes on surface
repetitive group from item I above
fr///\ new repetitive group letter designation from Residual Nitrogen Timetable
3. RESIDUAL NITROGEN TIME:
I 3 j +5 -\Do feet, depth of repetitive dive
A//A new repetitive group letter designation from item 2 above
o?S" minutes, residual nitrogen time from Residual Nitrogen Timetable or
bottom time of previous Sur D dive
k. EQUIVALENT SINGLE DIVE TIME:
t^v minutes, residual nitrogen time from item 3 above or bottom time of
s~*\ previous Sur D dive
+ ( *j£zL minutes, actual bottom time of repetitive dive
= tj-O minutes, equivalent single dive time
5. DECOMPRESSION FOR REPETITIVE DIVE:
fr 0 minutes, equivalent single dive time from item k above
/ UfS + 5" = / 1 0 feet, depth of repetitive dive
Decompression from (check one):
\~] Standard Air Table Q No-Decompression Table
[jpf Surface Table Using Oxygen Q Surface Table Using Air
Decompression Stops:
Depth
30 feet
Water
(o
4-
minutes
minutes
minutes
minutes
minutes
Chamber
minutes
f-O feet
SO feet
JCp minutes
minutes
60 feet
minutes
feet
minutes
II IU ICi
inutes 0Z + : °* Mr'^l
\JT0j H-Q schedule used (depth/time)
A//A repetitive group letter designation
i
Source: U.S. Navy (1988)
i
B-16
NOAA Diving Manual — October 1991
USN Air Decompression Tables
Figure B-7C
(Continued)
DIVING CHART - AIR
02
AMY 8$
DIVING APPARATUS
TYPE DRESS
EGS (PSIC)
NAME Of" DIVER I
MAcuAs\c\C
DlVlhC APPARATUS
MIC 12
i
EGS (PSIG)
NAME OT DIVER 2
TYPE DRES
CJJjJE
TENDERS (DIVER 2)
STOKES
Dru SviW\)nderuita.r
rr^ r-
TENDER5 (DIVER I)
LEFT SURFACE (LS)
AND
VELARDE
REACHED BOTTOM (RB)
DESCENT TIME
02.
/237
TttH-S'4a%-/llO
t
-f&tf-
TABLE & SCHEDULE USED
1 70/ WO Sur'O'Oi
LEFT BOTTOM (LB)
OSff
REACHED SURFACE (RS)
_JTT0MTIME(TB
■ H<> •*■ GlS)~' HO
TOTAL DECOMPR
(TDT) I
TIME TO FIRST STOP
15
TIME
TOTAL TIME OF DIVE (TTD)
REPETITIVE GROUP
A/one.
DESCENT
ASCENT
DEPTH
OF
STOPS
DECOMPRESSION TIME
WATER CHAMBER
TIME
WATER
CHAMBER
10
20
30
0U>
QzAfr 02
t\ll\--$lo
RI315 '• -S<o
kO
06
-Hi
Ll"5|«/--$4>
moi ■■ • su>
*\10(,'-'$U>
fSlto- -gCg
•o;
50
04
wao*; •••5fe
^
R /SO' ; : Sk
60
04
L /300 :'. Sk>
*'2S<0''S<e>
70
80
2
u.
90
r-
100
110
120
1^3
nn
L /Z^V
(ZSi
PURPOSE OF DIVE
W0H\£
REMARKS
Sur 50z Umif -Do KM RfpeT
DIVER'S CONDITION
DIVING SUPERVISOR
A/DKM^L
H/iaim fpr) ^H0/AAS
Note: In this example, travel time is shown in seconds. For most
diving operations, however, recording the travel time in
minutes is sufficient.
Source: U.S. Navy (1988)
October 1991 — NOAA Diving Manual
B-17
Appendix B
Figure B-8
Dive Chart for Dive Involving Surface Decompression
Using Air
DIVING CHART - AIR
DATE
OT M
NAME OF DIVER
V& blVER 2
NAME7)F blVER 2
fMrviiLTOA/
TEMDER5 (DIVER I)
DlVIMG APPARATUS
blVlNC APPARATUS
MK|Z
AND
£LL|S
LEFT SURFACE (LS)
LEFT BOTTOM (LB)
m~oo <jiy+s - '*?
IM8
REACHED SURFACE (RS)
ISl+'m'-0*//b/(,::/3
T^JT
'TulALBOTTOM TIME (TBT)
■4B
TOTAL DECOMPRESSION TIME
(TDT) / -Z?::/3
TYPE bRESa
Orj Svi+'Nnderivea.r
TEGS
£8
TENDERS (DIVER 2)
TYPE DRES5J
TT •
ECS (PSIC)
ECS (PSlG)
A/4
REACHED BOTTOM (RB)
t</02.
ANosrg^B^
TABLE & SCHEDULE USED
l$0/S0 Sur'DVl'V
TOTAL TIME OF DIVE (TTD)
2 :/fe::/3
DESCENT TIME
02.
TIME TO FIRST STOP
'01 ::33
REPETITIVE GROUP
A/one.
DESCENT
Si-
vr>
r-
ASCENT
"5
v9
o
DEPTH
OF
STOPS
10
20
30
40
50
60
70
80
90
100
10
120
12-3
-430-
DECOMPRESSION TIME
WATER CHAMBER
21
03
11
Zl
TIME
WATER
L \5!$::Hl
r/V£zl :: V3
l /V5z:*.3?
R W?.:33
/f*y
PURPOSE OF DIVE
R &&Z
CHAMBER
/<b/fc ::fl3
/S~39 ::g>3
/S3P--S3
/S/7 :: 53
$£AtcH P0£l1 6»L>4 6K. fro*"
DIVER'S CONDITION
A/OHMAU
REMARKS
Sur 'b'AiV-oK-r-p Pe.pe.-f"
DIVING SUPERVISOR
Note: In this example, travel time is shown in seconds. For most
diving operations, however, recording the travel time in
minutes is sufficient.
AAMC (hV) ASHfOA/
Source: U.S. Navy (1988)
B-18
NOAA Diving Manual — October 1991
USN Air Decompression Tables
depth. On completion of the specified stop time, the
divers ascend to the next stop or to the surface at the
designated ascent rate. Ascent time is not counted as
part of stop time.
Variations in Rate off Ascent
Since conditions sometimes prevent prescribed ascent
rates from being maintained, a general set of instruc-
tions has been established to compensate for any varia-
tions in rate of ascent. These instructions, along with
examples of their application, are listed below:
If the rate of ascent is less than 60 fpm (18.3 m/min)
and the delay occurs deeper than 50 fsw (15.2 m), add
the total delay time to the bottom time, recompute a
new decompression schedule, and decompress accordingly.
Example: A dive was conducted to 120 fsw (36 m)
with a bottom time of 60 minutes. According to the
120/60 decompression schedule of the Standard Air
Decompression Table, the first decompression stop is
at 30 feet (9 m). During ascent, the divers were delayed
at 100 fsw (33 m) and it actually took 4 minutes
55 seconds to reach the 30-foot (9 m) decompression stop.
What schedule should be used to determine the diver's
decompression requirements?
Solution: If an ascent rate of 60 fpm (18.3 m/min)
had been used, it would have taken the diver 1 minute
30 seconds to ascend from 120 fsw (40 m) to 30 fsw
(9 m). The difference between the actual and 60 fpm
(18.3 m/min) ascent times is 3 minutes 30 seconds. To
compensate, increase the bottom time of the dive from
60 minutes to 63 minutes 30 seconds and continue
decompression according to the schedule that reflects
this new bottom time, which is the 120/70 schedule.
(Note from the Standard Air Decompression Table
that this 3-minute 30-second delay increased the
diver's total decompression time from 71 minutes to
89 minutes — an increase of 18 minutes (Figure B-9).)
If the rate of ascent is less than 60 fpm (18.3 m/min)
and the delay occurs shallower than 50 fsw (15 m), add
the total delay time to the diver's first decompression
stop.
Example: A dive was conducted to 120 feet (40 m)
with a bottom time of 60 minutes. As shown in the
Standard Air Decompression Table, the first decom-
pression stop is at 30 fsw (9 m). During the ascent, the
divers were delayed at 40 feet (12.2 m) and it actually
took 5 minutes for them to reach the 30-foot (9 m)
stop. How much time does the diver need to spend at
the first stop?
Solution: As in the preceding example, the correct
ascent time should have been 1 minute 30 seconds, but
the diver was delayed by 3 minutes 30 seconds. To
compensate, increase the length of the 30-foot (9 m)
decompression stop by 3 minutes 30 seconds. This
means that, instead of 2 minutes, the divers must spend
5 minutes 30 seconds at 30 feet (9 m). (Note that in this
example the diver's total decompression time is increased
by only 7 minutes: the 3-minute 30-second delay in
ascent plus the additional 3 minutes 30 seconds they
had to spend at 30 feet (9 m) (Figure B-10).)
If the rate of ascent is greater than 60 fpm (18.3 m/min)
during a dive in which no decompression is required,
either slow the rate of ascent to allow the watches
to catch up or stop at 10 fsw (3 m) for an amount of
time equal to the difference between the length of
time the ascent should have taken and the time it
actually took.
Example: A dive was conducted to 100 fsw (33 m)
with a bottom time of 22 minutes. During ascent, the
diver momentarily lost control of his or her buoyancy,
which increased the ascent rate so that the diver reached
10 feet (3 m) in 1 minute 15 seconds. How will this
influence the diver's decompression?
Solution: At a rate of 60 fpm (18.3 m/min), the
ascent should take 1 minute 25 seconds to reach the
10-foot (3 m) stop. The diver must remain at 10 feet
(3 m) for the difference between 1 minute 25 seconds
and 1 minute 15 seconds, or an additional stop time
of 10 seconds (Figure B-l 1).
If the rate of ascent is greater than 60 fpm (18.3 m/min)
during a dive that requires decompression, stop 10 feet
(3 m) below the first decompression stop and allow
the watches to catch up.
October 1991 — NOAA Diving Manual
B-19
Appendix B
Figure B-9
Dive Chart for Decompression Dive; Delay Deeper
Than 50 fsw
DIVING CHART - AIR
DATE"
02.
MAY 83
dIvinc apparatus
M\L[ /H00 0
type dress
iurr
EGS (PSIG)
2.1-00
NAME OF DIVER I
5H/EL
NAME OF DIVER 2
WHl
DIVING APPARATUS
MKi M06 0
TYPE DRE55
burr
SUIT
ECS (PSIO
2115
LOW
TENDER5 (DIVER I)
PELT0A/
TENDERS (DIVER 2)
AtiO£flSO/S
SUIT
LEFT SURFACE (LS)
QgOO
AND
DOWlS
REACHED BOTTOM (RB)
AND
G&AY
DESCENT TIME
• 07.
LEFT BOTTOM (L&)
09 00
\Z0
TOtToM TimE (TbT)
lo0+:oy--30 =
OdOZr
TABLE & SCHEDULE USED
TIME TO FIRST STOP
REACHED SURFACE (RS)
/Oil ••: 25
TTTme
TOTAL TIME OF DIVE (TTD)
OZ -32. : ■ Z$
TOTAL DECOMPRESSION TIMI
(TDT)OI -SZ.- -2-S
REPETITIVE GROUP
o
DESCENT
ASCENT
DEPTH
OF
STOPS
DECOMPRESSION TIME
WATER CHAMBER
TIME
WATER
CHAMBER
10
\S5
/03Z''l6
^ 0911 ■■IS
20
;Z3
Q4y7::0S
*MJ}L£±0$
30
Lfl<?/3 ••65
fl<7o*/ :'SS
40
50
60
70
5
80
\T>
90
100
fov\td
l 01 0?>: .Lit
nO900:: IS
10
(IS
-m-
^OqOQ ::0O
R08QZ '■■00
nn
PURPOSE OF DIVE
ftf.Qunl i-Pica-r-i'oP
REMARKS
Foulfri &t /Pp-Fsw -for •'QS-'-SO
DIVER'S CONDITION
DIVING SUPERVISOR
A/p/LMAL
5MC>4l^tffly) 0ELAVT&&
Note: In this example, travel time is shown in seconds. For most
diving operations, however, recording the travel time in
minutes is sufficient.
Source: U.S. Navy (1988)
B-20
NOAA Diving Manual — October 1991
USN Air Decompression Tables
Figure B-10
Dive Chart for Decompression Dive; Delay Less
Than 50 fsw
DIVING CHART - AIR
DATE
02- /imY 88
NAME OF DIVER I
NAME OT DIVER 2
bit BSoA/
DMNC APPARATUS
AK 12.
DIVING APPARATUS
TYPE DRE5S
WET SUIT
TYPE DRESS
\A)BT
ECS (PSIC)
ECS (PSIC)
TENDERS (DIVER I)
TENDER5 (DIVER 2)
sore
AND
H/A/K
REACHED BOTTOM (RB)
AND (jtOfi-bOti
DESCENT TIME
02.
LEFT SURFACE (LS)
LEFT BOTTOM (LB)
O90O
REACHED SURFACE (RS)
ion ■' ss
sw)
OTT0M TIME (TBT) —
0&07-
(oO
TOTAL DECOMPRESSION TIME
(TDT) o\n : rr
TABLE & SCHEDULE USED
no/hO STQ Air
TOTAL TIME OF DIVE (TTD)
TIME TO
."0/
FIRST
STOP
•ZS"
REPETITIVE GROUP
_£_
DESCENT
ASCENT
DEPTH
OF
STOPS
DECOMPRESSION TIME
WATER CHAMBER
TIME
WATER
CHAMBER
:VS-
Llon '-45
* 09 *?.:•• 45
20
Z2L
L093Z::5S
g olio --ss
30
^09 to ••25'
g P9ol ::S6
40
Delay
03: '3,0
LO90^::^S'
RM0l'---l?
50
60
70
ii.
80
I/*
90
100
no
^
O30-
09 00
R 0fi02L
130 -
PURPOSE OF DIVE '
P^QlMU PI G/4T1QA/
REMARKS
SUP1
DIVER'S CONDITION
DIVING SUPERVISOR
A/MM >AU
HTC^U fyl/tftvA BuSM
Note: In this example, travel time is shown in seconds. For most
diving operations, however, recording the travel time in
minutes is sufficient.
Source: U.S. Navy (1988)
October 1991 — NOAA Diving Manual
B-21
Appendix B
Figure B-11
No-Decompression Dive; Rate of Ascent Greater
than 60 fpm
DIVING CHART - AIR
DATE"
oi May 88
NAME OF DIVER I
ANO£ RSQA/
NAME OF DIVER 2
M^CO&MICK
TENDERS (DIVER I)
A/ASH
DlVINC APPARATUS
MK. 12-
DlVINC APPARATUS
MK \1
LEFT SURFACE (LS)
08OQ
AND
W/lBA/A/
LEFT BOTTOM (LB)
082Z
REACHED SURFACE (RS)
0623 ■ • 35
DEEIfcHfsw)
<9sj-h5 - loo
roTXL BOTTOM TIME (t&T)
TOTAL DECOMPRESSION TIME
(TDT) •O/'-J'T
TYPE Dr£55
D'y SuiyUndervmf
TYPE DRESS
TENDERS (DIVER J)
WHITE
rrH
ECS (PSIG)
EGS(PSIC)
REACHED BOTTOM (RB)
AND
TABLE & SCHEDULE USED
100/25 M>lb
TOTAL TIME OF DIVE (TTD)
■23 ■•35
WHA fCTQA/
DESCENT TIME
TIME TO FIRST STOP
■on- -35
REPETITIVE GROUP
H
DESCENT
I
fe
.ASCENT
5
u*
DEPTH
OF
STOPS
10
20
30
40
50
60
70
80
90
9S
—100
H 10
426-
DECOMPRESSION TIME
WATER CHAMBER
: : 10
TIME
WATER
\-0823 •••25
RO&23 ••• /5
L tf£ZZ
r 0802.
CHAMBER
PURPOSE OF DIVE
WO£K
DIVER'S CONDITION
NORMAL
REMARKS fitfp 0f ASCe*)*-
DIVING SUPERVISOR
BMcfbv) PAAUWE
(
i
Note: In this example, travel time is shown in seconds. For most
diving operations, however, recording the travel time in
minutes is sufficient.
B-22
Source: U.S. Navy (1988)
NOAA Diving Manual — October 1991
(
USN Air Decompression Tables
U.S. NAVY STANDARD AIR DECOMPRESSION TABLE
Depth
(feet)
40
Total
Bottom
Time
Decompression stops (feet)
decompression
Repeti
tive
time
first stop
time
(min)
(minrsec)
50 40 30 20
10
(mln:sec)
group
200
0
0:40
*
210
0:30
2
2:40
N
230
0:30
7
7:40
N
250
0:30
11
11:40
O
270
0:30
15
15:40
O
300
0:30
19
19:40
Z
360
0:30
23
23:40
* *
480
0:30
41
41:40
* *
720
0:30
69
69:40
* *
50
100
0
0:50
*
110
0:40
3
3:50
L
120
0:40
5
5:50
M
140
0:40
10
10:50
M
160
0:40
21
21:50
N
180
0:40
29
29:50
O
200
0:40
35
35:50
O
220
0:40
40
40:50
z
240
0:40
47
47:50
z
60
60
0
1:00
*
70
0:50
2
3:00
K
80
0:50
7
8:00
L
100
0:50
14
15:00
M
120
0:50
26
27:00
N
140
0:50
39
40:00
O
160
0:50
48
49:00
Z
180
0:50
56
57:00
z
200
0:40
1
69
71:00
z
240
0:40
2
79
82:00
* *
360
0:40
20
119
140:00
* *
480
0:40
44
148
193:00
* *
720
0:40
78
187
266:00
70
50
60
1:00
70
1:00
80
1:00
90
1:00
100
•:00
110
120
0:50
0:50
130
0:50
140
0:50
150
0:50
160
0:50
170
0:50
0
1:10
*
8
9:10
K
14
15:10
L
18
19:10
M
23
24:10
N
33
34:10
N
2
41
44:10
O
4
47
52:10
O
6
52
59:10
0
8
56
65:10
z
9
61
71:10
z
13
72
86:10
z
19
79
99:10
z
*See No Decompression Table for repetitive groups
** Repetitive dives may not follow exceptional exposure dives
October 1991 — NOAA Diving Manual
Source: U.S. Navy (1988)
B-23
U.S. NAVY STANDARD AIR DECOMPRESSION TABLE
Appendix B
Depth
(feet)
80
Bottom
time
(min)
Time
first stop
(min:sec)
Decompression stops (feet)
50 40 30 20
10
Total
decompression
time
(min:sec)
Repeti
"tive
group
40
0
1:20
*
50
1
10
10
11:20
K
60
1
10
17
18:20
L
70
1
10
23
24:20
M
80
1
00
2
31
34:20
N
90
1
00
7
39
47:20
N
100
1
00
11
46
58:20
O
110
1
00
13
53
67:20
O
120
1
00
17
56
74:20
Z
130
1
00
19
63
83:20
z
140
1
00
26
69
96:20
z
150
1
00
32
77
110:20
z
180
1
00
35
85
121:20
* *
240
0
50
6
52
120
179:20
* *
360
0
50
29
90
160
280:20
* *
480
0:50
59
107
187
354:20
*
720
0:40
17
108
142
187
455:20
* *
::
90
30
40
1:20
0
7
1:30
8:30
J
50
1:20
18
19:30
L
60
1:20
25
26:30'
M
70
1:10
7
30
38:30
N
80
1:10
13
40
54:30
N
90
1:10
18
48
67:30
O
100
1:10
21
54
76:30
Z
110
1:10
24
61
86:30
Z
120
1:10
32
68
101:30
Z
130
1:00
5
36
74
116:30
Z
100
25
30
40
50
60
70
80
90
100
110
120
180
240
360
480
720
1:40
4:40
16:40
27:40
38:40
57:40
72:40
84:40
97:40
117:40
132:40
202:40
283:40
416:40
503:40
613:40
110
20
0
1:50
*
25
1
40
3
4:50
H
30
1
40
7
8:50
J
40
EC*
1
-*
30
2
Q
21
24:50
^RRf")
L
M
60
i
1
30
O
18
c.0
36
Ou.OU
55:50
IVI
N
70
1
20
1
23
48
73:50
O
80
1
20
7
23
57
88:50
Z
90
1
20
12
30
64
107:50
z
100
1
20
15
37
72
125:50
z
'See No Decompression Table for repetitive groups
"Repetitive dives may not follow exceptional exposure dives
B-24
Source: U.S. Navy (1988)
NOAA Diving Manual — October 1991
USN Air Decompression Tables
U.S. NAVY STANDARD AIR DECOMPRESSION TABLE
Depth
(feet)
120
Bottom
time
(min)
Time to
first stop
(min:sec)
15
20
1:50
25
1:50
30
1:50
40
1:40
50
1:40
60
1:30
70
1:30
80 1 '30
90
1:30
100
1:30
120
1:20
180 1:10
240
1:10
360
1:00
480
0:50
720
0:50
Decompression stops (feet)
70 60 50 40 30 20 10
3
32
18
41
5
23
45
64
10
27
35
64
2
9
15
19
23
19
37
60
5
15
22
23
27
37
45
47
76
97
93 142
Total
decompression Repeti-
time tive
(min:sec) group
93 122 142
74 100 114 122 142
0
2:00
2
4:00
6
8:00
14
16:00
25
32:00
31
48:00
45
71:00
55
89:00
63
107:00
74
132:00
80
150:00
98
176:00
137
284:00
179
396:00
187
551:00
187
654:00
187
773:00
130
10
0
2
10
*
15
2:00
1
3
10
F
20
2:00
4
6
10
H
25
2:00
10
12
10
J
30
1:50
3
18
23
10
M
40
1:50
10
25
37
10
N
50
1:40
3
21
37
63
10
O
60
1:40
9
23
52
86
10
Z
70
1:40
16
24
61
103
10
z
80
1:30
3
19
35
72
131
10
z
90
1:30
8
19
45
80
154
10
z
140
Bottom
time
(min)
Time to
first stop
(min:sec)
10
15
2:10
20
2:10
25
2:00
30
2:00
40
1:50
50
1:50
60
1:50
70
1:40
80
1:40
90
1:30
120
1:30
180
1:20
240
1:10
360
1:00
480
1:00
720
0:50
Decompression stops (feet)
90
Total
decompression Repeti-
tlme tive
80 70 60 50 40 30 20 10 (mlnrsec) group
16
0
2:20
2
4:20
6
8:20
2
14
18:20
5
21
28:20
2
16
26
46:20
6
24
44
76:20
16
23
56
97:20
4
19
32
68
125:20
10
23
41
79
155:20
2
14
18
42
88
166:20
12
14
36
56
120
240:20
10
26
32
54
94
168
386:20
8
28
34
50
78
124
187
511:20
9 32
42
64
84
122
142
187
684:20
31 44
59
100
114
122
142
187
801:20
56 88
97
100
114
122
142
187
924:20
*See No Decompression Table for repetitive groups
** Repetitive dives may not follow exceptional exposure dives
October 1991 — NOAA Diving Manual
Source: U.S. Navy (1988)
B-25
U.S. NAVY STANDARD AIR DECOMPRESSION TABLE
Appendix B
Depth
(feet)
150
Bottom Time to
time first stop
(min) (min:sec)
5
10
15
20
25
30
40
50
60
70
80
2:20
2:20
2:10
2:10
2:10
2:00
2:00
1:50
1:50
1:40
Decompression stops (feet)
90 80 70 60 50 40 30 20
3
11
17
5
12
19
19
19
2
4
8
19
23
26
39
50
Total
decompression Repeti-
time tive
10 (mln:sec) group
0
1
3
7
17
24
33
51
62
75
84
2:30
C
3:30
E
5:30
G
11:30
H
23:30
k
34:30
L
59:30
N
88:30
O
112:30
Z
146:30
173:30
z
z
160
5
10
2:30
15
2:20
20
2:20
25
2:20
30
2:10
40
2:10
50
2:00
60
2:00
70
1:50
0
2:40
D
1
3:40
F
1
4
7:40
H
3
11
16:40
J
7
20
29:40
K
2
11
25
40:40
M
7
23
39
71:40
N
2
16
23
55
98:40
Z
9
19
33
69
132:40
Z
17
22
44
80
166:40
* *
170
180
Bottom Time to
time first stop
(min) (min:sec) 110
Decompression stops (feet)
100 90 80 70 60
Total
decompression Repeti-
tlme tive
50 40 30 20 10 (mln:sec) group
5
0
2:50
D
10
2:40
2
4:50
F
15
2:30
2
5
9:50
H
20
2:30
4
15
21:50
J
25
2:20
2
7
23
34:50
L
30
2:20
4
13
26
45:50
M
40
2:10
1
10
23
45
81:50
O
50
2:10
5
18
23
61
1 09:50
Z
60
2:00
2
15
22
37
74
152:50
z
70
2:00
8
17
19
51
86
183:50
**
90
1:50
12
12
14
34
52 120
246:50
**
120
1 on
1:30
1 -on
A
2
1 n
10
oo
12
OQ
18
1A
32
42
7Q
82 156
1 on 1 ft7
356:50
c;Q^'Rn
**
l ou
240
1:20
4
18
IU
24
30
42
o4
50
70
(O
116
I £X) ID/
142 187
OoO.DU
681:50
**
360
1:10
22 34
40
52
60
98
114
122
142 187
873:50
**
480
1:00
14 40 42
56
91
97
100
114
122
142 187
1007:50
5
0
3:00
D
10
2:50
3
6:00
F
15
2:40
3
6
12:00
I
20
2:30
1
5
17
26:00
K
25
2:30
3
10
24
40:00
L
30
2:30
6
17
27
53:00
N
40
2:20
3
14
23
50
93:00
O
50
2:10
2
9
19
30
65
128:00
z
60
2:10
5
16
19
44
81
168:00
z
*See No Decompression Table for repetitive groups
* 'Repetitive dives may not follow exceptional exposure dives
B-26
Source: U.S. Navy (1988)
NOAA Diving Manual — October 1991
USN Air Decompression Tables
U.S. NAVY STANDARD AIR DECOMPRESSION TABLE
Depth
(feet)
190
Total
Bottom Time to Decompression stops (feet) decompression Repeti-
time first stop time tive
(min) (min:sec) 110 100 90 80 70 60 50 40 30 20 10 (mln:sec) group
5
2:50
10
2:50
15
2:50
20
2:40
25
2:40
30
2:30
40
2:30
50
2:20
60
2:20
1
1
4
6
11
13 22 33
17 19 50
0
3
7
20
25
8 19 32
8 14 23 55
72
84
3
7
14
31
44
63
103
147
183
:10
:10
D
G
:10 I
:10
K
:10
M
:10
N
:10
O
200
Total
Bottom Time to Decompression stops (feet) decompression
time first stop time
(min) (min:sec) 130 120 110 100 90 80 70 60 50 40 30 20 10 (min:sec)
5
3:10
10
3:00
15
2:50
20
2:50
25
2:50
30
2:40
40
2:30
50
2:30
60
2:20
90
1:50
120
1:40
180
1:20
240
1:20
360
1:10
12
1
4:20
1
4
8:20
1
4
10
18:20
3
7
27
40:20
7
14
25
49:20
2
9
22
37
73:20
2
8
17
23
59
112:20
6
16
22
39
75
161:20
2
13
17
24
51
89
199:20
1
10
10
12
12
30
38
74
134
324:20
6
10
10
10
24
28
40
64
98
180
473:20
1
10
10
18
24
24
42
48
70
106
142
187
685:20
6
20
24
24
36
42
54
68
114
122
142
187
842:20
22
36
40
44
56
82
98
100
114
122
142
187
1058:20
210
5
3:20
10
3:10
15
3:00
20
3:00
25
2:50
30
2:50
40
2:40
50
2:30
1
4:30
2
4
9:30
1
5
13
22:30
4
10
23
40:30
2
7
17
27
56:30
4
9
24
41
81:30
4
9
19
26
63
124:30
9
17
19
45
80
174:30
220
5
3:30
1
5:40
10
3:20
2
5
10:40
15
3:10
2
5
16
26:40
20
3:00
1
3
11
24
42:40
25
3:00
3
8
19
33
66:40
30
2:50
1
7
10
22
23
29
47
91:40
40
2:50
6
12
68
f40:40
50
2:40
3 12
17
18
51
86
190:40
*See No Decompression Table for repetitive groups
"Repetitive dives may not follow exceptional exposure dives
October 1991 — NOAA Diving Manual
Source: U.S. Navy (1988)
B-27
U.S. NAVY STANDARD AIR DECOMPRESSION TABLE
Appendix B
Depth
(feet)
230
Bottom Time to
time first stop
(mln) (mlrcsec)
Decompression stops (feet)
130 120 110 100 90 80 70 60 50 40 30 20
Total
decompression
time
10 (mlnrsec)
5
3:40
2
5:50
10
3:20
1
2
6
12:50
15
3:20
3
6
18
30:50
20
3:10
2
5
12
26
48:50
25
3:10
4
8
22
37
7450
30
3:00
2
8
12
23
51
99:50
40
2:50
1
7
15
22
34
74
1 56:50
50
2:50
5
14
16
24
51
89
202:50
240
5
3:50
2
6:00
10
3:30
1
3
6
14:00
15
3:30
4
6
21
35:00
20
3:20
3
6
15
25
53:00
25
3:10
1
4
9
24
40
82:00
30
3:10
4
8
15
22
56
109:00
40
3:00
3
7
17
22
39
75
167:00
50
2:50
1 8
15
16
29
51
94
218:00
Depth
(feet)
250
Bottom
time
(mln)
Time to
first stop
(mln:sec)
5
3:50
10
3:40
15
3:30
20
3:30
25
3:20
30
3:20
40
3:10
60
2:40
90
2:10
120
1:50
180
1:30
240
1:30
Decompression stops (feet)
200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20
14 21
4
10
10
8
1U
10
10
1U
1U
10
10
10
10
16
24
24
10
22
24
24
32
42
44
22
22
4U
41)
42
bb
/b
5
10
28
36
60
2
6
9
12
28
48
1
4
7
7
17
22
44
64
1
4
7
10
17
19
36
68
94
1
4
7
17
24
23
45
Total
decompression
time
10 (min:sec)
2
7
22
27
45
59
79
64 164
98 186
142 187
84 114 122 142 187
98 100 114 122 142 187
7:10
16:10
38:10
59:10
92:10
116:10
178:10
298:10
514:10
684:10
931:10
1109:10
260
5 4:00
10
3:50
15
3:40
20
3:30
2b
3:30
30
3:20
40
3:10
1
2
7:20
2
4
9
19:20
2
4
1U
22
42:20
1
4
/
20
31
67:20
3
8
11
23
bU
99:20
2
6
8
19
26
61
126:20
b
11
1b
iy
4y
84
190:20
270
b
4:10
10
4:00
15
3:50
20
3:40
25 3:30
30
3:30
40
3:20
1
3
8:30
2
b
11
22:30
3
4
11
24
46:30
2
3
y
21
23
35
53
74:30
■l
3
8
13
106:30
3
b
12
22
2/
b4
138:30
b
11
1 /
22
51
8b
204:30
B-28
Source: U.S. Navy (1988)
NOAA Diving Manual — October 1991
i
USN Air Decompression Tables
U.S. NAVY STANDARD AIR DECOMPRESSION TABLE
Depth
(leet)
280
Bottom
time
(min)
5
10
15
20
25
30
40
Time to
first stop
(mln:sec)
4:20
400
3:50
3:50
3:40
3:30
3:20
Decompression stops (feet)
200 190 180 170 160 150 140 130 120 110 100 90 80
0 60
50
40
30
20
Total
decompress!)
time
10 (mln:sec)
2
■■
840
1
2
5
13
25:40
1
3
4
11
26
49:40
3
4
8
23
39
81:40
2
b
7
16
23
56
113:40
1 3
7
13
22
30
70
150 40
6 6
13
17
21
51
93
218:40
290
5
4:30
10
4:10
15
4:00
20
4:00
25
3:50
30
3:40
40
3:30
3
6
9
17 23
3
16
12 26
23 43
3 5 8 17 23 60
1 5 6 16 22 36 72
5 7 15 16 32 51 95
9
29
52
89
120
162
228
300
5
4:40
3 3
11:00
10
4:20
1
3
6 17
32:00
15
4:10
2
3
6
15 26
57:00
20
4:00
2
3
7
10
23 47
97:00
25
3:50
1
3
6
8
19
26 61
129:00
30
3:50
2
5
7
17
22
39 75
172:00
40
3:40
4
6
9
15
17
34
51 90
231:00
60
3:00
4
10
10
10
10
10
14
28
32
50
90 187
460:00
90
2:20
3
8
8 10
10
10
10
16
24
24
34
48
64
90
142 187
693:00
120
2:00
4
8
8
8
8 10
14
24
24
24
34
42
58
66
102
122
142 187
890:00
180
1:40
6 8 8
8
14
20
21 21
28
40
40
48
56
82
98
100
114
122
142 187
1168:00
Source: U.S. Navy (1988)
NO-DECOMPRESSION LIMITS AND REPETITIVE GROUP DESIGNATION TABLE FOR
NO-DECOMPRESSION AIR DIVES
Depth
(feet)
No-decom
pression
limits
(min)
10
15
20
25
30
35
310
40
200
50
100
60
60
70
50
80
40
90
30
100
25
110
20
120
15
130
10
140
10
150
5
160
5
170
5
180
5
190
5
35
25
20
15
5
5
50
35
30
55
45
Group Designation
F G H I J
M
60 120 210 300
70 110 160 225 350
75 100 135 180 240 325
75 100 125 160 195 245 315
60
75
95 120 145 170 205 250 310
15
25
40
50
60
80
100
15
25
30
40
50
70
80
10
15
25
30
40
50
60
10
15
20
25
30
40
50
5
10
15
20
30
35
40
5
10
15
20
25
30
35
5
10
12
15
20
25
30
5
7
10
15
20
22
25
5
10
13
15
20
5
10
12
15
5
8
10
5
7
10
120
100
70
55
45
40
140
110
80
60
50
160
190
220
2/0
130
150
170
200
90
100
310
Source: U.S. Navy (1988)
October 1991 — NOAA Diving Manual
B-29
Appendix B
RESIDUAL NITROGEN TIMETABLE FOR REPETITIVE AIR DIVES
Locate the diver's repetitive group designation from his previous dive
along the diagonal line above the table. Read horizontally to the interval
in which the diver's surface Interval lies.
Next read vertically downward to the new repetitive group designation.
Continue downward in this same column to the row which represents
the depth of the repetitive dive. The time given at the inter-
section is residual nitrogen time, in minutes, to be applied
to the repetitive dive.
Dives following surface intervals of more than 12 hours
are not repetitive dives. Use actual bottom times in
the Standard Air Decompression Tables to compute
decompression for such dives.
A*
M*
**
\*
** If no Residual Nitrogen Time is given,
then the repetitive group does not
change.
vx*8
4&
J*
*?
**
JF
c&
<$
A°
*#
**
7
\ 0:10
S 0:23
~5
J
y
y
y
^y
y
y
y
y
y
y
>
0:10
0:22
0:23
0:34
0:10
0:24
0:24
0:36
0:35
0:48
0:10
0:25
0:25
0:39
0:37
0:51
0:49
1:02
0:10
0:26
0:26
0:42
0:40
0:54
0:52
1:07
1:03
1:18
0:10
0:28
0:27
0:45
0:43
0:59
0:55
1:11
1:08
1:24
1:19
1:36
0:10
0:31
0:29
0:49
0:46
1:04
1:00
1:18
1:12
1:30
1:25
1:43
1:37
1:55
0:10
0:33
0:32
0:54
0:50
1:11
1:05
1:25
1:19
1:39
1:31
1:53
1:44
2:04
1:56
2:17
0:10
0:36
0:34
0:59
0:55
1:19
1:12
1:35
1:26
1:49
1:40
2:05
1:54
2:18
2:05
2:29
2:18
2:42
0:10
0:40
0:37
1:06
1:00
1:29
1:20
1:47
1:36
2:03
1:50
2:19
2:06
2:34
2:19
2:47
2:30
2:59
2:43
3:10
0:10
0:45
0:41
1:15
1:07
1:41
1:30
2:02
1:48
2:20
2:04
2:38
2:20
2:53
2:35
3:08
2:48
3:22
3:00
3:33
3:11
3:45
0:10
0:54
0:46
1:29
1:16
1:59
1:42
2:23
2:03
2:44
2:21
3:04
2:39
3:21
2:54
3:36
3:09
3:52
3:23
4:04
3:34
4:17
3:46
4:29
0:10
1:09
0:55
1:57
1:30
2:28
2:00
2:58
2:24
3:20
2:45
3:43
3:05
4:02
3:22
4:19
3:37
4:35
3:53
4:49
4:05
5:03
4:18
5:16
4:30
5:27
0:10
1:39
1:10
2:38
1:58
3:22
2:29
3:57
2:59
4:25
3:21
4:49
3:44
5:12
4:03
5:40
4:20
5:48
4:36
6:02
4:50
6:18
5:04
6:32
5:17
6:44
5:28
6:56
0:10
2:10
1:40
2:49
2:39
5:48
3:23
6:32
3:58
7:05
4:26
7:35
4:50
7:59
5:13
8:21
5:41
8:40
5:49
8:58
6:03
9:12
6:19
9:28
6:33
9:43
6:45
9:54
6:57
10:05
REPETITIVE
DIVE \ J
DEPTH \/
0:10
12:00*
2:11
12:00*
2:50
12:00*
5:49
12:00*
6:33
12:00*
7:06
12:00*
7:36
12:00*
8:00
12:00*
8:22
12:00*
8:41
12:00*
8:59
12:00*
9:13
12:00*
9:29
12:00*
9:44
12:00*
9:55
12:00*
10:06
12:00*
0
N
M
L
NE
:w
j
GR
I
OU
P D
ES
H
IGNi
\TI
0
ON
F
E
0
c
B
A
V
V
\J
V
V
\/
V
\J
\J
\J
V
\J
V
k/
\J
10
**
**
**
**
**
**
«*
**
*•
**
**
**
279
159
88
39
20
**
**
**
**
**
**
**
399
279
208
159
120
88
62
39
18
30
**
**
469
349
279
229
190
159
132
109
88
70
54
39
25
12
40
257
241
213
187
161
138
116
101
87
73
61
49
37
25
17
7
50
169
160
142
124
111
99
87
76
66
56
47
38
29
21
13
6
60
122
117
107
97
88
79
70
61
52
44
36
30
24
17
11
5
70
100
96
87
80
72
64
57
50
43
37
31
26
20
15
9
4
80
84
80
73
68
61
54
48
43
38
32
28
23
18
13
8
4
90
73
70
64
58
53
47
43
38
33
29
24
20
16
11
7
3
100
64
62
57
52
48
43
38
34
30
26
22
18
14
10
7
3
110
57
55
51
47
42
38
34
31
27
24
20
16
13
10
6
3
120
52
50
46
43
39
35
32
28
25
21
18
15
12
9
6
3
130
46
44
40
38
35
31
28
25
22
19
16
13
11
8
6
3
140
42
40
38
35
32
29
26
23
20
18
15
12
10
7
5
2
150
40
38
35
32
30
27
24
22
19
17
14
12
9
7
5
2
160
37
36
33
31
28
26
23
20
18
16
13
11
9
6
4
2
170
35
34
31
29
26
24
22
19
17
15
13
10
8
6
4
2
180
32
31
29
27
25
22
20
18
16
14
12
10
8
6
4
2
190
31
30
28
26
24
21
19
17
15
13
11
10
8
6
4
2
RESIDUAL NITROGEN TIMES (MINUTES)
B-30
Source: U.S. Navy (1988)
NOAA Diving Manual — October 1991
USN Air Decompression Tables
SURFACE DECOMPRESSION TABLE USING OXYGEN
Time (min) breathing
Time at
Time to
air at water stops (ft)
40-foot
Total
Bottom
first stop
chamber stop
decompression
Depth
time
or surface
Surface
(min) on
time
(feet)
(min)
(min:sec)
60 50 40 30
interval
oxygen
Surface
(min:sec)
70
80
90
100
110
52
90
120
150
180
40
70
85
100
115
130
150
32
60
70
80
90
100
110
120
130
26
50
60
70
80
90
100
110
120
22
40
50
60
70
80
90
100
110
2:48
2:48
2:48
2:48
2:48
3:12
3:12
3:12
3:12
3:12
3:12
3:12
3:36
3:36
3:36
3:36
3:36
3:36
3:36
3:36
3:36
4:00
4:00
4:00
4:00
4:00
4:00
4:00
4:00
2:48
4:24
4:24
4:24
4:24
4:24
3:12
3:12
3:12
3:12
0
15
23
31
39
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
3
0
0
0
0
0
0
0
0
0
0
0
1
0
2
0
5
0
12
LU
o
X
o
o
z
0_
o
I-
w
<
X
o
h-
co
en
Q-
O
I-
co
EC
LU
l-
3
o
QC
o
0
14
20
25
30
34
39
43
48
0
14
20
26
32
38
44
49
53
0
12
19
26
33
40
46
51
54
o z
°u-x
Sg|
cotr<
<LUJjj
^55
2:48
23:48
31:48
39:48
47:48
3:12
23:12
29:12
35:12
40:12
46:12
53:12
3:36
23:36
29:36
34:36
39:36
43:36
48:36
52:36
57:36
4:00
24:00
30:00
36:00
42:00
48:00
54:00
59:00
65:48
4:24
22:24
29:24
36:24
43:24
51:12
58:12
66:12
76:12
120
18
30
40
50
60
70
80
90
100
4:48
4:48
4:48
4:48
3:36
3:36
3:36
3:12
3:12
0
0
0
0
2
4
5
7
15
0
9
16
24
32
39
46
51
54
4:48
19:48
26:48
34:48
44:36
53:36
61:36
72:12
86:12
October 1991 — NOAA Diving Manual
Source: U.S. Navy (1988)
B-31
Appendix B
SURFACE DECOMPRESSION TABLE USING OXYGEN
Depth
(feet)
Bottom
time
(min)
Time to
first stop
or surface
(min:sec)
Time (min) breathing
air at water stops (ft)
60 50 40 30
Surface
interval
Time at
40-foot Total
chamber stop decompression
(min) on time
oxygen Surface (min:sec)
OA
15
5:12
0
0
0
0
0
5:12
■%( 1
30
5:12
0
0
0
0
12
23:12
VJ\J
40
5:12
0
0
0
0
21
32:12
50
4:00
0
0
0
3
29
43:00
60
4:00
0
0
0
5
CO
i ii
37
53:00
70
4:00
0
0
0
7
i—
45
63:00
80
3:36
0
0
6
7
51
75:36
90
3:36
0
0
10
12
56
89:36
140
o
X
150
160
13
5:36
0
0
0
0
r\
0
25
5:36
0
0
0
0
11
30
5:36
0
0
0
0
\-
15
35
5:36
0
0
0
0
o
20
40
4:24
0
0
0
2
0_
24
45
4:24
0
0
0
4
O
29
50
4:24
0
0
0
6
t—
co
33
55
4:24
0
0
0
7
cr
38
60
4:24
0
0
0
8
LU
00
43
65
4:00
0
0
3
7
2
48
70
3:36
0
2
7
7
<
51
i
o
h-
co
cr
LL
o
11
6:00
0
0
0
0
1-
0
25
6:00
0
0
0
0
Q_
o
13
30
6:00
0
0
0
0
1-
18
35
4:48
0
0
0
4
co
23
40
4:24
0
0
3
6
DC
LU
27
45
4:24
0
0
5
7
h-
33
50
4:00
0
2
5
8
§
38
55
3:36
2
5
9
4
1-
co
3
44
o
cr
o z
■*LUUU
500
£*°
cocr<
<LUlu
CN?.<J
5:36
22:36
26:36
31:36
37:24
44:24
50:24
56:24
62:24
70:00
79:36
6:00
25:00
30:00
38:48
48:24
57:24
66:00
77:36
9
6:24
0
0
0
0
LL.
Ill
0
6:24
20
6:24
0
0
0
0
2
11
23:24
25
6:24
0
0
0
0
1-
16
28:24
30
5:12
0
0
0
2
_i
21
35:12
35
4:48
0
0
4
6
i*
26
48:48
40
4:24
0
3
5
8
0
32
61:24
45
4:00
3
4
8
6
\—
38
73:00
170
7
6:48
0
0
0
0
0
6:48
20
6:48
0
0
0
0
13
25:48
25
6:48
0
0
0
0
19
31:48
30
5:12
0
0
3
5
23
44:12
35
4:48
0
4
4
7
29
57:48
40
4:24
4
4
8
6
36
72:24
Source: U.S. Navy (1988)
B-32
NOAA Diving Manual — October 1991
USN Air Decompression Tables
SURFACE DECOMPRESSION TABLE USING AIR
Depth
(feet)
40
50
60
70
Bottom
time
(min)
80
90
100
110
40
50
60
70
80
90
100
110
120
130
40
50
60
70
80
90
100
110
120
30
40
50
60
70
80
90
100
Time to
first stop
(mimsec)
Time at water stops (min)
30 20 10
Total
Chamber stops
decompression
Surface
(air) (min)
time
Interval
20 10
(mlnrsec)
230
0:30
3
7
14:30
250
0:30
3
11
18:30
270
0:30
3
15
22:30
300
0:30
3
19
26:30
120
0:40
3
5
12:40
140
0:40
3
10
17:40
160
0:40
3
21
28:40
180
0:40
3
29
36:40
200
0:40
3
35
42:40
220
0:40
3
40
47:40
240
0:40
3
47
54:40
80
0:50
3
7
14:50
100
0:50
3
w
14
21:50
120
0:50
3
hi
i-
26
33:50
140
0:50
3
Z>
39
46:50
160
0:50
3
Z
48
55:50
180
0:50
3
5:
56
63:50
200
0:40
3
in
3
69
80:10
Q
in
60
1:00
3
LU
8
16:00
70
1:00
3
O
X
14
22:00
80
1:00
3
LU
18
26:00
90
1:00
3
O
23
31:00
100
1:00
3
1—
33
41:00
110
0:50
3
o
3
41
52:20
120
0:50
z
4
47
59:20
130
0:50
3
O-
6
52
66:20
140
0:50
3
CJ
8
56
72:20
150
0:50
3
C/3
9
61
78:20
160
0:50
3
CC
n i
13
72
93:20
170
0:50
3
CD
19
79
106:20
50
1
10
3
<
10
18:10
60
1
10
3
o
17
25:10
70
1
10
3
i-
23
31:10
80
1
00
3
CC
3
31
42:30
90
1
00
3
LL
7
39
54:30
100
1
00
3
o
11
46
65:30
110
1
00
3
t—
13
53
74:30
120
1
00
3
o
17
56
81:30
130
1
00
3
I-
19
63
90:30
140
1
00
26
rr
26
69
126:30
150
1
00
32
LU
32
77
146:30
40
30
30
30
20
20
20
20
1
7
12
15
3
3
18
23
23
30
37
October 1991 — NOAA Diving Manual
7 15:20
18 26:20
25 33:20
30 45:40
40 71:40
48 89:40
54 101:40
61 114:40
68 137:40
74 156:40
15 23:30
24 35:50
28 45:50
39 64:50
48 99:50
57 111:50
66 124:50
72 155:50
78 177:50
7 15:40
21 33:00
26 43:00
36 78:00
48 101:00
57 116:00
64 142:00
72 167:00
Source: U.S. Navy (1988)
B-33
Appendix B
SURFACE DECOMPRESSION TABLE USING AIR
Time at water stops (min)
50 40 30 20 10
Bottom
Time to
Depth
time
first stop
(feet)
(min)
(min:sec)
Total
Chamber stops
decompression
Surface
(air) (min)
time
Interval
20 10
(mln:sec)
120
130
140
150
160
170
180
190
25
30
1:50
1:50
3
6
14
14:50
22:50
40
1:40
3
5
25
39:10
50
1:40
15
15
31
67:10
60
1:30
2
22
22
45
97:10
70
1:30
9
23
23
55
116:10
80
1:30
15
27
27
63
138:10
90
1:30
19
37
37
74
173:10
100
1:30
23
45
45
80
189:10
25
2:00
3
10
19:00
30
1:50
3
ii i
3
18
30:20
40
1:50
10
I—
10
25
51:20
50
1:40
3
21
^
-^
21
37
8820
60
1:40
9
23
5
23
52
113:20
70
80
1:40
1:30
3
16
19
24
35
10
24
35
61
72
131:20
170:20
90
1:30
8
19
45
LU
45
80
203:20
f 1
20
2
10
3
X
6
15:10
25
2
00
3
3
14
26:30
30
2
00
5
0
1-
5
21
37:30
40
1
50
2
16
1—
16
26
66:30
50
1
50
6
24
0
24
44
104:30
60
1
50
16
23
23
56
124:30
70
1
40
4
19
32
0
32
68
161:30
80
1
40
10
23
41
1-
41
79
200:30
20
2:10
3
LU
3
7
19:40
25
2:10
4
CD
2
4
17
31:40
30
2:10
8
<
8
24
46:40
40
2:00
5
19
19
33
82:40
50
60
2:00
1:50
3
12
19
23
26
23
26
51
62
115:40
142:40
70
1 :50
1 1
19
39
LZ
39
75
189:40
80
1:40
1
17
19
50
r-\
50
84
227:40
H
20
2:20
3
Q_
3
11
23:50
25
2:20
7
O
| —
7
20
40:50
30
2:10
2
11
w
11
25
55:50
40
2:10
7
23
n 1
23
39
98:50
50
60
2:00
2:00
2
9
16
19
23
33
1-
<
>
23
33
55
69
125:50
169:50
70
1:50
17
22
44
>
■
44
80
214:50
w
15
2:30
3
3
5
18:00
20
2:30
4
2
4
15
30:00
25
2:20
2
7
O
7
23
46:00
30
2:20
4
13
DC
13
26
63:00
40
2:10
1
10
23
LL
LU
23
45
109:00
50
60
2:10
2 00
2
5
15
18
22
23
37
2
1—
23
37
61
74
137:00
194:00
2
00
8
17
19
51
_i
51
86
239:00
<
1—
15
2:40
3
0
3
6
19:10
20
2:30
1
5
h-
5
17
35:10
25
2:30
3
10
10
24
54:10
30
2:30
6
17
17
27
74:10
40
2:20
3
14
23
23
50
120:10
50
2:10
2
9
19
30
30
65
162:10
60
2:10
5
16
19
44
44
81
216:10
15
2:50
4
4
7
22:20
20
2:40
2
6
6
20
41:20
25
2:40
5
11
11
25
59:20
30
2:30
1
8
19
19
32
86:20
40
2:30
8
14
23
23
55
130:20
50
2:20
4
13
22
33
33
72
184:20
60
2:20
10
17
19
50
50
84
237:20
B-34
Source: U.S. Navy (1988)
NOAA Diving Manual — October 1991
APPENDIX C
TREATMENT
FLOWCHART AND
RECOMPRESSION
TREATMENT
TABLES
Page
Introduction C-l
Diving Accident Treatment Flowchart C-l
Recompression Treatment Tables C-l
«
<
APPENDIX C
TREATMENT FLOWCHART
AND RECOMPRESSION
TREATMENT TABLES
INTRODUCTION
This appendix contains a Diving Accident Treatment
Flowchart and a number of treatment tables used to
recompress divers who have experienced decompres-
sion sickness or arterial gas embolism as a result of
their diving activities. The information in this appen-
dix reflects treatment procedures recommended by the
NOAA Diving Safety Board* and taught in the NOAA
Diving Program. The tables presented here derive from
many sources, including the U.S. Navy, the Royal
Navy, NOAA, foreign organizations, and private compa-
nies. All of the tables in this appendix have been widely
used in the field and have been shown to be safe and
effective. Table C-l lists these recompression tables
and describes their application.
*The material in this appendix derives from C. Gordon Daugherty's
Field Guide for the Diving Medic.
Diving Accident Treatment Flowchart
The flowchart shown in Figure C-l is a decision tree
designed to aid dive supervisors, diving physicians,
Diving Emergency Medical Technicians, chamber
operators, and other health care professionals who must
decide how best to treat stricken divers. Use of the
decision tree requires only that the diver's condition be
observed; a medical diagnosis is not required for treat-
ment to begin. Explanatory material to be used with
the flowchart is shown on the facing page.
Recompression Treatment Tables
The recompression treatment tables recommended
by the NOAA Diving Safety Board are shown on the
following pages. Instructions for the use of these tables
appear with each table and should be followed precisely.
October 1991 — NOAA Diving Manual
C-1
Appendix C
Figure C-1
Diving Accident Treatment
Flowchart
START—
i
1
1. Are
symptoms life-
threatening?
(note E)
2. Stay at 60 fsw
on O2 for 20 min.
14. Was depth
of dive/blow up
deeper than
165 fsw?
-N-i
15. Is helium/oxygen
available?
16. Dive: Go to depth of
relief + 33 fsw, but not
deeper than dive.
Blowup: go to depth of
dive + 1-2 ATA. Use
Lambertsen 7-A or other
sat. table (note D)
17. Goto
230 fsw on air,
then use RN 71
X
3. Is patient
cured?
4. Was
patient treated
within 5
hours of
onset?
6. If pain-only,
relief in 10
min., use
USN 5
7. If symptoms
are serious or
pain relief takes
more than 10
min., use USN 6
5. Give patient a
5 min. air break,
followed by 2
more O2 -air
cycles
18. Compress
on air to
165 fsw for
30 min.
(note A)
19. Is patient cured
or much improved?
9. If
symptoms are
serious, use
USN 6 with
extensions
10. Is
patient cured? N
11. Use
USN 6
12. Is patient
improving? (note G)
13. Use
USN 6 with
extensions
i
20. Follow
USN 6-A
28. Stay at
165 feet
21 . Did deterioration
occur when traveling
to/at 60 fsw
22. Are
symptoms life-
threatening
or major?
rw
23. Compress
to 100 fsw
up to 5 min.
Y-
24. Is there
definite
improvement?
a
27. Complete
USN 6-A (no
deterioration) or
6-A with
extensions (minor
deterioration.)
(note F)
25. Follow CX 30 or
CX 30-A to 60 fsw,
then use USN 6 with
all extensions
26. Return to
165 fsw
29. Was patient
cured or much
improved in
2 nrs. or less?
30. Use USN 4
to 60 fsw, then
USN 6 with
extensions (note H)
31 . May hold
up to 4 hrs.,
then:
32. Is pure
nitrogen
available?
33. Use RN 71-72 to
100 fsw, then nitrox
sat. to surface
(notes B, C)
— OR-
34. Use RN
71-72, table 7-A,
or other air sat
table to surface
(notes B, C)
i
Courtesy C Gordon Daugherty
C-2
NOAA Diving Manual — October 1991
Treatment Flowchart and Recompression Treatment Tables
Flowchart Comments
Flowchart
Step Number
1 - The first step is to decide if the victim's life is potentially in danger as a result of shock, convulsions, or unconsciousness. If the
situation is potentially life threatening, the best immediate decision is to recompress deep. (Note that spinal symptoms, while
considered serious, are not life threatening.)
2,3 - Evaluation after the first oxygen period serves to separate cases of minor bends from more serious cases.
4 - Fresh cases usually respond to standard treatment; delayed cases usually benefit from longer treatment.
5 - This step completes the 60-fsw stop on USN Table 6.
6 - This is the standard use for USN Table 5.
7 - This is the standard use for USN Table 6.
8 - In delayed cases, joint pains do not always clear completely; some mild soreness often remains. If the neurologic exam is nor-
mal, Table 6 is probably adequate.
9 - This is probably the minimum treatment for a delayed case with serious symptoms.
10 - End of the 60-fsw stop on Table 6; this is a good time to estimate the probability of the table's success.
11 - This is the appropriate treatment for a diver who is cured at this point.
12 - The question here concerns the improving diver versus the diver showing no improvement. Where there is no improvement,
there is a question whether more depth will offer benefit, but this cannot be answered in advance. Long-delayed cases have a
poor cure rate with any treatment. Many authorities prefer aggressive use of oxygen at 60 and 30 fsw, even on a daily basis.
Assuming that a saturation treatment can be managed, it is probably advisable to go deeper.
13 - Depending on the original problem and the degree of improvement, the table can be extended at 60 fsw, 30 fsw, or both. A
diver who is improving at 60 fsw usually continues to improve at 30 fsw. All other factors being equal, the more oxygen the
better.
14 - In a diver with a life-threatening symptom, the first decision is how deep to go; going down to 165 fsw allows the standard
tables to be used for treatment; going deeper will probably require the use of a saturation table.
15 - If the depth is deeper than 165 fsw, both heliox and chambers that are rated for the necessary depth are generally available.
16 - For a bends case, it is usually not necessary to go deeper than the dive, and the depth of relief is often shallower. Adding 33
fsw (1 atmosphere) to the depth of relief provides a margin of safety. In a blowup, bubbles may continue to form, even at the
depth of the dive. Therefore, blowup cases should be compressed to the depth of the dive plus 1 or 2 ATA.
17 - If helium/oxygen is not available but the depth of the dive was greater than 165 fsw, the dive was probably a deep air dive with
a short bottom time. Royal Navy Table 71 goes to 230 fsw; it can be followed in its entirety or be followed only to 60 fsw and
then be replaced by USN Table 6.
18 - Cases at this step involve (1) a life-threatening accident at a depth less than 165 fsw (an embolism, for example) or (2) a
serious bends case that shows no improvement after the 60-fsw stop on USN Table 6.
19 - As the treatment approaches the 30-minute bottom time on USN Table 6A, the diver's response to depth must be evaluated.
20 - This is the standard use of USN Table 6A.
21 - Deterioration while traveling to 60 fsw is a common dilemma in embolism cases.
22 - Significant deterioration requires further steps; a minor amount of deterioration can be tolerated because it will resolve as treat-
ment continues.
23 - If deterioration is significant, it may not be necessary to return all the way to 165 fsw.
24 - Evaluate the diver after a short time at 100 fsw.
25 - If 100 fsw is sufficient, one of the Comex tables can be followed for the entire course of treatment or one of these tables can
be followed to 60 fsw, after which USN Table 6 is followed.
26 - If there is no improvement at 100 fsw, the only choice is to return to 165 fsw.
27 - If there is no deterioration, this is the standard use of USN Table 6A. If there is minor deterioration, the extensions should be
used.
28 - At this step, the diver's condition may either be unchanged or be improving after 30 minutes at 165 fsw.
29 - At this step, it will be possible to see either that the diver did not improve adequately after 30 minutes at 165 fsw or that the
diver deteriorated during travel to 60 fsw and it was therefore necessary to return to 165 fsw. A bottom time of 2 hours or less
at 165 fsw will still allow decompression to be conducted with standard tables.
30 - Table 4 will allow safe travel to 60 fsw, where USN Table 6 is substituted (with extensions). Deterioration in the diver's condi-
tion is unlikely, but this table is likely to bend the tender, who should be put on oxygen, along with the diver, at 60 fsw.
31 - If a decision is made not to decompress after 2 hours, it may be possible to hold for as long as 4 hours, depending on the
diver's previous oxygen exposure. Many authorities would commence saturation decompression after 2 hours.
32 - Self-explanatory.
33 - This method has been used successfully in hospital-based treatment chambers, usually with a long hold at 100 fsw. The diver's
nitrogen loading necessitates a long decompression.
34 - An alternative approach is to continue any standard saturation decompression. Although previous oxygen exposure may pre-
vent a hold at 100 fsw on air, very long holds (days) are possible in the range of 60-80 fsw and are limited only by symptoms of
pulmonary oxygen toxicity. Source: c Qordon Daugher(y (igfl3)
October 1 99 1 — NOA A Diving Manual C-3
Appendix C
Table C-1
List of Recompression Tables and Their Applications
Treatment
Table
.,■ m
Type of Table
Application
mamm i ■
USN5
USN6
USN6A
USN7
USN 1A
USN2A
USN 3
USN 4
COMEX CX 30
COMEX CX 30A
ROYAL NAVY
71 OR 72
LAMBERTSEN/
SOLUS OCEAN
SYSTEMS
TABLE 7A
MODIFIED
NOAA NITROX
SATURATION
TREATMENT
TABLE
Oxygen Treatment of Pain-Only (Type I)
Decompression Sickness
Oxygen Treatment of Serious (Type II)
Decompression Sickness
Air and Oxygen Treatment of Arterial
Gas Embolism
Oxygen/Air Treatment of Unresolved or
Worsening Symptoms of Decompression
Sickness or Arterial Gas Embolism
Air Treatment of Pain-Only (Type I)
Decompression Sickness — 100 fsw
(30 msw) Treatment
Air Treatment of Pain-Only (Type I)
Decompression Sickness— 165 fsw
(50 msw)
Air Treatment of Serious (Type II)
Decompression Sickness or Arterial Gas
Embolism
Air Treatment of Serious (Type II)
Decompression Sickness or Arterial Gas
Embolism
Helium - Oxygen or Nitrogen - Oxygen
Treatment of Vestibular or Neurological
(Type II) Decompression Sickness
Air Treatment of Pain-Only (Type I)
Decompression Sickness When Oxygen
Poisoning Has Occurred
Air Treatment of Decompression Sickness
or Arterial Gas Embolism in Cases Where
Decompression Depths Greater Than
165 fsw (50 msw) Are Needed and Mixed
Gas Is Not Available
Air-Oxygen Treatment Table for
Symptoms of Serious Decompression
Sickness That Develop Under Pressure
or for Symptoms Developing at Pressure
(Depths) Greater Than 165 fsw (50 msw)
Nitrox Treatment Table for Serious
Decompression Sickness Cases Where
Treatment Was Delayed
Treatment of pain-only (Type I) decompression sickness in
cases where symptoms are relieved within 10 minutes at
a pressure (depth) of 60 fsw (18.3 msw).
Treatment of serious decompression sickness (Type II) or
of pain-only (Type I) decompression sickness in cases where
symptoms are NOT relieved within 10 minutes at a pressure
(depth) of 60 fsw (18.3 msw).
Treatment of gas embolism. This table is to be used only
in cases where it is not possible to determine whether the
symptoms are caused by arterial gas embolism or by serious
decompression sickness.
This table is to be used only in cases that are life threatening
and that have not resolved after treatment on USN Table 4,
6, or 6A.
Treatment of pain-only (Type I) decompression sickness in
cases where oxygen is unavailable and the pain is relieved
at a pressure (depth) shallower than 66 fsw (20 msw).
Treatment of pain-only (Type I) decompression sickness in
cases where oxygen is unavailable and pain is relieved at
a pressure (depth) deeper than 66 fsw (20 msw).
Treatment of serious (Type II) decompression sickness or
arterial gas embolism in cases where oxygen is unavailable
and symptoms are relieved within 30 minutes at a pressure
(depth) of 165 fsw (50 msw).
Treatment of symptoms that have worsened during the first
20-minute oxygen breathing period at a pressure (depth)
of 60 fsw (18.3 msw) on Table 6, or for treatment in cases
where symptoms are not relieved within 30 minutes at a
pressure (depth) of 165 fsw (50 msw) when Table 3 is used.
Treatment of vestibular or serious (Type II) decompression
sickness that occurs either after a normal or a shortened
decompression. To be used in cases where the patient shows
deterioration at a pressure (depth) of 60 fsw (18.3 msw) on
USN Table 6A but shows good improvement when brought
to a pressure (depth) of 100 fsw (30 msw).
Treatment of pain-only (Type I) decompression sickness in
cases where the stricken diver shows signs of oxygen
poisoning. To be used in cases where the patient shows
deterioration at a pressure (depth) of 60 fsw (18.3 msw)
on USN Table 6A but shows good improvement when brought
to a pressure (depth) of 100 fsw (30 msw).
Treatment of decompression sickness or arterial gas
embolism to be used in cases where patient remains in poor
condition after 2 hours at a pressure (depth) of 165 fsw
(50 msw) and slow decompression is desired or in cases
where a pressure (depth) greater than 165 fsw (50 msw)
is needed and mixed gas is not available.
Use in cases where patient develops symptoms while under
pressure or where decompression sickness develops at
pressures (depths) greater than 165 fsw (50 msw) or where
extended recompression is necessary because symptoms
have failed to resolve.
Use in hospital chambers in severe cases of decompression
sickness with delayed access to treatment.
C-4
NOAA Diving Manual — October 1991
Treatment Flowchart and Recompression Treatment Tables
U.S. Navy Treatment Table 5
Descent Rate = 25 Ft./Min.
Ascent Rate = 1 Ft./Min.
Q.
Q
OXYGEN TREATMENT OF TYPE I DECOMPRESSION SICKNESS
1. Treatment of Type I decompression sickness when
symptoms are relieved within 10 minutes at 60 feet
and a complete neurological exam is normal.
2. Descent rate — 25 ft/min.
3. Ascent rate — 1 ft/min. Do not compensate for slower
ascent rates. Compensate for faster rates by halting
the ascent.
4. Time at 60 feet begins on arrival at 60 feet.
5. If oxygen breathing must be interrupted, allow 15
minutes after the reaction has entirely subsided
and resume schedule at point of interruption.
6. If oxygen breathing must be interrupted at 60 feet,
switch to Table 6 upon arrival at the 30 foot stop.
7. Tender breathes air throughout unless he/she has
had a hyperbaric exposure within the past 12 hours,
in which case he/she breathes oxygen at 30 feet.
Total
Depth
Time
Breathing
Elapsed Time
(feet)
(minutes)
Media
(hrs:min.)
60
20
Oxygen
0:20
60
5
Air
0:25
60
20
Oxygen
0:45
60 to 30
30
Oxygen
1:15
30
5
Air
1:20
30
20
Oxygen
1:40
30
5
Air
1:45
30 toO
30
Oxygen
2:15
Source: US Navy (1985)
October 1991 — NOAA Diving Manual
C-5
Appendix C
U.S. Navy Treatment Table 6
i
rr
50
40-
Q.
a
30
20
10
Descent Rate = 25 Ft./Min.
Ascent Rate = 1 Ft./Min. —
Total Elapsed Time: 285 Minutes
(Not Including
Descent Time)
2.4 20 5 20 5 20 5 30 15
Time (minutes)
60
15
OXYGEN TREATMENT OF TYPE II DECOMPRESSION SICKNESS
6.
Treatment of Type II or Type I decompression sick-
ness when symptoms are not relieved within 10 min-
utes at 60 feet.
Descent rate — 25 ft/min.
Ascent rate — 1 ft/min. Do not compensate for slower
ascent rates. Compensate for faster rates by halting
the ascent.
Time at 60 feet begins on arrival at 60 feet.
If oxygen breathing must be interrupted, allow 15
minutes after the reaction has entirely subsided
and resume schedule at point of interruption.
Tender breathes air throughout unless he/she has
had a hyperbaric exposure within the past 12 hours,
in which case he/she breathes oxygen at 30 feet.
Table 6 can be lengthened up to 2 additional 25
minute oxygen breathing periods at 60 feet (20
minutes on oxygen and 5 minutes on air) or up to 2
additional 75 minute oxygen breathing periods at
30 feet (15 minutes on air and 60 minutes on oxy-
gen), or both. If Table 6 is extended only once at
either 60 or 30 feet, the tender breathes oxygen
during the ascent from 30 feet to the surface. If
more than one extension is done, the tender begins
oxygen breathing for the last hour at 30 feet during
ascent to the surface.
Total
Depth
Time
Breathing
Elapsed Time
(feet)
(minutes)
Media
(hrsrmin.)
60
20
Oxygen
0:20
60
5
Air
0:25
60
20
Oxygen
0:45
60
5
Air
0:50
60
20
Oxygen
1:10
60
5
Air
1:15
60 to 30
30
Oxygen
1:45
30
15
Air
2:00
30
60
Oxygen
3:00
30
15
Air
3:15
30
60
Oxygen
4:15
30 toO
30
Oxygen
4:45
Source: US Navy (1985)
(
C-6
NOAA Diving Manual — October 1991
Treatment Flowchart and Recompression Treatment Tables
U.S. Navy Treatment Table 6A
Descent Rate = As Fast As Possible
Ascent Rate = 26 Ft./Min.
Total Elapsed Time: 319 Minutes
a.
a>
o
Time (minutes)
INITIAL AIR AND OXYGEN TREATMENT OF ARTERIAL GAS EMBOLISM
1. Treatment of arterial gas embolism where com-
plete relief obtained within 30 min. at 165 feet.
Use also when unable to determine whether symp-
toms are caused by gas embolism or severe decom-
pression sickness.
2. Descent rate — as fast as possible.
3. Ascent rate — 1 ft/min. Do not compensate for
slower ascent rates. Compensate for faster ascent
rates by halting the ascent.
4. Time at 165 feet — includes time from the surface.
5. If oxygen breathing must be interrupted, allow 15
minutes after the reaction has entirely subsided
and resume schedule at point of interruption.
6. Tender breathes oxygen during ascent from 30 feet
to the surface unless he/she has had a hyperbaric
exposure within the past 12 hours, in which case
he/she breathes oxygen at 30 feet.
7. Table 6A can be lengthened up to 2 additional 25
minute oxygen breathing periods at 60 feet (20
minutes on oxygen and 5 minutes on air) or up to 2
additional 75 minute oxygen breathing periods at
30 feet (15 minutes on air and 60 minutes on oxy-
gen), or both. If Table 6A is extended either at 60 or
30 feet, the tender breathes oxygen during the last
half at 30 feet and during ascent to the surface.
If complete relief is not obtained within 30 min. at
165 feet, switch to Table 4. Consult with a hyperbaric
physician before switching if possible.
Total
Depth
Time
Breathing
Elapsed Time
(feet)
(minutes)
Media
(hrs:min.)
165
30
Air
0:30
165 to 60
4
Air
0:34
60
20
Oxygen
0:54
60
5
Air
0:59
60
20
Oxygen
1:19
60
5
Air
1:29
60
20
Oxygen
1:44
60
5
Air
1:49
60 to 30
30
Oxygen
2:19
30
15
Air
2:34
30
60
Oxygen
3:34
30
15
Air
3:49
30
60
Oxygen
4:49
30 toO
30
Oxygen
5:19
Source: US Navy (1985)
October 1991 — NO A A Diving Manual
C-7
Appendix C
U.S. Navy Treatment Table 7
12 hrs minimum
No maximum limit
3 ft/hr — 2 ft every 40 min
4 hrs stop
ascent
1 ft/min
1
24.00
16.00
Time (hours)
30.00 j 36.00
32.00
OXYGEN/AIR TREATMENT OF UNRESOLVED OR WORSENING SYMPTOMS OF
DECOMPRESSION SICKNESS OR ARTERIAL GAS EMBOLISM
1. Used for treatment of unresolved life threatening
symptoms after initial treatment on Table 6, 6A, or 4.
2. Use only under the direction of or in consultation
with a hyperbaric physician.
3. Table begins upon arrival at 60 feet. Arrival at 60
feet accomplished by initial treatment on Table 6,
6A, or 4. If initial treatment has progressed to a
depth shallower than 60 feet, compress to 60 feet at
25 ft/min to begin Table 7.
4. Maximum duration at 60 feet unlimited. Remain
at 60 feet a minimum of 12 hours unless overriding
circumstances dictate earlier decompression.
5. Patient begins oxygen breathing periods at 60 feet.
Tender need breathe only chamber atmosphere
throughout. If oxygen breathing is interrupted, no
lengthening of the table is required.
6. Minimum chamber O2 concentration 19%. Maxi-
mum CO2 concentration 1.5% SEV (12 mmHg).
Maximum chamber internal temperature 85 °F.
7. Decompression starts with a 2 foot upward excur-
sion from 60 to 58 feet. Decompress with stops
every 2 feet for times shown in profile below. Ascent
time between stops approximately 30 sec. Stop time
begins with ascent from deeper to next shallower
step. Stop at 4 feet for 4 hours and then ascend to
the surface at 1 ft/min.
8. Ensure chamber life support requirements can be
met before committing to a Treatment Table 7.
Source: US Navy (1985)
(
C-8
NOAA Diving Manual — October 1991
Treatment Flowchart and Recompression Treatment Tables
U.S. Navy Treatment Table 1A
Q.
0)
Q
100
Descent Rate = 25 Ft./Min.
Ascent Rate = 1 Min. Between Stops
Total Elapsed Time: 380 Minutes
AIR TREATMENT OF TYPE I DECOMPRESSION SICKNESS— 100-FOOT TREATMENT
1. Treatment of Type I decompression sickness when
oxygen unavailable and pain is relieved at a depth
less than 66 feet.
2. Descent rate — 25 ft/min.
3. Ascent rate — l minute between stops.
4. Time at 100 feet — includes time from the surface.
5. If the piping configuration of the chamber does not
allow it to return to atmospheric pressure from the
10 foot stop in the l minute specified, disregard
the additional time required.
Total
Depth
(feet)
Time
(minutes)
Breathing
Media
Elapsed Time
(hrs:min.)
100
30
Air
0:30
80
12
Air
0:43
60
30
Air
1:14
50
30
Air
1:45
40
30
Air
2:16
30
60
Air
3:17
20
60
Air
4:18
10
120
Air
6:19
°
1
Air
6:20
Source: US Navy (1985)
October 1991 — NOAA Diving Manual
C-9
Appendix C
U.S. Navy Treatment Table 2A
Descent Rate = 25 Ft./Min.
Ascent Rate = 1 Min. Between Stops
Total Elapsed Time: 659 Minutes
Q.
0)
Q
Time (minutes)
AIR TREATMENT OF TYPE 1 DECOMPRESSION SICKNESS— 165-FOOT TREATMENT
1. Treatment of Type I decompression sickness when
oxygen unavailable and pain is relieved at a depth
greater than 66 feet.
2. Descent rate — 25 ft/min.
3. Ascent rate — 1 minute between stops.
4. Time at 165 feet — includes time from the surface.
Total
Depth
Time
Breathing
Elapsed Time
(feet)
(minutes)
Media
(hrs:min.)
165
30
Air
0:30
140
12
Air
0:43
120
12
Air
0:56
100
12
Air
1:09
80
12
Air
1:22
60
30
Air
1:53
50
30
Air
2:24
40
30
Air
2:55
30
120
Air
4:56
20
120
Air
6:57
10
240
Air
10:58
0
1
Air
10:59
Source: US Navy (1985)
C-10
NOAA Diving Manual — October 1991
Treatment Flowchart and Recompression Treatment Tables
U.S. Navy Treatment Table 3
Descent Rate = As Fast As Possible
Ascent Rate = 1 Min. Between Stops
Total Elapsed Time: 18 Hours 59 Minutes
a
a>
a
Time (minutes)
AIR TREATMENT OF TYPE II DECOMPRESSION SICKNESS OR ARTERIAL GAS EMBOLISM
1. Treatment of Type II symptoms of arterial gas embo-
lism when oxygen unavailable and symptoms are
relieved within 30 minutes at 165 feet.
2. Descent rate — as rapidly as possible.
3. Ascent rate — 1 minute between stops.
4. Time at 165 feet — include time from the surface.
Total
Depth
Time
Breathing
Elapsed Time
(feet)
(minutes)
Media
(hrs:min.)
165
30 min.
Air
0:30
140
12 min.
Air
0:43
120
12 min.
Air
0:56
100
12 min.
Air
1:09
80
12 min.
Air
1:22
60
30 min.
Air
1:53
50
30 min.
Air
2:24
40
30 min.
Air
2:55
30
720 min.
Air
14:56
20
120 min.
Air
16:57
10
120 min.
Air
18:58
0
1 min.
Air
18:59
Source: US Navy (1985)
October 1991 — NOAA Diving Manual
C-11
Appendix C
U.S. Navy Treatment Table 4
i
a.
Q
Descent Rate = As Fast As Possible
Ascent Rate = 1 Min. Between Stops
Total Elapsed Time: 36 hours 41 minutes
(1/2 hour at 165 FSW) to
38 hours 11 minutes
(2 hours 165 FSW)
Patient begins oxygen breathing at 60 feet. Both patient and
tenders breathe oxygen beginning 2 hours before leaving 30 feet.
i
Time (hours)
AIR OR AIR AND OXYGEN TREATMENT OF TYPE II DECOMPRESSION SICKNESS
OR ARTERIAL GAS EMBOLISM
1. Treatment of worsening symptoms during the first
20-minute oxygen breathing period at 60 feet on
Table 6, or when symptoms are not relieved within
30 minutes at 165 feet using air treatment Table 3
or 6A.
Descent rate — as rapidly as possible.
Ascent rate — 1 minute between stops.
Time 1 65 feet — includes time from the surface.
If only air available, decompress on air. If oxygen
available, patient begins oxygen breathing upon
arrival at 60 feet with appropriate air breaks.
Both tender and patient breathe oxygen beginning
2 hours before leaving 30 feet.
Ensure life support considerations can be met before
committing to a Table 4. Internal chamber temper-
ature should be below 85 °F.
If oxygen breathing is interrupted, no compensa-
tory lengthening of the table is required.
If switching from Treatment Table 6A at 165 feet,
stay the full 2 hours at 165 feet before decompressing.
6.
7.
Total
Depth
Time
Breathing
Elapsed Time
(feet)
(minutes)
Media
(hrs:min.)
165
1/2 to 2 hr.
Air
2:00
140
Vi hr.
Air
2:31
120
1/a hr.
Air
3:02
100
1/2 hr.
Air
3:33
80
1/2 hr.
Air
4:04
60
6hr.
Air or
10:05
50
6hr.
Oxygen/Air
16:06
40
6hr.
22:07
30
12 hr.
34:08
20
2hr.
36:09
10
2hr.
38:10
0
1 min.
38:11
«
C-12
NOAA Diving Manual — October 1991
Treatment Flowchart and Recompression Treatment Tables
COMEX Treatment Table CX 30
1. Use — treatment of vestibular and general neuro-
logical decompression sickness occurring after either
a normal or shortened decompression.
2. Descent rate — as quickly as possible (2 or 3 minutes).
3. Ascent rate — between 100 and 80 fsw — 1.5 min/ft.
— between 80 and 60 fsw — 1.5 min/ft.
4. Time at 100 fsw does not include compression time.
Total
Elapsed
Depth
Time
Breathing
Time
(fsw)
(minutes)
Medium
(hrsrmin)
100
40
50-50**
0:43
100-80
5
Air
25
50-50
1:13
80
5
Air
1:18
80
25
50-50
1:43
80-60
5
Air
25
50-50
2:13
Helium/Oxygen or Nitrogen/Oxygen
Source: C. Gordon Daugherty (1983)
COMEX Treatment Table CX 30A
1. Use — treatment of musculoskeletal decompression
sickness when signs of oxygen poisoning are present.
2. Descent rate — as quickly as possible (2 to 3 minutes),
using air.
3. Ascent rate — continuous ascent at the rates shown
below.
4. Time at 100 fsw does not include compression time.
Royal Navy Treatment Tables
71 and 72
1. Maximum pressures may be less than the above
depths.
2. Descent rate — 33 ft/min.
3. Ascent by continuous bleed. If rate is slowed, it
must not be compensated for by subsequent accelera-
tion. The ascent should be halted if rate is exceeded
or if the rate cannot be controlled accurately during
flushing of chamber.
4. Oxygen may be administered periodically in selected
cases, as advised.
5. Time at maximum pressure does not include com-
pression time.
Rate of
Depth
Stops/
Ascent
(fsw)
Ascent
(ft/hr)
Royal Navy Table 71
230
30 min.
230-208
7 min.
198
208-168
2hrs.
20
168-129
4 hrs.
10
129-96
5 hrs.
6
96-66
6 hrs.
5
66-33
10 hrs.
3
33-0
20 hrs.
Royal Navy Table 72
1.6
165
2 hrs.**
164-129
3 hrs. 40 min.
10
(then as
Table 71)
This period can be reduced if symptoms clear earlier.
Source: C Gordon Daugherty (1983)
Total
Elapsed
Depth
Time
Breathing
Time
(fsw)
(minutes)
Medium
(hrsrmin)
100
60
Air
1:03
100-80
6
Air
1:09
80-70
60
Air
2:09
70-60
66
Air
3:15
Source: C. Gordon Daugherty (1983)
October 1991 — NOAA Diving Manual
Lambertsen/Solus Ocean Systems
Treatment Table 7A
1. Use — for symptoms under pressure, for recompres-
sion deeper than 165 fsw, or where extended decom-
pression is necessary.
2. Descent rate — as fast as possible, at least 25 fsw per
minute.
3. Ascent rate — varies according to treatment depth;
refer to schedule. Do not compensate for slower
rates; for faster rates, halt the ascent.
C-13
Appendix C
4. If oxygen breathing must be interrupted, allow
30 minutes after reaction subsides and resume
schedule at point of interruption.
5. Patient is held at treatment depth for 30 minutes
as follows:
a) On air — limit depth to 200 fsw, stay 30 minutes,
go to 165 fsw in 1 minute, and then follow table.
b) On He/02 — g° to depth of relief plus 33 fsw but
not deeper than the dive. Hold 30 minutes,
then go to 165 fsw at 15 fsw per hour (4 min.
per foot), and then follow table.
Modified NOAA Nitrox Saturation
Treatment Table
1. Total decompression time — 55 hrs. 30 min.
2. Decompression time between stops = 10 minutes.
Depth
Ascent
Chamber
Breathing
Time
(fsw)
Rate
Atmosphere
Gas
(hrs:min)
Final treat-
Varies
Air or
Chamber
30 min.
ment depth
He/02
atmosphere,
+ ascent
(See 5,
(See 5,
according
to 165 ft.
above)
above)
to depth
165 to 150
15 ft/hr.
(4 min/(ft.)
Air
Air
1:00
150 to 100
10 ft/hr.
(6 min/ft.)
Air
Air
5:00
100 to 70
6 ft/hr.
(10 min/ft.)
Air
Residual
symptoms
and 50-50
nitrox
available; 5
cycles of 30
min. nitrox,
30 min. air.
Otherwise,
5:00
breathe air.
70 to 60
4 ft/hr.
(15 min/ft.)
Air
Air
2:30
60 to 40
4 ft/hr.
(15 min/ft.)
Air
5 cycles of
30 min. 02,
30 min. air
5:00
40 to 30
4 ft/hr.
(15 min/ft.)
Air
Air
2:30
30 to 20
2 ft/hr.
Air
5 cycles of
5:00
(30 min/ft.)
30 min. 02,
30 min. air
(both patient
and tender)
20 to 10
2 ft/hr.
(30 min/ft.)
Air
Air
5:00
10 to 2
2 ft/hr.
(30 min/ft.)
Air
4 cycles of
30 min. 02,
30 min. air
4:00
2 toO
2 ft/hr.
(30 min/ft.)
Air
Oxygen
1:00
Depth
Time at Stop
Breathing
(fsw)
(hrs:min)
Mixture
100
30 min. to 90 ft.
Air
90
00:50
Air
85
01:20
Air
80
01:30
Air
75
01:40
Air
70
01:50
Air
65
02:00
Air
60
06:00
Air
55
02:20
Air
50
02:40
Air
45
02:40
Air
40
00:10
Oxygen
40
02:30
Air
35
02:30
Air
30
12:00
Air
25
02:00
Oxygen/Air**
20
02:20
Air
15
02:40
Oxygen/Air**
10
02:30
Air
5
02:40
Air
(
Oxygen delivered in 4 recurrent cycles — 25 min. 02/5 min. air.
Source: C. Gordon Daugherty (1983)
Total Time 165 Feet to Surface = 36:00
Source: C. Gordon Daugherty (1983)
C-14
i
NOAA Diving Manual — October 1991
Page
APPENDIX D NOAA Nitrox I (68% N2, 32% O^ No-Decompression Limits and
NOAA NITROX I Repetitive Group Designation Table for No-Decompression Dives D-l
DIVING AND NOAA Nitrox I (68% N2, 32% 02) Decompression Table D-2
DECOMPRESSION Residual Nitrogen Times for NOAA Nitrox I (68% N2, 32% O^ Dives D-5
TABLES Residual Nitrogen Timetable for Repetitive NOAA Nitrox I
(68% N2, 32% 02) Dives D-5
<
<
APPENDIX D
NOAA NITROX I
DIVING AND
DECOMPRESSION
TABLES
WARNING
NOAA Nitrox I Tables May Be Used Only With
Open-Circuit Breathing Equipment and When
Breathing a Mixture of 68 Percent Nitrogen and
32 Percent Oxygen
NOAA Nitrox I is a standard breathing gas mixture
of 32% oxygen (±1%); the balance of the gas (68%)
is nitrogen. Use of this gas mixture significantly in-
creases the amount of time a diver can spend at depth
without decompression, and it may be used in routine
diving operations when it is advantageous. All oxygen
partial pressure-time combinations for use with this
mixture, except where noted, are within the normal
oxygen exposure limits given in Table 15-1.
The following limitations are placed on the use of
NOAA Nitrox I:
• All gases used in Nitrox I diving must be of breath-
ing quality.
• NOAA Nitrox I gas may be used only in standard
open-circuit breathing equipment.
• High-pressure storage cylinders, scuba tanks, regu-
lators, and all high-pressure gas transfer equipment
that is used with pure oxygen or with nitrox mixtures
that contain more than 40 percent oxygen must be
cleaned and maintained for oxygen service.
• The normal depth limit for use of this mixture shall
be 130 feet of sea water for dives that do not require
decompression.
• All NOAA divers who use NOAA Nitrox I must be
trained and certified in its use by the NOAA Diving
Coordinator.
Table D-1 NOAA Nitrox I (68% N2, 32% 02) No-Decompression Limits
and Repetitive Group Designation Table for No-Decompression Dives
No-decom-
pression
Depth,
limits,
fsw
min
A
B
C
D
E
F
G
H
1
J
K
L
M
N O
15
60
120
210
300
20
35
70
110
160
225
350
25
25
50
75
100
135
180
240
325
30
20
35
55
75
100
125
160
195
245
315
40
15
30
45
60
75
95
120
145
170
205
250
310
45
310
5
15
25
40
50
60
80
100
120
140
160
190
220
270 310
50
200
5
15
25
30
40
50
70
80
100
110
130
150
170
200
60
100
10
15
25
30
40
50
60
70
80
90
100
70
60
10
15
20
25
30
40
50
55
60
80
50
5
10
15
20
30
35
40
45
50
90
40
5
10
15
20
25
30
35
40
100
30
5
10
12
15
20
25
30
110
25
5
7
10
15
20
22
25
120
25
5
7
10
15
20
22
25
130
20
5
10
13
15
20
140
15
5
10
12
15
150
10
5
8
10
October 1991 — NOAA Diving Manual
D-1
Appendix D
Table D-2 NOAA Nitrox I (68% N2, 32% 02) Decompression Table
Bottom
Time
Decompression Stops, fsw
Total
Repeti-
Depth,
Time,
First Stop,
Ascent,
tive
fsw
min
min:sec
50 40 30 20
10
min:sec
Group
200
0:40
0
0:50
*
210
0:40
2
2:50
N
230
0:40
7
7:50
N
50
250
0:40
11
11:50
O
270
0:40
15
15:50
O
300
0:40
19
19:50
Z
360
0:40
23
23:50
* *
100
0
1:00
*
110
0:50
3
4:00
L
120
0:50
5
6:00
M
60
140
0:50
10
11:00
M
160
0:50
21
22:00
N
180
0:50
29
30:00
O
200
0:50
35
36:00
O
220
0:50
40
41:00
z
240
0:50
47
48:00
z
60
0
1:10
*
70
0:60
2
3:10
K
80
0:60
7
8:10
L
100
0:60
14
15:10
M
120
0:60
26
27:10
N
70
140
0:60
39
40:10
O
160
0:60
48
49:10
Z
180
0:60
56
57:10
z
200
0:50
1
69
71:10
z
240
0:50
2
79
82:10
* *
50
0
1:20
*
60
1:10
8
9:20
K
70
1:10
14
15:20
L
80
1:10
18
19:20
M
90
1:10
23
24:20
N
80
100
1:10
33
34:20
N
110
1:00
2
41
44:20
O
120
1:00
4
47
52:20
O
130
1:00
6
52
59:20
O
140
1:00
8
56
65:20
Z
150
1:00
9
61
71:20
z
160
1:00
13
72
86:20
z
170
1:00
19
79
99:20
z
See No Decompression Table for repetitive groups
Repetitive dives may not follow exceptional exposure dives
Oxygen partial pressure exceptional exposure
D-2
NOAA Diving Manual — October 1991
NITROX I Tables
Table D-2 NOAA Nitrox I (68% N2, 32% 02) Decompression Table— Continued
Bottom
Time
Decompression Stops, fsw
Total
Repeti-
Depth,
Time,
First Stop,
Ascent,
tive
fsw
min
min:sec
50 40 30
20
10
min:sec
Group
40
0
1:30
*
50
1:20
10
11:30
K
60
1:20
17
18:30
L
70
1:20
23
24:30
M
80
1:10
2
31
34:30
N
90
90
1:10
7
39
47:30
N
100
1:10
11
46
58:30
O
110
1:10
13
53
67:30
O
120
1:10
17
56
74:30
Z
130
1:10
19
63
83:30
z
140
1:10
26
69
96:30
z
150
1:10
32
77
110:30
z
30
0
1:40
*
40
1:30
7
8:40
J
50
1:30
18
19:40
L
60
1:30
25
26:40
M
100
70
80
1:20
1:20
7
13
30
40
38:40
54:40
N
N
90
1:20
18
48
67:40
O
100
1:20
21
54
76:40
z
110
1:20
24
61
86:40
z
120
1:20
32
68
101:40
z
130
1:10
5
36
74
116:40
z
25
0
1:50
*
30
1:40
3
4:50
I
40
1:40
15
16:50
K
50
1:30
2
24
27:50
L
60
1:30
9
28
38:50
N
110
70
80
1:30
1:30
17
23
39
48
57:50
72:50
O
0
90
1:20
3
23
57
84:50
z
100
1:20
7
23
66
97:50
z
110
1:20
10
34
72
117:50
z
120
1:20
12
41
78
132:50
z
25
0
2:00
*
30
1:50
3
5:00
I
40
1:50
15
17:00
K
50
1:40
2
24
28:00
L
120
60
70
1:40
1:40
9
17
28
39
39:00
58:00
N
O
80
1:40
23
48
73:00
O
90
1:30
3
23
57
85:00
z
100
1:30
7
23
66
98:00
z
110
1:30
10
34
72
118:00
z
120
1:30
12
41
78
133:00
z
* See No Decompression Table for repetitive groups
* * Repetitive dives may not follow exceptional exposure dives
*** Oxygen partial pressure exceptional exposure
October 1991 — NOAA Diving Manual
D-3
Table D-2 NOAA Nitrox I (68% N2, 32% 02) Decompression Table— Continued
Appendix D
Depth,
fsw
Bottom
Time,
min
Time
Decompression Stops, fsw
Total
Repeti-
First Stop,
Ascent,
tive
min:sec
50
40
30
20
10
min:sec
Group
0
2:10
*
2:00
3
5:10
H
2:00
7
9:10
J
1:50
2
21
25:10
L
1:50
8
26
36:10
M
1:50
18
36
56:10
N
1:40
1
23
48
74:10
O
1:40
7
23
57
89:10
Z
1:40
12
30
64
108:10
z
1:40
15
37
72
126:10
z
130
20
25
30
40
50
60
70
80
90
100
140
15
20
2:10
25
2:10
30
2:10
40
2:00
50
2:00
60
1:50
70
1:50
0
2:20
*
2
4:20
H
6
8:20
I
14
16:20
J
5
25
32:20
L
15
31
48:20
N
2
22
45
71:20
O
9
23
55
89:20
O
150
10
15
2:20
20
2:20
25
2:20
30
2:10
40
2:10
50
2:00
60
2:00
0
2:30
*
1
3:30
F
4
6:30
H
10
12:30
J
3
18
23:30
hh
10
25
37:30
N
3 21
37
63:30
O
9 23
52
86:30
Z
See No Decompression Table for repetitive groups
Repetitive dives may not follow exceptional exposure dives
Oxygen partial pressure exceptional exposure
D-4
NOAA Diving Manual — October 1991
NITROX I Tables
Table D-3 Residual Nitrogen Times for NOAA Nitrox I (68% N2, 32% 02) Dives
Repetitive
Repetitive Group Designation
Dive
Depth, fsw
Z
O
N
M
L
K
J
I
H
G
F
E
D
C
B
A
50
257
241
213
187
161
138
116
101
87
73
61
49
37
25
17
7
60
169
160
142
124
111
99
87
76
66
56
47
38
29
21
13
6
70
122
117
107
97
88
79
70
61
52
44
36
30
24
17
11
5
80
100
96
87
80
72
64
57
50
43
37
31
26
20
15
9
4
90
84
80
73
68
61
54
48
43
38
32
28
23
18
13
8
4
100
73
70
64
58
53
47
43
38
33
29
24
20
16
11
7
3
110
64
62
57
52
48
43
38
34
30
26
22
18
14
10
7
3
120
64
62
57
52
48
43
38
34
30
26
22
18
14
10
7
3
130
57
55
51
47
42
38
34
31
27
24
20
16
13
10
6
3
140
52
50
46
43
39
35
32
28
25
21
18
15
12
9
6
3
150
46
44
40
38
35
31
28
25
22
19
16
13
11
8
6
3
Values are minutes.
Table D-4 Residual Nitrogen Timetable for Repetitive NOAA Nitrox I (68% N2, 32% 02) Dives*
A
0:10
12:00 *
B
0:10
2:10
2:11
12:00 *
C
0:10
1:39
1:40
2:49
2:50
12:00 *
C**
D
0:10
1:10
2:39
5:49
_^e
*
1:09
2:38
5:48
12:00 *
W*
E
0:10
0:55
1:58
3:23
6:33
.**
0:54
1:57
3:22
6:32
12:00 *
«***
F
0:10
0:46
1:30
2:29
3:58
7:06
•'
0:45
1:29
2:28
3:57
7:05
12:00 *
.
G
0:10
0:41
1:16
2:00
2:59
4:26
7:36
^'
0:40
1:15
1:59
2:58
4:25
7:35
12:00 *
,#
H
0:10
0:37
1:07
1:42
2:24
3:21
4:50
8:00
0:36
1:06
1:41
2:23
3:20
4:49
7:59
12:00 *
I
0:10
0:34
1:00
1:30
2:03
2:45
3:44
5:13
8:22
***
0:33
0:59
1:29
2:02
2:44
3:43
5:12
8:21
12:00 *
*
#
J
0:10
0:32
0:55
1:20
1:48
2:21
3:05
4:03
5:41
8:41
^©v
0:31
0:54
1:19
1:47
2:20
3:04
4:02
5:40
8:40
12:00 *
K
0:10
0:29
0:50
1:12
1:36
2:04
2:39
3:22
4:20
5:49
8:59
0:28
0:49
1:11
1:35
2:03
2:38
3:21
4:19
5:48
8:58
12:00 *
L
0:10
0:27
0:46
1:05
1:26
1:50
2:20
2:54
3:37
4:36
6:03
9:13
0:26
0:45
1:04
1:25
1:49
2:19
2:53
3:36
4:35
6:02
9:12
12:00 *
M
0:10
0:26
0:43
1:00
1:19
1:40
2:06
2:35
3:09
3:53
4:50
6:19
9:29
0:25
0:42
0:59
1:18
1:39
2:05
2:34
3:08
3:52
4:49
6:18
9:28
12:00 *
N
0:10
0:25
0:40
0:55
1:12
1:31
1:54
2:19
2:48
3:23
4:05
5:04
6:33
9:44
0:24
0:39
0:54
1:11
1:30
1:53
2:18
2:47
3:22
4:04
5:03
6:32
9:43
12:00 *
O
0:10
0:24
0:37
0:52
1:08
1:25
1:44
2:05
2:30
3:00
3:34
4:18
5:17
6:45
9:55
0:23
0:36
0:51
1:07
1:24
1:43
2:04
2:29
2:59
3:33
4:17
5:16
6:44
9:54
12:00 *
0:10
0:23
0:35
0:49
1:03
1:19
1:37
1:56
2:18
2:43
3:11
3:46
4:30
5:28
6:57
10:06
New
0:22
0:34
0:48
1:02
1:18
1:36
1:55
2:17
2:42
3:10
3:45
4:29
5:27
6:56
10:05
12:00 *
Group Designation
Z
O
N
M
L
K
J
I
H
G
F
E
D
C
B
A
*Dives after surface intervals of more than 12 hours are not repetitive dives. Use actual bottom times in the NOAA
Nitrox I (68% N2,32% 02) Decompression Table to compute decompression for such dives.
October 1991 — NOAA Diving Manual
D-5
4
<
<
4
i
<
APPENDIX E
GLOSSARY
Abducens Nerve
The sixth cranial nerve; controls
the external rectus muscles of
the eye.
Amphibious
Camera
ACFM
An abbreviation for actual cubic
Acidosis
feet per minute.
Acid poisoning caused by the
abnormal production and accum-
ulation of acids in the body.
Analgesic
Angiosperm
Acoustic Grid
A method for determining the
position of an object relative to a
fixed network of transponders.
Anorexia
Anoxia
Acoustic
(Auditory) Nerve
The eighth cranial nerve; controls
hearing.
Antigen
Acoustic Relief
A discontinuity, such as a wreck
or rock outcrop on the seafloor,
that alters the reflection of an
acoustic signal in a way that
makes the object distinguishable
from the surrounding area.
Adsorption A type of adhesion that occurs at
the surface of a solid or a liquid
that is in contact with another
medium; an example of adsorp-
tion occurs when dirt adsorbs or
adheres to the hands.
Alidade An indicator or sighting instru-
ment used to determine direction
and range for topographic sur-
veying and mapping.
Alimentary The muscular-membranous tube,
Canal about 30 feet (9.1 meters) in
length, that extends in animals
and humans from the mouth to
the anus.
Alternobaric Dizziness caused by asymmetric
Vertigo clearing of the middle ear during
ascent or descent.
Alveolus A small membranous sac in the
lungs in which gas exchange takes
place.
Ama Divers Female pearl divers of Japan
known for their ability to make
deep and long breath-hold dives
and to tolerate cold water.
Amniotic Fluid The serous fluid within the sac
(amnion) that encloses a fetus.
October 1991 — NOAA Diving Manual
Aortic Stenosis
Aperture
Aphakia
Aphasia
Apnea
Apoplexy
Arthralgia
ASA Film Speed
(ASA ISO)
A camera that needs no special
housing for underwater photog-
raphy because all ports, lids, and
control rods on the camera are
O-ring sealed.
A medication that reduces or
eliminates pain.
A plant whose seeds are enclosed
in an ovary; a flowering plant.
The absence of appetite.
The absence of oxygen (see
Hypoxia).
Any bacterium or substance which,
when injected into an organism,
is capable of causing the forma-
tion of an antibody.
Constriction or narrowing of the
aortic artery.
In photography, the opening that
regulates the amount of light
passing through a camera lens
(see f Stop).
The absence of a lens in the eye.
Partial or complete loss of the
ability to express ideas in speech
or writing.
A brief cessation of breathing.
The name given to the complex
of symptoms and signs caused by
hemorrhage or blockage of the
brain or spinal cord. This term is
also applied to the signs and
symptoms resulting from burst-
ing of a vessel in the lungs,
liver, etc. Apoplexy can cause
both physical and mental signs
and symptoms and can be fatal.
Pain that occurs in the joints
during compression or decom-
pression.
In photography, a number refer-
ring to a film's sensitivity to light.
This number can be used, along
with the readout from an exposure
meter, to determine camera set-
tings for aperture and shutter
speed.
E-1
Appendix E
Aseptic Bone See Osteonecrosis.
Necrosis
Asphyxia Anoxia caused by the cessation
of effective gas exchange in the
lung.
Aspirator A device used to remove liquids
or gases from a space by suction.
Atherosclerosis Thickening of the outer layers
of an artery and degeneration of
the artery's elastic layer.
Atmospheric A pressure-resistant one-man
Diving diving system that has articulated
System arms and sometimes legs and that
is both equipped with life support
capability and designed to operate
at an internal pressure of one
atmosphere.
An instrument used to measure
hearing thresholds for pure tones
at normal frequencies.
A control on a camera that presets
an exposure for aperture (f stop)
and controls the light reaching
the film via a shutter.
A physiologic response that may
occur in a person with certain
spinal cord injuries and that can
be triggered by any irritating
stimulus, such as a full bladder;
autonomic dysreflexia can lead to
elevated blood pressure, reduced
heart rate, seizures, unconscious-
ness, and death.
An electrical or spring-driven
motor that automatically ad-
vances the film after the shutter
is triggered.
A link between an artery and a
vein that may be congenital, occur
spontaneously, or be created sur-
gically. It can cause blood to flow
prematurely from one vessel to
another.
A reflex characterized by exten-
sion of the big toe and flexion of
the other toes; the existence of
the Babinski reflex indicates
spinal cord involvement.
Backscatter In photography, light that is re-
flected back toward the camera
lens by particles suspended in the
water.
Audiometer
Automatic
Exposure
Control
Autonomic
Dysreflexia
Autowinder
A-V
(Arteriovenous)
Shunt
Babinski Reflex
Barodontalgia Pain in the teeth that is caused
by changes in barometric pressure.
Barotitis Media Also called "middle ear squeeze."
Barotitis media is an inflamma-
tion of the middle ear that is
caused by inadequate pressure
equalization between the middle
ear and the ambient atmosphere.
Barotrauma Mechanical damage to or distor-
tion of tissues that is caused by
unequal pressures.
Bathymetry The art or science of determining
or measuring depths of water.
Bed Forms A geologic feature of the seafloor
caused by environmental dynam-
ics, such as near-bottom or wave-
induced currents.
Bends A colloquial term meaning any
form of decompression sickness.
Benthic An adjective referring to the
benthos, or seafloor. Plants and
animals that live on the seafloor
are benthic organisms.
Beta Blockers Drugs used to treat a variety of
conditions, including cardiovas-
cular problems. A prominent ef-
fect of these drugs is a reduction
in heart rate, which causes, in
turn, a reduction in cardiac output
and oxygen consumption by the
heart muscles.
The amount of organic matter
per given volume.
The uncontrolled ascent of a diver
who is wearing a deep sea diving
suit or a variable-volume dry suit.
The thin layer of higher viscosity
or drag around a stationary body
or in a stationary conduit that is
created by the motion of a fluid
of low viscosity, such as air or
water.
Bradycardia Slowness of the heart beat, which
is evidenced by slowing of the
pulse to 60 beats a minute or less.
Brisance The shattering effect of a sudden
release of energy, such as occurs
in an explosion.
Bronchi Fibro-muscular tubes connecting
the trachea to the smaller por-
tions of the respiratory tract.
Biomass
Blowup
Boundary Layer
E-2
NOAA Diving Manual — October 1991
Glossary
Bronchospasm
Carapace
Carboxy-
hemoglobin
Carotid Artery
Carrier Wave
Cathodic
Protection
Cerebellum
Cervical Spine
Chokes
Cholecystitis
Clavicle
Close-Up
Attachment
Closed-Circuit
Breathing System
Coarctation
A sudden and involuntary con-
traction of the bronchial tubes.
A hard bony or chitinous outer
covering; examples of carapaces
are the fused dorsal plates of a
turtle or the portion of the exo-
skeleton covering the head and
thorax of a crustacean.
The compound of carbon monoxide
(CO) and hemoglobin that is
formed when CO is present in
the blood.
The principal artery on each side
of the neck in humans.
An electric wave that can be
modulated to transmit signals in
radio, telephonic, or telegraphic
systems.
A technique designed to reduce
the corrosion that occurs in sea-
water as a result of the presence of
dissimilar metals; when cathodic
protection is used, a sacrificial
metal is introduced to serve as
the anode (site of corrosion), which
protects nearby metal parts.
The part of the brain that lies
below the cerebrum and is con-
cerned with the regulation and
control of voluntary muscular
movement.
The upper seven vertebrae of the
spinal cord.
An imprecise term for the pul-
monary symptoms of decompres-
sion sickness.
Inflammation of the gall bladder.
The collar bone.
In photography, a close-up lens
that fits over the primary lens of
a camera.
A life support system or breathing
apparatus in which the breathing
gas is recycled, carbon dioxide is
removed, and oxygen is added to
replenish the supply as necessary.
Compression of the walls of a
vessel or canal.
Cochlea
Coelenterata
Colitis
Conductive
Hearing Loss
Constant-Volume
Dry Suit
Contrast
Copepod
Cornea
Counterdiffusion
Cricothyroidotomy
Cryogenics
CU
Cyanosis
Dead Space
October 1991 — NO A A Diving Manual
A snail-shaped cavity in the
temporal bone of the inner ear
that contains the organ of hearing.
A phylum of the animal kingdom
comprised of hydroids, jellyfish,
sea anemones, corals, and related
animals. Most species are marine
and all are aquatic.
Inflammation of the colon.
A type of auditory defect caused
by impairment of the conductive
mechanism of the ear; such im-
pairments can occur when the
eardrum is damaged, air passages
are blocked, or movement of the
bones of the inner ear is impaired.
A dry diving suit designed to
be partially inflated to prevent
squeeze and to provide insulation
against cold.
In photography, the difference
between the brightest and darkest
areas in a photograph.
A small planktonic crustacean
that is usually less than 2 milli-
meters in length.
The transparent anterior portion
of the eyeball.
The movement of two inert gases
in opposing directions through
a semi-permeable membrane;
when both gases are at the same
pressure, the phenomenon is called
isobaric counterdiffusion.
Incision through the ring-shaped
cartilage of the larynx.
The production of low tempera-
tures.
In photography, a close-up shot
that pinpoints the main action.
A bluish discoloration of the skin,
lips, and nail beds that is caused
by an insufficiency of oxygen in
the blood.
The space in a diving system in
which residual exhaled air re-
mains. The dead space in diving
equipment adds to the amount of
dead space that occurs naturally
in human lungs.
E-3
Appendix E
Decompression
Dive
Decompression
Schedule
Decompression
Sickness
Decompression
Stop
Demersal Fish
Depth of Field
Dermatitis
Dip
Diverticulitis
Doppler Bubble
Monitor
Do-Si-Do
Position
Dysbarism
Any dive involving a depth deep
enough or a duration long enough
to require controlled decompres-
sion, i.e., any dive in which ascent
to the surface must be carried out
through decompression stops.
A set of depth-time relationships
and instructions for controlling
pressure reductions.
An illness caused by the presence
of bubbles in the joints or tissues;
decompression sickness may occur
after a reduction in barometric
pressure.
The designated depth and time at
which a diver must stop and wait
during ascent from a decompres-
sion dive. The depth and time are
specified by the decompression
schedule being used.
Bottom-living fish, such as plaice
or flounder.
Term used in photography to
denote the distance between the
nearest and most distant objects
that will be in focus.
Inflammation of the skin.
A geological term for the angle
in degrees between a horizontal
plane and the inclined angle of
a rockbed, as measured down from
the horizontal in a plane perpen-
dicular to the strike (see Strike).
Inflammation of a diverticulum,
an outpouching of the colon that
may occur in humans.
A device that detects moving
bubbles in the circulatory system
by picking up changes in the fre-
quency of sound reflected by
moving objects.
A position used in diver rescues
on the surface that enables the
rescuer to administer mouth-to-
mouth resuscitation to an uncon-
scious victim.
A general term applied to any
clinical condition caused by a dif-
ference between the surrounding
atmospheric pressure and the
Dyspnea
Edema
EEG
Elastomer
Electronic Flash
Embolism, Air
or Gas
Emphysema
Emphysematous
Bullae
Envenom
Epilimnion
Epifauna
Epiphytic Plants
Equivalent Air
Depth (EAD)
Equivalent Single
Dive Bottom Time
Ester
total gas pressure in the various
tissues, fluids, and cavities of
the body.
Difficulty in breathing.
Swelling of a part of the body
that is caused by the buildup of
fluid.
Abbreviation for electroenceph-
alogram, a graphic record of the
electrical activity of the brain
made by an electroencephalo-
graph.
A rubberlike material, such as
neoprene or silicone rubber.
In photography, an electrical light
source that emits a brief burst of
light.
A bubble in the arterial system
that occurs when gas or air passes
into the pulmonary veins after
rupture of air sacs of the lung.
A pulmonary condition charac-
terized by loss of lung elasticity
and restriction of air movement.
Blebs or air-filled blisters in the
lungs caused by emphysema.
To poison or put venom into or
onto something.
The layer of water above a ther-
mocline.
Marine animals that live on the
surface of the seafloor.
Plants that are attached to or are
supported by another plant but
that obtain their food indepen-
dently.
The air-breathing depth that has
a nitrogen partial pressure that
is equivalent to the nitrogen partial
pressure at the diving depth.
The bottom time that is equal to
the sum of the residual nitrogen
time and the actual bottom time
of the dive.
A compound that reacts with
water, acid, or alkali to form an
alcohol plus an acid.
E-4
NOAA Diving Manual — October 1991
Glossary
Eustachian Tube
Exceptional
Exposure Dive
Exposure
Exposure Meter
Exudation
f Number
fStop
Facial Nerve
Fathometer
Fenestrated
Fenestration
Fixed Focus Lens
Flapper (Flutter)
Valve
The canal, partly bony and partly
cartilaginous, that connects the
throat (pharynx) with the middle
ear (tympanic cavity) and that
serves as an air channel to equalize
pressure in the middle ear with
pressure outside the ear.
Any dive in which a diver is
exposed to oxygen partial pres-
sures, environmental conditions,
or bottom times that are considered
extreme.
A term used in photography to
denote the amount of light striking
a film.
A meter that indicates the correct
aperture and shutter speed com-
bination for film exposure.
The passing of material, e.g.,
serum or pus, through the wall of
a vessel and into adjacent tissues.
(See f Stop).
A number used in photography to
refer to the relative diameter of
the aperture; the higher the num-
ber, the smaller the aperture.
Each consecutively higher-num-
bered stop admits half as much
light as the previously numbered
stop.
The seventh cranial nerve; con-
trols motion of the face, ear,
palate, and tongue.
An instrument used to measure
the depth of water by determining
the time required for a sound wave
to travel from the surface to the
bottom and for its echo to return
to the surface.
Perforated.
The cutting of an opening (window).
A camera lens with a preset focal
distance that cannot be changed.
A soft rubber tube collapsed at
one end. When the ambient water
pressure is greater than the air
pressure within the valve, the
valve remains collapsed. When
the air pressure within the valve
is greater than the ambient water
pressure, the valve opens.
Flashpoint
Focus
Gas Chromato-
graph
Geodesy
Glossopharyngeal
Nerve
Glaucoma
Grand Mai
Seizure
Ground Fault
Interrupter
Half Time
Hedron
Heliox
Hematopoietic
Tissues
Hemoglobin
Hemoptysis
The lowest temperature at which
a combustible liquid or solid will
generate enough vapor to ignite
in air.
In photography, the sharpness of
the image.
A laboratory instrument used to
identify and measure closely re-
lated chemical substances.
The science of describing the size
end shape of the earth in mathe-
matical terms.
The ninth cranial nerve; controls
sensation, motion, and taste asso-
ciated with the tonsils, pharynx,
middle ear, and tongue.
A condition caused by increased
fluid pressure in the eye.
A major convulsion that involves
unconsciousness, loss of motor
control, jerking of the extremities,
and biting of the tongue.
An electronic device that detects
electrical leakage by comparing
the current in a hot wire with the
current in an accompanying neu-
tral wire.
The time required to reach 50 per-
cent of a final state. In diving, a
half time is the time required for
a tissue to absorb or eliminate
50 percent of the equilibrium
amount of inert gas.
A geometric figure that has a
given number of faces or surfaces.
For example, a pentahedron has
five faces or surfaces.
A breathing mixture of helium
and oxygen that is used at greater
depths because it can be inhaled
without narcotic effect.
Blood-producing tissues, such as
the bone marrow.
The coloring matter of the red
corpuscles of the blood; hemo-
globin combines with oxygen,
carbon dioxide, and carbon mo-
noxide.
Spitting of blood from the larynx,
trachea, bronchi, or lungs.
October 1991 — NOAA Diving Manual
E-5
Appendix E
Hepatitis
Herbarium
Herniated
Nucleus Pulposis
High Pressure
Nervous Syndrome
(HPNS)
Holdfast
Hopcalite
Hypercapnia
Hyperoxia
Hyperpnea
Hyperthermia
Hyperventilation
Hypoallergenic
Hypocapnia
Hypoglossal
Nerve
Hypolimnion
Inflammation of the liver.
A collection of dried plants that
are mounted and labeled in prepa-
ration for scientific use.
A rupture of a disk in the spinal
cord that is caused by degenerative
changes or a trauma that com-
presses a nerve root or the cord
itself.
Neurological and physiological
dysfunction that is caused by
hyperbaric exposure, usually to
helium. The signs and symptoms
of HPNS include tremor, sleep
difficulties, brain wave changes,
visual disturbances, nausea, diz-
ziness, and convulsions.
The rootlike structure at the base
of a kelp that anchors the plant
to the seafloor.
A catalyst used in air compressors
and breathing apparatus to remove
carbon monoxide or other gases.
A condition characterized by ex-
cessive carbon dioxide in the
blood and/or tissues; hypercapnia
causes overactivity of the respira-
tory center.
A condition characterized by ex-
cessive oxygen in the tissues.
Panting or exaggerated respiration.
Elevation of the body temperature
to levels above normal.
Rapid, unusually deep breathing
at a rate greater than is necessary
for the level of physical activity.
An adjective given to materials
that are not likely to cause allergic
responses in contact with the skin.
A condition characterized by an
unduly low amount of carbon
dioxide in the blood; hypocapnia
causes underactivity of the respira-
tory center.
The twelfth cranial nerve; controls
movement of the tongue.
The layer of water below a ther-
mocline.
Hypothalamus
Hypothermia
Hypovolemic
Shock
Hypoxia
Inclinometer
Inert Gas
Narcosis
Inert Gases
Infauna
Inguinal
Inner Ear
In situ
Interchangeable
Lenses
The nerve center in the brain that
influences certain bodily functions,
such as metabolism, temperature
regulation, and sleep.
Reduction of the body's core tem-
perature to a level below 98.6 °F
(37°C); hypothermia can be
caused by environmental expo-
sure to cold or by failure of the
body's thermoregulatory system.
A physiological condition that is
caused by a reduction in the volume
of intravascular fluid and that
may cause a decrease in cardiac
output.
A condition characterized by tissue
oxygen pressures that are below
normal; hypoxia may be caused by
breathing mixtures that are defi-
cient in oxygen, by disease states,
or by the presence of toxic gases
such as carbon dioxide.
In geology, an instrument for
measuring the angle of inclination
(slope).
See Narcosis.
Gases that exhibit great stability
and extremely low reaction rates;
examples of inert gases are helium,
neon, argon, krypton, xenon, and,
sometimes, radon; these gases are
called inert because they are not
biologically active.
Marine animals living within the
seafloor sediment, such as worms
and some clams.
In mammals, pertaining to the
groin.
That portion of the ear that is
located within the confines of the
temporal bone and that contains
the organs of equilibrium and
hearing.
In the natural or original place
or position.
In photography, lenses that can
be attached and detached easily.
E-6
NOAA Diving Manual — October 1991
Glossary
Intercooler
Internal Waves
Intracranial
Surgery
Ischemia
A component of an air compressor
that is designed to cool the air
and to cause water and oil vapors
to condense and collect as the
air passes through the air/liquid
separator.
Waves arising at an internal
boundary that is formed between
layers of water that have different
densities; such an internal bound-
ary occurs when a layer of warm
surface water from a river runoff
overlays a layer of salty or cold
water.
Surgery within the skull.
A localized physiological condition
that is characterized by a defici-
ency in the supply of oxygen to
tissues and that is caused by a
contraction of the blood vessels.
See Hedron.
A strap worn by divers to prevent
the diving helmet from being
lifted off the shoulders, especially
during entry into the water. The
strap passes between the diver's
legs and is attached to the front
and back of the weight belt, which,
in turn, is linked to the helmet.
Keratitis Inflammation of the cornea of
the eye.
Kerf A groove or notch made by a saw,
ax, cutting torch, etc.
Isohedron
Jocking Belt
(Jockstrap)
Laminar Flow
Larynx
Leeway
Liveboating
Lockout
Submersible
Nonturbulent flow of a fluid.
The organ of the voice; the larynx is
situated between the trachea and
the base of the tongue.
Movement of an object through
the water as a result of the force
of the wind.
A search, inspection, or survey
technique in which one or two
divers are towed behind a boat
that is under way.
A submersible that has one com-
partment for the pilot and/or
observer that is maintained at a
pressure of one atmosphere and
another compartment that can be
Longshore
Current
LORAN-C
Lymphatic
System
Manometer
Mass
Spectrometer
Meckels
Diverticulum
Mediastinum
Mediastinal
Emphysema
October 1991 — NOAA Diving Manual
pressurized to ambient pressure
so that divers can enter and exit
(lock out) while under water.
A current that is generated by
waves that are deflected by the
shore at an angle. Such currents
run roughly parallel to the shoreline.
A long range, high-precision navi-
gation system in which hyperbolic
lines of position are determined by
measuring the difference in the
time at which synchronized pulse
signals are received from two
fixed transmitters.
A system of vessels and glands,
accessory to the blood vascular
system, which conveys the lymph
fluid throughout the body.
An instrument for measuring the
pressure of liquids and gases. In
its simplest form, a manometer
consists of a U-tube, one end of
which is open to the atmosphere
and the other end of which is open
to the region where the pressure
is to be measured. If the pressure
in the two areas is different, the
liquid will be higher in one leg of
the tube than in the other.
A laboratory instrument that uses
the masses of compounds to iden-
tify and quantitate them. The
principle of spectrometry involves
ionizing the substance and separa-
ting the resulting molecular and
fragment ions by means of elec-
tric and magnetic fields.
A congenital sac, resembling the
appendix, that occurs naturally
in 1-2 percent of the population.
This sac is located in the lower
intestine and can ulcerate, hemor-
rhage, or develop obstructions or
infections.
The space between the lungs and
under the breastbone where the
heart is located.
Excessive gas or air in the tissues
below the breastbone and near
the heart, major blood vessels, and
trachea. Mediastinal emphysema
is caused by air being forced into
this area from the lungs.
E-7
Appendix E
Meniere's Disease
Metabolism
Methemoglo-
binemia
Microbe
Modulation
Morbidity
Mucosa or
Mucous
Membranes
Mushroom Valve
Myelofibrosis
Myoclonic
Jerking
Myringotomy
Narcosis
A disease of the middle ear that is
characterized by vertigo, sudden
deafness, and symptoms of apo-
plexy.
The phenomenon of transforming
food into complex tissue-elements
and changing complex substances
into simple ones to produce energy.
The presence of methemoglobin
in the blood; this condition can
be caused by toxic agents that are
ingested, inhaled, or absorbed.
A living organism of very small
size; the term is often used synony-
mously with bacterium.
The process of varying a charac-
teristic of one wave in accordance
with that of another wave. Modu-
lation can be achieved by varying
the amplitude, frequency, or phase
of the carrier wave.
A scientific term meaning disease
or sickness.
The tissues lining those body
cavities and canals that are ex-
posed to air.
A type of poppet valve that has
a disk-like head attached to a
stem. The stem reciprocates in a
valve guide under the action of a
cam that bears against the end of
the stem or that operates a tappet
that, in turn, bears against the
valve stem.
A disease state in which the mar-
row is replaced by fibroplastic cells.
A series of involuntary movements
characterized by alternating con-
traction and relaxation of muscles.
Incision of the tympanic mem-
brane (eardrum).
A state of stupor or unconscious-
ness; in diving, it is caused by
breathing certain gases at pres-
sure. Gases vary in their narcotic
potency and may interact with
each other to produce effects that
are greater than those produced
individually. The signs and symp-
toms of narcosis include light-
headedness, loss of judgment,
and euphoria.
Nasal Septum
Neat's-Foot Oil
Neck Dam (Seal)
Nematocyst
Neuropathy
Niggles
Niskin Bottle
Nitrox Breathing
Mixture
NOAA Nitrox-I
Noble Gases
No- Decompres-
sion Dive
The partition between the two
nasal cavities in humans.
A light yellow oil obtained from
the feet and shinbones of cattle.
A rubber skirt that is attached
to some lightweight helmets in-
stead of a breastplate. A neck dam
is tapered to fit tightly around
the neck like a collar.
Necrosis The death of cells.
A structure consisting of a flask-
shaped body bearing barbs and a
long slender filament that can be
discharged by the stinging cells
of coelenterates.
Any disease of the nervous system.
Mild pains that indicate decom-
pression sickness and that begin to
resolve within 10 minutes of onset.
A water-sampling device that is
designed to collect water samples
in amounts ranging routinely from
1.8 quart (1.7 liter) to 31.7 quarts
(30 liters). Niskin bottles also can
be used in conjunction with revers-
ing thermometers to record tem-
perature and depth concurrently.
A breathing mixture containing
nitrogen and oxygen in varying
proportions. The amount of oxygen
in the mixture can be increased
to increase the no-decompression
bottom time or it may be reduced
to avoid oxygen poisoning during
deep dives.
A mixed gas breathing mixture
consisting of 68 percent nitrogen
and 32 percent oxygen.
Gases whose chemical structure
is characterized by closed shells
or subshells of electrons. These
gases are also called inert gases.
A dive to depths shallow enough
and for times short enough to
permit the diver to return to the
surface at a controlled rate without
having to spend time at specified
stops to allow inert gas to be
eliminated from the body.
E-8
NOAA Diving Manual — October 1991
Glossary
Nomogram
Normal Ascent
Rate
Normal Lens
Normoxic
Nystagmus
Oculomotor
Nerve
Olfactory
Nerve
A graphic representation of math-
ematical relationships or laws.
The ascent rate used under con-
ventional or routine conditions;
this rate is 60 feet (18.3 meters)
per minute.
A camera lens that covers an area
of about 1 .5 x 2.25 feet (45 x 68 cm)
at a distance of 3 feet (0.9 m).
A breathing gas mixture that
supplies a diver with the same
partial pressure of oxygen as that
prevailing in a "normal" atmos-
phere, i.e., about 0.21 ATA of
oxygen, at any specific depth.
A physiological condition charac-
terized by repeated, involuntary,
rapid movements of the eyes,
usually in the horizontal plane
but sometimes also in the vertical
plane.
The third cranial nerve; controls
the movement of the eyes.
The first cranial nerve; controls
the sense of smell.
Operculum The plate covering the gills of a
bony fish.
Optic Nerve The second cranial nerve; controls
sight.
Oropharyngeal That part of the airway in humans
Airway that consists of the mouth and
the pharynx {see Pharynx).
Osteomyelitis Inflammation of the bone marrow.
Osteonecrosis The death of cells in the long
(Dysbaric bones, such as the humerus, femur,
Osteonecrosis) or tibia; osteonecrosis can be
caused by exposure to compressed
air at pressures greater than atmos-
pheric pressure.
Otitis Externa Inflammation or superficial infec-
tion of the auditory canal.
Otitis Media Inflammation of the middle ear.
Otterboards Door-shaped boards that are at-
tached to trawling nets to keep the
nets open during trawling.
Oval Window The upper of two membrane-
covered openings in the cochlea
of the inner ear {see Cochlea).
Overboard Dump
(Discharge)
System
Overlap
Oxyhemoglobin
Paranasal
Sinuses
Paraparesis
Paraplegia
Parenteral Drug
Administration
Paroxysmal
Tachycardias
Partial Pressure
Patent
Pathogenic
Organisms
Peduncle
Pelagic
Organisms
Perfusion
pH
Pharynx
A system built into a hyperbaric
chamber and that transfers exhaled
gas out of the chamber.
In photography, a term used to
mean reshooting the same action
from a different camera angle.
Oxidized hemoglobin in the
arterial blood.
Pancreatitis Inflammation of the pancreas.
The air-filled cavities in the cra-
nial bones accessory to the nose;
the paranasal sinuses comprise
the frontal, sphenoidal, ethmoidal,
and maxillary sinuses.
Partial paraplegia.
Loss of function, and occasionally
of sensation, in the lower body.
Administration of drugs by a route
other than oral, e.g., by subcu-
taneous or intravenous injection.
Periodic bouts of fast heart beats.
The proportion of the total pres-
sure contributed to a mixture by
a single gas in that mixture.
Open, as in "a patent airway."
Organisms that produce disease.
Any stalklike structure that sup-
ports another structure or organ.
Plants and animals that live in
the open sea and that are not
associated with the shore or sea
floor.
The passage of fluid through
spaces.
A measure of the acidity or alka-
linity of a solution; a pH of 7 is
neutral, while one with a pH of 1
to 4.5 is strongly acidic and one
with a pH of 11.5 to 14 is strongly
alkaline.
That portion of the digestive and
respiratory tract situated back of
the nose, mouth, and larynx and
extending from the base of the
skull to a point opposite the sixth
vertical vertebra, where it becomes
contiguous with the esophagus.
October 1991 — NOAA Diving Manual
E-9
Appendix E
Phase Measure-
ment System
Phonetically
Balanced Word
Lists
Photogrammetry
Photon
Photophobia
Phytoplankton
Pinger
Pituitary
Plane Table
Plankton
Platelet
Pleura
A method for determining the
position of an object on the sea-
floor that uses a single transponder
placed on the object and three
receiving elements located on the
underside of the surface support
platform.
Lists of words that are selected
to ensure that each list contains
a balanced and equal cross-repre-
sentation of speech sounds. These
lists can then be read by experi-
mental subjects, e.g., divers, to
compare the effectiveness of dif-
ferent communication systems.
The application of photographic
principles to the science of map-
ping; photogrammetry involves the
use of special cameras to photo-
graph the earth's surface to pro-
duce mosaic pictures or scale
maps.
The basic unit (quantum) of the
electromagnetic field; photons
have zero mass, no electric charge,
and an indefinitely long lifetime.
Literally, a fear of light; in prac-
tice, a disinclination or inability
to use the eyes in strong light.
Minute marine plants that drift
in the sea and are usually micro-
scopic; phytoplankton are either
single-celled or loose aggregates
of a few cells.
An underwater locating device
that emits an acoustic signal.
A gland, located in humans at the
base of the brain, that influences
growth, metabolism, sexual cycles,
and many other bodily functions.
A surveying instrument used to
locate and map topographical
features.
Plant and animal organisms (usu-
ally microscopic) that float or
drift in fresh or salt water.
A component of blood that affects
its ability to clot.
The serous membrane that enve-
lops the lung and lines the thoracic
cavity.
Pneumatocysts
Pneumo-
fathometer
Pneumo-
mediastinum
Pneumothorax
Polycythemia
Prosthesis
Protozoa
Provenance Data
PSIG
Psychosis
Pulmonary
Pulmonary Edema
Purse Seine
Pyrolytic
Decomposition
Hollow floats found at the base
of the blades or fronds of certain
kelp plants and that cause the
fronds to float up to form a canopy.
A hollow tube that has one end
connected to a gauge at the sur-
face and another end that is open
under water. Pneumofathometers
are used to measure the water
pressure at the submerged end
of the tube.
See Mediastinal emphysema.
The presence of gas within the
chest cavity but outside the lungs.
A condition characterized by an
excessive number of corpuscles
(usually red) in the blood.
A man-made replacement for a
missing body part.
One of the lowest classes of the
animal kingdom, the protozoa are
organisms that consist of simple
cells or colonies of cells and that
possess no nervous or circulatory
system.
The original data.
Abbreviation for pounds per
square inch gauge; a term used to
express the difference between
absolute pressure and the specific
pressure being measured.
A disease of the mind charac-
terized by loss of contact with
reality.
Pertaining to or affecting the lungs.
An accumulation of fluid in the
lungs.
A fishing net that is made to hang
vertically in the water by weights
at the lower edge and floats at
the top and that is pursed or drawn
into the shape of a bag to enclose
the catch.
Chemical change caused by heat
or fire.
E-10
NOAA Diving Manual — October 1991
Glossary
Quadrat
Quadriparesis
Quadriplegia
Radiometer
Radular Teeth
Rebreather
Refraction
Remotely
Operated
Vehicle (ROV)
Repetitive Dive
Repetitive Group
Designation
Residual Air
Residual Nitrogen
Residual Nitrogen
Time
A device, which is usually a square
of polyvinyl chloride tubing, that
is placed on the seafloor and used
to estimate the density of marine
plants or animals in a defined
area.
Partial quadriplegia.
Loss of function, and occasionally
sensation, from the neck or chest
down.
An instrument, which is essentially
a heat flow meter, that is used
to detect and measure long wave
radiation and solar radiation.
Minute teeth that are imbedded
in a horny strip on the floor of
the mouth of a snail and that are
used to scrape up food.
A semi-closed-circuit or closed-
circuit breathing apparatus that
removes the carbon dioxide ex-
haled by the diver and adds oxygen
as required.
The bending of light rays as they
pass from one medium to another
of different density.
An unmanned, tethered or un-
tethered vehicle that is designed
for underwater observation, work,
or sample collection.
Any dive conducted within 1 2 hours
of a previous dive.
A letter that is used in decom-
pression tables to designate the
amount of nitrogen remaining
in a diver's body for 12 hours
after the completion of a dive.
The amount of air that remains
in the lungs after a person volun-
tarily expels all of the air possible.
A theoretical concept that de-
scribes the amount of nitrogen
that remains in a diver's tissues
after a hyperbaric exposure.
The time (in minutes) that is added
to the actual bottom time when
calculating the decompression
schedule for a repetitive dive.
Resolution
Respiration
Retinitis
Pigmentosa
Rip Current
Romberg's Sign
Round Window
Saturation
SCFM
Scrubber
Seborrheic
Dermatitis
In photography, the amount of
detail (lines per inch) in a photo-
graph.
The process by which gases, oxygen,
and carbon dioxide are inter-
changed among the tissues of the
body and the atmosphere.
An inflammation of the retina
that involves all layers of the
retina.
A strong surface current of short
duration that flows seaward from
the shore. Rip currents usually
appear as a visible band of agi-
tated water; they are generated
by the return movement of the
water that is piled up on the
shore by incoming waves and
wind.
A swaying of the body and an
inability to stand when the eyes are
closed and the feet are placed
close together; the presence of
this sign indicates neurological
impairment.
The lower of two membrane-
covered openings in the cochlea
of the inner ear (see Cochlea).
A term used in diving to denote
a state in which the diver's tissues
have absorbed all the nitrogen or
other inert gas they can hold
at that particular depth. Once
saturation has occurred, the
amount of decompression time
required at the end of the dive
does not increase even if the
diver spends additional time at
that depth.
An abbreviation for standard cubic
feet per minute; SCFM are com-
monly used to express the output
volume of air compressors.
A component of an atmospheric
control system that removes car-
bon dioxide from the breathing
gas by absorbing it with chemical
absorbents.
An inflammatory scaling disease
of the scalp, face, and, occasion-
ally, of other areas of the body.
October 1991 — NOAA Diving Manual
E-11
Appendix E
Seismic Waves
Seismic Profiling
Semi-Closed-
Circuit Breathing
System
Sessile
Sextant
Shear
Shutter Speed
Side-Scan Sonar
Single Lens
Reflex (SLR)
Solubility
Coefficient
of Gases
Sonic Pinger
Sound Pressure
Shock waves caused by earth-
quakes or explosions that travel
inside the earth or on its surface.
A method for obtaining a profile
of the seafloor or of the layers of
sediment and rock below the sea-
floor; seismic profiling uses a
strong energy source from the
surface and then measures the
strength of the reflected energy.
A self-contained underwater
breathing apparatus in which
the breathing gas is recirculated
through purifying and oxygen-
replenishing systems and a portion
of the exhaled gas is discharged
into the surrounding water.
Permanently attached or fixed;
not free-moving.
A navigational instrument that
is used to measure the altitude
of celestial bodies.
A force that lies in the plane of
an area or a parallel plane and
that tends to cause the plane of
an area to slide on the adjacent
planes.
In photography, the amount of
time a camera shutter exposes a
film to light.
A search system in which acoustic
beams are directed laterally and
downward in planes perpendicular
to the line of the advance of a
towed transponder-receiver unit.
Return signals are then processed
to present a picture of the sea-
floor on both sides of the towed
unit.
A camera that has a movable
mirror and a series of prisms
that allow the subject to be viewed
through the camera's lens.
Under the experimental condi-
tions of pressure and temperature,
the volume of gas dissolved by a
unit volume of solvent.
See Pinger.
In the presence of a sound wave,
the instantaneous pressure at any
Spectrometer
Spectro-
radiometer
Sphygmoma-
nometer
Spina Bifida
Spirit Level
Squeeze
Stadia
Stage
Decompression
Stapedectomy
Stipe
Stratigraphy
Strike
Sub-Bottom
Profile
point in a medium minus the
static pressure at that point.
An instrument used to measure
spectra or to determine the wave-
lengths of various kinds of radi-
ation, from infrared to gamma.
An instrument used to measure
the spectral distribution of radiant
energy.
An instrument used to measure
blood pressure.
A congenital anomaly in which
the spinal membranes protrude
through a congenital cleft (split)
in the lower part of the vertebral
column.
A level that is used in combination
with a telescope to compute the
difference in elevation between
two points.
Deformation of tissue or some
portion of the body caused by a
difference in pressure.
A method of surveying distances
that involves the use of two parallel
lines to intercept intervals on a
calibrated rod; the intervals are
proportional to the intervening
distance.
A decompression procedure in-
volving decompression stops of
specific durations at given depths.
Removal of the stirrup-shaped
bone in the middle ear.
The flexible stemlike structure of
seaweeds, such as kelp, that serves
as the shock absorber between
the upper leafy parts of the plant
and the anchored holdfast at the
bottom.
The study of rock strata, and
especially of their distribution,
deposition, and age.
In geology, the compass direction
that a rockbed would take if it
were projected to a horizontal
plane on the earth's surface.
See Seismic Profiling.
E-12
NOAA Diving Manual — October 1991
Glossary
Subcutaneous
Emphysema
Substernal
Supersaturated
Solution
Surface Interval
Surflcial Maps
Synchronization
Systole
Systolic Blood
Pressure
Talus
Taxa
Telemetry
Temporal
Mandibular
Joint (TMJ) Pain
Thallus
A condition in which air enters
the tissues beneath the skin of
the neck and extends along the
facial planes from the mediasti-
num; the presence of subcutaneous
emphysema means that air has
escaped from the lungs through a
rupture of the alveoli.
An adjective meaning beneath
the breast-bone.
A solution that holds more gas than
would be possible at the same
temperature and pressure at equi-
librium.
The period elapsing between the
time a diver surfaces from a dive
and the time the diver leaves the
surface to perform a subsequent
dive.
Maps showing the two-dimen-
sional character and distribution
of material comprising the seafloor
of an area.
In photography, the interval be-
tween the opening of the shutter
and the burst of light from the
strobe.
The rhythmic contraction of the
heart that drives the blood through
the aorta and pulmonary arteries.
The blood pressure recorded
during systole (contraction of the
heart).
The mass of coarse rock fragments
that accumulates at the foot of a
cliff as a result of weathering
and gravity.
In taxonomy, a category, such
as a species or genus.
The science and technology of
the measurement and transmission
of data by wire, radio, acoustic,
or other means.
Pain in the area of the temple and
the jaws; TMJ pain is often caused
by grinding the teeth or by grip-
ping a mouthpiece too firmly.
A plant that has a body that is not
differentiated into root, stem, or
leaf.
Theodolite
Thermistor
Thermocline
Thoracentesis
Thoractomy
Thrombus
Tidal Air
Tinnitus
Topographic
Chart
Torr
Total Bottom
Time
Toynbee
Maneuver
Trachea
Tracheobronchitis
Transducer
October 1991 — NOAA Diving Manual
An optical instrument used to
measure angles and distances.
An electrical resistor made of a
material whose resistance varies
sharply with temperature in a
known manner.
A transition zone of rapid tem-
perature change between contig-
uous layers of water.
A medical procedure involving
puncturing of the thorax to remove
accumulated fluid.
Incision of the thorax or chest wall.
A stationary plug or clot in a blood
vessel or in one of the cavities of
the heart.
The volume of air inspired and
expired by a person during rest.
A ringing, roaring, or hissing
sound in the ears.
A chart that graphically repre-
sents the exact physical configu-
ration of a place or region.
A unit of pressure equal to 1/760
of an atmosphere and very nearly
equal to the pressure of a column
of mercury 1 millimeter high at
0°C (32 °F) and standard gravity.
The total amount of time between
the time a diver leaves the surface
and the time (next whole minute)
that the diver begins ascent (in
minutes).
The act of swallowing while the
mouth and nose are closed.
That portion of the breathing
apparatus that extends from the
posterior oropharynx (the posterior
portion of the mouth) to the chest
cavity.
Inflammation of the trachea and
bronchi.
A device capable of being actu-
ated by waves from one or more
transmission systems or media,
e.g., electrical, mechanical, or
acoustical, and of supplying re-
lated waves to another trans-
mission system or media.
E-13
Appendix E
Transect
Transponder
Trigeminal Nerve
Trilateration
Trochlear Nerve
Turbulent Flow
Tympanic
Membrane
Upwelling
Vagus Nerve
Valsalva
Maneuver
Variable-Volume
Dry Suit
Vascular
Vasomotor
Control
In diving, a reference line attached
to the seafloor and designed to
provide directional orientation or
to serve as a base line for scientific
observations or surveys.
An electronic device consisting
of a receiver of signal impulses
and a responder that automatically
returns signal impulses to the
interrogator-responder.
The fifth cranial nerve; controls
motion and sensation of the face,
teeth, and tongue.
A method of determining the
relative positions of three or more
points and that involves treating
these points as vertices of a triangle
and then measuring their angles
and sides.
The fourth cranial nerve; controls
the superior oblique muscles of
the eye.
A type of flow in which the fluid
velocity at a fixed point fluctuates
with time in a nearly random way;
contrasts with laminar flow.
The thin membranous partition
(also called the eardrum) that
separates the external ear from
the middle ear.
In coastal areas, the replacement
of surface waters by deeper waters;
upwelling is caused by winds that
transport surface waters offshore.
The tenth cranial nerve; controls
sensation and motion of the ear,
pharynx, larynx, heart, lungs,
esophagus, and other parts of
the body.
The act of attempting to exhale
forcefully while the mouth and
nose are closed.
A type of dry suit that has both
an inlet gas valve and an exhaust
valve.
Consisting of, pertaining to, or
provided with vessels; usually
refers to blood or lymph vessels.
Regulation of the tension of blood
vessel walls.
Vasovagal Effects
Vector
Ventricle
Ventricular
Fibrillation
Venturi Effect
Venule
Vertigo
Vestibular
Decompression
Sickness
Vestibule of the
Ear
Viewfmder
A group of physiological effects
caused by fright, trauma, pain,
and other stress-inducing situa-
tions; vasovagal effects include
nausea, sweating, paleness, de-
creased cardiac output, and related
symptoms.
A quantity completely specified
by a magnitude and direction.
A small anatomical cavity or
chamber, as in the heart or brain.
The left ventricle of the heart
receives arterial blood and pumps
it into the aorta. The right ventricle
of the heart receives venous blood
and pumps it through the pulmo-
nary artery into the lungs.
A condition in which the ventricles
of the heart develop an irregular
and chaotic rhythm and the elec-
trical activity of the heart becomes
disorganized. If ventricular fibril-
lation is not stopped immediately,
it is fatal.
A type of flow in which the flow
rate is higher and the relative
pressure is lower; venturi effects
are caused by a smooth constric-
tion in a pipe or by a restriction
of an area through which gas or
liquid flows.
A small vein.
A disoriented state in which the
individual perceives himself or
herself, or the surroundings, as
rotating; vertigo is caused by
neurological damage and is some-
times a symptom of serious decom-
pression sickness.
Decompression sickness involving
the inner ear; inner-ear decom-
pression sickness is often asso-
ciated with vertigo.
The common central cavity of
communication between the parts
of the internal ear. The vestibule
is situated on the inner side of
the eardrum, behind the cochlea,
and in front of the semicircular
canals.
In photography, a device used
to aim the camera.
E-14
NOAA Diving Manual — October 1991
Glossary
Virtual Image
Viscosity
Vital Capacity
Vortex
Voucher Specimen
An image from which rays of
reflected or refracted light appear
to diverge, as from an image seen
in a plane mirror.
Resistance to flow, a property of
fluids.
In respiratory physiology, the
maximal volume that can be ex-
pired after maximal inspiration.
A type of flow that involves ro-
tation about an axis, such as occurs
in a whirlpool.
A specimen collected to provide
species identification or evidence
Weir
Wet Submersible
Zooplankton
that a given species was collected
from a certain place.
A dam or bulkhead over which
water flows, or a bulkhead con-
taining a notch through which
water flows; weirs can be used to
measure volume in a flow of water.
A free-flooding submersible de-
signed so that its occupants are
exposed to the ambient environ-
ment.
Drifting marine animals that range
in size and complexity from micro-
scopic single-celled animals to
large multicellular ones.
)
October 1991 — NOAA Diving Manual
E-15
i
i
(
i
(
(
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«
4
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NOAA Diving Manual — October 1991
i
i
i
INDEX
Page
Absolute Zero Temperature 2-1
Absorbent 15-8, 16-9
Absorption of Light Under Water 2-15
Accident
Causes of 19-1, 19-5
Management of 19-1, 19-19, 19-25
Prevention of 19-2
Reporting Procedures for 19-28
Acoustic
Communication Systems 5-26
Grids 9-4
Methods for Underwater Search 8-1 1
Pingers 8-17, 17-20
Telemetry 8-16
Transmission Under Water 2-16
Aegir Underwater Habitat 17-14
Aging and Diving 13-2
Air
Analysis of 15-13
Compressed 4-1
Compressors {see Compressors)
Consumption 13-1, 14-8, 14-12
Decompression Tables 14-20
Embolism {see Embolism)
Emergency Supply of 8-6
Evacuation, Emergency 20-13
Flow Requirements 6-6, 8-9
High-Pressure Storage Systems 14-18
Limits for Saturation Diving 16-8
Loss of, Diver's 8-6, 19-4
Low-Pressure Warning 4-1 1
Operational Requirements 14-16
Purity of 15-12
Supply, Chamber 6-6
Systems for Surface-Supplied Diving 8-9
Use of for Saturation Diving 16-7
Airlifts 8-27, 9-38, 9-40
Airway Obstruction 18-1, 18-3
Algae 9-17,9-20
Alligators 12-11
Altitude Diving
Decompression Treatment for 20-12
Diving Tables 10-24
No-Decompression Limits for 10-25
Alveoli 3-2
Ama Divers 1-1
American Academy of Underwater Sciences 7-10
American Heart Association 7-8
October 1991 — NOAA Diving Manual
Page
American Red Cross 7-8
Anatomical Differences Between Males and Females . 13-1
Anesthetics (for Fish) 9-42 to 9-48
Animals
Capture Techniques for 9-41
Geographic Distribution of 10-1 to 10-7
Hazardous Aquatic 10-2, 12-11
Anxiety 19-2
Aquaplane 8-29
Aquarius Underwater Habitat 17-17
Archeological Diving 9-36
Argon 2-7
Artifacts (Underwater)
Excavation of 9-38
Ownership of 9-40
Preservation of 9-40
Artificial
Reefs 9-20
Resuscitation {see Resuscitation)
Ascent
by Surface-Supplied Diver 8-7
Emergency 19-6
Pressure Effects During 14-19
Problems During 19-4
Rate of 14-20
Uncontrolled 19-15
Aseptic Bone Necrosis 3-20
Asphyxia 20-2
Atmospheric
Contaminants 4-1
Diving Systems 17-18
Pressure 2-2
Autonomic Dysreflexia A-l 1
Bag- Valve-Mask Resuscitator 18-5
Bailout Unit 5-8
Bang Stick 5-24
Barium Hydroxide (BaralymeR) 15-9, 16-9
Barnacles 12-1
Barometric Pressure Units 2-3
Barotrauma {see Squeeze)
Barracuda 12-10
Bathymetric Map 9-1
Bell Diving {see Diving Bells)
1-1
Index
Page
Bends (see Decompression Sickness)
Bends Watch (Emergency Phone Numbers) 14-3
Biological
Sampling 9-8
Surveys 9-6
Birth Control Methods and Diving 13-2
Birth Defects from Diving 13-3
Bites 12-8
Bleeding 18-7
Blood
Circulation 3-2
Color of, in Water 2-15
Bloodworms 12-4
Blowout Plugs 4-10
Blowup 8-6, 16-1 1
Blue-Water Diving 10-14
Body Fat 13-2
Bond, George 16-1
Botanical Sampling
Areas of 9-17
Field Procedures for 9-18
Specimen Preparation 9-19
Bottom
Conditions 8-2
Surveys 9-4
Timer 5-20
Box Cores 9-24
Boyle's Law 2-8
Bradycardia Appendix E
Breathing
Bag 3-8
Hoses 5-4
Media 4-1
Rate 3-2
Resistance 3-8
Breathing Gas (see also Air)
Air 4-1
Analysis of 15-13
Chamber 6-6
for Saturation Diving 16-7
Helium-Oxygen 15-1, 15-4, 16-8
Mixing 15-14
Moisture in 2-12
Nitrogen-Oxygen 15-1, 15-7, 15-10, 16-7
Oxygen 15-5
Purity of 15-12
1-2
Page
Breath-hold Diving 1-1
and Hyperventilation 3-8
Uses of 14-2
Bristleworms 12-4
Bubble Formation
and Contact Lenses 3-16
During Rewarming Following Hypothermia 3-27
Buddy
Breathing 19-5, A-8
Diving During Wire Dragging 8-25
Built-in-Breathing System (BIBS) 17-2
Buoyancy
Compensation 5-12, 19-4
Compensator (see Flotation Devices)
Control for Disabled Divers A-l, A-7
Definition of 2-3
Burns
Sunburn , 18-10
Treatment of 18-10
Caisson Disease (see Decompression Sickness)
Cameras, Underwater
Lenses and Housings 8-33
Motion Picture 8-42
Still 8-33
Telephoto Lens 9-7
Television 8-44
Carbon Dioxide
Analyzer 15-14
Cartridges for Flotation Devices 5-12
Definition of 2-6
Excess of 3-5
Gas Exchange 3-2
in Saturation Diving 16-8
Poisoning 20-1
Removal 15-8, 16-9
Shark Darts 5-25
Transport of, in Blood 3-2
Carbon Monoxide
Analyzer 15-14
Definition of 2-6
Filtration 4-4
in Ambient Air 4-1
in Saturation Diving 16-8
Poisoning 3-6, 20-2
Cardiac Arrest 18-5
Cardiopulmonary Resuscitation (CPR) 18-6, 19-16
Cartridges (C02) 5-12
Catheters for Disabled Divers A-10
Cave Diving 10-17
NOAA Diving Manual — October 1991
Index
Page
Central Nervous System (CNS) Oxygen Toxicity.. 15-3
Chamber {see Hyperbaric Chamber)
Charles' Law 2-10
Chart, Topographic 9-1
Chemical Hazards of Diving 1 1-2
Chokes 3-18
Ciguatera 12-12, 18-13
Circulatory System, Human 3-1
Closed Circuit Rebreather {see Rebreather)
Closed-Circuit Scuba
Oxygen Poisoning 20-2
Uses of 14-2
Coast Guard Search and Rescue Units 19-21
Coelenterates 12-1
Cold Water
Diving in 10-3, 10-6, 10-19
Effects of 3-4
Performance in 3-25
Protection Against 5-14
Rewarming Techniques 3-27, 18-9
Survival in 3-26
Color
Coding 2-15
Filters 8-35
Photography 8-34
Vision Under Water 2-15
Combustion 6-14
COMEX Treatment Table CX 30 Appendix C
COMEX Treatment Table CX 30A Appendix C
Communication
Cable 5-9
for Disabled Divers A-4
in Habitats 16-1 1
Loss of 8-7
Systems 5-25
Underwater 2-17
Compass
Use of, for Navigation 8-17
Use of, for Search 8-16
Wrist 5-21
Compressed Gas
Airborne Pollutants 4-1
Cylinders 4-5, 14-18
Production of 4-3
Purity of 15-12
Safety Precautions 4-1
October 1991 — NOAA Diving Manual
Page
Compressors, Air
Air Intake 4-1, 4-4
Filtration System 4-4
Habitats 4-2
Hyperbaric Chambers 6-5
Lockout Submersibles 4-2
Lubricants 4-2
Maintenance of 4-5
Rating of 4-2
Shipboard 10-32
Condensation (in Breathing Tubes or Mask) 2-13
Cone Shells
Description 12-4
Poisoning by 18-12
Contact Lenses 3-16, 5-7
Contaminated Water {see Polluted Water)
Coral, Fire (Stinging) 12-2, 18-13
Wounds 18-13
Coring
Box 9-24,9-30
Devices 9-9, 9-10, 9-26, 9-30
Samples 9-9,9-27
Corrosion Prevention
Chambers 6-9
Cylinders 4-7
Costs of Diving Medical Treatment 19-19
Counterdiffusion 3-19, 15-4
Crabs 9-13
Crocodiles 12-1 1
Currents
Diving in 8-2, 10-9, 14-5
Geographical Variation in 10-1 to 10-7
Measurement of 9-34
Rip 10-9
River 10-31
Search and Recovery in 8-13
Shore 10-9
Cutting, Underwater 8-22
Cyanosis 18-3
Cylinders
Aluminum 4-6
Capacity of 4-7, 14-14
Charging of 4-2
Color Coding of 4-2
Handling of 4-2
High-Pressure 14-18
Hydrostatic Tests for 4-6, 4-9
Inspection of 4-6, 4-9, 7-1 1
Low-Air Warning Device 4-1 1
1-3
Index
Page
Cylinders (Cont.)
Maintenance of 4-7
Manifolding of 4-10, 10-18
Marking of 4-5 to 4-8
Pressure Gauge 4-1 1
Steel 4-5, 14-14
Storage of 4-9
Dalton's Law 2-7
DAN (see Divers Alert Network)
David (Remotely Controlled Vehicle) 17-23
Dam and Reservoir Diving 10-28
Dark Adaptation 2-15
Dead
Reckoning 8-16
Space 3-8
Deck Decompression Chamber (DDC) 16-1
Decompression
After Air Diving 14-21
After Air or Nitrogen-Oxygen Dives 16-13
After Helium-Oxygen Dives 15-4
After Repetitive Dives 14-23
After Saturation Dives 16-13
Chamber 16-1
Definitions of 14-20
During Night Diving 10-28
In-Water 20-13
Omitted 14-26,20-13
Oxygen 15-4
Surface (Air) 14-25
Tables 14-20
Decompression Sickness
After Excursions from Habitats 16-12
Causes of 3-17
Impact of, on Fetus 13-3
in Disabled Divers A-l 1
in Female Divers 13-2
Pretreatment Procedures 20-13
Symptoms of 3-18, 20-9
Treatment of 16-12, 20-8, 20-12
Treatment Tables for 20-11, 20-15
Decompression Tables (see U.S. Navy)
Decontamination Procedures for Polluted-
Water Diving 1 1-5
Demand Regulators 5-1
Demolition, Underwater 8-31
Density, Definition of 2-1
Department of Transportation
Emergency Medical Technician Training 7-8
1-4
Page
Depth
Measurement of 8-2
Depth Gauges
Bourdon Tube 5-21
Capillary Tube 5-21
Correction for Altitude 10-26
Pneumofathometer 5-21
Descent
Line 8-4,8-7
Pressure Effects During 3-10
Problems During 19-3
Rate for Surface-Supplied Diver 8-5
Uncontrolled 19-15
Diluent Gases
Limitations of 15-1
Purity of 15-12
Dip (of Rock Bed) 9-26, 9-28
Disabled Diver A-l
Distress Signals (see Signals)
Dive
Flags 14-9
Ladders 10-13
Master 7-8, 10-32, 14-2
Planning for 14-1
Supervisor 8-2
Team for Surface-Supplied Diving 8-2
Timekeeper 8-2
Diver
Certification 7-1
Communication 5-26, 9-5
Disabilities A-l
Physical Examination for 7-11, 11-6
Propulsion Vehicle 9-5, 17-18
Selection of 7-1
Sled 8-15, 8-27, 10-34
Standby 8-2
Support 14-3
Tender 8-2
Towing 8-27
Divers Alert Network (DAN) .... 7-9, 14-3, 19-20, 19-28
Diving
After Decompression from Saturation 12-13
Air 14-1
at Altitude 10-24
at Dams and Reservoirs 10-28
at Water Withdrawal and Pumping Sites 10-30
Bells 17-1
Excursions 16-13
Freshwater 10-13
from a Coral Reef 10-10
from a Pier 10-10
NOAA Diving Manual — October 1991
Index
Page
Diving (Cont.)
from a Ship 10-32
from a Small Boat 8-27, 10-1 1
from a Stationary Platform 10-10
from Shore 10-7, 10-9
Gases 2-6
in Cold Water 10-19
in Contaminated Water 11-1
in Open Ocean 10-14
Locker 10-32
Medical Officer 14-3
Medical Technician 14-3
Mixed Gas 15-1
Oxygen 15-1
Scientific 9-1
Signals 14-8
Suits (see Suits)
Supervisor Training 7-8
Surface-Supplied 8-1, 9-6
Systems 17-18
Through Surf 10-7
Under Ice 10-21
While Under Way 10-33
Women and 13-1
Diving Bells 1-1, 17-1
Diving Equipment
for Smaller Divers 13-4
for Surface-Supplied Diving 8-3
Selection of 14-1
Drift Diving 8-27, 8-30
Drilling 9-27
Drowning (see Near Drowning)
Drugs
and Diving 3-28
for Equalization Problems 3-1 1
Dry Suit (see Suits)
Duke University Medical Center 19-20
Dye
for Core Samples 9-24
for Detecting Flow Patterns 9-32
for Marking Coral 9-17
for Marking Dive Sites 10-15
for Observing Currents 10-14
for Specimen Identification 9-10
for Tagging Fish 9-16
Tracers 9-33
Dysbaric Osteonecrosis (see Aseptic Bone Necrosis)
Ear
Anatomy of 3-10, 20-8
Care of, in Habitats 16-12
October 1991 — NOAA Diving Manual
Page
Cleaning Procedures for 1 1-6
Clearing of A-6
Drum 20-7
Dysfunction 20-3
Fullness 20-3
Infection 11-1
Medication 4-11, 16-12
Plugs 5-24
Round Window Rupture 20-7
Squeeze 3-10, 20-3, 20-6
Eardrum Rupture 3-1 1
Edalhab Underwater Habitat 17-10
Edema, Pulmonary 3-13
Electrocution 18-11
Embolism
Causes of 3-15, 20-9
Treatment of 3-15, 3-16, 20-8
Emergencies
Associated with Surface-Supplied Diving 8-5
Causes of 19-4
Emergency
Aid 14-3, 19-8, 19-20
Air Supply 8-6
Assistance 19-21
Breathing Station 17-1
Evacuation 19-27
Gas Supply (Bailout) 5-8
Medical Technician Training 7-8
Procedures for Habitats 16-10
Signals 19-20, 19-22
Telephone Numbers for 14-3
Emphysema 3-14, 20-17
Entanglement 19-7, 19-15
Entry (into Water)
by Disabled Divers A-5
by Surface-Supplied Divers 8-4
Problems During 19-3
Envenomation by Marine Animals 18-12
Environmental Conditions
Surface 14-4
Underwater 14-4
Epifauna 9-9
Equalization of Pressure 3-1 1
Equipment
for Disabled Divers A-l
for Diving in Polluted Water 1 1-3
for Smaller Divers 13-4
for Surface-Supplied Diving 5-6, 8-3
1-5
Index
Page
Equivalent Air Depth
Definition of 15-7
Nitrogen 15-7
Eustachian Tube 3-1 1
Evacuation, Emergency 19-27, 20-13
Examination
Neurological 19-23
of Injured Diver 19-19, 19-23
Physical (of Divers) 7-1
Excavation Techniques 8-27, 9-37
Excursion Diving
Decompression Sickness After 16-12
from Habitats 7-7, 16-7, 16-11 to 16-13
Using Air 16-7
Exit from Water
by Disabled Divers A-9
Problems During 19-3
with a Victim 19-18
Explosives, Underwater 8-31
Eye
Glasses (Underwater) 5-7
Infections 11-1
Squeeze 20-6
Face Mask {see Mask)
Fathometer 8-11
Film 8-38,8-42
Fins 1-5, 5-14, A-l
Fire
Coral 12-2
Detection of 6-10
Extinguishment of 6-17
Management of, in Chamber 6-14
Prevention of, in Chamber 6-10
-Resistant Materials 6-14
Safety for Saturation Diving Systems 16-10
First Aid
Basic Principles 18-1
Kits 20-20
Fish
Anesthetics 9-42
Capture of 9-41, 9-46
Poisoning by 12-1 1, 18-13
Rake 9-7
Screens 10-30
Tagging of 9-14
Traps 9-41
Venomous 12-5, 18-12
1-6
Page
Flag
Diver's 5-24, 14-9
Signal 14-8
Weather Warning 14-4
Flares 5-23
Floats 5-24
Flotation Devices 5-11, 19-4
Flying
After Diving 14-28
After Saturation Decompression 16-14
Fogging (Mask) 2-13, 5-8
Fractures 18-1 1
Free Diving {see Breath-hold Diving)
Free-Flooded Submersibles {see Submersibles)
Free Flow/ Demand Mask {see Mask)
Freshwater Diving 10-13
Gas
Analysis 15-12
Boyle's Law 2-8
Charles' Law 2-10
Compressibility of 15-15
Dalton's Law 2-7
Diluents 15-1
Diving 2-6
Embolism {see Embolism)
Exchange (in Blood) 3-2, 3-16
Flow 3-8,2-12
General Law 2-1 1
Handling of 15-1
Henry's Law 2-1 1
Mixing of 15-14
Moisture in 2-12
Overexpansion of Stomach and Intestine 3-16
Quality of 15-1
Supply of, for Hyperbaric Chamber 6-3
Supply Hose 5-9
Gatewell Diving {see Dam and Reservoir Diving)
Gauge
Depth 5-20
for Disabled Divers A-2
Submersible Cylinder Pressure 4-11,5-21,14-12
Surface Cylinder Pressure 5-21, 14-14
Testing of 4-12
General Gas Law 2-1 1
Geology, Underwater
Coring 9-27
Drilling 9-27
Experimentation 9-31
NOAA Diving Manual — October 1991
Index
Page
Geology, Underwater (Cont.)
Mapping 9-1,9-22
Sampling 9-11, 9-26
Study Techniques 9-22
Surveying 9-23
Testing 9-31
Gloves, Diver's 5-16, 10-19
Goggles, Diver's 5-24
Goosefish 10-2, 10-3
Gulf Stream 10-2, 10-3
Habitats
Definition of 16-1
Design Features of 17-7
Emergency Procedures for 16-10
History of 1-7
Life Support Systems for 16-8
Non-Saturation 17-17
Operational Procedures for 16-9
Saturation 17-10
Shelters 17-17
Special Problems of 7-7
Uses of 9-32, 17-7
Hand Signals 14-8
Hard-Hat (see Helmet)
Hazardous
Marine Animals (see Animals)
Materials in Habitats 16-12
Hearing
Loss 20-4
UnderWater 2-17
Heat Exhaustion 18-8
Heated Suits (see Suits)
Heatstroke 3-27, 18-8
Heimlich Maneuver 18-3
Helicopter Rescue 19-27
Helium
Decompression 15-4
Definition of 2-6
Effects of, on Speech 15-4
Oxygen Mixtures 15-1, 15-4, 16-8
Thermal Effects of 15-2, 15-4
Helmet
Air Supply 8-9
Diving 1-2,8-4
Lightweight Free-Flow 5-8
Maintenance of 8-8
October 1991 — NOAA Diving Manual
Page
Hemoglobin 3-2
Henry's Law 2-1 1
High Pressure
Air Storage System 14-18
Air Supply for Hyperbaric Chamber 6-5
Nervous Syndrome (HPNS) 3-22, 15-4
Hopcalite 4-4
Hose (see also Umbilical)
Breathing 5-2, 5-4
Gas Supply 5-9
Hot Water 5-10, 5-18
Pneumofathometer 5-9
Regulator 5-5
Hot-Water
Hose 5-10
Suit 5-18
Hydrogen 2-7, 15-2, 15-12
Hydrographic Operations 8-24
Hydroids 12-2
Hydrolab Underwater Habitat 9-32, 9-41, 17-1 1
Hydrostatic
Pressure 2-2
Test (of Cylinders) 4-5
Hyperbaric Chamber
Combustion in 6-14
Deck 16-1
Design and Certification of 6-3
Electrical System for 6-9
Equipment for 6-2
Fire Safety for 6-10
y Gas Supply for 6-3, 6-6
Maintenance of 6-9
Multiplace 6-2
Operation of 6-3
Operator Training for 7-7
Overboard Oxygen Dump for 6-7
Paints for 6-10
Personnel Transfer 16-1
Pressure Test of 6-1 1
Tender 20-14,20-18
Transportable 6-2
Ventilation of 6-6
Hyperbaric Physician Training 7-9
Hypercapnia 3-5
Hyperthermia
from Diving in Superheated Water 1 1-3
from Encapsulation in Diving Suits 1 1-3
from Heatstroke 18-8
Symptoms and Treatment of 3-27
1-7
Index
Page
Hyperventilation
and Breath-holding 3-8
Hypocapnia 3-9
Hypothermia {see also Cold Water)
Causes of 3-24
in Cold Water Near-Drowning 18-8
in Disabled Divers A-10
Protection Against 3-25
Symptoms of 3-25
Treatment of 18-9
Hypoxia
Causes of 20-1
During Altitude Diving 10-27
Effects of 3-5
when Using Rebreathers 15-10, 15-11
Treatment of 20-1
Ice Diving 8-13, 10-6, 10-21
Immunizations 1 1-6
Inert Gas Narcosis {see Narcosis)
Infauna 9-10
Infections
from Diving in Polluted Water 1 1-1
from Wounds 18-10
in Underwater Habitats 7-7
Injuries
Head and Neck 18-9
Spinal Cord 18-9
Instrument Implantation 8-23, 9-32
International
Aircraft-to-Surface-Craft Signals 19-22
Distress Signals 19-20
Isobaric Counterdiffusion {see Counterdiffusion)
Jellyfish
Hazard During Diver Towing 10-36
Poisoning by 18-12
Portuguese Man-o-War 12-2
Sea Wasp 12-2
JIM One-Atmosphere Diving System 17-18
J-Valve 4-11
K-Valve 4-11
Kelp
Diving in 10-22
Geographic Variation in 10-1, 10-5
Sampling of 9-17, 9-18, 9-19
Knife, Diver's 5-14
La Chalupa Underwater Habitat 17-1 1
1-8
Page
Ladders
on Small Boats 10-13
on Stationary Platforms 10-10
Lake Diving 10-13
Lake Lab Underwater Shelter 17-18
Lambertsen/Solus Ocean Systems
Treatment Table 7A Appendix C
Laminar Flow 3-8
Leeway 8-1 1
Lifeline 5-24
Life Support
First Aid Procedures 18-2
Systems for Underwater Habitats 16-8
Life Vest {see Flotation Devices)
Lift Bags 8-26, 9-40
Lifting Devices 8-26
Light
Absorption 2-14
Chemical Tube 5-23
Color of 2-16
Diver's 5-22, 10-18
for Disabled Divers A-2
Physics of Under Water 2-13
Refraction 2-13
Scatter 2-14
Underwater Measurement of 9-7, 9-19
Line
Communication 5-25
Descent or Shot 8-5, 8-13
Distance 8-5
for Disabled Divers A-9
Ground 8-13
Life 8-4
Safety 5-24, 10-15, 10-18, 10-24
Search 8-12
Signal 8-4, 14-8
Lionfish 12-6
Lithium Hydroxide 16-9
Liveboating 8-15, 8-27
Lobsters
Collection of 9-13
Study of 9-13
Tagging of 9-15
Lockers, Shipboard 10-32
Lockout Submersible {see Submersible)
NOAA Diving Manual — October 1991
Index
Page
Lost Diver 16-1 1
Low-Pressure
Air Compressors 4-3
Air Supply for Hyperbaric Chamber 6-5
Air Warning System 4-1 1
Lubricants, Compressor 4-3
Lungs
Capacity of 2-3
Compression of 3-13
Overpressurization of 3-14, 20-17
Squeeze (see Squeeze)
Maintenance and Repair
of Chambers 6-9
of Cylinders 4-7
of Masks 5-8
of Regulators 5-5
of Umbilicals 5-10
Tasks 8-23
Training in 7-1 1
Mapping
Archeological 9-37
Geological 9-22
Maps, Bathymetric 9-1
Mask
Breathing 6-7,6-17
Clearing of A-6
Face 5-7, 5-1 1
Flooding of 19-7
Fogging of 2-13, 5-8, 10-19
for Disabled Divers A-l
Free-Flow Demand 5-6
Full-Face 9-6
Lightweight 5-8
Maintenance of 5-8, 8-8
Oral-Nasal 5-7
Squeeze 20-6
Mediastinal Emphysema 3-14
Medical
Kits 20-20
Officer 7-9, 14-3
Standards for Diving 7-2
Technician 7-8, 14-3
Terms Appendix E
Menopause and Diving 13-2
Menstrual Period and Diving 13-1
Metric to English Conversion Units 2-2
Microbial Hazards 1 1-1
Midwater Sampling 9-1 1
October 1991 — NOAA Diving Manual
Page
Mixed Gas Diving
Definition of 15-1
Equipment for 15-7
Gas Analysis for 15-13
Gas Composition for 15-1
History of 1-3
Mixing Techniques for 15-15
Rebreather (see Rebreather)
Surface-Supplied Equipment for 15-12
Training for 7-6
Modified NOAA Nitrox Saturation
Treatment Table Appendix C
Moisture in Breathing Gas 2-12
Moray Eels 12-9
Motion Picture Photography 8-42
Motion Sickness (see Seasickness)
Mouthpieces 5-4
Mouth-to-Mouth Resuscitation 18-5
Muskrats 12-11
Narcosis
Adjustment to 3-21, 15-2
Causes of 3-20
Symptoms 3-21, 20-3
National Association for Cave Diving 10-19
National Association of Diver
Medical Technicians 7-8
National Speleological Society's
Cave Diving Section 10-19
Navigation, Underwater
Hazards to 8-24
Using Bottom Lines 16-1 1
Using Dead Reckoning 8-16
Using Sonar 8-17
Using Sound 2-17
Near Drowning 18-8, 19-8
Neckstrap 5-24
Nematocysts 12-2, 18-12
Neon 2-7, 15-2, 15-12
Nets
Diving Near 10-34
Gill 9-42,9-46
Plankton 9-8,9-42
Seine 9-42
Trawl 9-42
Neurological Examination of Injured Diver 19-23
1-9
Index
Page
Night Diving 10-27, 16-12
Night Vision 2-15
Nitrogen
Definition of 2-6
Limits for Saturation Diving 16-7, 16-8
Narcosis (see Narcosis)
Oxygen Mixtures 15-1, 15-2, 15-7, 15-10, 16-7
Purity of 15-12
Residual Time 14-23
Uptake and Elimination of 14-19
Nitrox
Mixtures (see Nitrogen-Oxygen Mixtures)
Saturation Diving 16-8
Nitrox-I Mixture 15-7
NOAA
Nitrox-I Diving 15-7, Appendix D
Weather Information 14-4
No-Decompression Diving 14-21
No-Decompression Limits and Repetitive
Group Designation Table for No-Decom-
pression Air Dives Appendix B
Normoxic Breathing Mixtures 15-3
Notice to Mariners 14-4
Oceanography (Physical)
Instrumentation 9-32
Micro-Techniques 9-33
Occupational Safety and Health
Administration (OSHA)
Diving Bell Regulations 17-2
Diving Regulations 7-10
Octopus Regulator System 19-5, A-8
Octopuses 12-5
Omitted Decompression 14-26, 20-13
Open-Circuit Scuba
Description of 5-1
Mixed Gas Systems 15-7
Uses of 14-2
Open Ocean Diving 10-14
Oral-Nasal Mask (see also Mask) 5-7
O-Ring Seals 4-10
Orthopedic Disabilities A-l
Osteonecrosis (see Aseptic Bone Necrosis)
Otitis Externa (Swimmer's Ear) 20-5
Overboard Dump System 6-7
1-10
Page
Oxygen
Analyzer 6-8, 15-14
Blood Transport of 3-2
Breathing 6-7, 14-31, 15-5
Combustion in Chamber 6-14
Concentration 6-6, 15-4, 15-5, 15-9
Consumption 3-2
Decompression 14-26, 15-4
Definition of 2-6
Depth-Time Limits 15-5
Dissolved in Seawater 9-35
Dump System 6-7
Exposure Time 15-3
Flammability of 6-14
Handling of 15-5
Impact of, on Fetus 13-3
Limits 15-5
Mixtures 15-2
Partial Pressure 15-3, 15-9, 15-10, 16-7
Purity of 15-12, 15-13
Rebreather 15-5, 15-10
Replacement in Semi-Closed-Circuit Scuba 15-9
Safety Precautions for 6-11, 15-5, 15-10
Service, Cleaning for 15-7
Tissue Requirements for 3-4
Tolerance Tests 3-24, 15-3, 20-19
Toxicity 3-22, 15-2, 15-3, 15-5, 15-12, 16-7, 20-2
Transport of, in Blood 3-2
Use in Saturation Diving 16-8
Paint, Toxic 8-23
Panic
Causes of 19-1
Signs of 19-1
Paralyzed Tissue A-l 1
Paraplegia (Paraparesis) A-l
Partial Pressure
Blood 3-4
Closed-Circuit Scuba 15-10
Dalton's Law 2-7
Definition of 2-3, 15-15
Gas Mixing by 15-15
Henry's Law 2-1 1
of Carbon Dioxide 3-4
of Oxygen 3-2
Pathogens 11-1
Personnel Transfer Capsule (PTC) 16-1,17-1
Phase Measurement 9-5
Photogrammetry 9-4
Photography, Underwater
Film for 8-38, 8-42
Flash Units for 8-36
NOAA Diving Manual — October 1991
Index
Page
Photography, Underwater (Cont.)
for Estimating Planktonic Density 9-12
Macro Method of 8-34, 8-36
Motion Picture 8-42
of Dyed Water Mass 9-34
Still 8-33
Time Lapse 8-41
Physical Examination
of Decompression Sickness Patients 20-13
of Divers 7-1, 11-6
Physical Oceanography 9-32
Pingers
Attached to Remotely Operated Vehicle 17-20
for Navigation 8-17
for Relocation of Instruments 8-24
for Shellfish Tracking 9-15
for Surveys 9-4
Plankton
Blooms 10-4
Density Estimation of 9-12
Nets 9-42
Preservation of 9-9
Sampling of 9-8, 9-33
Planning for Dives 8-1, 14-1
Pneumofathometer
Hose 5-9
Pressure Gauge 5-21
Pneumothorax
Causes of 3-14
Treatment of 20-17
Poiseuille's Equation for Gases 2-12
Poisoning
Carbon Dioxide 20-1
Carbon Monoxide 20-2
Ciguatera 12-11, 18-13
Fish 12-11, 18-12, 18-13
Oxygen (see Oxygen Toxicity)
Shellfish 12-11, 18-14
Pollutants, Airborne 4-1
Polluted-Water Diving
Chemical Hazards of
Equipment for 1 1-2,
Immunizations for
Microbial Hazards of
Procedures for
Thermal Hazards of
Training for
Portuguese Man-o-War
Power Head
October 1991 — NO A A Diving Manual
11-1
11-3
11-6
11-1
11-5
11-3
. 7-6
12-2
5-24
Page
Pregnancy and Diving
Birth Defects 13-3
Diving While Pregnant 13-4
Physiological Effects on Fetus 13-3
Pressure
Absolute 2-2
Atmospheric 2-2
Barometric 2-2
Conversions to Altitude and Depth 2-4
Definition of 2-1
Effects of 3-10
Equalization of 3-1 1
Gauge 2-3
Hydrostatic 2-2
Partial (see Partial Pressure)
Tests for Chamber 6-1 1
Waves Under Water 2-17
Pressure Points 18-7
Propulsion of Disabled Divers A-8
Prostheses for Divers A-3
Protective Clothing (see also Suits)
Pulmonary Oxygen Toxicity (see Oxygen Toxicity)
PVHO (Pressure Vessel for Human Occupancy)
(see Hyperbaric Chamber)
Quadrats 9-7, 9-9
Quadriplegia (Quadriparesis) A-l
Quarries 10-14
Quinaldine (Fish Anesthetic) 9-43
Radio
Citizens' Band 19-20
VHS 19-21
Weather 14-6, 19-21
Rays 12-5
Rebreather
Closed-Circuit 15-10
Mixed Gas 15-10
Oxygen 15-5, 15-10
Semi-Closed-Circuit 15-8
Recompression Chamber (see Hyperbaric Chamber)
Recompression Tables Appendix C
Recording Methods
Slates 9-5
Tape Recorders 9-6
Underwater Paper 9-5
Reefs
Artificial 9-20
Coral 10-10
Fish Collection on 9-44
1-11
Index
Page
Refraction of Light Under Water 2-13
Regional Diving 10-1 to 10-7
Regulator
Antifreeze Agent 10-19
Demand 4-10, 5-1
for Disabled Divers A-l, A-6
Freezing of 10-19
Loss of 19-7
Maintenance of 5-5
Neckstrap 5-24
Octopus 19-5
One-Stage 5-2
Single-Hose 5-2
Two-Hose 5-2
Two-Stage 5-2
Remotely Operated Vehicles (ROV's) 17-20
Reptiles
Alligators 12-11
Crocodiles 12-11
Turtles 12-10
Rescue Chambers 6-2
Rescue Procedures
Assessing the Problem 19-8, 19-10
Do-Si-Do 19-10
for Removing a Victim from Water 19-18
for Towing a Diver 19-11, 19-17
for Uncontrolled Descent or Ascent 19-15
for Victim on the Surface 19-16
Helicopter 19-27
Mouth-to-Snorkel 19-12
Research Diver
Selection 7-10
Training 7-10
Residual Nitrogen 14-23
Residual Nitrogen Timetable for
Repetitive Air Dives Appendix B
Respiration
Mechanism of 3-2
Minute Volume During Work 14-12
Summary of Process 3-4
Resuscitation
Artificial 18-5, 19-10
Bag-Valve-Mask 18-5
Cardiopulmonary (CPR) 18-6
Mouth-to-Mouth 18-5, 19-10
Mouth-to-Snorkel < 19-12
River Diving 10-31
Rock
Outcrop 9-27
Samples 9-26
1-12
Page
Round Window (see Ear)
Royal Navy Treatment Table 71 Appendix C
Royal Navy Treatment Table 72 Appendix C
Safety
Diver (Open Ocean) 10-15
Line 5-24, 10-18, 10-21, 10-24
Reel 10-18
Salvage
Methods 8-26,9-38
Rights 9-40
Sam (One Atmosphere Diving System) 17-18
Sampling
Advantages of 9-8
Airlift , 8-27, 9-1 1
Archeological 9-37
Benthic 9-9
Biological 9-8
Botanical 9-17
Core 9-27 to 9-30
Geological 9-11, 9-26
Infauna 9-10
Midwater 9-11
Plankton 9-8,9-33
Rock 9-26
Sediment 9-29
Substrate 9-10
Water 9-34
Sanctuaries, Marine 10-5, 10-7
Saturation
Decompression from 16-13
Diving from Underwater Habitats 17-7
Excursions During 16-9 to 16-12
Flying After 16-14
Gas Mixtures 16-7
History of 1-6
Life Support Systems for 16-8
Principles of 16-1
Sanitary and Health Measures for 16-12
Summary of Exposures 16-2
Surface-Based Diving System 16-1
Training for 7-7
Scatter (Light) 2-14
Science Coordinator 10-32, 14-3
Scorpionfish 12-6
Scripps Institution of Oceanography 7-10
Scrombroid Poisoning 18-14
Scrubber Systems 15-8, 16-9
NOAA Diving Manual — October 1991
Index
Scuba
Air Requirements 14-16
Auxiliary Cylinders 19-5
Closed-Circuit 1-4
Closed-Circuit Oxygen 1-4
Duration of Air Supply 14-13
Open-Circuit 5-1
Semi-Closed-Circuit {see Rebreather)
Training 7-3
Sculpins 12-6
Sea
Anemones 12-3
Lions 10-4, 12-1 1
Sickness 18-1 1
Snakes 12-7, 18-13
States 14-6
Urchins 12-5, 18-13
Wasps 12-3
Seafood Poisoning 12-1 1
Seals 12-11
Search and Recovery
Acoustic Methods 8-10
Arc Method 8-13
Circular Method 8-13
in High Currents 8-13
Jackstay Method 8-13
Patterns 8-10
Under Ice 8-13
Using a Tow Bar 8-15
Seawater, Characteristics of 2-1
Sediment
Coring of 9-30
Sampling of 9-29
Seines 9-42, 10-34
Self-Contained
Diving 14-13
Emergency Gas Supply 5-8
Sextant 9-1
Sharks
Dangerous 12-8
Defense Against 5-24
Encountered During Open Ocean Diving 10-17
Shellfish
Collecting of 9-13
Poisoning by 12-11, 18-14
Study of 9-13
Tagging of 9-15
Shelters, Underwater {see Habitats)
Shipboard Diving (Under Way) 10-32
October 1991 — NOAA Diving Manual
Page
Shipwrecks
Excavation of 9-37
Location of 9-37
Shock
Electric, by Marine Animals 12-11
Following Trauma 18-7
from Electrical Equipment 18-11
Hypovolemic 3-19
Treatment of 18-7
Wave 8-31
Signals
Aircraft 14-8
Aircraft to Surface 19-22
Audio 14-8
Devices for 5-22
Distress 19-20
Diving 14-8
Emergency Visual 19-22
Flag 14-9
Flare 5-23
for Disabled Divers A-4
Hand 14-10
Line 14-8
Radio 19-21
Recall 14-8
Surface 14-8
Whistle 5-23
Sinus
Anatomy of 3-12
Squeeze {see Squeeze)
Site
Marking 9-1
Relocation 9-31
Selection 9-1
Survey 9-1
Skip-Breathing 3-6
Slate (Underwater) 5-22, 9-5
Sled (Diver) 8-15, 10-34
Slurp Gun 9-46
Smoking
Effects of 3-7
in Hyperbaric Chambers 6-1 1
Snakes 12-7
Snorkel
and Breathing Resistance 3-8
Description of 5-19
for Artificial Resuscitation 19-12
for Disabled Divers A-l, A-6
Soda Lime (SodasorbR) 15-8, 16-9
1-13
Index
Page
Sonar
Danger to Divers 2-17
Hand Held 9-4
Side Scan 8-1 1
Use for Diver Navigation 8-17
Sound
Navigation Under Water 2-17
Transmission of, Under Water 2-16
Velocity in Water 9-4
Specific Gravity
Definition of 2-1
of Seawater 2-2
Specimen Preparation 9-19
Speech Intelligibility in Habitats 7-7
Spinal Cord
Cervical Control 18-5
Injury 18-3, 18-9
Squeeze
External Ear 20-8
Eye 20-6
Face Mask 20-6
Lung 3-13,20-8
Middle Ear 3-10, 20-6
Sinus 3-12,20-7
Tooth 3-14
Staggers 3-18
Standard Air Decompression Table Appendix B
Stinging Marine Animals 12-1
Stingrays 12-5
Stings 12-1, 18-12
Stonefish 12-6
Strike (of Rock Bed) 9-26, 9-28
Subcutaneous Emphysema 3-15
Subigloo Underwater Shelter 17-18
Sublimnos Underwater Shelter 17-18
Submersible
Cylinder Pressure Gauge 4-11, 5-21
Free-Flooded 17-5
Lockout (Wet) 1-7, 16-1, 17-3
Suits
Dry '. 5-16
for Cold Water 5-16
for Disabled Divers A-l
for Polluted-Water Diving 1 1-3, 1 1-4
History of 1-3
Hot-Water 5-18, 10-19
1-14
Page
Protective 5-14
Suit Under Suit (SUS) 1 1-4
Variable- Volume Dry Suit 5-17, 10-19
Wet 5-15, 10-19
Sunburn 18-10
Supersaturation (of Blood and Tissues) 3-17
Support Divers 14-3
Support Platforms 10-10, 10-32
Unanchored 8-27
Underwater 17-1
Surf
Diving Through 10-7
Exiting with Injured Diver 19-19
Geographical Variation in 10-1 to 10-6
Surface Decompression 14-26
Surface Decompression Table
Using Air Appendix B
Surface Decompression Table
Using Oxygen Appendix B
Surface Interval 14-24
Surface-Supplied Diving (see also Umbilical Diving)
Advantages of 8-1
Air Requirements for 8-9, 14-18
Ascent During 8-7
Communications for 9-6
Dressing for 8-2
Emergencies 8-5
Environmental Checklist for 8-1
Equipment for 5-6
from Diving Bell 17-2
History of 1-2
in Polluted Water 1 1-4
Mixed Gas Equipment for 15-12
Planning for 8-1
Post-Dive Procedures 8-8
Shipboard 10-33
Team Selection for 8-2
Tender for 8-4, 14-3
Training for 7-5
Under Ice 10-22
Weighting for 5-1 1
Surgeonfish 12-7
Surveys
Acoustic 9-4
Archeological 9-37
Bathymetric 9-3
Biological 9-6
Bottom 9-3
Direct Methods 9-2
NOAA Diving Manual — October 1991
Index
Page
Surveys (Cont.)
Geological 9-23
Indirect Methods 9-3
Oceanographic 9-32
Phase Measurement 9-5
Photographic 9-3
Underwater 9-2
Survival (in Cold Water) 3-26
Swimmer Propulsion Unit 17-18
Swimmer's Ear (see Otitis Externa)
Swimming Skills 7-3
Tachycardia Appendix E
Tagging Techniques 9-14
Tanks for Disabled Divers A-2
Tape Recording Under Water 9-6
Teeth 3-14
Tektite Underwater Habitat 17-1 1
Telemetry 8-16
Telephone, Emergency Numbers 14-3
Telescope (Underwater) 9-7
Television, Underwater
Equipment Selection 8-44
Low-Light Level 8-46, 14-7
Temperature
Core 3-24
Definition of 2-1
Geographic Variation in 10-1 to 10-7
Regulation in Women 13-2
Water 5-16, 14-5
Temporal Mandibular Joint (TMJ) Pain 5-4
Tender
Hyperbaric Chamber 20-19
Ice Diving 10-21
Shipboard 10-33
Surface-Supplied Diving 8-2, 8-4
Training and Qualifications 14-3
Tether
for Open-Ocean Diving 10-15
for Under-Ice Diving 10-22
Shipboard 10-33
Thermal Protection (see also Suits) 3-25
Thermocline
Geographical Variation in 10-1 to 10-7
Impact of, on Selection of Equipment 14-5
Measurement of 9-34
October 1991 — NOAA Diving Manual
Page
Tidal
Air 3-2
Current 10-9
Volume 10-9
Timing Devices 5-20
Tinnitus 20-4
Tools (Underwater) 8-18, 9-27, 9-29
Topographic Charts 9-1
Torpedo Ray 12-11
Tourniquet 18-7
Towing
Diver 10-34 to 10-37
Rescue Techniques 19-17
Toxic Substances
in Habitats 7-7
Oxygen (see Oxygen)
Trachea Appendix E
Training
Chamber Operator 7-7
Disabled Diver A-4
Diving Medical Technician 7-8
Diving Supervisor 7-8
for Contaminated Water Diving 7-6
for Equipment Maintenance and Repair 7-1 1
for Mixed-Gas Diving 7-6
for Use of Special Equipment 7-6
for Use of Variable- Volume Dry Suit 7-6
Hyperbaric Physician 7-9
Research Diver 7-10
Saturation Diver 7-7
Scuba Diver 7-3, 19-2
Surface-Supplied (Umbilical) Diver 7-5
Women Divers 13-4
Transect
for Estimating Population Density 9-12
for Photography 9-4
Transponder 9-4
Transportable Rescue Chamber 6-2
Traps 9-41
Trawls
Description of 9-42
Diving Near 10-34
Measurement of Efficiency 10-36
Treatment
at Site of Accident 19-22
Costs of 19-19
of Airway Obstruction 18-3
of Bleeding 18-7
1-15
Index
_ 51751*5
Treatment (Cont.)
of Blowup Victims 8-6
of Burns 18-10
of Cardiac Arrest 18-5
of Coral Wounds 18-13
of Decompression Sickness 20-8, 20-12
of Ear Squeeze 20-6
of Embolism 20-8
of Emphysema 20-17
of Fractures 18-5, 18-1 1
of Injuries and Infection 18-9
of Lung Squeeze 20-8
of Near Drowning 18-8
of Otitis Externa (Swimmer's Ear) 20-5
of Pneumothorax 20-17
of Poisoning 18-12, 18-14, 20-1, 20-2, 20-3
of Seasickness 18-1 1
of Sea Urchin Wounds 18-13
of Shock 18-7
of Sinus Squeeze 20-7
of Stings 18-12
of Vertigo 20-4
of Wounds 18-10
Treatment Tables Appendix C
Trendelenberg Position 19-22
Tropical Diving 10-6
Turtles 12-10
Tympanic Membrane 3-11
Umbilical
Assembly 5-8
Hoses 5-9
Maintenance 5-10
Storage 5-10
Weighting 5-11
Umbilical Diving
Air Supply 8-9
Dressing for 8-3
Emergencies 8-5
from Small Boats 8-8
Procedures for 8-1, 8-8
Tending for 14-3
Training for 7-5
Uses of 14-2
Unconscious Diver 19-10, 20-18
Undersea and Hyperbaric Medical Society, Inc 7-9
Underwater Classroom Habitat , 17-17
Upwelling 10-5
U.S. Coast Guard
Diving Bell Regulations 17-2
Emergency Assistance from 19-20
1-16
Page
USIC (Undersea Instrument Chamber) 9-32
U.S. Navy
Air Purity Guidelines 15-1 1
Decompression Tables Appendix B
Experimental Diving Unit 14-3
Gas Analysis Equipment 15-14
Gas Mixing 15-15
Helium-Oxygen Diving 16-7
National Naval Medical Center 14-3
No-Decompression Limits and Repetitive Group
Designation Table for No-Decompression
Air Dives Appendix B
Recompression Treatment Tables Appendix C
Residual Nitrogen Timetable for Repetitive
Air Dives Appendix B
Standard Air Decompression Table Appendix B
Surface Decompression Table Using
Air Appendix B
Surface Decompression Table Using
Oxygen Appendix B
Treatment Table 5 Appendix C
Treatment Table 6 Appendix C
Treatment Table 6A Appendix C
Treatment Table 7 Appendix C
Treatment Table 1A Appendix C
Treatment Table 2A Appendix C
Treatment Table 3 Appendix C
Treatment Table 4 Appendix C
Underwater Tools.... 8-20
Valsalva Maneuver 3-11, 20-4
Valves
Air Inlet 5-3
Check 5-5,5-8
Cylinder 4-10
Demand (History of) 1-4
Demand (Scuba) 4-10
Downstream 5-2
Exhaust 5-5, 5-17
Flapper 5-5
in Chamber 6-6
J 4-11
K 4-11
Mushroom 5-3, 5-5
Non-Return 5-2
Pilot 5-3
Piston 5-2
Reserve 4-1 1
Upstream 5-2
Vane Sheer Test 9-31
Variable- Volume Dry Suit (see also Suits)
Description of 5-17
Training in Use of 7-6
Venomous Fishes 12-5
NOAA Diving Manual— jOfttober 1 99 1
Index
Page
Ventilation
Chamber 6-6 to 6-8
Pulmonary 3-2
Veiugo 20-4
Vestibular
Balance System 3-10
Decompression Sickness 3-12
Viscosity
and Gas Flow 2-12
of Seawater 2-2
Visibility
Geographical Variation in 10-1 to 10-7
of Colors Under Water 2-14
Underwater Conditions Affecting 8-2,14-5,14-6
Underwater Physics of 2-13
Vision Under Water 2-1, 2-15, 5-7
Vital Capacity 3-2, 16-8
WASP One-Atmosphere Diving System 17-19
Watch, Diver's 5-20
Water
Density 2-1
Entry and Exit 10-7, 10-10, 10-1 1
Jet Excavation of 9-38
Page
Polluted 11-1
Samples 9-34
Specific Gravity of 2-1
Temperature 2-1, 10-1 to 10-6
Withdrawal and Pumping Sites 10-30
Waves
Geographic Variation in 10-1 to 10-7
Surface 10-7
Weather
Conditions 14-4
Information 14-4, 14-6, 19-21
Weight Belt 5-14, A-2
Welding, Underwater 8-22
Wet Sub {see Submersible)
Wet Suit {see Suits)
Whales 12-11
Whistle 5-23
Wire Dragging 8-25
Women Divers 13-1
Wounds 18-10
Wreck Diving 9-37, 10-23
October 1991 — NOAA Diving Manual
1-17
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