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Diving manual 



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Digitized by the Internet Archive 

in 2012 with funding from 

LYRASIS Members and Sloan Foundation 




October 1991 

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Sr AT ES O* ^ 

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. 



















































































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 


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: 


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 


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. 


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 

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: 


NOAA's Undersea Research Program, R/OR2 
1335 East-West Highway, Room 5262 
Silver Spring, Maryland 20910 

David B. Duane, 



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 
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 


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. 


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. 

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 


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 





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 


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 



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 


List of Figures 




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 



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 




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 N 2 -0 2 Mixtures 6-15 


List of Figures 


6-6 Combustion in N->-Ot Mixtures Showing the 

Zone of No Combustion 6-16 



No Figures 



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 



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 


List of Figures 


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 


List of Figures 




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 


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 



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 


List of Figures 


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 


13-1 Scientist on Research Mission 13-5 



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 



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 


No Figures 

List of Figures 




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 



18-1 Life-Support Decision Tree 18-2 

18-2 Jaw-Lift Method 18-4 

18-3 Bag-Valve-Mask Resuscitator 18-6 




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 


List of Figures 


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 




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 





No Tables 


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 



3-1 Carboxyhemoglobin as a Function of 

Smoking 3-8 

3-2 Narcotic Effects of Compressed Air Diving 3-22 



4-1 Composition of Air in its Natural State 4-1 



No Tables 




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 


List of Tables 




No Tables 



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 



9-1 Micro-Oceanographic Techniques 9-33 

9-2 Levels of Anesthesia for Fish 9-44 

9-3 Fish Anesthetics 9-47 



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 


No Tables 

List of Tables 




No Tables 


No Tables 



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 ft 3 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 



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% N 2 , 32% 2 ) 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 


List of Tables 



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 



17-1 Desirable Features of Underwater Habitats 17-1 1 



No Tables 




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 




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 












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 





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. 


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. 


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 


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 


Photos courtesy Suk Ki Hong 


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). 


The development of self-contained underwater breathing 
apparatus provided the free moving diver with a portable 


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 


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 

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 


Section 1 

Figure 1-7 

World War II Military Swimmer Dressed in 

Lambertsen Amphibious Respiratory Unit 

Courtesy C. J. Lambertsen 


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- 


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. 


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 









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 Refraction 2-13 Scatter 2-14 Absorption 2-14 Insufficient Light 2-15 

2.9 Acoustics 2-16 








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. 


This paragraph defines the basic principles necessary 
to an understanding of the underwater environment. 
The most important of these are listed below. 




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: 


(°F - 32) 

2.1.1 Pressure 

Pressure is force acting on a unit area. Expressed 

Pressure = 



P = 

Pressure is usually expressed in pounds per square inch 
(psi) or kilograms per square centimeter (kg/cm 2 ). 

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, 

2.1.3 Density 

Density is mass per unit volume. Expressed mathe- 

Density (D) = 


Density is usually stated in pounds per cubic foot (lb/ft 3 ) 
in the English system and in grams per cubic centi- 
meter (gm/cm 3 ) 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 

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 

October 1991 — NOAA Diving Manual 


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. 


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/cm 2 . At higher elevations, this value decreases. 
Pressures above 14.7 psi (1.03 kg/cm 2 ) 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/cm 2 per 9.75 meters) of 

To Convert 
Metric Units 

To English Units 

Multiply By 


1 gm/cm 2 

1 kg/cm 2 

1 kg/cm 2 

1 kg/cm 2 

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 



1 cc or ml 

1 m 3 
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) 





1 gram 



ounce (oz) 
pounds (lb) 



1 cm 
1 meter 
1 meter 
1 km 




1 cm 2 

1 m 2 
1 km 2 

square inch 
square feet 
square mile 


Adapted from NOAA (1979) 

descent in seawater and 0.432 psi per foot (1 kg/cm 2 
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 


NOAA Diving Manual — October 1991 

Physics of Diving 

Table 2-2 

Conversion Table for Barometric Pressure Units 


N/m 2 or 



kg/cm 2 

gm/cm 2 
(cm H 2 0) 

mm Hg 

in. Hg 

lb/in 2 

1 atmosphere 



1.013X10 5 








1 Newton (N)/m 2 or 
Pascal (Pa) 


9869X10" 5 


10 5 


1.02X10' 5 



2953X10" 3 

.1451X10" 3 

1 bar 



10 5 








1 millibar 


9869X10" 3 









1 kg/cm 2 



9807X10 5 








1 gm/cm 2 
(1 cm H 2 0) 




9807X10' 3 







1 mm Hg 











1 in. Hg 











1 lb/in 2 (psi) 











Adapted from NOAA (1979) 

submerged body. Absolute pressure is measured in 
pounds per square inch absolute (psia) or kilograms 
per square centimeter absolute (kg/cm 2 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/cm 2 . 

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). 


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 m 3 ). Seawater is heavier, having a density of 64.0 
pounds per cubic foot (29 kg/0.03 m 3 ). 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 


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 

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 

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 

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 

100 200 300 400 500 600 700 800 900 1013.2 

Newtons Per Square Meter x10 4 (n/m 2 x10 4 ) 

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 

i i i i i i m i 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 

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 

20 40 60 80 

50 100 150 200 250 300 
I ■ I I I I I I I I I 


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. 


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 ' 
Vi its 

At 1 32 Feet 

5 Atmospheres Absolute, 73.5 psi 
X A 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) 


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. 


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 

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 


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 

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 (C0 2 ) 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 
C0 2 at increased partial pressure may cause uncon- 
sciousness (see Sections and 20.4.1). For example, 
a person should not breathe air containing more than 
0.10 percent C0 2 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 C0 2 generated by 
the diver's breathing is essential to diving safety 
(see Sections and 

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). 


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: 

P Total = PPl + PP2 + PPn 


P Tola l = total pressure of that gas 

Ppi = partial pressure of gas component l 

Pp 2 = partial pressure of gas component 2 

Pp n = partial pressure of other gas components. 

An easily understood example is that of a container 
at atmospheric pressure, 14.7 psi (l kg/cm 2 ). 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 

Percent of Component x Total Pressure (Absolute) 
= Partial Pressure 


Percent of 

partial pressure 

N 2 

o 2 

co 2 










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 

Step 1 — Dalton's Law 

Percent of component gas X total pressure (abso- 
lute) = partial pressure 

Percent of com 


N 2 


.7808 N 2 


o 2 


.2095 2 


co 2 


.0003 C0 2 




.0094 Other 


Step 2 — Convert 2000 psi to atmospheres absolute 

(2000 psi) 

+ 1 = ATA 

14.7 psi 

136 + 1 = 137 ATA 

October 1991 — NOAA Diving Manual 


Section 2 

Step 3 — Partial pressure of constituents at 137 ATA 
Pp N = 0.7808 X 137 = 106.97 ATA 

Pp = 0.2095 X 137 = 28.70 ATA 

Pp co = 0.0003 X 137 = 0.04 ATA 

p P0ther = 00094 X 137 = 1.29 ATA 

Observe that the partial pressures of some compo- 
nents of the gas, particularly C0 2 , 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): 

P 2 V 2 = K 

P 2 = pressure at 33 feet in ATA 
V 2 = volume at 33 feet in ft 3 
K = constant. 

Step 3 — Equating the constant, K, at the surface and 
at 33 feet, we have the following equation: 

P.V, = p 2 v 2 

Transposing to determine the volume at 33 feet: 




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 


P 1 = 1 atmosphere (ATA) 

V, = 24 ft 3 

v 2 = 

2 ATA 

24 ft 3 

1 ATA X 24 ft 3 

2 ATA 

V 2 = 12 ft 3 . 

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 ft 3 
K = constant. 

Step 4 — Using the method illustrated above to deter- 
mine the air volume at 66 feet: 



P, = 3 ATA 

v 3 - 

1 ATA X 24 ft 3 

3 ATA 

V 3 = 8 ft 3 . 

Step 5 — For a 99-foot depth, using the method illus- 
trated previously, the air volume would be: 

v 4 = 



p 4 = 4 ATA 

V, = 6 ft 3 . 



NOAA Diving Manual — October 1991 

Physics of Diving 


Figure 2-3 
Boyle's Law 

October 1991 — NOAA Diving Manual 

Adapted from NOAA (1979) 


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) 


Pj = 14.7 psia (atmospheric pressure) 
T, = 80°F + 460°F = 540 Rankine 
T 7 = 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) 


P 2 = 

P.T 2 

P, _ 

14.7 X 493 

r 2 — 


P 2 = 

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) 


P( = initial pressure (absolute) 
P 2 = final pressure (absolute) 
Tj = initial pressure (absolute) 
T 2 = final pressure (absolute) 
V, = initial volume 
V 2 = 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 

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: 


Vj = volume at depth, 6 ft 3 

T, = 80 °F + 460 °F = 540 Rankine 

T 2 = 45 °F + 460 °F = 505 Rankine. 


NOAA Diving Manual — October 1991 

Physics of Diving 


V — 

V,T 2 

v 2 


V — 

6 X 505 


V, = 

5.61 ft 3 . 

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: 




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 

The formula for Henry's Law is: 


= aP, 



VG = volume of gas dissolved at STP 

(standard temperature and pressure) 

VL = volume of the liquid 

a = Bunson solubility coefficient at specified 

P| = partial pressure in atmospheres of that 
gas above the liquid. 

P, = initial pressure (absolute) 

V, = initial volume 

T| = initial temperature (absolute) 


P 2 = final pressure (absolute) 

V 2 = 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 2 v 2 



P, = 14.7 psia 

V, = 24 ft 3 

T, = 80°F + 460°F = 540 Rankine 

P 2 = 58.8 psia 

T 2 = 45 °F + 460 °F = 505 Rankine. 


V, = 


PiV.T 2 


V, = 5.61 ft 3 . 

October 1991 — NOAA Diving Manual 


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. 


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 = 

APr 4 7r 


V = gas flow, in cm 3 • sec 1 

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). 


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 



Note: Effects of gravity 
and water vapor are not 
considered in the illustration 
because they are so sma 









19. 3 


2 ATM 









3 ATM 






1 r 



(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 

Adapted from NO A A (1979) 

NOAA Diving Manual — October 1991 



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 

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) 


2.8.1 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. 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 

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 


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). 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). 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 


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 

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. 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- 

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 


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, 

Fluorescent yellow, orange, 
and red 

Yellow, orange, red, white 
(no advantage in fluorescent 

yellow-green and 

Regular yellow, orange, and 

Regular yellow, white 

Moderately turbid water 
(sounds, bays, coastal 

Any fluorescence in the 
yellows, oranges, or reds 

Any fluorescence in the 
yellows, oranges, or reds 

yellow-green or 

Regular paint of yellow, 
orange, white 

Regular paint of yellow, 
orange, white 

Regular yellow, white 

Clear water (Southern 
water, deep water offshore, 

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. 


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 


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 









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 Pulmonary Ventilation 3-2 Blood Transport of Oxygen and Carbon Dioxide 3-2 Gas Exchange in the Tissues 3-4 Tissue Need for Oxygen 3-4 Summary of Respiration Process 3-4 

3.1.3 Respiratory Problems 3-5 Hypoxia 3-5 Carbon Dioxide Excess (Hypercapnia) 3-5 Carbon Monoxide Poisoning 3-6 Smoking 3-7 Excessive Resistance to Breathing 3-8 Excessive Dead Space 3-8 Hyperventilation and Breath-holding 3-8 

3.2 Effects of Pressure 3-10 

3.2.1 Direct Effects of Pressure During Descent 3-10 The Ears 3-10 The Sinuses 3-12 The Lungs 3-13 

3 2.1.4 The Teeth 3-14 

3.2.2 Direct Effects of Pressure During Ascent 3-14 Pneumothorax 3-14 Mediastinal Emphysema 3-14 Subcutaneous Emphysema 3-15 Gas Embolism 3-15 Overexpansion of the Stomach and Intestine 3-16 Bubble Formation and Contact Lenses 3-16 

3.2.3 Indirect Effects of Pressure 3-16 Inert Gas Absorption and Elimination 3-16 Decompression Sickness 3-17 Counterdiffusion 3-19 Aseptic Bone Necrosis (Dysbaric Osteonecrosis) 3-20 Inert Gas Narcosis 3-20 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 






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). 


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 




Sphenoidal Sinus 

Hard Palate 


Larynx (Voice Box) 

Trachea (Windpipe) 
Alveoli Bronchial 

(Naso-Pharyngeal Tonsil) 

Soft Palate 

Esophagus (Food Tube) 
Right Lung 







Cut Edge 
of Pleura 


Cut Edge of 


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, 


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 


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. 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. 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 


Lung capillaries 

Tricuspid -f^lt 


Bicuspid valve 


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 

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. 


Section 3 

Figure 3-3 

Oxygen Consumption and 
Respiratory Minute Volume 
as a Function of Work Rate 


.E (20) 


"5 ^ 

= c 1.4 

8 I (40) 


E *■ 
2 ° 







S S. I Rest 
Sitting Quietly!* 



Heavy Work 

Severe Work 

Swim, 0.5 Knot 


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) 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. 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 Summary of Respiration Process 

The process of respiration includes six important 

(1) Breathing or ventilation of the lungs; 

(2) Exchange of gases between blood and air in the 

(3) The transport of gases carried by the blood; 


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. 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 

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. 


There Is No Natural Warning That Tells a Diver 
of the Onset of Hypoxia 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 


Section 3 

Figure 3-4 

Relation of Physiological Effects to Carbon 

Dioxide Concentration and Exposure Period 






\ Zone IV Dizziness, stupor, unconsciousness 

\ Zone III Distracting discomfort 

^^^^ Zone II Minor perceptible changes """"""■■"■——««», 


Zone I No effect 
I I I I I I I 

PC0 2 ATA 

10 20 30 40 50 60 70 
Exposure Time, minutes 

40 Days 


8 5 

6 .£ 




A • 


3 CM 



2 .o 


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. 


Skip-Breathing Is Not a Safe Procedure 
Because Carbon Dioxide Buildup Can Occur 
With Little or No Warning 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 


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 a f > 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 

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. 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 

Continuous Exposure 

Level of 

HbCO in Blood 

CO, ppm 













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 


Section 3 

Table 3-1 

Carboxyhemoglobin as a 
Function of Smoking 




Smoking Habits 

Level, % 

CO, ppm 

Light smoker (less than Vz pack/ 




Moderate smoker (more than Vz 

pack/day and less than 2 




Heavy smoker (2 packs or more/ 




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. 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- 


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 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). 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 

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). Hyperventilation and Breath-holding 

The respiratory system utilizes both carbon dioxide 
(C0 2 ) and oxygen (0 2 ) 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 

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 

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 


Section 3 


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. 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) 

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 


NOAA Diving Manual — October 1991 

Diving Physiology 

Figure 3-6 
Principal Parts 
of the Ear 

Semicircular canals 


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. 


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 


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 

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. 


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. 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 



Orbit Of Eye 




Opening To 





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 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) 


Section 3 

breathing, either voluntarily by breath-holding or invol- 
untarily because of windpipe or tracheal obstruction 
or convulsions. 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 


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. 


Do Not Hold Breath While Ascending 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. 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 


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 


Air Passes Along 
Bronchi To 

Air Enters- 
Pleural Cavity 

Air Enters 
Blood Vessel 


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. 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. 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 

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 


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. 


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). 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. 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. Inert Gas Absorption and Elimination 

While breathing air at sea level, body tissues are 
equilibrated with dissolved nitrogen at a pressure equal to 


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 

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. 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 


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- 


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 

(A) Steady State- 

( o o 1 

o o 

o ° ° o o 

°n\° o 

o I o ) ^-^ o 

o \ £Jftt&CQ 

°y^M \. 




r /•JZWv 









° •* 0-**° o 

(B) Transient 

O Gas 1 
• Gas 2 



• • 



*f \ 

I 1 

* 'W° • 




Q¥sV\ !• 


Jfe • 


L-^O/fcr^ 1 • 


cs*r°* 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 


Section 3 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 


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 

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). 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 


Section 3 

Table 3-2 
Narcotic Effects of 
Compressed Air Diving 







Mild impairment of performance on unpracticed tasks 
Mild euphoria 



Reasoning and immediate memory affected more than motor coordination and 
choice reactions. Delayed response to visual and auditory stimuli 



Laughter and loquacity may be overcome by self control 
Idea fixation and overconfidence 
Calculation errors 



Sleepiness, hallucinations, impaired judgment 



Convivial group atmosphere. May be terror reaction in some 
Talkative. Dizziness reported occasionally 
Uncontrolled laughter approaching hysteria in some 



Severe impairment of intellectual performance. Manual dexterity less affected 



Gross delay in response to stimuli. Diminished concentration 

Mental confusion. Increased auditory sensitivity, i.e., sounds seem louder 



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 



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.) 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 


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). 


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 


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- 

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. 


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 


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 


Section 3 

Figure 3-11 

Effect of Exposure Duration on 
Psychomotor Task Performance 
in Cold Water 







E - 


O I 






20 - 




Proper Decrement Curve 

Type Task 

Water Temperature "[ 





Fine Digital 










Gross Body & 
Power Move. 





,OStang& Wiener (1970) 

' * Bowen (1968) 

O Weltman & Egstrom Et Al (1970) 
D Weltman & Egstrom Et Al (1971) 








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 

• 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): 



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 

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). 


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 


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 


Section 3 

with water poured over the skin until the body temper- 
ature returns to normal. 


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 

• 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 

• 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). 


While taking medication, therefore, careful consid- 
eration should be given to the following elements before 

• Why are the drugs being used, and are there underly- 
ing medical conditions that may be relatively or 
absolutely contraindicated for divers (Kindwall 

• 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 






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 








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. 


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 


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 

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 

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 


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 

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 

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 

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 

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. 


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. 


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. 


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 



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- 

• 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 

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 


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 

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- 

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 


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 

• 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. 


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/cm 2 ) 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/cm 2 ) 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 


Section 4 

Figure 4-1 

Production of Diver's Breathing Air 


Pressure Gauge 


Back Pressure 


Magnetic Starter 
& Hour Meter 

Relief Valve 

Final Moisture Separator 



F T- . . 

Pressure Switch 



-i i ! i i : !_ 


Check Valve 

Check Valve 

Chemical Filters 

* ' i i i i i_ 

— Moisture Separator 
fS>-Auto Condensate Dump 

Low Oil Level Switch 
High Pressure Lines 

■ Electrical Lines 

Auto Air Distribution Panel 

High Pressure Air Booster 


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 


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/cm 2 ). 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. 


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- 


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 


4-83 + 


NOTE There are four major manufacturers of scuba cylinders in (he United States 
Their names and symbols are shown below 




Official Mark 

Name of 
Inspection Service 



Authorized Testing 

Pressed Steel 



T. H. Cochrane Laboratory 

Walter Kidde 

(k) of WK 
or WK&Co 

& ® 

Arrowhead Industrial Service 
or Hunt Inspection 

Norns Industries 



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 


Do Not Fill Cylinders Beyond Their Service 

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 


Section 4 

Figure 4-3 

Aluminum Cylinder Markings 

Agency Responsible 
for Standard 

Aluminum Alloy 

Service Pressure 

Scuba Service 

Serial Number 



/ SP6498 \ 
\ E6498 ) 

3000 S8oAr- 

Cylinder Volume 

(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 



Name of 



Official Mark 

Inspection Service 




Authorized Testing 

Pressed Steel 




H. Cochrane Laboratory 

Walter Kidde 

(k) or WK 
or WK&Co. 

& £> 

Arrowhead Industrial Service 
or Hunt Inspection 

Norns Industries 




H. Cochrane Laboratory 

■Initial Test 
Showing Testor's 
Mark, With 
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 


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 

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. 


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 

(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 

(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. 


Aluminum Cylinders Should Not Be Heated 
Above 350° F (177° C) Because This Reduces 
the Strength of the Cylinder and Could Cause 

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 


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. 


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 

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. 


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/cm 2 ) 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/cm 2 ) 
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/cm 2 ) 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. 


Reserve valves should be inspected annually 
for defects or whenever a malfunction is 

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 


Section 4 

Figure 4-5 

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/cm 2 ) 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. 


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. 


NOAA Diving Manual — October 1991 



5.0 General 5-1 

5.1 Open-Circuit Scuba 5-1 

5.1.1 Demand Regulators 5-1 Two-Stage Demand Regulators 5-2 Breathing Hoses 5-4 Mouthpieces 5-4 Check Valves and Exhaust Valves 5-5 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 


Diver Equipment. 






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 


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 Dry Suit Insulation 5-17 Variable-Volume Neoprene or Rubber Dry Suits 5-17 

5.4.3 Hot-Water Suit Systems 5-18 Open-Circuit Hot-Water Suits 5-18 Hot-Water Heater and Hoses 5-18 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 








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. 


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); 

• 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 

• 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 


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. 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 


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 

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- 



Upstream Adjustable 

Valve To 2nd Tension 

Stage Spring 

b. Balanced Diaphragm 

"O" Ring 

HP Air- 


* Water 

Valve To 2nd Diaphragm 
Seat Stage 


c. Unbalanced Piston 


HP Air 



"O" Ring To 2nd \ Ambient 
Seals Stage x Water 

d. Balanced Piston Adjustable 

Hollow /Tension 
Stem / Spring 


HP Air 

'O" Ring Ambient 
Seals Water 


To 2nd 


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 


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. 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 


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. 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 

A. Double Hose 

B. Single Hose 

Courtesy U.S. Divers 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 

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. 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 


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 


Hoses (especially exhaust hoses) should be 
removed periodically and should then be 
washed with surgical soap to prevent bac- 
terial buildup. 



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 

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 

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 

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 

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 

• 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 


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 ft 3 to 140 ft 3 , 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, 


®Diving Systems International 
1990 All Rights Reserved. 

standardized interchangeable fittings, improved valves, 
unbreakable faceplates, better ventilation (low C0 2 
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 C0 2 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. 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. 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 

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. 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. 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 


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. 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. 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 

• If a whip and special auxiliary air supply line valve 
are used for helmet diving, their length should be 

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 

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. 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. 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 


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 

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. 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. 


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 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 


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 


Section 5 

Figure 5-7 
Face Masks 

A. Separate Masks 

Courtesy Glen Egstrom 

B. Full Face Mask 

' B Diving 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. 


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 C0 2 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 C0 2 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 


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 

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 C0 2 release mechanism, oral 
and power inflators, and other movable mechanical 
parts to ensure that they operate freely and easily. The 
C0 2 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 C0 2 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 C0 2 cartridge. 


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 C0 2 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 C0 2 to escape. 


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 


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 


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 


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 

• It takes time, rest, and food to replace lost heat 

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 


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 



Diver s 
May Suffice 

Suits etc. 





— 4 Resting 


4 Working 










Resting Diver Chills 
In 1 -2 Hours 


Tolerance Time 

Of Working 

Diver Without 



1 2 







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 


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. 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). Variable-Volume Neoprene or Rubber Dry 

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 


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 
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. 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. 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 


NOAA Diving Manual — October 1991 

Diver and Diving Equipment 

Figure 5-14 

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. 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. 


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 


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 


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. 




Figure 5-16 
Depth Gauges 



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 

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 

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 


Section 5 

Figure 5-17 
Pressure Gauges 

A. Cylinder Gauge 

Courtesy Dacor Corporation 

B. Submersible Cylinder Pressure Gauge 


the gauge range and ± 100 psig at the lower end 
between 500 and psig (Cozens 1981a). 


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 

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 

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 

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 


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. 


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 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 


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 

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. 


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 


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 (C0 2 ) 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 C0 2 cartridge. The expanding gas 
creates a nearly instantaneous embolism and forces 
the shark toward the surface. The size of the C0 2 
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 


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. 


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 


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 

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 



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 



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 










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 Detection 6-17 Extinguishment 6-17 Breathing Masks and Escape 6-17 

6.5.5 Summary of Fire Protection Procedures 6-17 





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 


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 


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 

Nitrox Regulator Inert Gas Inner Lock Analyzer Communications Outer Lock Outer Lock 
Lifting Eye (Therapy Gas) Regulator Gauge j / y Gauge Viewport 


C0 2 Scrubber 

Design and 
Cert. Plate 


2 Overboard 

Air Exhaust 

Oxygen and Therapy 
Gas Cylinders 

Photo Dick Rutkowski 

October 1991 — NOAA Diving Manual 


Section 6 

Figure 6- 1B 

Double-Lock Hyperbaric Chamber— Interior View 

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 

• 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 


NOAA Diving Manual — October 1991 

Hyperbaric Chambers and Support Equipment 

Figure 6-2 

Mask Breathing System for Use in Hyperbaric 


C0 2 Scrubber Motor 

Sound Powered 



C0 2 Scrubber 

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. 


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 


If structural modifications such as those 
involving welding or drilling are made, the 
chamber must be recertified before further 

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. 


6.3.1 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 

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 


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 


DIV I 1973 

W « 


MIA 73 25 




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 



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 


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 



Primary system operational 


Secondary system operational. 

Free of all extraneous equipment 

Free of noxious odors 


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 


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 


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) . 



Cylinders full; marked as BREATHING OXYGEN; 


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 


Fittings tight, gauges calibrated 

U.S. Navy recompression treatment tables 

Oxygen manifold valves closed. 

U.S. Navy decompression tables 


NITROX (Therapy Gas) 

List of emergency procedures 

Cylinders full; marked 60% N 2 /40% 2 ; 

Secondary medical kit 

cylinder valves open 

Oxygen analyzers functioning and calibrated. 

Replacement cylinders on hand 

Inhalators installed and functioning 


Regulator set between 75 and 100 psig 

C0 2 scrubber functional 

Fittings tight, gauges calibrated 

Adequate C0 2 absorbent 

NITROX valves closed. 

C0 2 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. 


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 


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. 


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. 


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) 



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: 




Cp = 10V + 48,502 

total capacity of primary system (scf); 

chamber volume (ft 3 ); 

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 


Cs = total capacity of secondary system (scf); 

V = chamber volume (ft 3 ); 

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 


Table 6-2 

Ventilation Rates and Total 

Air Requirements for Two 

Patients and One Tender 

Undergoing Recompression Treatment 

Section 6 

Depth Ventilat 


of Rate (scfm) 

Ventilation Air Required at Stop (scf) 

Using 2 

Stop Air 



Treatment Table 

from 60' 

(fsw) Stop 

Stop 5 








165 47.9 






140 41.9 





120 37 






100 32.2 






80 27.3 






60 22.5 

70.4 2929 








50 20.1 







40 17.7 

55.3 1772 








30 15.3 

47.7 1107 








20 12.8 







10 10.4 

32.6 1090 








Total for Ventilation 









NOTE: Total air requirements are dependent on chamber size. 

Depth of Stop 



r Required 


4 Hr. 2 
4 Hr. Air 
4 Hr. 2 





4 Hr. Air 



4 Hr. 2 



2 Hr. Air 



2 Hr. Air 



4 Hr. 2 



4 Hr. Air 



4 Hr. 2 




at 4' 

2 Hr. Air 


2 Hr. Air 


2 Hr. 2 



4 Min. 


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 

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 


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 


Close all valves 

Recharge, gauge, and record pressure of air banks 
Fuel compressors 

Clean compressors according to manufacturer's 
technical manual. 


Check viewports for damage; replace as necessary 
Check door seals; replace as necessary 
Lubricate door seals with approved lubricant. 


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. 


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. 


Check inhalators, replace as necessary 

Close 2 cylinder valves 
__ Bleed 2 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% N 2 /40% 2 , as required 

Ensure spare cylinders available. 


Test primary and secondary systems; make repairs as 


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). 


Lights Inside the Chamber Must Never Be 
Covered With Clothing, Blankets, or Other 
Articles That Might Heat Up and Ignite 


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 


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. 


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 

• Electrical wiring or apparatus 

• Cigarettes or other smoking materials 


• 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: 


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, 


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- 


Table 6-5 

Standard NOAA Recompression Chamber 

Air Pressure and Leak Test 


Type of Chamber: Double Lock Aluminum 
Double Lock Steel 
Portable Recompression Chamber 

* (Description) 

Section 6 




Date of Manufacture 
Serial Number 

Maximum Working Pressure 
Date of Last Pressure Test . 
Test Conducted by 


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: 


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 






3. Increase inner lock pressure to 225 fsw (100 psig) operating pressure (not hydrostatic pressure) and hold for 5 minutes. 

Record Test Pressure 


(NOTE: Disregard small leaks at this pressure) 

Initials of 
Test Conductor 


NOAA Diving Manual — October 1991 

Hyperbaric Chambers and Support Equipment 

Table 6-5 












Depressurize lock slowly to 165 fsw (73.4 psig) 

Secure all supply and exhaust valves and hold for 1 hour. 

Start time 


165 fsw 

Fnd timp 


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 


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 


n outer door) 

those portions 

of the char 

nber not 

Initials of 

165 fsw 

Initials of 


Door Seals 

Door Dog Shaft Spals 

Valve Connections and Stems 

Pipe Joints 

Shell Welds 

Maximum Chamber Operating Pressure Test (5 minute hold) 


Inner and Outer Lock Chamber Drop Test (Hold for 1 Hour) 
Start time 



Fnd time 


Inner and Outer Lock Pressure Drop Test Passed Satisfactorily 
. All above tests have been satisfactorily completed. 


Test Director 


Diving Officer/ UDS 


Director, NDP 


October 1991 — NOAA Diving Manual 


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 

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 


6.5.3 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 

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 N 2 -0 2 Mixtures 







P0 2 =2Atm 
99.6% 2 







10.1 ATA 


1 00 1 50 




300 FSW 

October 1991 — NOAA Diving Manual 


Section 6 

Figure 6-6 

Combustion in N 2 -Oo Mixtures Showing 

the Zone of No Combustion 












4 8 12 


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 


breathe for short periods only (adapted from Shilling, Werts, and 
Schandelmeier 1976) . 

NOAA Diving Manual — October 1991 


Hyperbaric Chambers and Support Equipment 

life. It is therefore essential that chamber personnel be 
trained in fire safety techniques. 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). 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. 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 

• 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. 














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 Classroom 7-4 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 








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. 


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. 


• 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 

• History of sensitization or severe allergy to marine 
or waterborne allergens should be disqualifying. 


• 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- 

• Careful attention should be paid to the maturity of 
prospective candidates, their ability to adapt to 


Section 7 

stressful situations, their motivation to pursue div- 
ing, and their ability to understand and follow 
decompression tables and directions. 


• 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 

• 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. 


• 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- 


• 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 


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- 

• 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 

• Badly decayed or broken teeth should be dis- 


• 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- 

— 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 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- 

• Coronary artery disease should be evaluated by 
an expert. 

• Peripheral vascular disease requires case-by-case 

• 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. 


• 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. 


• Any disorder that predisposes a diver to vomiting 
should be disqualifying (including Meckel's di- 
verticulum, acute gastroenteritis, and severe sea 

• Unrepaired abdominal or inguinal hernia should 
be disqualifying. 

• Active peptic ulcer disease, pancreatitis, hepatitis, 
colitis, cholecystitis, or diverticulitis should be dis- 
qualifying until resolution. 


• 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. 


• Paralytic disorders should be relatively disqual- 

• Bone fractures that are incompletely healed and 
osteomyelitis that is actively draining should be 

• 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 


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 and 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 


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. 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 

— rescue carries 

— in-water mouth-to-mouth artificial resuscita- 

• 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 

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 

• 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 

When initial training is completed, an open-water 
qualification test that includes both general diving 
techniques and actual working procedures should be 

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 


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 

— 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 

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 


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 

• Nitrogen/oxygen breathing media mixing pro- 

• 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 

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 


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 


Introduction to the physics of pressure; 
Decompression theory and calculation of decom- 
pression tables; 

Recompression theory and treatment tables; 

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. 


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 


Although there are obvious advantages in having 
a qualified hyperbaric physician at a diving site, this 


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 

Lecture (158 hours) 
• orientation, anatomy, medical terminology, legal 

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- 

• 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. 


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 


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 


Section 7 


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 

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 

• 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 

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. 


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 

• 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 

• Diver communication, including diver tending, 
hardwire, and acoustic and diver recall systems; 


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 

The cylinder inspection course covers the following 

• 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 







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 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 Lenses and Housings 8-33 Light and Color 8-34 Selection of Film 8-38 Time-Lapse Photography 8-41 

8.12.2 Motion Picture Photography 8-42 Selection of Film 8-42 Procedures 8-42 

8.12.3 Special Procedures 8-44 

8.13 Underwater Television 8-44 












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. 


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 

• 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; 


Section 8 

Figure 8-1 

Surface-Supplied Diver 
in Deep-Sea Dress 


.Jocking Harness 

/ Yvr^^rlrfu". 


Hip Weight 

W -i iv*' 

Pocket > — ^ 

^S P ii^^oidS. 

Thigh Weight 

Calf Weight 



, Boots 




Rear Jocking 

Dry Suit 

Boot Safety 


Air 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, 


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 







Temperature (air) 




Cloud Description/Cover 

Wind Direction/Force 


Sea Surface 

Sea State 

Wave Action: 









Water Temperature _ 
Local Characteristics 


Underwater and Bottom 


Water Temperature: 

degrees at 

degrees at 

degrees at 




feet at 

feet at 

feet at 


degrees at bottom 

feet at 






Bottom Type: 








High Water 

Low Water 

Ebb Direction Velocity 

Flood Direction _ Velocity _ 

Marine Life: 




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 

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. 


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 


Figure 8-3 

Lightweight Surface-Supplied 


Steady Flow 
Valve (defogger) 

"Adjustment knob 


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 

• 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. Diver Emergencies 


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 


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 

• 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 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 


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 

• 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 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 


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 

• 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 

• 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 

• 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 


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 m 3 ) 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 C0 2 , 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. 


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 


Section 8 

Figure 8-5 

Major Components of a Low-Pressure 

Compressor-Equipped Air Supply System 



^i+J Regulator 


/Valve / W \ 

^^^^ Air Intake 
D*0— I J to Wea ther 

(if req) 




Volume Tank 


Manifold | 


"C£<|_ Drain 

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). 


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 


Figure 8-6 

Typical High-Pressure 

Cylinder Bank Air Supply System 

Air Supply to Divers 




— t>~0- 


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): 

P s = 0.445D + 65 + Pj 

where P s = 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): 
p s = 0.445D + 115 + P; 
where 115 = absolute hose pressure (100 psi + 14.7 psi). 


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 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: 


R = radius 

k = safety factor (between 

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 (d e ). The drift error is assumed to be one-eighth 
of the total drift. The total probable error, C, is: 

C = (d e : + x 2 + y 2 )' /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) 


(0.5- 1.5) 

2 (3.2) 


(2.0- 3.0) 

4 (6.4) 


(3.5- 5.0) 

7 (11.3) 


(5.5- 8.0) 

11 (17.7) 



16 (25.8) 



21 (33.9) 



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 


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- 


,, Descending Line 
If* — — 

, ^ , j 

rft. \ Marker Line VwTT^ 

M 7==4s= == _-L /AD "■ 
^V J J SS ^ ==:== 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 





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 


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 


Section 8 

Figure 8-9 

Circular Search Pattern 

Through Ice 


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 


Section 8 

Figure 8-11 

Jackstay Search Pattern 

6 Rectangular Search t 

^\ Buoy 

Buoy /" \ 










^ I 


Buoy ''^ 

J | 


' ; 


' J 

Source: NOAA Diving Pn 


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 

• 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 

• 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. 


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 


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: 

T = - 



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 


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: 


S = - 

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. 


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 


NOAA Diving Manual — October 1991 

Working Dive Procedures 



















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October 1991 — NOAA Diving Manual 


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 


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 

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. 


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 


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 

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 


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 

NOAA Diving Manual — October 1991 

Working Dive Procedures 


Diver Training and Experience Are Essential 
in Underwater Cutting or Welding 


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; 

• 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. 


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 

• The alignment of the instrument in position, its 
height above the bottom, and its sensitivity to 

• Bottom conditions, the bearing strength of the 
bottom, anticipated currents, and the type of marine 

• The precise markings of instrument location and 
the methods used for recovery at completion of the 

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 


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 

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. 


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, 


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. 


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. 


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 

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 


Section 8 

Figure 8-18 
Salvaging an Anchor 
With Lift Bags 


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. 


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 


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 

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. 


Do Not Use Your Buoyancy Compensator as 
a Lifting Device While Wearing the Compen- 

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 

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. 


Diving from an unanchored barge, small boat, or 
vessel can be an efficient method of covering a large 

October 1991 — NOAA Diving Manual 


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 


Line, inches 


























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. 


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. 


Liveboat Divers Should Be Careful to Moni- 
tor and Control Their Depth to Avoid Devel- 
oping an Embolism 


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 

• If the boat is equipped with a propeller, a propeller 
cage or shroud should be fabricated to protect the 

• 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 

• 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 

• 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 

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 

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 


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. 


NOAA Diving Manual — October 1991 

Working Dive Procedures 


Liveboating or Drift Diving Should Never Be 
Conducted With Inexperienced Personnel 


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 

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. 


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 

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. 


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/cm 2 ). 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 


Section 8 









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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. 


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 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 


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) 



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). 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 


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. 

0sa ble Angle of Sunlight 

Low-angle sunlight is nearly 
totally reflected by the water's 

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 


Section 8 

Table 8-5 

Color Correction Filters 

Underwater path 

length of the 

light (feet) 

1 . 

2 . 
5 . 
8 . 


CC 05R 
CC 10R 
CC 20R 
CC 30R 
CC 40R 
CC 50R 

in stops 


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 

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 



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 



NOAA Diving Manual — October 1991 

Working Dive Procedures 

Table 8-6 

Manual and Through-the-Lens 

(TTL) Strobes for Closeup 





In Air 







No. of 








6 x 3.5" 

2.75 lbs. 

500 ft. 



4,500 K 







4 sec. 
3 sec. 
2 sec. 
1 sec. 






S-200 TTL 

6 x 3.5" 

2.75 lbs. 

500 ft. 



4,500 K 







4 sec. 
3 sec. 
2 sec. 
1 sec. 








Whale Strobe 

7 x 4" 

2.3 lbs. 

165 ft. 



5,600 K 

4 AA 
Dry Cells 



7 sec. 
2 sec. 






6 x 5" 

3.8 lbs. 

165 ft. 



5,600 K 

6 AA 
Dry Cells 



10 sec. 
1 sec. 





28 TTL 

6 x 5" 

3.8 lbs. 

165 ft. 



5,600 K 

6 AA 
Dry Cells 



10 sec. 
1 sec. 





150 TTL 

10 x 6" 

7 lbs. 

300 ft. 



4,800 K 






6 sec. 
3 sec. 
2 sec. 






225 TTL 

10 x 6" 

8 lbs. 

300 ft. 



4,800 K 






6 sec. 
3 sec. 
2 sec. 






7 x4" 

2 lbs. 

160 ft. 



5,500 K 

4 AA 
Dry Cells 




12 sec. 
4 sec. 
1 sec. 






8.5 x 5.5" 

4.3 lbs. 

160 ft. 




Dry Cells 





14 sec. 
5 sec. 
2 sec. 







3000 Master 

9 x 5.7" 

4.8 lbs. 

300 ft. 



5,700 K 






3 sec. 
1 sec. 




& Sea 


9.5 x 5" 

5.4 lbs. 

350 ft. 



5,400 K 






5 sec. 
3 sec. 





& Sea 

YS-100 TTL 

6 x 4" 

2 lbs. 

200 ft. 



5,400 K 

4 AA 
Dry Cells 



12 sec. 
12 sec. 
12 sec. 
12 sec. 






Mark 150RG 

11 x 6" 

8.5 lbs. 

350 ft. 



5,500 K 





5 sec. 
3 sec. 
2 sec. 





Courtesy Gen Murphy 

starting to photograph; these variables can cause 
exposures to vary by as much as 4 or 5 stops (see 

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 


Section 8 

Table 8-7 

Through-the-Lens (TTL) Mini 
Strobes for Automatic and 
Manual Exposure 



Head Size 










Recycle * ' 








Whale Strobe 





(95 degrees) 

5,600 K 






• Confirm 

• Test Fire 



Aqua Flash 
28 TTL 



(95 degrees) 

5,600 K 







• Slave 

• Confirm 

• Test Fire 



Substrobe MV 

4.5 x 3.5" 

" 65 


5,800 K 


4 AA 




• Inter- 
sync cords 






(95 degrees) 

5,500 K 


4 AA 






• Confirm 


Sea & 





(80 degrees) 

5,400 K 


4 AA 




• Slave 

• Audio 

• Exposure 


Sea & 

YS-50 TTL 




5,400 K 


4 AA 





*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 


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 


with brackets that permit them to be either mounted or 
hand held. 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 

NOAA Diving Manual — October 1991 

Working Dive Procedures 

Table 8-9 

Underwater Photographic 

Light Sources 

Type of 




of Color 

Ability to 
Light Subject 
for the Human 
Eye as Camera 
Will See If 

of Effects 




Means of 




of Use 



50 to 100 





very good 

fair to 


good at surface 
but decreases 
with depth 







fairly good 

very good 

/ery good 


relatively low 

guide number 
by experiment 

high ( 1 2 


at greater 

Flash bulbs 



fairly good 



1 50 to 1 100 

guide numbers 




Diver must 






foirly good 


fair to 



1 1 000 to 
1 2 000 or 

very high 

guide numbers, 



flash is 
flash for 
use under 

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. 


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 


Helix Aquaflush 28TTL Insert: Helix Universal Slave Strobe 

Courtesy Sea & Sea, Hydro Vision International, Nikonos®, and Helix 

NOAA Diving Manual — October 1991 


Working Dive Procedures 

Table 8-10 

Still Films Suited 

for Underwater Use 

Film Type 







Eastman Kodak Ektachrome 64 




A medium-speed color slide film for 
general picture-taking purposes, e.g., 
macro, closeup, flash, available light 




Eastman Kodak Ektachrome 200 


A high-speed color slide film for 
general picture-taking purposes (e.g., 
deep available light) 




Eastman Kodak Ektachrome 400 


A very high-speed color slide film for 
general picture-taking purposes (e.g., 
deep available light) 


Eastman Kodak Kodachrome 25 


Moderate speed, daylight balanced 
(e.g., macro photography) 




Eastman Kodak Kodachrome 64 


A medium-speed color slide film for 
general picture-taking (e.g., closeup, 
flash, available light) 




Eastman Kodak Kodachrome 400 


A very high-speed color slide film for 
general picture-taking (e.g., deep 
available light) 




Vericolor II S 


Professional color negative film for 
short exposure times (1/10 sec. or 




Panatomic X 

Black and White 

32 Slow-speed film for a very high degree 
of enlargement 




Plus-X Pan 


Medium-speed film for general purpose 
photography where a high degree of 
enlargement is required 




Tri-X Pan 


Fast, general purpose film when the 
degree of enlargement required is 
not great 




Verichrome Pan 


Medium-speed film for general purpose 
photography where a high degree of 
enlargement is required 




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. Time-Lapse Photography 

Many biological and geological events occur so slowly 
that it is neither possible nor desirable to record them 


Table 8-11 

Processing Adjustments 

for Different Speeds 

Section 8 


Ektachrome 200 




Ektachrome 160 




Ektachrome 64 




Ektachrome 50 



Change the time 

in the first 

developer by 



Normal 200 




Normal 160 




Normal 64 




Normal 50 


+ 5 1 /2 minutes 
+ 2 minutes 

— 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. 

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. 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. 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- 


NOAA Diving Manual — October 1991 

Working Dive Procedures 

Table 8-12 

Motion Picture Films 

Suited for Underwater Use 

Film Type 



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- 

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) 


. 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) 


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 

Reversal Eastman Ektachrome . . 
Video News High Speed 7250 

. 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 


Section 8 

cedures to be observed when taking motion pictures 

• 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 

• 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 

• 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. 


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" 


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 


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 

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. 


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 























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 Underwater Photographic Surveys 9-3 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 








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 


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 


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. 



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 

• 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 z 2 - y 2 . 

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. Underwater Photographic Surveys 

Obtaining reliable measurements by means of 
photography — photogrammetry — though not as advanced 


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 

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 

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. 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 

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 


NOAA Diving Manual — October 1991 

Procedures for Scientific Dives 

Figure 9-3 
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. 


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 


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 

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. 


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 


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. 


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 m 2 ) 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 

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 

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 

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 


Section 9 

Figure 9-5 

Counting Square for Determining 

Sand Dollar Density 

Figure 9-6 
Diver-Operated Fishrake 

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 


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 

Underwater operations have several advan- 
tages over sampling from the surface for 
ecological studies involving quantitative 
sampling or observations of behavior. Prob- 


s j* \s /-Z 

J^y \^~~^SF 

/ ss. yy~~~--~~~A\) 




* yyyy copper pipe 


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 

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- 

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 

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. 


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 cm 2 ) 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 

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 m 2 ) 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/ 


NOAA Diving Manual — October 1991 

Procedures for Scientific Dives 

Figure 9-11 

Infauna Sampling Box 

701 mm 2 
Mesh Screen 

Stainless Steel 

1.2 cm Diameter 

0701 mm 2 
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 m 2 ). 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 


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 cm 3 /0.589 x (average nearest neighbor's 
distance in cm) 3 = 

Number of organisms per meter 3 

is preferred because isohedrons pack symmetrically 
along all three axes, whereas spheres do not. 


ftp' * • ~WM 




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. 


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 


Section 9 

Figure 9-14 
Benthic Environment 
of the American Lobster 


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 


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. 


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 


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 

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 


(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. 


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 


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- 

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 

October 1991 — NOAA Diving Manual 


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 

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 


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 

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 


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 

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. 


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. 


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 

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 


Section 9 

total biomass within a given area without detracting 
from biomass potential in other areas. 


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- 


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 

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 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 


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 

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. 


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 / 



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 


Section 9 

Figure 9-25 
Greased Comb for 
Ripple Profiling 

Figure 9-26 

Diver Using Scaled 

Rod and Underwater Noteboard 

' / / m 


■^*' , -^.*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 


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 


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 


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/cm 2 ), 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 m 3 ) 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 

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 


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 

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 


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 

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. 


Section 9 

Figure 9-33 

Undersea Instrument Chamber 


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 

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. 



NOAA Diving Manual — October 1991 

Procedures for Scientific Dives 

Table 9-1 

Micro-Oceanographic Techniques 








Thermometer array 


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 



Same as above 
but secure to 


Equipment flooding. 
Electronic failure. 
Only one data point unless 
multiple units used. 

Relocation of units. 

Remote readout 


Same as above. 

Same as above 

Excellent for use in 


Water samples 


Bottle rack 
carried by 

Number of samples. 
Processing procedures. 

Limited by bottom 
time in conventional 

Recording salino- 

Same as for Temperature, above 

Remote readout 

Same as tor Temperature, above 


Water samples 


Bottle rack 
carried by 

Outgassing when brought 
to surface. 

Best used from 
a habitat 

Remote readout 

Same as for Temperature, above 

Sensor Unit 


Same as for Temperature, above 

Remote readout 


Reverse vertical 
profiling using 
floats and pulley 

Fouling of cables. 
Interface at surface. 

Excellent for 
habitat operations. 



Same as for Temperature, above 

Remote readout 

Same as for Temperature, above 

Dye studies 


Recording (waves) 

Same as for Temperature, above 

Ambient pressure 
gauge inside 


Gauge inside 

"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 


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 

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- 


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 

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 




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 

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 

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 


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 

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. 


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 


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 


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 

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 


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 

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 



October 1991— NOAA Diving Manual 

Courtesy: NOAA (1979) and Duncan Mathewson 


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 


NOAA Diving Manual — October 1991 

Procedures for Scientific Dives 

Figure 9-40 

Prop Wash System Used 

for Archeological Excavation 



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 


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 


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 

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 


9.13.4 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. 


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 = LC 50 /EC is sometimes 
used in evaluating an anesthetic, where LC 50 = 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 


Section 9 

Table 9-2 

Levels of Anesthesia 

for Fish 





Normal for the species. 



Decreased reaction to visual stimuli and/or tapping on the tank; opercular rate 
reduced; locomotor activity reduced; color usually darker. 


Partial loss of equilibrium 

Fish has difficulty remaining in normal swimming position; opercular rate usually 
higher; swimming disrupted. 


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. 


Loss of reflex 

Does not respond to peduncle squeeze; opercular rate slow — often may be erratic. 
This is the surgical level. 


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 


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. 


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 

Summary. The use of anesthetics as collecting agents 
for aquarium fish is controversial, primarily because 


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 

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 


NOAA Diving Manual — October 1991 

Procedures for Scientific Dives 

Table 9-3 

Fish Anesthetics 



Dosage (varies 
with species, 
temperature, etc.) 






25-100 mg/L 

deep anesthesia 

Widely used 
in human 
medicine; safe 
and effective 
with fish. 

Caldarelli 1986 


Solid, soluble, 

1-4 g/L 


Low potency; 
not widely used. 

McFarland 1959 
McFarland 1960 
Bell 1967 


Liquid; mix 
50:50 with 
acetone to 

20-40 mg/L for 


Cresols have 
toxic effects; 
para-cresol is 
the most effec- 
tive isomer. 

Howland 1969 

Etomidate 5 

Make 1 percent 
solution in 

2-10 mg/L 


High potency; 
analog of 
longer seda- 
tion times 
and safer than 
quinaldine and 
MS-222 mixture. 

Amend et al. 1982 
Limsowan et al. 

Dormison ') 




0.5-2 ml/L 
1500-8000 mg/L 

Sedation or deep 

Widely used but 
less desirable 
than other 
low potency. 

Bell 1967 
Klontz and Smith 

Howland and 
Schoettger 1969 




Oily liquid 

0.1-1 ml/L 


Used frequently 
with salmonids. 

Klontz and Smith 


Bell 1967 

(McNeil R7464) 


1-4 mg/L 


Good collecting 

Thienpoint and 
Niemegeers 1965 
Howland 1969 


Oily liquid, 
soluble with 
difficulty; dis- 
solve in 10-50 
percent acetone, 
ethanol, or 
isopropyl alcohol 
to facilitate 

5-70 ml/L 

Widely used 
for collection, 


No sedation 
state; poor 
efficacy varies 
widely with 
species and water 
long exposures 

Schoettger and 
Julin 1969 
Locke 1969 
Moring 1970 
Gibson 1967 
Howland 1969 

October 1991 — NOAA Diving Manual 


Section 9 

Table 9-3 

Dosage (varies 

with species, 




temperature, etc.) 






15-70 mg/L 


Prepared from 

Allen and Sills 




liquid quinaldine 


(QdS0 4 ) 

and has same 

Gilderhus, Berger, 
Sills, Harman 


Powder or emul- 

0.5 ppm 


Used to salvage 

Tate, Moen, 


used for 

fish from fresh- 
water ponds. 
Limited use in 
seawater for 
live collecting. 

Severson 1965 




Used in 

Dangerous to humans; 


and elsewhere 
for collecting 

causes high 
mortality in 


White powder; 

20-50 mg/L 


Not widely used 

Klontz and Smith 

ridine (4- 


deep anesthesia 

but a successful 






White crystalline 

15-40 mg/L for 


Expense bars its 

Klontz and Smith 

(MS-222, tri- 

powder; readily 


deep anesthesia; 

use for collecting; 


caine meth- 


40-100 mg/L for 

most widely used 

used extensively 

Bell 1967 


deep anesthesia 
100-1000 mg/L 
for rapid 


in surgery, fish 






deep anesthesia 


Wood 1956 

Mixtures of 

Powder, readily 

Various, e.g., 10:20 


Combines desirable 

Gilderhus, Berger, 

MS-222 and 


ppm QdS0 4 : MS-222 

deep anesthesia 

properties of each 

Sills, Harman 

QdS0 4 

equals 25 ppm QdS0 4 or 
80-100 ppm MS-222 

combination can be 
used in lower 
concentration than 


either anesthetic 

Source: Donald Wilkie 


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 





















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 







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. 


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 


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. 


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 


Arctic and Antarctic 


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, 


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. 


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 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 

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, 

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 

Visibility in Alaskan waters varies drastically from 
place to place and from time to time. The best visibility 


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 


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 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 

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 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 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 

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 


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 

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 

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 

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 


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 

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. 



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 


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 


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. 


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 


Section 10 

Figure 10-2 

Near-shore Current System 





-£ O'l 

\ 4 <f \ MassTranspo 

\ \ \ 


\ I » 

III * 


-*► -»- •*" "\Feeder ^>*~ Longshore 
Current Curren t 

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. 


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 


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. 


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 

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 


Small Deep Coves 


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) 


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 

• 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 


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 

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- 


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 

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 


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 


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 

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. 


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. 


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. 


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 


Section 10 

Figure 10-8 

Three Multiple Tether Systems (Trapezes) 

Used for Open-Ocean Diving 

Brass Snaps 

Working Diver's Tether 

Bottom Weight 


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) 


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. 


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. 


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 

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 


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 

(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 

double tanks 

double manifolds 

two regulators 

submersible pressure gauge 

buoyancy compensator with automatic inflator hose 

depth gauge 


decompression tables 

wet or dry suit 

safety reel with line 





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 


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. 


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 


Figure 10-10 

Water Temperature Protection Chart 

Section 10 


*"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) ^ 







Wet or Dry Suit 

Or Wet Suit 

Pain 60°F (15°C)^ 

Dry Suit 
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 



25 — 

20 — 


10 — 

5 — 

5 — 

^| Rest 

— 90 

— 70 





— 40 




Diver Will 

Diver At 
Rest Chills In 
1-2 Hours 

^ Water Freezing 

<4 Sea Point 


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 

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 


If a Diver Is Extremely Cold, the Decompres- 
sion Schedule Should Be Adjusted to the 
Next Longer Time 


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 

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. 


Section 10 


Divers Lost Under the Ice Should Ascend to 
the Ice Cover and Wait Calmly to Conserve 
Air. They Should Not Search for the Entry 

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. 


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 


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 

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 


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 


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. 



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 
















15 ( + 3 at 2 m) 




6 (+ 3 at 2 m) 




4 ( + 3 at 2 m) 





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. 


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. 


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 


Section 10 

Table 10-2 

Theoretical Ocean Depth (TOD) 
(in fsw) at Altitude for a 
Given Measured Diving Depth 


Altitude in 













TOD in fsw at Altitude