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DECEMBER 1935
UNITED STATES DEPARTMENT OF AGRICULTURE!
WASHINGTON, D.C. Taree
INDUSTRIAL FUMIGATION AGAINST INSECTS * ©
By E. A. Back, principal entomologist, and R. 'T. Corron, senior entomologist,
Bureau of Entomology and Plant Quarantine
CONTENTS
Page Page
Introduction 2-2-2 -s6se 2 ta ee 1 | Fumigation of various commodities—Contd.
General mill or warehouse fumigation. ------ 2 CWonlectionenye: @ 78 5. Sense ae ns 38
Requirements for a successful fumigation _ 5 Vault fumigation for nuts____________ 38
Preparing the building for fumigation - -- 6 Vacuum fumigation for nut meats__- 38
Desirability ofa high temperature during Fumigation schedule for candy fac-
them sapionse ee 8 CORIES EE tae 5 ee ee ee ee es 39
Effect of wind velocity --.-.--_---------- 9 DOSA2 OS S26 eee eee ee 39
Choicelofaiumigant==2 ===) 9 MUEnITe= ss Ste Be ae eee a ee 39
Quantity of fumigant needed__-_----_____ 9 Hursiand earmentsese== eee ae eae 40
Anplyin= the fumigant- 2.2 = =.=" — 10 Construction ofstoragerooms_______ 40
Fumigation with hydrocyanic acid gas__ 11 ID) OSAP CS Eee 18 ae neat a eee ee eet 40
The barrel or pot method____________ 11 Effect offumigation on furs__________ 42
‘Rhe liquid methods = === 17 RUeSandtapestniesa = 22 = a 42
The discoid method__________----__-_ 20 ICC Gee era ees Sr ee 43
‘he powdermet hod = 5 23 ‘Treating the finished product________ 44
Fumigation with chloropicrin--_-_-_--____- 24 Infestations in warehouses___________ 44
Fumigation with ethylene oxide-carbon Cured meats and cheeses________________ 45
GiOxidoHMIXt lessee = ees 25 SUONG | THO ORK Co ee 45
Fumigation with methyl] formate-carbon IM Oyb Op SUS ses ces a te ce caer eae ener a ee 47
GioxiGOunixtunesss= = eee ee 26 Preparing the mill for fumigation____ 47
Vauliumuigaions= 2-222 - 5 — ae = 27 Choiceiotiumigants-2-— == ee 48
Use of fumigants suitable also for large Hydrocyanie acid gas for mill fumi-
SPACES See ea ee bs DS 30 CALlOneeses seat ee eae eee eae. 48
Wseohopmerntmmicantse ss 30 Chloropicrin as a millfumigant______ 48
Carhbonidistlpmidek= = s_ =) 22 a_ ==! 30 iocaliumimi ca tionm asses ean a ee 49
Carbon tetrachloride_----_---------- 31 Fumigation of flour warehouses______ 49
Ethylene dichloride-_---------------- 31 Vault fumigation for flour or cereal
NE nwlene Oxides ss =2s=- == = es EL 32 mT ee eee, SS Uk 49
Binsin iO ness ee ee ee pos 32 | Safeguards to be employed in fumigation
Viaculimnina SaitOnea ss a= 2 oe 33 SWOT Kole ste ee an Ne PAE he ge eo 50
HG Mie MGs see ee ee eee 33 | First aid for poisoning from hydrocyanic acid
PeTOCEGUIC =e we ee aoe eee Ek Se 35 SAGES See eee Dee ee ite Pa 51
Fumigation of various commodities___---__-- 37 | Shaefer prone-pressure method of artificial
ji slespiratio nes see ee eres | eee 52
INTRODUCTION
Insect infestation is frequently a problem of considerable impor-
tance in the storage of many types of merchandise. During warm
weather or in heated buildings, foodstuffs, cereals, seeds, tobacco, furs,
fabrics, etc., are highly susceptible to infestation by insects, and
heavy losses are likely to occur unless adequate protection is given
them. If cold-storage facilities are available, such commodities can
be protected from insect damage by holding them at temperatures
below 45° to 50° IF Many times, however, it is impossible or
1 The investigations upon which this circular is based were made in the former Division of Household
and Stored Product Insects, and the manuscript was prepared and submitted by that Division.
430°—35——1
2 CIRCULAR 369, U. 8S. DEPARTMENT OF AGRICULTURE
impractical to use cold storage, and it is necessary to resort to fumi-
gation. This circular describes various methods by which products
in storage or the establishments in which they are manufactured
can be protected from insect attack by the use of fumigants.
In the protection of stored commodities four methods of fumiga-
tion are in common use: (1) The general or large-scale fumigation
of warehouses and mills (fig. 1), (2) vault fumigation (fig. 2),
(3) bin fumigation (fig. 8), and (4) vacuum fumigation (fig. 4).
Each method is adapted to a certain type of work and will be dis-
cussed separately. In most industries a combination of two or more
FIGURE 1.—Interior view in flour mill ready for funtigation with hydrocyanie acid gas
generated by the barrel method. The eight barrels containing the acid-water mixture
stand in galvyanized-iron washtubs, and a sack of sodium cyanide is ready to be
lowered into each barrel.
of these methods can be used to advantage; and sometimes special
methods, such as fumigation under tarpaulins (fig. 5) or the treat-
ment of the individual pack of a commodity (fig. 6), are developed.
GENERAL MILL OR WAREHOUSE FUMIGATION
All mulls, factories, warehouses, and storage rooms in which ma-
terial subject to insect attack is handled become infested at one time
or another and need a general fumigation. The managers of many
such places realize the importance of maintaining a clean plant and
fumigate one or more times a year as a general practice. Others,
fearing the trouble and expense, wait until conditions become so
bad that they are forced to shut down their mills for a thorough
cleaning and fumigation.
INDUSTRIAL FUMIGATION AGAINST INSECT 3
FIGURB 2.— formed which the gas does not
penetrate and which, therefore, act as a protection to ‘insects. To
break up such pockets some means of circulating the air in a building
during fumigation is desirable.
IicurgE 11.—Opening to elevator shaft sealed ready for fumigation in same manner as
the doorway in figure 10. In both cases the sealing was ‘done at the Naval Supply
Depot, Naval Operating Base, Hampton Roads, Norfolk, Va.
CHOICE OF A FUMIGANT
In choosing a fumigant several factors must be taken into con-
sideration. If the building is modern and very tight, several fumi-
gants can be used with success, and a choice can be ; governed by such
items as cost, efficiency, availability, safety, and effect upon the com-
modity to be fumigated. If the building is not particularly tight,
it will be impossible to maintain a strong concentration of any gas
for very long, and a quick-acting gas is ‘the only kind that will be
effective. Hydrocyanic acid is the “only gas available that will kill
quickly.
QUANTITY OF FUMIGANT NEEDED
The quantity of fumigant to be used will vary according to the
length of exposure, the ‘tempel ‘ature, the tightness of the building,
Ange 35 9
10 CIRCULAR 369, U. S. DEPARTMENT OF AGRICULTURE
the amount of absorption and adsorption by the commodities to be
fumigated and by the walls and floors of the building itself, and the
insect to be eradicated. The shorter the exposure, the lower the
temperature, the looser the construction of the building, the greater
the absorption and adsorption, and the more resistant the insect,
the greater must be the dosage. The fumigator must exercise his
own judgment in each case.
APPLYING THE FUMIGANT
The fumigant should be apphed in such a way that a maximum
concentration will be obtained as quickly as possible. If the concen-
tration is slow in building up, the natural leakage from a building
is often great enough to prevent a killing concentration from ever
being attained.
Where it is desirable to maintain a heavy concentration over a long
period, it may be necessary to use a combination of fumigants, one
that will act quickly and another that will work more slowly and
will serve to maintain a lethal concentration for an extended period.
This is of particular importance in the fumigation of flour mills
and similar structures where a deep penetration of the fumigant
is essential.
The distribution of the fumigant will depend upon the structure
of the building and the nature of the gas. If a lighter-than-air gas
is used, the heaviest dosage must be placed on the lower floors, and
if the flooring has many cracks and apertures, a much heavier
dosage than usual must be placed on the lower floors. In some cases
floors are so poorly constructed or so worn that the entire dosage
should be applhed on the first floor.
If the fumigant is not applied from the outside, the fumigating
crew should be supphed with gas masks having canisters adapted for
the gas that is to be used. Each operator should be familiar with
the entire plan of procedure as well as with his own particular job.
One man should be delegated to watch the others and to give aid in
case anyone gets into trouble. Help given at the right time will
prevent possibly fatal accidents.
Before the fumigation is started, the building should be thoroughly
searched to make sure that no workmen or visitors are inside. Dur-
ing the fumigation all entrances to the building should be kept
locked and usually guarded by watchmen. Placards warning people
to keep out should always be tacked on all doors.
After the fumigation the building should be aired out by opening
windows and doors. If possible, these should be opened from the
outside. This is sometimes done by pulling open the windows on the
upper floors by means of cords extending from a screw eye attached
to the sash and long enough to be tied to the iron grille of the base-
ment windows. If some such arrangement is not feasible, the win-
dows can be opened from the inside by workmen wearing gas masks.
In order to avoid accidents, two men should always work together
when ventilating a building. It is important that the watchmen be
instructed to prevent anyone from entering the building while it is
being ventilated. A large proportion of the fatalities connected
with fumigation have been due to criminal neglect on the part of
watchmen,
INDUSTRIAL FUMIGATION AGAINST INSECTS 11
FUMIGATION WITH HYDROCYANIC ACID GAS
For the fumigation of large buildings there is no more efficient gas
than hydrocyanic acid. It is relatively inexpensive, kills with great
rapidity, and, although deadly poisonous, can be handled with
reasonable safety by
experienced men. It
can be used in nearly
all types of build-
ings and will not in-
jure most articles of
commerce.
Hydrocyanic acid
gas 1s commonly pro-
duced=sim “le “of 4
ways: (1) By gen-
erating it in a bar-
rel, earthen ware
crock, or other con-
tainer from a mix-
ture of sodium cyar-
ide, sulphuric acid,
and water—the so-
calleds) = barrel *or
pot” method; (2)
by pumping it into
the building in
liquid form from
cylinders—the liquid
meth od: (3) by
spreading on the
floor of the buildin»
an absorbent mat--
rial saturated with
liquid hydroeyanic
acid—the discoid
m : FIGURE 12.—Man wearing gas mask about to lower bag of
etho d; (4) by sodium cyanide into a barrel containing sulphuric acid
spreading on the and wu aLer. IGE the EEE is Dut a a ey sa phere
: : is no danger of the bottom of the bag breaking an
floor of the building spilling the cyanide. The cyanide should not be
1etINo dropped into the acid-water mixture; it shou e
a powder consisting Tee eea Ga noraLe
of calcium cyanide,
which combines with moisture from the air to form hydrocyanic
acid gas—the powder method.
THE BARREL OR POT METHOD
The barrel or pot method of generating hydrocyaniec acid gas 1s so
called because the chemicals used are placed together in a barrel (figs.
1 and 12) or some similar container (fig. 18). This method, while
more laborious than others, gives excellent results and is the safest
for the use of other than professional fumigators. It can be made
the cheapest method of fumigation.
12 CIRCULAR 369, U. S. DEPARTMENT OF AGRICULTURE
CHEMICALS REQUIRED
Sodium cyanide (96 to 98 percent, containing 54 percent HCN), a
commercial grade of sulphuric acid (66° B.), and water are the eae
materials required. Sodium cyanide is a white crystalline substance,
which for fumigation purposes is prepared in egg-shaped lumps
: weighing approx1-
mately 144 to 1 ounce
each. It is a violent
stomach poison, and
can also cause seri-
ous poisoning by be-
ing absorbed through
open cuts on the
hands. For this rea-
son it is best handled
with a scoop or
shovel or with gloved
hands, (hes 14) eit
ean be purchased in
100-pound lots for
from 16 to 22 cents
per pound, and in
smaller lots at a
proportionally high-
er price.
Pure _ sulphuric
acid 1S @ heavy,
colorless liquid, but
the commercial acid
fumigation work is
slightly discolored,
or “murky, owing to
impurities. It is
highly corrosive and
will cause injury if
it is spattered on the
clothing or body of
the operator or upon
the floor. It can be
purchased in 11-gal-
FIGURE 1S s = ChOGs for the SeESE IOS (ob hydrocyanic aad lon carboys for about
gas by the pot method, set in small galvanized-iron tub :
to prevent injury to floors in case the crock cracks. 4 cents per pound.
When large quan-
tities of acid are required, a tilting frame will be found convenient
in pouring the acid from the carboys.Workmen should learn to
pour acid slowly and with caution (fig. 15), for their clothing or
shoes will be damaged if a drop of acid falls on them. It is well to
have easily accessible a pail of water in which some washing soda
has been dissolved, for quickly washing away droplets of acid that
may spatter on face, hands, or clothing.
used in large-scale |
INDUSTRIAL FUMIGATION AGAINST INSECTS 13
FORMULA
For best results the chemicals should be mixed according to the
following formula:
SSOCHUEETIN 0 VEEN CLG ee eue sy! eS Te be ee yey) SanounGd== i
SUM TOURER EE GICG |e SS Set aed aS es ee De eee pints_- 1%
VAG REL oe a eS Se ee eo ee (0 See
PROPER ORDER OF PLACING CHEMICALS IN GENERATOR
To generate hydrocyanic acid gas by this method, the operator
should first pour the water into the generator and then add the acid.
if the procedure is reversed, the re action is so violent that the oper-
Figure 14.—Workmen weighing sodium cyanide for large warehouse funrigation. Man
at right shoveling cyanide in 1-ounce lumps from 100-pound case into gunny sack
held by m Man in center. Man at left with charge weighed about to enter warehouse
and place sack beside generator.
ator may be dangerously burned by the spattering of the acid-water
mixture. ‘The sodium cyanide is not added to the mixture of water
and acid until everything is in readiness for the fumigation, as it
causes an immediate chemical reaction in which hydrocyanic acid
gas is given off (fig. 16). The pure gas is colorless, but when mixed
with steam produced by the chemical reaction it has the appearance
of a light bluish smoke. It has an odor resembling that of peach
kernels.
2 Chemical tests indicate that a 1—114—2 formula yields more gas than the 1-1%—-3
formula here recommended. The smaller quantity of water often results in a erystalliza-
tion of the residue which mrakes the emptying of the containers after fumigation more
difficult. In general large-scale work the authors have found the 1—114—3 formula more
practical and the results satisfactory.
14 CIRCULAR 369, U. S. DEPARTMENT OF AGRICULTURE
DOSAGE
The dosage is computed on the basis of the quantity of sodium
cyanide required, For general mill or factory fumigation where no
large quantities of materials are stored, 1 pound of sodium cyanide
will produce enough gas to fumigate 1,000 cubic feet of space, if
the building is of reasonably tight construction. If the building
to be fumigated is filled with merchandise, the dosage required will
vary according to the nature of the merchandise. Dosages have been
computed for the fumigation of the more important commodities and
will be discussed in
a later section of this
circular.
THE GENERATOR
For large-scale
fumigations a water-
tight 50-gallon
wooden oil barrel
(figs. 1, 12, and 16)
is the most suitable
generator to use.
Metal barrels are not
satisfactory. Barrels
in which paint, glue,
molasses, pitch, etc.,
have been — stored
should be avoided,
for when the acid is
added it may eat out
these materials from
between the staves,
thus causing a bar-
rel thought to be
hiquid-tight to leak.
Barrels should be
FIGURE 15.—A good illustration of workmen’s indifference
to spattering sulphuric acid. Most industrial plants have cleaned and allowed
crews familiar with pouring acid; yet few are particular
to avoid spattering and dropping acid. to - stand hull -ok
water overnight pre-
vious to the day of fumigation. Each barrel will hold a maximum
charge of 30 pounds of sodium cyanide, or enough to fumigate 30,000
cubic feet of space. When it is necessary to fumigate small rooms of
a few thousand cubic feet as separate units, earthenware or stone
crocks (fig. 183) of appropriate size can be used. Oil barrels sawed
in half are used less often.
Each barrel generator should be set in a galvanized-iron washtub
in which has been placed a pailful of water containing several hand-
fuls of washing soda. This precaution provides for catching and
neutralizing any of the acid-water mixture that may leak out of the
barrel.
If 3 or 4 bricks are placed in the bottom of the washtubs for the
barrels to rest on, they will not become stuck in the tubs. It is much
better to have tubs large enough in diameter at the bottom so that
the barrels will not come in contact with the sides,
INDUSTRIAL FUMIGATION AGAINST INSECTS 15
If earthenware crocks are used, these also should be set each in a
small galvanized tub. It is seldom practical to use crocks of more
than 4-gallon capacity. A 3-pound charge of cyanide is the most
that can be safely used in a crock of this size without danger of
spattering during the evolution of the gas.
HANDLING CYANIDE FOR THE GENERATOR
The weighing of cyanide should be delayed as late as possible be-
fore the fumigation is begun. The cyanide absorbs moisture, and if
it remains in a paper package for a long time before fumigation,
the moisture gathering on the lumps of cyanide will moisten the
paper so that when the sack is picked up it may break and dis-
charge the cyanide. Where small charges of cyanide are used.
as in 4-gallon crocks, it is best to use two paper sacks, one of which
FIGURE 16.—Seven 50-gallon oil barrels, in tubs, arranged in line near the door of a
woollen factory. The sodium cyanide has been dropped into the acid-water mixture.
Note gas mixed with steam rising from the barrels. Each of these barrels had a
charge of 25 pounds of sodium cyanide, the battery of 7 barrels generating enough gas
for 175,000 cubic feet of mill space.
will fit easily inside the other. By wrapping the unoccupied por-
tion of the sacks tightly about the cyanide and tying with a string,
a compact package is obtained, which can easily be lowered into the
acid-water mixture with one hand. If two bags are used, the
operator can lower 6 or 8 charges of cyanide into the containers before
the acid eats through the paper of the charge first dropped, and
often he can be out of the building before any gas is evolved. Ii
the sacks are merely tied close above the cyanide, or twisted, without
wrapping, during the reaction the acid-water mixture may be forced
up along the neck of the bag and over the edge of the container.
If the cyanide is properly packaged, however, there will be no
overflow.
When large dosages are used in barrels, sometimes as large as 30
pounds, it is safer to place the cyanide in gunny sacks. When charges
in such sacks are lowered into the barrels, gas is evolved at once
16 CIRCULAR 369, U. 8. DEPARTMENT OF AGRICULTURE
and the operator must work with dispatch. The evolution of gas
can be delayed by wrapping the sack in paper and tying the bundle
with cord strong enough so that the bundle can be lifted and lowered
into the barrel without danger of breakage. A person can then lower
several charges before gas is discharged from the first.
PLACING THE GENERATORS
In the fumigation of large open mills or warehouses, all the gener-
ators for one floor can be grouped in a position reasonably close to
the exit. It is not necessary to distribute them throughout the room,
for the gas is quickly dispersed to all parts of the enclosed space. In
fact, where it is impractical to seal off the several floors of a rather
small, tight building, excellent results can be obtained in calm weather
by placing all the generators on the lower floor so that the gas will
rise from floor to floor.
How To GENERATE THE GAS
After the mill or warehouse has been prepared for the fumigation
and the generators have been placed in their proper positions, the
water and acid are measured out and distributed in the generators.
The acid can be poured from the carboys into heavy galvanized-iron
buckets, which will resist the action of the acid long enough for it to
be distributed without accident. If crocks are used for generators,
the acid must be poured into the water slowly with a rotating motion,
lest the heat developed by the chemical reaction between the acid and
water cause the crocks to break. If the crock should crack, the
operator must empty it immediately into some handy container pro-
vided for such an eventuality.
When the water and acid have been mixed, the sodium cyanide,
which has previously been weighed into the proper quantities and
wrapped, should be lowered carefully into the generators. If several
floors are to be fumigated separately, the cyanide should be dropped
first into the generators on the top floor, and then on the next lower
floor, and so on to the bottom. Starting with the one farthest from
the exit (previously determined), proceed from generator to gener-
ator calmly and without delay. Do not retrace steps to a generator
accidentally overlooked. If several lines of generators converge at
one exit, an operator should be assigned te each line and at a prede-
termined signal each should start dropping the cyanide in the most
distant generator in his line.
Since the gas is generated as soon as the acid-water mixture comes
in contact with the sodium cyanide, the operators engaged in drop-
ping the cyanide should wear gas masks, except for very small jobs
where only 1 or 2 generators are used.
EMPTYING THE GENERATORS
When the fumigation is finished and the building has been thor-
oughly ventilated, the residue must be emptied from the generators.
Sometimes the chemical reaction is incomplete because some of the
sodium cyanide has not come in contact with the acid-water mixture
or because the wrong proportions of the materials have been used.
INDUSTRIAL FUMIGATION AGAINST INSECTS 17
Therefore, when the generator is moved, the contents are shaken up
and additional small quantities of gas may be given off. For this
reason the operator should breathe as little as possible or use gas
masks while handling the barrels and should not hold his head over
the barrel.
The residue, which is poisonous, can be disposed of by dumping
it down a street drain (fig. 17) or by pouring it into a hole in the
ground and covering it with soil.
THE LIQUID METHOD
Liquid hydrocyanic acid is a volatile, colorless liquid which boils
at 79° F. It is marketed in cylinders containing 30 or 75 pounds.
On exposure to air it
gives off the same gas
that is generated by
mixing sodium cyan-
ide with sulphuric
acid and water. In
the hands of an ex-
pert fumigator it is
an almost ideal fumi-
gant for use in large
enclosures.
After a building
has been prepared for
fumigation, the gas is
apphed entirely from
the outside (figs. 18
and 19). The cylin-
ders containing the
liquid hydrocyanic
acid are lined up near
the building, and the
fumigant is forced in
by compressed air. A
proper distribution of
the gas within the Ficure 17.—Men carrying containers from a warehouse
=a ae : - to empty into a city drain the residue from a hydro-
building 1s obtained cyanic acid gas fumigation.
by means of lines of 2
pressure rubber tubing or metal piping equipped with spray nozzles.
A gas mask should be worn or close at hand.
PIPING THE BUILDING
In small enclosures the gas can be distributed through rubber tub-
ing, but in large warehouses or mills it is desirable to install a per-
manent system of piping. This may be constructed of iron, brass, or
copper. The iron piping is the least expensive, but, owing to its
tendency to rust and cause clogging of the spray nozzles, it is rarely
used. Either brass or.copper tubing is recommended. A flexible
copper tubing three-eighths inch in diameter (fig. 20) costs about 6
cents a foot. Since it can be readily bent, elbow fittings are unneces-
450°—35 3
Figure 18.—Fumigating a tobacco warehouse with hydrocyanie acid gas, using the
liquid method. The liquid hydrocyanic acid in the cylinder on the scales is being
forced, by air pressure generated by a small electrically driven compressor, through the
rubber tubing from the cylinder to the piping system installed inside but protruding
through the walls.
Figtre 19.—Equipment for fumigation of flour mill from loading platform. Note 6
cylinders of liquid hydrocyanic acid, 2 electric motors, outlets in the wall leading to
6 piping systems to carry fumigant to 6 separate compartments, floors, or pipe lines
within. The 2 motors are forcing, by air pressure, the liquid hydrocyanie acid in 2
of the cylinders through rubber hose into 2 of the systems of copper piping within.
Note placard on door warning of danger.
INDUSTRIAL FUMIGATION AGAINST INSECTS 19
sary, and compression couplings can be used, except at the main inlet,
where the cylinders are connected.
In large buildings, where there are several floors and numerous
branch lines must be used, each floor should be provided with a
separate riser, which should be of larger tubing. A spray nozzle
(fig. 21) should be provided for at least every 25,000 cubic feet of
space, but there should be not more than 10 spray nozzles to a riser.
Most buildings can be piped with copper tubing at a cost of about
10 or 12 cents per 1,000 cubic feet of space. Brass tubing costs about
two and one-half times as much as copper.
The piping system should be so arranged that the gas pressure
will be approximately the same at all nozzles, thus insuring an even
distribution. Each
riser is connected to
a special inlet pipe
leading through the
outside wall of the
building to the cyhn-
ders of gas.
APPLYING THE GAS
Each cylinder of
liquid hydrocyanic
acid is supphed with
an inlet valve and an
outlet valve. The
outlet valve is at-
tached to a steel tube
connected with the
bottom of the cylin-
der. The inlet valve
leads directly into
the top of the cylin-
der, and through it
air is pumped, by
means of a_ small Ficure 20.—Installation of three-eighths inch copper pip-
o ing for introduction of liquid hydrocyaniec acid. ‘This
ULE OSSSSUL (figs. 18 piping, being flexible and easily cut with a saw, as in-
and Le): until a dicated, can be run along side walls and out alone
: r rafters, or to an oint where it seems best to insta
pressure of about 100 Hie uw musa poe
pounds is obtained.
The outlet valve, which has previously been connected with
the inlet pipe to the building, is then opened and the gas
is forced in. The pressure must be maintained until the liquid is
blown through the pipes into the space to be fumigated. As soon as
the required quantity of liquid hydrocyanic acid has been forced into
the building, the pipe lines are blown clear and the inlet tubes capped.
The time needed to pump the contents of a 75-pound cylinder into a
building is approximately 7 minutes.
SAFETY PRECAUTIONS
At the conclusion of the fumigation and after the building has
been well ventilated, the spray nozzles should be removed and cleaned
20 CIRCULAR 369, U. S. DEPARTMENT OF AGRICULTURE
for storage and the pipes capped. In removing these nozzles, care
must be taken to avoid accidents from the small ‘quantities of liquid
hydrocyanic acid that sometimes remain in the pipes after a fumigia-
tion. ‘The operator should never stand directly in front of or be-
neath a spray nozzle that is being removed. T he presence of liquid
hydrocyanic acid behind a nozzle that is being unscrewed is usuall
revealed by a well-defined
cooling sensation and
sometimes by aslightodor.
In fumigating with
liquid hydrocyanic acid,
there is always some
danger that the rubber
connecting hose may
burst under the pressure,
showering the operator
with the deadly fluid.
It is therefore a wise
precaution to wear a gas
mask while manipulating
the valves of the cylin-
ders, and also to have
the clothing covered with
a smock, which can be
snatched off in an emer-
gency.
THE DISCOID METHOD
For the fumigation of
warehouses that are di-
vided into sections, of
mills containing machin-
ery that cannot be easily
opened up, or of apart-
ment buildings, etc., the
use of some form of solid
from which hydrocyanic
acid gas can be produced
is often desirable, since
it does away with the
FIGURE 21.—Various attachments for spray nozzles necessity for an elaborate
used in fumigating a warehouse, mill, or factory
with liquid hydrocyanie¢ acid. pipe” system. or for
crock or barrel generators.
There are two types of such solids now on the market. One of
these consists of liquid hydrocyanic acid absorbed in some inert
material, from which it evaporates on exposure to air. This inert
material is pressed into waferlike discoids each containing approxi-
mately one-half ounce of liquid hydrocyanic acid (fig. 22). These
discoids are marketed in tightly sealed cans of various sizes and sold
on the basis of the net content of hydrocyanic acid. The other type
of solid is calcium cyanide, and the hydrocyanic acid is produced by
chemical reaction with the moisture in the air. Its use will be dis-
cussed under the Powder Method.
A A TE I a «
INDUSTRIAL FUMIGATION AGAINST INSECTS Zt
APPLYING THE DISCOIDS
When large quantities of discoids are used, especially in hot
weather, it is advisable to chill the cans before fumigating. This
will greatly retard the generation of the gas and thus increase the
safety of operation. If solid carbon dioxide is available, a liberal
quantity thrown over the tops of the cans in each opened case a few
hours before fumigating will chill the discoids. Solid carbon dioxide
can usually be purchased for from 3 to 5 cents per pound. Placing
cans of discoids in cold storage will have the same effect.
FIGURE 22.—Lobby of apartment house being fumigated. with hydrocyanic acid gas
generated by the discoid method, showing round white wafers distributed over the paper
runner and the empty cans from which they have been shaken. These wafers are
wet aynen distributed, but after the evolution of the gas they become dry and
armless, -
The proper number of cans of discoids should be placed on each
floor to be fumigated, and the distribution of the fumigant should
be started on the top floor, always from a predetermined point and
approaching the exit. One man should open the cans, using a spe-
cially devised can opener that makes a clean cut close to the rim
(fig. 23), while two or more men take the opened cans and scatter
the discoids over the floor or among the machinery.
Discoids should not be placed directly on painted or varnished
floors or woodwork, for the liquid hydrocyanic acid is likely to injure
the finish. Two or three thicknesses of newspaper or wrapping paper
will provide adequate protection against any liquid that may ooze
from the discoids.
=]
D2, CIRCULAR 369, U. S. DEPARTMENT OF AGRICULTURE
When discoids are used, the fumigators are exposed to the gas
while they are opening the cans and distributing the contents. Good
gas masks are necessary and will prevent them from breathing poi-
sonous fumes, but there is also some danger from the direct absorp-
tion of hydrocyanic acid gas through the skin. Williams? has esti-
mated that a man protected by a good gas mask can remain in air
containing 2 ounces of hydrocyanic acid gas per 1,000 cubic feet for
half an hour without
being affected; in a con-
centration of 4 ounces
per 1,000 cubic feet this
time should be reduced
to 15 minutes, and in
one of 8 ounces to 5 min-
utes. The same author
calculates that, in dis-
tributing discoids at the
rate of 8 ounces of hy-
drocyanic acid per 1,000
cubic feet, a fumigator
will be actually exposed
for the greater part of
the time to from 1 to 2
ounces per 1,000 feet.
Allowance is made for
the fact that the fumi-
gator is constantly mov-
ing away from the dis-
colds and that the full
quantity of the gas is not
given off immediately.
If the discoids are chilled
before being used, the
concentration to which
the fumigator is exposed
will be less.
From the foregoing
data it is evident that,
where large quantities
of discoids are used, the
Ficure 23.—Man, protected by gas mask, removing : :
the top from a tin can containing discoids im- fumigating crew must
pregnated with liquid hydrocyanic acid. be large enough so that.
the distribution of the
fumigant will be speedy and no one man is exposed to the gas for
a dangerously long period.
DISPOSING OF SPENT DISCOIDS
When the fumigation is finished and the building has been well
ventilated, the spent discoids and the empty cans can be gathered up
and thrown away. At the end of a 24-hour fumigation the discoids
will retain not more than a trace of hydrocyanic acid.
3 WILLIAMS, C. L. FUMIGANTS. Pub. Health Repts. [U. S.] 46: 1018. 1931.
INDUSTRIAL FUMIGATION AGAINST INSECTS 23
THE POWDER METHOD
Calcium cyanide in dust form is used in much the same way as the
discoids. On exposure to the air the powder absorbs moisture and a
chemical reaction takes place by which hydrocyanic acid gas is given
off.
APPLYING THE POWDER
The required number of cans of calcium cyanide are distributed
throughout the building. They are then opened and the contents
scattered over the floor in a layer not more than half an inch thick.
To facilitate removal of the dust after the fumigation, it may be
scattered on strips of paper previously laid on the floor, although it is
sometimes placed directly upon the floor (fig. 24). Each can of
fumigant is equipped with a special top, which the fumigator puts
in place of the friction top when he is ready to use it.
Figurb 24.—Warehouse being fumigated with hydrocyanic acid gas by the powder
method. Calcium cyanide in dust form is spread on the floor, usually from tin cans
with perforated covers.
Inasmuch as the gas is given off very rapidly after the dust is
exposed to the air, the fumigator should wear a gas mask while dis-
tributing it. As in the case of the discoids, he should begin distribut-
ing the dust at the point farthest from the exit, so that he will be
working away from the gas that is being given off.
After the fumigation, the paper on which the dust is spread can
be rolled up and thrown away, or the dust can be swept from the
floor and placed in containers, to be disposed of immediately. The
residue, which is mostly calcium hydroxide, is likely to absorb some
of the hydrocyanic acid from the air; hence it is advisable to dispose
of it outside the building, where small quantities of escaping hydro-
eyanic acid gas will harm no one. After all the hydrocyanic acid
has been given off, the residue is nonpoisonous.
As the dust may be blown about while the building is being ven-
tilated, it should be removed as soon as possible. To obviate this
difficulty, as well as for other reasons, the gas is sometimes liberated
24 CIRCULAR 369, U. S. DEPARTMENT OF AGRICULTURE
in a special apparatus (fig. 25). Air is forced by a small motor into
a rubberized sack containing the calcium cyanide dust, which is kept
agitated until all the hydrocyanic acid gas is liberated. The gas
enters the space to be fumigated through a filtering device, which
frees it of the dust.
THE DOSAGE
To figure the quantity of calcium cyanide needed for a fumigation,
it is necessary to know the percentage of available hydrocyanic acid
it contains. This percentage will be found on the label of the can.
If, for example, the dust
contains 50 _ percent
available hydrocyanic
acid, 1 pound will give
off as much gas as 8
ounces of liquid hydro-
cyanic acid or 1 pound
of sodium cyanide. Cal-
cium cyanide sells for
about $1.35 per pound.
FUMIGATION WITH
CHLOROPICRIN
Chloropicrin, although
not so popular as hydro-
eyanic acid, is some-
times used as a general
fumigant for mills and
warehouses, Chloro-
picrin is a colorless or
shghtly yellowish lquid
a little more than one
and a half times as
heavy as water. It hasa
boiling point of 233.6°
F. and on exposure to
air evaporates slowly,
forming a vapor that is
, about five times as heavy
FIGURE 25.— Apparatus for passing air through cal- as airs. Ait ean be pur-
cyanie weld cas igen al ye ue BORER EE chased in cylinders of
from 1 to 100 pounds’
capacity at a cost of about $1.35 per pound. The gas 1s nonexplosive
and noninflammable as ordinarily used, is extremely toxic to insects
and also to man, and has an extremely irritating effect upon the eyes
and respiratory passages of man. This last characteristic insures
against the probability of anyone accidentally entering a building
filled with the gas. A gas mask equipped with a canister especially
designed for the purpose must be worn when fumigating with
chloropicrin.
There are several methods of applying chloropicrin: as a general
mill or warehouse fumigant. The simplest of them is to draw the
required quantity of liquid from the cylinder in which it is mar-
INDUSTRIAL FUMIGATION AGAINST INSECTS 25
keted into a sprinkling can and sprinkle it over the floor or commod-
ity or into the machinery. It should not be applied directly on
painted or varnished surfaces. Where there are several stories to a
building, each floor should be sealed off from the others, since the
fumes are so heavy that they tend to concentrate on the lower floor.
If the floors cannot be made gastight, a greater concentration should
be appled on the upper floors.
Owing to the rather high boiling point of chloropicrin and conse-
quent slow rate of evaporation, it is sometimes desirable to hasten
the process of vaporization by applying the lquid in the form of a
spray or fine mist, or by using a mixture of equal parts of chloro-
picrin and carbon tetrachloride or trichloroethylene. At tempera-
tures above 70° F., however, satisfactory results can be obtained by
merely applying the straight chloropicrin with a sprinkling can.
In mills that are equipped with machinery for handling food-
stuffs, it may be desirable to apply the chloropicrin directly into the
machinery where the heaviest infestation is likely to be found. In
such cases the fumigant cam be apphed with either a sprinkling can
or an atomizer. One-pound cylinders of chloropicrin charged with
carbon dioxide, to which a short length of hose and a spray nozzle
are connected, can also be obtained for treating machinery. The
nozzles are inserted into holes bored into elevator legs or other parts
of the equipment, and the gas is released by opening a valve on the
cylinder.
An objectionable feature of chloropicrin is that considerable time
is required to ventilate a building after a fumigation. Because it
does not evaporate rapidly, it clings to fumigated commodities with
great tenacity. :
FUMIGATION WITH ETHYLENE OXIDE-CARBON DIOXIDE MIXTURE
Warehouses and storage rooms that are of modern tight construc-
tion can be successfully fumigated with a mixture of ethylene oxide
and carbon dioxide. This mixture is put up in cylinders in the pro-
portion of 1 part by weight of ethylene oxide to 9 parts of carbon
dioxide. It is noninflammable, and is not sufficiently toxic to human
beings to make its application unpleasant or dangerous. It leaves
no obnoxious odor or poisonous residue on the commodity fumi-
gated. The mixture is sold in 30- and 60-pound cylinders at prices
ranging from 14.5 to 16 cents per pound, f. o. b. the factory.
The application of the ethylene oxide-carbon dioxide mixture is
exceedingly simple. The requisite number of cylinders are placed
in the room to be fumigated and the valves opened. The pressure
of the carbon dioxide automatically discharges the contents of the
cylinders in the form of a very fine mist, which vaporizes at once (fig.
26). A cylinder of the mixture will empty itself in about 5 minutes
after the valve has been opened wide.
When the valves are opened wide, the force of the escaping gas
often causes the cylinders to topple over. To avoid this, the cylin-
ders can be lashed to the walls of any stationary object, or several
cylinders can be lashed together with the discharge vents pointing
in opposite directions.
430°—35———4
26 CIRCULAR 369, U. S. DEPARTMENT OF AGRICULTURE
Unless a large number of cylinders are used in a fumigation, the
valves can be opened without the use of a gas mask, although it is
not advisable to stay in a strong concentration of the gas for any
appreciable length of time. Before starting the fumigation it is
well to see if the valves on all the cylinders can be opened easily by
hand; any that are stuck should be loosened with a wrench.
If desirable, a storage room can be piped in the same manner as
for liquid hydrocyanic acid, and the ethylene oxide-carbon dioxide
released into the room from the outside. ‘The cylinders are all
(eo with fittings that can be connected with the piping system
27)
Wier the floors are painted or varnished, the cylinders should be
placed in shallow pans or on several thicknesses’ of newspaper, to
prevent damage in case the liquid should run down the sides of the
cylinder.
EWiGgurRE 26.—Cylinders of ethylene oxide-carbon dioxide mixture being emptied auto-
matically by the pressure of carbon dioxide within.
This mixture is very effective in rooms that are nearly airtight,
but it should not be used in rooms that are loosely constructed.
After the fumigation and ventilation all that is necessary is to roll
the empty cylinders out of the room and return them to the owner.
FUMIGATION WITH METHYL FORMATE- Cane DIOXIDE
MIXTURES
Warehouses and storage rooms that are thoroughly modern in
construction can be fumigated with mixtures of methyl formate and
carbon dioxide. Ordinar ily these mixtures are used only in special
fumigation vaults. The value of methyl formate as a fumigant was
first established by the experimental work of this Department.
Alone, its vapors are explosive and inflammable in the presence of
fire in any form; hence, mixtures with carbon dioxide have been
developed, the vapors cf which are entirely free from the fire and
explosion hazard.
INDUSTRIAL FUMIGATION AGAINST INSECTS 27
The methyl formate-carbon dioxide mixtures are sold at 10 cents
per pound, f. o. b., in steel pressure cylinders containing’ 50 pounds.
The liquid is discharged under its own pressure. When used in con-
nection with vault fumigation, the cylinder is set on platform scales
close to the vault wall, through which the desired dosage is dis-
charged into the vault by means of easily made metal connections.
When the scales indicate that the required poundage has been dis-
charged, the cylinder valves are closed.
The mixture is discharged as a fine mist, which immediately
vaporizes. ‘The vapors seem to be harmless to food and other com-
modities thus far treated, and they are only slightly toxic to man as
he ordinarily comes in contact with them in fumigation work. The
FiecurH 27.—Battery of 10 cylinders of ethylene oxide-carbon dioxide mixture attached to
manifold, heaters, and distributing pipes connecting with storage vaults (not Shown)
in room. In lower background is a 6- by 8- by 10-foot metal fumigation yault, which
opens into the room beyond.
recommended dosage, per 1,000 cubic feet of empty space, is 28
pounds, with an exposure of from 12 to 24 hours. Several mixtures
have been offered to the public, but one containing about 15 percent
of the methy! formate seems to be the most effective and safe. This
fumigating mixture is similar to the ethylene oxide-carbon dioxide
mixture in the manner in which it is marketed and used.
VAULT FUMIGATION
Many establishments have use for a small fumigation vault for
the treatment of incoming raw materials, returned goods, outgoing
products, ete. Such a vault may be constructed of any material that
can be made gastight or reasonably so.
28 CIRCULAR 369, U. S. DEPARTMENT OF AGRICULTURE
Several types of metal vaults (fig. 28) can be purchased knocked
down ready for assembling. These are excellent in every way.
Highly satisfactory vaults can be constructed of concrete, brick, or
hollow tile. The ‘brick (fig. 29) and hollow-tile (fig. 30) vaults
should be finished inside ere a layer of Keen’s cement and 1 or 2
coats of paint. Wooden vaults with a metal lining are also popular.
It is possible to purchase 14-gage sheet metal cut up into sections
for constructing a vault 8 by 10 by 1 12 feet. When welded together,
the sections form an excellent gastight lining.
The cheapest type of vault is made of wood, An efficient vault
can be constructed of two layers of 2-inch standard flooring sepa-
rated by a layer of heavy roofing paper. If the edges of each board
are painted with heavy white- lead paint just before the tongue and
groove are forced tightly together, the walls are even tighter. The
floor, walls, and roof should be of the same tight construction. The
FIGURE 28.—Two types of metal vaults such as can be purchased or built according to
space and commodity need. These vaults are used for treating the day’s arrival of
fur coats offered for summer storage. After an overnight fumigation in these vaults
the furs are removed to large permanent storage vaults.
interior should be given 2 or 3 coats of any good paint. An
aluminum paint is sometimes used to advantage.
All types of vaults should be equipped with a refrigerator or safe
type of door, well gasketed to make it gastight.
A ventilating system capable of quickly removing the fumigant
from the vault after the fumigation is essential. If ‘the vault is set
up inside a building, the ventilating stack must extend outside the
building and pr eferably above the roof.
It is sometimes desirable to install an electrical heating unit, con-
trolled by a thermostat, so that a constant high temperature can be
maintained throughout ‘the fumigation.
For applying the fumigant several different methods can be used.
For heavier-than-air gases a shallow evaporating pan or trough
should be installed near the ceiling of the vault, with a feed pipe ex-
tending outside (fig. 830). The fumigant can then be run into the
}
:
F
INDUSTRIAL FUMIGATION AGAINST INSECTS 29
RD 2 9 ELSIE ER SLA CE EISELE TOT
Canepa wie ae He PTSD RO ES LORE TOT.
oR: dost PS
quan maa om : et :
Santen’ RRR EO i Ree S
Figure 29—Two outdoor fumigation vaults under one roof, built of brick, finished on
the inside with Keen’s cement, and equipped with doors shutting against rubber
gaskets to prevent gas leakage. Note ventilators in roof to aid in ventilation when
lighter-than-air gas is used. (Photograph by Perez Simmons.)
Figure 30.—Outdoor structure built for fumigation of dried fruits. It is made of
hollow tile, plastered on the inside with Keen’s cement, and equipped with a Tre-
frigerator-type door. Note funnel-shaped openings above the door, through which
a liquid fumigant can be poured into evaporating trays suspended from the ceiling
of the vault. (Photograph by Perez Simmons.)
30 CIRCULAR 369, U. S. DEPARTMENT OF AGRICULTURE
evaporating pan by gravity or compressed air. If liquid hydrocyanic
acid or the ethylene oxide-carbon dioxide mixture is to be used, a
short piping system with one or more spray nozzles can be installed
(figs. 20, 21, and 27).
USE OF FUMIGANTS SUITABLE ALSO FOR LARGE SPACES
Hydrocyanic acid, chloropicrin, ethylene oxide-carbon dioxide
mixture, and the methyl formate-carbon dioxide mixtures are all
suitable for vault fumigation, and they can be used in the manner
described for the fumigation of large spaces. If hydrocyanic acid
is used, the pot or the discoid method is best adapted for vault fumi-
gation, since only small quantities of the chemical are used at one
time. Chloropicrin can be applied by pouring the dosage into the
evaporating pan or by forcing it in through a piping system with
compressed air. The ethylene oxide-carbon dioxide mixture and the
methyl formate-carbon dioxide mixtures are applied through a pip-
ing system and can be administered by connecting the cylinder to
the system (fig. 27) and opening the valve. If the cylinder is placed
on a platform scale, it is an easy matter to let in the quantity desired.
USE OF OTHER FUMIGANTS
Various other fumigants, not suitable for warehouse fumigation,
can also be used successfully for vault fumigation. These are car-
bon disulphide, ethylene oxide, ethylene dichloride-carbon tetrachlo-
ride, and carbon tetrachloride.
CARBON DISULPHIDE
Carbon disulphide is a colorless, volatile liquid, which boiis at
114.8° F. On exposure to air it evaporates, forming a heavy vapor
that is very toxic to insects.
It is applied by pouring the liquid into the evaporating pan of a
vault at the rate of about 5 pounds per 1,000 cubic feet of space. If
the vault is not tight, more fumigant should be used. It should not
be used at temperatures below 70° F., and the exposure should be at
least 12, and preferably 24 hours.
The vapors of carbon disulphide, when mixed with air in certain
proportions, are highly inflammable and explosive; hence this fum1-
gant should be used only where the fumigation vault is isolated from
other buildings, and where the fire hazard can be controlled.
Mixtures of carbon disulphide with other chemicals, such as carbon
tetrachloride and sulphur dioxide, for the purpose of reducing the
fire hazard are now on the market. Although not absolutely nonin-
flammable, they can be used with comparative safety. Their efficacy
is directly proportional to the carbon disulphide content, and they
should be used accordingly.
The vapors of carbon disulphide are poisonous to human beings if
breathed for an extended period. Exposure to light concentrations
may induce a feeling of giddiness, which, however, will quickly pass
off on coming out into the fresh air. Small quantities of carbon
disulphide can be handled without danger by the ordinary person,
although persons having any heart trouble should take little part
in its application.
INDUSTRIAL FUMIGATION AGAINST INSECTS 31
Carbon disulphide ranges in cost from about 6 cents a pound in
500-pound lots to 380 cents a pound in 1-pound lots.
CARBON TETRACHLORIDE
Carbon tetrachloride is a colorless, volatile liquid having a boiling
point of 170° F. Its vapors are noninflammable, and therefore it
1s sometimes recommended as a fumigant in place of carbon disul-
phide.
It is not very effective when used alone against insects that infest
stored products and should be chosen only when no other fumigant
will do. Its chief use is for mixing with more toxic fumigants to
reduce the fire hazard.
To be at all effective, it must be used at a temperature of 75° F. or
higher, and at the rate of at least 30 pounds per 1,000 cubic feet of
space. It is applied by pouring it into the evaporating pan of the
vault. The vapors of carbon tetrachloride have an anesthetic effect
when breathed by man. Although they are not quickly toxic, it is
not safe to remain for any length of time in a strong concentration of
the gas.
The cost of carbon tetrachloride ranges from about 5.8 cents per
pound in large quantities to 10 cents per pound in small lots.
ETHYLENE DICHLORIDE
Ethylene dichloride is a colorless liquid with an odor similar to
that of chloroform. It has a boiling point of 183.2° F., and on ex-
posure to air it evaporates, forming a gas that is more than three times
as heavy as air. It is an effective fumigant in gastight vaults, but
owing to its high boiling point it should be used at a temperature
of at least 70° F. and preferably somewhat higher.
The vapors of ethylene dichloride are slightly inflammable. It
is therefore customary to use this fumigant in combination with
some noninflammable chemical, such as carbon tetrachloride or
trichloroethylene. A mixture of 3 volumes of ethylene dichloride
with 1 volume of carbon tetrachloride or trichloroethylene is free
from fire hazard under ordinary conditions, and is an effective fumi-
gant when used at the rate of 14 pounds per 1,000 cubic feet of
space.
This fumigant is apphed by pouring it or forcing it under pres-
sure into the evaporating pan of the vault. A small fan blowing
on the surface of the liquid insures a more rapid vaporization of the
fumigant and hastens its killing action.
The vapors of ethylene dichloride have an anesthetic effect upon
man, and although it is safe to use in small quantities, one should
not be exposed to a heavy concentration of the gas for more than
a very brief pericd without a gas mask.
The mixture of ethylene dichloride and carbon tetrachloride or
trichloroethylene has no corrosive action on metals or any bleaching
or staining action on textiles of ary sort. It is suitable for treat-
ing grains and seed, but shou!d not be used for foodstuffs with a
high fat content, for they are likely to retain a disagreeable odor
and taste after fumigation.
Ethylene dichloride can be purchased separately or already mixed
with carbon tetrachloride or trichloroethylene. Alone or mixed
By) CIRCULAR 369, U. S. DEPARTMENT OF AGRICULTURE
with carbon tetrachloride it sells for from 6.4 to 9.9 cents per
pound, f. o. b. the factory, plus certain freight allowances. There —
are approximately 10 pounds to the gallon.
ETHYLENE OXIDE
Ethylene oxide is a colorless gas at ordinary temperatures, but
below 50° F. it is a colorless hquid. It has a boiling point of about
57.2°, and therefore it can be used with success at temperatures
considerably below 70°.
The concentrated vapor of ethylene oxide is inflammable, but
concentrations up to 314 pounds per 1,000 cubic feet of space are
nonexplosive and noninflammable.
A dosage of 2 pounds per 1,000 cubic feet will give satisfactory
results in a tight vault, with an exposure of from 10 to 20 hours.
The liquid, which is sold in cylinders, can be drawn off into a
measuring container and poured into the evaporating pan of the
vault. Owing to its extreme volatility, it should not be drawn from
the cylinder until the fumigation chamber is ready for the charge.
Ethylene oxide gas is not injurious to fumigated commodities,
and no obnoxious odor or poisonous residue is left upon them. The
gas is not highly toxic to man and can be handled in small quan-
tities without danger or discomfort. Nevertheless, the operator
should avoid breathing the fumes for any length of time and should
not enter a heavy concentration without wearing a gas mask.
If ethylene oxide is used alone, it is advisable not to operate an
electric fan inside the vault, lest an inflammable concentration of
the gas has been accidentally obtained.
Ethylene oxide can be purchased in cylinders containing 314, 1814,
75, or 195 pounds, at prices ranging from 50 cents to $2 per pound,
according to the quantity purchased and size of cylinders, f. o. b
factory, east of the Rocky Mountains; for deliveries from the Los
Angeles and San Francisco warehouses prices are 5 cents per pound
higher.
BIN FUMIGATION
Bins used for the storage of foodstuffs. yarn, hosiery, etc., fre-
quently need to be fumigated. For this purpose any of the heavier-
than-air gases, such as carbon disulphide, chloropicrin, ethylene
oxide, or ethylene dichloride-carbon tetrachloride mixture, can be
used, provided it is suitable for treating the commodity stored in
the bin. :
The fumigant should be sprinkled evenly over the surface of the
contents of the bin, and the bin should then be covered as tightly
as possible. As the fumigant evaporates, the vapor, being heavier
than air, gradually penetrates the material from the top to the
bottom.
The quantity of fumigant needed will depend upon the tightness
of construction of the bin, the type of material to be fumigated, and
the fumigant being used. Bins are seldom so tight as fumigation
vaults; hence larger dosages are necessary.
INDUSTRIAL FUMIGATION AGAINST INSECTS 33
VACUUM FUMIGATION
Fumigation by vacuum (figs. 31, 32, and 33) consists in placing
the commodities to be fumigated in a gastight steel chamber, remov-
ing the air, and replacing it with a gas lethal to insects. By this
method there is immediate penetration of commodities by the gas,
and insects are killed with a rapidity that is not obtainable in an
atmospheric vault. The length of exposure required in vacuum fumi-
gation ranges from 1 to 3 hours, as compared with from 10 to 24
hours under atmospheric conditions. This process, therefore, has a
considerable appeal in industries where speed is essential, as in the
handling of foodstuffs and other commodities.
In addition to reducing the time of exposure, vacuum fumigation
has several other advantages. At the end of a fumigation the gas
can be speedily removed from the treated commodities by a process
known as “alr washing”, which consists in drawing a vacuum of
27 inches and breaking it with air. Furthermore, by this method
workmen are not exposed to the fumes of the gas. The disadvan-
tages are the original cost and upkeep of the equipment and the
larger quantity of fumigant needed.
EQUIPMENT
Vacuum chambers are usually cylindrical, although rectangular
tanks are increasing in popularity. They are made in all sizes, from
laboratory outfits with a capacity of about 1 cubic foot up to those
capable of holding one or more carload lots. The size of the cham-
ber will depend on the type and quantity of material to be fumi-
gated and the space available for it in the factory. Some firms prefer
to have two tanks that can be operated with one set of equipment.
While one tank is under fumigation, the other can be loaded or
unloaded and the fumigation crew kept continuously busy.
The tanks are usually installed so that small trucks or factory
skids on narrow-gage tracks can be run into them. If the vacuum
chamber is equipped with a door at each end, the trucks can be run
in at one end and out the other, so that the fumigated products will
not interfere with the next load. In some factories one end of the
vacuum chamber opens into the receiving room and the other end
into the general storage room. Raw materials likely to be infested
are then fumigated before they are placed in the general storage
rooms.
The doors of the vacuum tank should be so balanced and hung
that they can be quickly opened and closed by one man. The gaskets
should be durable and at the same time provide a gastight seal. The
efficiency of a tank depends largely on the tightness with which the
doors fit. A well-built tank should hold a vacuum without perceptible
loss throughout the average fumigation period.
Many tanks are equipped with steam coils or electric heating units
to maintain a favorable temperature during fumigation. A thermo-
stat should be used to maintain a constant temperature and to pre-
vent overheating.
Each installation requires a vacuuin pump capable of drawing a
28-inch vacuum in 10 minutes or less.
lac = el
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DEPARTMENT OF AGRICULTURE
fo 1S
+
CIRCULAR 369,
o4
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INDUSTRIAL FUMIGATION AGAINST INSECTS 35
The use of a vaporizer in connection with a vacuum chamber in-
creases its efficiency by insuring the entrance of the fumigant in a
gaseous state. The most common type of vaporizer consists of a
steel tank in which steam is generated by means of electric heating
elements. A copper coil, through which the fumigant is conducted,
runs through this steam-heated tank and is so designed that the
fumigant is in gaseous form by the time it reaches the vacuum
chamber. If carbon disulphide is used, a specially designed vaporizer
is required, since it must be mixed with carbon dioxide before it is
admitted to the fumigating chamber.
In some modern vacuum outfits an accumulator tank is utilized to
vaporize and heat the fumigant before drawing it into the vacuum
Figure 32.—End view of vacuum equipment shown in figure 31. Tank at left closed
and under fumigation. Tank at right nearly loaded with 43,000 pounds of Turkish
tobacco. These tanks will treat all incoming tobacco placed in this storage establish-
ment. Note end of cylindrical accumulator on top of tank at right.
chamber. It consists of a tank with a heating coil into which the
dosage is drawn, and in which it can be held until ready for use.
Hydrocyanic acid, chloropicrin, ethylene oxide-carbon dioxide
mixture, methyl formate-carbon dioxide mixture, and carbon di-
sulphide-carbon dioxide mixture are used in vacuum fumigation.
The dosage required depends on the commodity to be fumigated
and the length of exposure.
PROCEDURE
The commodity to be fumigated is first loaded into the vacuum
chamber, the doors are tightly closed, and a vacuum of about 28 or
ee nn ro
ee
———E
36 CIRCULAR 369, U. S. DEPARTMENT -OF AGRICULTURE
29 inches is drawn. The proper dosage of fumigant is then admitted
through the vaporizer or accumulator. The remaining vacuum
should be held without change for the duration of the fumigation,
since it has been found that better results are obtained if the vac-
uum is held instead of being broken with air. A chart record (fig.
34) should be made of each fumigation in case it is needed for
future reference.
At the end of the fumigation the gas is pumped out of the cham-
ber and the vacuum is broken with air. If desired, the fumigated
FIGURE 33.—Portion of vacuum fumigator installed in a large candy establishment.
Note vacuum pump in left foreground; cylindrical accumulator on tank; gages for
automatically recording pressure, vacuum, and temperature; and cylinder of the
ethylene oxide-carbon dioxide mixture in front of operator. Cylinders of methyl
formate-carbon dioxide mixture are attached in the same manner.
products can be “ air-washed ” several times by alternately drawing
and breaking a vacuum of about 27 inches.
Commodities taken from cold storage should be allowed to come
up to room temperature before they are loaded into the vacuum
tank. Insects that have been chilled are in a dormant state, and
their resistance to fumigants is increased. ‘This resistance is re-
tained for several hours after they are brought into a heated atmos-
phere, and is therefore not overcome during the time they are in
the heated vacuum chamber. If the infested commodities are
allowed to warm up to room temperature before fumigation, the
insects will regain their normal activity and lose their resistance
to fumigants.
a
INDUSTRIAL FUMIGATION AGAINST INSECTS 37
FUMIGATION OF VARIOUS COMMODITIES
Since it is impossible to discuss here in detail the fumigation of
all the many types of commodities that become infested with in-
sects, only those commodities most often fumigated in commercial
establishments are included in this circular. The fumigation of
grain in bulk on the farm and in the terminal elevator is discussed
in other publications of the Department.* | No attempt is made to
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FigurRE 34.—Automatic record of four vacuum fumigations conducted during a period
of 24 hours. Hours of day and night are indicated on the circunrference of the ehart.
Figures in circles indicate: (1) vacuum pump started; (2) chamber exhausted to
28.5 inches of mereury; (38) fumigant (ethylene oxide-carbon dioxide mixture) intro-
duced; (4) treatment period of 2 hours; (5) vacuum pump operating and breaker
valve opened simultaneously, providing an air wash of product fumigated; (6) treat-
ment cycles similar to (4); (7) last fumigation of day allowed to continue over-
night; (8) doors opened, contmodity removed, and a new lot placed in chamber; (9)
vacuum pump started before breaker valves were opened, accounting for the rise in
vacuum at this point.
discuss the fumigation of any commodity from a quarantine stand-
point. For more detailed information regarding the treatment of
any commodity discussed in the following pages, or regarding
commodities not mentioned, the reader should direct inquiries to
the Bureau of Entomology and Plant Quarantine, United States
Department of Agriculture, Washington, D. C.
4Farmers’ Bulletin 1260, Stored-Grain Pests, and Farmers’ Bulletin 1483, Control of
Insect Pests in Stored Grain.
SS ee ee ee
—— ee Oo
38 CIRCULAR 369, U. S. DEPARTMENT OF AGRICULTURE
CONFECTIONERY
Since the insect problems of the candy and nut-meat industries are
rather closely associated, it seems logical to discuss them under one
heading. Nut meats are highly susceptible to insect attack, and
because they are used in large quantities in the manufacture of
candy, they constitute an important source of insect infestation in the
candy factory.
Most firms handling nut meats attempt to ship only insect-free
nuts. To do this they keep their factories and storage warehouses
as free from infestation as possible, in addition to fumigating all
outgoing merchandise. A yearly fumigation of the factory with
hydrocyanic acid gas, supplemented by constant attention to clean-
liness, will reduce insect infestation to a minimum. A dosage of 8
ounces of liquid hydrocyanic acid or its equivalent per 1,000 cubic
feet is sufficient for this purpose. An exposure of 24 hours is
desirable.
Where nut meats in the shell are stored without cold storage, it
sometimes becomes necessary to fumigate the warehouses also. Hy-
drocyanic acid is the best fumigant for this purpose and should be
apphed at the rate of 16 ounces of liquid hydrocyanic acid or its
equivalent per 1,000 cubic feet. Excellent results can be obtained
in tightly constructed warehouses, even though the bagged nuts are
piled in large stacks. If possible, a 48-hour exposure should be
given.
Nuts absorb considerable hydrocyanic acid gas, and therefore a
warehouse that has been fumigated cannot be aired out very quickly.
Large stacks of bagged nuts hold the gas and give it off slowly over
a period of several days. In one fumigation conducted by the writ-
ers in an exceptionally tight warehouse, bagged peanuts retained
so much of the gas that it was unsafe for workmen to enter the ware-
house until it had been aired for 5 days.
VAULT FUMIGATION FOR NUTS
Nuts are usually fumigated in atmospheric vaults or vacuum tanks
before they leave the factory or go from the storage warehouse to the
factory. A 1,000-cubic-foot atmospheric vault will hold about half
a carload of bagged nuts, such as peanuts—about two hundred and
fifty 100-pound bags of shelled peanuts or 125 such bags of peanuts
in the shell.
A dosage of 3 pounds of ethylene oxide or 25 pounds of the ethy-
lene oxide-carbon dioxide mixture per 1,000 cubic feet of space, with
an exposure of from 20 to 24 hours, will give excellent results at
a cost of from 1 to 3 cents per 100-pound bag, including labor
charges. co
Hydrocyanic acid can also be used for fumigating nuts in atmos-
pheric vaults, although it is not so popular for this purpose as
ethylene oxide. A dosage of one-half pound of liquid hydrocyanic
acid or its equivalent is required for each 1,000 cubic feet of space.
VACUUM FUMIGATION FOR NUT MEATS
For the vacuum fumigation of nuts the ethylene oxide-carbon
dioxide mixture is excellent. A dosage of 380 pounds per 1,000 cubic
INDUSTRIAL FUMIGATION AGAINST INSECTS 39
feet for a period of from 1 to 2 hours gives satisfactory results at a
cost of from 344 to 4 cents per 100 pounds of nuts. A mixture of
carbon disulphide and carbon dioxide has been used in the vacuum
treatment of nuts, but owing to the need for special equipment for
applying it safely and to the fact that it is unsuitable for the
treatment of pecans, Brazil nuts, and cashews, it is not recommended.
FUMIGATION SCHEDULE FOR CANDY FACTORIES
The adoption of a regular fumigation schedule would largely
eliminate insect losses in the candy industry. Infested raw materials
and returned goods constitute the main sources of infestation in the
factory. Insects from these sources spread all over the factory and
lay eggs on the finished product. These eggs hatch after the candy
is packed and produce costly infestations in packages that leave the
factory apparently in good condition.
Every candy factory should have a fumigation vault or a vacuum
chamber, and all returned goods should be fumigated before they are
admitted to the factory. All incoming raw materials that are sus-
ceptible to insect attack, such as nut meats, cocoa beans, farinaceous
materials, dried fruits, milk powders, and chocolate, should be rigidly
inspected on their arrival at the plant and, if infested or suspected
of being infested, should be fumigated before being placed in the
main storage sections. If possible, raw materials should be stored
away from the main part of the factory, and in sections that are
adapted for separate fumigation.
DOSAGES
Returned goods and raw materials other than nut meats can be
fumigated in tight vaults with one of the following fumigants at the
dosages indicated per 1,000 cubic feet: Ethylene oxide, 2 pounds;
ethylene oxide-carbon dioxide mixture, 20 pounds; or liquid hydro-
cyanic acid or its equivalent, 8 ounces.
Large storage sections can best be fumigated with hydrocyanic
acid at the rate of 8 ounces of liquid hydrocyanic acid or its equiva-
lent per 1,000 cubic feet.
As a general precaution it is advisable to fumigate the entire fac-
tory at least once a year. For this purpose hydrocyanic acid should
be used at the same rate as for the treatment of the large storage
sections.
FURNITURE
Insect-infested furniture is usually fumigated in an atmospheric
vault, although a vacuum vault can be used and is preferable in
cases where infestation is due to wood-boring insects.
Hydrocyanic acid, ethylene oxide, ethylene oxide-carbon dioxide
mixture, carbon disulphide, chloropicrin, carbon tetrachloride, and
the ethylene dichloride-carbon tetrachloride mixture can all be used
for the fumigation of furniture in atmospheric vaults.
Hydrocyanic acid and the ethylene dichloride-carbon tetrachloride
mixture are used most commonly. A dosage of 8 ounces of liquid
hydrocyanic acid or its equivalent, or of 14 pounds of ethylene di-
chloride-carbon tetrachloride mixture, per 1,000 cubic feet of space,
for a period of 12 to 24 hours will give satisfactory results unless
40 CIRCULAR 369, U. S. DEPARTMENT OF AGRICULTURE
wood borers are involved, when the exposure should be at least 48
hours. If any of the other fumigants are used, the following dosages
should be applied per 1,000 cubic feet of space: Ethylene oxide, 2
pounds; ethylene oxide-carbon dioxide mixture, 20 pounds; carbon
sulphide, 5 pounds; chloropicrin, 1 pound; or carbon tetrachloride,
30 pounds.
FURS AND GARMENTS
The protection of furs and fur garments in storage by fumigation
instead of cold storage is becoming more and more common. The
method consists merely in storing fur garments in tight rooms (fig.
35) that are so arranged that they can be fumigated regularly. The
fur garments are fumigated in a small fumigation vault (figs. 2 and
28) before being placed in the storage rooms (fig. 36).
CONSTRUCTION OF STORAGE ROOMS
The large storage rooms may be of any type of construction that
is sufficiently tight for fumigation purposes. Usually they are of
concrete or of hollow tile covered with Keen’s cement. The surface
should be finished with 2 or 3 coats of gas-resistant paint. Large,
shallow evaporating pans are fastened along the walls near the ceil-
ing. These pans are connected by pipes to the storage tank (fig.
37) containing the fumigant. If ethylene dichloride-carbon tetra-
chloride mixture is used as the fumigant, it can be run into the
evaporating pans by gravity or by the use of a small compressor.
If ethylene oxide-carbon dioxide or methyl formate-carbon diox-
ide mixture is to be used, the evaporating pans are unnecessary, and
a piping system with one or several spray nozzles or cones should be
used instead. The cylinders containing one of these mixtures with
carbon dioxide are connected to the piping system outside of the
room (fig. 27), and the fumigant is apphed by merely opening the
valve on the cylinders and allowing the required poundage to be
discharged.
The door of the storage room is usually of the safe or refrigerator
type, well gasketed so that it will be airtight. An adequate venti-
lating system must be installed, so that the gas can be quickly re-
moved after the fumigation. As in the case of small fumigation
vaults, the ventilating stack should extend well outside the building.
In cold climates there should be some means of heating the storage
room to at least 70° F. during the fumigation.
If it is necessary to enter the storage room while it is under fumi-
gation, the operator should wear a gas mask equipped with a canister
designed for protection against the particular gas that is being used
and should remain in the room only long enough to obtain the
garment needed.
DOSAGES
For the fumigation of the large storage sections a dosage of 14
pounds of the ethylene dichloride-carbon tetrachloride mixture, 20
pounds of ethylene oxide-carbon dioxide mixture, or 28 pounds of
a methyl formate-carbon dioxide mixture, per 1,000 cubic feet of
space and an exposure of at least 48 hours should be used.
41
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AGAINST INSECTS
INDUSTRIAL FUMIGATION
42 CIRCULAR 369, U. S. DEPARTMENT OF AGRICULTURE
For the preliminary fumigation of fur garments in small vaults
the same fumigants and the same dosages recommended for the large
storage sections can be used, although an exposure of 12 to 24 hours
is sufficient.
EFFECT OF FUMIGATION ON FURS
Fur garments appear to be in no way affected by the vapors of the
fumigants recommended, and dry storage has no deleterious effect
upon the furs. A few instances of change in color of furs stored in
tumigable storage have been reported, but in no case has this been
clearly shown to be the result of fumigation. Thousands of dollars’
FigURE 36.—Interior of fur-storage vault with racks installed for holding garments in
best possible position for ready access and effective fumigation.
worth of furs are being stored annually in fumigable storages
throughout the country, to the satisfaction of all concerned.
RUGS AND TAPESTRIES
Rugs and tapestries in storage can be protected by the same meth-
ods and equipment that are recommended for the storage of furs.
Many firms, however, prefer to use naphthalene flakes or paradi-
chlorobenzene crystals in place of liquid fumigants. On exposure to
air at ordinary room temperatures, both these solid fumigants give
off a heavy vapor, which gradually permeates the atmosphere of the
storage room. If a saturated atmosphere of either of these materials
is maintained in the storage room, adequate protection from insects
‘an be obtained (fig. 38). |
INDUSTRIAL FUMIGATION AGAINST INSECTS 43
At a temperature of 77° F., 8 ounces of paradichlorobenzene or
0.64 ounce of naphthalene is required to saturate the atmosphere in
1,000 cubic feet of space. Under ordinary storage conditions, how-
ever, it is advisable to use an excess of these fumigants i in order to
counteract. losses by absorption and leakage and to insure a con-
tinuously saturated atmosphere.
When no attempt is made to hasten evaporation by the applica-
tion of heat, the vapors of naphthalene and paradichlorobenzene are
not so quickly toxic to insects as are the hquid fumigants. Their
chief value lies in the continuous protection that they afford. Since
vapors are evolved
but slowly from the
crystals, one applica-
tion may last for
several months.
Aside from having
an irritating effect
upon the eyes, the va-
pors of naphthalene
and paradichloroben-
zene are apparently
not injurious to man
unless inhaled in
strong concentrations
for an extended pe-
riod,
Reaneadeuc hil oxo=
benzenecrystalscan be
purchased for from
1G Stoe-o0- cents per:
pound in small lots.
Naphthalene flakes
are quoted at 214 to
10 cents per pound.
Pte tinct ne eooaceiaens sonia,
i
DRIED FRUIT FIGURE 37.—Exterior view of commercial fur-storage vault
quinned for fumigation with ethylene dichloride-carbon
c oF, x tetrachloride mixture. Note storage drum at right,
Dried fruit is very pump at left, and pressure tank in center connected
susceptible to insect witmvarious fumigating vaults, not shown, by pipe lines
attack and must be
protected from infestation at all times. Growers and packers usually
find it necessary to fumigate dried fruit before it 1s stored, and for
this purpose should equip themselves with fumigation chambers or
fumigable storage bins (fig.3). The fumigation of dried fruits un-
der rubberized tarpaulins is reasonably effective. The fruit can be
fumigated and then placed in an insect-tight storage section, or it
can be placed directly in storage bins that are so constructed that
they can be fumigated from time to time as needed. Any type of
construction that is gastight is suitable for storage bins.
On ranches (figs. 29 and 30), where the fire hazard can be euarded
against, carbon disulphide can be used. It is both cheap and effec-
tive. A dosage of 20 pounds per 1,000 cubic feet of space and an
exposure of 24 hours at a temperature of 70° F. or higher will give
44 CIRCULAR 369, U. S. DEPARTMENT OF AGRICULTURE
satisfactory results. Chloropicrin is often used as a fumigant in
special farm storages.
In packing houses or storage sections where fumigation dhanibers
or fumigable storage bins are not isolated, a fumigant that does not
have the fire hazard of carbon disulphide i is desirable. In such cir-
cumstances ethylene oxide or a mixture of ethylene oxide and carbon
dioxide can be used. Ethylene oxide at the rate of 2 pounds, or the
ethylene oxide-carbon dioxide mixture at the rate of 20 pounds, per
1,000 cubic feet of space should be for a period of 24 hours.
Hydrocyanic acid can also be used in airtight vaults at the rate of
1 pound of liquid hydrocyanic acid or its equivalent per 1,000 cubic
feet. Hydrocyanic acid gas is absorbed in considerable quantities
by dried fruit, but is quickly 9 oiven off after the fruit is aerated.
FIGURE 38.—Rug-storage vault in which rugs are protected against fabric pests by
vapors of paradichlorobenzene or flake naphthalene.
TREATING THE FINISHED PRODUCT
It is sometimes desirable to fumigate the finished package prior
to shipping it from the packing plant. For this purpose a fumiga-
tion room or a vacuum tank is necessary. If a fumigation chamber
is used, the fumigants and dosages recommended for the raw prod-
ucts can be used. If vacuum fumigation is resorted to, excellent
results can be obtained with a dosage of 30 pounds of the ethylene
oxide-carbon dioxide mixture per 1,000 cubic feet for a period of
from 1 to 2 hours.
INFESTATIONS IN WAREHOUSES
Infestations that develop in storage warehouses can be handled by
fumigating the infested fruit in a “fumigation chamber or vacuum
tank or by fumigating the entire storage section with hydrocyanic
acid. If the entire storage section is fumigated, a dosage of from
8 to 16 ounces of quid hydrocyanic acid or its equivalent per 1,000
cubic feet of space should be used for a period of 24 hours. The
dosage will depend on the tightness of the storage section and the
quantity of fruit in storage.
INDUSTRIAL FUMIGATION AGAINST INSECTS 45
CURED MEATS AND CHEESES
Infestation of cured meats and cheeses by mites, ham beetles, or
skippers frequently makes fumigation necessary. Meat-storage houses
that are reasonably tight can usually be successfully fumigated with
hydrocyanic acid at the rate of 1 pound of liquid hydrocyanic acid or
its equivalent per 1,000 cubic feet for a period of 24 hours. Such
treatment does not injure the meats, but if the infestation has pene-
trated deeply into the meat, it is difficult. to get a perfect kill. The
Federal meat-inspection regulations * require that permission for each
fumigation be obtained from the Federal méat inspector.
Cheeses that are protected by an unbroken layer of paraffin can be
safely fumigated with hydrocvanic acid, but, owing to the danger of
FiGURE 39.—Interior of tobacco storage with tobacco stored in hogsheads.
their absorbing large quantities of the gas, unprotected cheeses should
be removed from a warehouse that is to be fumigated.
For the treatment of small quantities of cur ed meats or cheeses, a
fumigation vault or other tight container is recommended. Carbon
disulphide at the rate of 10 pounds, ethylene oxide at the rate of 2
pounds, or the ethylene oxide-carbon dioxide mixture at the rate of
20 pounds, per 1.000 cubic feet of space can be used for a period of
24 hours.
STORED TOBACCO
Tobacco that is held in storage (figs. 39 and 40) often becomes in-
fested with the tobacco beetle “(Lastoder ma serricorne Fab.) or the
tobacco moth (£phestia elutella Hbn.). If the infested tobacco is
>U. S. Department of Ap uaure: Bureau of Animal Industry, Service and Regulatory
Announcements, January 192 , p. 3, and August 1927, p. 62. :
46 CIRCULAR 369, U. S. DEPARTMENT OF AGRICULTURE
held in closed storage, fumigation with hydrocyanic acid gas is the
most effective means of preventing further loss from insect attack.
One fumigation a season should be sufficient to control the tobacco
beetle unless additional infested stocks are moved into the storage sec-
tion after the fumigation. If the tobacco moth is present, it will prob-
ably be necessary to fumigate 2 or 3 times during a season. Where
only one fumigation is given, a dosage of 1 pound of liquid hydro-
cyanic acid or its equivalent should be used per 1,000 cubic feet of
space, but if more than one is to be given, a dosage of 8 ounces is suffi-
cient. If possible, an exposure of from 48 to 72 hours should be given
in each instance.
Figure 40.—Tobacco in bales and stacked as closely as shown here cannot be fumigated
satisfactorily by ordinary atmospheric fumigation. - The bales should either be more
loosely stacked or removed to vacuum chambers for fumigation.
For the fumigation of tobacco factories a dosage of 8 ounces of
liquid hydrocyaniec acid or its equivalent per 1,000 cubic feet for a
period of 24 hours is sufficient.
In order to keep down infestation in tobacco factories, many firms
make a practice of fumigating all incoming tobacco in airtight
vaults. For this purpose hydrocyanic acid in a dosage of 10 ounces
of liquid hydrocyanic acid or its equivalent, ethylene oxide at the
rate of 2 pounds, ethylene oxide-carbon dioxide mixture at 20
pounds, or carbon disulphide at 10 pounds, per 1,000 cubic feet of
space should be used for a period of from 48 to 72 hours. Carbon
disulphide should not be used unless the vault is isolated from the
rest of the buildings and the fire hazard can be controlled. The
fumigation of an entire tobacco warehouse with carbon disulphide
is a dangerous procedure and is not recommended.
INDUSTRIAL FUMIGATION AGAINST INSECTS 47
Vacuum fumigation is sometimes used for the treatment of tightly
baled tobacco (figs. 31 and 32). In order to penetrate the bales and
to insure a quick kal, large quantities of fumigant are necessary.
A dosage of from 3 to 5 pounds of liquid hydrocyanic acid or 45
pounds of the ethylene oxide-carbon dioxide mixture per 1,000
cubic feet is required for a 214-hour exposure.
FLOUR
For controlling insects in flour mills and reducing insect damage
to milled products, some form of fumigation is usually pr acticed.
Many millers are satisfied to fumigate their mills once a year, while
others find it profitable to fumigate several times a year. One
thorough fumigation a year will usually control the Mediterranean
flour moth (Ephestia kuehniella Zell.), but the various flour beetles
are not so easily controlled.
PREPARING THE MILL FOR FUMIGATION
On account of the milling machinery the preparation of a flour
mill for fumigation is more of a problem than is the case in the
ordinary building. Instead of each floor being treated separately.
the whole building is considered as a unit. In addition to the ordi-
nary procedure for preparing a building for fumigation, the direc-
tions suggested by Dean and Schenk ° should be followed :
Before Stopping Mill
1. Shut off feed (wheat) at mixing bin.
2. Continue running all machinery until material is emptied from spouts,
elevators, conveyors, rolls, sifters, reels, purifiers, feed duster, suction trunk-
ing, and dust collectors.
3. Meanwhile, hammer elevator legs, machinery, frames, tubular dust collec-
tors, and spouts with a rubber mallet or other device which will not bruise
or injure the equipment.
After Stopping Mill
1. Open all machines, elevator boots, conveyor boxes, and flour bins.
2. Remove covers of all conveyors, making certain that all dead-end spaces
are readily accessible.
3. Thoroughly clean all conveyors, including dead-end spaces.
4. Clean out accumulations from bottom section of the bran duster.
5. Clean all elevator belting that may be webbed; drag spouts of same.
6. Remove the adjustable feed gage above grinding rolls and clean out
accumulations above rolls and feeders.
7. Examine tubular dust collectors and clean out all accumulations.
8. Clean out suction trunks, conveyors, and dust-collector systems.
9. Open dust-collector trap boxes, main trunks, and hand openings.
10. Loosen all sifter doors to permit entrance of gas during fumigation.
11. Leave every machine open; also all hand openings to spouts, elevator
legs, ete.
12. Remove and burn all infested materials accumulated in cleaning the mill.
13. All infested lots of flour and other milled products should be removed
(or reconditioned) before cleaning the mill. These products should not be
returned.
14. If the above procedure is followed, no accumulation of more than 1 inch
in depth will be present in the mill.
15. Special attention should be given to the cleaning of the “dead” spouts
and “dead” spaces in corners of spouts and machines.
16. Remove all bags and other materials used to plug spouts.
6DHAN, G. A., and SCHENK, G. THE CONTROL OF STORED GRAIN AND FLOUR MILL
INSECTS. Fourth Internatl. Cong. Ent. Trans. (1928) 2: 217-218, illus. 1929.
t
—— —
4S CIRCULAR 369, U. S. DEPARTMENT OF AGRICULTURE
CHOICE OF FUMIGANT
Chloropicrin and hydrocyanic acid are the two fumigants that can
be used successfully for mill fumigation. Hydrocyaniec acid is more
popular and gives more consistent results.
HYDROCYANIC ACID GAS FOR MILL FUMIGATION
In general, a dosage of 8 ounces of quid hydrocyanic acid or its
equivalent per 1,000 cubic feet of space has been found most satis-
factory for flour-mill fumigation. All the methods that have been
described for generating this gas may be used with good results.
For the miller who does his own fumigating, the pot or barrel
method is safer and cheaper, and therefore more desirable, although
the hot gas produced by this method is likely to escape from the
building faster than the cold gas produced by other methods.
Professional fumigators generally use hquid hydrocyanic acid. An
initial dosage of 4 ounces per 1,000 cubic feet of space, followed
by two dosages of 2 ounces at intervals of 2 hours, is sometimes used,
though it is doubtful whether the results are any better than when
the entire dosage is applied at one time.
A combination of the liquid hydrocyanic acid and the calcium
cyanide (40 to 50 percent Ca(CN).) methods has also been used
with success. An initial high concentration is obtained from the
liquid hydrocyanic acid, and this is maintained for from 4 to 6
hours by the gas that is slowly evolved from the calcium cyanide.
Four ounces of liquid hydrocyanic acid and 1 pound of calcium cyan-
ide per 1,000 cubic feet of space produce approximately the same
quantity of gas as 8 ounces of liquid hydrocyanic acid, and this is a
good combination to use. The calcium cyanide is applied first, and
after all the fumigators have left and closed the building the hquid
hydrocyanic acid is forced in through the piping system from the
loading platform.
DISTRIBUTION OF THE FUMIGANT
In general the gas should be equally distributed on all floors of a
mill. If, however, the floors are not well separated one from the
other on account of belt openings, poorly fitting doors, floors, ele-
vator openings, etc., the gas will tend to concentrate on the top floors;
hence the dosage on the lower floors should be somewhat heavier.
Floors that contain more machinery than others should also receive
a heavier dosage.
LENGTH OF EXPOSURE
Since it is difficult to hold a killing concentration of the gas in the
average miil for more than a few hours, an exposure of from 18
to 20 hours is all that is practical.
CHLOROPICRIN AS A MILL FUMIGANT
Under favorable conditions chloropicrin at the rate of 1 pound
per 1,000 cubic feet of space is a satisfactory flour-mill fumigant.
Tt should be used only in a tight building and when the temperature
is above 70° Ff’.
CORRECTION
Circular 369, United States Department
of agriculture, "Industrial Fumigation
against Insects": Page 49, line 1, sub—
stitute "page 24" for "page 48".
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INDUSTRIAL FUMIGATION AGAINST INSECTS 49
As indicated on page 48, there are several ways of applying the
pas, but the most effective method is to introduce the entire dosage
for the building into the machinery itself. If the machinery is run
for a short time while the gas is being applied, the vapor will be
distributed to all parts of the mill.
The vapors of chloropicrin have a deleterious effect on the baking
qualities of flour, but flours fumigated with chloropicrin show com-
plete recovery after being properly aerated. After a fumigation
with chloropicrin, it is advisable to lay aside the first few bags of
fiour that come through the mill and feed them back slowly into
the mill. In this way the chloropicrin is soon dissipated.
LOCAL FUMIGATION
Since insect infestation in a flour mill is confined largely to the
machinery, many millers prefer to fumigate the machinery alone
instead of the entire mill. The cubic content of the machinery being
only a fraction of that of the mill, the miller can afford to fumigate
more often. With a little sealing and plugging, each machine can be
separated from the others and fumigated when necessary. Instead of
only on week-ends, this type of fumigation can be utilized any night
after the mill is shut down. Hydrocyanie acid, chloropicrin, ethylene
dichloride-carbon tetrachloride mixture, or the ethylene oxide-carbon
dioxide mixture can be used. The machinery can be specially piped
and the fumigants sprayed in through nozzles, or the hquids can be
apphed by hand. ‘Two or three times the ordinary dosage for general
mill fumigation can be used in the machinery without great expense.
As in regular mill fumigations, the operator should wear a gas mask
when applying the fumigant and also when airing out the machinery
the following morning.
FUMIGATION OF FLOUR WAREHOUSES
It is often desirable to fumigate warehouses containing flour, feed,
or other cereal products. A complete kill cannot always be obtained,
however, since fumigants will not penetrate more than 1 or 2 inches
into bagged flour. Fortunately, insect infestation of bagged flours is
usually near the surface, and under favorable conditions the kill is
good enough to make fumigation well worth while. y