FUMIGANTS by C.L. Williams (c. 1931)

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FUMIGANTS by C.L. Williams (c. 1931)

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" Fumigants "

Author(s): C. L. Williams
Source: Public Health Reports (1896-1970),
Vol. 46, No. 18 (May 1, 1931), pp. 1013-1031
Published by: Association of Schools of Public Health

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VOL. 46 MAY 1, 1931 NO. 18

Surgeon, United States Public Health Service

Hydrocyanic acid is one of the most rapidly fatal poisons known to man. Because of this fact its use as a fumigant is attended by grave hazards to human life. These hazards may be guarded against, but their elimination requires the most meticulous care as well as a wide and thorough knowledge of behavior of the gas. Handled by experts it is reasonably safe, but in the hands of the ignorant, reckless, or careless, it is a frequent cause of fatal accidents, as may be verified in the files of our daily newspapers.

Hydrocyanic acid gas is our nearest approach to the ideal fumigant. Confined in enclosed spaces, quite small amounts destroy all animal life therein; but when liberated in the open air its dissipation is so rapid that it requires very large quantities to produce fatal results in human beings. It is this property of rapid dissipation in the open that permits its use as a fumigant. If it were not for this, fumigators could hardly handle the gas, and upon opening a fumigated building passers-by would be killed, whereas, as a matter of fact, it is practically impossible to force gas out of a building in sufficient volume to become dangerous to persons in the open air.

The gas is very penetrating; it will actually penetrate a brick wall if given sufficient time, although within the time allowed for fumigation this rarely occurs. Of course penetration through cracks in a wall is another matter. It will penetrate into the center of a sack of flour in about two hours; and if the concentration is maintained sufficiently high, enough gas will penetrate a sack of flour in six hours to kill weevils. Highly porous material is very rapidly penetrated by this gas-a fact of considerable importance to fumigators, since the gas penetrates their clothing almost at once.

Penetration being merely one feature of diffusion, it is not surprising to find that the gas also rapidly passes out of materials it has penetrated. A comparatively short stay in the open air will remove most of the gas from fumigated articles. An hour's airing, for ex-ample, renders a mattress safe to sleep on, unless an excessively

1Read before the police school in New York City, January 9, 1931.

517360-31 1 (1013)

May 1, 1931
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heavy concentration of gas has been used. Water, however, absorbs hydrocyanic acid and holds it, particularly in cold weather, so that after fumigation, moist articles require longer airing than dry ones. Ordinarily, gas absorbed by collections of water is given off so slowly that it is not dangerous; but occasionally a relatively large amount is taken up on a cold day, and when a warm day follows, the gas is then given off more rapidly. One or two accidents on ships have been attributed to gas absorbed and later released from bilge water under such circumstances. On one occasion the ship passed into the warm waters of the Gulf Stream.

From what has been said of dissipation of the gas in the open air it will be realized that it is only when gas is liberated in closed spaces, such as closed rooms or ships' holds, that it becomes dangerous. Foods absorb the gas, but not in dangerous quantities from the concentrations generally used in building fumigations. It is well, how- ever, to air fumigated foods for two or three hours before eating them. Foodstuffs fumigated in fumigation chambers with high concentrations of this gas (10 to 20 ounces HCN per 1,000 cubic feet) should be aired at least 24 hours.

Hydrocyanic acid gas is not injurious to the vast majority of the articles of commerce. In the concentrations used for ship fumigations to kill rats it is not injurious to any known material, including such delicately flavored commodities as tea and tobacco. This is a very important consideration and one of the dominating ones in the establishment of this gas as a fumigant. In heavier concentrations (10 ounces per 1,000 cubic feet) it is injurious to delicate vegetables, such as lettuce and probably to bananas, interfering with the ripening processes. It probably would kill living foods, such as oysters, although the necessity of fumigating oysters has never arisen. Fumigated eggs usually will not hatch. (Probably few people would suspect that the gas penetrates through the shells of eggs.)

Because only small amounts are required, hydrocyanic acid gas is a cheap fumigant, probably the cheapest effective fumigant. For the destruction of rats, only two ounces of HCN per 1,000 cubic feet of space is required. At $1 a pound, this amount costs 12½ cents.

Hydrocyanic acid is used as a fumigant in one of three ways:

(1) It is generated on the premises.

(2) It is supplied ready prepared as a liquid in steel cylinders, from which it is forced by air pressure and introduced as a fine spray, which at once evaporates.

(3) It is supplied as a solid which is spread on the floor. This solid form may be liquid HCN absorbed in an inert material, from

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p. 1015
which it evaporates, or it may be calcium cyanide powder, which absorbs moisture from the air and generates HCN.

The following is a list of the cyanide fumigants generally employed arranged according to the method of preparation:

(1) Hydrocyanic acid gas generated by adding sodium cyanide to 50 per cent sulphuric acid.

(2) Hydrocyanic acid, cyanogen chloride mixture. ─ The gas is generated by adding NaCN and sodium chlorate to 50 per cent hydrochloric acid.

(3) Safti-fume. ─ This is the same as the hydrocyanic acid-cyanogen chloride mixture, except that the NaCN and NaCl are ready mixed with sand and other more or less inert ingredients in the form of briquettes, which are dropped into HCl.

(4) Zyklon. ─ Liquid HCN absorbed in Fuller's earth. Packed in heavy cans.

(5) HCN discoids. ─ Liquid HCN absorbed in unsized paper disks. Packed in heavy cans.

(6) Cyanogas. ─ Calcium cyanide, a fine powder, packed in heavy cans.


(7) Liquid hydrocyanic acid in heavy steel cylinders. Forced through a hose and out a spray nozzle by air pressure.

Of these various preparations the most effective is liquid hydrocyanic acid. It is the most dangerous to use, both to the fumigators and to the innocent bystanders. The Interstate Commerce Commission requires that it be shipped only in heavy steel cylinders, the size usually employed holds 75 pounds. Since the liquid is extremely volatile, should a cylinder be broken in a traffic accident the results might be disastrous; for despite its rapid diffusion in the open air, the large amount immediately liberated would probably overcome those in the immediate vicinity at once. However, these cylinders are very strong and no accident due to their being broken by outside force has been reported. For use on ships the liquid is transferred to smaller and lighter (tested to 600 pounds pressure) steel cylinders holding 18 and 30 pounds. These are transported on the fumigating boat. In fumigating buildings the heavy cylinders are invariably used.

Set in the tops of the cylinders are two valves. From the outlet valve a steel tube leads to the bottom, the other opens directly into the cylinder, and through it air is pumped, just before use, until a

May 1, 1931
p. 1016
pressure of 75 to 100 pounds is reached. To the outlet valve is attached rubber pressure tubing ending in a spray nozzle; this is led into the space to be fumigated, the valve is opened, and the liquid forced out by the air pressure is sprayed into the air. The amount used is measured by placing the cylinder on a platform scale and noting the progressive loss of weight. In large buildings it is necessary to lay the hose to various parts before starting. Flour mills and similar large structures frequently fumigated are often equipped with a built-in system of lead or copper piping with an outside connection for the cylinders.

The dangers particularly attendant on the use of liquid hydrocyanic acid are from two sources: One is the fact that the gas reaches full concentration immediately, so that anyone caught in the building does not have time to get out. The other comes from leaks in the tubing, particularly at the joints. It is the latter that is the main danger to fumigators. As regards the former, of course, no one should be permitted to be in a building or ship about to be fumigated, and it is the fumigators' particular business to see that all are out; but despite the most careful guarding, unauthorized persons sometimes get caught. If liquid hydrocyanic acid is the fumigant they will never be caught again. This danger is a very real one, even to the best-trained fumigators. Recently on a ship a hose line, inadvertently left under pressure, was being uncoupled when a spray of liquid suddenly flared out from the loosened coupling. It missed the fumigator's face by a few inches and his trained instinct told him to keep breathing out till he was 20 feet away, so that he escaped; but for a moment it looked as though there would be a vacancy in that fumigating crew. A fumigator of 16 years' experience was killed in New Orleans by pulling apart a clogged hose line. The liquid hydrocyanic acid shot back into his face.

There is one other danger connected with liquid hydrocyanic acid and that is spontaneous explosion in the cylinders. This is not a serious danger at present, but its possibility should be kept in mind in case of cylinders that have been in storage six months or longer. When hydrocyanic acid is permitted to acquire an alkaline reaction, it disintegrates, the chemical change becoming progressively faster and faster. Nitrogen and ammonia gases are formed and these accumulating in the cylinder increase the pressure. At a certain point the reaction becomes violently explosive, sufficiently so more or less to wreck everything in the immediate vicinity. Commercially it is now preserved by the addition of acetic acid. No explosive accidents have occurred during the past several years, but the companies supplying hydrocyanic acid keep track of the cylinders and call them in three months after shipping. Tests have shown that acetic acid in proper amounts prevents explosive deterioration for a

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p. 1017
year or more, so that the safety margin is large. Explosion in fires will be referred to later.

Somewhat less effective in equivalent amounts, but far more easily and safely handled, are Zyklon and HCN discoids. These products are essentially the same. Zyklon has the advantage that the cans may be opened with a hammer, while discoid cans must be opened with a special opener making a clean cut close to the rim. Discoids have the advantage that each disk holds approximately one-half ounce of hydrocyanic acid, thus permitting reasonably accurate dosage of small compartments. Both come packed in 40-ounce cans of much heavier gauge than the ordinary tin can. To use them, the can is opened and the contents are shaken out and spread on the floor. The cans may be opened out of doors and carried in, but usually they are opened inside, in which case the operators must wear gas masks. The gas begins to come off immediately, and within one hour most of it has evaporated. If fumigation time is two hours or more and ventilation is continued for an hour or more after fumigation, the spent discoids or Zyklon residue will be found quite dry and harmless and may safely be left where they are. An exception must be noted here: One would suppose that even a very ignorant fumigator would realize the necessity of spreading out the fumigant to insure rapid evaporation, but it does sometimes occur that careless men will pour these materials out in piles or stacks which may retain some liquid HCN for as long as four or five hours, possibly longer in severely cold weather. An overnight (12 hours or longer) fumigation, however, insures that the residue will be found dry and free from all but traces of HCN.

The simplicity of use of HCN discoids and Zyklon is quite apparent. One merely takes his fumigant, in cans of convenient size, into the building, opens them, spreads the contents, and goes out, closing the door behind him. After fumigation, the residue is swept up and, with the empty cans, thrown into the trash. What could be simpler? Yet, it has its attendant danger and one that is equally inherent in all the generation methods of fumigation. That is, the fumigator must take the fumigant into the space fumigated and remain long enough to open the cans and spread it around. In the case of generated gases he must remain long enough to drop the cyanide into the various acid barrels or crocks. This means that he must be exposed to the gas for a certain length of time. In small buildings or on ships this is a trifling consideration, the time of exposure being quite short; but in large buildings, in which spreading the fumigant may take an hour or more, it is often a serious problem, sometimes requiring the arrangement of relays of fumigators. The danger arises through the absorption of HCN through the skin.

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A good gas mask protects completely against cyanide in the inspired air, at least up to a concentration materially above the concentrations usually used in fumigation of buildings or ships; but to protect the surface of the entire body, a complete rubber suit would be required. This is impractical for several reasons, not the least of which is that it would -soon be most uncomfortably hot on the inside. Yet it is not so very unlikely that skin absorption of cyanide may force some such protection in certain kinds of fumigation procedure.

It was in order to stress this point that I mentioned earlier that HCN rapidly penetrated clothing. In fact the penetration through clothing, promoted as it is by the motion of the fumigators and air currents set up by the heat of the body, is practically immediate. A person may go into a relatively concentrated gas, say 2 or 3 ounces per 1,000 cubic feet, without noting any skin effect; but if he enters a concentration of 6 to 10 ounces per 1,000 cubic feet, he will at once experience a sensation of warmth over the entire body which becomes more and more pronounced. After five minutes spent in such an atmosphere the entire skin surface becomes noticeably reddened, and sensitive persons may experience an actual burning sensation. If this warning is disregarded, a feeling of weakness appears, followed by nausea and vomiting and often by headache. A still more advanced sign of poisoning is difficulty in breathing, the subject feeling as though giant hands were holding the chest and preventing its expansion. This is the last warning, being the forerunner of loss of consciousness and paralysis of the respiratory nerve center. Experienced fumigators seldom reach this stage, but it is not unusual to see them emerge from a large building decidedly wobbly in the knees and distressingly sick. While there is not available at present any exact data regarding absorption through the skin, it is, I believe, safe to state that, protected with a good gas mask, one may remain in air containing 2 ounces HCN per 1,000 cubic feet for one-half hour without experiencing signs of poisoning. In a concentration of 4 ounces per 1,000 cubic feet, this should be reduced to 15 minutes, and in 8 ounces per 1,000 cubic feet to 5 minutes. Of course the distribution of 8 ounces of Zyklon or discoids per 1,000 cubic feet, in a building does not mean that the fumigators are exposed to such a concentration, since the full amount will not have entered the air short of one hour. Since the fumigators are nearly always going away from the gas it is unlikely that they are actually exposed for the greater part of the time to more than 1 or 2 ounces per 1,000 cubic feet.

Zyklon and HCN discoids do not present the transportation dangers of liquid HCN. Being in a solid form they do not flow; and with the evaporation rate much slower, quite a large amount

May 1, 1931
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(relatively, not in terms of tons, of course, but of pounds) may be spilled in the open without immediate disaster. Leaking cans are not a menace in the open, since the gas is given off so slowly through ordinary leaks that one would have to hold such a can close to his face to become poisoned. Because of this reduced danger from breakage, the Interstate Commerce Commission permits shipment in heavy-gauge cans. Leaking cans in storage may be a source of danger, since the gas is then liberated in an enclosed space. For this reason it should be stored only in well-ventilated rooms.

Cyanogas, which is the trade name for calcium cyanide, differs from Zyklon and HCN discoids in one important respect: This is that the residue is poisonous. Calcium cyanide is a very fine powder, usually packed in cans. When the cans are opened and this powder is spread out, it absorbs moisture from the air. This causes a chemical change to calcium hydroxide and HCN, the latter being given off into the air. But, and here is the difficulty, some of the HCN is absorbed by the calcium hydroxide and changed to calcium cyanide and water. Under any circumstances there is always some calcium cyanide left in the residue which, therefore, must be gathered up and safely disposed of. One method of getting around this is to take advantage of the fine powder form of the material and to blow it into the air, from which it settles as a fine dust. There appears to be no great objection to this, in the absence of foods, from a safety standpoint, it being inconceivable that anyone would sweep up this powder and eat it; but where foods are fumigated they become inseparably mixed with the fumigant. If calcium cyanide is left for several days' airing, the cyanide content finally becomes so low as to be negligible.

The so-called barrel methods, or generation methods, of fumigation, which require the placement of barrels or other containers, in which sodium cyanide is mixed with an acid, all involve the same essential procedure. There are two main variations: In one only HCN is generated; in the other, a mixture of HCN and cyanogen chloride is produced. The procedure in either case is to mix the acid -with an equal amount of water in a barrel or crock (depending on the size of the space to be fumigated), put it in place, drop into it sodium cyanide in a paper or cloth bag, and leave. It sounds simple; but if this has to be done on each of five floors of 40,000 square feet each, and each one cut up into various sized compartments, the difficulties will be multiplied. Yet, I once saw this feat performed by five men, none of whom wore a gas mask or even had a mask among them. They decided they would never get out alive if they tried to drop the cyanide by hand, but got around the difficulty after considerable tedious labor by suspending the cyanide in bags over each barrel and leading the suspending cords over pulleys all the way to the front door on the

May 1, 1931
p. 1020
street level. They had over 100 cords tied at the door, representing more than 6 miles of cord. When all was ready they cut all the cords and shut the door. With gas masks the dropping is usually done by hand, in which case the fumigators became exposed to absorption through the skin, as occurs with Zyklon and similar materials.

The generation method involves a large amount of work. The ingredients must be mixed in the proper proportions and amounts, and this involves measuring the acid and water and weighing the cyanide, although the latter procedure is much simplified by the use of cyan-eggs, that is, sodium cyanide in the shape of balls, each weighing 1 ounce. The apparatus is bulky and cumbersome and must not only be put in place but must also be removed. The spent acid cyanide mixtures must be safely disposed of.

Aside from cyanide dangers, the acids used are injurious. Sulphuric acid is a highly corrosive poison, either internally or externally. It is ruinous equally to the fumigators' clothing and their skins; several serious accidents have been caused by breaking of jugs of acid. It is also highly injurious to floors and fittings. Its corrosive action on barrels often causes them to spring leaks, and if too much material is put in a barrel it may boil over. Hydrochloric acid used in the generation of cyanogen chloride mixture is far less injurious than sulphuric acid, but it is by no means harmless.

The generation method, like all other cyanide methods, has its own peculiar danger. Here it is the spent acid cyanide mixture, which is not truly spent at all. When the barrels are removed, the shaking up of the mixture often causes the liberation of considerable volumes of HCN gas. It is hardly necessary to discuss this further; the danger is obvious. It might be said that experienced fumigators are aware of this danger, and on smelling the gas get out at once or put on masks. I have seen some very rapid ascents up the ladders leading out of ships' holds in the days before gas masks became generally used. Several fatalities from this cause have occurred, though none I believe, of recent date.

Cyanogen chloride mixtures are generated by putting diluted hydrochloric acid in the barrels and dropping into it a mixture of sodium cyanide and sodium chlorate. The resultant gas is a mixture of about one-third HCN and two-thirds CNCl. Recently a modification of this method, commercially known as "Safti-fume," has been put on the market. It consists of the cyanide and chlorate mixed with sand and some other materials put into the form of solid, but porous, briquettes, which are dropped into the acid. The cyanogen chloride is a very highly irritant gas, particularly to the eyes, nose, throat, and lungs. In even moderate concentrations it is practically intolerable, causing pain and weeping in the eyes, discomfort in the nose and

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throat, and pain and coughing in the chest. It is not as effective a fumigant as HCN, but is largely used on account of its warning properties.

This brings up the subject of warning gases. These are substances added to the fumigant for the purpose of giving warning of the presence of the gas. Hydrocyanic acid has a distinctive odor and may be detected by experienced fumigators in quite a low concentration. To the uninitiated, however, its odor does not indicate danger, nor in lethal concentration does it cause discomfort. Persons have been killed without ever knowing that they were in danger, as occurred recently when three members of a family were found dead sitting at the breakfast table while the fourth, also dead, was reading a news- paper when overcome.

Because of such accidents, numerous attempts have been made to incorporate in the fumigant gas, other gases which, due to highly irritant properties, give a distinct warning of their presence, even when in quite small amounts. The aim has been to render a fumigated space literally intolerable until airing has removed all but traces of the fumigant. This objective has never been completely realized. Nearly always the warning substance used has been a tear gas, although evil smelling gases and some that primarily cause coughing or choking sensation have been tried with some success. Usually the warning gas is present in small amounts; chloropicrin, the gas most commonly added to HCN, seldom constitutes more than 5 per cent of the mixture. In some cases, however, advantage is taken of the fact that most warning gases are themselves poisonous and may be used as fumigants. Chloropicrin, for example, is advocated by the manufacturers as a fumigant. The use of cyanogen chloride is another attempt in this direction.

There are two distinct dangers connected with the use of warning gases. One is, that when present in sufficient quantity to be actually intolerable, they constitute a menace to the fumigators, who may be rendered helpless by the effects of the warning gas. Tear gases, for example, may get inside a gas mask in sufficient amount to blind the fumigator. The other is that the warning gas may disappear before the HCN, so that fumigators misled by the absence of warning gas may declare a place safe when it is not. Two cases of this nature have occurred on ships in my own experience. This failure of after- warning appears to be due to the warning gases being much less penetrating than the HCN. The latter is absorbed by porous materials, while the warning gas, not being absorbed, is blown away by air cur- rents. Upon its disappearance, the room is declared safe and is closed; but the absorbed HCN, slowly liberated, passes into the now confined air where it produces an unsuspected dangerous concentration.

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Another way in which warning gases sometimes fail is when penetration occurs through a porous partition. It is my belief that this occurred in a recent fumigation accident. The gas apparently penetrated through a brick wall, probably mainly through numbers of small cracks. The HCN portion of the gas, being much more penetrative than the CNCl, came through first and caused poisoning of several persons (fortunately not fatal) before the CNCl penetrated in sufficient quantity to give a positive warning.

Thoroughly competent fumigators do not rely on warning gases alone. They do, however, use them as a help, both as a warning to others and to assist in detecting the gas themselves.

There is one fumigant, still used often enough to be considered, that is quite intolerable in amounts far below the immediate lethal concentration for man, and that is sulphur dioxide, produced by burning sulphur. This gas is highly irritant to the lungs, however, and while human deaths by being directly fumigated with it are rare, severe bronchitis and fatal pneumonia following exposure to it have been by no means uncommon. Formaldehyde is practically intolerable in relatively small amounts, but it is rarely used as a fumigant to-day because it has little effect on animal life.

Hydrocyanic acid and other gaseous cyanogen compounds, including cyanogen chloride, are distinct from all other fumigants in general use, in the rapidity with which poisoning is induced. A man walking into a concentration of 8 ounces or more per 1,000 cubic feet and breathing normally therein will become unconscious in 30 seconds and will be dead beyond hope of recovery in from 3 to 5 minutes. If he goes into the much lower concentration of 2 ounces per 1,000 cubic feet, used to kill rats, and breathes normally, he will lose consciousness within a minute and will be dead within 10 minutes. If a person rendered unconscious is brought at once into the open air before he stops breathing, he will usually recover unaided and will suffer, as a rule, no serious aftereffects, of which the principal ones are headache of very variable duration, nausea and vomiting, and rapid pulse rate. If he has stopped breathing, artificial respiration must be instituted. If the heart is still beating, his chances of recovery are good, but the aftereffects are more severe, as a rule, the most important being weakness of the heart, which may persist for several months. There are cases on record of recovery from cyanide poisoning after artificial respiration for as long as eight hours. As long as the heart continues to beat, there is hope. When the heart beat has definitely ceased, all chance of recovery has gone with it.

It is the rapidity of poisoning, particularly the rapidity with which the victim is rendered helpless through loss of consciousness, that has

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given rise to the fear and respect exhibited toward the cyanides in any form. Particularly is this true of the gas. The gas taken into the lungs is absorbed over a large surface rapidly and directly into the blood stream, which takes it at once all through the body. The amount of cyanogen that will poison is so minute that its effect is felt at once. In the case of all other fumigants at present in use, much larger amounts must be taken into the body to cause immediate poisoning. This requires time. But there is another factor: Cyanogen acts first on the nerve cells, particularly the more highly developed and specialized cells. Thus the cells controlling consciousness are the first affected, their failure rendering the victim utterly helpless to effect his own rescue. Next, the respiratory center is paralyzed and breathing ceases. Apparently the lower nerve centers are at first stimulated, or at least rendered more sensitive, for generalized convulsions are a constant accompaniment of cyanide poisoning, though they cease, as a rule, before the heart stops.

Persons breathing small amounts of cyanides over relatively long periods, say one-half hour to several hours, are likely to be affected in various ways. They may lose consciousness but continue breathing, and may finally die in convulsions or recover after several hours of coma. Then, again, they may retain consciousness but fall dead of heart failure on making some extra exertion. Usually a prominent symptom in cases of slow poisoning is extreme weakness and headache. Convalescence in such cases is likely to be slow, sometimes taking several months to a year or more. This type of poisoning may occur when persons have entered closed places still holding a small amount of gas.

While the possibilities have been stated, the usual occurrence is death or recovery within a relatively short time. In the great majority of cases the issue is definite within a half hour. Once natural breathing is reestablished, recovery may be expected, and usually it is rapid, the patient often being able to walk away from the scene and usually feeling quite well within two or three days. Nearly always the determining factors are the amount of gas and the length of time the patient has been exposed to it.


There is just one treatment of cyanide poisoning, and that is fresh air and plenty of it. Fresh air must enter and leave the lungs as in normal respiration. If the subject is breathing normally, carrying him into the open is enough. If his breathing, has stopped, is materially slowed, is shallow, or is irregular, artificial respiration is required. When normal breathing reappears, artificial respiration may be discontinued, but may have to be resorted to again if breathing again becomes irregular. There is no known antidote for cyanogen, and so

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the only method of recovery is to throw it off. Fortunately it is given off by the lungs quite rapidly, though not as rapidly as it is absorbed.

Usually the ordinary methods of artificial respiration are sufficient. If a mechanical respirator is used, it is essential that it be one that does not cause re-breathing of the expired air. Since the expired air is laden with the cyanogen being thrown off from the lungs, it is obvious that if any of this is re-breathed the patient is re-poisoned by his own breath. Pulmotors [resuscitators] and other mechanical respirators are certainly labor-saving devices; but it is doubtful whether they are any more effective than artificial respiration by hand in cases of cyanide poisoning.


The rescue of persons overcome by cyanide fumigation is likely to be a rather futile procedure, for the reason that by the time the emergency squad reaches the scene there will only be dead bodies to rescue (and this is stated without reflection on the speed of the emergency squad). By rescue, of course, is meant the removal of persons overcome from the presence of the gas. As a rule, rescue must be at least as prompt as rescue from drowning, the situations being quite analogous. Immersion in water for 10 minutes or more is generally fatal, and immersion in cyanide gases for the same length of time is likely to be equally so. In the latter case, however, there are exceptions, depending on the concentration of the gas. The lower the gas concentration, the longer the exposure that can be withstood. Consequently it is never proper to give up a person who has been in gas, even for considerable periods, until it has been definitely deter- mined (by use of a stethoscope) that the heart has ceased beating.

The subject of rescue is inseparably bound up with gas concentration, and so a slight digression may be allowed for its consideration. The usual practice in preparing a building for fumigation is to close all openings to the outside, including sealing, with strips of gummed or greased paper, the cracks around doors and windows. The purpose of course, is to keep the gas within the building. Despite the most painstaking care, however, it is practically impossible to seal a building 100 per cent. There is always considerable leakage. If there is any considerable wind blowing, the leakage will be greatly increased. In addition to leakage, a very considerable amount of HCN gas is absorbed by the walls, floors, fittings, and stored materials, still further reducing the concentration in the air. As a result of this leakage and absorption it is very rare to find at any time an actual concentration of gas in the air as high as that calculated on the basis of the amount of fumigant introduced. If liquid HCN has been used, the maximum concentration appears at once. If the solid fumigants are used, or any of the generation methods, the highest concentration appears in from one-half to one hour after starting.

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The loss of gas is usually fairly rapid, particularly during the first two or three hours, becoming progressively less and less. At the end of four hours it is probable that more than half of the gas introduced has been lost; at the end of six hours two-thirds or more is gone. At the end of 12 hours there is rarely enough gas left to be immediately dangerous. At the end of 24 hours there is seldom more than the odor. However, one can not depend on this general rule entirely. The gas distribution is likely to vary, some compartments or rooms retaining more than others. If a wind is blowing, there will always be a higher concentration on the side away from the wind. The greater the amount of gas originally introduced, the longer a lethal concentration will persist, but not proportionately longer. Even with quite large initial doses one seldom finds any considerable amount left after 12 hours.

The practical bearing of concentration on rescue relates to the relative time at which victims are overcome. If they have been caught in the building at the beginning of fumigation, the rescuers must work in a high and increasing gas concentration, but if they have entered it several hours later, they will be in a much lower gas concentration which not only makes it much easier for the rescuers to reach and remove them, but also increases their chance of recovery.

Another condition wherein concentration is important is the case of persons overcome in buildings adjoining the one fumigated. There are two classes of such accidents. In one, the gas leaks into the adjoining building through some connecting avenue, such as breaks in a party wall, pipe tunnels for plumbing, or similar openings. The other is where gas escaping from a building is blown into an adjoining one; this is most likely to occur when the fumigated building is opened after a relatively short exposure. In either instance, the concentration is necessarily much lower in the adjoining building than in the fumigated building. Usually, it is not high enough to necessitate the use of gas masks by the rescuers, who, as a rule, can count on five minutes or more that they will be able to withstand the gas. Poisoning in these cases is slow. It is in this type of accident that persons are overcome without being aware of their danger. It is in preventing such accidents that warning gases have their most useful field in the fumigation of buildings.

When gas masks are available, they should always be worn in rescue work; but if not available, persons may yet often be rescued without serious danger to the rescuers if the rescuers keep their heads. Time is a most important factor to the victim, and so any material wait for gas masks is not justified in cases where the victims can be quickly reached. The immediate danger is from inspired air; therefore the precaution to be taken is not to breathe. Almost anyone can hold his breath for as long as one minute. In this length of time

May 1, 1931
p. 1026
it is quite possible to reach a man as far as 100 feet from the entrance and drag him out. In the vast majority of cases the rescuer can count on taking at least one full breath without being overcome. This assurance will permit him to continue his efforts until forced to breathe, when he should stop and return at once to the open air. This is in the interest of both himself and the victim; for if he too is overcome there are then two to be rescued instead of one. After taking four or five breaths in the open it will be possible for the rescuer to return; but on this occasion the breath can not be held as long as at first, a condition that should be kept in mind. When the taking of a breath can no longer be postponed, some 10 seconds additional time before taking an inspiration may be gained by consciously prolonging expiration. That is, when you must take a breath, breathe out first as slowly as you can and as much as you can. This extra 10 seconds is sufficient time to get to a door from a location as much as 100 feet away. When two or more rescuers are at work, one may drag the victim part way out, the other then coming in and bringing him the rest of the way.

Rescuers should, whenever possible, work in pairs, even when equipped with gas masks. If not equipped with gas masks, one man should remain in the open watching the other till he comes out. The reason for this is obvious. If the rescuer falls, the second man should go in and bring him out first; he can surely be saved, while the chances for the other victim are already problematical.

If there is reason to believe that the gas concentration is low, say, for example, the building has been under fumigation for six hours or more, or if persons in an adjoining building have been overcome, the rescuers may be more venturesome; but in any case they should remember that, the victim having been overcome, they too will be overcome if they stay too long. The best guide in such cases is the appearance of a sensation of weakness, particularly weakness of the legs. If difficulty in breathing in the shape of a sensation of pressure preventing expansion of the chest appears, the warning is imperative; get out at once. In any case it is usually unwise to remain in even low concentrations without a gas mask for longer than five minutes.

When a tear gas has been used as a warning, rescue work without gas masks is greatly complicated. When the warning gas is chloropicrin, it is often possible to remain in the gas for a minute or more without being actually blinded, although pain in the eyes may become quite severe. Chloropicrin is seldom more than 5 per cent of the gas present, sufficient to warn, but in concentrations of less than 4 ounces HCN per 1,000 cubic feet, not enough to blind one. If cyanogen chloride mixture is the fumigant, the rescuer without a mask is likely to find himself in the same fix as the victim. In this mixture, the cyanogen chloride constitutes 60 to 70 per cent of all the gas

May 1, 1931
p. 1027
present and is so extremely irritating to the eyes as to blind those entering it unprotected. The blinding effect lasts as long as one is in the gas, but this is quite long enough to prevent one from finding his way out. The irritative effect of cyanogen chloride, however, is so immediate and severe that it is doubtful whether the most courageous rescuer would proceed more than a few feet into it before turning back. A man deprived of his sight in a deadly gas is practically helpless, and so further attempt would be merely foolhardy.

In rescue work there is no point to throwing open the building under fumigation as a preliminary act to the removal of the victims. The time so lost is likely to be fatal to those overcome, whose only chance is immediate removal to fresh air. There is no hope that the building will clear of gas in time to save those within. In fact, opening the building may complicate matters by liberating large volumes of gas into the immediately surrounding air. An exception should be noted in the case of gas getting into adjoining buildings. While here, too, the first object is to remove the victims the next step should usually be prevention of further unwanted gas infiltration by opening the fumigated building.

Any gas mask that uses charcoal as a filtering material will protect for a time against cyanide gases. If only charcoal is present in the canister, it can not be relied upon for longer than 10 or 15 minutes. Against the cyanides far greater protection is afforded by a canister containing an alkali such as sodium hydroxide. One type of HCN canister contains caustic pumice (a mixture of pumice and an alkali) and charcoal and protects against all types of cyanide gases for a considerable period, as much as an hour. Against cyanogen chloride the best protection is a mixture of caustic pumice and iron gel (iron hydroxide). The army canister for HCN-CNCl mixture contains these substances. Of course we are speaking of gas concentrations used in fumigation. Very high gas concentrations go through the canisters; that is, some of the gas gets through. This occurs some- times to fumigators opening cans of Zyklon or discoids, the gas concentration from the freshly opened cans directly under their masks being for the moment quite high. It also occurs in the fumigation of tobacco warehouses, where concentrations as high as 200 ounces per 1,000 cubic feet are sometimes used. The so-called all service canisters will protect against cyanide for a sufficient time to effect rescues, although in the presence of cyanogen chloride they are likely to let through enough of this substance to cause considerable discomfort.

Gas masks used in cyanide gases must fit closely to the face. This is essential in the presence of a substance that is poisonous in such small amounts. Leaks in the face piece or around the edges can not

May 1, 1931
p. 1028
be permitted. Most gas masks are made in different sizes, commonly three sizes, so that it is usually necessary for each individual to learn which size fits his face. The No. 2 size fits the average face.

The life of the canister is limited. Those designed for the cyanides will generally protect against the amounts used in fumigation for from one to four hours of steady breathing. When the canister is becoming ineffective, breathing through it becomes much more difficult. Experienced fumigators can tell from the smell of the gas when a dangerous amount is coming through; but the best procedure for the inexperienced person is whenever there is any cause to suspect the reliability of the canister to get a new one. After a canister has been used in cyanide, the next time it is used a cyanide smell will be noticed for a few breaths; but this should soon disappear. When one enters the gas a slight odor of cyanide generally comes through. This, too, should cease within two or three minutes. If it persists or gets strong, the mask or the canister is leaking. In the case of cyanogen chloride, determination of leaks is very easy; if sufficient gas to be dangerous comes through, the wearer will be practically blinded by the eye irritation. If he can stand the irritation, then only very small amounts are getting through.


There are a number of other substances employed in fumigation, none of which at present, however, are used in this country to the extent that cyanides are used. All that have come into use to date are very much less poisonous than the cyanide gases, but they are used in very much larger amounts.

Sulphur dioxide, generally produced by burning sulphur, either on the premises in iron pots set in pans of water, or in special furnaces from which the gases are led through a large pipe into the space under fumigation, is the gas par excellence in the matter of warning of its presence. In concentrations far below the quickly fatal level it causes severe irritation of the throat, producing a sensation of choking as well as persistent coughing. It is not rapidly fatal like HCN and so persons caught in it have ample time to make their way out. Although eye irritation occurs, it is not blinding. It is the only nearly safe fumigant that we know.

Sulphur fumigation has been almost entirely abandoned in this country, because the gas penetrates very slowly and not very deeply so that its results are unreliable, because it is highly injurious to many foodstuffs, most fabrics, and nearly all metals, and because of the fire hazard due to burning it inside of the space fumigated.

Sulphur is mentioned principally because sometimes an emergency call is made from a house the occupant of which has bought a sulphur candle at a drug store and burned it in a room. The amount of sulphur dioxide produced in such a case is usually much too little to be

May 1, 1931
p. 1029
dangerous. The principal result is that everyone is driven out of the house.

Formaldehyde is an irritant gas, irritating the eyes, nose, and throat. It is not dangerous to human life unless it is in an enormously high concentration and then only after long exposure.

Within the past five years these substances have been developed as fumigants which will probably become quite wide spread in use. These are ethylene dichloride, ethylene oxide, and a mixture of ethylene oxide and carbon dioxide, marketed under the trade name of "Carboxide." The first named, ethylene dichloride, is not greatly used at present; and when used it is generally mixed with carbon tetrachloride to remove the fire hazard. It is for the same purpose that carbon dioxide is mixed with ethylene oxide. Ethylene oxide, however, is also used alone.

These fumigants are much less poisonous than HCN and, hence, must be used in much higher concentration. Their value comes from two properties: They are relatively more poisonous to insects than to warm-blooded animals, including human beings, and they are relatively slow in their action. These properties permit fumigation for the destruction of insects with greatly reduced hazard to human life. They are not nearly so rapid in their action as HCN, permitting more time for those trapped to escape.

These gases are not highly irritating and, hence, small amounts do not give positive warning of their presence. That they are irritants and cause damage to the lungs have been shown by some recent studies of the United States Bureau of Mines. Up to date there has been comparatively little use of them for the fumigation of buildings, and it is doubtful whether they will ever come into general use for such purpose. They must be used in a high concentration, maintained over several hours-conditions that involve a cost several times that of HCN fumigation. However, they may come into use in the fumigation of buildings so placed that the use of HON involves too great a hazard. At present they are employed in connection with specially constructed fumigation rooms or vaults.

From what we know at present, these gases may be entered for short periods, three to five minutes, without serious risk; but if longer stay is necessary, gas masks should be worn. Gas masks containing charcoal in the canisters will protect against them for a time. I am not aware whether special gas masks for them have been as yet developed.

Ethylene dichloride, alone or mixed with carbon tetrachloride, is a liquid at ordinary temperatures and is marketed in steel drums. Ethylene oxide and Carboxide are both gases at room temperatures. The former may be packed under pressure as a liquid and is shipped in this form, the latter remains as a gas and is supplied in heavy steel

517360-313 2

May 1, 1931
p. 1030
pressure cylinders. The immediate danger in handling these materials is much less than that with HCN. In using Carboxide, for example, the required number of cylinders is placed in the space to be fumigated and a man opens the valves on one after another till all are opened, and then goes out. This has been done in relatively large spaces where as many as a dozen cylinders were used by fumigators unequipped with gas masks, without apparent injury.

These gases require considerable study before any very definite statements can be made concerning them. We are steadily gaining knowledge of their action on human beings through their growing use in medicine as anesthetics. In ship fumigation for quarantine purposes they are of little value, because to kill rats they must be used in relatively enormous doses.

Fire hazards fall into two categories: One is the hazard of starting or increasing a fire; the other is the danger of poisoning to those fighting a fire. The latter danger would appear only when fire breaks out in a building that is being fumigated. In this instance, of course, it would be impossible for firemen to enter a building under fumigation with HCN unless they were protected by gas masks. This is an important consideration, since many fires that may be rapidly extinguished from inside a building are difficult to fight from the outside. If the firemen do not have gas masks, the only thing to do is to break open doors and windows as rapidly as possible so that the gas may escape. It is realized that the fire itself may be greatly augmented by feeding it fresh air. Once a fire really gets under way, the draft produced will very rapidly clear out the gas.

There is no danger of explosion from the amounts of HCN used in building fumigation, except with the very heavy dosages sometimes used in tobacco warehouses. The lowest explosive mixture of HCN is 6 per cent of the vapor in the air, while in fumigation it is rare to have more than 2 per cent. Apparently there is little danger of explosion or combustion of Carboxide, or ethylene dichloride with carbon tetrachloride; but either ethylene oxide or ethylene dichloride alone is very inflammable and may be used in such amounts as will cause explosion or direct extension of the fire by the gas.

Fires have been started with the solid forms of HCN (Zyklon, discoids) by their being scattered close to stoves in which the fires had not been extinguished. In the generation methods of producing HCN a considerable amount of heat is evoked by the reaction. With straight HCN (NaCN and sulphuric acid) the heat produced is not sufficient to start a fire; but with the original HCN-CNCl technique, spontaneous combustion sometimes occurred. Safti-fume, in the form of briquettes, appears to have overcome this hazard by slowing the reaction.

May 1, 1931
p. 1031
In storage, HCN, Zyklon, HCN discoids, ethylene dichloride, ethylene oxide, and Safti-fume briquettes, somewhat increase the fire hazard. They are not themselves likely to start a fire, but being inflammable may materially increase its proportions. In a fire Zyklon and discoid cans soon explode, without much violence, but the liberated combustible gases spread the flames. It requires a relatively hot fire to cause the explosion of the fumigants packed in heavy steel cylinders; but when these do let go the explosion is a violent and destructive one. Safti-fume briquettes contain sodium chlorate. The heat of a fire causes multiple small explosions of this chemical.

Fortunately, in cases where fire reaches stored fumigants, HCN is burned, the resultant gases being relatively innocuous. The same is true of ethylene dichloride and ethylene oxide, so that poisoning by the gases in such cases is not to be feared. This is not to be confused with fires starting in buildings under fumigation. In this case the already diffused gases are in too low concentration to burn, but quite sufficient to poison; and until removed by ventilation (which may be accomplished by the fire itself), they must be reckoned with.

Sulphur and carbon bisulphide are two fumigating materials which produce a poisonous gas, sulphur dioxide, when burned. When produced in dangerous quantities, however, it is intolerable without gas-mask protection.


In this talk the dangers and difficulties of fumigation have been somewhat overstressed. It is quite true, as has been frequently demonstrated, and is daily demonstrated in New York City, that trained fumigators can do their work and handle the most deadly gases with safety, both to themselves and to others. It is, on the other hand, quite as true that, in the hands of the ignorant or care- less, fumigation is a menace to all concerned. Hydrocyanic-acid gas is a deadly gas. It is not, however, so deadly as popular belief would make it. A single whiff of it will not kill you; in fact in the great majority of instances a good many whiffs may be taken with safety. Yet, one unfamiliar with its effect should not needlessly expose him- self. Above all remember this advice: Keep your head and do not be stampeded because there is cyanide. On the other hand, do not rush in headlong; stop a moment and think.


For several years the United States Public Health Service has secured from State health departments current mortality data and has published from time to time death rates from certain important causes from as many States as could furnish the information to the [continued on p. 1032.]

1 From the Office of Statistical Investigations, United States Public Health Service.

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