Some Aspects of Ship Fumigation / Experiments with Certain Fumigants used for the Destruction of Cockroaches / Effect of Fumigation on Cockroaches on Ships / The Air Jet Hydrocyanic Acid Sprayer / The Fumigation of Loaded Ships

Published: 1931-07-03

Zyklon B is the principle agent typically cited in the mass extermination of Jews in the Holocaust. The name itself stirs up vivid horrifying images. Zyklon B in common thought was developed for the purpose of genocide. This however is far from the truth. Period documents tell quite a different story about Zyklon B and even point to its common use in the years between the two world wars. What follows are excerpts from the United States Public Health Reports for 1931. There are many pages of these reports. We have generally attempted to focus on passages which specifically address Zyklon B. A larger excerpt was taken out of the first report to give the reader greater familiarity with the type of material we are dealing with.

Source: U.S. Public Health Reports, Vol. 46, No. 27, July 3, 1931

Some Aspects of Ship Fumigation

By J. R. Ridlon, Surgeon, United States Public Health Service

The fumigation of ships for the destruction of rodents is a problem which has received much study and attention from various officers of the Public Health Service. The use of suitable cyanogen products has practically replaced the use of sulphur in fumigation at all of the quarantine stations of the larger ports.

Several cyanogen products have been used at San Francisco during the past few years. These, together with the methods, include the following:

1. The generation of straight hydrocyanic-acid gas by a mixture of sodium cyanide, sulphuric acid, and water.

2. The generation of hydrocyanic-acid and cyanogen-chloride gas by a mixture of sodium cyanide, sodium chlorate, hydrocholoric acid, and water.

3. Liquid hydrocyanic acid with either cyanogen chloride or chloropicrin as a warning gas.

4. Zyklon-B, which consists of an earthy substance impregnated with liquid hydrocyanic acid and marketed at present with 5 per cent chloropicrin as a warning gas.

The two latter methods of fumigation afford a saving in time and labor and have almost entirely displaced the generation methods at the San Francisco station. Generation of cyanide gas on shipboard with the use of crocks and barrels was a laborious process.

Liquid Hydrocyanic Acid


Both of the warning gases which have been used with liquid cyanide produce a tear effect. The effect of the 20 per cent cyanogen-chloride gas is greater than that of 5 per cent chloropicrin, i.e., lachrimation is much more marked; and it is believed that, on account of the tear effect, a person unfamiliar with fumigation could escape from a small room containing hydrocyanic-acid gas with 20 per cent cyanogen chloride before inhaling a dangerous amount of cyanide.

The lachrimation which is produced by 5 per cent chloropicrin is much less, and even when used by experienced fumigators it would seem desirable to have a more pronounced warning effect. One should always use test animals to see whether a ship's hold is free of cyanide gas after using this irritant as a warning gas.

Liquid gas with 5 per cent chloropicrin is quoted at a cheaper price than with 20 per cent cyanogen chloride. Since the former mixture contains 91 per cent hydrocyanic acid as against 76 per cent in the latter mixture, more lethal power is purchased for less money. Experiments at this station with roaches indicate that the former mixture is more deadly for that insect and presumably so also for rats.




Zyklon-B is liquid hydrocyanic acid absorbed by an earthy substance called "diatomite" and packed in strong tin containers. Cans are provided containing 15 grams, 120 grams, 480 grams, and 1,200 grams of hydrocyanic acid with 5 per cent chloropicrin as a warning gas. The cans at present are packed with a slight vacuum, which is shown by dents or sinking in of the sides of the cans.

The fumigator opens the cans by knocking holes in each end with a special hammer and sprinkling the contents on the floor of the hold or spreading in a thin layer on canvas or paper on the floor of a compartment. The hold may be dosed by a fumigator standing on deck, and the residue of diatomite, which is left after the hydrocyanic acid has evolved, may be left on the floor of the hold (3). It is customary to throw the residue overboard after use in the superstructure compartments.

Directions on the cans state that Zyklon-B may be satisfactorily used in the proportion of 60 grams per 1,000 cubic feet. Experiments by Akin and Sherrard (3) show that rats are killed under laboratory conditions in 30 to 45 minutes by one-twelfth of this dose, or 5 grams per 1,000 cubic feet. This applies to straight liquid hydrocyanic acid 96 to 98 per cent pure and should equally apply to Zyklon-B. Experiments at this station on ships show that it is not safe to rely in practice upon less than the standard dose of 60 grams per 1,000 cubic feet.

The time of exposure is prescribed as two hours for an empty vessel and four hours for a vessel with cargo aboard. The longer time allows for more complete penetration. It must be understood that all holds or compartments are tightly sealed during fumigation.

Safety Measures

Gas masks must be worn by fumigators when in any way exposed to the fumes of cyanide gas in dangerous concentration. This is necessary when opening cans of Zyklon-B, when dosing compartments with liquid cyanide, and when opening up compartments for ventilation. The canister attached to the mask is charged with chemicals which neutralize hydrocyanic-acid and cyanogen-chloride gas. These absorbent chemicals are a caustic silicate and an impregnated charcoal (4). They offer little resistance to breathing and are effective for several hours' use. The absorptive and neutralizing capacity of the canister becomes exhausted gradually, so that ample warning is given to replace the worn-out canister.

Two men should always work together in any place where there is danger from gas, such as in the holds or in compartments not immediately adjacent to an exit

Test animals, such as rats or guinea pigs, should always be lowered into holds following fumigation, to test for the presence of gas in dangerous quantity before the fumigator himself goes below to make the final inspection.

Hydrocyanic-acid gas is one of the most deadly gases known and should be used with great care and caution. A person exposed for a short period to a strong concentration of cyanide gas, even though wearing an efficient gas mask, will suffer a marked effect from the gas. This is probably explained by absorption through the clothing and moist skin.

Comparative Merits

At present the cost of liquid hydrocyanic acid with 5 per cent chloropicrin is slightly less than that of Zykon-B.

The two fumigants possess equal lethal power. They are both convenient to use and require an equal number of fumigators on shipboard. In dosing the holds it is necessary only to open a valve when using the liquid gas; and the new cylinder which delivers small accurate does is convenient for use in small rooms.

In using Zyklon-B it is necessary only knock holes in the cans and sprinkle out the contents. The empty cans are thrown away.

The preparations for the use of liquid gas require a little more attention, as the dosing cylinders of liquid gas can be received at frequent intervals, this fumigant is very satisfactory. Loaded cylinders, however, should not be stored with air pressure applied, as there may be a degree of deterioration of the gas.

If only infrequent fumigations are done, Zyklon-B would be very satisfactory, as this material can be stored for a longer time before use.

The opening of many small cans of Zyklon-B in a closed space is attended with danger from absorption through the clothing, especially if fumigators are perspiring. In using liquid gas the operator need not be in intimate exposure to the applied gas.

It is found that a combination of the two methods makes an ideal way of fumigation. It is common practice at this station to use both methods in combination on the same vessel.

Source: U.S. Public Health Reports, Vol. 46, No. 28, July 10, 1931

Experiments with Certain Fumigants used for the Destruction of Cockroaches

By J. R. Ridlon, Surgeon, United States Public Health Service

The officers of the United States Public Health Service fumigate nearly 4,000 vessels each year in connection with the enforcement of the Federal maritime quarantine regulations. The purpose of these fumigations is the destruction of rats on shipboard in order to prevent the spread of bubonic plague. It is also important, for several reasons, that vermin, including cockroaches, be killed by these fumigations. It is customary for ships' officers and agents to judge the efficiency of fumigation by the success shown in the destruction of cockroaches. While such insects are ordinarily of little or no quarantine importance, evidence is available that they may be of some sanitary importance on account of their contamination of foodstuffs and for other reasons.


The experiments here described were conducted at the San Francisco Quarantine Station, Angel Island, Calif., in a tightly sealed room containing approximately 500 cubic feet. The room was not heated, and so conditions were comparable as to temperature with those prevailing on shipboard at this port.

The tests extended from August, 1929, to February, 1930. The room opened off the laboratory, and apertures were arranged so that roaches or chemicals could be placed in the room without opening the door. There was a glass in the door through which one could observe the effect of the gas upon the roaches. All of the roaches had been captured alive on shipboard. They were kept in wooden cages with screened sides, 6 by 4 by 4 inches, and were subjected to the gases in these containers. The cages contained varying numbers of roaches, from 2 to 200.

The following chemicals were used for fumigation: Hydrocyanic acid gas, generated from sodium cyanide, sulphuric acid, and water; hydrocyanic acid-cyanogen chloride gas mixture, generated from sodium cyanide, sodium chlorate, hydrochloric acid, and water; liquid hydrocyanic acid with 10 per cent chloropicrin; liquid hydrocyanic acid with 20 per cent cyanogen chloride, liquid hydrocyanic acid with 5 per cent chloropicrin, and Zyklon-B with 5 per cent chloropicrin.



Zyklon-B in the proportion of 60 gm. per 1,000 cubic feet for 1 hour exposure was effective in killing all roaches in 13 tests. Eggs were seen to hatch after exposure to this chemical in the amount of 30 gm. per 1,000 cubic feet.

It is thus seen that Zyklon-B and liquid hydrocyanic acid with 5 per cent chloropicrin probably have equal lethal effect and are effective in killing roaches in the proportion of 60 gm. per 1,000 cubic feet during a 2-hour exposure. This is the usual time of exposure for an empty vessel.

Source: U.S. Public Health Reports, Vol. 46, No. 29, July 17, 1931

Effect of Fumigation on Cockroaches on Ships

By C. L. Williams, Surgeon, United States Public Health Service


It has been noted that clearing, even in the superstructure, was considerably prolonged when a concentration of 300 gm. (10 oz.) per 1,000 cu. ft. was employed. Occasionally storerooms ventilated only through a small hatch in the floor of the pantry are encountered. Heavy doses in these will require artificial ventilation, unless overnight airing can be had with safety. Since , with only 60 gm. (2 oz.) per 1,000 cu. ft., it has been noted that bedding may absorb a dangerous quantity of the fumigant, it must be obvious that greater amounts may be absorbed when the dosage is increased.

Influence of Warning Gas

For the purpose of giving warning of its presence, it is customary to mix a lachrimatory gas with HCN. The gas generally used in the United States is chlorpicrin, in the amount of 5 per cent or 10 per cent (by weight) of the HCN present.

There was reason to suspect that the presence of this warning gas might interfere with the lethal action of HCN on insects. Insects breath through spiracles in the thorax and abdomen, which probably are contractile and capable of closure. It is known that insects apparently dead from asphyxiation may recover after considerable intervals of time. On these premises the theory has been advanced that the irritant warning gas may cause the spiracles to close, resulting in the partial asphyxiation of the insect without, however, its poisoning by the HCN, so that upon the return of fresh air it recovers.

This theory was experimentally tested in the laboratory by first determining the minimum lethal concentration of HCN, without warning gas, and then subjecting cockroaches to greater concentrations containing 5 per cent or 10 per cent chloropicrin.

It may be briefly stated that the chloropicrin exerted no influence that could be noted.

Source: U.S. Public Health Reports, Vol. 46, No. 30, July 24, 1931

The Air Jet Hydrocyanic Acid Sprayer

By C. L. Williams, Surgeon, United States Public Health Service

The past 20 years has seen both a tremendous increase in the use of fumigation for the destruction of vermin on ships and great improvements in fumigation methods. In both cases the advances are due to the introduction of hydrocyanic acid as a fumigant.

Leaving the cumbersome, laborious, and time-consuming sulphur fumigation, we have passed through the method of generating HCN, with its still cumbersome apparatus and paraphernalia, through the period of liquid HCN, complicated by the difficulty of transporting so dangerous a material, and have arrived at the exceedingly simple procedure of knocking a hole in a can of Zyklon, pouring the contents down the hold, and throwing the can overboard.

Source: U.S. Public Health Reports, Vol. 46, No. 31, July 31, 1931

The Fumigation of Loaded Ships

By C. L. Williams, Surgeon, United States Public Health Service

Fumigating with Zyklon

Zyklon may be effectively used to fumigate loaded ships, but it can not be as accurately distributed as can the liquid hydrocyanic acid. Since Zyklon is a granular solid, it can not be directly discharged through a tube; therefore, in fumigating locations that can be reached only with a tube it is necessary to use a special apparatus with which air is forced through the Zyklon, becoming charged with hydrocyanic acid. It is not nearly so accurate as using the liquid. The first air passed through the Zyklon picks up much more cyanide than the following air, the amount taken up diminishing progressively on account of the marked chilling effect of rapid evaporation.

Source: U.S. Public Health Reports, Vol. 46, No. 35, August 28, 1931

Report on Some Tests of the Use of a New Cyanogen Product in Ship Fumigation The Fumigation of Loaded Ships

By C. L. Williams, Surgeon, United States Public Health Service

Brief History of Development

For some time the American Cyanamid Co., of New York, has been endeavoring to develop a practical means of measuring small doses of "sold type" cyanide products for use in fumigating super-structure compartments on ships. The New York Quarantine Station has cooperated with representatives of this company by suggesting possible lines of development and by testing containers and material. The selection of a porous material seems undoubtedly influenced by the growing popularity of Zyklon, and with the HCN discoids the difficulty of measuring small doses required for use in fumigating small compartments has apparently been overcome. This has been done by developing a product, representing HCN in a solid form, in units, each unit carrying a definite and relatively small amount of fumigant.

Additional information about this document
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Author(s): J.R. Ridlon , C.L. Williams
Title: Some Aspects of Ship Fumigation / Experiments with Certain Fumigants used for the Destruction of Cockroaches / Effect of Fumigation on Cockroaches on Ships / The Air Jet Hydrocyanic Acid Sprayer / The Fumigation of Loaded Ships
Sources: U.S. Public Health Reports, Vol. 46, No. 27&28-31, July 3, 10, 17-28 Aug. 1931
Published: 1931-07-03
First posted on CODOH: June 29, 1996, 7 p.m.
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