The Holocaust Historiography Project

Fact File 5 — Zyklon B

Note: The fact file series is intended to present facts of history, free from the polemics and misinformation so often presented in this medium. Hopefully the facts contained herein will serve the cause of truth in history.

Fact File No. 5 presents background and technical information regarding Zyklon B. Zyklon B or in English, Cyclone B was a trade name of the German firm Degesch which supervised the distribution of this product during World War II. The product was designed as a fumigant for the purpose of pest and vermin control. Zyklon B was a special preparation which contained hydrocyanic acid (HCN). HCN was used as a fumigant even prior to World War I by the United States. Zyklon B was HCN absorbed in a carrier, typically wood pulp or diatomaceous earth. This preparation of pellets was sealed in an airtight can to make handling and transportation safer. Zyklon B would be a forgotten footnote of World War II except for the allegation that it was used as a poisonous gas to execute millions of concentration camp inmates. Much was made of the bills of lading for deliveries of this fumigant at the Nuremberg Trials. It is reasoned that most of the concentration camps used Zyklon to kill vermin and fight disease thereby reducing the camp death rates. Other camps, designated by “experts” as extermination camps used the same Zyklon to kill inmates and thereby increase the camp death rates. Therefore, deliveries of Zyklon to Dachau was beneficial and humane while delivery of Zyklon to Auschwitz was criminal.

Specifications For HCN

HCN, hydrocyanic acid; prussic acid
Boiling point:
25.7 C / 78.3 F at 760 mm Hg
Specific gravity:
0.69 at 18 C / 64 F
Vapor density:
0.947 (air = 1)
Melting point:
-13.2 C / 8.2 F
Vapor pressure:
750mm Hg at 25 C / 77 F 1200mm Hg at 38 C /100F
Solubility in water:
slightly bluish
bitter almond, very mild, non-irritating (odor is not considered a safe method of determining presence of the poison)


  1. Unstable with heat, alkaline materials and water.
  2. Will explode if mixed with 20% sulfuric acid.
  3. Polymerization (decomposition) will occur violently with heat, alkaline material or water. Once started, reaction is autocatalytic and uncontrollable. Will explode.
  4. Flash point: -18 C / 0 F
  5. Autoignition temperature: 538 C / 1000 F
  6. Flammable limits in air (by volume): lower 6%, upper 41%

Source: Hydrogen Cyanide, Dupont Publication 7-83.


As long as 80 years ago it was recognized that hydrocyanic acid could be useful in pest control but it took half this time to popularize the method.

Deficiencies and disadvantages had first of all to be eliminated from the method of application. First this had been done in such a way that hydrocyanic acid was no more developed on the spot by mixing cyanides and acid, but this process already took place in the factory: The so-called “pot method” was replaced by liquid hydrocyanic acid. The few deficiencies of this procedure were removed in the early twenties by the ZYKLON method: One added liquid HCN to a “carrier substance", thus simplifying handling whilst all favourable properties of liquid HCN were maintained. At the same time, danger to the operator was reduced to a minimum. Hydrocyanic acid in the form of ZYKLON can be safely stored for considerable periods and under all climatic conditions, any quantity of gas can be easily measured, quickly and cleanly released. Any residures are completely harmless.


In ZYKLON pure (98%-99%) liquid hydrocyanic acid is chemically stabilized and absorbed in a porous, inert material. It is supplied in snippets or discs prepared from wood pulp. Snippets generally are preferred as in view of their larger surface they give off the gas more rapidly. Upon request also discs can be supplied. The aborbent material can easily be collected at the end of the fumigation.


ZYKLON is packed in handy, gas-tight tins of various sizes which are packed in strong wooden cases. One case, measuring 72 × 50 × 36 cm contains:

Imperial — units 16 tins, each containing 40 ozs. HCN — total 40 lbs HCN or 30 tins, each containing 16 ozs. HCN — total 30 lbs HCN.


No thoroughly effective pesticide is known to exist which could be considered to be harmless to human beings or mammals. Fatal concentrations of HCN impede or completely cut off the oxygen supply to the cells. The poison can enter the body in three ways: through the mouth, the respiratory organs, or the pores of the skin. The latter will occur in particular if the body is exposed to high concentration for any length of time and in unfavourable conditions (great heat).


Prior to fumigation, the tins must be distributed about the building. The tins are opened, and the ZYKLON is scattered so as to reach even the remotest parts of the building. If this is done correctly the gas will develop evenly and instantaneously throughout the premises. Spaces difficult to reach may be charged separately. In multi-storied buildings one begins with the top floor, and then works towards the exit, taking care that nobody re-enters rooms already charged. Even under mask protection it is not advisable to expose oneself to the gas more than is absolutely necessary. The exit door is sealed after everybody has left the building; warning notices must be put up before gassing commences and a guard placed near the building to prevent unauthorised persons from entering. Time of exposure depends on the type of pests to be attacked; for the destruction of the various types of moths and their pre-adult stages 24 hours will suffice, against other kinds of insect pests one should fumigate for 48 hours. If there are any dense stowages or bulkss of commodities to penetrate, the time of exposure may need to be extended to 72 hours.


During this operation gas-masks must be worn. The ventilation takes place in the reverse direction to the gassing. All windows near the entrance are opened first, then gradually those in the rest of the building. It is advisable to work only for 10 to 15 minutes at a time and then to make interruptions of half an hour, as a precaution against skin poisoning.

Depending on concentration, outdoor tempature and weather conditions, ventilation will take at least 10 hours. Clearing of tins and residues may be commenced before the end of airing. Windows and doors must remain open, and gas-masks kept available. ZYKLON tins and absorbent material must always be collected and cleared away before the resumption of work.

Source: Zyklon for Pest Control, Degesch Publication

A short list of books for further reading

The following are works by Fred A. Leuchter Jr., unquestionably an expert in the design and fabrication of execution hardware. Mr. Leuchter’s career and personal life have been destroyed due to the publication of these works.

Every slander, every weapon has been used to silence Fred Leuchter. Prior to the defamation, Fred Leuchter was featured on Prime Time Live where he was called, “the country’s reigning expert on execution.” The New York Times ran a first page story with photo. According to the Times, Mr. Leuchter is “a consultant to 16 states on executions.”

  • The Leuchter Report: The First Forensic Examination of Auschwitz (Focal Point Publications — 81 Duke Street, London W1M 5DJ
  • The Second Leuchter Report: Dachau, Mauthausen, Hartheim
  • The Third Leuchter Report: A Technical Report on the Execution Gas Chamber — Mississippi State Penitentiary Parchman, Mississippi
  • The Fourth Leuchter Report: An Engineering Evaluation of Jean-Claude Pressac’s Book “Auschwitz: Technique and Operation of the Gas Chambers”

(All are published by :History Buff Books and Video — P.O. Box 3061, Station C — Hamilton, Ontario — Canada L8H 7J3) The above mentioned items can be obtained by writing to : Samisdat Publ. 206 Carlton St. Toronto, Ontario, Canada M5A 2L1

Institute of Forensic Research, An Official Polish Report on the Auschwitz Gas Chambers- Journal of Historical Review, Vol XI, No. 2 Summer 1991.

Walter Lüftl, The Lüftl Report: An Austrian Engineer’s Report on the Gas Chambers of Auschwitz and Mauthausen — Journal of Historical Review, Vol XII, No. 4 Winter 92-93.(Published by the IHR P.O. Box 2719 Newport Beach, CA 92659)

Germar Rudolf, Gutachten uber die Bildung und Nachweisbarkeit von Cyanidverbindungen in den Gaskammern von Auschwitz (Technical Report on the formation and detection of cyanide compounds in the gas chambers of Auschwitz) (Cromwell Press, 27 Old Gloucester St., London WC1N 3XX, England, UK)

One should also obtain the Translation of document No. NI-9912 Office of Chief Counsel for War Crimes: Directives for the use of Prussic Acid (Zyklon) for the Destruction of Vermin (Disinfestation).