The Holocaust Historiography Project

Use of HCN and Zyklon B as a Fumigant

Hydrogen cyanide gas (HCN or hydrocyanic acid) has been utilized as a fumigant since before WWI. It has been used side by side with steam and hot air and during WWII with D.D.T. by the United States and its Allies.

HCN is generally manufactured by a chemical reaction of sodium cyanide with dilute sulfuric acid. The chemical reaction results in HCN being given off into the air with a remainder of prussic acid (hydrocyanic acid). This reaction is normally contained in a ceramic crock pot.

This procedure has been utilized for pest and vermin control on ships, in buildings and in specially designed chambers and structures. Special design and handling considerations must be followed to ensure the safety of the users (technicians). Hydrogen cyanide is one of the most powerful and dangerous of all fumigation chemicals. Buildings especially constructed or modified for this purpose were used by all militaries and health organizations throughout the world. HCN has been used everywhere for disease control; specifically for plague and typhus i.e. rat, flea and lice control.

Special chambers were used since WWI in Europe and the United States. Some of these chambers were used by the German Army in Europe before and during WWII and much earlier by the United States Immigration Service at Ellis Island, New York Harbor. Many of these fumigation chambers were made for DEGESCH, a German firm located in Frankfurt am Main, Germany. During the war, DEGESCH supervised the distribution of Zyklon B. DEGESCH presently manufactures HCN.

Zyklon B was a special commercial preparation containing hydrocyanic acid. The name “Zyklon B” was itself a trade name. HCN was prepared at the factory and delivered in a form where the HCN was absorbed in a porous carrier, either wood pulp or diatomaceous earth (chalk). It was supplied either in discoids or snippets or pellets. This preparation was sealed in an airtight can which required a special can opener. In this form the HCN — Zyklon B was much safer and easier to handle. The resultant Zyklon B gas was HCN.

The discoids, snippets or pellets had to be spread on the floor of the area to be fumigated or utilized in a chamber which circulated and heated the air within the chamber in excess of 78.3 degrees Fahrenheit (25.7 degrees Centigrade). If used in buildings, ships, or tents to fumigate trees and produce, the area must be heated to an excess of 78.3 degrees Fahrenheit temperature, the boiling point of HCN. Failure to do this will result in a much longer time to complete the fumigation. Fumigation takes a minimum of 24 to 48 hours.

After the fumigation, the ventilation of the area must take a minimum of ten hours, depending on the location (and volume), and longer if the building has no windows or exhaust fans. The fumigated area must then be chemically tested for the presence of gas before entering. Gas masks are sometimes used, but are not safe and should not be used for more than ten (10) minutes. A complete chemical suit must be worn to prevent skin poisoning. The warmer the temperature and the drier the location, the faster and safer the handling will be.

The specifications for the gas are found in Table 1.

Table 1: Specifications for HCN
Name: 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: 750 mm Hg at 25°C/77°F 1200 mm Hg at 38°C/100°F
Solubility in water: 100%
Appearance: clear
Color: slightly bluish
Odor: 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
Flammable limits in air
Volume %
Source: Hydrogen Cyanide, Dupont Publication, 7-83