Hydrogen Cyanide 1782

What is this old sneaker smell?

Historical background of hydrogen cyanide (AC/HCN)

The production of hydrogen cyanide (hydrocyanic acid) out of the sulfuric acid and Berlin-blue was discovered by Swedish chemist Carl Wilhelm Scheele in 1782. French chemist and physicist Joseph Louis Gay-Lussac prepared pure liquefied hydrogen cyanide in 1811.

Hydrogen cyanide was used as a chemical weapon in WW1 by the French army in 1916, by the United States, and by Italy in 1918, but it was not found to be effective enough due weather conditions. The gas is lighter than air and rapidly disperse up into atmosphere whereas denser agents such as chlorine and phosgene tend to remain at a ground level.  Compared to these agents it also requires higher concentrations in order to be fatal. Hydrogen cyanide concentration of 100-200 ppm in the air will kill a human within 10 to 60 minutes and concentration of 2000 ppm (approx. 2380 mg/m3) will kill a human in about one minute.   

Inside a synthetic fiber factory, a leaked estimated at 4,000 liters of acid solution, containing 200 kg of hydrocyanic acid (HCN), occurred within an acrylonitrile production unit. Only one employee sustained slight HCN intoxication. This accident happened in October 14th 1999 in the town of Born, a town in the Dutch municipality of Sittard-Geleen in an acrylonitrile plant.

Commercial uses of hydrogen cyanide

Hydrogen cyanide is currently produced in great quantities by several processes, as well as being a recovered waste product from the manufacture of acrylonitrile. It is used commercially for fumigation, electroplating, mining, chemical synthesis, and the production of synthetic fibers, plastics, dyes, and pesticides. Hydrogen cyanide is typically transported as a compressed gas or liquid, but may be produced by the reaction of cyanide salts.


Hydrogen cyanide is colourless gas or liquid, being highly volatile. It is also non-persistant and lighter than air. In military classification hydrogen cyanide is a blood agent.

Hydrogen cyanide has a distinctive bitter almond odour which others describe a musty “old sneaker smell”, but a large proportion of people cannot detect it.  The odour does not provide adequate warning of hazardous concentrations. It also has a bitter burning taste and is often used as a solution in water.

Immediate signs and symptoms of hydrogen cyanide exposure can be increased rate and depth breath or great difficulty breathing, dizziness, nausea and vomiting, not forgetting headaches, convulsions and cardiac symptoms.


Leave the area and evacuate the exposed people into fresh air. First responders’ protection level should be the highest in an unknown situation.  In a small spill or leak (less than 200 litres) the initial isolation distance in all directions is 60 meters and protection distance during day is 200 meters, and nights 0,6 kilometres.  In large spill/leak (more than 200 litres) the isolation area is 150 meters in all directions protection distance, day 500 meters, nights 1,6 kilometres. This agent is reactive, extremely flammable and may ignite combustible materials.

Did you know, that only 60-70% of the population can detect a bitter, almond odour from hydrogen cyanide?

Published by Toni Leikas

CBRN Officer (CPT.ret), CBRN Specialist. I'm always wondering, why so many makes and thinks that CBRN is rocket science? It's simple following few basic rules and common sense.

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