Hydrogen cyanide

Agent Name
Hydrogen cyanide
CAS Number
Major Category
Toxic Gases & Vapors
Formonitrile; Hydrocyanic acid; Prussic acid; [NIOSH] Formic anammonide; Carbon hydride nitride (CHN); [CHEMINFO]
Chemical Asphyxiants
Colorless or pale-blue liquid or gas (above 78 degrees F) with a bitter, almond-like odor. [Note: Often used as a 96% solution in water.] [NIOSH]
Used to manufacture other chemicals and to fumigate enclosed spaces; [ATSDR ToxProfiles] Used in the following processes: electroplating, metallurgy, and photo development; HCN is a byproduct of blast furnaces, coke ovens, photoengraving, petroleum refining, and some metal mining processes. HCN is released when burning nitrogen containing compounds, e.g., wool, silk, and plastics. HCN is present in plants such as cassava roots, lima beans, and almonds. [CHEMINFO]
Virtually any substance containing both carbon and nitrogen can release cyanide when burned under certain conditions. The ability to smell cyanide is a genetically determined trait, absent in 20% to 40% of the population. Two common scenarios for generation of HCN include the accidental mixing of acid and cyanide solutions in electroplating baths and the accidental pouring of cyanide waste solutions into acid waste containers or into other waste solutions with pHs below 10.5-11. What is even less recognized by workers is the potential for generation of large quantities of HCN simply from mixing water-soluble cyanide salts with water, e.g. showering in clothes contaminated with cyanides. Short exposures of large areas of skin to solid cyanide salts or their aqueous solutions can result in dermal absorption of lethal quantities of cyanide. [Sullivan, p.705] Inhaling 600 to 700 ppm HCN for 5 min. or 200 ppm for 30 min. may be fatal. In smoke inhalation victims, hypoxia from carbon monoxide is initially indistinguishable from that due to cyanide. [ATSDR Case Studies # 15] The following chemicals can release large amounts of HCN when spilled in water: Acetone cyanohydrin, Potassium cyanide, and Sodium cyanide. [ERG 2016] See "CYANIDES."
No longer used as a fumigant in the U.S. [EPA Pesticides]
Biomedical References

Exposure Assessment

Skin Designation (ACGIH)
Ceiling (ACGIH)
4.7 ppm, as CN
10 ppm
1.9 ppm
50 ppm
Excerpts from Documentation for IDLHs
It has been reported that 45 to 54 ppm can be tolerated for 0.5 to 1 hour without immediate or delayed effects while 110 to 135 ppm may be fatal after 0.5 to 1 hour or later, or dangerous to life [Flury and Zernik 1931].
Vapor Pressure
742 mm Hg
Odor Threshold Low
2 ppm
Odor Threshold High
10 ppm
Lethal Concentration
LC50 (rat) = 160 ppm/30 min
Explanatory Notes
The ability to detect a bitter almond smell at 2-10 ppm is genetically deterimined: 20-40% of the population cannot. The ERG guide is for "hydrogen cyanide, stabilized" or "Hydrocyanic acid, aqueous solutions, more than 20% Hydrogen cyanide."
Reference Link #2
burn readily
Not appropriate
10 ppm
25 ppm

Adverse Effects

Other Poison
Chemical Asphyxiant

Diseases, Processes, and Activities Linked to This Agent


Occupational diseases associated with exposure to this agent:


Activities with risk of exposure: