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]

Reference Link

ATSDR Medical Management - Hydrogen cyanide

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

630 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

ATSDR - ToxFAQs - Cyanide

Adverse Effects
Other Poison

Chemical Asphyxiant

Links to Other NLM Databases
Health Studies

Human Health Effects from Hazardous Substances Data Bank:

Toxicity Information


Chemical Information

Search ChemIDplus

Biomedical References

Search PubMed

Related Information in HazMap

Occupational diseases associated with exposure to this agent:


Industrial Processes with risk of exposure:


Activities with risk of exposure: