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Hydrogen cyanide

May 1994
Immediately Dangerous to Life or Health Concentrations (IDLH)

CAS number: 74–90–8

NIOSH REL: 4.7 ppm (5 mg/m3) STEL [skin]

Current OSHA PEL: 10 ppm (11 mg/m3) TWA [skin]

1989 OSHA PEL: 4.7 ppm (5 mg/m3) STEL [skin]

1993-1994 ACGIH TLV: 10 ppm (11 mg/m3) CEILING [skin]

Description of Substance: Colorless or pale-blue liquid or gas (above 78°F) with a bitter, almond-like odor.

LEL:. . 5.6% (10% LEL, 5,600 ppm)

Original (SCP) IDLH: 50 ppm

Basis for original (SCP) IDLH: The chosen IDLH is based on the statements by Patty [1963] that 45 to 54 ppm is "tolerated by man for 0.5 to 1 hour without immediate or late effects; 110 to 135 ppm, however, may be fatal after 0.5 to 1 hour or later, or dangerous to life [Flury and Zernik 1931; Dudley et al. 1942]."

Short-term exposure guidelines: None developed


Lethal concentration data:





TimeAdjusted 0.5-hr

LC (CF*)

Derived value
MammalAAPCO 1966-----2005 min103 ppm (0.52)10 ppm
MammaArena 1970-----362 hr60 ppm (1.67)6.0 ppm
HumanDudley et al. 1942-----10710 min71 ppm (0.67)7.1 ppm
RatDudley et al. 1942503-----5 min259 ppm (0.52)26 ppm
MouseDudley et al. 1942323-----5 min166 ppm (0.52)17 ppm
RabbitGates et al. 1946-----7591 min216 ppm (0.28)22 ppm
CatGates et al. 1946-----7591 min216 ppm (0.28)22 ppm
RatHartzell et al. 1985275-----15 min213 ppm (0.77)21 ppm
RatHartzell et al. 1985170-----30 min170 ppm (1.0)17 ppm
HumanIzmerov et al. 1982-----3572 min131 ppm (0.37)13 ppm
RatLevin et al. 1987160-----30 min160 ppm (1.0)16 ppm
RatVernot et al. 1977323-----5 min166 ppm (0.52)17 ppm
HumanWHO 1970-----1791 hr231 ppm (0.69)23 ppm

*Note: Conversion factor (CF) was determined with "n" = 2.7 [ten Berge et al. 1986].

Other animal data: The median effective concentrations to produce incapacitation (EC50s) in rats have been determined to be 139 ppm and 115 ppm in 15 and 30 minutes, respectively [Hartzell et al. 1985].

Other human data: 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].

Revised IDLH: 50 ppm [Unchanged]

Basis for revised IDLH: Based on acute inhalation toxicity data in humans [Flury and Zernik 1931], the IDLH for hydrogen cyanide (50 ppm) is not being revised at this time.


1. AAPCO [1966]. Pesticide chemicals official compendium. Topeka, KS: Association of the American Pesticide Control Officials, Inc., p. 596.

2. Arena JM [1970]. Poisoning; toxicology, symptoms, treatments. 2nd ed. Springfield, IL: C.C. Thomas, 2:73.

3. Dudley HC, Sweeney TR, Miller JW [1942]. Toxicology of acrylonitrile (vinyl cyanide). II. Studies of effects of daily inhalation. J Ind Hyg Toxicol 23:255-258.

4. Flury F, Zernik F [1931]. Schädliche gase dämpfe, nebel, rauch- und staubarten. Berlin, Germany: Verlag von Julius Springer, p. 404 (in German).

5. Gates M, Williams J, Zapp JA [1946]. Arsenicals. In: Summary technical report of Division 9, NRDC. Vol. 1. Chemical warfare agents, and related chemical problems. Part I. Washington, DC: Office of Scientific Research and Development, National Defense Research Committee, pp. 83-114.

6. Hartzell GE, Priest DN, Switzer WG [1985]. Modeling of toxicological effects of fire gases. II. Mathematical modeling of intoxication of rats by combined carbon monoxide and hydrogen cyanide. J Fire Sci 3:115-128.

7. Izmerov NF, Sanotsky IV, Sidorov KK [1982]. Toxicometric parameters of industrial toxic chemicals under single exposure. Moscow, Russia: Centre of International Projects, GKNT, p. 75.

8. Levin BC, Paabo M, Gurman JL, Harris SE [1987]. Effects of exposure to single or multiple combinations of the predominant toxic gases and low oxygen atmospheres produced in fires. Fundam Appl Toxicol 9:236-250.

9. Patty FA, ed. [1963]. Industrial hygiene and toxicology. 2nd rev. ed. Vol. II. Toxicology. New York, NY: Interscience Publishers, Inc., p. 1998.

10. ten Berge WF, Zwart A, Appelman LM [1986]. Concentration-time mortality response relationship of irritant and systematically acting vapours and gases. J Haz Mat 13:301-309.

11. Vernot EH, MacEwen JD, Haun CC, Kinkead ER [1977]. Acute toxicity and skin corrosion data for some organic and inorganic compounds and aqueous solutions. Toxicol Appl Pharmacol 42:417-423.

12. WHO [1970]. Technical report series 30. Geneva, Switzerland: World Health Organization.

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