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

Methyl isocyanate

CAS number: 624–83–9

NIOSH REL: 0.02 ppm (0.05 mg/m3) TWA [skin]

Current OSHA PEL: 0.02 ppm (0.05 mg/m3) TWA [skin]

1989 OSHA PEL: Same as current PEL

1993-1994 ACGIH TLV: 0.02 ppm (0.047 mg/m3) TWA [skin]

Description of substance: Colorless liquid with a sharp, pungent odor.

LEL: . . . 5.3% (10% LEL, 5,300 ppm)

Original (SCP) IDLH: 20 ppm

Basis for original (SCP) IDLH: The chosen IDLH is based on the statement by ACGIH [1971] that the rat 2-hour LC50 is 21 ppm [Kimmerle and Eben 1964].

Short-term exposure guidelines: None developed


Lethal concentration data:


SpeciesReferenceLC50 (ppm)LCLo (ppm)TimeAdjusted 0.5-hr LC (CF)Derived value


G. pig


Dodd et al. 1986

Dodd et al. 1986

Dood et al. 1986

Kimmerle & Eben 1964









6 hr

6 hr

6 hr

2 hr

14 ppm (2.3)

28 ppm (2.3)

12 ppm (2.3)

34 ppm (1.6)

1.4 ppm

2.8 ppm

1.2 ppm

3.4 ppm

Lethal dose data:


SpeciesReferenceRouteLD50 (mg/kg)LDLo (mg/kg)Adjusted LDDerived value


Vernot et al. 1977

Vijayarachavan & Kaushik 1987







354 ppm

152 ppm

35 ppm

15 ppm

Human data: Volunteers experienced eye irritation and lacrimation after 1 to 5 minutes at 2 ppm, with more marked irritation at 4 ppm; exposures were unbearable at 21 ppm [Kimmerle and Eben 1964]. In another study, volunteers noted eye irritation and lacrimation at 5 ppm in less than 50 seconds [Mellon 1963].


Revised IDLH: 3 ppm

Basis for revised IDLH: The revised IDLH for methyl isocyanate is 3 ppm based on acute inhalation toxicity data in humans [Kimmerle and Eben 1964; Mellon 1963].


1. ACGIH [1971]. Methyl isocyanate. In: Documentation of the threshold limit values. 3rd ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, p. 167.

2. Dodd DE, Fowler EH, Snellings WM, Pritts IM, Baron RL [1986]. Acute inhalation studies with methyl isocyanate vapor. I. Methodology and LC50 determinations in guinea pigs, rats, and mice. Fundam Appl Toxicol 6:747-755.

3. Kimmerle G, Eben A [1964]. Zur toxicitat von methylisocyanat und dessen quantitativer bestimmung in der luft (Toxicity of methyl isocyanate and its quantitative determination in the air). Arch Toxikol 20:235-241 (in German).

4. Mellon [1963]. Special report 26-23. Pittsburgh, PA: Mellon Institute (March 13, 1963).

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

6. Vijayarachavan R, Kaushik MP [1987]. Acute toxicity of methyl isocyanate and ineffectiveness of sodium thiosulphate in preventing its toxicity. Indian J Exp Biol 25:531-534.

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