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Methyl isocyanate
May 1994
Immediately Dangerous to Life or Health Concentrations (IDLH)
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
ACUTE TOXICITY DATA:
Lethal concentration data:
| Species | Reference | LC50 (ppm) | LCLo (ppm) | Time | Adjusted 0.5-hr LC (CF) | Derived value |
|---|---|---|---|---|---|---|
| Rat | Dodd et al. 1986 | 6.1 | —– | 6 hr | 14 ppm (2.3) | 1.4 ppm |
| Mouse | Dodd et al. 1986 | 12.2 | —– | 6 hr | 28 ppm (2.3) | 2.8 ppm |
| G. pig | Dood et al. 1986 | 5.4 | —– | 6 hr | 12 ppm (2.3) | 1.2 ppm |
| Rat | Kimmerle & Eben 1964 | 21 | —– | 2 hr | 34 ppm (1.6) | 3.4 ppm |
Lethal dose data:
| Species | Reference | Route | LD50 (mg/kg) | LDLo (mg/kg) | Adjusted LD | Derived value |
|---|---|---|---|---|---|---|
| Mouse | Vernot et al. 1977 | oral | 120 | —– | 354 ppm | 35 ppm |
| Rat | Vijayarachavan & Kaushik 1987 | oral | 51.5 | —– | 152 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]. |
REFERENCES:
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.