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May 1994

Documentation for Immediately Dangerous To Life or Health Concentrations (IDLHs)

Methyl mercaptan

CAS number: 74–93–1

NIOSH REL: 0.5 ppm (1 mg/m3) 15-minute CEILING

Current OSHA PEL: 10 ppm (20 mg/m3) CEILING

1989 OSHA PEL: 0.5 ppm (1 mg/m3) TWA

1993-1994 ACGIH TLV: 0.5 ppm (0.98 mg/m3) TWA

Description of substance: Colorless gas with a disagreeable odor like garlic or rotten cabbage.

LEL:. . 3.9% (10% LEL, 3,900 ppm)

Original (SCP) IDLH: 400 ppm

Basis for original (SCP) IDLH: Because no useful data on acute inhalation toxicity are available on which to base the IDLH for methyl mercaptan, the chosen IDLH is based on an analogy with hydrogen sulfide. ACGIH [1971] reported that some investigators show toxicities of the same magnitude for hydrogen sulfide and methyl mercaptan [Ljunggren and Norberg 1943]; others indicate that the toxicity of methyl mercaptan is somewhat less than that of hydrogen sulfide [DeRekowski 1893; Frankel 1921]. Patty [1963] reported that 400 to 700 ppm hydrogen sulfide is dangerous after exposure of 0.5 to 1 hour [Henderson and Haggard 1943]. AIHA [1971] reported that concentrations of 400 to 700 ppm hydrogen sulfide caused loss of consciousness and possible death in 0.5 to 1 hour [MCA 1950]. Based on the data cited above, an IDLH of 400 ppm is chosen.

Short-term exposure guidelines: None developed


Lethal concentration data:


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


Seluzhitsky 1972

Tansy et al. 1981





2 hr

4 hr

4 ppm (1.25)

1,350 ppm (2.0)

0.4 ppm

135 ppm

Lethal dose data:


SpeciesReferenceRouteLD50 (mg/kg)LDLo (mg/kg)Adjusted LDDerived value
MammalSeluzhitsky 1972 ?60.67-----212 ppm21 ppm

Human data: Students accidentally exposed to about 4 ppm for several hours experienced headaches and nausea [Clayton and Clayton 1981]. Some investigators have reported that the toxicity of methyl mercaptan is similar to hydrogen sulfide while others report the toxicity to be somewhat less than hydrogen sulfide [DeRekowski 1893; Frankel 1921].


Revised IDLH: 150 ppm

Basis for revised IDLH: The revised IDLH for methyl mercaptan is 150 ppm based on acute inhalation toxicity data in animals [Tansy et al. 1981] and an analogy to hydrogen sulfide [DeRekowski 1893; Frankel 1921] which has a revised IDLH of 150 ppm.


1. ACGIH [1971]. Methyl mercaptan (methanethiol). In: Documentation of the threshold limit values for substances in workroom air. 3rd ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, pp. 167-168.

2. AIHA [1955]. Hydrogen sulfide. In: Hygienic guide series. Am Ind Hyg Assoc Q 16:335.

3. Clayton GD, Clayton FE, eds. [1981]. Patty's industrial hygiene and toxicology. 3rd rev. ed. Vol. 2A. Toxicology. New York, NY: John Wiley & Sons, Inc., pp. 2063-2070.

4. DeRekowski L [1893]. Arch de Sc Biologie (St. Petersbourg) 2:305. [From ACGIH [1971]. Methyl mercaptan (methanethiol). In: Documentation of the threshold limit values for substances in workroom air. 3rd ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, pp. 167-168.]

5. Frankel J [1921]. Die Arzenermittel-Synthese. Berlin, Germany: Julius Springer, p. 108 (in German).

6. Henderson Y, Haggard HW [1943]. Noxious gases. 2nd ed. New York, NY: Reinhold Publishing Corporation, p. 245.

7. Ljunggren G, Norberg B [1943]. On the effect and toxicity of dimethyl sulfide, dimethyl disulfide and methyl mercaptan. Acta Physiol Scand 5:248-255.

8. MCA [1950]. Chemical safety data sheet SD-36: hydrogen sulfide. Washington, DC: Manufacturing Chemists Association, p. 12.

9. Patty FA, ed. [1963]. Industrial hygiene and toxicology. 2nd rev. ed. Vol. II. Toxicology. New York, NY: Interscience Publishers, Inc., p. 899.

10. Seluzhitsky GV [1972]. Experimental data for substantiation of the threshold of methyl mercaptan, dimethyl sulfide, and dimethyldisulfide in the air of the working zone of paper industries. Gig Tr Prof Zabol 16(6):46-47 (in Russian).

11. Tansy MF, Kendall FM, Fantasia J, Landin WE, Oberly R [1981]. Acute and subchronic toxicity studies of rats exposed to vapors of methyl mercaptan and other reduced-sulfur compound. J Toxicol Environ Health 8:71-88.

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