Immediately Dangerous to Life or Health Concentrations (IDLH)
CAS number: 74–87–3
NIOSH REL: None established; NIOSH considers methyl chloride to be a potential occupational carcinogen as defined by the OSHA carcinogen policy [29 CFR 1990].
Current OSHA PEL: 100 ppm TWA, 200 ppm CEILING,
300 ppm 5-minute MAXIMUM PEAK IN ANY 3 HOURS
1989 OSHA PEL: 50 ppm (105 mg/m3) TWA, 100 ppm (210 mg/m3) STEL
1993-1994 ACGIH TLV: 50 ppm (103 mg/m3) TWA, 100 ppm (207 mg/m3) STEL [skin]
Description of substance: Colorless gas with a faint, sweet odor which is not noticeable at dangerous concentrations.
LEL: . . . 8.1% (10% LEL, 8,100 ppm)
Original (SCP) IDLH: 10,000 ppm
Basis for original (SCP) IDLH: The chosen IDLH is based on the statement by Patty  that 20,000 to 40,000 ppm is dangerous to animals in 30 to 60 minutes [Flury and Zernik 1931] and the report by MacDonald  that a worker repeatedly walked in and out of an area in which concentrations greater than 10,000 ppm were measured.
Short-term exposure guidelines: None developed
ACUTE TOXICITY DATA:
Lethal concentration data:
|Species||Reference||LC50(ppm)||LCLo(ppm)||Time||Adjusted 0.5-hrLC (CF)||Derived value|
|Rat||Bakhishev 1975||72,000||—–||30 min||72,000 ppm (1.0)||7,200 ppm|
|Mouse||Chellman et al. 1986||2,200||—–||6 hr||5,060 ppm (2.3)||506 ppm|
|Mammal||Clayton & Clayton 1981||2,760||—–||4 hr||5,520 ppm (2.0)||552 ppm|
|G. pig||Clayton 1967||—–||20,000||2 hr||32,000 ppm (1.6)||3,200 ppm|
|Rat||Izmerov et al. 1982||2,524||—–||4 hr||5,048 ppm (2.0)||505 ppm|
|Dog||von Oettingen 1949||—–||14,661||6 hr||33,720 ppm (2.3)||3,372 ppm|
Other animal data: It has been reported that 20,000 to 40,000 ppm is dangerous in 30 to 60 minutes [Flury and Zernik 1931].
Human data: It has been reported that a worker repeatedly walked in and out of an area in which concentrations greater than 10,000 ppm were measured; symptoms included blurring of vision, dizziness, and a slight headache [MacDonald 1964]. A worker exposed to concentrations of 2,000 to 4,000 ppm for 13 days stated that during the first week he was very sleepy and became quite dizzy; during the second week headache, blurring of vision, slurring of speech, dizziness, mental confusion, and a staggering gait occurred [MacDonald 1964]. Another worker exposed to concentrations of 1,000 to 2,000 ppm during the workshift experienced dizziness, blurring of vision, headache, nausea, and vomiting [MacDonald 1964]. It has been stated that exposures to 20,000 ppm for 2 hours may be fatal [Deichmann and Gerarde 1969].
|Revised IDLH: 2,000 ppmBasis for revised IDLH: The revised IDLH for methyl chloride is 2,000 ppm based on acute inhalation toxicity data in humans [MacDonald 1964]. [Note: NIOSH recommends as part of its carcinogen policy that the “most protective” respirators be worn for methyl chloride at any detectable concentration.]|
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2. Chellman GJ, White RD, Norton RM, Bus JS . Inhibition of the acute toxicity of methyl chloride in male B6C3F1 mice by glutathione depletion. Toxicol Appl Pharmacol 86:93-104.
3. Clayton GD, Clayton FE, eds. . Patty’s industrial hygiene and toxicology. 3rd rev. ed. Vol. 2B. Toxicology. New York, NY: John Wiley & Sons, Inc., pp. 3436-3442.
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