Immediately Dangerous to Life or Health Concentrations (IDLH)
CAS number: 71–55–6
NIOSH REL: 350 ppm (1,900 mg/m3) 15-minute CEILING
Current OSHA PEL: 350 ppm (1,900 mg/m3) TWA
1989 OSHA PEL: 350 ppm (1,900 mg/m3) TWA, 450 ppm (2,450 mg/m3) STEL
1993-1994 ACGIH TLV: 350 ppm (1,910 mg/m3) TWA, 450 ppm (2,460 mg/m3) STEL
Description of substance: Colorless liquid with a mild, chloroform-like odor.
LEL:. 7.5% (10% LEL, 7,500 ppm)
Original (SCP) IDLH: 1,000 ppm
Basis for original (SCP) IDLH: The chosen IDLH is based on the statement by MCA  that “humans exposed to 900 to 1,000 ppm experience prompt, though minimal impairment of coordination. Above 1,700 ppm, obvious disturbances of equilibrium in humans have been observed.” Deichmann and Gerarde  stated that “the earliest symptoms of a single vapor exposure are lightheadedness and lassitude. The earliest sign of intoxication is an impaired Romberg test. In humans an abnormal Romberg test is usually observed shortly after exposures to 900 to 1,700 ppm.” Because data are not available to indicate at what concentrations above 1,000 ppm a person’s equilibrium would be affected enough to impede escape, 1,000 ppm is used as the IDLH. AIHA  reported that humans exposed to 800 to 1,000 ppm exhibit early anesthetic effects including incoordination [Stewart et al. 1961; Torkelson et al. 1958]. Browning  reported that several human subjects exposed to 920 ppm for periods ranging from 5 to 45 minutes showed a slight loss of coordination and equilibrium [Stewart et al. 1961].
Existing short-term exposure guidelines: American Industrial Hygiene Association [AIHA 1964] Emergency Exposure Limits (EELs):
5-minute EEL: 2,500 ppm
15-minute EEL: 2,000 ppm
30-minute EEL: 2,000 ppm
60-minute EEL: 1,000 ppm
ACUTE TOXICITY DATA:
Lethal concentration data:
|Species||Reference||LC50 (ppm)||LCLo (ppm)||Time||Adjusted 0.5-hrLC (CF)||Derived value|
|MouseRat||AIHA 1964Sangyo Igaku 1971||3,91118,000||———-||2 hr4 hr||6,258 ppm (1.6)36,000 ppm (2.0)||626 ppm3,600 ppm|
Lethal dose data:
|Species||Reference||Route||LD50 (mg/kg)||LDLo (mg/kg)||Adjusted LD||Derived value|
|Pal’gov et al. 1990Pal’gov et al. 1990
Torkelson et al. 1958
|12,108 ppm7,568 ppm
|1,211 ppm757 ppm
Other animal data: No significant signs of intoxication were seen in rats inhaling 500 ppm, 6 hours per day for 4 days [Savolainen et al. 1977]; in mice inhaling up to 1,300 ppm for 1 hour [Kjellstrand et al. 1985]; in rats inhaling up to 3,000 ppm for 0.5 to 4 hours [Mullin and Krivanek 1982]; or in baboons inhaling up to 1,400 ppm for 4 hours [Geller et al. 1982].
Human data: The onset of central anesthesia has occurred in individuals exposed for up to 7 hours to concentrations approaching 500 ppm [Stewart et al. 1969]. It has been stated that exposure to 900 to 1,000 ppm causes prompt, though minimal impairment of coordination; obvious disturbances in equilibrium have been noted above 1,700 ppm [MCA 1965]. Those exposed to 800 to 1,000 ppm have exhibited early anesthetic effects including incoordination [Stewart et al. 1961]. Volunteers exposed to 920 ppm for 5 to 45 minutes showed a slight loss of coordination and equilibrium [Stewart et al. 1961].
|Revised IDLH: 700 ppmBasis for revised IDLH: The revised IDLH for methyl chloroform is 700 ppm based on acute inhalation toxicity data in humans [MCA 1965; Stewart et al. 1961, 1969].|
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