Skip directly to search Skip directly to A to Z list Skip directly to navigation Skip directly to page options Skip directly to site content


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

CAS number: 67–66–3

NIOSH REL: 2 ppm (9.78 mg/m3) 60-minute STEL; NIOSH considers chloroform to be a potential occupational carcinogen as defined by the OSHA carcinogen policy [29 CFR 1990].

Current OSHA PEL: 50 ppm (240 mg/m3) CEILING

1989 OSHA PEL: 2 ppm (9.78 mg/m3) TWA

1993-1994 ACGIH TLV: 10 ppm (49 mg/m3) TWA, A2

Description of Substance: Colorless liquid with a pleasant odor.

LEL: . . Noncombustible Liquid

Original (SCP) IDLH: 1,000 ppm

Basis for original (SCP) IDLH: The chosen IDLH is based on the statement by Patty [1963] that 1,024 ppm produced dizziness, intracranial pressure, and nausea after 7 minutes with definite after-effects [Lehmann and Flury 1943]. Also, Lehmann et al. [1936] reported that a 2-minute exposure to 1,107 ppm caused dizziness and vertigo. Because a person may become disoriented at concentrations greater than 1,000 ppm and be unable to escape, 1,000 ppm is chosen as the IDLH.

Existing short-term exposure guidelines: National Research Council [NRC 1984] Emergency Exposure Guidance Levels (EEGLs):

1-hour EEGL: 100 ppm

24-hour EEGL: 30 ppm


Lethal concentration data:






Adjusted 0.5-hr




G. pig




Clayton 1967

Lehmann and Flury 1943

Lehmann et al. 1936

Tab Biol Per 1933









2 hr

4 hr

4 hr

5 min

32,000 ppm (1.6)

19,235 ppm (2.0)

14,113 ppm (2.0)

13,750 ppm (0.55)

3,200 ppm

1,924 ppm

1,411 ppm

1,375 ppm

Other animal data: It has been reported that inhalation of 10,000 ppm has produced clinical anesthesia [NIOSH 1974] and that exposure for 2 minutes to 1,107 ppm has caused dizziness and vertigo [Lehmann et al. 1936]. Workers exposed 4 hours/day to concentrations of 57 to 71 ppm complained of lassitude, loss of appetite, and nausea [Challen et al. 1958]. Exposures to 390 ppm were tolerated for 30 minutes without complaint, whereas 1,030 ppm resulted in dizziness, intracranial pressure, and nausea in 7 minutes, with headache for several hours [Lehmann and Flury 1943].

Revised IDLH: 500 ppm

Basis for revised IDLH: The revised IDLH for chloroform is 500 ppm based on acute inhalation toxicity data in humans [Lehmann and Flury 1943]. [Note: NIOSH recommends as part of its carcinogen policy that the "most protective" respirators be worn for chloroform at concentrations above 2 ppm.]


1. Challen PJR, Hickish DE, Bedford J [1958]. Chronic chloroform intoxication. Br J Ind Med 15:243-249.

2. Clayton JW Jr [1967]. Fluorocarbon toxicity and biological action. Fluor Chem Rev 1(2):197-252.

3. Lehmann KB, Flury F, eds. [1943]. Toxicology and hygiene of industrial solvents. Translated by E. King and H.F. Smyth, Jr. Baltimore, MD: Williams & Wilkins Company, p. 141.

4. Lehmann KB, Schmidt-Kehl L, Ruf H, Crescitelli, Dahl, Eppinghausen, Eshe, Falker, Grotefendt, Junkenita, Maier, Mergner, Pantehtsch, Schlitzer, Shoenes, Spettmann, Wirges, Bamsreiter, Benninger, Lazarus, Manasse, Kummeth, Reuss, Schwarzweller [1936]. The 13 most important chlorinated hydrocarbons of the aliphatic series from the standpoint of occupational hygiene. Arch Hyg Bakteriol 116:132-200 (translated).

5. Lundberg I, Ekdahl M, Kronevi T, Lidums V, Lundberg S [1986]. Relative hepatotoxicity of some industrial solvents after intraperitoneal injection or inhalation exposure in rats. Environ Res 40:411-420.

6. NIOSH [1974]. Criteria for a recommended standard: occupational exposure to chloroform. Cincinnati, OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health, DHEW (NIOSH) Publication No. 75-114.

7. NRC [1984]. Emergency and continuous exposure limits for selected airborne contaminants. Vol. 1. Washington, DC: National Academy Press, Committee on Toxicology, Board on Toxicology and Environmental Health Hazards, Commission on Life Sciences, National Research Council, pp. 57-76.

8. Patty FA, ed. [1963]. Industrial hygiene and toxicology. 2nd rev. ed. Vol. II. Toxicology. New York, NY: Interscience Publishers, Inc., p. 1261.

9. Tab Biol Per [1933]; 3:231 (in German).