Skip directly to local search Skip directly to A to Z list Skip directly to navigation Skip directly to site content Skip directly to page options
CDC Home
May 1994

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


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).

Contact Us: The U.S. Government's Official Web PortalDepartment of Health and Human Services
Centers for Disease Control and Prevention   1600 Clifton Road Atlanta, GA 30329-4027, USA
800-CDC-INFO (800-232-4636) TTY: (888) 232-6348 - Contact CDC–INFO