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May 1994

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


CAS number: 7782–50–5

NIOSH REL: 0.5 ppm (1.45 mg/m3) 15-minute CEILING

Current OSHA PEL: 1 ppm (3 mg/m3) CEILING

1989 OSHA PEL: 0.5 ppm (1.5 mg/m3) TWA, 1 ppm (3 mg/m3) STEL

1993-1994 ACGIH TLV: 0.5 ppm (1.5 mg/m3) TWA, 1 ppm (2.9 mg/m3) STEL

Description of Substance: Greenish-yellow gas with a pungent, irritating odor.

LEL: . . Nonflammable Gas

Original (SCP) IDLH: 30 ppm

Basis for original (SCP) IDLH: The chosen IDLH is based on the statement by ILO [1971] that exposure to 30 ppm will cause intense coughing fits, and exposure to 40 to 60 ppm for 30 to 60 minutes or more may cause serious damage.

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

1-hour EEGL: 3 ppm

24-hour EEGL: 0.5 ppm


Lethal concentration data:







Adjusted 0.5-hr

LC (CF*)





G. pig



Back et al. 1972

Back et al. 1972

Lehmann 1887

Prentiss 1937

Tab Biol Per 1933











1 hr

1 hr

3 hr

30 min

5 min

357 ppm (1.22)

167 ppm (1.22)

5,342 ppm (1.67)

858 ppm (1.0)

330 ppm (0.60)

36 ppm

17 ppm

534 ppm

86 ppm

33 ppm

*Note: Conversion factor (CF) was determined with "n" = 3.5 [ten Berge et al. 1986].

Other animal data: RD50 (mouse), 9.34 ppm [Alarie 1981].

Other human data: Exposures to 30 ppm have been reported to cause intense coughing fits and exposure to 40 to 60 ppm for 30 to 60 minutes or more may cause serious damage [ILO 1971]. A concentration of 34 to 51 ppm has been reported to be lethal in 1 to 1.5 hours [Freitag 1941] while 14 to 21 ppm has been suggested as being dangerous within 0.5 to 1 hour [NPIRI 1983].


Revised IDLH: 10 ppm

Basis for revised IDLH: The revised IDLH for chlorine is 10 ppm based on acute inhalation toxicity data in humans [Freitag 1941; ILO 1971; NPIRI 1983].


1. Alarie Y [1981]. Dose-response analysis in animal studies: prediction of human responses. Environ Health Perspect 42:9-13.

2. Back KC, Thomas AA, MacEwen JD [1972]. Reclassification of materials listed as transportation health hazards. Wright-Patterson Air Force Base, OH: 6570th Aerospace Medical Research Laboratory, Report no. TSA-20-72-3, pp. A-182 to A-183.

3. Freitag [1941]. Danger of chlorine gas. Z. Gesamte Schiess Sprengstoffwes.

4. ILO [1971]. Chlorine and compounds. In: Encyclopaedia of occupational health and safety. 2nd ed. Vol. I (A-K). Geneva, Switzerland: International Labour Office, pp. 287-288.

5. Lehmann KB [1887]. Experimentelle studien uber den einfluss technisch und hygienisch wichtiger gase und dampfe auf den organismus. Thiel III und IV: Chlor und brom. Arch Hyg 7:231-285 (in German).

6. NPIRI [1983]. Raw materials data handbook, physical and chemical properties, fire hazard and health hazard data. Vol. II. 2nd ed. Organic solvents. Bethlehem, PA: National Printing Ink Research Institute, pp. 831-857.

7. NRC [1984]. Emergency and continuous exposure limits for selected airborne contaminants. Vol. 2. Washington, DC: National Academy Press, Committee on Toxicology, Board on Toxicology and Environmental Health Hazards, Commission on Life Sciences, National Research Council, pp. 5-11.

8. Prentiss AM [1937]. Chemicals in war. A treatise on chemical warfare. New York, NY: McGraw-Hill Book Company, Inc., p. 150.

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

10. ten Berge WF, Zwart A, Appelman LM [1986]. Concentration-time mortality response relationship of irritant and systematically acting vapours and gases. J Haz Mat 13:301-309.

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