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

CAS number: 71-43-2

NIOSH REL: 0.1 ppm TWA, 1 ppm STEL; NIOSH considers benzene to be a potential occupational carcinogen as defined by the OSHA carcinogen policy [29 CFR 1990].

Current OSHA PEL: 1 ppm TWA, 5 ppm STEL

1989 OSHA PEL: Same as current PEL

1993-1994 ACGIH TLV: 10 ppm (32 mg/m3) TWA, A2

Description of substance: Colorless to light-yellow liquid with an aromatic odor.

LEL: 1.2% (10% LEL, 1,200 ppm)

Original (SCP) IDLH: 3,000 ppm

Basis for original (SCP) IDLH: The chosen IDLH is based on the report in Patty [1963] that for man, a single exposure to 3,000 ppm is endurable for 0.5 to 1 hour [Flury 1928].

Existing short-term exposure: National Research Council [NRC 1986] guidelines

Emergency Exposure Guidance Levels (EEGLs):
1-hour EEGL: 50 ppm
24-hour EEGL: 2 ppm


Lethal concentration data:

LC50 LCLo 0.5-hr Derived
Species Reference (ppm) (ppm) Time LC (CF) Value
Rabbit Carpenter et al. 1944 ----- 44,000 30 min 45,000 ppm (1.0) 4,500 ppm
Dog Spector 1955 ----- 44,923 ? ? ?
Cat Spector 1955 ----- 52,308 ? ? ?
Human Tab Biol Per 1933 ----- 20,000 5 min 11,000 ppm (0.55) 1,100 ppm

Other human data: It has been stated that 3,000 ppm is endurable for 0.5 to 1 hour [Flury 1928]. It has also been stated that exposure at 19,000 to 20,000 ppm for 5 to 10 minutes is fatal; exposure at 7,500 ppm for 30 minutes is dangerous; exposure at 1,500 ppm for 60 minutes induces serious symptoms; exposure at 500 ppm for 60 minutes leads to symptoms of illness; exposure at 50 to 150 ppm for 5 hours produces headache, lassitude, and weakness; and exposure at 25 ppm for 8 hours has no effect [Gerarde 1960].

Revised IDLH: 500 ppm

Basis for revised IDLH: The revised IDLH for benzene is 500 ppm based on acute inhalation toxicity data in humans [Gerarde 1960]. [Note: NIOSH recommends as part of its carcinogen policy that the "most protective" respirators be worn for benzene at concentrations above 0.1 ppm. OSHA currently requires in 29 CFR 1910.1028 that workers be provided with and required to wear and use the "most protective" respirators in concentrations exceeding 1,000 ppm (i.e., 1,000 x the PEL).]


  1. Carpenter CP, Shaffer CB, Weil CS, Smyth HF Jr [1944]. Studies on the inhalation of 1:3-butadiene; with a comparison of its narcotic effect with benzol, toluol, and styrene, and a note on the elimination of styrene by the human. J Ind Hyg Toxicol 26(3):69-78.
  2. Flury F [1928]. Moderne gewerbliche vergiftungen in pharmakologisch-toxikologischer hinsicht (Pharmacological-toxicological aspects of intoxicants in modern industry). Arch Exp Pathol Pharmakol 138:65-82 (translated).
  3. Gerarde HW [1960]. Toxicology and biochemistry of aromatic hydrocarbons. New York, NY: Elsevier Publishing Company.
  4. NRC [1986]. Emergency and continuous exposure guidance levels for selected airborne contaminants. Vol. 6. Benzene and ethylene oxide. Washington, DC: National Academy Press, Committee on Toxicology, Board on Toxicology and Environmental Health Hazards, Commission on Life Sciences, National Research Council, pp. 7-33.
  5. Patty FA, ed. [1963]. Industrial hygiene and toxicology. 2nd rev. ed. Vol. II. Toxicology. New York, NY: Interscience Publishers, Inc., p. 1221.
  6. Spector WS, ed. [1955]. Handbook of toxicology. Vol. 1. Acute toxicities of solids, liquids and gases to laboratory animals. Philadelphia, PA: W.B. Saunders Co., p. 324.
  7. Tab Biol Per [1933]; 3:231 (in German).
Page last reviewed: December 4, 2014