Benzene (CAS number 71-43-2) is a colorless to light-yellow liquid with an aromatic odor. This NIOSH document sets its Immediately Dangerous to Life or Health (IDLH) concentration.
The revised IDLH for benzene is 500 ppm, based on acute inhalation toxicity data in humans.
Exposure limits
| Limit | Value |
|---|---|
| NIOSH REL | 0.1 ppm TWA, 1 ppm STEL — NIOSH considers benzene a potential occupational carcinogen under OSHA's carcinogen policy (29 CFR 1990) |
| Current OSHA PEL | 1 ppm TWA, 5 ppm STEL — the same as the 1989 PEL |
| 1993–1994 ACGIH TLV | 10 ppm (32 mg/m³) TWA, A2 |
| LEL | 1.2% (10% of the LEL: 1,200 ppm) |
| Emergency Exposure Guidance Levels (EEGLs), National Research Council, 1986 | 50 ppm for 1 hour; 2 ppm for 24 hours |
The original value
The original (SCP) IDLH was 3,000 ppm. It rested on the statement, in Patty (1963), that for people a single exposure to 3,000 ppm is endurable for half an hour to an hour (Flury, 1928).
Lethal concentrations
| Species | Source | LCLo (ppm) | Time | Adjusted 0.5-hour LC | Derived value |
|---|---|---|---|---|---|
| Human | Tab Biol Per, 1933 | 20,000 | 5 min | 11,000 ppm (factor 0.55) | 1,100 ppm |
| Rabbit | Carpenter et al., 1944 | 44,000 | 30 min | — | — |
| Dog | Spector, 1955 | 44,923 | not given | — | — |
| Cat | Spector, 1955 | 52,308 | not given | — | — |
No LC50 values are listed.
What exposure does to people
According to Gerarde (1960):
| Concentration | Time | Effect |
|---|---|---|
| 19,000–20,000 ppm | 5–10 minutes | fatal |
| 7,500 ppm | 30 minutes | dangerous |
| 1,500 ppm | 60 minutes | serious symptoms |
| 500 ppm | 60 minutes | symptoms of illness |
| 50–150 ppm | 5 hours | headache, lassitude, weakness |
| 25 ppm | 8 hours | no effect |
Sources
Based on "Benzene," Immediately Dangerous to Life or Health Concentrations (IDLH), National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, citing Carpenter et al. (1944), Flury (1928), Gerarde (1960), the National Research Council (1986), Patty (1963), Spector (1955) and Tab Biol Per (1933); a work of the United States government in the public domain. For rabbits the source gives an adjusted 0.5-hour concentration (45,000 ppm) that does not match its LCLo of 44,000 ppm at a factor of 1.0, so neither the adjusted nor the derived rabbit value is repeated.
Licence: CC0 1.0 (public domain) · Adapted from www.cdc.gov
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