BUTANE
OSHA comments from the January 19, 1989 Final Rule on Air Contaminants Project extracted from 54FR2332 et. seq. This rule was remanded by the U.S. Circuit Court of Appeals and the limits are not currently in force.
CAS: 106-97-8; Chemical Formula: C4H10
Previously, OSHA had no limit for butane. The ACGIH has a TLV-TWA of 800 ppm for this colorless, flammable gas. The proposed PEL was 800 ppm as an 8-hour TWA, and NIOSH (Ex. 8-47, Table N1,) concurs with this limit. The final rule promulgates an 8-hour TWA of 800 ppm.
The primary risk of exposure to butane is narcosis, which occurs at high exposure levels. Exposure to 10,000 ppm butane for 10 minutes causes drowsiness, but there are no reports of systemic toxicity or irritation at this level (Gerarde 1963a, as cited in ACGIH 1986/Ex. 1-3, p. 10).
In rats, the 4-hour LC(50) for butane is 658 g/m3, or about 280,000 ppm (NIOSH 1977i/Ex. 1-1182). Humans exposed to 1000 ppm for a single eight-hour day, or to 500 ppm for two-week periods of eight-hour workdays, showed no harmful subjective or abnormal physiological responses but did show a reduced visual evoked response (VER) wave amplitude during the second week (Stewart, Herrman, Baretta et al. 1977/Ex. 1-575). OSHA received no comments, other than NIOSH’s, on butane.
In the final rule, OSHA is establishing a permissible exposure limit of 800 ppm TWA for butane. The Agency concludes that this limit will protect workers against the significant risks of drowsiness and other narcotic effects, which together constitute material health impairments and are associated with exposures at the uncontrolled levels permitted in the past by the absence of an OSHA limit.