OSHA formerly had no limit for exposure to boron tribromide. The ACGIH has a 1-ppm ceiling limit for boron tribromide, which is a colorless, fuming liquid that is decomposed by water and alcohol. The proposed PEL, with which NIOSH (Ex. 8-47, Table N1) concurred, was a ceiling of 1 ppm; this limit is established in the final rule.
Boron tribromide has a high potential for acute local irritation, and its potential for systemic toxicity is analogous with that of hydrogen bromide (HBr). On decomposition, one molecule of boron tribromide would be expected to produce three molecules of HBr (ACGIH 1986/Ex. 1-3, p. 62).
Animals repeatedly exposed to boron tribromide develop pneumonia, and exposure to 100 ppm caused a uniformly high mortality rate in animals from six laboratory species (Stokinger, Spiegel et al. 1953, as cited in ACGIH 1986/Ex. 1-3, p. 63). Rats, rabbits, and mice exposed at 1.5, 3.4, or 12.8 ppm boron trifluoride developed pneumonitis and dental fluorosis, although, at the lowest level tested, the evidence of pneumonitis was described as "marginal" (Torkelson, Sadek, and Rowe 1961, as cited in ACGIH 1986/Ex. 1-3, p. 63).
Based on this evidence of boron tribromide's severe pulmonary toxicity at exposure levels of 3.4 ppm, OSHA is establishing a ceiling limit of 1 ppm. The Agency concludes that this limit will protect workers from the significant risk of serious pulmonary damage, a material health impairment that is associated with exposure to this substance at levels above the new PEL.