OSHA formerly had no limit for o-chlorostyrene. The proposed limits were an 8-hour TWA of 50 ppm and a STEL of 75 ppm, and NIOSH (Ex. 8-47, Table N1) concurred with these limits. The final rule establishes a 50-ppm TWA PEL and a 75-ppm STEL, limits that are consistent with those of the ACGIH. o-Chlorostyrene is a colorless liquid at room temperature.
In an unpublished report, the Dow Chemical Company (1973a, as cited in ACGIH 1986/Ex. 1-3, p. 136) describes the results of an o-chlorostyrene inhalation study in rats, rabbits, guinea pigs, and dogs. Dow exposed the animals to an average concentration of 101 ppm for seven hours daily, five days per week, for a total of 130 exposures in 180 days. No adverse effects were observed in any species in terms of appearance, growth, behavior, mortality, hematology, BUN, alkaline phosphatase, SGPT, BSP, organ weights, or gross pathology (Dow Chemical Company 1973a, as cited in ACGIH 1986/Ex. 1-3, p. 136). Microscopic examination of animal tissue revealed a somewhat higher incidence of pathological changes in the liver and kidneys. There is evidence indicating that the warning properties of o-chlorostyrene do not permit workers to be aware of o-chlorostyrene concentrations of 100 ppm. Based on o-chlorostyrene's structural analogy to styrene, for which short-term exposures of 100 ppm have been demonstrated to produce neuropathic and narcotic effects (Stewart, Dodd, Baretta, and Schaffer 1968/Ex. 1-380), OSHA finds that a short-term limit is necessary. OSHA received no comments (other than NIOSH's) on this substance.
The final rule establishes a PEL of 50 ppm as an 8-hour TWA and a 15-minute STEL of 75 ppm for o-chlorostyrene. The Agency concludes that both of these limits will protect workers from the significant risks of liver and kidney damage, narcosis, and neuropathy to which they could potentially be exposed in the absence of any OSHA limit. OSHA finds that these health effects constitute material health impairments and that the TWA and STEL limits will substantially reduce these significant occupational risks.