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: 78-87-5; Chemical Formula: CH3CHClCH2Cl
OSHA’s former limit for propylene dichloride was 75 ppm as an 8-hour TWA. The proposal retained the 75-ppm TWA and added a STEL of 110 ppm, and these are the limits being promulgated in the final rule. Propylene dichloride is a colorless, flammable, mobile liquid with an odor like that of chloroform.
The primary hazards associated with exposure to propylene dichloride are inhalation-induced toxicity to liver tissue and skin and eye irritation. Repeated inhalation exposures to 1000 ppm have been reported to kill dogs (after 24 exposures), guinea pigs (after 22 exposures), and rats (in some cases after only seven exposures); however, some animals survived more than 100 seven-hour exposures. Necropsy showed severe liver damage; the hepatotoxicity of propylene dichloride appears to be greater than that of carbon tetrachloride and less than that of ethylene dichloride (Heppel, Neal, Highman, and Porterfield 1946/Ex. 1-510). Animals of these same species (rats, dogs, and guinea pigs) survived 128 to 140 seven-hour exposures to 400 ppm propylene dichloride for five days/week without histologic effects, while mice died from similar exposures; surviving mice displayed hepatomas (Heppel, Highman, and Peake 1948/Ex. 1-605). The oral LD(50) for rats has been reported as 1.19 ml/kg (Smyth, Carpenter, Weil et al. 1969/Ex. 1-442); the acute 8-hour inhalation LC(50) for rats is 3000 ppm (Pozzani, Weil, and Carpenter 1959/Ex. 1-608). NIOSH (Ex. 150A, Comments on Propylene Dichloride) noted that an NTP (1986c) bioassay showed some evidence that propylene dichloride was carcinogenic in mice and caused an increased incidence of hepatocellular adenomas; NIOSH indicated (Ex. 8-47, Table N6B) that a separate 6(b) rulemaking might be appropriate for this substance. The finding of tumors was not reproduced in rats, in that female rats showed only a marginally increased incidence of mammary adenocarcinomas, and male rats showed no response. NIOSH was the only commenter on propylene dichloride.
In the final rule, OSHA is retaining the 8-hour TWA PEL for propylene dichloride of 75 ppm and adding a 15-minute STEL of 110 ppm. The Agency concludes that this combined limit will protect workers against the significant risks of serious hepatotoxic effects, which constitute material impairments of health, that are associated with exposures at the elevated levels permitted by the absence of a short-term limit. OSHA finds that the TWA and short-term PELs will act together to reduce this risk substantially.