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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: 7572-29-4; Chemical Formula: C2Cl2

OSHA previously had no limit for dichloroacetylene. The ACGIH has a TLV-ceiling of 0.1 ppm for this liquid, which explodes upon boiling. OSHA proposed a ceiling limit of 0.1 ppm, and this is the limit established by the final rule.

In preliminary inhalation exposure studies, guinea pigs demonstrated a 4-hour LC(50) of 20 ppm; death occurred two or three days after exposure and was caused by pulmonary edema. In rats, similar exposures to dichloroacetylene in the presence of 330 ppm of trichloroethylene indicated an LC(50) of 55 ppm (Siegel 1967, as cited in ACGIH 1986/Ex. 1-3, p. 177). When dichloroacetylene was mixed with 9 parts of ether, the 4-hour LC(50) in rats was 219 ppm; in combination with 7 parts of trichloroethylene, the 4-hour LC(50) in rats was 55 ppm; and exposure to dichloroacetylene with 10 parts of trichloroethylene caused a 4-hour LC(50) in guinea pigs of 15 ppm (Siegel, Jones, Coon, and Lyon 1971/Ex. 1-371).

In humans, dichloroacetylene exposure causes headache, loss of appetite, extreme nausea, and vomiting; it affects the trigeminal nerve and facial muscles and exacerbates facial herpes. Disabling nausea was experienced by approximately 85 percent of individuals exposed for prolonged periods of time (not further specified) at concentrations from 0.5 to 1 ppm (Saunders 1967/Ex. 1-361). A number of occupational fatalities have been attributed to exposure to dichloroacetylene (Humphrey and McClelland 1944/Ex. 1-491; Firth and Stuckey 1945, as cited in ACGIH 1986/Ex. 1-3, p. 177). Humphrey and McClelland (1944/Ex. 1-491) reported 13 cases of cranial nerve palsy, nine of which had labial herpes, following exposure to dichloroacetylene. These patients also had symptoms of nausea, headache, jaw pain, and vomiting. Autopsies of two of these fatalities revealed edema at the base of the brain (Humphrey and McClelland 1944/Ex. 1-491).

NIOSH concurs with OSHA's limit for dichloroacetylene but believes that this substance should be designated as a potential occupational carcinogen (Ex. 8-47, Table N6A). However, as explained elsewhere in the preamble, OSHA has decided not to designate substances specifically as carcinogens since so many other organizations already do so. OSHA received no other comments regarding the health effects of dichloroacetylene.

In the final rule, OSHA is establishing a ceiling limit of 0.1 ppm for dichloroacetylene. The Agency concludes that this limit will substantially reduce the significant risks of disabling nausea and serious systemic effects posed to workers exposed to dichloroacetylene at the levels formerly permitted by the absence of any OSHA limit. OSHA finds that these health effects constitute material impairments of health.