HYDRAZINE

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: 302-01-2; Chemical Formula: H₂N – NH₂

The former OSHA limit for hydrazine was 1 ppm as an 8-hour TWA, with a skin notation. OSHA proposed an 8-hour TWA PEL of 0.1 ppm, also with a skin notation, and the final rule establishes this limit. Hydrazine is an odorless, fuming, oily liquid with an ammonia-like odor. Because of hydrazine’s potential carcinogenic hazard, NIOSH (1978e/Ex. 1-263; Ex. 8-47) has recommended that workplace exposures to hydrazine not exceed 0.03 ppm, as determined by a two-hour air sample; this level represents the lowest detectable concentration over this sampling period.

A hepatotoxic response in mice and anemia and weight loss in dogs were reported to occur following a six-month exposure to 1 ppm of hydrazine for six hours per day, five days per week, or to 0.2 ppm continuously (Haun and Kinkead 1973/Ex. 1-824). The ACGIH has assigned an A2 designation (suspect human carcinogen) to hydrazine, based on a study by MacEwen, Vernot, and Haun (1979/Ex. 1-193) showing significant increases in nasal tumors in rats exposed to 1 or 5 ppm hydrazine, in thyroid adenocarcinomas in rats exposed to 5 ppm, and in lung adenomas among mice exposed to 1 ppm. NIOSH (1978e/Ex. 1-263) cites studies that demonstrate the carcinogenicity of hydrazine in rodents by a variety of dose routes. NIOSH (Ex. 8-47, Table N6B) believes that hydrazine should be labelled a potential occupational carcinogen. Based on sufficient evidence of hydrazine’s carcinogenicity in animals, IARC (1987) classified hydrazine as a Group 2B (possible human) carcinogen.

The animal studies conducted by Haun and Kinkead (1973/ Ex. 1-824) and by MacEwen, Vernot, and Haun (1979/Ex. 1-193) clearly demonstrate that exposure to hydrazine at the former 1-ppm PEL presents a significant risk of respiratory cancer, liver disease, and adverse blood effects; animals exposed to airborne concentrations at this level have exhibited all of these responses. Reported dermal LD(50)s in rabbits and dogs were 91 and 90 mg/kg, respectively, showing that hydrazine can readily penetrate the skin and cause systemic effects.

Some commenters (Ex. 8-16, 194, Tr. 9-218; Tr. 3-309) misunderstood the classification scheme used by OSHA to group substances in the proposal and commented that, in their opinion, hydrazine should have been classified as a carcinogen rather than a hepatotoxin. However, as discussed in other sections of the preamble, OSHA did not intend this classification scheme to have regulatory implications but to facilitate generic rulemaking. OSHA’s approach was to classify substances in accordance with the health effect on which the ACGIH has based its TLV. In response to the American Industrial Hygiene Association’s question about a risk assessment for hydrazine, OSHA notes that, in this rulemaking, OSHA has performed risk assessments only for some of the substances classified in Section VI.C.15 of the preamble.

The Agency is establishing an 8-hour TWA PEL of 0.1 ppm, with a skin notation, for hydrazine. OSHA concludes that this limit will substantially reduce the significant risks of cancer, liver disease, and hematopoietic effects, all clearly material impairments of health, that have been demonstrated to occur in animals at exposures above the revised PEL.