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: 100-63-0; Chemical Formula: C6H5NHNH2

OSHA’s former limit for phenylhydrazine was 5 ppm TWA as an 8-hour, with a skin notation. The ACGIH has a TLV-TWA of 5 ppm with a STEL of 10 ppm, and a skin notation. NIOSH (1978e/Ex. 1-263) recommends that workplace exposures not exceed 0.14 ppm as measured over a two-hour period. OSHA proposed to retain the PEL of 5 ppm as an 8-hour TWA and to add a STEL of 10 ppm, with a skin notation, and these limits are established in the final rule. Phenylhydrazine may be either yellow crystals or an oily liquid that darkens on exposure to air and light.

No data are available on the effects of phenylhydrazine resulting from inhalation. The ACGIH limits are based on the high acute toxicity of the compound when administered orally or subcutaneously to animals; single doses on the order of 20 mg/kg have resulted in the death of dogs within 22 days (Hesse, Franke, and Hering 1935/Ex. 1-785) and produced a marked decrease in erythrocyte count in rodents (von Oettingen and Deichmann-Greubler 1936/Ex. 1-771). Anemia and hemolysis are the characteristic responses seen in animals fed or injected with phenylhydrazine.

In its criteria document on the hydrazines, NIOSH (1978e/Ex. 1-263) reviewed four studies on the carcinogenicity of phenylhydrazine in mice. One study (Toth and Shimizu 1976/Ex. 1-675) found significant increases in blood vessel tumors. Another study (Clayson, Biancifiori, Milia, and Santilli 1966, as cited in ACGIH 1986/Ex. 1-3, p. 477) reported increased incidences of lung adenomas and adenocarcinomas. Two other studies (Roe, Grant, and Millican 1967/Ex. 1-659; Kelly, O’Gara, Yancy et al. 1969/Ex. 1-703) were negative. NIOSH concluded that phenylhydrazine should be considered a potential human carcinogen and recommended that exposures not exceed 0.14 ppm over a two-hour sampling period, which represents the lowest level that can be detected reliably. The ACGIH (1986/Ex. 1-3) has placed phenylhydrazine on its A2 (suspected human carcinogens) list.

NIOSH (Ex. 8-47, Table N6B; Tr. 3-97 to 3-98), the Workers Institute for Safety and Health (WISH) (Ex. 116), the AFL-CIO (Ex. 194), the Oil Chemical and Atomic Workers (Tr. 9-218), and the American Industrial Hygiene Association (Ex. 8-16) were of the opinion that OSHA’s proposed revision of the PEL for phenylhydrazine was not sufficiently protective. NIOSH (Ex. 8-47) indicated that phenylhydrazine may be a suitable candidate for an individual 6(b) rulemaking. Typical of the views of these commenters was the statement of WISH (Ex. 116), which commented that the ACGIH had, at one time, considered reducing its 5-ppm TLV-TWA, and cited a 1974 study in which rabbits given intravenous injections of phenylhydrazine showed blood and liver effects. The evidence of phenylhydrazine’s possible carcinogenicity was also cited by WISH as additional support for a more stringent limit. In response, OSHA notes that the Agency is also concerned about the evidence for these adverse effects of phenylhydrazine exposure and will continue to monitor and evaluate the toxicologic literature on phenylhydrazine to determine whether there is a need in the future for a further reduction in the occupational exposure limit.

However, at the present time, OSHA is retaining the 5-ppm 8-hour TWA and adding a 10-ppm STEL for phenylhydrazine; the skin notation is also retained. The Agency concludes that these two limits will work together to keep workplace exposures well controlled and will reduce the significant health risks associated with exposure to this substance. These risks include acute blood-related toxicity and may also include cancer; these effects clearly constitute material impairments of health. OSHA finds that the TWA and STEL limits established in the final rule will substantially reduce these significant risks.

Page last reviewed: September 28, 2011