n-PROPYL NITRATE

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: 627-13-4; Chemical Formula: CH₃CH₂CH₂ONO₂

OSHA formerly had an 8-hour TWA limit of 25 ppm for n-propyl nitrate. The ACGIH has a 25-ppm TWA and a 15-minute STEL of 40 ppm; these limits were proposed by OSHA. NIOSH (Ex. 8-47) concurred with these proposed limits, and these limits are established in the final rule. n-Propyl nitrate is a pale yellow liquid with a sickly sweet odor.

Rats inhaling propyl nitrate vapor for four hours at a concentration of 10,000 ppm exhibited cyanosis and methemoglobinemia before they died (Hood 1953, as cited in ACGIH 1986/Ex. 1-3, p. 505). The intravenous LD(50) in unanesthetized rabbits has been reported to be between 200 and 250 mg/kg; in anesthetized dogs and cats, intravenous doses of between 100 and 200 mg/kg were usually fatal (Murtha, Stabile, and Wills 1956/Ex. 1-649). Murtha and associates (1956/Ex. 1-649), who conducted these studies, concluded that n-propyl nitrate exerts a direct action on the vascular smooth muscle and that the ensuing cardiac effects and respiratory depression contribute to the compound’s hypotensive action (Murtha, Stabile, and Wills 1956/Ex. 1-649). Inhalation trials in mice, rats, hamsters, guinea pigs, and dogs have established 4-hour LC(50) values ranging from 9000 to 10,000 ppm for rats, 6000 to 7000 ppm for mice, and 2000 to 2500 ppm for dogs. Dogs survived repeated exposures (six hours/day, five days/week) at 260 ppm for six months, although slight clinical signs were observed during the first two weeks of exposure (Rinehart, Garbers, Greene, and Stoufer 1958/Ex. 1-524). The percutaneous toxicity of n-propyl nitrate is low but may cause inflammation and thickening of the skin after repeated exposures; these effects are sometimes transient (ACGIH 1986/Ex. 1-3, p. 505). To protect against cardiovascular and respiratory depressant effects requires both TWA and STEL limits. NIOSH (Ex. 8-47) was the only commenter to the rulemaking record for this substance.

In the final rule, OSHA is retaining the PEL of 25 ppm TWA and adding a STEL of 40 ppm for n-propyl nitrate. The Agency concludes that this combined PEL-STEL limit will protect workers against the significant risk of cyanosis, methemoglobinemia, and hypotension, all material health impairments are potentially associated with exposure to n-propyl nitrate at levels above the 8-hour TWA PEL.