Previously, OSHA had no limit for cyclopentane. The proposed PEL was 600 ppm as an 8-hour TWA, and NIOSH concurred with this limit (Ex. 8-47, Table N1). The final rule promulgates this limit, which is consistent with that of the ACGIH. Cyclopentane is a mobile, colorless, and flammable liquid.
The existing animal data indicate that cyclopentane is a narcotic agent. As with other alicyclic hydrocarbons, exposure to high concentrations causes excitement, loss of equilibrium, stupor, coma, and, rarely, respiratory failure (Gerarde 1963a, as cited in ACGIH 1986/Ex. 1-3, p. 164). No major animal studies on the effects of cyclopentane exposure have been reported, and evaluations of the toxic properties of this substance have therefore relied on the animal data for n-pentane. n-Pentane has been shown to cause narcosis in animals at exposures of 90,000 to 120,000 ppm for 5 to 60 minutes (Abbritti, Siracusa, Cianchetti et al. 1976/ Ex. 1-406). Swann, Kwon, and Hogan (1974/Ex. 1-124) reported that a concentration of 130,000 ppm is fatal. Almost no data are available concerning the chronic effects of cyclopentane exposure. Abbritti, Siracusa, Cianchetti et al. (1976/Ex. 1-406) reported that petroleum solvents used in the Italian shoe industry contain up to 18 percent cyclopentane. Workers exposed to these solvents have developed polyneuropathy, and Oettel (1936/Ex. 1-921) reported that skin exposure to such solvents caused burning and skin blistering after 15 minutes of confined contact. It has not been determined whether the irritation was caused by cyclopentane or by cyclopentane and other substances, such as n-hexane, in the solvent. OSHA received no comments other than those from NIOSH.
In the final rule, OSHA is establishing a PEL of 600 ppm as an 8-hour TWA for cyclopentane. OSHA concludes that occupational exposure to cyclopentane poses a significant risk of irritation and narcosis, which constitute material impairments of health that occur at levels somewhat above the PEL established in the final rule.