Previously, OSHA's limit for pentane was 1000 ppm TWA. In 1976, the ACGIH adopted a 600-ppm TLV-TWA and a 750-ppm TLV-STEL. NIOSH (1977a/Ex. 1-233; Ex. 8-47, Table N2) has recommended that workplace exposures to pentane not exceed 120 ppm as a 10-hour TWA and 610 ppm as a 15-minute short-term limit. The proposed and final rule PELs are 600 ppm as an 8-hour TWA and 750 ppm as a 15-minute STEL. Pentane, a colorless, flammable liquid with a gasoline-like odor, is usually encountered in volatile petroleum fractions, some of which are used as solvents. Pure pentane is used as a blowing agent for plastics, in solvent extraction, and in ice manufacture.
Fairhall (1957c/Ex. 1-184) stated that narcosis and mucous membrane irritation were the only reported toxic effects resulting from exposure to pentane. The reported lethal concentration in humans is 130,000 ppm (Flury and Zernik 1931j/Ex. 1-994; Swann, Kwon, and Hogan 1974/Ex. 1-124). According to Patty and Yant (1929, as cited in ACGIH 1986/Ex. 1-3, p. 463), humans exposed for 10 minutes to 5000 ppm did not complain of any adverse symptoms.
In a report by Gaultier, Rancurel, Piva, and Efthymioc (1973/Ex. 1-123), five cases of polyneuropathy occurred among employees exposed to a solvent containing 80 percent pentane, 14 percent heptane, and 5 percent hexane. Based largely on this report, NIOSH (1977a/Ex. 1-233) recommended the same occupational limit for all C(5) - C(8) alkanes as for the neuropathic agent n-hexane (350-mg/m3 TWA and 1800-mg/m3 15-minute short-term limits; these limits are equal to about 120-ppm TWA and 610-ppm 15-minute short-term limits for pentane).
OSHA points out that the rationale used by NIOSH in setting a limit for pentane ignores the theory that n-hexane is uniquely neuropathic via metabolism to 2,5-hexanedione, which is the same metabolite that is formed during exposure to another neuropathic agent, methyl butyl ketone (see the discussion in Section V of this preamble). OSHA finds that all C(5) - C(8) alkanes are not equally toxic; the Agency concludes that a metabolite of n-hexane exhibits unique neurotoxic properties. In OSHA's view, the Gaultier, Rancurel, Piva, and Efthymioc (1973/Ex. 1-123) study does not provide specific isomer exposure data supporting the NIOSH RELs of 120 ppm (TWA) and 610 ppm (STEL).
The Chevron Corporation (Ex. 3-896) objected to the proposed STEL for pentane because, in Chevron's opinion, the health evidence did not justify this addition. However, OSHA finds that the STEL is needed to protect workers from the significant neurotoxic effects of pentane exposure by ensuring that the high short-term excursions possible in the absence of a STEL do not occur. The Workers Institute for Safety and Health (Ex. 116) and the UAW (Ex. 197) submitted the same comments on pentane as on heptane (which see).
In the final rule, the Agency is establishing an 8-hour TWA of 600 ppm and a 15-minute STEL of 750 ppm as the permissible exposure limits for pentane. OSHA concludes that these limits will protect exposed workers from the narcosis long known to be associated with pentane exposure; the Agency finds that narcosis constitutes a material health impairment within the meaning of the Act.