OSHA's former limit for octane was 500 ppm as an 8-hour TWA. The ACGIH has a 300-ppm TWA and a 375-ppm STEL; NIOSH (1977a/Ex. 1-233) recommends a 75-ppm 10-hour TWA and a 385-ppm 15-minute ceiling limit. The proposed PELs were an 8-hour TWA of 300 ppm and a 15-minute STEL of 375 ppm, and these are the limits promulgated in the final rule. n-Octane is a colorless, flammable liquid with an odor like that of gasoline.
Mice exposed to octane concentrations of 6600 to 13,700 ppm developed narcosis within 30 to 90 minutes (Fuhner 1921, as cited in ACGIH 1986/Ex. 1-3, p. 448). Flury and Zernik (1931h, as cited in ACGIH l986/Ex.l-3, p. 448) believed the narcotic concentration in humans to be 5000 ppm; Patty and Yant (1929, as cited in ACGIH 1986/Ex. 1-3, p. 448) placed the narcotic concentration at 8000 ppm. Based on this information, the ACGIH concluded that octane was 1.2 to 2 times more toxic than heptane, and recommended TLVs of 300 ppm TWA and 375 ppm STEL.
As discussed in more detail in Section V of the preamble and in the discussions above for the other C(5)-C(8) alkanes, the NIOSH (1977a/Ex. 1-233) recommended limits for octane are based on NIOSH's belief that all C(5)-C(8) alkanes present a neurotoxic hazard similar to that of n-hexane. OSHA disagrees with this conclusion and has found instead that the neurotoxic properties of n-hexane are unique among the substances in the alkane series. NIOSH continues to recommend these lower limits for all of the C(5)-C(8) alkanes, including octane (Ex. 8-47, Table N2; Tr. 3-86 to 122). The AFL-CIO (Ex. 194) and the UAW (Ex. 197) made the same comments for octane as for heptane (see the discussion, above).
The Chevron Corporation (Ex. 3-896) objected to the proposed short-term exposure limit for octane on the grounds that studies showing narcosis at concentrations of 5000 and 8000 ppm do not provide a justification for a STEL. In addition, Chevron stated that, "as a practical matter, a STEL that is only 25 percent greater than the TWA value suggests a level of precision that simply does not exist in exposure assessment techniques. Variations in sampling and analytical methodologies combined with normal statistical variability in exposure patterns make it impossible to reliably distinguish between exposures that differ by only 20 to 25 percent. Intuitively, it is not reasonable to conclude that a concentration that is slightly above an acceptable 8-hour exposure level would be unsafe for a 15-minute exposure" (Ex. 3-896, p. 3).
In response to Chevron, OSHA notes that octane is considered more toxic than heptane, for which OSHA is establishing limits of 400 ppm as an 8-hour TWA and 500 ppm as a 15-minute STEL. Short-term effects have been observed in humans and animals exposed to the hexane isomers at levels below 500 ppm (Nelson, Enge, Ross et al. 1943/Ex. 1-66), and OSHA finds it appropriate to establish a STEL for octane and several other alkanes to protect against these narcotic effects. OSHA disagrees with Chevron that it is not possible to distinguish between octane exposures of 300 ppm and those of 375 ppm; although a + 25-percent level of precision may be difficult to achieve at very low contaminant concentrations, there should be no sampling and analytical difficulty at the levels being considered here. Finally, OSHA notes that a theoretically possible, although unlikely, exposure scenario that could occur with an 8-hour TWA limit of 300 ppm alone would be an excursion of up to 9600 ppm; such an exposure could produce serious CNS effects in exposed workers. Thus, the purpose of the 375-ppm STEL is to ensure that the TWA limit is not exceeded for any substantial period of time and that exposures are effectively controlled.
In the final rule, OSHA is revising its limits for octane to 300 ppm as an 8-hour TWA and 375 ppm as a 15-minute STEL. The Agency concludes that these limits will protect workers from the significant risks of narcosis, a material health impairment that is associated with octane exposures. OSHA believes that these limits will substantially reduce these significant risks.