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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: 142-82-5; Chemical Formula: CH3(CH2)5CH3

The former OSHA limit for heptane was 500 ppm as an 8-hour TWA. The ACGIH TLVs for heptane are 400 ppm as a TWA and 500 ppm as a STEL. NIOSH (1977a/Ex. 1-233) has recommended that workplace exposures to heptane not exceed 85 ppm as a full-shift TWA or 440 ppm as a 15-minute ceiling limit. The proposed PEL and STEL were 400 and 500 ppm, respectively, and these limits are established by the final rule. Heptane is a clear, flammable liquid which is highly volatile.

Patty and Yant (1929, as cited in ACGIH 1986/Ex. 1-3, p. 297) reported that exposure to 1000 ppm of heptane for 6 minutes caused slight dizziness in humans; exposures to higher levels caused vertigo, incoordination, and inappropriate behavior. These authors also reported that a four-minute exposure to 5000 ppm produced complaints of loss of appetite and nausea. Based on this information, as well as on animal data showing 10,000 to 15,000 ppm to be an effect level for heptane-induced narcosis (Fuhner 1921, as cited in ACGIH 1986/Ex. 1-3, p. 297), the ACGIH concluded that heptane was more acutely toxic than hexane. The ACGIH therefore recommended limits for heptane that are somewhat lower than the limits for the hexane isomers.

As discussed in connection with pentane and the hexane isomers, NIOSH (1977a/Ex. 1-233) has recommended the same occupational exposure limits for all of the C(5) - C(8) alkanes (i.e., 350 mg/m3 TWA and 1800 mg/m3 as a 15-minute ceiling). This recommendation is based on NIOSH's belief that all C(5) - C(8) alkanes possess a potential neurotoxic capability similar to that of n-hexane. OSHA disagrees with this concept (see the discussion of this issue in Section V of the preamble); the Agency finds that the neurotoxicity caused by exposure to n-hexane is the result of the action of a unique metabolite, 2,5-hexanedione; the majority of record commenters agreed with OSHA that n-hexane is uniquely toxic (Exs. 3-593, 3-896, and 3-1246).

NIOSH does not concur with the limits being established for heptane (Ex. 8-47, Table N2) because NIOSH believes that "it would be incorrect to conclude that the neurotoxic properties ascribed to n-hexane are unique to this compound [n-hexane]. Other alkanes or related chemicals [such as heptane] that are ultimately metabolized to gamma diketone may have similar toxicity" (Tr. III, p. 110). However, OSHA does not agree with NIOSH that all of the C(5) - C(8) alkanes have equal toxicity (see the discussion in Section V of the preamble); OSHA believes that n-hexane is uniquely toxic.

The AFL-CIO (Ex. 194, p. A-7) reiterated its position that OSHA should promulgate a 10-ppm limit for all of the petroleum solvents, including heptane. However, OSHA has determined (see Section IV.D) that it would be inappropriate at this time to enlarge the scope of this already extensive regulation. The United Auto Workers (Ex. 197) described engineering controls that could be used to achieve the lower levels the unions advocate for all petroleum solvents; these are discussed in Section VII.

Because heptane is considered to be more acutely toxic than hexane, OSHA concludes that it is appropriate to revise its limit for heptane to a level below that established for the hexane isomers to reduce the significant risk of narcosis, which is a material health impairment. Therefore, OSHA is revising its limit for heptane to 400 ppm as an 8-hour TWA and 500 ppm as a 15-minute STEL. The Agency concludes that the TWA and STEL together will substantially reduce this significant occupational risk.