The former OSHA limit for 2-pentanone was 200 ppm as an 8-hour TWA. The ACGIH has a 200-ppm TLV-TWA and a 250-ppm TLV-STEL; NIOSH (1978k, as cited in ACGIH 1986/Ex. 1-3, p. 408) has recommended a 150-ppm limit as a 10-hour TWA. The proposed PELs were 200 ppm as an 8-hour TWA and 250 ppm as a 15-minute STEL, and these limits are established in the final rule. 2-Pentanone is a clear, flammable liquid with a strong odor resembling acetone and ether.
Both the ACGIH- and NIOSH-recommended limits are based on a study by Specht, Miller, Valaer, and Sayers (1940/Ex. 1-1179), which found that guinea pigs exhibited irritation and weakness on exposure to 2500 ppm, and that exposure to 5000 ppm produced narcosis and coma. The authors concluded that 2-pentanone is considerably less toxic than methyl butyl ketone but is more toxic than methyl ethyl ketone, and, in addition, is likely to be more irritating than either methyl ethyl ketone or acetone. The ACGIH-recommended limits are based on a judgment that the 200-ppm TLV-TWA and 250-ppm TLV-STEL are low enough to prevent narcosis and irritation.
NIOSH (1978k, as cited in ACGIH 1986/Ex. 1-3, p. 408) applied the findings of the Specht, Miller, Valaer, and Sayers (1940/Ex. 1-1179) study to the results of the Nelson, Enge, Ross et al. study (1943/Ex. 1-66); these latter authors reported that volunteers complained of slight irritation on exposure to 100 ppm methyl ethyl ketone. Because 2-pentanone was found by Specht, Miller, Valaer, and Sayers (1940/Ex. 1-1179) to be at least as irritating as methyl ethyl ketone, NIOSH (1978k, as cited in ACGIH 1986/Ex. 1-3, p. 408) stated that a "slight reduction" in the standard was warranted for 2-pentanone. Therefore, NIOSH recommended a 150-ppm limit for 2-pentanone, and NIOSH reiterates this recommendation in the present rulemaking (Ex. 8-47, Table N2; Tr. 3-86). No other comments were submitted regarding the health effects of 2-pentanone.
OSHA has concluded that the combination of a 200-ppm TWA and a 250-ppm STEL will work together to ensure that workplace levels are maintained at levels that will prevent the occurrence of the adverse health effects associated with exposures to this chemical. In the final rule, OSHA is establishing these limits to reduce the significant risks of narcosis, a material impairment of health, which is associated with exposures to 2-pentanone at elevated short-term levels.