ISOPHORONE
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: 78-59-1; Chemical Formula: C9H14O
The former OSHA limit for isophorone was 25 ppm as an 8-hour TWA. The ACGIH has established a 5-ppm TLV as a ceiling limit, and NIOSH recommends a workplace standard of 4 ppm as an 8-hour TWA for isophorone. Isophorone is a colorless liquid at room temperature, and it has a camphor-like odor. The proposed limit was 4 ppm as an 8-hour TWA; NIOSH (Ex. 8-47, Table N1) concurs. This is the limit promulgated by the final rule.
Studies in animals and with human volunteers indicate that exposures to high concentrations of isophorone cause nephrotoxic and other adverse effects. A paper by Smyth, Seaton, and Fischer (1942/Ex. 1-378) reported that guinea pigs and rats exposed to 550 ppm isophorone for six weeks demonstrated degenerative changes in the kidneys and liver. At an exposure level of 25 ppm, no adverse effects were noted, but at 50 ppm, the liver of one animal and the kidneys of four others were damaged. The entire group of 20 animals exposed at 50 ppm survived, but 2 of 16 animals died after this level was raised to 100 ppm (Smyth, Seaton, and Fischer 1942/Ex. 1-378). Volunteers exposed for a few minutes to isophorone vapor at concentrations between 40 and 400 ppm experienced eye, nose, and throat irritation; several subjects exposed at the 200-ppm level developed headache, nausea, faintness, dizziness, and a feeling of suffocation (Smyth and Seaton 1940a/Ex. 1-377). Silverman, Schulte, and First (1946/Ex. 1-142) reported that volunteers exposed to 25 ppm isophorone, the former OSHA PEL, complained of irritation of the eyes, nose, and throat. Another study conducted by the Western Electric Company (Ware 1973, as cited in ACGIH 1986/Ex. 1-3, p. 333) reported that workers exposed for a one-month period to levels of 5 to 8 ppm isophorone demonstrated fatigue and malaise. When the workplace level was reduced to between 1 and 4 ppm, there were no complaints of adverse effects. The NIOSH criteria document for the ketones (1978f, as cited in ACGIH 1986/Ex. 1-3, p. 333) notes that all of the ketones are central nervous system depressants and that workplace exposures to more than one ketone may produce additive effects.
A comment from the New Jersey Department of Public Health (Ex. 144) urged OSHA to use EPA’s IRIS data to set a limit for isophorone. The use of IRIS data is discussed in Section VI.A.
In the final rule, OSHA is reducing its 8-hour TWA PEL of 25 ppm to an 8-hour TWA of 4 ppm to protect workers against the significant risk of fatigue, nausea, and headaches, which together constitute material health impairments that have been demonstrated to occur at isophorone levels between 5 and 8 ppm. The Agency concludes that this limit will substantially reduce these occupational risks.