The previous PEL for isopropyl alcohol was 400 ppm as an 8-hour TWA. OSHA proposed adding a 15-minute STEL of 500 ppm to this TWA, based on the ACGIH recommendation, and the final rule establishes these limits. In its posthearing comment, NIOSH (Ex. 150, Comments on Isopropyl Alcohol) endorsed OSHA's proposal, stating that a STEL is necessary to reduce the risks of irritation and narcosis that can occur on short-term exposure to elevated concentrations of isopropyl alcohol. Isopropyl alcohol is a colorless, flammable liquid with a slight odor resembling that of rubbing alcohol.
Rats exposed at isopropyl alcohol concentrations of 12,000 ppm for four hours survived, but extending the duration of exposure to eight hours killed the animals (Smyth 1937-1955, as cited in ACGIH 1986/Ex. 1-3, p. 337).
Isopropyl alcohol has been demonstrated to be irritating to the eyes, nose, and throat in humans exposed for brief periods to 400 ppm (Nelson, Enge, Ross et al. 1943/Ex. 1-66); at 800 ppm, these symptoms were more intense. In addition, isopropyl alcohol has narcotic and irritative acute effects at higher concentrations. Weil and associates have reported that an excess of paranasal sinus cancers has been observed among workers manufacturing isopropyl alcohol (Weil, Smith, and Nale 1952/Ex. 1-453). However, it has been established that the cancers associated with isopropyl alcohol manufacture were caused by isopropyl oil and not by the isopropyl alcohol itself (NIOSH 1976g, as cited in ACGIH 1986/Ex. 1-3, p. 337).
No comments, other than NIOSH's, were received on this substance. The irritant effects associated with exposure to isopropyl alcohol occur at concentrations only twice as high as the 8-hour TWA limit, even when the exposure lasts only for a brief period; exposures at this level clearly cause irritation, as documented by the study by Nelson et al. (1943/Ex. 1-66).
OSHA concludes that, in the absence of a STEL, workers are at significant risk of experiencing the narcotic and irritative effects associated with short-term exposures to isopropyl alcohol above the 8-hour TWA PEL of 400 ppm. Therefore, the Agency is retaining its 400 ppm 8-hour TWA limit for isopropyl alcohol and adding a 500 ppm 15-minute STEL to substantially reduce this significant risk. OSHA has determined that the narcosis and eye and mucous membrane irritation associated with chronic and acute exposures to isopropyl alcohol constitute material impairments of health and that a STEL is needed to protect workers from experiencing these harmful effects.