OSHA's former limit for the isoamyl alcohols was 100 ppm as an 8-hour TWA. The ACGIH has established an 8-hour TLV-TWA of 100 ppm and a 15-minute STEL of 125 ppm for these substances, which are colorless liquids that have pungent tastes and an alcoholic odor that causes coughing. OSHA proposed to retain the 8-hour TWA limit of 100 ppm and to add a 125-ppm 15-minute STEL; NIOSH (Ex. 8-47, Table N1) concurs with these limits. The final rule retains the 100-ppm 8-hour TWA and adds a 125-ppm STEL for isoamyl alcohol.
In rats, the oral LD(50) for the primary isoamyl alcohol is 7.07 ml/kg (Smyth, Carpenter, Weil et al. 1969/Ex. 1-442). Haggard, Miller, and Greenberg (1945/Ex. 1-956) determined that isoamyl alcohol's anesthetic toxicity was approximately 12 times higher than that of ethyl alcohol, which has a TLV-TWA of 1000 ppm. Exposure to isoamyl alcohol is not associated with chronic effects.
Smyth (1956/Ex. 1-759) reported that the principal effect of inhalation exposure to this substance is narcosis, and that a 100-ppm level would protect exposed workers against significant narcosis but not against some irritation. Nelson, Enge, Ross, and co-workers (1943/Ex. 1-66) stated that unacclimatized human volunteers reported upper respiratory tract irritation after brief exposures to an isoamyl alcohol concentration of 100 ppm, and objectionable eye and mucous membrane irritation at short-term exposures to 150 ppm. With the exception of NIOSH's submittal, OSHA received no comments on isoamyl alcohol.
In the final rule, OSHA is retaining the 8-hour TWA of 100 ppm and adding a 15-minute STEL of 125 ppm for the isoamyl alcohols (primary and secondary). OSHA concludes that a short-term limit is necessary because the chemically induced eye and throat irritation associated with exposure to the isoamyl alcohols is an acute effect that occurs at concentrations only slightly higher than the 100-ppm 8-hour TWA; in addition, significant narcosis occurs at the levels permitted by the absence of a STEL. The Agency concludes that both the TWA and STEL limits are necessary to ensure that workers are protected against the material impairments represented by significant narcosis, as well as the eye, nose, and upper respiratory tract irritation known to be associated with brief exposures to isoamyl alcohol at levels above 100 ppm.