METHYL ISOBUTYL CARBINOL

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: 108-11-2; Chemical Formula: CH₃CHOHCH₂CH(CH₃)₂

OSHA previously had an 8-hour TWA limit of 25 ppm, with a skin notation, for methyl isobutyl carbinol. OSHA proposed supplementing these limits with a STEL of 40 ppm, based on the ACGIH (1986/Ex. 1-3) recommended limits, and NIOSH (Ex. 8-47, table N1) concurred with this proposal. The final rule establishes a TWA limit of 25 ppm and a STEL of 40 ppm for this substance, with a skin notation. Methyl isobutyl carbinol is a colorless, stable liquid.

In rabbits, a 24-hour skin application of 3.56 ml/kg (2.9 g/kg) was lethal to half the animals (Smyth, Carpenter, and Weil 1951/Ex. 1-439). Rats exposed by inhalation to 2000 ppm of methyl isobutyl carbinol vapor died, and the same authors report that the oral LD(50) for rats is 2.6 g/kg (Smyth, Carpenter, and Weil 1951/Ex. 1-439).

Human volunteers exposed to methyl isobutyl carbinol reported eye irritation upon 15-minutes’ exposure to 50 ppm (Silverman, Schulte, and First 1946/Ex. 1-142). Other than NIOSH’s, OSHA received no comments regarding the basis for its proposed limits for methyl isobutyl carbinol.

In view of the finding that exposure to 50 ppm can result in eye irritation in as little as 15 minutes, OSHA has determined that a risk of eye irritation exists in the absence of a limit on short-term exposure. The Agency considers the eye irritation caused by exposure to this substance to be a material impairment of health. Therefore, to reduce this risk, OSHA is establishing a 15-minute STEL of 40 ppm, while retaining the 25-ppm 8-hour TWA PEL and skin notation for this substance.