ISOBUTYL ALCOHOL

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: 78-83-1; Chemical Formula: (CH₃)₂CHCH₂OH

OSHA formerly had a limit of 100 ppm as an 8-hour TWA for isobutyl alcohol. The ACGIH has a limit of 50 ppm TWA for this flammable, refractive, colorless liquid. The proposed PEL was 50 ppm as an 8-hour TWA; NIOSH (Ex. 8-47, Table N1) concurs. The final rule establishes a 50 ppm 8-hour TWA PEL for isobutyl alcohol.

Limited inhalation studies have reported a somewhat higher acute toxicity for isobutyl alcohol than for n-butyl alcohol (which has a ceiling of 50 ppm) (Smyth, Carpenter, and Weil 1951/Ex. 1-439; Smyth, Carpenter, Weil, and Pozzani 1954/Ex. 1-440). A 4-hour LC(50) of 8000 ppm has been reported in rats for isobutyl alcohol. Ingestion studies in rabbits have reported an acute oral toxicity of 3.75 g/kg for isobutyl alcohol (Smyth, Carpenter, and Weil 1951/Ex. 1-439; Smyth, Carpenter, Weil, and Pozzani 1954/Ex. 1-440). The dermal LO50 is 4.2 g/kg (Stokinger 1976, as cited in ACGIH 1986/Ex. 1-3, p. 331). Weese (1928/Ex. 1-1073) reported that the narcotic inhalation dose over a total of 136 hours is 6400 ppm in mice. Slight changes in the liver and kidneys were reported, but no fatalities occurred after repeated narcotizing doses (Weese 1928/Ex. 1-1073).

The effects of liquid isobutyl alcohol on the human eye appear to be comparable to those of n-butanol; no data are available on ocular exposure to the isobutyl alcohol vapor. Dermal application of isobutyl alcohol has caused slight erythema and hyperemia in humans (Schwartz and Tulipan 1939/Ex. 1-1167; Oettel 1936/Ex. 1-921).

OSHA received one comment on this substance in addition to NIOSH’s; the Motor Vehicle Manufacturers Association (MVMA) (Ex. 3-902) lists isobutyl alcohol as a substance for which, in the opinion of the MVMA, rulemaking should be delayed. The MVMA provided no substantive information in support of its position.

In the final rule, OSHA is reducing the former 8-hour TWA PEL of 100 ppm to 50 ppm for isobutyl alcohol. The Agency concludes that a 50-ppm limit will reduce the significant risk of skin irritation, which is a material impairment of health that is associated with exposure to concentrations at levels above the revised PEL.