METHYLCYCLOHEXANOL

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: 25639-42-3; Chemical Formula: CH₃C₆H₁₀OH

OSHA formerly had an 8-hour TWA limit of 100 ppm for methylcyclohexanol. The Agency proposed a limit of 50 ppm TWA for this substance, and is establishing this limit in the final rule. NIOSH (Ex. 8-47, Table N1) concurred with OSHA’s proposed limits for methylcyclohexanol. Methylcyclohexanol is a colorless, viscous liquid with an aromatic odor, and usually exists as a mixture of isomers in which the meta and para forms predominate.

Exposure to methylcyclohexanol produces liver and kidney impairment, narcotic effects, and eye and respiratory irritation. Treon, Crutchfield, and Kitzmiller (1943a/ Ex. 1-393) have reported the oral LD(50) in rabbits to be between 1.25 and 2 g/kg; liver damage was observed in surviving animals. Repeated inhalation exposures to the vapor caused salivation, eye irritation, and lethargy in rabbits exposed at 500 ppm, but exposures to 230 ppm caused no observable effects. Fifty 6-hour exposures at a level of 120 ppm caused microscopic changes in the liver and kidney tissue of rabbits (Treon, Crutchfield, and Kitzmiller 1943b/Ex. 1-394).

In humans, headaches and eye and respiratory irritation have been reported to occur following prolonged exposures to high concentrations of methylcyclohexanol (Fillipi 1914, as cited in ACGIH 1986/Ex. 1-3, p. 385). Smyth (1956/Ex. 1-759) considered an exposure limit of 100 ppm to be sufficiently low to prevent narcotic effects and, perhaps, significant liver or kidney damage. OSHA received no comments (other than NIOSH’s) on this substance.

The Agency is establishing an 8-hour TWA of 50 ppm for methylcyclohexanol. OSHA concludes that this limit will protect workers against the significant risks of hepatic and renal damage and narcosis, which constitute material health impairments and are associated with exposures to this substance at levels above the revised PEL. The Agency finds that the revised limit will substantially reduce these risks.