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: 108-87-2; Chemical Formula: C7H14
OSHA had an 8-hour TWA limit of 500 ppm for methylcyclohexane, and the ACGIH has a limit of 400 ppm TWA for this colorless liquid. The proposed PEL was 400 ppm; NIOSH concurred that this reduction in the TWA was appropriate (Ex. 8-47, Table N1). The final rule reduces the 8-hour TWA for methylcyclohexane from 500 ppm to 400 ppm.
Lehmann and Flury (1943e, as cited in ACGIH 1986/Ex. 1-3, p. 384) indicate that the acute toxicity of methylcyclohexane is greater than that of heptane but less than that of octane. Lazarew (1929/Ex. 1-1059) found that a two-hour exposure to a concentration of 7500 to 10,000 ppm caused prostration in mice, and exposure to 10,000 to 12,500 ppm caused death. Treon, Crutchfield, and Kitzmiller (1943b/Ex. 1-394) reported that exposure to 1200 ppm had no effect in rabbits, and prolonged exposures to 370 ppm had no effect in monkeys. Methylcyclohexane’s histologic effects in animals resemble those of cyclohexane; the liver and kidney are the sites affected (ACGIH 1986/Ex. 1-3, p. 384). Only NIOSH commented on methylcyclohexane.
OSHA establishes an 8-hour TWA limit of 400 ppm for methylcyclohexane in the final rule. The Agency concludes that this limit will protect workers against the significant risk of irritation, a material health impairment that is associated with exposure to methylcyclohexane at levels above the new PEL.