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: 118-52-5; Chemical Formula: C5H6Cl2N2O2

OSHA previously had a limit of 0.2 mg/m3 TWA for 1,3-dichloro-5,5-dimethyl hydantoin (DCDMH). Based on the ACGIH (1986/Ex. 1-3) recommendation, the Agency proposed a TWA limit of 0.2 mg/m3 and a STEL of 0.4 mg/m3 for this white powder, which has a mild odor similar to that of chlorine. NIOSH (Ex. 8-47, Table N1) concurred with OSHA’s proposed limits for this substance, and they are established in the final rule.

1,3-Dichloro-5,5-dimethyl hydantoin produces systemic toxicity in laboratory animals. The acute oral LD(50) in rats of both sexes is 542 + 84 mg/kg when DCDMH is administered as a 10-percent aqueous suspension. Rats dying within 48 hours of administration showed gastrointestinal hemorrhage at necropsy. The animals tolerated aqueous solutions of DCDMH maintained at 20 ppm available chlorine (Industrial Bio-Test Laboratories 1961 and 1962, as cited in ACGIH 1986/Ex. 1-3, p. 183).

Limited human exposure data have been provided by Baier, who reported that individuals experienced extreme respiratory irritation at an average level of 1.97 mg/m3, but that some experienced this degree of irritation even at 0.7 mg/m3 (Baier 1964, as cited in ACGIH 1986/Ex. 1-3, p. 183). Other than the NIOSH submission, OSHA received no comments on its proposal to revise the limit for DCDMH.

The 0.2-mg/m3 TWA and 0.4-mg/m3 STEL limits that were proposed are based on evidence of systemic toxicity in laboratory animals and respiratory irritation at low exposure levels in human subjects. The Agency concludes that both a TWA and a STEL are required to protect exposed workers from the risk of respiratory irritation that has been shown to occur at levels only slightly above the level specified by the 8-hour TWA limit. OSHA considers the respiratory irritant effects associated with exposure to DCDMH to represent material impairment of health and functional capacity. OSHA also concludes that the combined TWA-STEL limits will reduce this risk substantially and is therefore establishing a 0.2-mg/m3 TWA and a 0.4-mg/m3 STEL for DCDMH.

Page last reviewed: September 28, 2011