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.