OSHA formerly had a limit of 1000 ppm TWA for dichloromonofluoromethane (FC-21). The ACGIH has a TLV-TWA of 10 ppm for this colorless gas; this limit is based on FC-21's similarity to chloroform in terms of hepatotoxic effects. The proposed PEL for FC-21 was 10 ppm, and NIOSH (Ex. 8-47, Table N1) concurs with this limit. The final rule promulgates an 8-hour TWA PEL of 10 ppm for FC-21.
FC-21 is considered more toxic than the related difluorinated methanes. The major health hazards associated with exposure to this substance are liver damage, cardiac sensitization, and narcosis. Freon-21 has a 4-hour LC(50) of 49,900 ppm in rats (Tappan and Waritz 1964, as cited in ACGIH 1986/Ex. 1-3, p. 187). Within an hour, exposure to 100,000 ppm killed rats and guinea pigs (Weigand 1971/Ex. 1-1102); other tests with guinea pigs and mice demonstrated that concentrations of 50,000 ppm and higher cause unconsciousness or death (Nuckolls 1935, as cited in ACGIH 1986/Ex. 1-3, p. 187; Booth and Bixby 1932/Ex. 1-1079). The clinical signs of overexposure include loss of coordination, tremors, narcosis, and prostration, as well as possible lung and liver changes (Tappan and Waritz 1964, as cited in ACGIH 1986/Ex. 1-3, p. 187).
Two-week exposures of rats to 10,000 ppm for 6 hours daily caused hepatic failure or marked liver damage (Trochimowicz, Moore, and Chiu 1977/Ex. 1-34). A series of 90-day exposures of rats and dogs to concentrations of 1000 and 5000 ppm dichloromonofluoromethane resulted in bilateral hair loss, cirrhosis, and excessive mortality in rats at both exposure levels; dogs exhibited weight loss at both levels, but mild liver changes were observed only at the 5000-ppm level (Trochimowicz, Lyon, Kelly, and Chiu 1977, as cited in ACGIH 1986/Ex. 1-3, p. 187). Another uncompleted study reported liver pathology in rats repeatedly exposed for 90 days at 500 ppm, and probable liver pathology from similar exposures to 200 ppm; no hepatic effects were observed after exposure to 50 ppm (Allied Chemical Company 1978, as cited in ACGIH 1986/Ex. 1-3, p. 187).
Two of 12 dogs exposed to 10,000 ppm FC-21 plus intravenous epinephrine developed serious arrhythmia (Mullin, as cited in ACGIH 1986/Ex. 1-3, p. 187). Dogs and monkeys (anesthetized) demonstrated tachycardia and hypotension after exposure to FC-21 at levels between 50,000 and 100,000 ppm; bronchoconstriction was observed at 25,000 ppm (Aviado and Smith 1975/Ex. 1-82; Belej and Aviado 1975/Ex. 1-462). Anesthetized mice exposed to a concentration of 100,000 ppm FC-21 showed arrhythmia and cardiac sensitization to epinephrine (Aviado and Belej 1974/Ex. 1-615). Pre-implantation loss has been reported in pregnant rats exposed to FC-21 at 10,000 ppm on days 6 through 15 of gestation (Belej and Aviado 1975/Ex. 1-462). OSHA received no comments other than NIOSH's on FC-21.
In the final rule, OSHA is establishing a TWA limit of 10 ppm for dichloromonofluoromethane. The Agency concludes that this limit will protect workers against the significant risks of hepatotoxic effects, cardiac sensitization, and narcosis associated with exposure to this substance. OSHA finds that these exposure-related effects constitute material impairments of health within the meaning of the Act.