OSHA formerly had no limit for chlorodifluoromethane (Freon22). The Agency proposed an 8-hour TWA PEL of 1000 ppm, supplemented by a STEL of 1250 ppm. NIOSH (Ex. 8-47, Table N1) supported this proposal. The ACGIH has a TLV-TWA of 1000 ppm for this substance. In the final rule, OSHA is establishing an 8-hour TWA for chlorodifluoromethane of 1000 ppm; the Agency has decided not to establish a STEL for chlorodifluoromethane (see Section VI.C.17 for a discussion of OSHA's rationale with regard to STELs in this rulemaking). Chlorodifluoromethane is a colorless, nearly odorless, nonflammable gas.
Exposure to very high atmospheric levels of Freon 22 causes stimulation and then depression of the central nervous system, followed by asphyxiation. Rats and guinea pigs exposed to concentrations of 75,000 to 100,000 ppm over a two-hour period exhibited excitation and disequilibrium; narcosis was observed at 200,000 ppm and mortality at 300,000 and 400,000 ppm (Weigand 1971/Ex. 1-1102). In mice, similar exposures to 320,000 ppm were the maximum tolerated, and the minimum lethal dose was 370,000 ppm (Karpov 1963, as cited in ACGIH1986/Ex. 1-3, p. 127). In rabbits, the minimum concentration altering reflex responses was 11,000 to 20,000 ppm (Karpov 1963, as cited in ACGIH 1986/Ex.1-3, p. 127). Studies of guinea pigs reported no fatalities as a result of exposure for two hours at 200,000 ppm, but mild clinical changes were observed at 50,000 ppm and minimal effects at 25,000 ppm (Underwriters' Laboratories, Inc. 1940, as cited in ACGIH 1986/Ex. 1-3, p. 127). Thirty-minute exposures at 500,000 ppm were lethal to guinea pigs (Booth and Bixby 1932/Ex. 1-1079). Karpov (1963, as cited in ACGIH1986/Ex. 1-3, p. 127) also reported the results of a 10-month study of inhalation effects in rats, guinea pigs, dogs, and cats. Six-hour inhalation exposures to 14,000 ppm or 2000 ppm for five days/week were studied, and alterations in weight, endurance, blood chemistry, and pathology of the lungs, central nervous system, heart, liver, kidney, and spleen were seen at the 14,000-ppm level in rats, mice, and rabbits. At the 2000-ppm daily inhalation level, rats and mice showed no effects (Karpov 1963, ascited in ACGIH 1986/Ex. 1-3, p. 127). In dogs, cardiac sensitization was not observed at the 25,000-ppm level but did occur at the 50,000-ppm level (Reinhardt, Azar, Maxfield, Smith, and Mullin 1971/Ex. 1-78). No data have been published concerning the carcinogenicity, mutagenicity, or teratogenicity of this substance. OSHA received a few comments on Freon 22, from NIOSH (Ex. 8-47, Table N1), the American Industrial Hygiene Association, the du Pont Company (Ex. 3-660), and Dr. Grace Ziem (Ex. 46). du Pont and the AIHA stated that OSHA should not adopt limits (short-term, ceiling, or skin notations) for substances for which the ACGIH has deleted, or is on record as intending to delete, such limits (Exs.8-16, 3-660). Discussions of OSHA's policy on STELs and skin notations in this rulemaking can be found in Sections VI.C.17 and VI.C.18,respectively. OSHA notes that cardiac sensitization does not occur in animals until levels reach 25 to 50 times the 1000-TWA limit and, therefore, a STEL that is 1.25 times that limit is unwarranted. Dr. Ziem (Ex. 46) reported that Freon 22's effects on heart rhythm have been seen at the 300-ppm level.
The Agency is establishing an 8-hour TWA limit of 1000 ppm for chlorodifluoromethane. OSHA concludes that this limit will provide protection against the CNS effects, asphyxiant effects, and cardiac sensitization effects (which together constitute material health impairments) that could occur as the result of exposure to Freon 22 at levels above the new PEL. The Agency finds that the new limit will substantially reduce these significant risks.