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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: 126-99-8; Chemical Formula: CH2=CClCH=CH2

The former OSHA limit for ß-chloroprene was an 8-hour TWA of 25 ppm, with a skin notation. The ACGIH has a 10-ppm TLV-TWA, with a skin notation, and NIOSH (1977c/Ex. 1-277) recommended a limit of 1 ppm, measured over a 15-minute period. The proposed PEL was an 8-hour TWA of 10 ppm, and the final rule establishes this limit and retains the skin notation. NIOSH (Ex. 8-47, Table N1) concurs that this limit is appropriate. Chloroprene is a colorless, highly flammable liquid.

The ACGIH recommended a reduction in the TLV for chloroprene from 25 ppm to 10 ppm in 1981, based on a review of the world literature by Trochimowicz, who prepared the 1980 ACGIH documentation, and by Reinhardt (1980, as cited in ACGIH 1986/Ex. 1-3, p. 135). Reinhardt concluded that there was no evidence indicating that the former 25-ppm PEL was not protective, but OSHA believes the systemic effects (i.e., growth retardation) seen in rats and hamsters exposed to 39 ppm chloroprene for four weeks or to 50 ppm for a lifetime suggest that the 25-ppm PEL is not sufficiently protective.

In recommending a 1-ppm 15-minute exposure limit for chloroprene, NIOSH (1977c/Ex. 1-277) cited three reports on facilities in the Soviet Union. Katsova (1973, as cited in ACGIH 1986/Ex. 1-3, p. 135) reported finding a significant excess of chromosomal abnormalities in the blood of workers exposed to approximately 5 ppm chloroprene. Volkova, Fomenko, Bagdinov et al. (1976/Ex. 1-1025) reported similar findings in a plant where chloroprene levels ranged from 0.8 to 1.95 ppm. In the third study, Sanotskii (1976/Ex. 1-662) reported abnormal sperm morphology among workers exposed at levels of from 0.28 to 1.94 ppm; a threefold increase in the rate of spontaneous abortion among wives of these workers was also found. In addition, NIOSH (1977c/Ex. 1-277) cited a study by Davtian, Fomenko, and Andreyeva (1973/Ex. 1-1032) that reported a significant excess of embryonic mortality in female rats that were mated to male rats exposed to 1 ppm chloroprene. These investigators also found chromosomal aberrations in the bone marrow cells of exposed male rats. NIOSH (1977c/Ex. 1-277) also cited a number of reports showing chloroprene to be mutagenic in a variety of test systems. NIOSH concluded that it was prudent to reduce exposure to 1 ppm over a 15-minute period, to reduce the risk of genetic abnormalities being transmitted to subsequent generations. This exposure represents the lowest concentration that can be measured reliably over a 15-minute period.

The Workers Institute for Safety and Health (WISH) and the AFL-CIO commented on OSHA’s proposed limit for chloroprene (Ex. 116; Tr. VII, pp. 130-131; Ex. 194). WISH raised questions about the adequacy of the ACGIH documentation for this substance, which is critical of the Soviet literature that served as the basis for the issuance of the first NIOSH Current Intelligence Bulletin on Chloroprene (l975c). OSHA notes that sizeable discrepancies exist between the findings from the Russian studies and results from other studies that were undertaken to confirm the Soviet claims. Torkelson and Rowe (1981c, in Patty’s Industrial Hygiene and Toxicology, 3rd rev. ed., Vol. 2B, Clayton and Clayton 1981) offer two possible explanations for these discrepancies:

  • ß-Chloroprene is a very unstable compound, which, unless handled with extreme care,…[epoxidizes] and polymerizes to toxic compounds. This might explain the alleged effects in animals. Alleged effects in humans may be due to this same cause or to the use of different chemical processes which produce different types of impurities. Many other causes can be postulated, but in our opinion more credence must be given to animal studies in which the sample is known to have been handled with extreme care and to the results of experience in U.S. industry where the method of handling has been reported (Torkelson and Rowe 1981c, p. 3578).

These authors report that when the purity of the sample was carefully controlled, repeated exposures to 25 ppm or less of the vapor have caused no reproductive, teratological, or embryotoxic effects in rats:

  • Despite frank clinical toxicity in exposed pregnant rats, fetuses showed no teratogenic effects at ß-chloroprene levels as high as 175 ppm (Trokelson and Rowe 1981c, pp. 3579-80).

WISH also expressed concern about the “unscientific” use by the ACGIH of uncertainty factors with regard to this substance. WISH notes that the ATSDR protocol for uncertainty factors would require a TLV of 0.05 ppm based on lowest effect level data on growth retardation (Ex. ll6). (See OSHA’s discussion of the use of safety factors in establishing occupational exposure limits in Section VI.A. of this preamble.)

The 1-ppm (15-minute STEL) value recommended by NIOSH is based on studies reported in the Soviet literature; in addition, this limit is set at the analytical limit of detection. OSHA’s 10-ppm PEL is based on a 1981 critical review of the world literature (Trochimowicz 1980, as cited in ACGIH 1986/Ex. 1-3, p. 135) and on the observation that only mild systemic effects are observed at 38 ppm. In the final rule, OSHA is establishing an 8-hour TWA PEL of 10 ppm, with a skin notation, to substantially reduce the significant risk of reproductive and systemic effects, which constitute material health impairments that are potentially associated with exposure to chloroprene. The Agency concludes that this limit will substantially reduce this significant risk.