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: 7782-50-5; Chemical Formula: Cl2

The previous OSHA limit for chlorine was 1 ppm as a ceiling limit. OSHA proposed to revise this limit to 0.5 ppm measured over 15 minutes, which was the limit recommended by NIOSH (1976b/Ex. 1-276) in its criteria document; NIOSH (Ex. 8-47, Table N1) concurred with the proposed limit. However, the final rule establishes a PEL of 0.5 ppm TWA with a 15-minute short-term exposure limit of 1 ppm for chlorine. Chlorine is a greenish-yellow, noncombustible gas at atmospheric pressure; it has a suffocating odor. At -35 C, it condenses to an amber liquid.

Exposure to chlorine at concentrations around 5 ppm has been associated with respiratory symptoms, erosion of the teeth, and inflammation of the mucous membranes (Flury and Zernik 1931c/Ex. 1-1199; Patty 1963c/Ex. 1-854). Ferris, Burgess, and Worcester (1967/Ex. 1-316) reported slight effects on the respiratory system in workers exposed to chlorine concentrations ranging from negligible to 7 ppm. Rupp and Henschler (1967/Ex. 1-1122) reported burning of the eyes among human subjects exposed to 0.5 ppm; an unspecified number of these subjects reported painful eyes after 15 minutes’ exposure to this level. In a separate test, subjects reported respiratory irritation on exposure to 0.5 ppm, and a concentration of 1 ppm was described as being uncomfortable.

At the time of OSHA’s proposal, the limits adopted by the ACGIH were a 1-ppm TLV-TWA and a 3-ppm TLV-STEL; these limits were based on the reports described above and were established to “minimize chronic changes in the lungs, accelerated aging, and erosion of the teeth” (ACGIH 1986/Ex. 1-3, p. 117). NIOSH (1976b/Ex. 1-276) reviewed these studies, as did others (Matt 1889, as cited in Flury and Zernick 1931c/Ex. 1-1199; Beck 1959, as cited in NIOSH 1976b/Ex. 1-276) that reported ocular and respiratory irritation associated with exposure to chlorine levels of around 1 ppm for 30 minutes or less. NIOSH (1976b/Ex. 1-276) recommended a 15-minute 0.5-ppm limit to prevent possible eye and respiratory tract irritation.

The United Paperworkers International Union (UPIU) (Ex. 8-37) cited the NIOSH Criteria Document (Ex. 1-276) and ACGIH Documentation (Ex. 1-3) as evidence that exposure to 0.5 ppm chlorine causes respiratory irritation. The UPIU also submitted several studies indicating that decrements in pulmonary function may persist for several days or weeks following acute exposure to concentrations of chlorine requiring medical treatment. In addition, the UPIU cited a number of studies indicating that pulp mill workers and chlorine production plant workers experience declines in pulmonary function as a result of chronic exposure to low levels of chlorine (Ex. 8-37); however, interpretation of many of these studies is complicated by a lack of exposure data or the presence of confounding exposure to other respiratory toxins, such as sulfur dioxide. The UPIU (Ex. 8-37) supported the promulgation of a 0.2 ppm limit for chlorine.

In 1986, the ACGIH proposed revising the TLVs for chlorine to 0.5 ppm as an 8-hour TWA and 1 ppm as a 15-minute STEL. This proposal was based on a review of two recent studies. One study, a 1981 doctoral dissertation by Anglen (Ex. 108A), was sponsored by the Chlorine Institute and was conducted on 29 human subjects. This study reported statistically significant changes in pulmonary function and subjective irritation resulting from exposure to 1 ppm chlorine for eight hours. No significant ocular effects were noted at this exposure level and duration. Exposure to 0.5 ppm for eight hours was not associated with significant declines in pulmonary function, and subjective irritation was also less severe at this level than at 1 ppm (Anglen 1981, Ex. 108A). During the eight-hour exposure to 1 ppm, sensory responses of itching or burning of the throat were reported to be “just perceptible” or “distinctly perceptible.” A short-term (30-minute) exposure to 2 ppm produced no increase in subjective irritation compared with controls.

These findings were confirmed in a study of eight healthy volunteers exposed to 0.5 or 1 ppm chlorine concentrations (Rotman, Fliegelman, Moore et al. 1983/Ex. 108B). Significant declines in pulmonary function were associated with exposure to 1 ppm but not to 0.5 ppm.

The Chlorine Institute (Ex. 3-828) described a recent animal study conducted by the Chemical Industry Institute of Toxicology (CIIT). In this study, groups of 20 rats were exposed to 1, 3, or 9 ppm chlorine for six hours/day, five days/week, for six weeks. Exposure to the two highest levels resulted in significant decreases in body weight. Inflammation of the upper and/or lower respiratory tract was observed in the 9-ppm group and, to a lesser extent, in the 3- and 1-ppm groups. Pathological and clinical changes were not observed in the 1-ppm group, but were seen in the 3- and 9-ppm groups.

Several rulemaking participants urged OSHA to adopt the more recent ACGIH limits of 0.5 ppm TWA and 1 ppm STEL (Exs. 3-677, 3-741, 3-828, and 3-1150; Tr. pp. 10-165 to 10-170; Tr. pp. 10-178 to 10-180). For example, the Chlorine Institute commented as follows:

  • The imposition of an instantaneous ceiling PEL is inappropriate. The Chlorine Institute’s University of Michigan and CIIT studies demonstrate conclusively that sensory effects and adverse pulmonary function effects are directly related to prolonged chlorine exposures and are correctly controlled by a PEL expressed as a Time Weighted Average (TWA)…. The Chlorine Institute supports…[the ACGIH limits] as the correct PEL for adoption by OSHA, and we submit that the evidence is conclusive that such a PEL is totally protective of worker health in chlorine-producing and chlorine-using industries (Ex. 3-828, p. 3).

In its posthearing comment, NIOSH (Ex. 150) reaffirmed its recommended TWA of 0.5 ppm as a 15-minute limit, based on the findings of Rupp and Henschler (1967/Ex. 1-1122):

  • The studies of Anglen (1981) and Rotman (1983), as summarized by the ACGIH, if considered alone, would support the ACGIH TWA TLV of 0.5 ppm with a STEL of 1 ppm. However, in the studies of Rupp and Henschler (1967), exposure to chlorine at concentrations of approximately 0.5 ppm resulted in conjunctival pain in several subjects after 15 minutes; in their second study, subjects reported respiratory irritation after exposure to 0.5 ppm for 25 minutes…. The Rupp and Henschler study (1967), although it has been criticized for lack of a control group (Ex. 3-685) confirms the Anglen (1981), Rotman et al. (1983), and CIIT studies (Ex. 3-828) that there is a significant risk of irritation and a risk of respiratory inflammation at the present PEL of 1 ppm ceiling. Reduction of the current PEL to 0.5 ppm ceiling will reduce the risk of respiratory irritation and pulmonary function changes, and minimize the subjective complaints of irritation (Ex. 150, Comments on Chlorine).

The Dow Chemical Company submitted a critical review of the NIOSH (1976b/Ex. 1-276) criteria document on chlorine and the Rupp and Henschler (1967/Ex. 1-1122) study that was prepared in 1979 by Dr. Ralph G. Smith, who directed the University of Michigan (Anglen 1981) study (Ex. 3-741, Appendix B; Tr. pp. 10-165 to 10-170). In his review, Dr. Smith criticized the Rupp and Henschler (1967/Ex. 1-1122) study because the design of the exposure facility led to uncertainties in determining actual exposure levels present in the test room. He also remarked that the chlorine was passed through “liquid paraffin,” which may have produced chlorinated hydrocarbons. In addition, Dr. Smith felt that the air compressor used may have caused contamination of the air in the test room by carbon monoxide and other impurities. Dr. Smith believed these observations were important “because one of the effects allegedly resulting from short exposures to low levels of chlorine was headaches, a symptom which we have never had reported to us by a subject in the University of Michigan (Anglen 1981) exposures” (Ex. 3-741, Appendix B, pp. 9-10).

After reviewing the evidence and testimony presented in the record on the effects of exposure to chlorine gas, OSHA concludes that there is clearly a significant risk of pulmonary function impairment and sensory irritation at the current 1-ppm ceiling PEL; such effects have been demonstrated by the Anglen (1981/Ex. 108A) and Rotman, Fliegelman, Moore et al. (1983/Ex. 108B) studies in human subjects exposed to 1 ppm for 8 hours, an exposure level and duration that would be permitted by the former PEL. In addition, pulmonary inflammation has been observed in rats exposed daily for six weeks to 1 ppm chlorine. Therefore, OSHA finds that it is necessary to revise its current limit for chlorine.

The human studies by Anglen (1981/Ex. 108A) and by Rotman, Fliegelman, Moore et al. (1983/Ex. 108B) also indicate that exposure to 0.5 ppm chlorine for as long as 8 hours is not associated with impairment of pulmonary function or significant sensory irritation; these findings are in contrast to the earlier German reports upon which the NIOSH REL of 0.5 ppm (15 minutes) is based. However, the German studies, in particular those of Rupp and Henschler (1967/Ex. 1-1122), appear to have had methodological shortcomings that call into question the finding that exposure to 0.5 ppm chlorine is associated with significant acute effects. Therefore, OSHA judges, based on the more recent University of Michigan study, that an exposure limit of 0.5 ppm TWA with a 1-ppm 15-minute STEL will reduce the risk of irritation and pulmonary function decline in workers, and is today revising its limit for chlorine to these values. OSHA considers the effects of respiratory irritation and the declines in pulmonary function associated with chlorine exposure to be material impairments of health.

Page last reviewed: September 28, 2011