The former OSHA PEL for ozone was 0.1 ppm TWA. In the interval since this limit was adopted in 1971, the ACGIH has recommended that 15-minute short-term exposures to ozone not exceed 0.3 ppm. NIOSH has no REL for ozone. OSHA proposed, and the final rule establishes, permissible exposure limits of 0.1 ppm TWA and 0.3 ppm STEL for ozone. The Agency notes that the ACGIH has placed ozone on its 1988-89 Notice of Intended Changes and is proposing a new TLV of 0.1 ppm as a ceiling value. Ozone is a liquid or an explosive gas.
Ozone is highly injurious and lethal in experimental animals at concentrations as low as a few parts per million (Stokinger 1957/Ex. 1-97). A study in which young mice were exposed to 1 ppm ozone for one or two days reported damage to alveolar tissue (Bils 1970/Ex. 1-58). Human populations chronically exposed to lower concentrations of ozone have been observed to have changes in lung function. In one study, human volunteers exposed to 0.5 ppm ozone for three hours per day, six days per week, for 12 weeks showed significant changes in lung function (Jaffe 1967/Ex. 1-101). Other authors reported a 20-percent reduction in timed vital capacity in persons exposed to average concentrations of ozone of 1.5 ppm (range not indicated) for two hours (Griswold, Chambers, and Motley 1957/Ex. 1-128). Welders exposed to maximal ozone concentrations of 9 ppm were observed to have pulmonary congestion (Kleinfeld and Giel 1956/Ex. 1-120).
OSHA received a number of comments on the proposed PEL for ozone. The Edison Electric Institute (EEI) (Ex. 133A, pp. 22-23) stated that the studies by Bils (1970/Ex. 1-58), Jaffe (1967/Ex. 1-101), and Griswold et al. (1957/Ex. 1-128), cited above, do not provide substantial evidence for the proposed PEL. With regard to Bils' (1970/Ex. 1-58) finding of damaged alveolar tissue in mice exposed to a 1-ppm concentration of ozone for one or two days, EEI notes that "OSHA does not explain how these data can be translated to humans in the workplace" (Ex. 133A, p. 22). In addition, EEI is concerned that "OSHA neither critically evaluates...nor explains why the changes in lung function reported by [the Jaffe (1967/ Ex. 1-101)] study represent a significant risk...," and OSHA has not presented a substitute for a STEL of 0.3 ppm. Finally, EEI questions the relevance of the study by Griswold et al. (1957/Ex. 1-128) to the formulation of the proposed PEL (Ex. 133A, p. 23). The Agency believes that these three studies point to the short-term effect (i.e., less than eight hours) of ozone exposure; the Bils (1970/Ex. 1-58) data demonstrate that the lung is the target organ; the Jaffe (1967/Ex. 1-101) data point to an effect level of 0.5 ppm and show that a STEL of 0.3 ppm will afford protection; and the Griswold et al. (1957/Ex. 1-128) data provide further evidence of reduced lung function as a result of short-term, acute exposure, rather than chronic exposure.
In addition, EEI commented that "OSHA's health assessment and feasibility analysis with respect to the facilities of the electric utility industry are deficient. Thus, EEI recommends that OSHA consider explaining that its ozone proposal does not apply to that industry" (Ex. 133A, p. 22). This same concern was reflected in the submission of the second commenter, Gulf Power Company (Ex. 3-938, p. 3). In response to these comments, OSHA emphasizes that the standards established in this rulemaking are based on the evidence of adverse health effects associated with exposure to toxic substances in the workplace. These effects would be the same, regardless of industry sector, if the exposure levels were the same. If, as EEI and Gulf Power Company contend, ozone exposures in power plants pose no significant risk to workers' health because they are controlled at or below the permissible exposure limits being promulgated in this rulemaking, then the electric utility industry is already in compliance and will not be impacted by the new PELs. The Agency has determined that the scientific evidence establishes the need for a short-term limit to substantially reduce the significant risk of pulmonary dysfunction that exists as a result of acute or chronic intermittent exposure to ozone.
The Gulf Power Company also expressed its belief that the 0.3-ppm short-term limit proposed by OSHA is unsubstantiated:
The Agency notes, again, that an effect level of 0.5 ppm is demonstrated by the Jaffe (1967/Ex. 1-101) data. Further justification for a STEL of 0.3 ppm is found in Proctor, Hughes, and Fischman (Chemical Hazards of the Workplace, 2nd ed., 1988), who report that, "except for one report, the threshold for effects in humans appears to be between 0.2 and 0.4 ppm" (Menzel 1984, as cited in Proctor, Hughes, and Fischman 1988, p. 388). The selection of 0.3 ppm as a short-term limit was neither invalid nor arbitrary, but rather, was based on the best available scientific evidence.
NIOSH (Ex. 8-47, Table N2) believes that ozone's toxicity requires an even more stringent limit. According to NIOSH, "Ozone is a chemical capable of inducing serious adverse health effects at low exposure concentrations, tenths of a part per million...." The AFL-CIO (Ex. 194) agrees with NIOSH's assessment. OSHA agrees that ozone's health effects require a protective limit, and it is for this reason that the final rule promulgates TWA and STEL limits for ozone.
In the final rule, OSHA is retaining the 8-hour TWA limit of 0.1 ppm and establishing a 15-minute STEL of 0.3 ppm for ozone based on observations that significant declines in pulmonary function can result from repeated intermittent exposures or even from a single short-term exposure (Bils 1970/Ex. 1-58; Jaffe 1967/Ex. 1-101; Griswold, Chambers, and Motley 1957/Ex. 1-128). OSHA believes that, in the absence of a STEL, employees will continue to be at significant risk of material impairment in pulmonary functional capacity associated with short-term exposures that could occur if exposures are controlled only by an 8-hour TWA. Thus the Agency concludes that it is necessary to supplement the former PEL with a STEL of 0.3 ppm to substantially reduce this risk.