OSHA's former Z tables had no exposure limits for sulfur tetrafluoride. The proposed PEL was 0.1 ppm as a ceiling; NIOSH (Ex. 8-47, Table N1) concurs with this limit, and the final rule establishes it. This limit is consistent with that of the ACGIH. Sulfur tetrafluoride is a colorless, noncombustible gas.
On contact with moisture, sulfur tetrafluoride produces sulfur dioxide and hydrogen fluoride (HF) (Lester 1971, as cited in ACGIH 1986/Ex. 1-3, p. 546), and it is the release of HF that is primarily responsible for sulfur tetrafluoride's toxic effects (Zapp 1971, as cited in ACGIH 1986/Ex. 1-3, p. 546). A du Pont (1961, as cited in ACGIH 1986/Ex. 1-3, p. 546) study of rats exposed for four hours to 4 ppm sulfur tetrafluoride over a period of 10 days reported that the animals demonstrated nasal discharge, difficulty in breathing, and weakness. Autopsies of these animals revealed evidence of emphysema, but those rats surviving exposure and given a two-week rest period after exposure showed no significant pathological changes. In the same study by du Pont (1961, as cited in ACGIH 1986/Ex. 1-3, p. 546), a four-hour exposure to 20 ppm sulfur tetrafluoride proved lethal to one of two rats. In a study by Clayton (1962/Ex. 1-409), irregular breathing and signs of irritation were observed following exposures to concentrations of 20 ppm and lower; animals receiving lethal amounts of sulfur tetrafluoride showed pulmonary edema on autopsy, and those with sublethal exposures demonstrated no pathologic changes 14 days later.
In the final rule, OSHA is establishing a 0.1-ppm ceiling limit for this highly toxic gas. The Agency concludes that establishing this limit for this previously unregulated chemical will reduce the significant risk of chronic respiratory effects potentially associated with exposure to sulfur tetrafluoride at the levels permitted by the absence of any OSHA limit. OSHA considers the chronic respiratory effects caused by exposure to sulfur tetrafluoride to be material impairments of health. NIOSH was the only commenter to the rulemaking record on this substance.