OSHA's former PEL for sulfur monochloride was 1 ppm as an 8-hour TWA. Based on the ACGIH recommendation, the Agency proposed revising this limit to 1 ppm as a ceiling limit. NIOSH (Ex. 8-47, Table N1) concurred with OSHA's proposed limit for this substance, and the final rule establishes it. Sulfur monochloride is an amber, oily, nonflammable, fuming liquid, and has a penetrating odor.
Sulfur monochloride is a primary irritant that affects the upper respiratory tract by releasing hydrochloric acid (HCl) on contact with moisture (Henderson and Haggard 1943g, as cited in ACGIH 1986/Ex. 1-3, p. 545). This same study noted that "undecomposed vapor [of sulfur monochloride] might reach the lungs, in which case it would be more toxic than an equivalent quantity of HCl." The ACGIH (1986/Ex. 1-3, p. 545) considers these data indicative of a far greater acute toxicity for sulfur monochloride than for hydrochloric acid. Animal toxicity studies revealed that a dose of 150 ppm sulfur monochloride resulted in death to mice exposed for one minute (Flury and Zernik 1931k/Ex. 1-979). Cats exposed to 60 ppm sulfur monochloride for 15 minutes all died within a few days, but concentrations of 12 ppm for 15 minutes were tolerated (Henderson and Haggard 1943g, as cited in ACGIH 1986/Ex. 1-3, p. 545).
A study by Elkins (1959g, as cited in ACGIH 1986/Ex. 1-3, p. 545) of workers in the rubber industry found that concen-trations of 2 to 9 ppm sodium monochloride were mildly irri-tating; however, the concentrations to which these workers were exposed may have included a high proportion of hydrochloric acid. NIOSH was the only commenter on sulfur monochloride.
The Agency concludes that the former TWA PEL of 1 ppm is inadequate to protect exposed workers against the risk of primary irritation that could occur upon short-term exposure to elevated concentrations of sulfur monochloride. Since 2 ppm was reported to be an effect level for mild irritation, OSHA finds that revising its limit to 1 ppm as a ceiling limit is a reasonable and necessary action to protect workers from the significant risk associated with lung irritation, which constitutes a material impairment of health. Therefore, OSHA is establishing a ceiling limit for sulfur monochloride of 1 ppm.