SULFUR MONOCHLORIDE

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: 10025-67-9; Chemical Formula: S₂Cl₂

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.