OSHA formerly had a limit of 1 mg/m3 as an 8-hour TWA for phosphorus pentasulfide. The ACGIH also has a limit of 1 mg/m3 TWA but adds a 15-minute STEL of 3 mg/m3. The proposal retained the 8-hour TWA PEL of 1 mg/m3 and added a STEL of 3 mg/m3; NIOSH (Ex. 8-47, Table N1) concurs with these limits. The final rule retains the 8-hour TWA PEL of 1 mg/m3 for phosphorus pentasulfide and adds a STEL of 3 mg/m3. Phosphorus pentasulfide is a greenish-yellow crystalline mass with an odor like that of rotten eggs.
The primary hazard associated with exposure to phosphorus pentasulfide is respiratory irritation (Smyth 1956/Ex. 1-759). In the presence of moisture, phosphorus pentasulfide is rapidly hydrolyzed to phosphoric acid and hydrogen sulfide. The ACGIH (1986/Ex. 1-3, p. 485) considers phosphorus pentasulfide to be as toxic as phosphoric acid. Only NIOSH commented on this substance.
In the final rule, OSHA is retaining the 8-hour TWA PEL of 1 mg/m3 and adding a 15-minute STEL of 3 mg/m3 for phosphorus pentasulfide. The Agency concludes that both of these limits are necessary to reduce the significant risk of respiratory irritation, a material health impairment that is associated with exposure to this substance at the higher concentrations permitted in the past by the TWA alone.