OSHA's former limit for phosphorus trichloride was 0.5 ppm as an 8-hour TWA. The Agency proposed revising this limit to 0.2 ppm as an 8-hour TWA with a STEL of 0.5 ppm; NIOSH (Ex. 8-47, Table N1) concurred with this proposal. The final rule establishes these limits, which are consistent with the limits recommended by the ACGIH. Phosphorus trichloride is a fuming, colorless, noncombustible liquid.
The primary occupational hazards associated with exposure to phosphorus trichloride are respiratory irritation and intoxication involving cough, bronchitis, pneumonia, and conjunctivitis (Henderson and Haggard 1943e/Ex. 1-1086; International Labour Office 1934b, as cited in ACGIH 1986/ Ex. 1-3, p. 486; Sassi 1954/Ex. 1-931).
Early studies indicate that severe symptoms did not occur in cats and guinea pigs until concentration levels reached 50 to 90 ppm for exposures lasting one hour, although slight illness was observed at 0.7 ppm after an exposure of six hours (Butjagin 1904, as cited in ACGIH 1986/Ex. 1-3, p. 486). However, by 1934, the effects of phosphorus trichloride were considered to be 5 to 10 times as intense as those of hydrolyzed hydrochloric acid (International Labour Office 1934b, as cited in ACGIH 1986/Ex. 1-3, p. 486). More recently, Weeks, Musselman, Yevich et al. (1964, as cited in ACGIH 1986/Ex. 1-3, p. 486) reported studies in which 4-hour LC(50) values of 104 ppm for rats and 50 ppm for guinea pigs were obtained.
OSHA received comments only from NIOSH on its proposal to establish a PEL of 0.2 ppm TWA and a STEL of 0.5 ppm for phosphorus trichloride. Because of the acutely irritating effects of this substance, the Agency concludes that both a TWA and a STEL are required to reduce the risk of respiratory and eye irritation that exists for workers exposed to this substance. OSHA considers these effects to be material impairments of health. Therefore, OSHA is revising its limit for phosphorus trichloride to 0.2 ppm as an 8-hour TWA and 0.5 ppm as a 15-minute STEL; these PELs are promulgated in the final rule.