OSHA previously had an 8-hour TWA PEL of 1 ppm for dibutyl phosphate. The Agency proposed to supplement this limit with a 2-ppm STEL, based on the ACGIH recommendation. NIOSH (Ex. 8-47, Table N1) concurred with this proposal, and the final rule establishes a 1-ppm TWA limit with a 2-ppm STEL for this substance.
There are no published reports of toxic reactions caused by exposure to dibutyl phosphate. However, in a personal communication to the ACGIH, Mastromatteo reported that workers exposed to relatively low levels of dibutyl phosphate developed respiratory tract irritation and headache (Mastromatteo 1964a, as cited in ACGIH 1986/Ex. 1-3, p. 236). No additional data or health effects comment was introduced into the record during the rulemaking proceeding.
OSHA concludes that both a TWA and a STEL are necessary to protect workers from the risk of respiratory tract irritation and headaches reported to occur at low levels of exposure. OSHA judges it likely that, in the absence of a STEL, short-term exposure permitted by the 1-ppm TWA limit alone may be sufficiently high to present a significant risk of respiratory tract irritation and headache to workers; the Agency considers these exposure-related effects to be material impairments of health. Therefore, the Agency is supplementing its 1-ppm 8-hour TWA limit with a 2-ppm 15-minute STEL in the final rule.