OSHA's previous limit for n-isopropylamine was 5 ppm as an 8-hour TWA. The Agency proposed retaining this TWA limit and adding a 10-ppm 15-minute STEL, based on the ACGIH recommendation. NIOSH (Ex. 8-47, Table N1; Tr. p. 3-86) concurred with this proposal, and these limits are established in the final rule. This substance is a flammable, volatile, colorless liquid that has an odor similar to that of ammonia.
The most serious effect of n-isopropylamine in laboratory animals is respiratory tract irritation, which can be severe enough to cause lung edema (Smyth 1956/Ex. 1-759). Rats survived a four-hour inhalation at 4000 ppm, but an 8000-ppm exposure resulted in fatalities (Smyth, Carpenter, and Weil 1951/Ex. 1-439). Proctor and Hughes (1978/Ex. 1-1136) have reported that the odor of n-isopropylamine becomes strong and unpleasant at the 10- to 20-ppm level; nose and throat irritation is experienced even as a result of brief exposures.
Except for NIOSH, no rulemaking participants commented on OSHA's proposal to issue a 5-ppm TWA and 15-minute STEL of 10 ppm for this substance. The Agency concludes that both a TWA and STEL are required to protect exposed workers from the significant risk of upper respiratory tract irritation that is known to occur even at brief excursions above the 8-hour PEL. The Agency considers upper respiratory tract irritation resulting from exposure to this substance to be a material impairment of health. Therefore, OSHA is revising the PEL for n-isopropylamine to 5 ppm as an 8-hour TWA and 10 ppm as a 15-minute STEL; these limits are established in the final rule.