OSHA had no former limit for dicyclopentadiene (DCPD); the proposed limit was a TWA of 5 ppm, and NIOSH (Ex. 8-47, Table N1) concurred with this limit. The final rule establishes a 5-ppm 8-hour TWA PEL for this substance, which is consistent with the ACGIH's limit. DCPD is a solid at room temperature and has a disagreeable odor.
The health effects associated with exposure to DCPD include mild eye, skin, and respiratory irritation, as well as renal damage and possible pulmonary damage. By the oral and intraperitoneal routes, DCPD is extremely toxic, with an oral LD(50) value of 0.35 ml/kg and an intraperitoneal LD(50) value of 0.31 ml/kg in rats; rat fatalities occurred within 60 minutes of exposure to an unspecified concentration of the saturated vapor (Kinkead, Pozzani, Geary, and Carpenter 1971/Ex. 1-606). However, Gage (1970/Ex. 1-508) regards approximately 660 ppm as the 4-hour LC(50) in rats and reports that 10 six-hour daily exposures to DCPD at a concentration of 250 ppm were survived only by three of four rats; when the animals were subjected to a concentration of 100 ppm for 15 similar exposures, all survived (Gage 1970/Ex. 1-318). Although other species were less susceptible than mice to the effects of DCPD exposure, they exhibited eye irritation, incoordination, and convulsions preceding death (Kinkead, Pozzani, Geary, and Carpenter 1971/Ex. 1-606).
Kinkead and associates (1971/Ex. 1-606) report that rats exposed repeatedly for 10 days survived concentrations of 72 or 146 ppm but succumbed at the 332-ppm level, with convulsions, lung hemorrhage, and blood in the intestines; female rats also suffered hemorrhage of the thymus. Mice similarly exposed succumbed at all three concentration levels (Kinkead, Pozzani, Geary, and Carpenter 1971/Ex. 1-606). Chronic exposures of seven hours/day for 89 days produced kidney damage and some pulmonary effects in rats exposed at levels of 35 and 74 ppm; the no-effect level for these endpoints in rats was determined to be below 19.7 ppm. Dogs exposed at concentrations of 9, 23, or 32 ppm on the same regimen exhibited only minimal effects (Kinkead, Pozzani, Geary, and Carpenter 1971/Ex. 1-606).
Human sensory response tests resulted in findings of mild eye and throat irritation within seven minutes' exposure to 1 ppm DCPD vapor, and of olfactory fatigue within 24 minutes; a 30-minute exposure to 5.5 ppm produced no olfactory fatigue (ACGIH 1986/Ex. 1-3, p. 194). Subjective complaints of headache during the first two months of occupational exposure disappeared during the following three months of exposure, suggesting a developed tolerance for this substance (ACGIH 1986/Ex. 1-3, p. 194). No comments (other than NIOSH's) on this substance were received.
OSHA is establishing an 8-hour TWA PEL of 5 ppm TWA for dicyclopentadiene. The Agency concludes that this limit will protect workers against the significant risks of kidney injury, pulmonary effects, and irritation, which constitute material health impairments that are associated with workplace exposure to DCPD at levels above the new PEL.