Risk analysis for mortality from respiratory tumors in a cohort of refractory ceramic fiber workers

Although workers in refractory ceramic fibers (RCF) manufacturing facilities have experienced no elevations in lung cancer or mesothelioma rates, the historical experience of asbestos together with animal studies of RCF have led to ongoing studies of the respiratory health of RCF workers. We have compared lung cancer and mesothelioma in the accumulated mortality experience of a cohort of male RCF production workers (Lemasters et al., 2001, submitted for publication) to that which would have been expected if RCF had a carcinogenic potency similar to that of various forms of asbestos. To accomplish this, we used risk models recently formalized by Hodgson and Darnton (2000, Ann. Occup. Hyg. 41, 13-36) for asbestos cohorts together with the RCF exposure measurements and historical reconstructions of Rice and colleagues (1997, Appl. Occup. Environ. Hyg. 12, 54-61). Deaths from lung cancer in the RCF cohort are statistically significantly below that which would be expected if RCF had the potency of either crocidolite or amosite. The mortality is also lower than would be expected if RCF had the potency of chrysotile, but the difference is not statistically significant. For mesothelioma, the anticipated numbers of deaths under hypotheses of asbestos-like potency are too small to be rejected by the zero cases seen in the RCF cohorts. The current epidemiologic studies do not rule out risk, but they clearly do rule out lung cancer risks like those of crocidolite or amosite. The residual uncertainty justifies ongoing workplace surveillance.