Installation and removal of conventional refractories and refractory ceramic fiber (RCF) in industrial furnaces may lead to occupational exposure to respirable crystalline silica (including quartz, cristobalite, and tridymite). Exposure to elevated concentrations of these materials has been linked to adverse respiratory effects, including silicosis and lung cancer. Unlike conventional refractories, RCF does not contain any of these materials as produced. However, depending upon time and temperature during the service life of the insulation, RCF may partially devitrify, creating the potential for exposure upon removal of after-service insulation. For removal of after-service RCF, exposure data collected as part of a 5-year consent agreement with EPA are presented and analyzed. Because of relatively low concentrations of these materials, limitations on the sensitivity of the analytical method, and the relatively short duration of furnace removal activities, many measurements are less than the limits of detection (LODs), creating challenges for data analysis. Several methods of analysis of censored data are illustrated and the theory of maximum likelihood estimates is generalized to cover the case of multiple LODs. Average exposures to these materials associated with removal of after-service RCF are compared to those in various industries.
Copyright 1999 Academic Press.