Respirable crystalline silica exposure associated with the installation and removal of RCF and conventional silica-containing refractories in industrial furnaces

Installation and removal of conventional refractories and refractory cerami c fiber (RCF) in industrial furnaces may lead to occupational exposure to r espirable crystalline silica (including quartz, cristobalite, and tridymite ). Exposure to elevated concentrations of these materials has been linked t o adverse respiratory effects, including silicosis and lung cancer. Unlike conventional refractories, RCF does not contain any of these materials as p roduced. However, depending upon time and temperature during the service li fe of the insulation, RCF may partially devitrify, creating the potential f or exposure upon removal of after-service insulation For removal of after-s ervice RCF, exposure data collected as part of a 5-year consent agreement w ith EPA are presented and analyzed. Because of relatively low concentration s of these materials, limitations on the sensitivity of the analytical meth od, and the relatively short duration of furnace removal activities, many m easurements are less than the limits of detection (LODs), creating challeng es for data analysis. Several methods of analysis of censored data are illu strated and the theory of maximum likelihood estimates is generalized to co ver the case of multiple LODs. Average exposures to these materials associa ted with removal of after-service RCF are compared to those in various indu stries. (C) 1999 Academic Press.