Respirable crystalline silica exposure associated with the installation and removal of RCF and conventional silica-containing refractories in industrial furnaces
Ld. Maxim et al., Respirable crystalline silica exposure associated with the installation and removal of RCF and conventional silica-containing refractories in industrial furnaces, REGUL TOX P, 29(1), 1999, pp. 44-63
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.