Workplace monitoring of refractory ceramic fiber in the United States

This paper summarizes data hom a comprehensive workplace exposure monitorin g program for refractory ceramic fiber (RCF) conducted since 1990, includin g data collected under a B-year consent agreement (1993-1998) between the U .S. Environmental Protection Agency and the Refractory Ceramic Fibers Coali tion. It presents additional data and analyses, which complement an earlier article published in this journal (L. D, Maxim et at, 1997, Regul. Toxicol . Pharmacol. 26, 156-171). As part of this exposure monitoring program, dat a mere collected at plants operated by RCF manufacturers and at customer fa cilities. Beginning in 1993, at least 720 samples teach sample consisting o f one or more cassettes) were collected annually, distributed according to a stratified random sampling plan. The strata consisted of workers in eight functional job categories (FJCs) at manufacturing and customer plants. Tim e-weighted average (TWA) and task length average data were gathered and ana lyzed using phase contrast optical microscopy and (for a subset of samples) transmission electron microscopy methods. Data on respirator usage (by typ e) were also collected. Statistical analysis indicates that there are signi ficant differences in TWA fiber concentrations (exposure) among FJCs (insta llation, finishing, and removal categories have the highest average concent rations), that workplace concentration data are approximately lognormally d istributed, and that weighted average fiber concentrations decreased over t he period from 1990 to 1998-although trend curves leveled out as exposures have decreased and further improvements became more difficult. Material dif ferences exist in exposure between RCF manufacturers and their customers (l argely because the mix of jobs differ), but these differences have narrowed over the years. Respirator usage varies with exposure. Respirator data are used to derive improved estimates of actual worker exposure. Alternative c riteria for selecting FJCs for control efforts are de fined and illustrated . Lessons learned for future monitoring efforts are summarized. (C) 2000 Ac ademic Press.