OCCUPATIONAL EXPOSURES TO FIBERS AND QUARTZ AT 19 CRUSHED STONE MINING AND MILLING OPERATIONS

From 1979 to 1982, the National Institute for Occupational Safety and Health (NIOSH) conducted a cross-sectional exposure assessment and mor tality study of selected crushed stone facilities in the United States . This study was undertaken in part to address concerns that asbestos exposures could be occurring in some crushed stone operations due to t he presence of amphibole and serpentine minerals. The investigation wa s also designed to characterize exposures to crystalline silica and ot her mineral compounds. Nineteen crushed stone operations, mining limes tone, granite, or traprock were surveyed to assess exposures to respir able and total dusts, mineral compounds including crystalline silica, asbestos, and mineral fibers. At the initiation of the study, crushed stone operations were selected from a Mine Safety and Health Administr ation (MSHA) listing of the active industry in 1978. With the exceptio n of requiring inclusion of the traprock operation in Maryland where a sbestos fibers were initially discovered, a stratified sample of opera tions was randomly selected by rock type (granite, limestone, traprock , or sandstone). However, because of reluctance or refusal of some com panies to participate and because of the closures of some of the selec ted operations, replacements were randomly selected. Some replacement selections were likewise replaced due to lack of cooperation from the companies. The studied sample included only 10 of the 27 randomly sele cted operations in the original sample. Asbestos fibers were detected at one traprock facility, the Maryland operation where asbestos was or iginally found. Measured personal exposures to fibers exceeded the NIO SH Recommended Exposure Limit (REL) for two out of 10 samples. All of the samples were below the MSHA Permissible Exposure Limit (PEL), whic h was in effect at the time of the survey. However, due to the presenc e of nonasbestos mineral fibers in the environment, it could not be st ated with certainty that all of the fibers counted by phase contrast m icroscopy were asbestos. A variety of silicate mineral fibers (other t han those classified by NIOSH as asbestos) were detected in the trapro ck operations and at one granite operation. Crystalline silica was det ected at 17 of the 19 surveyed crushed stone operations. Overexposures to crystalline silica were measured at 16 of the crushed stone operat ions; approximately one in seven personal-respirable dust samples (14% ) exceeded the MSHA PEL for crystalline silica. Approximately 25% of t he respirable dust samples exceeded the NIOSH REL for crystalline sili ca. Mill operators and mill laborers consistently had the highest and most frequent overexposures to crystalline silica. (C) 1995 Wiley-Liss , Inc.