Occupational exposures to fibers and quartz at 19 crushed stone mining and milling operations

Our plain-English summary of Occupational exposures to fibers and quartz at 19 crushed stone mining and milling operations, by G.J. Kullman, A.L. Greife, J. Costello, et al (American Journal of Industrial Medicine, 1995).

The study

• Authors: G.J. Kullman, A.L. Greife, J. Costello, F.J. Hearl
• Journal: American Journal of Industrial Medicine
• Published: 1995;27(5):641-60
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

From 1979 to 1982, the National Institute for Occupational Safety and Health (NIOSH) conducted a cross-sectional exposure assessment and mortality 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 the presence of amphibole and serpentine minerals. The investigation was also designed to characterize exposures to crystalline silica and other mineral compounds. Nineteen crushed stone operations, mining limestone, granite, or traprock were surveyed to assess exposures to respirable 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 Administration (MSHA) listing of the active industry in 1978. With the exception of requiring inclusion of the traprock operation in Maryland where asbestos fibers were initially discovered, a stratified sample of operations was randomly selected by rock type (granite, limestone, traprock, or sandstone). However, because of reluctance or refusal of some companies to participate and because of the closures of some of the selected 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 selected operations in the original sample. Asbestos fibers were detected at one traprock facility, the Maryland operation where asbestos was originally found. Measured personal exposures to fibers exceeded the NIOSH Recommended Exposure Limit (REL) for two out of 10 samples. All of the samples were below the MSHA Permissible Exposure Limit (PEL), which was in effect at the time of the survey. However, due to the presence of nonasbestos mineral fibers in the environment, it could not be stated with certainty that all of the fibers counted by phase contrast microscopy were asbestos. A variety of silicate mineral fibers (other than those classified by NIOSH as asbestos) were detected in the traprock operations and at one granite operation. Crystalline silica was detected at 17 of the 19 surveyed crushed stone operations. Overexposures to crystalline silica were measured at 16 of the crushed stone operations; approximately one in seven personal-respirable dust samples (14%) exceeded the MSHA PEL for crystalline silica. Approximately 25% of the respirable dust samples exceeded the NIOSH REL for crystalline silica. Mill operators and mill laborers consistently had the highest and most frequent overexposures to crystalline silica.

In plain English

From 1979 to 1982, researchers from the US National Institute for Occupational Safety and Health (NIOSH) measured airborne dust, crystalline silica, asbestos and other mineral fibers at 19 crushed stone operations in 13 states: nine limestone, five granite and five traprock. Fibers classified as asbestos, both tremolite and chrysotile, were found only at one Maryland traprock operation. There, personal fiber exposures for 10 workers ranged from nondetectable to 0.31 fibers/cm3. Two of them, a mill maintenance worker and a mill laborer, exceeded the NIOSH recommended limit of 0.1 fibers/cm3, and all were below the 2.0 fibers/cm3 limit of the Mine Safety and Health Administration (MSHA). Because other mineral fibers were present, the authors could not say that all counted fibers were asbestos. Non-asbestos mineral fibers appeared at traprock sites and at one granite site, and none at limestone sites. Crystalline silica was detected at 17 of 19 operations. Of 559 respirable dust samples, 25% exceeded the NIOSH limit and 14% the MSHA limit. Mill operators and mill laborers had the highest and most frequent overexposures. The authors concluded that a significant silicosis hazard and a potential lung cancer risk from silica existed. They noted that the sites were not representative of the industry.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Cross-sectional industrial hygiene (workplace air) exposure survey, part of a NIOSH study whose mortality part was reported separately
• Who was studied: 19 US crushed stone mining and milling operations (9 limestone, 5 granite, 5 traprock) in 13 states, surveyed 1979 to 1982. Only 10 of the 27 originally randomly selected operations were in the final sample.
• Exposure: Airborne respirable and total dust, crystalline silica (alpha-quartz, cristobalite, tridymite), asbestos (chrysotile, tremolite) and other mineral fibers, from mining and milling jobs. Personal asbestos exposure was quantified only at the Maryland traprock plant (Plant T1).
• Main results:
  • Fibers classified as asbestos (tremolite and chrysotile) were found at only one operation, the Maryland traprock plant (Plant T1), along with other fibrous minerals.
  • At Plant T1, electron microscopy of five personal air samples identified the fibers as 68.2% serpentine, 19.1% tremolite, 7.0% olivine, 3.8% magnesite and 1.9% hornblende.
  • At Plant T1, the 10 area samples ranged from below the detection limit up to 0.39 mineral fibers/cm3, and 5 of the 10 had detectable fibers.
  • At Plant T1, personal time-weighted fiber exposures for 10 workers ranged from nondetectable to 0.31 fibers/cm3, and 8 of the 10 were above the detection limit.
  • At Plant T1, two personal samples, from a mill maintenance worker (0.31 fibers/cm3) and a mill laborer (0.18 fibers/cm3), exceeded the NIOSH recommended limit of 0.1 fibers/cm3. All samples were below the MSHA limit of 2.0 fibers/cm3.
  • At the other traprock operations and the granite operations, area samples of non-asbestos mineral fibers ranged from nondetectable to 3.6 fibers/cm3. Asbestos was not detected in these samples.
  • Across 603 personal samples, the geometric mean respirable dust level was 0.28 mg/m3 for all operations: 0.39 mg/m3 at limestone, 0.23 mg/m3 at traprock and 0.17 mg/m3 at granite operations.
  • Crystalline silica was detected at 17 of 19 operations. 17 plants had at least one sample over the NIOSH recommended limit, 16 over the MSHA limit and 15 over the ACGIH limit. Of 559 samples, 25% exceeded the NIOSH limit, 14% the MSHA limit and 13% the ACGIH limit.
  • Mill operators and mill laborers had the highest and most frequent crystalline silica overexposures.
• The authors' conclusion: The authors concluded that a significant silicosis hazard and a potential lung cancer risk from silica exposure existed in the facilities during the study period. They also concluded that asbestos exposure occurred at one facility mining an ore body contaminated with chrysotile and tremolite asbestos.
• Limitations the authors state:
  • Replacing companies that declined to take part may have introduced selection bias, so the results cannot be considered representative of the crushed stone industry.
  • Because non-asbestos mineral fibers were present, the authors could not be certain that all fibers counted by phase contrast microscopy were asbestos.
  • The microscopy methods cannot always tell asbestiform from nonasbestiform mineral forms in individual fibers.
  • The data describe a single point in time, and historical exposure data could not be obtained for the operations.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, NIOSH, Asbestos Exposure, Amphibole Group, Serpentine Group, Crystalline, Mineral Fiber, MSHA.

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