Industrial Hygiene Survey of Respirable Crystalline Sillica Dust Exposure in the Ready-Mixed Concrete Industry

摘要

As part of the U.S. Department of Health and Human Services initiative 'Health People 2000,' the National Institute for Occupational Safety and Health (NIOSH) is investigating respirable crystalline silica exposure in industries where silica is a constituent material. Ready-mix concrete was identified as an industry to investigate because of the potential for respirable crystalline silica exposure from the silica sand which comprises 10%-20% of concrete. The Occupational Safety and Health Administration's Integrated Management Information System (OSHA's IMIS) listed 64 instances of personal and/or area sampling for respirable silica dust at ready-mixed concrete plants (SIC' 3273) between September 1980 and December 1993. Fourteen (22%) were listed as measuring above the OSHA Permissible Exposure Limit (PEL) for respirable crystalline silica. The exposures measured ranged up to 7 times the PEL. As a pilot project, six local ready-mixed plants were contacted and site visits arranged to learn how extensively NIOSH should investigate the silicosis potential in the industry. Personal and area sampling for respirable dust was conducted to gauge exposures to respirable crystalline silica. Area samples were collected at areas with the highest visible dust, which was generally below the loading point for the cement component. Personal samples were collected for employees who were willing to participate. Dust concentrations were calculated by weighing the dust collected on the filters for personal and area samples. Filters with significant weight gain were submitted for crystalline silica analysis. None of the airborne dust samples contained enough crystalline silica for a quantitative measurement. Two of these dust samples had a 'detectable' but not a 'quantifiable' amount of crystalline silica. Although most of the measurements were below detectable levels during our survey, day-to-day variability in work practices and weather conditions could produce higher levels of exposure. The presence of crystalline silica in two airborne dust samples suggests a 'potential' for higher exposures. Road dust from around the plant's lots was the only apparent source of respirable crystalline silica. Operators might consider wetting-down dusty roadways to suppress potential exposures on their properties.