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NIOSH Report on Respirable Crystalline Silica Reviews Health Effects Data, Discusses Research Needs

NIOSH Update:

Contact: Fred Blosser (202) 401-3749
May 20, 2002

A new report by the U.S. Centers for Disease Control and Prevention’s (CDC) National Institute for Occupational Safety and Health (NIOSH) examines the health risks and diseases associated with occupational exposure to respirable crystalline silica, discusses findings from recent epidemiological studies, and suggests areas for further research to help answer ongoing questions about the hazards of exposure.

NIOSH Hazard Review: Health Effects of Occupational Exposure to Respirable Crystalline Silica,” DHHS (NIOSH) Publication No. 2002-129, was prepared with extensive technical input and review from occupational health specialists in industry, labor, the academic community, and other government agencies.

At least 1.7 million U.S. workers are exposed to respirable crystalline silica in a variety of industries and occupations, including construction, sandblasting, and mining, the NIOSH document reports. Silicosis, an irreversible but preventable disease, is the illness most closely associated with occupational exposure to the material, which also is known as silica dust. Recent data indicate that a risk of silicosis, over a working lifetime, may occur even at the current NIOSH recommended exposure limit. Some studies also have linked respirable crystalline silica with risks for lung cancer and some auto-immune diseases.

Conclusions and recommendations in the report, based on a comprehensive review of the current scientific literature, include these:

• Available sampling and analytical methods are not accurate enough to quantify exposures below NIOSH’s recommended exposure limit of 0.05 milligrams of respirable crystalline silica per cubic meter of air. As a result, scientists currently lack the tools to determine, with confidence, what levels of exposure below 0.05 mg/m3 may or may not pose a health risk. Until more precise methods are developed, NIOSH will continue to recommend an exposure limit of 0.05 mg/m3 . To reduce risk, NIOSH recommends substituting less hazardous materials for crystalline silica when feasible, using appropriate respiratory protection when controls cannot keep exposures below the recommended limit at the source of exposure, and making medical examinations available to exposed workers.

• Findings from numerous recent studies support NIOSH’s longstanding policy that respirable crystalline silica should be considered a potential occupational carcinogen. Further research is needed to better understand the nature and extent of potential risk. For example, what levels of occupational exposure pose a risk for lung cancer in non-smokers? Among workers in occupations associated with exposure to respirable crystalline silica, why do workers with silicosis appear to have a higher risk for lung cancer than workers without silicosis?

• In addition to research that would help answer current questions about potential disease risk (such as cellular and molecular studies to better understand the processes that may lead to illness), research is needed on methods to reduce exposures in a variety of industries, to quantify exposures to low airborne concentrations of silica dust, and to effectively communicate to workers the risks of silica dust.

Copies of the NIOSH document are available from the toll-free NIOSH information number, 1-800-35-NIOSH (1-800-356-4674) and from the NIOSH web page at