Crystalline silica or quartz is one of the most common minerals on Earth. When finely powdered silica gets in the air it becomes a significant health hazard. Respirable quartz is associated with the development of silicosis, lung cancer, pulmonary tuberculosis and other airway diseases.
The National Institute for Occupational Safety and Health (NIOSH) has estimated that 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 (1991 data). Other industries with significant exposure include building construction and medical and dental laboratories. To help safeguard workers, the Occupational Safety and Health Administration (OSHA) enforces strict regulatory limits on the emission of respirable crystalline silica in the work place.
Monitoring silica dust in the workplace typically is done by collecting samples over a period of hours on a special air filter and using X-ray diffraction (XRD) to determine the amount of silica present in the sample. To be effective, monitoring requires accurate measurements of micrograms of silica on the filters, which in turn requires precise calibration of the measurement system. NIOSH has identified calibration errors as a significant factor in inconsistent results from different laboratories.
To help environmental laboratories perform these demanding calibrations, NIST has developed a series of Standard Reference Materials (SRMs) with precisely measured quantities of respirable quartz deposited on typical filters. The NIST materials cover the range between 5 micrograms and 1000 micrograms of quartz per filter, the typical range encountered in the field, and can be used to validate the accuracy of lab measurements needed to meet OSHA regulations. The reduction to ash technique must be used to prepare the quartz-on-filter specimens for XRD measurements. Details on SRM series 2950--2958, "Respirable Alpha Quartz on Filter Media" are available at https://srmors.nist.gov/tables/view_table.cfm?table=105-10.htm.
A related series of reference materials using cristobalite, the second-most important form of respirable crystalline silica, also is being developed. Standard Reference Materials are among the most widely distributed and used products from NIST. The agency prepares, analyzes and distributes well over a thousand different materials that are used throughout the world to check the accuracy of instruments and test procedures.
Michael Baum | EurekAlert!
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