Presence of airborne fibers in tungsten refining and manufacturing processes: preliminary characterization.
In tungsten refining and manufacturing processes, a series of tungsten oxides (WO(X)) are typically formed as intermediates in the production of tungsten powder. Studies in the Swedish tungsten refining and manufacturing industry have shown that intermediate tungsten refining processes can create WO(X) fibers. The purpose of the present study was to identify and provide a preliminary characterization of airborne tungsten-containing fiber dimensions, elemental composition, and concentrations in the U.S. tungsten refining and manufacturing industry. To provide the preliminary characterization, 10 static air samples were collected during the course of normal employee work activities and analyzed using standard fiber sampling and counting methods. Results from transmission electron microscopy analyses conducted indicate that airborne fibers with length > 0.5 microm, diameter > 0.01 microm, and aspect ratio > or = 3:1, with a geometric mean (GM) length of approximately 2.0 microm and GM diameter of approximately 0.25 microm, were present on 9 of the 10 air samples collected. Energy dispersive X-ray spectrometry results indicate that airborne fibers prior to the carburization process consisted primarily of tungsten and oxygen, with other elements being detected in trace quantities. Results from an air sample collected at the carburization process indicated the presence of fibers composed primarily of tungsten with oxygen and carbon, and traces of other elements. Based on National Institute for Occupational Safety and Health standard fiber counting rules, airborne fiber concentrations ranged from below the limit of detection to 0.14 f/cm(3). The calcining process was associated with the highest airborne fiber concentrations. More than 99% (574/578) of the airborne fibers identified had an aerodynamic diameter <or =10 microm, indicating that they were capable of reaching the thoracic regions. Until more is known about the durability and potential health effects associated with airborne tungsten-containing fibers, it would be prudent to take steps to limit or eliminate occupational exposures.
McKernan
John L
JL
Division of Surveillance, Hazard Evaluations and Field Studies, National Institute for Occupational Safety and Health, Cincinnati, Ohio 45226, USA. JMcKernan@cdc.gov
Toraason
Mark A
MA
Fernback
Joseph E
JE
D000395:Air Pollutants, Occupational / Q000009:adverse effects / Q000032:analysis*; D016902:Air Pollution, Indoor / Q000009:adverse effects / Q000032:analysis; D004784:Environmental Monitoring / Q000379:methods; D006801:Humans; D019570:Inhalation Exposure / Q000009:adverse effects; D016013:Likelihood Functions; D008171:Lung Diseases / Q000139:chemically induced; D008669:Metallurgy; D008851:Micropore Filters; D046529:Microscopy, Electron, Transmission; D019016:Mineral Fibers / Q000009:adverse effects / Q000032:analysis; D009314:National Institute for Occupational Safety and Health, U.S.; D016273:Occupational Exposure / Q000009:adverse effects / Q000032:analysis* / Q000592:standards; D014414:Tungsten / Q000009:adverse effects / Q000032:analysis*; D014481:United States
D000395:Air Pollutants, Occupational; D019016:Mineral Fibers; D014414:Tungsten