Annals of Occupational Hygiene Advance Access originally published online on January 6, 2009
Annals of Occupational Hygiene 2009 53(3):215-224; doi:10.1093/annhyg/men078
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Published by Oxford University Press on behalf of the British Occupational Hygiene Society
Presence of Tungsten-Containing Fibers in Tungsten Refining and Manufacturing Processes
1 Division of Surveillance, Hazard Evaluations and Field Studies, National Institute for Occupational Safety and Health, 4676 Columbia Parkway, Cincinnati, OH 45226, USA
2 Division of Applied Research and Technology, National Institute for Occupational Safety and Health, 4676 Columbia Parkway, Cincinnati, OH 45226, USA
* Author to whom correspondence should be addressed. Tel: +1-513-569-7415; fax: +1-513-569-7158; e-mail: mckernan.john{at}epa.gov
In tungsten refining and manufacturing processes, a series of tungsten oxides are typically formed as intermediates in the production of tungsten powder. The present study was conducted to characterize airborne tungsten-containing fiber dimensions, elemental composition and concentrations in the US tungsten refining and manufacturing industry. During the course of normal employee work activities, seven personal breathing zone and 62 area air samples were collected and analyzed using National Institute for Occupational Safety and Health (NIOSH) fiber sampling and counting methods to determine dimensions, composition and airborne concentrations of fibers. Mixed models were used to identify relationships between potential determinants and airborne fiber concentrations. Results from transmission electron microscopy analyses indicated that airborne fibers with length >0.5 µm, diameter >0.01 µm and aspect ratios 
3:1 were present on 35 of the 69 air samples collected. Overall, the airborne fibers detected had a geometric mean length 
3 µm and diameter 0.3 µm. Ninety-seven percent of the airborne fibers identified were in the thoracic fraction (i.e. aerodynamic diameter 
10 µm). Energy dispersive X-ray spectrometry results indicated that airborne fibers prior to the carburization process consisted primarily of tungsten and oxygen, with other elements being detected in trace quantities. Based on NIOSH fiber counting ‘B’ rules (length > 5 µm, diameter < 3 µm and aspect ratio 5:1), airborne fiber concentrations ranged from below the limit of detection to 0.085 fibers cm–3, with calcining being associated with the highest airborne concentrations. The mixed model procedure indicated that process temperature had a marginally significant relationship to airborne fiber concentration. This finding was expected since heated processes such as calcining created the highest airborne fiber concentrations. The finding of airborne tungsten-containing fibers in this occupational setting needs to be confirmed in similar settings and demonstrates the need to obtain information on the durability and associated health effects of these fibers.
Keywords: airborne mineral fiber • electron microscopy • hard-metal manufacturing • metal oxide whisker • tungsten blue oxide
Received February 24, 2008; in final form November 20, 2008