- Correspondence to Dr Susan Burt, Industrywide Studies Branch, Division of Surveillance Hazard Evaluations and Field Studies, National Institute for Occupational Safety and Health, 4676 Columbia Pkwy, Mail Stop R-15, Cincinnati, OH 45226, USA;
- Received 20 November 2012
- Revised 26 March 2013
- Accepted 22 April 2013
- Published online 9 July 2013.
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