1. Department of Occupational & Environmental Safety & Health, University of Wisconsin-Whitewater, Whitewater, Wisconsin
2. Pittsburgh Mining Research Division, National Institute for Occupational Safety and Health, Pittsburgh, Pennsylvania
3. Department of Occupational and Environmental Health, University of Iowa, Iowa City, Iowa
4. Department of Health, West Chester University, West Chester, Pennsylvania
5. School of Health Sciences, Purdue University, West Lafayette, Indiana
6. Respiratory Health Division, National Institute for Occupational Safety and Health, Morgantown, West Virginia