Pittsburgh Mining Research Division, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, 626 Cochrans Mill Rd., Pittsburgh,PA 15236, USA;
Pittsburgh Mining Research Division, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, 626 Cochrans Mill Rd., Pittsburgh,PA 15236, USA;
Pittsburgh Mining Research Division, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, 626 Cochrans Mill Rd., Pittsburgh,PA 15236, USA;
J.H.Fletcher, Inc., Huntington, WV, USA;
Marshall University, Huntington, WV, USA;