Pittsburgh Mining Research Division, Office of Mine Safety and Health Research, National Institute for Occupational Safety and Health, PO Box 18070, 626 Cochrans Mill Road,Pittsburgh, PA 15236, USA;
Pittsburgh Mining Research Division, Office of Mine Safety and Health Research, National Institute for Occupational Safety and Health, PO Box 18070, 626 Cochrans Mill Road,Pittsburgh, PA 15236, USA;
Pittsburgh Mining Research Division, Office of Mine Safety and Health Research, National Institute for Occupational Safety and Health, PO Box 18070, 626 Cochrans Mill Road,Pittsburgh, PA 15236, USA;
University of Pittsburgh, Pittsburgh, PA, USA;