[1]Pittsburgh Mining Research Division, Office of Mine Safetyand Health Research, National Institute for OccupationalSafety and Health, PO Box 18070, 626 Cochrans Mill Road,Pittsburgh, PA 15236, USA;
[1]Pittsburgh Mining Research Division, Office of Mine Safetyand Health Research, National Institute for OccupationalSafety and Health, PO Box 18070, 626 Cochrans Mill Road,Pittsburgh, PA 15236, USA;
[1]Pittsburgh Mining Research Division, Office of Mine Safetyand Health Research, National Institute for OccupationalSafety and Health, PO Box 18070, 626 Cochrans Mill Road,Pittsburgh, PA 15236, USA;
[2]University of Pittsburgh, Pittsburgh, PA, USA;