1. National Institute for Occupational Safety and Health, Division of Applied Research and Technology, Cincinnati, Ohio
2. National Institute for Occupational Safety and Health, Western States Division, Denver, Colorado
3. University of the Witwatersrand, School of Public Health, Johannesburg, South Africa
4. National Institute for Occupational Safety and Health, Spokane Mining Research Division, Spokane, Washington
5. National Institute for Occupational Safety and Health, Pittsburgh Mining Research Division, Pittsburgh, Pennsylvania