Information Circular 9448 Proceedings of the Second International Workshop on Coal Pillar Mechanics and Design Edited by Christopher Mark, Ph.D., Keith A. Heasley, Ph.D., Anthony T. Iannacchione, Ph.D., and Robert J. Tuchman U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES Public Health Service Centers for Disease Control and Prevention National Institute for Occupational Safety and Health Pittsburgh Research Laboratory Pittsburgh, PA June 1999