1. DHHS (NIOSH) Publication No. 98-126,1998
2. DHHS (NIOSH) Publication No. 96-136,1996
3. U.S. Department of Labor, Mine Safety and Health Administration. http://www.msha.gov/ACCINJ/ALLCOAL.htm“Mining Industry Accident, Injuries, Employment, and Production Statistics, All Coal Mining Data, Table 03, Average Number of Employees at Coal Mines in the United States, by Primary Activity, 1978–2003” [Online] Available at: (Accessed August 8, 2005)