1. A Noise Control for Continuous Miners;Kovalchik,2002
2. U.S. Department of Labor Bureau of Labor Statistics. (2006a, May). web site http://www.bls.gov/iif/oshwc/osh/os/osnr0025.txt
3. U.S. Department of Labor Bureau of Labor Statistics. (2006b, May). web site http://www.bls.gov/oes/current/oes475041.htm
4. U.S. Department of Labor, Mine Safety and Health Administration. (2008). web site ttp://www.msha.gov/30CFR/62.130.htm
5. Form 7000-2, Quarterly Mine Employment and Coal Production Report, 2005;U.S. Department of Labor, Mine Safety and Health Administration,2005