1. Jiangsu Engineering Research Center for Dust Control and Occupational Protection, China University of Mining and Technology, Xuzhou 221116, Jiangsu, P.R. China
2. Department of Occupational Hygiene Engineering, School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, Jiangsu, P.R. China
3. Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Cincinnati, Ohio 45226, United States