1. College of Safety and Environmental Engineering, Shandong University of Science and Technology, 579 Qianwangang Road, Huangdao District, Qingdao 266590, P. R. China
2. State Key Laboratory of Mining Disaster Prevention and Control Co-founded by Shandong Province and the Ministry of Science and Technology, Shandong University of Science and Technology, Qingdao 266590, P. R. China
3. State Key Laboratory of Coal Mine Safety Technology, Shenyang Research Institute, CCTEG, Fushun, Liaoning 113122, P. R. China
4. China Coal Research Institute, Beijing 100013, P. R. China