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Engineering control of longwall machine noises.

Luo Y; Peng SS; Guffey S
Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, R01-OH-007732, 2009 Apr; :1-75
Longwall mining is a highly productive and very safe mining method employed in underground coal mine. In recent years, about 52 coal mines employing longwall mining method account for more than 50% of underground coal production while nearly 1,000 room and pillar mines make up the remaining production. However, due to the high degree of mechanization and the confined environment, noise levels at longwall mining faces are normally high. Constant exposure to such a noisy environment for an extended period could lead to permanent hearing loss for the workers. The two major sources of noise in a longwall face are: (1) the machine noises produced by the mining machines, and (2) the background noises produced by the breakage and movement of surrounding rock strata in the process for them to reach a new equilibrium after being disturbed by the mining activities. The machine noises contribute the major portion of the noise exposures to the workers. The background noise is a piece of very useful information for the workers to detect and predict harmful ground movement events. Therefore, it is desirable to leave the background noise intact. The main objectives of this research are: (1) to characterize the noise environment in longwall mining with the particular emphasis on the noise sources generated by various mining machines, (2) to identify the main noise sources that the miners are exposed to, and (3) to develop engineering controls to reduce noise exposure in longwall working faces. The main tasks performed in this research are: (1) Noise surveys in two longwall coal mines. In conducting the field surveys, noise dosimeters were used to measure the noise level (signified as sound pressure level or SPL) along the longwall faces as well as at various job-related activities. The sound meters were used to perform the Octave Band Analysis (OBA) so that the frequency distribution of the noise sources can be determined. During the field trips, noise from mining machines was also recorded using a high fidelity sound recorder for laboratory analysis and experiments. (2) Laboratory analysis and experiments. The recorded noise segments were analyzed using Oros analyzer to examine the frequency spectrum of various machine noise sources. The analysis results were also used to identify the significant noise sources. (3) Development of Active Noise Cancellation (ANC) Technology for stage loader. The field surveys showed that the stage loader, a piece of machine located at the end of the longwall face where the loose coal is crushed and transferred to a belt conveyor, is the most noisy machine in a longwall face. Its enclosed compartments are good candidate places for applying the ANC technology. A range of noise reduction methods including ANC method have been experimented on a retired stage loader denoted by a mining company with the recorded noise segments. Significant reduction in noise level have been achieved with proper ANC setups and operating parameters. In this final report, the methodologies of and the instruments for the field noise surveys are described. The frequency contents as well as the associated working activities of the identified significant noise sources resulted from the field surveys and laboratory analyses in the longwall faces are presented. Based on these findings, ANC setup was prepared for canceling the noise waves in a range of sound frequency and reducing the overall sound pressure level for the most noisy machine in the longwall faces - the stage loader. The experimental setups and the range of operating parameters for the ANC technology to be effective in reducing overall noise for the stage loader are explored and the effectiveness of the ANC in such application is studied.
Coal-mining; Longwall-mining; Mine-shafts; Mining-equipment; Mining-industry; Confined-spaces; Noise-control; Noise-exposure; Noise-levels; Noise-protection; Hearing-conservation; Hearing-impairment; Hearing-protection; Exposure-assessment; Miners; Underground-mining
Yi Luo, Ph.D., P.E., Department of Mining Engineering, College of Engineering and Mineral Resources, West Virginia University, 359A Mineral Resources Building, Morgantown, WV 26506-6070
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Engineering Control of Longwall Machine Noises
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West Virginia University
Page last reviewed: March 18, 2022
Content source: National Institute for Occupational Safety and Health Education and Information Division