Acoustic characteristics of machinery noises and estimates of noise exposure of workers employed in typical work processes in underground workspaces

摘要

Recently, many kinds of large-scale machinery have been introduced to underground workspaces to improve work efficiency and productivity. Such equipment is powerful, and it generally emits noises at a high level of sound pressure. Furthermore, since the noises are reflected by underground walls and propagate within confined spaces, noise levels underground are frequently higher than those at the surface. From field measurement of underground machinery noises in an operating coal mine, the noises are broadband, and their spectra usually fluctuate according to the working conditions. The predominant frequencies are relatively high for most machinery. The allowable time duration for protecting against hearing impairment depends strongly on the operating conditions, and frequencies of several kHz generally make the permissible duration shorter. Speech interference levels range form 70 to 90 dB, which indicate some difficulties in speech communication. Noise exposures of workers in typical work processes mostly satisfy the permissible levels, as compared to the present allowable levels for noise exposure. It is noted that the level of noise exposure can be reduced by the use of hearing protectors, with restrictions for avoiding a drop of efficiency and potential hazards such as speech interference.