Prior to 2004, the Bureau of Labor Statistics (BLS) classified hearing loss in the "all other illnesses" category. However, in 2004 hearing loss was categorized as a separate illness that accounted for 11% of work related illnesses. Most categories of illnesses and injuries associated with mining have improved, with the exception of hearing loss. The drilling of rock in a confined work environment contributes to high levels of noise exposure. Information gathered from the Mine Safety and Health Administration (MSHA) coal database from 2000 to 2005 has shown that roof bolting machines were second among all equipment whose operators exceed the MSHA Permissible Exposure Limit (PEL). In response, the National Institute for Occupational Safety and Health (NIOSH) at the Pittsburgh Research Laboratory (PRL) has been conducting research to reduce noise overexposure caused by roof bolting machines and to prevent additional cases of noise-induced hearing loss (NIHL). This is achieved through the development and application of engineering noise controls. This paper describes the procedure used to evaluate noise generated by a roof bolting machine and its components. Two engineering noise controls for the roof bolting machine were evaluated: a bit isolator and a drill chuck isolator. Acoustic beamforming measurements were performed at the PRL hemi-anechoic chamber to assess the noise controls developed for the roof bolting machine. Results showed that in combination, the bit isolator and the drill chuck isolator provided a 7 dB(A) reduction in sound pressure level at the operator position.
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