Noise controls for roof bolting machines

Prior to 2004, the Bureau of Labor Statistics (BLS) classified hearing loss in the “all other illnesses” cat­ egory. 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 excep­ tion 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 re­ sponse, the National Institute for Occupational Safety and Health (NIOSH) at the Pittsburgh Research Labo­ ratory (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 gener­ ated 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. Introduction The Bureau of Labor Statistics (BLS) classifies hearing loss as a separate illness category. Hearing loss accounted for 11% of all illnesses in 2005 (U.S. Department of Labor Bureau of Labor Statistics, 2006a). According to occupational data for coal mining provided by the Mine Safety and Health Ad­ ministration (MSHA) from 2000 to 2005, operators that exceeded 100% noise dosage were from only seven types of machines: auger miners, bulldozers, continuous mining machines, front end loaders, roof bolters, shuttle cars (electric) and trucks (Title 30 CFR Part 62, 2000-2005). Roof bolting machine operators rank second among all underground machine operators that exceed 100% noise dose. There are approximately 600 underground coal mines with 3,930 roof bolting machine operators (U.S. Department of Labor, Mine Safety and Health Administration, 2005; U.S. Department of Labor Bureau of Labor Statistics, 2006a). Figure 1 shows the percentage of roof bolting machine operators that exceeded 100% noise dose from 2000 to 2005 according to the MSHA database (Title 30 CFR Part 62, 2000-2005).