Experimental methods to reduce noise generated by haul trucks and LHDs).

The National Institute for Occupational Safety and Health (NIOSH) maintains the Pittsburgh Mining Research Division (PMRD) where a wide variety of mining-related health and safety research is conducted. Part of this research is devoted to reducing the incidence of noise-induced hearing loss (NIHL) among the nation's mining workforce. The need for this research is particularly important, as NIHL is the second most common occupational-related disease among miners. Many types of equipment operators are overexposed to noise, and NIOSH has worked to develop noise controls that reduce the sound level at the equipment operator's location and, thus, operator noise exposure. Examples of these include a urethane-coated flight bar chain for continuous mining machines and a drill bit isolator for roof bolting machines. This article discusses the development of a retrofitted noise control package for haul trucks and load-haul-dumps (LHDs) used in underground metal/nonmetal mines. Experimental methods under discussion include dosimetry and time motion studies, to determine when an operator accumulates the most noise dose. Noise source identification techniques are used to determine the primary noise contributors to the sound level at the operator's position. Proof-of-concept testing using rudimentary noise controls is undertaken to confirm that treating the suspected noise sources will actually reduce the sound level at the operator's location. Next, a description is given of the development of noise controls-an iterative process where noise controls are fabricated, evaluated in an acoustic laboratory, refined, and tested again. Those noise controls that show promise are then field tested under actual mine operating conditions.