Mining haul truck cab noise: an evaluation of three acoustical environments

摘要

Mining haul trucks comprise the majority of the equipment used in underground limestone mining operations and are known to emit high levels of noise. A previous study conducted by the National Institute for Occupational Safety and Health (NIOSH) indicates that 70-90 % of all miners have a noise-induced hearing loss (NIHL) great enough to be classified as a hearing disability by retirement age. These results demonstrate the public health need to protect the hearing of workers in the mining industry, including haul truck drivers. Cab enclosures present an opportunity to isolate the haul truck operator from both truck and other noise in the mining environment. A total of 25 haul truck cabs were studied. They were divided into three style (treatment) categories determined by soundproofing features and technology for noise reduction: old-, new- and retrofitted-style. This study examines the contribution of cab acoustics, operator performance and maintenance to noise reduction for each cab style. Dosimeters were used to measure eight-hour time weighted average sound pressure levels (TWA^sub 8^ SPLs) inside and outside the cabs. The main objective was to determine the noise levels inside of the three types of cabs (with different acoustical treatments) and determine if the noise levels were significantly different. Adherence to the Mine Safety and Health Administration (MSHA) permissible exposure limit (PEL) of 90 dB TWA^sub 8^ (with a 90 dB threshold) was used as the main indicator of overall noise reduction achieved. Dosimetery results indicated that all but two samples measured outside of the cab exceeded the MSHA PEL. However, only 2% of the samples measured inside of the cabs exceeded the PEL, but samples could still be reduced much further. Descriptive and comparative statistics indicate that noise levels inside the new-style cabs are significantly lower than the other two cab styles. Also, data suggest that there is no difference in noise exposures when comparing the old-style to retrofitted cab styles. Operator influence (opening doors and windows) was a significant factor for increasing noise exposure. This paper demonstrates that properly designed cabs can achieve major noise reductions, but noise levels could still be reduced much further below the MSHA PEL. New-style cabs, equipped with modern noise-reduction treatments, exhibit much lower noise exposures than the other two cabs styles, and the effectiveness of the current noise-reduction treatments for retrofitted cabs is questionable. Haul truck driver observations indicate that improved noise exposure reduction training is needed. Finally, specific targets for future noise reduction research are suggested that will further contribute to the prevention of hearing loss for haul truck operators. [PUBLICATION ABSTRACT]