Field evaluations of a noise control for roof bolting machines

Roof bolting machine (RBM) noise is a significant health hazard in underground coal mining because the sound levels at the operator’s station often exceed 100 dB(A). Drilling the hole prior to installing a roof bolt is the most significant source of RBM operator noise exposure. The dominant source of drilling noise is the drill steel. NIOSH has developed an enclosure to surround the drill steel as it is drills the hole to reduce the noise reaching the machine operator. The collapsible drill steel enclosure, or CDSE, is designed to collapse upon itself as the drill steel is further advanced into the mine roof so the drill steel can remain enclosed during the entire hole-drilling process. Original versions of this device effectively reduced noise exposure, but were deemed unacceptable by the mining community due to various usability and durability issues. A modified version has been developed and NIOSH laboratory tests revealed a 2–4 dB(A) noise reduction. This paper describes the in-mine evaluation of the redesigned CDSE. The field tests focused on the noise reduction as well as miner acceptance of the device. The results confirm improved usability as well as a 42% reduction in noise dose at the operator position.