Quieted Hand-Held Percussion Drills - Objective

Develop quieted, hand-held pneumatic percussion drills that can replace standard hand-held drills in many underground mining applications. The Problem Percussion drills are the noisiest machines used in underground mines; noise levels of 115 to 120 dBA are common, requiring the use of hearing protectors and limiting the time a miner is permit-ted to operate the drill during an 8-hour shift. Hand-held pneumatic percussion drills pose a particularly difficult problem because the operator cannot be isolated from the noise source (e.g., an acoustical cab), and alternative technologies for drilling roof bolt holes and blastholes in tight quarters are not readily available.