Mining Project: Noise Controls for Jumbo Drills Used in Metal/Nonmetal Mines

Research Summary

Jumbo drill operators are exposed to some of the highest noise levels in metal/nonmetal mining. In the worst cases, operators’ may be exposed to noise levels in excess of 105 dB(A). In such instances, their noise exposure exceeds the MSHA permissible exposure level (PEL) in less than one hour and operators are highly likely to incur permanent hearing loss. Based on data provided by the Parker Bay Company & Raw Materials Group, which does market research on mining equipment, NIOSH estimates that roughly 50% of the jumbo drill machines used in the world do not have enclosed cabs. Therefore, operators are directly exposed to the noise generated by the machine.

This project sought to develop noise controls that reduce exposure while not interfering with effective operation of the jumbo drill. Engineering noise controls were developed to reduce the noise emission of jumbo drills. The effectiveness of these controls was evaluated in laboratory settings and in underground settings to quantify this noise reduction.

The jumbo drill drifter and drill string were confirmed as prominent noise contributors to the sound level at the operator location. Prototype noise controls to address these noise sources were fabricated and tested under laboratory and field conditions. Of these prospective noise controls, the most effective in reducing noise emissions were constrained layer damped drill strings and damped drill string centralizers. Several versions of each of these were tested.

Laboratory testing of constrained layer damped drill strings resulted in a 2-3 dB reduction in the sound power level when compared to drilling with stock drill strings. Field testing of a second set of constrained layer damped drill strings proved to be promising as well. Here, testing results indicated that there was a 2-5 dB reduction in the sound pressure level at the operator location when compared with drilling with stock drill strings. Laboratory testing of damped drill string centralizers resulted in a 2-dB in the operator location sound pressure level. Given a 2-5 dB reduction in noise exposure and a 5-dB exchange rate, an operator’s noise dose would be reduced by roughly 25% to 50%. That is, an operator’s noise dose may be reduced by as much as one half of its baseline value.

Fully enclosing the jumbo drill operator location within a cab is an effective method of reducing noise exposure for the operator. A well-designed cab forms a noise barrier between the operator and the noise sources when the operator remains within the cab with the doors and windows closed. Field testing to evaluate the effectiveness of cabs at reducing the sound pressure level at the operator location were also conducted. Cabs proved to be very effective, reducing the operator location sound pressure level by 35-50 dB when compared to outside the cab.

The impact of this research will be to reduce the likelihood and magnitude of hearing loss for jumbo drill operators. The amount of reduction will vary with operating conditions, but in many instances the use of noise controls should reduce the noise exposure of the operator.