What will the program achieve?
Research Goal 3.4 - Additional expected activities, outputs and outcomes
What’s Ahead in Facilities?
Acoustic Test Chamber
To effectively develop and evaluate engineering noise controls for large mining equipment, the HLR program has a large reverberation chamber that is designed and equipped to determine sound power level emissions. The Acoustic Test Chamber (ATC) is at PRL. The ATC is yielding scientifically valid and reliable testing of engineering controls because the influences of varied equipment and operator underground environments can be controlled in the chamber. The HLR program has been NVLAP accredited for the ATC for sound power level testing per ISO 3741/ANSI S12.51 standard for broadband precision grade measurements.
Acoustic Test Chamber at PRL
Because sound power level testing acoustic standards state that a device under test, such as a roof bolting machine, should be a small percentage (2.0 or 2.5 %) of the volume of the test chamber, the sheer size of mining equipment precludes testing in other facilities. With available HLR program personnel and the ATC, the HLR program is in a unique position to conduct scientific research on engineering noise controls for mining equipment manufacturers, mine operators, members of the Noise Partnership Council and other stakeholders.
The HLR program is currently building a large hemi-anechoic chamber at PRL to support the development of engineering noise controls for large mining equipment. The interior dimensions of the room will be approximately 17.7 meters long by 10.4 meters wide by 7.0 meters high, approximately 1,300 cubic meters. The chamber will be the largest available to the mining research community.
The HLR program will be able to identify noise sources associated with large mining equipment, determine the frequency components of those noise sources, and rank the sources quickly. Test methods used to evaluate and develop engineering noise controls on machinery such as sound intensity measurement, near-field acoustic holography, and beam-forming have traditionally been conducted in the field or other uncontrolled acoustic environments. The ability to perform these test measurements in the hemi-anechoic chamber will enhance the development of engineering noise controls. The first machines that will be tested in the facility are continuous mining machines and roof bolting machines, which together account for more than half of the overexposures to noise in underground coal mines.
Representation of the hemi-anechoic chamber
The hemi-anechoic chamber, used for the development of the noise control, along with the ATC, used for the assessment of the noise control, will offer the two largest chambers in the mining community for the development of noise controls for large pieces of mining equipment. These chambers will be a unique addition to the research capability for the HLR program and are expected to begin contributing to the HLR program by early 2006.
What’s Ahead in Research?
Reducing Noise on Horizontal Vibrating Screens
The HLR program Cross-sectional Survey Project indicated that 20 out of 46 surveyed coal preparation plant workers (43.5%) had noise exposures exceeding the MSHA PEL. Based on the survey and MSHA data, it appears that more than 3,400 coal preparation plant workers are overexposed to noise across the country. Horizontal vibrating screens generate high noise levels in coal preparation plants. Noise level measurements taken by the HLR researchers show that the levels around a group of eight horizontal vibrating screens ranged from 94 to 98 dB(A).
Sound levels around a group of 8 horizontal vibrating screens used to process clean coal
The goal of this project is to develop engineering noise controls that reduce the noise level generated by vibrating screens by 10 dB(A). The HLR program is working with mining companies and screen manufacturers to evaluate currently available controls. To raise industry awareness of the engineering noise controls developed through this effort, the research results will be published in peer-reviewed journals and trade magazines and presented at technical conferences and industry briefings concerning noise exposure in the mining industry. In addition, an informational DVD/CD that summarizes the development and safety benefits of the developed engineering noise controls will be produced for vibrating screen manufacturers and industries that use vibrating screens. This work has the potential to eliminate noise overexposures for approximately 3,400 coal preparation plant workers by 2009.
Definition and Assessment of Engineering Noise Controls – Underground Metal Noise Control Guide
The purpose of this project is to document and evaluate noise control technologies for the mining industry. An important enabling step for the application of existing control technology or the development of new technology is the identification of existing controls and their effectiveness. HLR program scientists visited a number of underground metal mines to evaluate the effectiveness of existing engineering controls for noise. The investigators are also gathering data on other problems these engineering controls might introduce. Another project purpose is to better understand noise generating mechanisms. That understanding will aid the development of new noise control technologies that can reduce miner noise levels.
Based on the findings of this study, a Noise Control Guidebook for Underground Metal Mines is being developed. The Guidebook will provide information on basic noise controls currently in use in the industry and emphasize lessons learned over the course of the research such as:
- How to identify effective engineering noise controls,
- Some controls that work on the surface may not work as well underground,
- Properly installed barriers provide effective noise reduction, but improperly placed absorptive material has little to no effect on noise levels, and
- A noise problem should be verified before a solution is attempted.
The Guidebook will distribute information gained from field investigations of the underground metal mining industry across the industry. Use of the Guidebook should lead to more effective noise control practices which will reduce worker noise exposure and the risk of noise-induced hearing loss. It will be disseminated to the industry through partnership efforts, at conferences, and at workshops. The impacts of the Guidebook on the mining industry are expected to begin in 2006 after the research findings are published.
Measuring the sound intensity of an engineering noise control on an underground loading machine
 Peterson JS, Bartholomae RC . Design and instrumentation of a large reverberation chamber. In: Proceedings of NOISE-CON 2003. Ames, IA: Institute of Noise Control Engineering of the USA, pp. 8.
 Yantek, DP, Jurovcik, Bauer E, 2005. “Noise and Vibration Reduction of a Vibrating Screen” SME Preprint No. 05-71, 2005 SME Conference, Salt Lake City, UT.