NIOSH Mining Safety and Health Research

Overexposure to noise remains a widespread, serious health hazard in the U.S. mining industries despite 25 years of regulation. The use of heavy equipment, the drilling of rock, and the confined work environment are just a few factors that contribute to high levels of noise exposure in mining. Every day, 80% of the Nation´s miners go to work in an environment where the time-weighted average (TWA) exceeds 85 dBA. Moreover, 25% of the miners are exposed to a TWA noise level that exceeds 90 dBA, which is the permissible exposure limit (PEL). A recent NIOSH analysis of a large sample of audiograms showed that at age 50, about 90% of coal miners and 49% of metal/nonmetal miners had a hearing impairment. By contrast, only 10% of the non-occupational noise-exposed population had a hearing impairment at age 50. Simply stated, most miners have a hearing loss by the time they retire. A balanced approach to preventing NIHL includes not only education, surveillance, and intervention, but also a research emphasis on engineering controls for noise. Engineering controls are a permanent solution, whereas the use of personal hearing protection (PHP) is seen as an interim one. The Health Branch has several independent and overlapping projects focusing on engineering controls, education, training, and surveillance.

One of the engineering controls projects is investigating continuous miners and roof bolters. Investigations have demonstrated that the use of water on the conveying system decreases the sound level of the continuous miner by at least 5 dB at the frequency range between 1,000 and 6,000 hertz (Hz). An additional engineering control on the continuous miner that shows promise is coating the flight bars on the conveyor system. Preliminary investigations show lower noise levels, but more investigations are needed for wear verification. Wet drilling for roof bolters is also being examined to determine if it is a viable engineering noise control solution.

Another project that focuses on engineering noise controls and characterization of noise exposures pertains to the surface drilling industry. Preliminary investigations show that drillers are being exposed to excessive noise levels. Data collected from 11 different drill sites show that drillers are exposed to excessive noise levels above the 90-dBA PEL. Extensive field investigations have led to an awareness-training program that has been presented at 12 different national and State conferences to date. Recently, collaboration has been established with a major drill rig manufacturing company to research engineering noise controls for several different types of drilling rigs.

A possible remedy to this problem is developing a engineer control called a "Partial Cab" that can be used on surface drilling equipment to protect the drill operator from over exposure to noise during drilling operations.

A surveillance research project is focusing on a cross-sectional field study of the noise exposure of mine workers. This study includes a variety of mining methods, equipment, a range of geographic locations, and different mine sizes. The initial emphasis is on underground coal mines. The main task is to establish representative noise exposure profiles for the various occupations. These results will provide a baseline for future surveys and allow targeting of high-exposure occupations for further assessment. This research will be used to update the database of noise exposures as a function of equipment and activity-specific work practices. These surveillance studies are a crucial part of PRL´s effort to develop engineering noise controls because they will define the sources of miners´ dosages and the characteristics of those sources.

The Health Branchs mobile audiometric test facility is being used in several projects for training-related intervention at various mine sites and conferences. The aim is to personalize the hearing loss problem and identify short-term education and training techniques that have high-impact intervention potential. The intent is to provide a large group of miners with objective feedback about their hearing and their ability to use earplugs to prevent additional noise-induced hearing loss. By varying the timing of feedback, it will also evaluate the motivational potential of hearing tests for promoting self-protective skills. Follow-up studies are planned to more rigorously evaluate the underlying motivational processes that intervene between the feedback and observed behavior. The mobile audiometric test facility has been at a 28 mine sites and conferences to date.

Another research project is underway to measure pressure histories from the unconfined detonation of explosives. The initial focus of this new exploratory study is intended to address the following important questions: (1) Is the current practice of keeping the blasting team at two right angles from the detonation sufficient to prevent hearing damage? (2) Do audiometric models correctly predict the risk and damage criteria associated with impulse noise in the mining industry? Close collaboration with the U.S. Army Research Laboratory and the mining industry is continuing.

Along with noise investigations in the mining industry, best practices in other industries are being investigated. Round-table discussions have been held to bring together mine operators, union officials, mining equipment manufacturers, trade organizations, and government researchers and regulators to develop a strategy for noise control in mining.

Finally, a major NORA noise project has recently been started to survey and evaluate existing engineering noise control technologies in the mining and heavy construction industries. The initial focus of the project will be on engineering noise controls in the underground metal mining industry. A cooperative effort is underway with the Nevada Mining Association to study existing noise controls in its member mines. The outcome of this project will be the production of handbooks that will detail existing noise controls and their benefits, costs, and impact on other health and safety considerations.