Although reducing noise to safe levels is a high priority, for the foreseeable future noise exposures will continue to be high and protection of hearing will depend mostly on how effectively hearing protective devices (HPD) are used. Given the continued loss of hearing in miners, clearly either HPD are not fitted properly or are used ineffectively or some combination of the two. The goal of this research is to improve the effective use of HPDs by validating and exploiting a practical method to determine the actual effectiveness of HPD during use and by rigorously testing two promising methods of motivating miner compliance in using HPD appropriately. Specifically, we will develop and validate a """"""""Microphone in Real Ear"""""""" model of insertion loss (IL) for hearing protectors based on minute by minute measurements taken in the ear canal or in a muff and at the crest of the shoulder. We will use this tool to identify how much of the true internal dose at work is due to initial poor fit, how much is due to insufficient attenuation from the HPD in actual use, and how much is due to miners loosening the HPD or not wearing it at all. We will determine if insertion loss values measured during pre-shift """"""""fit-tests"""""""" adequately predict the actual real-time IL values obtained in the field during normal work, and we will track how IL varies over time during actual mining work using the same minute by minute data logging of internal and external sound levels. We also will compare these observed IL values to those predicted using current rating methods for the same protectors. Finally, we will conduct an intervention study of miners to determine to what degree two types of feedback to the miners on their own exposure levels leads to reduced IL values for those miners. As part of that, we will determine how successful miners can be in controlling their cumulative doses if given appropriate real-time feedback and are allowed to remove their HPD when they judge noise levels are sufficiently low. Although it may seem paradoxical to some, given such flexibility miners may prove to be more """"""""responsible"""""""" rather than less. The potential implications of this study for HPD practice are great: 1) evaluation of current NRR values, 2) dramatically reduced need for supervision to require miner compliance, and 3) high degree of certainty about the cause of high internal doses. The potential results are dramatic reductions in miners' hearing loss over their years of work.
