Improved hearing protection in a mining environment

Conventional hearing protectors, while adequate for basic hearing conservation in mine operations are less than ideal in terms of related requirements such as signal audibility and comfort/acceptability. A design specification for a hearing protector ideally suited to mineworkers requirements was produced from general guidelines developed in a previous project and initial studies in this project covering comfort and acceptability.The crucial element in the design specification, which is not achieved in any conventional protector was a flat frequency response within the range 15dB-18dB attenuation. Three methods of achieving the required attenuation performance were investigated, ie passive non-linear, electronic non-linear and active noise reduction. The first two were selected as offering the best chances of success. An existing, commercially available, passive non-linear hearing protector was found to have an attenuation profile close to that required and was selected as the passive option. An electronic non-linear hearing protector which had been developed under a previous ECSC project was selected, with modification to the attenuation profile, as the second option.Both hearing protectors were modified for helmet mounting and evaluated for signal audibility by comparing them to traditional high and low attenuation hearing protectors, using a computerised purpose built signal design window technique. Both were found to provide improved audibilty of signals and were given limited field acceptability trials. Further development was found necessary, as expected, on factors concerned with hearing protector/helmet compatibility and some aspects of wearer comfort resulting from the ad hoc modifications which were necessary to make the protectors helmet mounted. During the project other electronic hearing protectors were evaluated for attenuation and operational features as they became commercially available.Four defenders were identified as close to the overall requirements although each would need some degree of further development. The four were the EAR 9000 (passive), the ISVR prototype, the DAC and the Peltor (all electronic).