The degree of protection (attenuation) against noise given protection devices (HPDs) such as earplugs and earmuffs is generally much less in actual use than in laboratory certification tests upon which HPD ratings are based. Also, the attenuation varies so much between individuals even for a specific HPD model that the amount of protection provided to any particular individual is almost completely unknown. One result is that workers exposed to high noise levels may not have sufficient protection to prevent hearing loss, even when regularly using HPDs. Another adverse result of the attenuation uncertainly is that some workers may be protected to a significantly greater degree than is necessary, leading to a loss of ability to communicate with co-workers or to hear warning signals and therefore to a reluctance to wear HPDs. There is a real need for a simple, reliable procedure to assess field performance of HPDs and thus to improve occupational hearing conservation programs. A recently developed alternative procedure called bone conduction loudness balance (BCLB) seems to meet all requirements for universally usable field HPD attenuation measurement method. Laboratory feasibility testing indicated that it gives close agreement with the standard HPD attenuation rating method and has no significant drawbacks or limitations. The primary objective of this research is to further simplify the procedure for field use and to demonstrate its value and to uncover and correct any potential limitations or problems by implementing it in a variety of actual workplaces. A secondary objective of the research is to further demonstrate the value of the BCLB method by using it to study a new class HPDs which are designed to improve speech understanding for hearing impaired users by equalizing the degree of attenuation across all frequencies, rather than providing more attenuation at high frequencies as do most HPDs. Because of low attenuation ratings, these HPDs can not normally be used without a reliable means of assuring that they are delivering adequate protection. The BCLB procedure will be used to demonstrate the value of this kind of HPD when appropriately used.
