Personal hearing protection devices (HPDs) are a major countermeasure against the insidious occupational health problem of noise-induced hearing loss, for which compensatory claims are increased by 20 percent per year. Manufacturer-provided, EPA-required, noise reduction ratings of HPDs overestimate the protection achieved in the workplace, bacause the ratings are obtained under optimal conditions. Based on these ratings, workers may feel secure that they are adequately protected, but in fact, may not be.
The aim of the laboratory-based experiment in the first project year is to assess the degree that important on-the-job factors actually reduce frequency-specific attenuation provided by industrial earplugs, earmuffs, and ear canal caps. Such factors include degree and type of worker movement, time-on-task, and HPD fitting procedure (e.g., by an experimenter or by the user). A factorial design will be used so that interactive effects can be assessed, and the susceptibility of specific types of HPDs to attenuation redution caused by the independent variables will be determined. Subjects will undergo occluded and unoccluded hearing tests, using real-ear attenuation at threshold (REAT) procedures. The resultant attenuation data, obtained before and after performance of the work tasks, will then be compared to the """"""""optimal"""""""" manufacturer-provided attenuation data. Comfort ratings will also be obtained for each HPD usign a psychometrically-derived and validated scale. The second project year will concentrate on the determination of actual spectral attenuation achieved by industrial workers wearing earmuffs or canal caps while on the job. This in-field research will complement prior NIOSH studies on earplugs. Industrial workers will be supplied with pre-selected earmuffs or canal caps and initially presented with one of two fitting conditions (experimenter-fit or user-fit). After one-month's HPD use on-the-job, workers will be pulled (unannounced) from their work on random occasions, and REAT tested for HPD attenuation as they are found wearing the device. Actual industrial protection levels will be determined in this manner. Furthermore, attenuation data on the effects of proper HPD-fitting and extended-use comfort ratings will be obtained in-field. In effect, the second-year study will serve as a validation check on the first-year study, in that the accuracy and feasibility of a laboratory simulation study for predicting actual in-field protection and comfort will be determined.
