This project tested the hypothesis that microphone site influences the individual noise exposure experienced by workers exposed to industrial noise. It also examined inter-individual differences in outer ear pressure gain. The following sequential 20 minute measures were taken with three microphone placements: probe tube microphone in the ear canal; on the right shoulder; attached to the left breast pocket. The subjects were instructed to follow their normal work routines during noise monitoring. Data were downloaded to a personal computer and statistically analyzed for differences between treatment levels and between subject variability. The study was conducted with the cooperation of the Division of Safety at the NIH air conditioning chiller plant using NIH employees. Six adult subjects were monitored. Sound field-to-eardrum pressure gain measures taken from an additional subject and existing data from 29 subjects enrolled in another protocol were used to construct norms. Results showed higher sound pressure levels when recorded at the eardrum vs. the shoulder and chest (p<.001). Large between subject variability was observed for eardrum measurements only. Sound field-to-eardrum pressure gains showed a normal distribution, from which parametric statistics were calculated. ISO 1999 """"""""Acoustics - Determination of occupational noise exposure and estimation of noise-induced hearing impairment"""""""" is an international standard which attempts to predict hearing loss based partly on exposure level. The values are taken from a large population mean using traditional measurement protocols, i.e., torso microphone placement. The norms established in this study were for application to ISO 1999 in order to allow a comparison of an individual's exposure level to the ISO data.
