The primary purpose of audiometric monitoring is to identify hearing changes while they are still small. Hopefully, these changes can be identified before they represent permanent changes, i.e., while they are temporary threshold shifts. The susceptibility to developing a hearing loss is not the same at all frequencies. Assuming that a worker's ears are otherwise healthy, that there is no excess build-up of cerumen, and that appropriate audiometric test methods are followed, hearing changes due to noise are first detected and grow most rapidly at the higher frequencies. The American National Standards Institute (ANSI) provides data estimating expected hearing loss as a function of noise level, years of exposure, and audiometric frequency (ANSI, 1996).
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