Impairment to hearing from exposure to noise

It is found that methods commonly used in medicine for the evaluation of impairment to hearing and the relation of this impairment to noise exposure may lead to significant underestimates of the severity of noise-induced hearing impairment and overestimations of tolerable limits for exposure to noise. Criteria of acceptable degrees of hearing impairment for speech and a criterion of an acceptable percentage of people to suffer noise-induced impairment to hearing are suggested. Procedures are derived for calculating Speech Impairment Risk Percent (SIR) which represents damage effect on hearing of a wide variety of noise environments and which can be used for specifying noise exposure limits that would be rated as tolerable for the suggested, or for other, criteria. The proposed procedures appear to be valid, within the state of present knowledge, for daily continuous or intermittent exposures to steady-state or impulsive noises.