A comprehensive strategy for the assessment of noise exposure and risk of hearing impairment

A comprehensive strategy is presented for the evaluation of the daily noise exposure level [LEX,d in dB(A)] and the assessment of the risk of hearing impairment. The risk is defined as the probability for a worker with a given exposure history to noise to develop a hearing deficit above a given threshold. It is shown that for a given accuracy to be obtained on the risk prediction, the precision required on the LEX,d is low at levels around 90 dB(A) and increases at higher levels. The strategy uses the concepts of homogeneous group of exposure (HGE) and stationarity interval (S.I.), defined as the period over which the exposure distribution is the same for the members of the HGE. The number of workers to sample, the number of samples to take for each worker and their duration are discussed. A semi-random sampling is recommended, excluding the periods with low noise exposure. Tests are proposed for the homogeneity of the group and the validity of the S.I.. A corrected standard deviation is defined in order to take into account the skewness of the distribution of the noise equivalent levels of the samples and formulas are presented to estimate the LEX,d, its standard error and the corresponding risk of hearing impairment.