Noise-induced hearing loss and hearing protective devices

Abstract

Longitudinal studies of hearing in workers in selected industries in Canada have shown that the effect of continuous high-level noise exposure is an increase in detection threshold of about 1 1/2 decibels per year. This is in contrast to 1/2 dB per year for non noise-exposed office workers in the same plants. Personal hearing protectors, in the form of ear plugs and muffs, have been chosen as an effective, inexpensive and easily implemented method of hearing conservation. However, behavioural experiments simulating the noise background in the industrial environment have shown that the use of these devices may give rise to difficulties in detecting warning signals and defects in the materials worked on, as well as in the perception of speech. This is particularly true in the case of individuals who have already sustained a moderate to severe sensorineural hearing loss, either through noise exposure or aging. To improve both hearing and comfort, many try to alter the device physically. This, of course, will result in a decrease in its sound attenuating capabilities. An experiment in progress is investigating the possibility of prescribing protectors on an individual basis, taking into account both hearing status and shape and size of the ear canal. Relatively little information is available on ear canal morphology. It appears that some types of widely used insert devices are less effective in reducing sound for women because of poor fit to their relatively smaller ear canals