85 dBA: is it protective enough to prevent hearing loss in South African miners?

Abstract

The Occupational Exposure Limit (OEL) for noise is legislated to be 85 dBA. However, owing to the energy of different frequencies the effect on the ear by sounds of different frequencies is known to vary. Also, there is recent evidence of the synergistic effect of chemicals and noise on the inner ear. Similarly, previous studies have shown that combined exposure to noise and exercise (workload) will cause greater cochlea stress than exposure to noise in isolation. A miner is not exposed only to noise in isolation. The environmental stressors that a miner may be exposed to simultaneously can include noise, heat and exercise, amongst others. The hypothesis is that the OEL which does not take into account complex exposure patterns may not provide adequate protection for miners’ ears. A pilot study to evaluate the impact on the inner ear used otoacoustic emissions as a measure of stress to the cochlea was undertaken. Controlled exposure to noise, heat and exercise on a group of young healthy males and females was conducted using less than the prescribed OEL for noise. Pre-exposure and post-exposure otoacoustic measurements were compared to evaluate the impact of individual and combined exposures. Statistically significant differences were found between the pre-exposure and post-exposure otoacoustic measurements for noise as a stressor. Exposure to other health stressors did not appear to accentuate the effect on the cochlea. The results appear to indicate that further investigation of the current OELs and the methods and aspects being measured is needed.