Mean hearing threshold levels upon adopting 85 and 90 dBA as permissible exposure limits over six months

Abstract

The progression to noise-induced hearing loss depends on a few factors such as frequency, intensity and duration of exposure. Countries such as the USAand Malaysia, is adopting 90 dBA as the permissible exposure limit. The aim of this study was to explore mean hearing threshold levelsover six months where the permissible exposure limits were85 and 90 dBA. In this intervention study, 203 participants from two factories in the automobile industry were exposed to noise levels above the action level of 85 dBA in one factory and 80 dBA in the other factory, where permissible exposure limitswere 90 and 85 dBA respectively. Universal sampling was adopted in both study locations. Noise level was measured using personal exposure noise dosimeter and sound level meter. Data on hearing threshold levels were measured using manual audiometer. Hearing protection devices with appropriate noise reduction rate were used to reduce noise exposure among participants. The mean hearing threshold level on the right ear of participants at 3000 and 4000 Hz was statistically significantly lower in Factory 2 with exposure limit at 85 dBA compared to Factory 1 at 90 dBA, [3.17 (95% CI, 0.04 to 6.30) dBA, p = 0.048, partial η2 = 0.045] and [4.45 (95% CI, 0.05 to 8.84) dBA, p = 0.047, partial η2 = 0.045], respectively. Hence, adopting different permissible exposure limits showed an effect on hearing threshold level at 3000 and 4000 Hz. This study concludes that mean hearing threshold levels at the two frequencies were higher among employees where 90 dBA is adopted as the permissible exposure limitcompared to 85 dBA. Countries adopting 90 dBA as the permissible exposure limit should review their policy as a limit adoption of 85 dBA may lower the risk of noise-induced hearing loss. © IDOSI Publications, 2014.