Comparing the Effect of Different Permissible Exposure Limits on Hearing Threshold Levels above 25 dBA over Six Months

Abstract

OBJECTIVE: Countries such as Malaysia, India, and the US are still adopting 90 dBA as the permissible exposure limit for noise. Purpose of the article is to assess the development of hearing threshold levels above 25 dBA on adoption of an 85 dBA permissible exposure limit compared with a 90 dBA limit. STUDY DESIGN:Intervention study done in two factories. MATERIALS and METHODS:The minimum sample size required was 43 in both factories.Hearing protection devices were distributed to reduce noise levels between the permissible exposure limit and action level. The permissible exposure limits were 90 and 85 dBA, while action levels were 85 and 80 dBA for Factory 1 and Factory 2, respectively. Hearing threshold levels were measured at the outset (baseline) and in the sixth month using a manual audiometer. McNemar's and Chi-square tests were used in the statistical analysis. RESULTS:There were statistically significant associations between participants of both factories at 4000 Hz (right ear), with a continuing level of 'deterioration'; χ² (1)=4.27, φ=-0.145, p=0.039 in Factory 1 and at 6000 Hz (right ear) with a 'preserved' hearing level, χ² (1)=9.84, φ=0.220, p=0.002 in Factory 2. CONCLUSION:The findings suggest that the adoption of 85 dBA as the permissible exposure limit preserves hearing threshold level more at 4000 and 6000 Hz compared with an exposure limit of 90 dBA. This study suggests that the countries should review their permissible exposure limit policy.