title: The Impact of Different Permissible Exposure Limits on Hearing Threshold Levels Beyond 25 dBA.
abstract: BACKGROUND
  Development of noise-induced hearing loss is reliant on a few factors such as frequency, intensity, and duration of noise exposure. The occurrence of this occupational malady has doubled from 120 million to 250 million in a decade. Countries such as Malaysia, India, and the US have adopted 90 dBA as the permissible exposure limit. According to the US Occupational Safety and Health Administration (OSHA), the exposure limit for noise is 90 dBA, while that of the US National Institute of Occupational Safety and Health (NIOSH) is 85 dBA for 8 hours of noise exposure.
  
  
  OBJECTIVE
  This study aimed to assess the development of hearing threshold levels beyond 25 dBA on adoption of 85 dBA as the permissible exposure limit compared to 90 dBA.
  
  
  METHODS
  This is an intervention study done on two automobile factories. There were 203 employees exposed to noise levels beyond the action level. Hearing protection devices were distributed to reduce noise levels to a level between the permissible exposure limit and action level. The permissible exposure limits were 90 and 85 dBA in factories 1 and 2, respectively, while the action levels were 85 and 80 dBA, respectively. The hearing threshold levels of participants were measured at baseline and at first month of postshift exposure of noise. The outcome was measured by a manual audiometer. McNemar and chi-square tests were used in the statistical analysis.
  
  
  RESULTS
  We found that hearing threshold levels of more than 25 dBA has changed significantly from pre-intervention to post-intervention among participants from both factories (3000 Hz for the right ear and 2000 Hz for the left ear). There was a statistically significant association between participants at 3000 Hz on the right ear at 'deteriorated' level ( χ² (1) = 4.08, φ = - 0.142, P = 0.043), whereas there was worsening of hearing threshold beyond 25 dBA among those embraced 90 dBA.
  
  
  CONCLUSIONS
  The adoption of 85 dBA as the permissible exposure limit has preserved hearing threshold level among participants at 3000 Hz compared to those who embraced 90 dBA.
authors.affiliation: Centre for Occupational and Environmental Health, University of Malaya, Kuala Lumpur, Malaysia ; Department of Ministry of Health, Kuala Lumpur, Malaysia.
authors.forename: Balachandar S
authors.initials: BS
authors.lastname: Sayapathi
authors.affiliation: Department of Community Medicine and Public Health, Faculty of Medicine and Health Sciences, University Malaysia Sarawak, Sarawak, Malaysia ; Department of Hygiene, School of Medicine, Wakayama Medical University, Wakayama, Japan.
authors.forename: Anselm Ting
authors.initials: AT
authors.lastname: Su
authors.affiliation: Occupational Health and Medicine Center, PAPRSB Institute of Health Sciences, University Brunei Darussalam, Bandar Seri Begawan, Brunei ; SSH School of Public Health, National University of Singapore, Singapore, Singapore.
authors.forename: David
authors.initials: D
authors.lastname: Koh
keywords: Effects 85 or 90 dBA; Noise; Noise-Induced Hearing Loss; Threshold Shift