Environmental noise and workers hearing standard threshold shift

Abstract: Standard threshold shifts (STS) as an early indicator to identify those employees with deteriorating hearing are necessary aspects of hearing conservation programs in industry. Regardless of the advances being made in noise control technology, Iranian industry still relies heavily on hearing protection devices (HPDs) to reduce occupational noise exposures to acceptable limits. This study investigated the occurrence of standard threshold shift (STS) among workers of a metal industry using audiometric data and noise measurement levels. Methods: The exposure to noise was determined for each workplace by the direct or indirect measurements of noise levels. The choice of the method depended on the variability of the noise. Exposure to steady-state noise was assessed on the basis of measurement 8 hours TWA. Exposure to non steady-state noise was measured directly by noise-dose meter .The baseline and periodic audiometric results of 2016 workers exposed to noise TWA 85 dB or Dose 50% and above from different plant areas performed by the company routinely according to the Iranian health ministry Law were analyzed for the standard threshold shift (STS). Result: Workers frequency of HPD use reported by company hygienist or safety officer on a 3-point scale (seldom=189, sometime=865, always=962) on the basis of their observation. The finding shows that was relation between STS and age but not with tenure (P< 0.05) . There was dependence between STS with noise level, time exposure, and HPDs wearing time (P< 0.05). Our Study showed 29.9 % of worker has STS. Discussion: The STS rates exceeding from 5 percent considered hearing conservation program is weak and evidence of a deficient hearing protection devices.