Syed Mosaddaque Iqbal, Ishtiaq Ahmed Khan.
Occupational noise induced hearing loss.
Pak J Otolaryngol Jan ;23(1):12-6.

OBJECTIVE: To determine the frequency of hearing loss among the noise exposed workers when they are not aware about their deafness. DESIGN: A descriptive study. PLACE & DURATION: Department of Ear Nose & Throat, Baqai Medical University Karachi, during June 1996 to December 2000. SUBJECTS & METHODS: Our study is based on the 50 workers of Karachi Shipyard Engineering Works (KSEW), compared with equal number of non exposed individuals from all walks of life. Noise level at work place was recorded with noise level meter. Otoscopic examination and conventional frequency (0.25-8.0 KHz pure tone audiometry were used to assess the hearing loss in each individual. RESULTS: This study includes 50 factory workers of KSEW who were exposed to the loud noise above the permissible level of 85 dB(A) for more than 2 years, they were selected for further training in France having no hearing complaint were compared with equal number of controlled persons with no history of exposure to loud noise. None of the workers had ever used any form of hearing protecting device at their work place. Audiometer revealed sensory neural hearing loss which was bilateral and nearly symmetrical in all the factory workers, while there were no hearing loss recorded by pure tone audiometery in any of the none exposed controlled individuals. CONCLUSION: It is seen then on an average, changes starts after 2 years of noise exposure and the first change is seen at 4KHz. In many workers till this time they are not aware of this hearing loss. Thus occupational exposure to loud noise has been demonstrated to cause noise induced sensory neural hearing loss started at 4KHz and it also involves both lower and higher frequencies after prolonged exposure of 8 to 12 years. It is a widespread problem of the industrial world while strategies of noise assessment and control are introduced which may help to improve the working environment and preserve hearing of the factory workers.

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