Noise Induced Hearing Loss in Hard Rock Miners of Kadapa, A.P. India.

ABSTRACT

Background: Noise is excessive, unwanted sound stimulus in the atmosphere produced by extraneous sources resulting in permanent pathological changes in the inner ear, the cochlear nerve and its ganglia. It is one of the constituents of atmospheric pollution. Noise in the vicinity of workplaces is termed as occupational noise trauma which is imminent in workers in certain industries and unavoidable in them, but preventable to some extent. The present study is to measure such audiological threshold values to correlate the pathological changes in the workers with the help of audiometry. The aim of the study is to measure the noise levels in the industry and its effect on hearing capabilities of miners working there with audiological data and to formulate effective preventive measure for them. Methods: Miners from a Hard Rock cutting industry near Kadapa, A.P. are chosen and divided into 2 groups depending upon their work experience between 3 to 14 years. Audiometry is performed to record their Air Conduction thresholds in both ears at all the frequencies, before and after working hours. The data are analyzed and looked for statistical significance. Results: Miners with less than 7 years work experience had smaller temporary threshold shifts compared to miners above 7 years experience. The base level A.C threshold values were higher compared to miners with less than 7 years experience. The threshold shift was mostly observed in the frequency 6000KHZ, in both the ears. The average of mean thresholds of Air Conduction was found to be higher in the higher frequencies. Conclusion: Prolonged exposure to noise levels above 85dB for 8 hours in a day, 6 days per week for 3 to 14 years results in hearing loss due to permanent changes in the inner ear. Higher frequencies are more affected than the lower frequencies with higher base level thresholds. All the frequencies showed temporary threshold shifts ranging from 1.69 to 4.37dB when recorded immediately after the working periods. There was statistical significance observed for all frequencies in both ears for the threshold shifts with a P value less than 0.05.