Noise induced hearing loss and its relationship with dose and exposure length

Abstaract Background: Noise Induced Hearing Loss (NIHL) is an important occupational disorder and the protection of workers against noise is essential. Objective: To ‏ evaluate the noise induced hearing loss and also presenting a statistical model based on effective variables such as the duration of employment and dose of received noise. Methods: ‏This study was carried out on workers of a cleaners manufacturing industry. The study group composed of 209 subjects who were selected out of a total of 400 workers. The hearing loss was measured after rejection of age related loss. Following elimination of the effect of ear protective device, the dose of pure received noise for each subject was determined. Finding: The results indicated that the noise pressure level in different parts of the manufacturing unit was 76-107 dBA. The mean of employment duration, dose of pure received noise and total permanent hearing loss were 9.96.9, 135.411.51, and 12.524.1, respectively. The regression analysis of results showed that there was a direct and positive correlation between permanent hearing loss, dose of noise and the duration of employment (r=0.84,r2=0.77). This was a significant correlation for both right (r=0.77, r2=0.6) and left ears (r=0.8, r2=0.64). The survey of hearing loss in both ears showed that the hearing loss in left ear was greater than that in right ear. Regarding the data obtained in our study, models for calculating the either, left or right hearing loss, were recommended by determining dose and the duration of employment in study group. Conclusion: Considering the NIHL, the necessity for improvement of controlling and protection measures is of prime importance.