A Study On Noise Induced Hearing Impairment Of Workers In Boiler-Manufactured Factory

Occupational noise-induced hearing loss (NIHL) is a progressively sensorineural hearing loss, a chronically acoustic damage, which caused by exposure to noise in the process of produce for a long time. Occupational NIHL is irreversible. When NIHL is detected, speech discrimination and worker's everyday life has been affected. Dates from all over the country about occupational disease showed that there were about 10 millions of workers who worked under conditions beyond the national hygiene criterion about noise and about 1 million of them suffered from different degrees of noise-induced deaf at present. Noise is still one of main risk in occupational factors. By virtue of absence of valid treatment for NIHL , prevention is very important. This study was performed to study the dose-response relationship between the prevalence rate of noise-induced hearing impairment and the noise exposure, to analyze factors affected noise-induced hearing impairment, to make a suggestion of prevention of NIHL.Method: Noise levels were measured using an integrating sound level meter (HS-5633, China). Pure-tone air conduction audiometric tests were done using Audiometer (GSI-16, U.S.A) at 8 frequencies, i.e, 250, 500, 1000, 2000, 3000, 4000, 6000, 8000Hz to evaluate the hearing ability of thesubjects. The subjects were examined after cessation of noise exposure for more than 12hr. The examinations were conducted in a quiet room with a background noise level less than 30dB. To rule out the presence of hearing loss from other causes, an otologic examination was done in all subjects. Subjects with histories of ear disorders and of pre-occupational exposure to noise were excluded from this study. By linear regression analysis, the relationship between the prevalence rate of noise-induced the hearing impairment and the noise exposure was analyzed. Length of service, type of work, age, smoking, drinking was investigated and effects of them on noise induced hearing impairment was analyzed by Chi-square test.Result: The prevalence rate of noise-induced hearing impairment was 57.36%, the prevalence rate of noise-induced deaf 9.30%, there was a dose-response relation between the incidence of noise-induced hearing impairment and the doses of the noise exposure. Length of service, type of work, age had effect on the prevalence rate of the noise-induced hearing impairment, smoking and drinking had no effect.Conclusion:The noise-induced hearing impairment in boiler-manufactured factory is very serious. Noise is the main cause of noise-induced hearing impairment of workers in boiler- manufactured factory. By the linear regression formula, in order to protect 85% workers against the noise-induced hearing impairment, the noise exposure dosage must be controlled below 94 dB-years, in order to prevent workers from the noise-induced hearing impairment, the national criterion must be strictly carried out, hearing level measured once a year, training of security reinforced, self-protective consciousness reinforced.