A study on diagnostic criteria of noise-induced hearing loss among workers in an iron foundry

Kim, Ji Yong; Lim, Hyun Sul; Cheong, Hae Kwan; Moon, Ok Ryun

Abstract

This study was carried out to evaluate diagnostic criteria of noise-induced hearing loss (NIHL) among workers in an iron foundry. Of 1,093 workers under the observation of noise-specific health examination, 184 workers were selected by way of first and second screening audiometric examination. A questionnaire survey, otological examinations, Rinne test and audiometric test were performed and the results were as follows; The degree of hearing impairment in the left ear was more severe than in the right ear(p<0.05). The difference between hearing threshold of the first and the second hearing test at 1,000 Hz was about 5 dB with a narrow range of deviations while the difference at 4,000 Hz was about -7dB with a wide range. Of the total study workers, 84.8% were tested within 15 hours away from noise exposure, and the rest after 16 hours. This study has identified that mean hearing loss at 4,000 Hz showed a significant statistical difference among the two study groups while mean hearing loss by 4-divided classification did not. The same phenomena were observed between the group with and without tinnitus and between the group with and without difficulty in hearing(p<0.05). Among 184 workers, 10 workers(5.4%) diagnosed as NIHL by old diagnostic criteria in contrast to 150 workers diagnosed as NIHL by the new diagnostic criteria. There was a significant difference between the two groups in the average hearing loss at 4,000 Hz and 4-divided classification(p<0.01), but there were no significant difference in age, the duration of employment, blood pressure and the duration wearing the personal hearing protector(p>0.05). If we apply Early Loss Index(ELI) method, some workers in younger age group diagnosed as NIHL by the new diagnostic criteria were fallen into within the normal range. In the mean time older age group show reverse results in contrast to the above finding. It is too early to confirm the value of the usage of the new diagnostic criteria in hearing examination. Further study is called for to verify the value of this criteria.