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Long-term hearing threshold shifts from moderate noise exposure (< 85 dBA time-weighted average) in semiconductor
Sanghyun Kim1, Seung Nam Min1, Dong Joon Kim2
1School of Smart Safety System, Dongyang University, Pyeonghwa-ro 2741, Dongducheon-si, 11307, Gyeonggi-do, Republic of Korea.
Objective:
Long-term hearing effects of occupational noise exposure below 85 dBA TWA remain insufficiently characterized in semiconductor manufacturing environments. This study evaluated longitudinal hearing-threshold changes among silicon wafer manufacturing workers exposed to moderate workplace noise over approximately 20 years.
Methods:
This retrospective cohort study examined serial pure-tone air-conduction audiometry (0.5-6 kHz) in 71 male semiconductor workers exposed to process-specific noise levels ranging from 72.2 to 80.9 dBA TWA. Participants were classified into normal-hearing (n = 53) and hearing-impaired (n = 18) groups according to Korean special health examination criteria and further categorized by manufacturing process: Process A (utilities), Process B (ingot processing), and Process C (wafer slicing). Longitudinal hearing-threshold changes were analyzed using repeated-measures ANOVA and compared with ISO 1999:2013 reference predictions.
Results:
Both groups demonstrated significant deterioration in high-frequency hearing thresholds, particularly at 4-6 kHz (p < 0.001). Workers with normal baseline hearing showed threshold shifts of approximately 6-8 dB at 4 kHz and 8-10 dB at 6 kHz during follow-up, whereas workers with pre-existing hearing impairment demonstrated substantially greater progression. Process C, which had the highest recent exposure levels, showed the most pronounced longitudinal deterioration. Observed high-frequency threshold shifts were greater than conservative ISO 1999 reference predictions despite exposure levels below 85 dBA.
Conclusions:
Prolonged exposure to moderate occupational noise below current regulatory limits was associated with progressive high-frequency hearing deterioration in semiconductor manufacturing workers. These findings suggest that cumulative exposure duration and process-specific exposure characteristics should be considered in occupational hearing conservation programs.
