Long-term hearing threshold shifts from moderate noise exposure (< 85 dBA time-weighted average) in semiconductor silicon-wafer manufacturing process

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.

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.

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.

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.