Abstract
BackgroundSouth Korea and surrounding countries in East Asia are believed to have the highest proportion in the world of high frequency hearing loss due to occupational noise exposure, yet there has been limited information published in international journals, and limited information for control of noise in local workplaces beyond strategies from western countries. We exploit medical surveillance information from two worker groups to enhance local knowledge about noise-induced hearing loss and explore the possible importance of shift work to risk.MethodsFour-years of hearing data were evaluated for 81 male farm machine factory workers and 371 male firefighters who had successfully completed a health examination and questionnaires for the duration of the study period. The averages of hearing thresholds at 2, 3, and 4 kHz were used as the primary end-point for comparison. Repeat measure analysis adjusted for age, exposure duration and smoking status was used to measure the difference in hearing threshold between the two groups.ResultsNoise levels were measured in the factory at a mean of 82 dBA, with a range of 66-97. No concurrent measurements were taken for the firefighters, but historic comparison values showed a wider range but a similar mean of 76-79 dBA. Although losses during follow-up were negligible, the factory workers had significantly (P < 0.0001) more hearing loss at the baseline of the study than the firefighters in both ears at 2, 3, and 4 kHz, adjusted for age, duration of employment and smoking status. Among those with 10 years of employment, mean losses at these frequencies among the factory workers fell into the impairment range (> 25 dB loss). Firefighters also showed increased losses associated with longer exposure duration, but these were significantly less marked. Losses at lower frequencies (< or = 1 kHz) were negligible in both groups.ConclusionsKorean work environments with continuous noise exposure in the measured range should consider implementation of a hearing conservation program. Further evaluation of hearing loss in workers exposed to irregular or intermittent high noise levels, such as firefighters, is also warranted.
Highlights
South Korea and surrounding countries in East Asia are believed to have the highest proportion in the world of high frequency hearing loss due to occupational noise exposure, yet there has been limited information published in international journals, and limited information for control of noise in local workplaces beyond strategies from western countries
Despite systemic approaches to prevent noise induced hearing loss (NIHL) such as a NIHL surveillance system with periodic annual audiometric examinations for workers exposed to a mean equivalent sound levels of 85 dBA time weighted average (TWA) based on 40 h per week [2] and a hearing-conservation program published by the Ministry of Employment and Labor
The surveillance was designed for control purposes and not research per se, we present our findings to contribute further knowledge about noise induced hearing loss (NIHL) in this region and to provide some new empirical data on the effects on hearing loss by noise exposure pattern
Summary
South Korea and surrounding countries in East Asia are believed to have the highest proportion in the world of high frequency hearing loss due to occupational noise exposure, yet there has been limited information published in international journals, and limited information for control of noise in local workplaces beyond strategies from western countries. In Korea, work-related noise induced hearing loss (NIHL) is defined as hearing levels above 30 dB for the average 0.5, 1 and 2 kHz and 50 dB at 4 kHz [2]. Despite systemic approaches to prevent NIHL such as a NIHL surveillance system with periodic annual audiometric examinations for workers exposed to a mean equivalent sound levels of 85 dBA time weighted average (TWA) based on 40 h per week [2] and a hearing-conservation program published by the Ministry of Employment and Labor [3] Korean workers in noisy industries remain at high risk of acquiring NIHL [4,5]. There are virtually no regulations regarding training (employer and employee), control of the source of noise and other factors which may affect progression to NIHL such as work schedule
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