Epidemiological Investigation And Risk Assessment Of Noise-induced Hearing Loss In Chinese Automotive Industry

Objective:This study aimed to describe the epidemiological features of noise-induced hearing loss(NIHL)among workers in the automotive industry in China and to evaluate the risk assessment model suggested in ISO-1999:2013(E)"Acoustics-estimation of noise-induced hearing loss" when using it to predict the risk of NIHL among workers exposed to occupational complex noise.Methods:A cross-sectional survey was conducted with 6,557 participants selected from an original pool of 8,836 from 4 automotive manufacturing factories and 18 auto part manufacturing and powertrain factories in the Hubei province of North China based on strict inclusion criteria.The questionnaire survey was administered and individual noise exposure level(LAeq.8h)and hearing loss level were measured.The mean hearing thresholds for the left and right ears at overall frequencies were compared using paired t tests.A chi-square test was applied to analyze the correlation between the category of work and AHFNIHL.The Cochran-Armitage Trend Test was performed to analyze the trend between the proportion of workers using HPD regularly and noise exposure level,as well as the prevalence of adjusted high-frequency noise-induced hearing loss(AHFNIHL)and noise exposure level.Logistic regression analysis was used to determine the influence of age,CNE,and HPD usage on the prevalence of AHFNIHL.The frequencies and fences of high-frequency hearing loss and noise-induced deafness were determined according to the Diagnosis of Occupational Noise Deafness(GBZ 49-2014)and the percentage of populations beyond the selected fence were calculated to acquire the risk of’NIHL.Combining the results of audiometric testing and ISO-1999 database,the actual noise-induced permanent threshold shift(NIPTS)was obtained.According to the level of individual noise exposure,NIPTS was predicted by using ISO-1999 model.The median NIPTS for each type of work was compared to the ISO-1999 predicted median NIPTS using paired t-test.Results:Of participants,96.43%were male;the median age was 27.0 years and the duration of noise exposure for workers was at the range of 2.1～6.6 years with a median of 3.5 years.Due to the diversity of noise sources,the type of noise in the automotive industry is mostly non-Gaussian.Each typical noise source such as casting.welding,grinding and stamping generated its own unique temporal waveform shape with the type of non-Gaussian noise.62.53%exceeded 85 dB(A),where the noise exposure level of the stamping in automotive manufacturing factories was the highest,followed by the surface treatment in automotive manufacturing factories.Concerning individual noise levels(LAeq,8h),Of workers,53.15%regularly used hearing protector devices(HPD),and the proportion of regular HPD use increased with LAq.81.28.82%had NIHL defined as AHFNIHL.Of workers,0.40%(26 cases)meet the diagnostic criteria of noise-induced deafness(NID),with 21 cases meeting the diagnostic criteria of mild NID and 5 cases meeting the diagnostic criteria of moderate NID.The overall mean left minus right threshold difference across all frequencies was determined to be 0.79 dB,which met statistical significance(p<0.05).The differences between binaural threshold shifts at each frequency among subjects with a asymmetry in terms of worse left ear and worse right ear were at the range of 6.28 dB～10.20 dB and 6.35 dB～11.26 dB,respectively.With the increase of high-frequency hearing thresholds(HFHTs),the proportion of subjects with a asymmetry at 2 and 3 kHz of more than 10 dB in terms of worse left ear and worse right ear increased.The trend test showed that the prevalence of AHFNIHL in male workers significantly increased with an increase in LAeq.8h at<94 dB(A)and cumulative noise exposure(CNE)in each age group(P<0.05 or P<0.01).The multivariate analysis showed that sex,age,CNE,and HPD usage frequency and duration were important factors contributing to AHFNIHL.An increase in workers’ age by one year could result in 1.0%increase in the odds of AHFNIHL(OR:1.010:95%CI:1.001-1.019).An increase in CNE by 1 dB(A)·year could result in 10.4%increase in the odds of AHFNIHL(OR:1.104;95%CI:1.085-1.124).The frequency of HPD usage showed a protective effect on the odds of having AHFNIHL(OR:0.478;95%CI:0.425-0.539).The odds of AHFNIHL in terms of duration of HPD usage was 0.949.Male stamping workers in auto part manufacturing factories were at the highest risk of getting noise-induced high-frequency hearing loss and noise-induced deafness,followed by male surface treatment workers in auto part manufacturing factories.The risk of noise-induced high-frequency hearing loss of exposure of male stamping workers in auto part manufacturing factories was at the range of 9.1～14.1%at 20 years of exposure,26.9%at 30 years of exposure,29.1%at 35 years of exposure,and 28.3%at 40 years of exposure.The risk of noise-induced deafness of exposure of male stamping workers in auto part manufacturing factories was at the range of 3.5～8.5%at 30 years of exposure,8.8～13.8%at 35 years of exposure,and 12.1%at 40 years of exposure.The risk of noise-induced high-frequency hearing loss of exposure of male surface treatment workers in auto part manufacturing factories was 11.7%at 30 years of exposure.14.5%at 35 years of exposure,and 14.6%at 40 years of exposure.The risk of noise-induced deafness of exposure of male surface treatment workers in auto part manufacturing factories was at the range of 2.3～7.3%at 35 years of exposure,and 4.3%at 40 years of exposure.Male assembly workers in auto part manufacturing factories were at the lowest risk of getting noise-induced high-frequency hearing loss and noise-induced deafness.The risk of noise-induced high-frequency hearing loss of them was 1.7%and 2.5%at 30 and 35 years of exposure,respectively.The risk of noise-induced high-frequency hearing loss and noise-induced deafness of them was 2.8%and 0.4%at 40 years of exposure,respectively.In automotive manufacturing factories,the actual median NIPTS ranged from 12.5 dB to 20.0 dB and the ISO-1999 predictions ranged from 0.1 dB to 7.1 dB.As a result,the ISO-1999 predictions underestimated the median NIPTS at the range of 7.5～19.2 dB(median:13.1 dB).In auto part manufacturing factories,the actual median NIPTS ranged from 12.5 dB to 26.5 dB and the ISO-1999 predictions ranged from 0.0 dB to 13.6 dB.As a result,the ISO-1999 predictions underestimated the median NIPTS at the range of 1.9～23.8 dB(median:14.2 dB).Conclusions:Noise is still the main occupational hazard in the automotive industry.With the increase of age and CNE,the prevalence of NIHL is increasing.Much more human surveys are needed to understand the prevalence and determinants of NIHL in the automotive industry.Workers of most types of work in automotive industry in this study have the potential risk of high-frequency hearing loss and noise-induced deafness.The current risk assessment method has certain limitations.Noise-induced hearing loss risk assessment model ISO-1999 based on the equal energy hypothesis underestimated hearing loss of workers in automotive industry in this study.Further research needs to supplement the kurtosis of noise to confirm the role of kurtosis in the ISO-1999 noise-induced hearing loss risk assessment model.