The Risk Assessment For Hearing Loss Caused By Occupational Exposure To Complex Noise In The Metal Processing Manufacturing Industry

Objective:Complex noise is more harmful to hearing than steady-state noise.Kurtosis was used to distinguish the type of noise,then the distribution of complex noise exposure was investigated in metal manufacturing,and the relationship between complex noise exposure and hearing loss was explored,especially the noise time domain structure（kurtosis）,and the ability of multiple hearing loss diagnostic criteria to identify complex noise risks and the applicability of kurtosis-corrected noise metric in metal manufacturing hearing loss risk assessment was evaluated.Methods:The cross-section method was used to investigate the noise exposure and worker hearing loss of three metal manufacturing industries in Zhejiang Province from October 2017 to December 2017.Use questionnaires to collect general demographic information,past history of hearing,occupational history,etc.;collect noise exposure data of workers using individual noise meters,calculate noise intensity L_Aeq,8h,time domain structure（kurtosis）,etc.,and comprehensive metric（Cumulative noise exposure CNE,as well as the kurtosis corrected CNE）;the hearing thresholds of 0.5,1,2,3,4,6,and 8 kHz for the left and right ears of the workers were examined.The statistical description was used to analyze the noise exposure of each type of work;the Cochran-Armitage test for trend was used to test the relationship between noise exposure and hearing loss;the logistic regression was used to analyze the risk of complex noise and noise-induced hearing loss.The dose-response relationship between each noise indexes and the high-frequency hearing threshold was compared using Pearson correlation analysis.Results:A total of 737 metal manufacturing worker exposed to noise was surveyed,of which 71.51% were 18-40 years old,77.34% were men,and 56.45% were junior high school students.Noise exposure exceeded 85dB（A）accounted for 77.62%,complex noise contacts accounted for 75.70%,and people under8 years of service accounted for 86.02%.Among the 30 types of work investigated,the types of work with noise intensity reaching 100% are the stamping workers,electric welders and other types of work of company A,operators of C enterprises,chamfering workers,tapping workers,and thread rolling workers;The jobs with a rate of 100% exposed to complex noise are:the grinding workers of the A company,the assemblers of the B company,the final assembly workers,others,and the polishing workers of the C company.The trend chi-square test P values between L_Aeq,8h,kurtosis,length of service,CNE and hearing loss were 0.032,0.605,0.007,0.008.After adjusting for age,gender,and CNE,logistic regression found that the risk of hearing loss at 3,4,and 6 kHz was higher than that of steady-state noise at complex frequencies of 33 years old（OR（95%CI） adjusted by Bonferroni are 4.37（1.78-10.71）,and 2.39（1.13-5.05）,respectively）;hNIHL and NIOSH criteria for the diagnosis of hearing loss risk for complex noise are 2.77 and 4.39 times of steady-state noise（OR（95%CI） are 2.77（1.49-5.14）,4.39（1.8-10.68）,respectively）.The aCNE（100.29±12.86） after kurtosis correction was significantly higher than CNE（92.44±6.19）,P<0.001,and the cv of aCNE was also larger than CNE.L_Aeq,8h,CNE,aCNE,and HTL₃₄₆ were significantly correlated,and the correlation coefficients were 0.073,0.118,and 0.132,respectively,and the P values were all less than 0.05.The P value of the Cochran-Armitage test for trend between aCNE and hearing loss detection rate is 0.003.Conclusions:1.Metal manufacturing noise intensity exceeds the standard rate,and complex noise exposure rate is high.2.The hearing loss detection rate increases with the increase of noise intensity and service age,but it is not found to increase with the increase of noise kurtosis.3.Young people with noise exposure,the risk of high-frequency hearing loss caused by complex noise is much higher than steady state noise.4.hNIHL,and NIOSH diagnostic criteria are more suitable for discovering complex noise risks.5.The dose-response relationship between aCNE using kurtosis correction and the binaural high-frequency hearing threshold is stronger than single-metric(L_Aeq,8h,kurtosis,length of service),and uncorrected CNE.