Objective: To analyze the noise exposure and hearing loss of workers in railway transportation equipment manufacturing enterprises, and to assess the risk of hearing loss caused by noise.
Methods: From 2018 to 2020, an investigation was carried out on 3 railway transportation equipment manufacturing enterprises in Hubei Province and Hunan Province. A total of 840 noise-exposed workers were selected, the individual noise exposure level(L_(Aeq·8 h)) and hearing loss level were measured, the cumulative noise exposure(CNE) was calculated, and the relationship between hearing loss and technological process, working time and CNE were analyzed. ISO1999:2013 was used to calculate the change of hearing threshold and the risk of noise-induced hearing loss after 40 years old.
Results: The median age of workers was 32 years old, and the median working age for noise exposure was 10 years. The distribution of positions is mainly welding, machining, assembly and painting.79.5%(120/151) of the individual noise exposure doses exceeded 85 dB(A), and the average L_(Aeq.8 h) was 89.9(A). There were significant differences in the proportion of hearing loss among workers in different process units(χ~2= 29.597, P<0.001), and the proportion of hearing loss in the preparation and steel structure units was higher. The proportion of hearing loss showed an upward trend with the increase of working years(χ~2=164.462, P<0.001), and the high-frequency combined speech-frequency hearing loss(26.7%) increased significantly after working for more than 20 years. With the increase of CNE, the proportion of high-frequency hearing loss and the proportion of high-frequency combined speech-frequency hearing loss increased accordingly(χ~2=192.544, P<0.001). The proportion of high frequency combined speech frequency hearing loss increased significantly in the group with CNE greater than 105 dB(A)·years. It is predicted that the risk of hearing loss caused by noise in assemblers appears earliest and the risk is the greatest. The risk of high noise-induced frequency hearing loss of assemblers was 3.6%-8.6% at the age of 40, 20.2% at the age of 50, 22.0% at the age of 60. The risk of high-frequency combined speech-frequency hearing loss of assemblers was 1.2%-6.2% at the age of 50 and 8.6% at the age of 60.
Conclusion: The noise hazard is serious and widely distributed in railway transportation equipment manufacturing enterprises, and the proportion of hearing loss increases with the increase of working time and CNE. Although ISO1999:2013 predicts that there may be an underestimation of noise-induced hearing loss in workers, it can be used as an early warning of hearing loss to identify the potential risk of hearing loss in the population.
Keywords: equipment manufacturing; hearing loss; noise; rail transport; risk assessment.