A survey on changes of the threshold of hearing in noise-exposed workers

Objective To survey the changes of threshold of hearing in workers occupationally exposed to noise in an iron and steel enterprise.Methods Hearing abilities were surveyed for 1 628 noise-exposed workers.The data were analyzed with years of service,noise intensity of working environment and types of work.Results Hearing damages of high frequency and language frequency often occurred in workers that had been working in noise-exposed environment for 10 years and 20 years respectively.There were significant differences in hearing damage of high frequency between workers with 5 years of the service and those with 10 to 30 years of the work experience.There were also significant differences in hearing damage of language frequency between workers with 5-10 years of the service and those with 15-30 years of the work experience.Hearing damages of high frequency and language frequency often occurred in workers exposed to noise above 86 dB(A)and 92 dB(A),respectively.There were significant differences in hearing threshold between low-noise[noise below 92 dB(A)or 86 dB(A)]and high-noise exposure groups[noise above 97 dB(A)or 103 dB(A)].The hearing damages were worse in workers exposed to non-stationary noise than in those with other types of work.Conclusion The average hearing threshold increases with length of service and intensity of noise.The hearing damage of high frequency occurred 10 years earlier than that of language frequency.Hearing damage of language frequency was 5-10 dB(A)higher in workers exposed to non-stationary noise than in those exposed to stationary noise.