Retrospective analysis on the protection of custom-made hearing earplugs worn by oceangoing seafarers

Abstract

Objective To investigate long-term protective effects of custom-made hearing earplugs on the hearing of oceangoing seafarers,so as to provide scientific evidence for the development of related countermeasures against noise-induced hearing damage.Methods One hundred and twenty noise-exposed ship crew members,who were randomly selected from the engineering department of the surveillance ship and wore custom-made hearing protection earplugs (HPE) were chosen as the custom-made hearing protection earplug group.Other 40 ship crew members with similar age,years of sea service and gender,who wore earlyplugs readily available from market,were chosen as the market ear-plug group.A follow-up study was made for successively 4 years from 2007 to 2011,and then,changes in hearing thresholds and adverse reactions were compared between the crews of the 2 groups.Results Noise in the engineering department of the surveillance ship was mainly medium and high frequency noise and intensity was between 73.3 dB (A) and 102.7 dB (A),with LEX,8h ≥ 85 dB (A).A 4-year consecutive investigation on the seafarers wearing the custom-made earplugs indicated that there was no significant changes in the hearing threshold at various frequencies (P ＞0.05).Four years later,incidence of deafness among the seafarers increased from 7.5％ to 9.6％,but without statistical significance (P ＞ 0.05).Custom-made earplugs were more comfortable to wear,with little discomfort,and statistical significance could be noted,when compared with the control group (P ＜ 0.05).Conclusions Noise environment onboard the surveillance ship had adverse effects on the hearing of seafarers during prolonged operation at sea.Custom-made earplugs were individual hearing protection devices that were designed and built according to individual outer ear canal structures,for that reason,they could offer positive hearing protection for the ship crew. Key words: Seafarers of ocean-going ship; Custom-made earplug; Hearing loss; Retrospective study