Effectiveness of the hearing protection programin preventing noise-induced hearing loss inauto part factory workers, Saraburi and Rayong, Thailand

Abstract

Occupational noise exposure is the most important problem in auto part factories. Machinery system is mostly used for resistance spot welding in welding unit. Excessive noise could generate from the robot machine and steel part transporting and can cause noise-induced hearing loss. However, most workers do not use hearing protection device. The main objective of this study aimed to assess the effective hearing protection program in preventing noise induced hearing loss in auto part factory workers in Thailand. The specific objectives were 1) To investigate the noise exposure among Thai workers in auto part factory workers. 2) To evaluate the hearing threshold shift among Thai workers in auto part factory workers. 3) To evaluate the hearing protection device using among Thai workers in auto part factory workers. 4) To find the association between the hearing protection device using and hearing threshold shift. This was a Quasi-experiment study. Systemic random sampling was applied to recruit the eligible sixty subjects in welding unit from each factory in Saraburi and Rayong provinces. Subjects in auto part factory at Saraburi were received the intervention and subjects in auto part factory at Rayong were the control group. Subjects in both groups were studied by interviewing with questionnaire, noise exposure level measurement by noise dosimeter audiogram and ear plug using inspection. Major noise exposure level of subjects was at least 85 dB (A). Most Subject (95.0-80.0%) with continuous training in the intervention group increased the use of earplug correctly and consistently during 6 months. Meanwhile, all subjects in the control group did not use earplug. All subjects in the intervention group had the hearing threshold shift level from the first audiogram below 15 dB at 500-6000 Hz in either ear. Most subjects (85.0%) in the control group had the hearing threshold shift level from the first audiogram below 15 dB at 500-6000 Hz in either ear but 15% of those had the hearing threshold shift level from the first audiogram 15 dB at 4000 Hz in either ear. There was significant difference of normal hearing threshold shift between the intervention and the control group (p<0.05, Fisher’s Exact test). The proportion of subjects with earplug using correctly and consistently had the normal hearing threshold shift 11.39% (95% CI: 1.39, 20.25) higher when compared with those who used earplug inconsistently and did not use earplug. Continuous training of noise hazard by lecture and refresher training by DVD every 8 weeks for 6 months can maintain the knowledge of noise hazards and increase the use of earplug correctly and consistently. In addition, the proper earplug using consistently can prevent hearing threshold shift level reach to 15 dB.