What do workers know and practise? : Occupational noise exposure and noise-induced hearing loss among Tanzanian iron and steel workers

Abstract

Background: Employees work to earn a living. Noise-induced hearing loss (NIHL) due to occupational noise is an underrated public health problem that has been increasing during the past two decades, mostly in low-income countries. Iron and steel factories are among the workplaces that have high levels of noise exposure, and because of heavy industrial investments, a significant number of people are employed in these factories. However, little is known about the status of occupational noise exposure and prevalence of NIHL. In addition, we have no information on workers’ knowledge, attitude and practices in terms of occupational noise, NIHL and the use of hearing protection devices (HPDs). Objectives: We aimed at gaining knowledge about occupational noise exposure levels and NIHL among iron and steel workers in Tanzania. We also wanted to assess the level of knowledge, attitude and practice (KAP) regarding noise exposure, NIHL and the use of hearing protection devices. Material and methods: We randomly selected 253 male production line workers from four randomly selected iron and steel factories in Tanzania. All the selected workers participated in a KAP study, 163 participated in an exposure study, and 221 workers in prevalence of NIHL study together with external control group of 107 workers. We did a Walk-through survey (with checklist) and assessed both personal and area noise exposure respectively using personal noise dosimeter (Brüel and Kjaer type 4448) and sound level meter (Brüel and Kjaer type 2250). We assessed NIHL by Pure Tone Audiometry (PTA) using Interacoustics AD 226. In addition, we used an interview questionnaire to conduct a KAP study and to acquire information about basic sociodemographic characteristics. Results: Workers were exposed to an average personal noise exposure (LEX,8h) of 92.0 dB (A) (n=326). Workers did not use HPDs. About 90% of all measurements were above the OEL of 85 dB(A). The average area noise level was 90.5 dB(A). The personal noise exposure was significantly higher (2.6 dB (A); 95 CI = 2.1- 3.1) compared to the corresponding area measurements. A total of six determinants for noise exposure (three in each section) were identified. These were; - the furnace installation, billet weighing/transfer and manual handing or raw materials/ billets/crowbars for furnace section and the size of cutting machine, the steel billet weight and feeding re heating furnace in the rolling mill section. The overall prevalence of hearing loss was significantly higher among exposed workers (48%) than among the controls (31%). The mean scores for attitude and practice related to occupational noise, NIHL and the use of hearing protection devices (HPDs) differed significantly between the four factories (one-way ANOVA, p<0.001) while mean knowledge scores did not differ between any of the four factories. In addition, the majority of workers had poor knowledge and practice but had a positive attitude. Conclusions: The workers in Tanzania’s iron and steel factories were exposed to high noise levels above the occupational exposure limit of 85dB(A) and they did not use HPDs. The prevalence of NIHL was higher than among the controls. The workers had poor knowledge regarding noise exposure and related NIHL. Implementation of noise control measures such as provision of HPDs and establishment of a hearing conservation programme (HCP) is recommended.