Temporary threshold shift among small-scale metal workers exposed to noise levels above 85 db (a) in Dar es salaam, Tanzania

Abstract

ABSTRACT: Background: Workers in small-scale metal industries in Tanzania are often exposed to noise levels above 85 dB(A) without using hearing protection. This exposure is linked to temporary threshold shifts (TTS), a precursor to permanent hearing damage. While global data highlight the prevalence of TTS in noisy workplaces, there is a lack of studies from African contexts on informal small-scale metal workers, particularly in Tanzania. Nevertheless, Effective control measures to reduce TTS effects, are crucially lacking in these settings. Objective: The study aimed to determine Temporary Threshold Shift before earplug use and during earplug intervention among small-scale metal workers exposed to noise levels above 85 dB(A) in Dar es Salaam, Tanzania. Methods: The study employed a controlled before-and-after design to investigate temporary threshold shift (TTS) among 55 small-scale metal workers. Participants exposed to noise levels above 85 dB underwent baseline audiometry tests without earplugs and post-intervention tests during earplug use. Data on factors influencing TTS, including age, smoking status, and ear infections, were collected through questionnaires and statistically analyzed and the impact of earplugs use on TTS was observed. Results: Among 55 workers, 27% experienced temporary threshold shifts (TTS) at 4 kHz after noise exposure. Mean hearing threshold shifts at 1000, 2000, 3000, and 4000 Hz were not statistically significant. The highest shift was at 4000 Hz (1.6 dB), with TTS greater than 10 dB was most common at this frequency. Factors like age, smoking, earphone use, and ear infections did not significantly affect TTS. Noise exposure of 4-6 hours significantly increased TTS risk. Earplug use significantly reduced TTS at 4000 Hz from 27% to 12.7%, and at 1000 Hz from 14.6% to 9.1%, showing their effectiveness in preventing TTS. Conclusion: The significant reduction in TTS at 4 kHz with earplug use highlights their pivotal role in safeguarding against noise-induced hearing damage. Addressing this frequency-specific vulnerability is crucial for protecting workers' hearing health in noisy environments.