The effects of noise exposure and work-related fatigue on the acceptable noise level test in normal-hearing people

Background and Aim: The acceptable noise level (ANL) assesses the noise that a person can tolerate during a running speech. Although it is a strong test, it has not yet become popular in clinical practice. One of the reasons is its contradictory results. Since it is a psychoacoustic test, psychological factors can affect its output. Investigation of these factors can provide more accurate results. This study aims to investigate the effects of noise and work-related fatigue on the ANL in normalhearing people. Methods: Participants were the male workers in the administration (n = 26) and production (n = 26) departments of an automotive manufacturing industry in Iran. They were evaluated before and after leaving the workplace in order to determine the effects of noise exposure, fatigue as well as their simultaneous effects on the ANL. Results: In both groups, the ANL showed a significant increase after work compared to its level before work, and the background noise level (BNL) was significantly decreased. There was no significant difference in the BNL between administration and production groups before work. The most comfortable level (MCL) showed no significant increase. Moreover, the MCL changes were not significantly different in the production group compared to administration group, but the BNL and ANL changes were significantly higher. Conclusion: Noise exposure and work-related fatigue affect the ANL. During the ANL test, earlier exposure to noise and the amount of fatigue should be controlled.