IRSST - Institut de recherche Robert-Sauvé en santé et en sécurité du travail

Study of sound transmission through hearing protectors and application of a method for evaluating their efficiency in the workplace


The method for evaluating the noise attenuation characteristics of hearing protectors is based on laboratory tests. However, many studies have shown that the actual effectiveness of this protective equipment is, more often than not, much lower than the results thus obtained. The authors examined the time evolution of the performance of this equipment during one work shift, with 24 workers, in different sound environments. This mainly enabled them to develop a method for measuring the real effectiveness of earmuffs and moulded ear plugs, and then to compare it to measurements taken in the laboratory.

The results obtained are consistent with what is found in the literature on this subject, with the protection values lower than those documented by the manufacturers (measured in the laboratory); for a given worker, the protection varies significantly in relation to the time during a work shift; the protection can vary greatly from one worker to the next but also from one ear to the other for a given worker. The developed attenuation index shows a high dependence on the frequency content of the ambient noise, thus highlighting the inadequacy of some hearing protectors at low frequencies and the importance of properly knowing the ambient noise so that a judicious choice of hearing protectors can be made. The project also demonstrated the potential of the developed method. Scenarios for improving it, and for making it more complete and accessible to a greater audience are presented at the end of the report.

Additional Information

Type: Project
Number: 0099-4940
Status: Completed
Year of completion: 2010