occupational noise hearing protectors human behaviour attenuation real world derating subject-fit comfort research

Assessing occupational noise exposure "beneath" Hearing Protection Devices (HPD) is a topical subject. Standardized methods allow to calculate the exposure by using the HPD attenuation. The HPD attenuations declared by manufacturers are much higher from the "real-world" ones. To reduce this difference, some "compensation" methods are proposed. The methods and their rules vary a lot from one country to another. The "derating" rmethod reduces the declared values from a certain amount, according to the HPD kind. "Double-labelling" method uses attenuation values measured in laboratory with untrained subjects. "Statistical range enlargement" widens the statistical confidence of the laboratory-test results. All these methods propose a global solution: the reasons due to human behaviour (mainly bad HPD wearing) , products quality, and the difference between laboratory and industrial situations are mixed. This "blind" approach could be considered as endorsing the lack of workers' training, and could impede the progress in HPD developments. But a "short-term" answer to the problem is needed. It should allow to build a more relevant medium-term answer, which could be worked out possibly on an international scale.

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