Pedro Arezes es Profesor Catedrático en la Universidad de Minho (Portugal), donde coordina el Grupo de Investigación en Ingeniería Humana. En 2005, fue nombrado como el Director del Laboratorio de Ergonomía de la misma Universidad y miembro del Consejo de Dirección de la Maestría de Ingeniería Humana y de la tesis doctoral, Programa de Ingeniería Industrial y de Sistemas. Fue autor de más de 150 artículos en revistas internacionales y actas de congresos y como él ha colaborado con varias reistas internacionales en el ámbito de la ergonomía y seguridad, tanto como reviewer y como miembro del comité editorial. Él es también el Vice-Presidente de la Sociedad Portuguesa de Seguridad e Higiene (SPOSHO) desde su fundación en 2004.
Pedro Arezes is a Full Professor at the University of Minho (Portugal), where he coordinates the Human Engineering Research Group. In 2005, he was appointed as the Director of the Ergonomics Laboratory at the same University and member of the Direction Board of the Human Engineering MSc. and of the PhD. Programme in Industrial Engineering and Systems. He authored more than 150 papers in international journals and conference proceedings and, as he has been collaborating with several international peer-reviewed scientific journals in the domain of Ergonomics and Occupational Safety, both as a reviewer and member of the editorial committee. He is also the Vice-President of the Portuguese Society for Occupational Safety and Hygiene (SPOSHO) since its foundation in 2004.
The control of the risk to develop noise induced hearing loss, the main physiological effect of noise exposure, is more often than desirable achieved through the use of hearing protection devices (HPDs). However, and despite the apparent simplicity of this measure, its adoption is a complex issue and it involves the consideration of several physical factors, such as noise characterization, psychological factors, for example linked to the idiosyncrasy of the users and their specific behaviour, and health aspects, related to their hearing function.
The adoption of HPDs, in particular in occupational settings, is currently a common practice in situations where noise exposure exceeds certain threshold values. Despite being regarded as the last resource when observing the hierarchy of priority for intervention measures, hearing protection has become increasingly popular, not only in occupational environments, but also among general users.
In general terms, HPDs are devices developed to prevent that sound pressure levels reach the inner ear. Thus, all the obstacles or barriers assuming this role can be classified as HPDs. Nowadays, there are a lot of devices developed to this end, ranging from simple earplugs and earmuffs to electronic devices with high-end technological developments.
The efficiency of the HPDs, i.e. the ability to protect users’ hearing, will depend on the type of device and on its features, among which the configuration of the device, the used materials, and the previewed attenuation behaviour are the most relevant. In addition, it is necessary to consider other factors, such as those related to the characteristics of the noise and noise sources, the users’ physiological and anatomical characteristics and also the way the devices are used.
It is also important to acknowledge that, even with the use of HPDs, one cannot prevent that the sound pressure energy reach the inner ear. This may occur due to several reasons, for example, due to noise propagation through bone conduction, the existence of holes between the HPD and the head, the vibration associated with the device and the transmission through the HPDs structure.
Regarding noise attenuation, and despite the similarity between all the available devices, the truth is that every HPD, depending on its characteristics, presents a specific acoustic attenuation. Since the determination of the specific acoustic attenuation afforded by HPDs is a key-step in providing information to users, several methods have been developed during the last years, which, by considering the certification and homologation requirements, are able to inform users about the attenuation characteristics of the devices. These methods can be different according to the country legislation, but all of them are based on the estimated attenuation of the devices obtained by laboratory methods.
It is also important to refer that, despite the high usage of this type of personal protective equipment, its effectiveness is not always clear and there are several factors contributing to this. Actually, HPDs are labelled with attenuation information obtained through laboratory tests, also called nominal attenuation, which may be very different from the attenuation afforded by the devices in real settings, also called real attenuation. The difference between estimated and real attenuation is partly due to the fact that sound propagates up to the inner ear through small holes. These holes exist when the earplug is not fully obstructing the ear canal or the earmuff does not completely isolate the ear from the outside noise, and are typically caused by a lack of pressure of the protector against the head.
Among the many reasons for the inefficiency of the HPDs, it is particularly important the comfort during the use of HPDs, which may be affected by several factors, such as the prolonged use of the devices, the compatibility with other personal protective devices and users (ear dimensions), and the readjustment and changes introduced by the users themselves. The issue of comfort, or more broadly the ergonomics of these devices, is even more important when we consider that the non-continuous use of the devices may greatly reduce the performance of protectors. Accordingly, the design of these devices should necessarily consider the ergonomic aspects of the HPDs’ performance.
Based on the fact that the attenuation of certain protectors under real conditions of use can be half (and sometimes less) of its nominal attenuation, it is necessary to assume that these nominal values are not reliable enough to estimate the real protection afforded by the devices. That is why it is so important to estimate the protection afforded by the HPDs by using the most accurate method. However, if on one hand it is necessary to take into account the fact that the catalogued attenuation can be too optimistic, on the other hand it is also important to recognise that there is a risk of using HPDs with an over, or excessive, attenuation. This may also represent an unwanted situation, with the corresponding drawbacks and direct effects resulting from the users’ overprotection.
Last but not least, it is also important to acknowledge that there are several recent developments concerning the use of technology in HPDs. Accordingly, it seems that the future of HPDs is strongly associated to the use of devices with nonlinear attenuation behaviour, which can be used to improve the perceptibility of useful sounds in noisy environments. Nevertheless, this type of HPDs still have some unsolved drawbacks, and it is recognised that its application on occupational environments still has a long way to go.