Search

Hearing Protection Device (HPD) rated attenuation is measured using the Real Ear Attenuation at Threshold (REAT) method specified in Standard ISO 4869-1. This statistical method assumes optimal fitting and is applied under laboratory conditions to predict the hearing protector performance for an individual wearer. The rated attenuation is therefore generally higher than that measured in the field. A consequence is the emergence of commercially available systems, which offer the capability of individual fit testing of hearing protectors in the field to control the attenuation actually received by the wearer. The purpose of this paper is to assess the suitability of these systems. Three commercially available systems dedicated to earplugs were used under laboratory conditions to assess the performance of pre-formed, foam or custom-molded earplugs for at least 20 test subjects. Results were compared with REAT attenuations for the same group of subjects. Two of these systems ensure mean attenuations close to benchmark values and individual comparisons are acceptable for these systems, although discrepancies with respect to benchmark values can be wide. These systems can therefore be used to validate a choice of hearing protection as long as a large but acceptable safety margin is considered. They are also quick and easy to use, and can contribute to worker training and motivation.

Electronic amplitude-sensitive earmuffs (EASEs) are hearing protectors designed to provide electroacoustic restoration of ambient sounds at low levels, progressively reduced as the ambient level increases. No standardized procedure is available, at the present time, for assessing the attenuation given by such protectors, at different ambient sound levels. Several possible methods have been examined. The microphone-in-real-ear (MIRE) technique appears interesting but still difficult to be used as a ‘routine’ method. The alternative procedure proposed here allows measuring of the EASEs attenuations on a standardized acoustic test fixture (ATF), at different ambient sound levels and in different frequency bands. The measures are then corrected, using a correction formula which introduces the real-ear attenuation in passive mode (electroacoustic restoration ‘off’). The relevance of this procedure has been checked on five models of EASEs. For a reference, attenuations were measured, in different frequency bands and at different ambient sound levels, by the MIRE technique. On the other hand they were measured by the proposed corrected-ATF procedure. The approximation of the real-ear attenuation by the present corrected ATF method is rather good for all five EASEs, particularly at the higher sound levels: corrected ATF values asymptotically tended to those found using MIRE for the passive mode (MIREPM). If, for practical purposes, MIREPM values were replaced by real-ear attenuation at threshold (REAT) values for the passive mode (REATPM) measured according to ISO 4869-1, the corrected ATF values will then approach those found by REATPM. The procedure proposed here, based on standardized measurements, allows efficient correction of measurements made on ATF, particularly at the higher noise levels, which are the most troublesome for hearing conservation purposes. It can provide an alternative to MIRE measurements for situations in which an alternative technique is preferred.

In some specially noisy environments, double protection (generally earplugs and earmuffs) can be needed for efficient worker audition protection. Some data has already been published on attenuation provided by several combinations of commercially available plugs and muffs. In the present study, data were collected from different laboratories and completed by our own tests. On the basis of these data, an empirical formula was derived, which expresses the global attenuation ENR 80 (according to ISO/DIS 8353) given by a couple of protectors from the global attenuation given by each of them. The accuracy of the assessments made by this formula is around ±4 dB (95% confidence interval) when considering all the protectors, and ±3 dB when considering those protectors having an attenuation higher than 15 dB. These confidence intervals have to be increased by 1 dB when considering ENR 90 instead of ENR 80 .