Ann. occup. Hyg., Vol. 47, No. 4, pp. 338, 2003
© 2003 British Occupational Hygiene Society
Published by Oxford University Press
Letters to the Editor |
Reply
Human Engineering Group, Department of Production and Systems, School of Engineering of the University of Minho, 4800-058 Guimaraes, Portugal
Received 6 January 2003;
We are grateful for the comments made on our article (Arezes and Miguel, 2002) in the letter by Edwards (2003). However, we think that we should clarify some aspects he refers to.
It was not the goal of the article to define the best type of hearing protection devices (HPDs), but rather to analyse the acceptability (represented by the time of use) of four specific devices. Therefore, none of our conclusions intended to imply some kind of superiority of a particular device.
We agree that there are now many studies that show that ‘real world’ performance is often considerably worse than the performance claimed by manufacturers. The differences widely found between ‘real world’ and manufacturers’ data (e.g. Berger et al., 1998) are essentially due to the HPD fit and, for earplugs, the method of insertion. Beyond these aspects, there are additional key parameters of performance, such as comfort, which can lead to workers’ dissatisfaction and, consequently, misuse of HPDs, which may alter drastically the attenuation afforded by the device. This particular aspect, the comfort during extended usage, is not, as far as we know, specifically included in the newly developed methods for testing HPDs.
We are aware of the attenuation variability, in particular of earplugs, but our study intended to emphasize the time of use of each tested device, which may represent its acceptability, but does not necessarily correlate with effectiveness.
In Table 11, we intended to illustrate and emphasize the implications of the time that workers do not use their HPDs and verify if this is correlated with the subjective feeling of comfort that each one expresses, rather than verifying the claimed attenuation. Based on this concept of acceptability, and sound pressure levels in workplaces, we made an estimation of the HPD attenuation, considering the reduction in attenuation by the non-use of HPDs during a certain period. This ‘real’ attenuation, as stated in the article, is exclusively based on the reduction of attenuation resulting from the reduction of time of use of the HPD. Moreover, the influence of some factors, such as the fit and the type of insertion, were minimized, as all workers were regular users of HPDs, and with previous training and motivation for the ‘correct’ use of the HPDs.
Finally, we are aware of some limitations of our study, namely those regarding the small number of tested devices. We agree with the expressed suggestion, as far as it concerns the extension of this work to a wider range of HPDs, and, accordingly, to test the robustness of the correlation between time of use and comfort index.
REFERENCES
Arezes PM, Miguel AS. (2002) Hearing protectors acceptability in noisy environments. Ann Occ Hyg; 46: 531–6.
Berger EH, Franks JR, Behar A et al. (1998) Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices, Part III. The validity of using subject-fit data. J Acoust Soc Am; 103: 665–72.[CrossRef][Medline]
Edwards J. (2003) The comfort and effectiveness of hearing protection devices. Ann Occup Hyg; 47: 337.
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