Measurement of Hearing Protection Devices Performance in the Workplace during Full-Shift Working Operations

HUGUES NE LISSE 1 MARC-ANDRE GAUDREAU 0 J ERO ME BOUTIN 1 JE RE MIE VOIX 0 FRE DE RIC LAVILLE 0 0 De partement de Ge nie Me canique , E 1 Service de la recherche, Institut de Recherche Robert-Sauve en Sante et Se curite au Travail (IRSST) , 505, Boulevard de Maisonneuve Ouest, Montre al, Que bec H3A 3C2 , Canada Objectives: The effectiveness of hearing protection devices (HPDs), when used in workplace conditions, has been shown over the years to be usually lower than the labeled values obtained under well-controlled laboratory conditions. Causes for such discrepancies have been listed and discussed by many authors. This study is an attempt to understand the issues in greater details and quantify some of these factors by looking at the performance of hearing protectors as a function of time during full work shift conditions. Methods: A non-invasive field microphone in the real ear (F-MIRE)-based method has been developed for measuring the effectiveness of different HPDs as a function of time in the workplace. Details of the test procedures, the equipment used, and the post-processing operations are presented and discussed. The methodology was developed in such a way that a complete time and frequency representation are possible. The system was used on a total of 24 workers in eight different companies. Work shifts of up to 9-h long were recorded. Various types of earmuffs and one type of molded earplugs were tested. Results: Attenuation data reported as a function of time showed, for most workers tested, considerable fluctuations over entire work shift periods. Parts of these fluctuations are attributed to variations in the low-frequency content in the noise (in particular for earmuffs) as well as poor insertion and/or fitting of earplugs. Lower performances than laboratory-based ones were once again observed for most cases tested but also, important left and right ear differences were obtained for many individuals. When reported as a function of frequency, the attenuation results suggested that the few approximations used to relate the measurements to subjective real-ear-attenuation-at-threshold (REAT) data were realistic. Conclusions: The use of individualized attenuation data and performance ratings for HPDs as well as a good knowledge of the ambient noise in the workplace are key ingredients when evaluating the performance of hearing protectors in field conditions. - INTRODUCTION Most regulations require employers to provide employees with proper protection against the effects of *Author to whom correspondence should be addressed. Tel: 1-514-288-1551 x 221; fax: 1-514-288-9399; e-mail: exposure to excessive noise levels. Protective measures may be provided either through engineering [e.g. noise reduction (NR) at the source] or through administrative controls (e.g. exposure controls). Unfortunately, these control measures often fail, for practical or economical reasons, to reduce the noise below the acceptable limits. Hearing protection devices (HPDs) have then to be offered by employers and used by the workers. The effective performance of HPDs not only depends on attenuation levels of the device but also on how well and how long it is worn. In terms of attenuation, HPDs are typically characterized by ratings such as the noise reduction rating (NRR) in the USA. These ratings are notably used to estimate the workers effective exposure when the HPDs are worn by subtracting the rating from a measured sound field level or exposure. Ratings calculations rely on attenuation measurements performed under well-controlled laboratory conditions prescribed in various standards [e.g. ANSI S3.19 (ANSI, 1974) or ISO 4869-1 (ISO, 1990)]. For obvious reasons, these laboratory conditions differ considerably from typical workplace environments. Consequences are that discrepancies between the labeled attenuation rating data and field measurement data have been observed and reported over the years (Behar, 1985; Casali and Park 1991; Berger et al., 1996; Giardano and Durkt, 1996; Neitzel and Seixas, 2005) for all types of HPDs. Multiple reasons have been put forward to explain the aforementioned discrepancies between the socalled laboratory and field data. Berger (1980) listed some of the causes of poor HPD sealing: (i) comfort, (ii) utilization, (iii) fit, (iv) compatibility, (v) readjustment, (vi) deterioration, and (vii) abuse. The lack of comfort, often cited as one of the main factor affecting the attenuation, may lead to a misuse or intermittent use of HPDs in order to increase their comfort or to improve communication. In a study over a population of printing workers (Morata et al., 2001), it was found that only 64% of the 124 workers in the study indicated that they were wearing their hearing protectors. Of this group, only 20% indicated wearing their HPDs all the time. The most significant reasons mentioned for not wearing the protectors included interference with communication, interference with job performance, comfort issues and self-perception of hearing condition. The intermittent or irregular use of an HPD is one of the most important factors influencing the effective protection obtained by a worker. As an example, using a 5 dB exchange rate, a worker wearing an HPD labeled at 25 dB would see his effective protection dropped to 17 dB if the HPD is not worn for 30 min over an 8-h shift. A good illustration can be found in a study held in the construction industry (Neitzel and Seixas, 2005). In particular, it is mentioned that when the measured HPD attenuation levels and use time data were combined, the effective protection afforded by HPDs was ,3 dB, a negligible amount given the high exposure levels associated with construction work. Comparable results (Lusk et al., 1998), obtained on 400 workers also from the construction industry, showed HPDs utilization rate ranging from 18 to 46% depending on the task performed. In a report from the Health & Safety Executive (HSE) in the UK (Hughson et al., 2002), the results on workers attitude toward hearing protection were obtained using questionnaires filled by 280 employees in 19 companies. Only 132 of these 280 employees said that they were using their HPD all the time, while only 112 were wearing theirs occasionally. Of the 180 employees, 30 said not wearing their HPD at all [which is in accordance with the results presented in another paper (Berger, 2000)]. As in the work of Morata et al. (2001) discussed previously, the main reasons presented to explain the misuse of hearing protectors are interference with communications, interference with job performance, comfort issues and self-perception of hearing condition. Additionally, the authors pointed out certain workers negative attitudes, which can have an influence on the usage of HPDs. In a study on circumaural protectors (Chung et al., 1983), personal noise dosimeters were used to measure exposures inside and outside of earmuffs and the authors concluded that a major (...truncated)