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Speech recognition in noise under hearing protection: A computational study of the combined effects of hearing loss and hearing protector attenuation
International Journal of Audiology
Abstract
Objective:
To investigate the effects of hearing protection on speech recognition in noise.
Design:
Computational study using a speech recognition model that was previously empirically validated.
Study sample:
Recognition scores were calculated in unprotected and protected conditions for four sets of hearing protector attenuation functions in two different noises, for three simulated hearing profiles illustrative of those anticipated in the noisy workplace.
Results:
For a normal-hearing profile, recognition scores were not sensitive to the slope of the attenuation function and the overall amount of noise reduction, but protected conditions provided a small but consistent 7-12% benefit compared to unprotected listening. For profiles simulating hearing loss, recognition scores were much more sensitive to the attenuation function. Substantial drops of 30% or more were found compared to unprotected listening in some conditions of steep attenuation slopes and large noise reductions. Attenuation functions modelled from real hearing protectors with nearly-flat attenuation yielded a benefit compared to unprotected listening for all hearing profiles studied. These findings were true in both noises.
Conclusions:
Limiting the slope of the hearing protector attenuation function and/or the overall amount of noise reduction is useful and warranted for workers with hearing loss to prevent adverse effects on speech recognition.
... Intelligibility improvement in high noise level is attributed to a release from cochlear overload [2] whereas the degradation in low noise levels is due to the fact that the noise level under the HPD is sufficiently low so that a greater amount of speech cues are attenuated below audibility. Using the speech recognition model developed by Giguère et al. [29], Giguère and Berger [34] show that the recognition of a shouted speech by a normal-hearing individual immerged in a loud noise environment (of 95-96 dB(A)) is always improved by the HPD. This positive effect is independent of the surrounding noise spectrum or of the HPD attenuation function. ...
... Contrary to normal-hearing individual (already covered in the section 3.1.3), Giguère and Berger [34] confirm that HPD use decreases the speech recognition for hearing impaired individuals since audible speech cues fall below the hearing threshold. They show that this decrement is worsen for (1) The hearing acuity of workers is mostly quantified through an audiogram which (i) measures the minimal sound pressure required for pure-tone detection and (ii) partly quantifies hair cell damage. ...
... This cochlear synaptopathy-driven functional deficit, also known as 'hidden hearing loss', is suspected to impair speech understanding in noisy environments. Speech-in-noise testing could thus be recommended in future comfort studies in addition to audiograms to have a more complete objective measurement of participants' hearing acuity [34,71]. ...
Structured abstract:Objective: This paper proposes a comprehensive literature review of past works addressing Hearing Protection Devices (HPDs) comfort with the aim of identifying the main sources of variability in comfort evaluation.
Design:
Literature review. Study samples: Documents were hand searched and Internet searched using 'PubMed', 'Web of Science', 'Google Scholar', 'ProQuest Dissertations and Theses Professional', 'Scopus' or 'Google' search engines. While comfort constructs and measurement methods are reviewed for both earplugs and earmuff HPD types, results and analyses are provided for earplugs only.
Results:
The literature shows that the multiple sources of the perceived comfort measurement variability are related to the complexity of the concept of comfort and to the various physical and psychosocial characteristics of the triad 'Environment/Person/Earplug' which differ from one study to the other.
Conclusions:
Considering the current state of knowledge and in order to decrease comfort measurements variability, it is advised to (i) use a multidimensional construct of comfort and derive a comfort index for each comfort dimensions, (ii) use exhaustive and valid questionnaires, (iii) quantify as much as triad characteristics as possible and use them as independent or control variables, and (iv) assess the quality of the earplug fitting and the attenuation efficiency.
... Intelligibility improvement in high noise level is attributed to a release from cochlear overload [2] whereas the degradation in low noise levels is due to the fact that the noise level under the HPD is sufficiently low so that a greater amount of speech cues are attenuated below audibility. Using the speech recognition model developed by Giguère et al. [29], Giguère and Berger [34] show that the recognition of a shouted speech by a normal-hearing individual immerged in a loud noise environment (of 95-96 dB(A)) is always improved by the HPD. This positive effect is independent of the surrounding noise spectrum or of the HPD attenuation function. ...
... Contrary to normal-hearing individual (already covered in the section 3.1.3), Giguère and Berger [34] confirm that HPD use decreases the speech recognition for hearing impaired individuals since audible speech cues fall below the hearing threshold. They show that this decrement is worsen for (1) The hearing acuity of workers is mostly quantified through an audiogram which (i) measures the minimal sound pressure required for pure-tone detection and (ii) partly quantifies hair cell damage. ...
... This cochlear synaptopathy-driven functional deficit, also known as 'hidden hearing loss', is suspected to impair speech understanding in noisy environments. Speech-in-noise testing could thus be recommended in future comfort studies in addition to audiograms to have a more complete objective measurement of participants' hearing acuity [34,71]. ...
Objective: This article presents a comprehensive literature review of past works addressing Hearing Protection Devices (HPD) comfort and to put them into perspective regarding a proposed holistic multidimensional construct of HPD comfort.
Design: Literature review.
Study samples: Documents were hand searched and Internet searched using “PubMed”, “Web of Science”, “Google Scholar”, “ProQuest Dissertations and Theses Professional”, “Scopus” or “Google” search engines. While comfort constructs and measurement methods are reviewed for both earplugs and earmuff types, results and analyses are provided for the earplug type only.
Results: This article proposed a multidimensional construct of HPD comfort based on four dimensions: physical, functional, acoustical and psychological. Seen through the prism of the proposed holistic construct of HPD comfort, the main comfort attributes of earplugs have been identified for each comfort dimension.
Conclusions: The observed lack of consensus on the definition of HPD comfort in the scientific community makes it difficult to prioritise the importance of comfort attributes yet necessary for future design of comfortable earplugs.
... However, most existing developments rely on architected microstructures, which are not tunable after fabrication; in fact, their properties cannot be modulated once the structures are realized [18]. In addition, the effectiveness of sound protectors comes from the sound attenuation they provide but depends on correct and continuous use throughout the exposure [19]. This last factor is significantly affected by the lack of comfort associated with the help of these protectors. ...
... This last factor is significantly affected by the lack of comfort associated with the help of these protectors. There is a significant acoustic discomfort in using these ear protectors, i.e., the comfort associated with the intelligibility of external sounds [19], which causes workers not to use them continuously. ...
This study aims to enhance and tune wave-propagation properties (Bandgaps) of periodic structures featuring magnetorheological elastomers (MREs). For this purpose, first, a basic model of periodic structures (square unit cell with cross-shaped arms), which does not possess noise filtering properties in the conventional configuration, is considered. A passive attenuation zone is then proposed by adding a cylindrical core mass to the center of the conventional geometry and changing arm angles, which permitted to have new bandgap areas. It was shown that better wave-filtering performance may be achieved by introducing a large radius of the cylindrical core as well as low negative cross-arm angles. The modified configuration of the unit cell was subsequently utilized as the basic model for the development of magnetoactive metamaterial using MRE capable of varying the bandgaps areas upon application of an external magnetic field. The finite element model of the proposed MRE-based periodic unit cell was developed, and the Bloch theorem was employed to systematically investigate the ability of the proposed adaptive periotic structure to attenuate low-frequency noise and vibration. Results show that the proposed MRE-based periodic wave filter can provide wide bandgap areas which can be adaptively changed and tuned using the applied magnetic field. The findings in this study can pro-vide an essential guide for the development of novel adaptive periodic structures to filter low-frequency noises in the wide frequency band.
... Differences at the endpoints can be converted to a "slope" measurement by expressing the endpoint differences as dB per Hz, dB per kHz, or dB per octave ratios, with dB per octave being the preferred convention. [26,27] Conversion to slope provides a more intuitive measurement of "flatness;" however, the simple differences may be more readily adopted in clinical settings. From a statistical perspective, the results are equivalent for dB difference, dB per kHz, and dB per octave ratios, as the slope is simply the dB difference normalized by the number of octaves or range of frequencies over which the difference occurred (4 octaves, or 3.75 kHz, for the endpoints of 0.25 and 4 kHz). ...
High-fidelity premolded earplugs (HiFi HPDs) are designed to provide relatively uniform attenuation across frequencies. The primary goal of this study was to verify the amount and flatness of individual user attenuation. HiFi HPD attenuation was measured using real-ear attenuation at threshold (REAT) measurements under circumaural earphones. Participants were 16 adults tested using commercial HiFi HPDs marketed for use at recreational music events and/or for use by musicians. There was significant individual variation in attenuation both within and across HiFi HPD brands. In addition to significant differences in achieved attenuation, there were significant differences in the uniformity of the attenuation. These data suggest verification of attenuation is important in musicians who are at risk for music-induced hearing disorders even when using "over-the-counter" uniform-fit HPDs.
... Higher attenuations were observed at higher frequencies, consistent with a previous study conducted by NIOSH. 10 As individuals with hearing losses have elevated absolute hearing thresholds, it is likely that high attenuation provided by HPDs will decrease the signal or speech below their audible limit, especially at high frequencies where the degree of hearing loss is often the most severe and the attenuation of HPDs the largest. 33 Giguere and Berger 33 measured the noise spectrum and the hearing status of workers and reported that the hypothetical worker with a moderately severe hearing loss largely suffered performance deficits from hearing protection. More studies on the utility of HPD with a flat attenuation response into preventing overprotection of workers with hearing loss are needed. ...
Background
The purpose of this study was twofold: (1) to measure the personal attenuation ratings (PARs) in Chinese workers wearing hearing protection devices (HPDs), to evaluate the effectiveness of the single number rating (SNR), the noise reduction rating (NRR), and the associated derated values of earplugs; and (2) to evaluate the effectiveness of one-on-one training along with earplug fit testing on PAR improvement.
Methods
Noise exposure measurements, one-on-one training, and fit tests to measure earplug attenuation were conducted at nine manufacturing facilities located in eastern China from 2016 to 2017. 503 workers participated in the study. Ninety-three percent were male. 199 workers were provided one-on-one training.
Results
Before training, 14% and 15% of the workers achieved the attenuation predicted by the manufacturer's SNR and NRR, 56% and 65% exceeded the derated SNR and NRR, respectively. Following one-on-one training, mean PAR improved significantly by 15 dB (p < 0.01); 26% of the workers achieved SNR and NRR, 79% and 91% met the associated derated values, respectively.
Conclusions
Labeled noise attenuation ratings and their derated values overestimated the actual level of attenuation among workers wearing HPDs. One-on-one training along with earplug fit testing contributed to improved PARs.
... Previous studies showed that the irregular use of HPDs in work environments can be due to lack of comfort, and interference in conversations. For employees, communication with colleagues and also hearing signals from the equipment and devices is of great importance [9,10,11]. Nelisse et al. determined that only 64% of employees in that environment used HPDs, and only 20% used them consistently during full shifts [12]. Hashimoto et al. revealed that a decrease in the noise reduction rates of hearing protectors cannot be considered as a factor for improving speech intelligibility [13]. ...
Objective: This study aimed to investigate the effect of hearing protection devices (HPDs) on speech intelligibility in Persian work environments. Three current earmuffs and three earplugs and one of the prototypes of molded earplug were tested on 15 male subjects which were randomly selected. The noise reduction of HPDs was measured based on the Real Ear Attenuation at Threshold (REAT) method. Speech intelligibility during using HPDs was determined based on the speech discrimination score (SDS) at two signal to noise (S/N) ratios (0 and +5). Data were analyzed using SPSS 22.
Results: The actual to nominal noise reduction rating values were from 47% to 84% for HPDs. At two S/N ratios, no significant differences were observed in speech intelligibility using HPDs (p >0.05). At S/N ratio=0, the speech intelligibility descriptively has been only improved by using common earmuffs up to 9.07 %. There was a significant difference up to 21.27% in speech intelligibility for proposed molded earplugs at S/N ratio=0 (p <0.05). Increase the HPDs' noise attenuation values lead to increase interference in the speech (p <0.05). The HPDs with the minimum required noise attenuation while maintaining acceptable speech intelligibility should be worn by employees exposed to medium noise levels.
... Previous studies showed that the irregular use of HPDs in work environments can be due to lack of comfort, and interference in conversations. For employees, communication with colleagues and also hearing signals from the equipment and devices is of great importance [9][10][11]. Nelisse et al. determined that only 64% of employees in that environment used HPDs, and only 20% used them consistently during full shifts [12]. ...
Objective
This study aimed to investigate the effect of hearing protection devices (HPDs) on speech intelligibility in Persian work environments. Three current earmuffs and three earplugs and one of the prototypes of molded earplug were tested on 15 male subjects which were randomly selected. The noise reduction of HPDs was measured based on the Real Ear Attenuation at Threshold (REAT) method. Speech intelligibility during using HPDs was determined based on the speech discrimination score (SDS) at two signal to noise (S/N) ratios (0 and + 5). Data were analyzed using SPSS 22.
Results
The actual to nominal noise reduction rating values were from 47 to 84% for HPDs. At two S/N ratios, no significant differences were observed in speech intelligibility using HPDs (p > 0.05). At S/N ratio = 0, the speech intelligibility descriptively has been only improved by using common earmuffs up to 9.07%. There was a significant difference up to 21.27% in speech intelligibility for proposed molded earplugs at S/N ratio = 0 (p < 0.05). Increasing the HPDs' noise attenuation values led to an increase in speech interference (p < 0.05). The HPDs with the minimum required noise attenuation while maintaining acceptable speech intelligibility should be worn by employees exposed to medium noise levels.
... Previous studies showed that the irregular use of HPDs in work environments can be due to lack of comfort, and interference in conversations. For employees, communication with colleagues and also hearing signals from the equipment and devices is of great importance [9,10,11]. Nelisse et al. determined that only 64% of employees in that environment used HPDs, and only 20% used them consistently during full shifts [12]. Hashimoto et al. revealed that a decrease in the noise reduction rates of hearing protectors cannot be considered as a factor for improving speech intelligibility [13]. ...
Objective: This study aimed to investigate the effect of hearing protection devices (HPDs) on speech intelligibility in Persian work environments. Three current earmuffs and three earplugs and one of the prototypes of molded earplug were tested on 15 male subjects which were randomly selected. The noise reduction of HPDs was measured based on the Real Ear Attenuation at Threshold (REAT) method. Speech intelligibility during using HPDs was determined based on the speech discrimination score (SDS) at two signal to noise (S/N) ratios (0 and +5). Data were analyzed using SPSS 22.
Results: The actual to nominal noise reduction rating values were from 47% to 84% for HPDs. At two S/N ratios, no significant differences were observed in speech intelligibility using HPDs (p >0.05). At S/N ratio=0, the speech intelligibility descriptively has been only improved by using common earmuffs up to 9.07 %. There was a significant difference up to 21.27% in speech intelligibility for proposed molded earplugs at S/N ratio=0 (p <0.05). Increasing the HPDs' noise attenuation values led to an increase in speech interference (p <0.05). The HPDs with the minimum required noise attenuation while maintaining acceptable speech intelligibility should be worn by employees exposed to medium noise levels.
... Previous studies showed that the irregular use of HPDs in work environments can be due to lack of comfort, and interference in conversations. For employees, communication with colleagues and also hearing signals from the equipment and devices is of great importance [9,10,11]. Nelisse et al. determined that only 64% of employees in that environment used HPDs, and only 20% used them consistently during full shifts [12]. Hasahimito et al. revealed that a decrease in the noise reduction rates of hearing protectors cannot be considered as a factor for improving speech intelligibility [13]. ...
Objective: This study aimed to investigate the effect of hearing protection devices (HPDs) on speech intelligibility in Persian work environments. Three current earmuffs and three earplugs and one of the prototypes of molded earplug were tested on 15 male subjects which were randomly selected. The noise reduction of HPDs was measured based on the Real Ear Attenuation at Threshold (REAT) method. Speech intelligibility during using HPDs was determined based on the speech discrimination score (SDS) at two signal to noise (S/N) ratios (0 and +5). Data were analyzed using SPSS 22.
Results: The actual to nominal noise reduction rating values were from 47% to 84% for HPDs. At two S/N ratios, no significant differences were observed in speech intelligibility using HPDs (p >0.05). However, at S/N ratio=0, the speech intelligibility descriptively has been improved by using common earmuffs up to 9.07 %. There was a significant difference up to 21.27% in speech intelligibility for proposed molded earplugs at S/N ratio=0 (p <0.05). Increase the HPDs' noise attenuation values lead to increase interference in the speech (p <0.05). The HPDs with the minimum required noise attenuation while maintaining acceptable speech ineligibility should be worn by employees exposed to medium noise levels.
... Previous studies showed that the irregular use of HPDs in work environments can be due to di culty in communication. For employees, communication with colleagues and also hearing signals from the equipment and devices is of great importance [9,10,11]. Nelisse et al. determined that only 64% of employees in that environment used HPDs, and only 20% used them consistently during full shifts. Some main reasons why employees did not use hearing protectors consistently were loss of their performance, lack of comfort, and interference in conversations with colleagues [12]. ...
Objective: This study aimed to investigate the effect of hearing protection devices (HPDs) on speech intelligibility in Persian work environments. Three current earmuffs and three earplugs and one of the prototypes of molded earplug were tested on 15 male subjects which were randomly selected. The noise reduction of HPDs was measured based on the Real Ear Attenuation at Threshold (REAT) method. Speech intelligibility during using HPDs was determined based on the speech discrimination score (SDS) at two signal to noise (S/N) ratios (0 and +5). Data were analyzed using SPSS, version 22.
Results: The actual to nominal noise reduction rating values were from 47% to 84% for HPDs. The earmuffs showed higher ratios of actual to nominal noise reduction compared with the earplugs. At two S/N ratios, no significant differences were observed in speech intelligibility using HPDs (p >0.05). However, at S/N ratio=0, the speech intelligibility descriptively has been improved by using common earmuffs up to 9.07 %. There was a significant difference up to 21.27% in speech intelligibility for proposed molded earplugs at S/N ratio=0(p <0.05). It is concluded that, if the trend of signal to noise ratio is positive, the HPDs will reduce the ability to understand speech.
... Previous studies showed that, the irregular use of HPDs in work environments can be due to di culty in communication. For employees, communication with colleagues and also hearing signals from the equipment and devices is of great importance [9,10,11]. Nelisse et al. determined that only 64% of employees in that environment used HPDs, and only 20% used them consistently during full shifts. Some the main reasons why employees did not use hearing protectors consistently were loss of their performance, lack of comfort, and interference in conversations with colleagues [12]. ...
Objective
This study aimed to investigate the effect of hearing protection devices (HPDs) on speech intelligibility in Persian work environments. Three current earmuffs and three earplugs and one of the prototype of molded earplug were tested on 15 male subjects which were randomly selected. The noise reduction of HPDs was measured based on the Real Ear attenuation at Threshold (REAT) method. Speech intelligibilities during using HPDs were determined based on the speech discrimination score (SDS). Data were analyzed using SPSS, version 22.
Results
The actual to nominal noise reduction rating values were from 47–84% for HPDs. The earmuffs show higher ratios of actual to nominal noise reduction compared with the earplugs. At two signal to noise ratios, no significant differences were observed in in speech intelligibility using HPDs (p > 0.05). However, at S/N = 0, the speech intelligibility descriptively has been improved by using common earmuffs up to 9.07%. There was a significant difference up to 21.27% in speech intelligibility for proposed molded earplugs at S/N = 0(p < 0.05). It is concluded that, if the trend of signal to noise ratio is positive, the HPDs will reduce the ability to understand speech.
... Electronic HPD products have significantly supplemented passive HPD products in recent years (Casali, 2010b,a); use of electronic HPD products may improve performance on some DRILCOM test elements (Robinson and Casali, 2003;Casali et al., 2009;Talcott et al., 2012;Clasing and Casali, 2014). Several long-term systematic efforts have sought to understand how passive HPD use (Lindeman, 1976;Chung and Gannon, 1979;Abel et al., 1980;Abel et al., 1982;Pekkarinen et al., 1990) and use of electronic HPD technology (Abel et al., 1991;Arlinger, 1992;Gower and Casali, 1994;Bockstael et al., 2011;Norin et al., 2011;Brown et al., 2015;Giguère et al., 2015;Hiselius et al., 2015;Giguère and Berger, 2016) impact speech understanding. Sound localization acuity during use of HPDs continues to be a topic of interest (Brungart et al., 2004;Brown et al., 2015;Joubaud et al., 2017), and the detection and identification of non-speech signals (Clasing and Casali, 2014) is of interest. ...
Animal models have been used to gain insight into the risk of noise-induced hearing loss (NIHL) and its potential prevention using investigational new drug agents. A number of compounds have yielded benefit in pre-clinical (animal) models. However, the acute traumatic injury models commonly used in pre-clinical testing are fundamentally different from the chronic and repeated exposures experienced by many human populations. Diverse populations that are potentially at risk and could be considered for enrollment in clinical studies include service members, workers exposed to occupational noise, musicians and other performing artists, and children and young adults exposed to non-occupational (including recreational) noise. Both animal models and clinical populations were discussed in this special issue, followed by discussion of individual variation in vulnerability to NIHL. In this final contribution, study design considerations for NIHL otoprotection in pre-clinical and clinical testing are integrated and broadly discussed with evidence-based guidance offered where possible, drawing on the contributions to this special issue as well as other existing literature. The overarching goals of this final paper are to (1) review and summarize key information across contributions and (2) synthesize information to facilitate successful translation of otoprotective drugs from animal models into human application.
... Electronic HPD products have significantly supplemented passive HPD products in recent years (Casali, 2010b,a); use of electronic HPD products may improve performance on some DRILCOM test elements (Robinson and Casali, 2003;Casali et al., 2009;Talcott et al., 2012;Clasing and Casali, 2014). Several long-term systematic efforts have sought to understand how passive HPD use (Lindeman, 1976;Chung and Gannon, 1979;Abel et al., 1980;Abel et al., 1982;Pekkarinen et al., 1990) and use of electronic HPD technology (Abel et al., 1991;Arlinger, 1992;Gower and Casali, 1994;Bockstael et al., 2011;Norin et al., 2011;Brown et al., 2015;Giguère et al., 2015;Hiselius et al., 2015;Giguère and Berger, 2016) impact speech understanding. Sound localization acuity during use of HPDs continues to be a topic of interest (Brungart et al., 2004;Brown et al., 2015;Joubaud et al., 2017), and the detection and identification of non-speech signals (Clasing and Casali, 2014) is of interest. ...
This article reviews the research for the special issue of the Journal of the Acoustical Society of America, Noise-Induced Hearing Loss: Translating Risk from Animal Models to Real-World Environments. It synthesizes the information to facilitate translation of the research into otoprotective drugs from animal models to humans applications.
... For employees with normal hearing, wearing HPDs in a noisy environment does not generally interfere with verbal communication, perception of warning signals, or monitoring equipment sounds. In contrast, individuals with hearing loss experience reduced perception of speech and signals while wearing typical HPDs [23]. Hearing-impaired workers may minimize communication interference by using HPDs with less attenuation, especially at higher frequencies, thus improving both safety and willingness of workers to wear their HPDs consistently. ...
Noise-induced hearing loss (NIHL) is second only to presbycusis, age-related hearing loss, as a cause of hearing impairment; yet, it is preventable. This commentary summarizes the effects of noise on hearing, relevant workplace regulations, and ways to minimize excessive noise's deleterious impact on individuals' quality of life on and off the job.
Objectives:
This study utilized personal noise measurements and fit-testing to evaluate the association between noise exposures and personal attenuation rating (PAR) values among participating workers, and second, to compare the attenuated exposure levels received by the workers and the British Standards Institute's recommended noise exposure range of 70 to 80 dBA.
Design:
We measured hearing protection device (HPD) attenuation among a sample of 91 workers at 2 US metal manufacturing facilities, through performance of personal noise dosimetry measurements and HPD fit-testing over multiple work shifts. We compared this testing with participant questionnaires and annual audiometric hearing threshold results.
Results:
The average 8-hr time-weighted average noise exposures for study participants was 79.8 dBA (SD = 7.0 dBA), and the average PAR from fit-testing was 20.1 dB (±6.7 dB). While differences existed between sites, 84% of the 251 PAR measurements resulted in effective protection levels below the recommended 70 dBA (indicating overprotection), while workers were underprotected (i.e., effective exposures >80 dBA) during <1% of monitored shifts. Our results also demonstrated a significant positive relationship between measured noise exposure and PAR among non-custom-molded plug users (p = 0.04). Non-custom-molded plug wearers also showed a significant increase in PAR by sequential fit-test interaction (p = 0.01), where on average, subsequent fit-testing resulted in increasingly higher HPD attenuation. Workers at site 1 showed higher PARs. PARs were significantly related to race, even when adjusting for site location. While age, hearing threshold level, task, and self-reported tinnitus showed no significant effect on individual PAR in an unadjusted model, site, race, and sand- or water-blasting activities were significant predictors in adjusted models. Within-worker variability in time-weighted averages and PARs across repeated measurements was substantially lower than variability between workers.
Conclusions:
Careful selection of HPDs is necessary to minimize instances of overprotection to workers in low and moderate occupational noise environments. The use of fit-testing in hearing conservation programs to evaluate PAR is recommended to avoid overprotection from noise exposure while also minimizing instances of under-attenuation.
The ability to communicate verbally when wearing hearing protectors is an important aspect to consider for compliance in the use of these devices as well as for safety and operational efficiency in the workplace. Speech recognition with hearing protectors is influenced by many factors such as the overall amount of noise reduction, the slope of the attenuation-frequency function and the presence of hearing loss [Giguère and Berger, Int. J. Audiol. 55, S30-S40 (2016)]. Interestingly, results from subjective and modelling studies sometimes show a benefit of using passive hearing protectors on speech recognition in noise compared to unprotected listening, especially with normal-hearing individuals in high-noise levels. The purpose of this modeling study is to further explore the conditions promoting such a facilitative effect of hearing protectors on speech recognition, with a particular attention to the noise level in the environment and the hearing status of the user. This information is important to better guide the selection of the most appropriate hearing protection device, given the characteristics of the user and workplace noise.
A speech intelligibility model was developed and validated for use in workplace environments with hazardous noise levels that require the use of hearing protection devices (HPDs). Two speech perception studies were carried out in laboratory simulations of eight workplace noise environments. The first experiment (n = 32 normal-hearing individuals) was used to develop a general model for speech intelligibility that can be tuned to the specific characteristics of the noise. The second experiment (n = 35) was used to validate the general model for use with listeners covering a wide range of hearing profiles (up to severe hearing loss) and wearing HPDs (earplugs or earmuffs). The model took into account the characteristics of the noise, the signal-to-noise ratio (SNR), the attenuation of the hearing protector, and the hearing status of the listener. Good prediction of speech intelligibility scores in noise with HPDs required the use of correction factors to deal with both audibility (threshold) and distortion (supra threshold) effects arising from hearing loss. Correction factors due to audibility effects were computed from the Speech Intelligibility Index and the pure-tone audiogram. Correction factors due to distortion effects were based on the Hearing-in-Noise Test.
Few studies document the exact conditions when flat/uniform hearing protectors can be beneficial in the noisy workplace. This modeling study reports on the interaction between the user’s hearing loss profile and the shape and amount of the attenuation function on sound detection thresholds in noise. For normal-hearing users, detection thresholds are found to be hardly affected by use of hearing protectors, even in extreme conditions of low-frequency noise and steeply sloping attenuation functions. With aging and noise-induced hearing loss, sound detection above about 2000 Hz becomes progressively more sensitive to the slope of the attenuation function as well as to the overall protected level achieved. Shallower slopes may be warranted for users with hearing loss to limit the upward spread of masking in low-frequency noise, while controlling the total amount of attenuation at high frequencies prevents excessive elevation of absolute thresholds. Decisions regarding hearing protector selection also entail consideration of the principal auditory tasks that are anticipated and the important sounds to which a worker may need to attend.
Flat-response devices are a class of hearing protectors with nearly uniform attenuation across frequency. These devices can protect the individual wearer while maintaining the spectral balance of the surrounding sounds. This is typically achieved by reducing the muffling effect of conventional hearing protectors which provide larger attenuation at higher than lower frequencies, especially with earmuffs. Flat hearing protectors are often recommended when good speech communication or sound perception is essential, especially for wearers with high-frequency hearing loss, to maintain audibility at all frequencies. However, while flat-response devices are described in some acoustical standards, the tolerance limits for the definition of flatness are largely unspecified and relatively little is known on the exact conditions when such devices can be beneficial. The purpose of this study is to gain insight into the interaction between the spectrum of the noise, the shape of the attenuation-frequency response, and the hearing loss configuration on detection thresholds using a psychoacoustic model of sound detection in noise.
The gold standard in measuring hearing protector attenuation since the late 1950s has been real-ear attenuation at threshold (REAT). Though well understood and standardized both in the U. S. (ANSI S3.19-1974 and ANSI S12.6-2008) and internationally (ISO 4869-1:1990), and known to provide valid and reliable estimates of protection for the test panel being evaluated, an area that is not clearly defined is the variability of the test measurements within a given laboratory. The test standards do provide estimates of uncertainty, both within and between laboratories, based on limited test data and interlaboratory studies, but thus far no published within-laboratory data over numerous tests and years have been available to provide empirical support for variability statements. This paper provides information from a one-of-a-kind database from a single laboratory that has conducted nearly 2500 studies over a period of 35 years in a single facility, managed by the same director (the lead author). Repeat test data on a controlled set of samples of a foam earplug, a premolded earplug, and two different earmuffs, with one of the data sets comprising 25 repeat tests over that 35-year period, will be used to demonstrate the inherent variability of this type of human-subject testing.
Objectives:
To determine the effects of different control settings of level-dependent hearing protectors on speech recognition performance in interaction with hearing loss.
Design:
Controlled laboratory experiment with two level-dependent devices (Peltor® PowerCom Plus™ and Nacre QuietPro®) in two military noises.
Study sample:
Word recognition scores were collected in protected and unprotected conditions for 45 participants grouped into four hearing profile categories ranging from within normal limits to moderate-to-severe hearing loss.
Results:
When the level-dependent mode was switched off to simulate conventional hearing protection, there were large differences across hearing profile categories regarding the effects of wearing the devices on speech recognition in noise; participants with normal hearing showed little effect while participants in the most hearing-impaired category showed large decrements in scores compared to unprotected listening. Activating the level-dependent mode of the devices produced large speech recognition benefits over the passive mode at both low and high gain pass-through settings. The category of participants with the most impaired hearing benefitted the most from the level-dependent mode.
Conclusions:
The findings indicate that level-dependent hearing protection circuitry can provide substantial benefits in speech recognition performance in noise, compared to conventional passive protection, for individuals covering a wide range of hearing losses.
A technology of backup alarms based on the use of a broadband signal has recently gained popularity in many countries. In this study, the performance of this broadband technology is compared to that of a conventional tonal alarm and a multi-tone alarm from a worker-safety standpoint. Field measurements of sound pressure level patterns behind heavy vehicles were performed in real work environments and psychoacoustic measurements (sound detection thresholds, equal loudness, perceived urgency and sound localization) were carried out in the laboratory with human subjects. Compared with the conventional tonal alarm, the broadband alarm generates a much more uniform sound field behind vehicles, is easier to localize in space and is judged slighter louder at representative alarm levels. Slight advantages were found with the tonal alarm for sound detection and for perceived urgency at low levels, but these benefits observed in laboratory conditions would not overcome the detrimental effects associated with the large and abrupt variations in sound pressure levels (up to 15-20 dB within short distances) observed in the field behind vehicles for this alarm, which are significantly higher than those obtained with the broadband alarm. Performance with the multi-tone alarm generally fell between that of the tonal and broadband alarms on most measures.
Although a great many brass players, and trumpet players in particular, successfully use high-fidelity earplugs, others report problems with their use. This article discusses factors that may discourage a brass player from using hearing protection: These include (a) a lack of acclimatization time; (b) a loss of "fortissimo blare" from the aural distortion generated by the 110- to 120-dB SPL produced at the open ear with fortissimo playing; (c) a shallow earmold seal, leading to a large occlusion effect; (d) a poor seal combined with incorrect acoustic mass in the sound channel; and (e) hearing loss where many harmonic overtones of even moderately loud playing may become inaudible with earplugs to a lifelong trumpet player with high-frequency hearing loss. The limitations imposed by each of these can usually be overcome with modifications of the hearing protection device (HPD) or with acclimatization time, allowing a lifetime of playing without the all-too-common "musicians' hearing loss" and/or tinnitus. A review of these factors helps to delineate some of the perceptual issues that musicians may have with any change in the spectrum of their instrument-whether it is related to attenuation or amplification.
Noise attenuation by linear hearing protection devices (HPDs) is considered to be independent of the environmental noise level. Linearity of HPDs is one of the basic assumptions underlying the Real Ear Attenuation at the Threshold (REAT) method of HPD testing, which utilizes quiet conditions. However, non-linear growth of masking at high intensity levels may result in the effects of HPDs on detection of speech and warning signals being different from those at high noise levels. The purpose of this study was to determine if the non-linear growth of masking can affect detection of warble signals by persons using HPDs in wideband noise presented at the 100 dB(A) level. Audiometric thresholds of hearing of 10 listeners were measured under four experimental conditions: (1) noise off, HPDs off (condition C1); (2) noise off, HPDs on (condition C2); (3) noise on, HPDs on (condition C3); and (4) noise on, HPDs off (condition C4). The results of this study indicate that detection of signals by persons using HPDs in noise < 100 dB(A) can be well predicted from noise attenuation characteristics of HPDs measured in quiet without the need for a correction factor accommodating non-linear growth of masking. This finding has implications for predicting the audibility of warning signals in noise by persons wearing HPDs.
People working in noisy environments often complain of difficulty communicating when they wear hearing protection. It was hypothesized that part of the workers' communication difficulties stem from changes in speech production that occur when hearing protectors are worn. To address this possibility, overall and one-third-octave-band SPL measurements were obtained for 16 men and 16 women as they produced connected speech while wearing foam, flange, or no earplugs (open ears) in quiet and in pink noise at 60, 70, 80, 90, and 100 dB SPL. The attenuation and the occlusion effect produced by the earplugs were measured. The Speech Intelligibility Index (SII) was also calculated for each condition. The talkers produced lower overall speech levels, speech-to-noise ratios, and SII values, and less high-frequency speech energy, when they wore earplugs compared with the open-ear condition. Small differences in the speech measures between the talkers wearing foam and flange earplugs were observed. Overall, the results of the study indicate that talkers wearing earplugs (and consequently their listeners) are at a disadvantage when communicating in noise.
A psychoacoustic model is presented to facilitate the installation of acoustic warning devices in noisy settings, reflecting a major upgrade of a former tool, Detectsound. The model can be used to estimate the optimal level and spectrum of acoustic warning signals based on the noise field in the workplace, the hearing status of workers, and the attenuation provided by hearing protectors. The new version can be applied to a wider range of situations. Analyses can now be conducted to meet the functional requirements for a specific worker or to suit the needs for a group of co-workers sharing a work area. Computation of optimal warning signals can also be made from estimated hearing parameters based on the worker age, gender, and level and duration of noise exposure. The results of a laboratory validation study showed that the mean error in estimating detection thresholds for normal hearing individuals is typically within +/-1 dB with a standard deviation of less than 2.5 dB in white noise or continuous noise fields. The model tends to yield slightly overestimated warning signal detection thresholds in fluctuating noises. Proper application of the tool also requires consideration of the variability in estimating noise levels, hearing status, and hearing protector attenuation under field conditions to ensure that acoustic warning signals are sufficiently loud and well adjusted in practice.
Objective:
Speech production in noise with varying talker-to-listener distance has been well studied for the open ear condition. However, occluding the ear canal can affect the auditory feedback and cause deviations from the models presented for the open-ear condition. Communication is a main concern for people wearing hearing protection devices (HPD). Although practical, radio communication is cumbersome, as it does not distinguish designated receivers. A smarter radio communication protocol must be developed to alleviate this problem. Thus, it is necessary to model speech production in noise while wearing HPDs. Such a model opens the door to radio communication systems that distinguish receivers and offer more efficient communication between persons wearing HPDs.
Design:
This paper presents the results of a pilot study aimed to investigate the effects of occluding the ear on changes in voice level and fundamental frequency in noise and with varying talker-to-listener distance.
Study sample:
Twelve participants with a mean age of 28 participated in this study.
Results:
Compared to existing data, results show a trend similar to the open ear condition with the exception of the occluded quiet condition.
Conclusions:
This implies that a model can be developed to better understand speech production for the occluded ear.
Augmentations or enhancements to conventional HPDs, that is, those which attenuate noise strictly through static, passive means, are generally delineated into passive (non-electronic) and active (powered electronic) designs. While powered electronic augmentations are reviewed in Casali 1 (a parallel paper elsewhere in this issue), passive augmentations are represented by mechanical networks to achieve flat-by-frequency attenuation; level-dependent leakage pathways that house acoustically-variable occluders to yield minimal attenuation during quiet periods but sharply increasing attenuation upon intense noise bursts (such as gunfire); quarter-wave resonance ducts to bolster attenuation of specific frequencies; selectable cartridges or valves that enable passive attenuation to be adjusted for specific exposure needs; and dynamically adjustable-fit devices that provide adjustment features to enable personalized fit to the user as well as some degree of attenuation control. Intended benefits of passive augmented HPDs (akin to those of active devices as well) include (1) more natural hearing for the user, (2) improved speech communications and signal detection, (3) reduced noise-induced annoyance, (4) improved military tactics, stealth maintenance and gunfire protection, and (5) provision of protection that is tailored for the user's needs, noise exposure, and/or job requirements. This paper provides a technical overview of passive augmented HPDs that were available or have been prototyped circa early-2010. In cases where no empirical research results on the passive augmentations and their performance were available in the research literature, this review relied on patents, corporate literature, and/or the author's experience. For certain augmentations, a limited amount of empirical, operational performance research was available and it is covered herein. Finally, in view that at the juncture of this article the United States (U.S.) Environmental Protection Agency (EPA) was in the process of promulgating a comprehensive new federal law to govern the testing and labeling of hearing protectors of various types, those elements of the proposed law that pertain only to specific passive augmentation technologies are mentioned herein, 2 along with references to relevant standards on hearing protector attenuation testing.
Augmented or enhanced hearing protection devices (HPDs), as contrasted with conventional HPDs, which attenuate noise strictly through static, passive means, have proliferated in the past decade. These advancements in HPDs are generally delineated into passive (non-powered) and active (powered electronic) designs. While passive augmentations are reviewed in a parallel paper elsewhere in this issue, 1 active augmentations include various analog and digital circuits for achieving electronic phase cancellation of noise; electronic modulated sound transmission circuits, which amplify a passband of ambient sound and transmit it through the HPD (ceasing to amplify at a predetermined noise level); and tactical communications and protection systems (TCAPS), which may include any of the aforementioned electronic elements plus microphone/receiver communications elements. The intended benefits of electronic augmented HPDs, some of which are realized in practice and others not, include more natural hearing for the user, improved speech communications and signal detection, reduced noise-induced annoyance, improved military tactics, stealth and gunfire protection, and provision of protection that is somewhat tailored for the user's needs, noise exposure, and/or job requirements. This paper provides a technical overview of active augmented HPDs that were available or have been prototyped circa early-2010. In some cases, no empirical research on the augmentations and their performance was available in the research literature; in these cases, this review relied on patents, corporate literature, and/or the author's experience. For other technologies, a limited amount of empirical, operational performance research was available and it is covered herein. Finally, in view that at the juncture of this article the United States (U.S.) Environmental Protection Agency (EPA) was in the process of promulgating a comprehensive new federal law to govern the testing and labeling of hearing protectors of various types, those elements of the proposed law pertaining to specific augmentation technologies are mentioned herein, 2 along with that proposed law's cited ANSI standards, as well as ISO standards that address hearing protector attenuation testing.
This research investigated the effect of ear protectors on the intelligibility of speech in noise. Listeners with normal hearing, high‐frequency, and flat loss were tested. Half the subjects in each group were fluent in English and half poorly conversant. Taped lists of 25 words were presented free field under conditions defined by the speech‐to‐noise ratio, spectrum of noise background, and presence of ear protection. The results showed that intelligibility decreased with speech‐to‐noise ratio and was poorer in crowd noise than in white noise. The protector had no effect for the normal listener, but caused a substantial decrement in those with impairment. In all groups nonfluency contributed an additional loss of 10% to 20%. Significant differences in performance were noted for different muff and plug types.
The mission of the National Institute for Occupational Safety and Health (NIOSH) is to generate new knowledge in the field of occupational safety and health and to transfer that knowledge into practice for the betterment of workers. Since its establishment in 1970, NIOSH has provided national and world leadership in efforts to prevent occupational hearing loss. In 1996, NIOSH established the National Occupational Research Agenda (NORA). Because occupational hearing loss is one of the most common occupational illnesses among American workers, it was identified as a priority research area, and a NORA Hearing Loss Team was established. The NORA Hearing Loss Team was composed of representatives from industry, academia, labor, professional organizations, and other governmental agencies. The team was tasked with developing a national research agenda for the prevention of occupational hearing loss. Each team member contributed to the original draft, which continued to evolve over time. The current document represents the culmination of several years of deliberation and revision with the goal of identifying needed research to prevent occupational hearing loss. This is Part 1 of the document, outlining research needs on the mechanisms and consequences of occupational exposure to noise and other ototoxicants.
Musicians need to hear well, and safely, when they play. Standard industrial-type hearing protectors muffle sound and frequently provide too much attenuation and occlusion to be acceptable for musicians. This article describes the selection of high-fidelity earplugs for musicians. Musicians experience significant sound exposures, and according to Chasin, 1 most will develop some degree of music-induced hearing loss. Other professionals in the music industry (eg, audio engineers, recording engineers, managers, disk jockeys, etc) also experience significant sound exposures, and they are also at risk for cochlear damage and hearing loss. Perhaps even more damaging than hearing loss are the secondary effects that often accompany it or occur in isolation: tinnitus, diplacusis, and hyperacusis. Most professionals involved in hearing care are familiar with tinnitus, the perception of noise (ringing, etc) in the ears. However, fewer of us may routinely recognize diplacusis, a pathological matching of frequency and pitch that ultimately results in some notes sounding flat; due to this, diplacusis can be career-threatening to those in the music industry. Hyperacusis, a reduced tolerance of suprathreshold sound, is also career-threatening to those in the music industry. In the hyperacousic ear, sounds that are easily tolerated by most people (eg, laughter, a telephone ring, or live music) are uncomfortable or intolerable. There are no known cures for noise-induced hearing loss (NIHL), tinnitus, diplacusis, or hyperacusis; early identification of auditory dysfunction and prevention of cochlear damage is the only viable treatment at this time.
The author discusses the refusal of employees to wear hearing protectors, reasons for removal of hearing protectors, and criteria for hearing protectors with good signals and audibility in the German industry. Industrial practitioners observe that employees refuse to wear hearing protectors as they are not comfortable because it impede communication among colleagues. The conditions for the removal of hearing protectors are humidity, informative sounds in the working process, warning signals, speech communication, and localization of the noise source. BIA, Institute of Occupational Safety, Germany, explored several options using its database, which includes uniform sound attenuation characteristics over frequency ranges.
The authors investigated the manner in which noise, as well as the wearing of ear protectors, hinder verbal communication. For this purpose, 180 speaker-hearer couples, on whom the wearing of ear protection was varied systematically, were exposed to various levels of noise. The speaker read various texts to the hearer who was asked to repeat what he understood. The main results of the investigation were the following: when wearing ear protectors, subjects speak an average of 4 db lower; language is understood less by about 40 percent.
Member States of the European Economic Community are required to introduce Regulations which, in part, make the wearing of hearing protection mandatory under certain noise exposure conditions. Provisions are also to be introduced which can take into account possible difficulties that the wearer may have in the perception of warning sounds. This paper reviews the evidence that is relevant to any expert appraisal which formed part of a scheme of exemptions from the otherwise mandatory requirement.The evidence indicates that, when worn by people with normal hearing, the protectors will not in general impair the perception of appropriately selected alarm sounds. However, specific conditions are identified where the hearing protectors may reduce the effectiveness of some warning sounds, in particular for those machinery sounds which are associated with potential danger and for those people with an existing noise-induced hearing loss. It is recommended that the design of warning systems and the development of work practices should take account of possible failures in the perception of auditory warnings.
IntroductionTypes of Hearing Protection DevicesDispensing, Fitting, use, and CareSound Pathways to the Occluded EarMeasuring AttenuationAttenuation Characteristics of Hearing Protection DevicesUsing Attenuation Data to Estimate ProtectionEffects of HPDs on Auditory Perception and IntelligibilityHPDs with Special FeaturesHPD Standards, Regulations, and Government ListingsReferences
Abstract: Occupational hearing conservation regulations neither address issues related to speech intelligibility in noise for normal-hearing or hearing-impaired workers, nor do the regulations comment on the safety of hearing aid use by hearing-impaired workers. Do certain types of hearing protection devices (HPDs) allow for better speech intelligibility than others? Would use of hearing aids with earmuffs provide better speech intelligibility for hearing-impaired workers? Is this method of accommodation safe? To answer these questions, a method for evaluating speech intelligibility with HPDs was developed through a series of pilot tests. The test method allows for evaluation of both normal-hearing and hearing-impaired listeners. Speech intelligibility for normal-hearing listeners who wore uniformly attenuating earmuffs was found to be significantly better than for the same listeners who wore conventional earmuffs. Hearing-impaired listeners were tested with each type of earmuff and while wearing their own hearing aids in combination with each earmuff. Unlike the normal hearing listener group, the hearing-impaired listener group did not exhibit better speech intelligibility with the uniformly attenuating earmuffs than with the conventional earmuffs. However, earmuffs worn in combination with hearing aids allowed for significantly better speech intelligibility than with either earmuff alone. To determine the safety of hearing aid use under earmuffs, a model was developed to predict occupational noise exposure for the aided-protected worker. Data from real ear measures with an acoustic mannequin was found to be in agreement with model predictions. Title from first page of PDF file. Document formatted into pages; contains xvi, 162 p. Includes abstract and vita. Advisor: Lawrence L. Feth, Dept. of Speech and Hearing Science. Thesis (Ph. D.)--Ohio State University, 2002. Includes bibliographical references (p. 141-148). System requirements: World Wide Web browser and PDF viewer.
The German transport and personal protective equipment (PPE) technical committees of the German Social Accident Insurance have laid down criteria, which have since become established, for hearing protectors to be used in railway systems and road traffic in Germany: only hearing protectors which do not significantly impair the audibility of auditory warning signals may be used. In addition, the Institute for Occupational Safety and Health of the German Social Accident Insurance (BGIA) has proposed a simple criterion for the selection of hearing protectors for workplaces outside railway systems and road traffic which perform well with regard to signal audibility (general), speech intelligibility, and perception of informative operating sound (AIP). This criterion is based upon the research carried out in the field of signal audibility in railway systems and road traffic and upon an additional study. It has been established by the German PPE technical committee and is presented here.
On theoretical grounds, it is usually assumed that the use of hearing protectors in a noisy working environment has no influence upon speech intelligibility - in fact, may even increase it. In practice, however, people often do not wear hearing protectors, since these are widely believed to reduce speech intelligibility. In the present article, a description is given of an investigation, carried out among 537 subjects, into the influence of hearing protectors upon the speech intelligibility of people suffering from noise-induced hearing loss. From this analysis, it has become clear that the use of ear-muffs only leads to an improvement in speech intelligibility in persons who, according to their pure-tone audiogram, suffer from relatively small hearing losses. In general, it may be said that an increase in the severity of hearing losses will result in a reduced speech intelligibility.
The present study examined the application of the articulation index (AI) as a predictor of the speech-recognition performance of normal and hearing-impaired listeners with and without hearing protection. The speech-recognition scores of 12 normal and 12 hearing-impaired subjects were measured for a wide range of conditions designed to be representative of those in the workplace. Conditions included testing in quiet, in two types of background noise (white versus speech spectrum), at three signal-to-noise ratios (+ 5, 0, - 5 dB), and in three conditions of protection (unprotected, earplugs, earmuffs). The mean results for all 21 listening conditions and both groups of subjects were accurately described by the AI. Moreover, a single transfer-function relating performance to the AI could describe all the data from both groups.
The detection of one-third octave signals superimposed on backgrounds of steady-state and intermittent industrial noise of 84 dBA was investigated for observers with normal hearing or moderate to severe noise-induced hearing loss (NIHL). Variables included age, noise exposure history, configuration of the audiogram and the wearing of insert hearing protectors. Detection thresholds were obtained binaurally over headphones using a two- interval forced-choice procedure. For unprotected listening all observers showed a masked threshold of about 80 dBA for a one-third octave band cented at 3.15 kHz. Neither variation in noise exposure history nor configuration of the audiogram were significant factors. Using insert protectors in noise, observers with normal hearing showed an advantage on average of 3 dB. Those with NIHL gave masked detection thresholds greater than 100 dBA. Detection of a one-third octave band centred at 1 kHz by hearing-impaired observers with mild to moderate loss at 1 kHz was similar to that for normal observers. A model of the detection process was developed and evaluated.
This research investigated the effect of car protectors on the intelligibility of speech in noise. Listeners with normal hearing, high-frequency, and flat loss were tested. Half the subjects in each group were fluent in English and half-poorly conversant. Taped lists of 25 words were presented free field under conditions defined by the speech-to-noise ratio, spectrum of noise background, and presence of ear protection. The results showed that intelligibility decreased with speech-to-noise ratio and was poorer in crowd noise than in white noise. The protector had no effect for the normal listener, but caused a substantial decrement in those with impairment. In all groups nonfluency contributed an additional loss of 10% to 20%. Significant differences in performance were noted for different muff and plug types.
The question of whether or not an individual suffering from a hearing loss is capable of hearing an auditory alarm or warning is an extremely important industrial safety issue. The ISO Standard that addresses auditory warnings for workplaces requires that any auditory alarm or warning be audible to all individuals in the workplace including those suffering from a hearing loss and/or wearing hearing protection devices (HPDs). Research was undertaken to determine how the ability to detect an alarm or warning signal changed for individuals with normal hearing and two levels of hearing loss as the levels of masking noise and alarm were manipulated. Pink noise was used as the masker and a heavy-equipment reverse alarm was used as the signal. The rating method paradigm of signal detection theory was used as the experimental procedure to separate the subjects' absolute sensitivities to the alarm from their individual criteria for deciding to respond in an affirmative manner. Results indicated that even at a fairly low signal-to-noise ratio (0 dB), subjects with a substantial hearing loss [a pure-tone average (PTA) hearing level of 45-50 dBHL in both ears] were capable of hearing the reverse alarm while wearing a high-attenuation earmuff in the pink noise used in the study.
Recognition of acoustic signals when perception is subject to interference from noise has already been extensively studied. In this study the influence of hearing protectors (HP) (plugs, muffs) and hearing loss on signal recognition is examined. Different spectrums and levels of the noise are also included. The test results are shown as the masked threshold for the signals heard and identified. In the case of normally hearing subjects a frequency-independent HP (plug) improves hearing performance, while frequency-dependent HP (muffs) tends to worsen it, especially with low-frequency noise. Hearing losses even worsen hearing performance when plugs are worn. Design suggestions are made to optimise signal recognition. Minimum signal-to-noise ratio and the use of HP are discussed.
Workers with hearing loss face special problems, especially when working in noise. However, conventional hearing conservation practices do not distinguish between workers with normal hearing versus impaired hearing. This study collected information from workers with self-reported noise exposure and hearing loss, supervisors of such workers, and hearing conservation program managers through focus groups and in-depth interviews to evaluate their perspectives on the impact of hearing loss on safety and job performance, the use of hearing protection, and information needed to appropriately manage hearing-impaired workers who work in noisy environments.
Concerns about working in noise with a hearing loss could be grouped into the following 10 categories: impact on job performance, impact on job safety, impaired ability to hear warning signals, impaired ability to monitor equipment, interference with communication, stress and/or fatigue, impaired communication caused by hearing protector use, reduced ability to monitor the environment as the result of hearing protector use, concerns about future quality of life, and concerns about future employability. Mostly, there was an agreement between the perceptions of workers, supervisors, and hearing conservation program managers regarding difficulties associated with hearing loss and consequent needs. These findings suggest that noise-exposed workers with hearing loss face many of the same problems reported in the literature by noise-exposed workers with normal hearing, with additional concerns primarily about job safety as the result of a reduced ability to hear environmental sounds, warning signals, and so forth.
The study outlines potential challenges regarding job safety and hearing conservation practices for noise-exposed, hearing-impaired workers. Awareness of these issues is a necessary first step toward providing appropriate protective measures for noise-exposed, hearing-impaired workers.
The Canadian military instituted a hearing conservation program over 45 yr ago. Yet the prevalence of noise-induced hearing loss is escalating. A focus group study involving four combat arms occupations was carried out to probe individuals' knowledge, attitudes, and behaviors relating to hearing loss prevention to find ways to improve compliance.
One group each of 4-5 Infantry Soldiers, Artillerymen, Armored Soldiers, and Combat Engineers, with the rank of Warrant Officer, Sergeant, or Master Corporal, and at least 5 yr of service participated. Discussions were led by a Moderator and recorded by an Assistant Moderator. Questions posed related to susceptibility and consequences of hearing loss, benefits and drawback of hearing protection, and preferences.
Age range was 28-48 yr and length of service 10-30 yr. Individuals were exposed to noise from weapons, explosives, vehicles, and aircraft. Infantry Soldiers and Artillerymen had confirmed moderate to severe hearing loss. Armored Soldiers and Combat Engineers had not perceived a change in hearing. Main concerns of using hearing protection were interference with detection and localization of auditory warnings, and perception of orders. Devices were often incompatible with other gear and difficult to fit.
Good hearing was critical to the occupations studied. Difference in hearing loss among groups was related to type and level of noise exposure. Loss of hearing and/or the use of hearing protection compromised situational awareness, exchange of information, and auditory task performance. Participants favored opportunities to try recommended devices, policies governing use, and sufficient funding to ensure protection for both regular and special forces.
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