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   Abstract
   Introduction
   Technologies
   Real-ear-attenua...
   Loudness Balance
   Field Microphone...
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ARTICLE  
Year : 2011  |  Volume : 13  |  Issue : 51  |  Page : 147-151
Fit-testing hearing protectors: An idea whose time has come

Hearing Loss Prevention Consultant, 3M Occupational Health and Environmental Safety Division, IN, USA

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Date of Web Publication1-Mar-2011
 
  Abstract 

The performance of hearing protection devices (HPD) worn by individual workers in specific noise-exposure environments has been difficult to assess using the hearing protector ratings printed on HPD packages. Because the role of the HPD in prevention of hearing loss remains as a vital last line of defense against the effects of noise exposure, proper assessment of their performance is increasingly critical. HPD fit-testing procedures now allow the individual fit-testing of HPD to assist in appropriate selection of HPD for individual workers, to aid in training workers on proper use of HPDs, and a range of other applications. Understanding these technologies, their strengths and weaknesses, and appropriate application of the results of fit-testing may enable employers to make improvements in their hearing loss prevention program performance.

Keywords: Hearing protector, HPD, PAR, fit testing, attenuation

How to cite this article:
Hager LD. Fit-testing hearing protectors: An idea whose time has come. Noise Health 2011;13:147-51

How to cite this URL:
Hager LD. Fit-testing hearing protectors: An idea whose time has come. Noise Health [serial online] 2011 [cited 2020 Nov 25];13:147-51. Available from: https://www.noiseandhealth.org/text.asp?2011/13/51/147/77217

  Introduction Top


The evidence of a discrepancy between hearing protection devices (HPDs) performance in the laboratory and in the workplace is substantial. Berger [1],[2] compared laboratory and field HPD test results and found no correspondence other than field attenuation consistently underperforming laboratory values. Even using uninformed subject-fit laboratory test protocols, where test subjects are selected based on their inexperience with HPD and were provided no personal instruction in HPD use, laboratory ratings regularly exceed values from field tests. [3] While various methods have been developed to express HPD performance as a single-number attenuation value, [4],[5] none of these methods have proven effective in predicting real-world performance.

Laboratory tests have been found to be so inaccurate in predicting HPD performance in the real world that regulatory and advisory agencies in the US and elsewhere require a mathematical "derating" of the labeled attenuation of the devices when used in certain hearing loss prevention applications. [6],[7]

As a result, industrial users typically select HPD based in large part on high-labeled attenuation values regardless of the actual amount of protection needed by the noise-exposed worker, with many industrial purchasers feeling that devices with higher label values are "better" HPDs. This, in turn, has led many manufacturers to develop products with the highest-possible label attenuation values to meet market demands. Reliance on the single number has become, for many, the sole indication of HPD effectiveness and the sole metric for HPD comparison and selection.

This reductionist approach obscures the individual, person-to-person variability that underlies inconsistency in field HPD use. It fails to account for significant variability in the protection provided to individuals in the noise-exposed workforce due to insertion and use technique, individual anatomy (size and shape of individual ear canal), and other issues. [8] If it is important to determine how well HPD work for individual users, the only way to determine that is to test them on individual users.


  Technologies Top


Several approaches have been developed to enable individual fit-testing of earplugs. Legacy protocols are described in Berger. [9] Currently available commercial test methods fall into two primary groups: subjective, where test subjects respond in some fashion to auditory stimuli and objective, where measurements are made that do not require subject response. Although most of the different test methods yield a metric called the Personal Attenuation Rating, or PAR, there is no standardized method for calculating PAR. As a result, there may be significant differences in the precision and accuracy of the PAR measurements and PAR values derived from different protocols may not yield comparable results. Overall comparison of technologies is provided in [Table 1].
Table 1: Technology comparison summary

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Each of the systems yields a point-test, which describes the HPD fit and performance for the person on whom it was tested, for the specific model tested, under the conditions in which it was tested, at the point in time during which it was tested, and with the insertion or application that was tested. Extrapolation of these point-test results to long-term protected exposure requires careful consideration of the intrasubject variability of each person tested; repeated point tests over time will yield more reliable data. Fit-testing systems that provide an indication of the uncertainty of the measured values allow the user to better estimate reliability.


  Real-ear-attenuation at Threshold Top


The most common subjective test method is an adaptation of real-ear-attenuation at threshold (REAT) testing. This process consists of a hearing test with the HPD removed and another hearing test with the HPD in place, with the difference between the tests (ears open and ears occluded) providing a measure of HPD performance. Various means of extrapolating results, from test panel group size to application of various statistical methodologies, are applied. The REAT process is the legacy approach for laboratory evaluation of HPD, [10] and is considered the "gold standard." Stimuli are typically pulsed 1/3 octave bands of noise rather than the pure-tones employed for industrial hearing testing, but the general approach is similar. The lowest level that each subject can hear at each frequency band (the threshold of hearing) is measured twice; once with the HPD in and once with the HPD out.

Industrial audiometric equipment can be used to test HPD noise reduction using REAT protocols, [11] with some adaptations and caveats. The most common barrier to use of common industrial audiometers for fit-testing is the small space beneath the TDH-49 and TDH-39 headphones mandated for use in many hearing conservation regulations.[12] The small residual space beneath the headphones does not allow testing of devices that protrude from the earcanal entrance. This barrier can be circumvented by using larger volume headphones or by using loudspeakers to deliver the test signal in the hearing test environment.

Fit-testing systems that use a REAT test method and versions thereof are commercially available from Michael and Associates (Michael and Associates, State College, Pennsylvania) as FitCheck™ [13] and Workplace Group (Workplace Integra, Greensboro, North Carolina) as IntegraFit™ . [14]

Other threshold-shift methods are available as well. National Institute for Occupational Safety and Health (NIOSH) has developed QuickFit, [15] where a user adjusts the volume on a noise-generation device (either contained in an earmuff cup, via an MP3 player or delivered via internet) to be "just audible," with no HPD in place. After inserting the earplug, QuickFit increases the output of the signal by 15 decibels (dB); if the signal is still audible to the test subject, the HPD is assumed to be providing <15 dB of attenuation, and is probably improperly fit or is insufficient. While this system does not yield a PAR, it does give a "pass-fail" indication of HPD fit.

Results from REAT tests should be directly comparable to laboratory tests and, in most cases, any type of insert HPD can be tested using these systems. However, the test can be time consuming as each frequency is typically tested separately for each ear, both occluded and unoccluded, resulting in (at minimum) the equivalent of two binaural hearing tests. Some systems test a limited range of frequencies with the assumption that performance in this limited range can be a reliable indicator of performance across frequencies. Additionally, because the REAT tests are hearing threshold tests, the variability to be expected from these protocols will be similar to that experienced in hearing testing commonly ±5 dB. Most REAT protocols require relatively quiet background sound levels, similar to those needed for hearing testing.


  Loudness Balance Top


Loudness balance test methods have also been adapted to fit-testing hearing protectors. [16] This subjective protocol entails the user adjusting the volume output from the test system through headphones until the sound is perceived as equally loud, binaurally, with ears open. Then, one ear is occluded with an HPD and the process is repeated as the subject rebalances perceived loudness. The amount the occluded ear must be "turned up" to be equally as loud as the unoccluded ear gives an indication of the attenuation provided by the HPD in that ear. The process is repeated by occluding the remaining open ear and rebalancing to obtain an estimate of attenuation.

A loudness balance system is commercially available from Sperian (Sperian, Smithfield, Rhode Island) as VeriPro™ . [17]

The loudness balance system described here is capable of providing tests for any type of insert HPD. Although it is not a particularly difficult task, judging differences in loudness between ears is a different response paradigm than that to which most users are accustomed, and the learning curve varies among subjects. Hard-of-hearing subjects may have difficulty with the loudness balance process as localization and interfering tinnitus can be problematic with this condition. If each frequency is tested separately, the time required is similar to that for the REAT testing. Loudness balance protocols, because they use sound levels well above the hearing threshold, do not require quiet environments.


  Field Microphone-in-real-ear Top


The field microphone-in-real-ear (F-MIRE) approach is an objective method that typically uses a multimicrophone array to measure the sound pressure level (SPL) outside the HPD and beneath the HPD while it is in use. While the technical difference between these two measures is noise reduction and not attenuation, correction factors may be applied to the difference to yield equivalent attenuation values. [18]

A key technical consideration with traditional MIRE procedures is location of the measurement microphone. While it is possible to place a small microphone in the earcanal, between the end of the inserted HPD and the eardrum, consistent placement of that microphone can be challenging. To permit data collection, some procedures require that a connecting wire running from the internal microphone to the data collection equipment be placed between the HPD and the earcanal wall, which may introduce an acoustic leak, artificially degrading the attenuation provided by the HPD.

One way to avoid this problem is to introduce a probe tube with known acoustical properties into the earplug and connect the measurement microphone to the probe to allow measurement of the SPL under the HPD in the occluded ear. This process requires the development of specially probed earplugs to be used for testing as surrogates for the HPD used regularly by test subjects. Appropriate selection of tubing material and manufacturing techniques can minimize the effect of the probe on PAR measurements, but these aspects of the process must be carefully considered and effectively managed for F-MIRE systems to provide reliable attenuation findings.

F-MIRE systems are commercially available from 3M (3M, St Paul, Minnesota) as E-A-Rfit™ [19] and Phonak (Phonak Warrenville, Illinois) as SafetyMeter™ . [20]

Depending on the test signal and the data acquisition system, F-MIRE testing can be completed quickly. For example, the E-A-Rfit system uses a single pink-noise test signal and real-time analysis to obtain attenuation measurements over a broad frequency range in about 10 s. Findings are objective, requiring no response from the test subject, making them well suited for persons with hearing difficulties and eliminating the need to train the subject to respond to the signal. Because surrogate probed earplugs are used for testing, rather than the unprobed devices normally worn by each subject, the only hearing protectors that can be tested using the F-MIRE technique are those for which probed earplugs are available. A quiet test environment is not necessary with most F-MIRE systems because they measure the difference in SPL at two locations rather than assessing the subject's hearing threshold.


  Applications of HPD Fit-testing Findings Top


Individual fit-testing findings can be used for a variety of purposes to improve hearing loss prevention program performance. These guidelines are included in a document generated by a formal alliance among the National Hearing Conservation Association, the US Occupational Safety and Health Administration, and the the National Institute for Occupational Safety and Health. The Alliance published the Best Practice Bulletin Emerging Trends: Individual Fit-Testing[22] in 2008.

Train and motivate employees

Providing noise-exposed workers immediate and quantified feedback as to how well the HPD is performing, and how changes in users' fitting techniques have an immediate and dramatic effect of attenuation, can be an excellent training tool. See accompanying article by Schulz in this issue for examples and case studies.

Train the trainer

In practice, most HPD are dispensed and distributed by people with little or no training in HPD selection, fitting, or proper use and care. Fit-testing systems can help show persons responsible for HPD distribution how to properly fit the devices, the effect of proper fitting, and, in a general sense, what a good HPD fit should look and feel like.

Assign/select HPD

Variability in earcanal size and shape and ergonomic issues such as ease of insertion can have a significant effect on HPD performance. Fit-testing enables the proper selection of HPD to match the physical and noise exposure needs of individual workers.

Provide standard-threshold-shift follow-up

The HPD of persons exhibiting hearing loss in hearing conservation programs should (and in some jurisdictions, must) be evaluated to determine sufficiency. Individual fit-testing can be used to ensure that noise-susceptible persons are using HPD that are appropriate for their noise exposure.

Determine HPD adequacy/sufficiency

Related to the above, the fit test can help to determine whether the HPD is providing sufficient noise reduction, especially in high-noise areas.

Audit departments

Macroanalysis of group fit test data can help when comparing departments, work shifts, or groups within an organization. If more hearing loss is seen in Department A than in Department B, the selection and performance of HPD can be analyzed in conjunction with noise exposure and other data to help determine root causes.

Demonstrate adequacy of training

Some users find that application of fit-testing in initial worker safety training helps improve the effectiveness of the training and facilitates learning and retention of proper fitting techniques.

Provide documentation

Most systems generate records of HPD performance for each individual tested. These records may aid appropriate professionals in determination of hearing loss etiology and work-relatedness.


  Conclusion Top


Reliability of HPD is a key aspect of effective hearing loss prevention programs, and variability of individual protection levels is significant. It is important to develop an understanding of the implications of HPD fitting and selection and to improve use techniques among noise-exposed workers. Quantifying individual HPD performance via the types of fit-testing systems described above enables workers to understand clearly the effect of their HPD choices, including use techniques. Individual fit-testing of HPD is a viable enhancement to on-going hearing loss prevention efforts and the variety of systems and protocols currently available makes it likely that there is an approach suitable for almost every application. The ability to quantify HPD performance serves as a motivator for noise-exposed workers, [23],[24] and provides valuable information to assist in the prevention of work-related noise-induced hearing loss.

 
  References Top

1.Berger EH. EARLog 20 - The Naked Truth About NRRs. Available from: http://www.e-a-r.com/hearingconservation/earlog_main.cfm [last cited on 2011 Feb 21].  Back to cited text no. 1
    
2.The NIOSH Compendium of Hearing Protection Devices, Appendix C, 1995, DHHS Publication No. 95-105.  Back to cited text no. 2
    
3.Gauger D, Berger EH. A new hearing protector rating: The noise reduction statistic for use with a weighting (NRS A ), Report prepared for US EPA. Available from: http://www.regulations.gov/search/Regs/home.html#documentDetail?R=090000648015641b [last cited on 2011 Feb 21].  Back to cited text no. 3
    
4.Berger EH. Review and tutorial - Methods of measuring the attenuation of hearing protection devices. J Acoust Soc Am 1986;79:1655-87.  Back to cited text no. 4
[PUBMED]  [FULLTEXT]  
5.Schulz, Review of the Emerging Trend of Individual Fit-Testing for Earplugs, pending publication.  Back to cited text no. 5
    
6.OSHA guideline CPL 2-2.35A - 29 CFR 1910.95(b)(1), Guidelines for Noise Enforcement; Appendix A. Available from: http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=DIRECTIVES&p_id=1548 [last cited on 2011 Feb 21].  Back to cited text no. 6
    
7.Criteria for a Recommended Standard: Occupational Noise Exposure, NIOSH, Available from: http://www.cdc.gov/niosh/docs/98-126/chap6.html [last cited on 2011 Feb 21].  Back to cited text no. 7
    
8.Hager LD. Individual Fit Testing of Hearing Protectors: A Field Study, Presentation at 33 rd Annual National Hearing Conservation Association Conference, 2008.  Back to cited text no. 8
    
9.Berger, Assessment of the Performance of Hearing Protectors for Hearing Conservation Purposes, Noise & Vibration Control Worldwide, 1984. Vol. 15.  Back to cited text no. 9
    
10.American National Standard ANSI S12.6-2008, Methods for Measuring the Real Ear Attenuation of Hearing Protectors.   Back to cited text no. 10
    
11.Owens P. Evaluating ear plug attenuation in a petroleum refinery using a portable audiometer, Presentation at 2009 American Industrial Hygiene Conference and Exhibition, Minneapolis, Minnesota.  Back to cited text no. 11
    
12.29CFR1910.95, US DOL Hearing Conservation Amendment, Acoustic calibration of audiometers - Appendix E.   Back to cited text no. 12
    
13.Available from: http://www.michaelassociates.com/fitcheck/fitcheck.htm [last cited on 2011 Feb 21].  Back to cited text no. 13
    
14.Available from: http://www.workplaceintegra.com/equip-integrafit.html [last cited on 2011 Feb 21].  Back to cited text no. 14
    
15.Available from: http://www.cdc.gov/niosh/mining/pubs/pdfs/2009-112.pdf [last cited on 2011 Feb 21].  Back to cited text no. 15
    
16.Soli S, Vermiglio A, Larson V. A system for assessing the fit of hearing protectors in the field, Annual Meeting of the National Hearing Conservation Association, Tucson, AZ, 2005.  Back to cited text no. 16
    
17.Available from: http://www.sperianprotection.com.au/content/datasheets/Hearing/Additional%20information/VeriPro.pdf [last cited on 2011 Feb 21].  Back to cited text no. 17
    
18.Voix J, Laville F. The objective measurement of individual earplug field performance. J Acoust Soc Am 2009;125:3722-32.  Back to cited text no. 18
    
19.Available from: http://www.e-a-rfit.com/ [last cited on 2011 Feb 21].  Back to cited text no. 19
    
20.Available from: http://www.phonak-communications.com/en/hearing-protection/hearing-protection-products/safetymeter-fit-testing-system/ [last cited on 2011 Feb 21].  Back to cited text no. 20
    
21.American National Standard ANSI S3.1-1999, Maximum Permissible Ambient Noise Levels for Audiometric Rooms.  Back to cited text no. 21
    
22.OSHA/NHCA/NIOSH Alliance, Best Practice Bulletin: Hearing Protection-Emerging Trends: Individual Fit Testing. Available from: http://www.hearingconservation.org/as_allianceNHCA_OSHA.html [last cited on 2008].   Back to cited text no. 22
    
23.Berger EH. Fit testing hearing protectors. CAOHC Update 2007;19:5-8.  Back to cited text no. 23
    
24.Hager LD. Hearing protector evaluation: Current standards and pending developments. Hearing Rev 2007;14:26-8.  Back to cited text no. 24
    

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Correspondence Address:
Lee D Hager
248 Church St, Portland, MI 48875
USA
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1463-1741.77217

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    Tables

  [Table 1]

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