Physics:Hearing protection fit-testing

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Short description: Test for determining the effectiveness hearing protection devices
Fit testing (MIRE)[1]

Hearing protector fit-testing measures the degree of noise reduction obtained from an individual wearing a particular hearing protection device (HPD) - for example, an earplug or earmuff. Such measurements are necessary because noise attenuation varies across individuals (and sometimes can be close to zero) due to anatomical differences and inadequate training as to the proper wear and use.[2] Labeled HPD attenuation values (for example, the Noise Reduction Rating, or NRR) are average values that cannot predict noise attenuation for an individual; in addition, they are based on laboratory measurements which may overestimate the noise reduction obtained in the real world.[3]

Hearing protection devices such as earplugs or earmuffs must be worn correctly for the wearer to be protected from noise.[4] Correct use of hearing protection includes:

  • Choosing the most appropriate hearing protection device, both with appropriate level of attenuation and appropriate fit for the individual.[5] Ideally, the device should limit the sound intensity that reaches the ear to levels below 85 dBA. If the attenuation does not limit the noise levels to that level, other alternatives should be sought. If the attenuation is greater than that, it can also interfere with the HPD use by making it difficult to hear important sounds.[6]
  • Wearing or inserting the hearing protection device correctly so it seals the wearer's ear canal, using the "roll-pull-hold" method for foam earplugs, and ensuring earmuffs create an unbroken seal around each ear.[7]

Fit-testing hearing protection can facilitate an appropriate choice of hearing protection, and allow for the professional administering the fit-test to train users on proper techniques for wear.[8][9][10][11][12][13]

Requirements and Recommendations for HPD Fit Testing

The Occupational Safety and Health Administration, National Hearing Conservation Association and National Institute for Occupational Safety and Health recommend it for all workers used HPD as a best practice,[14] and describes existing testing methods and how to incorporate them in hearing conservation programs.[15]

Effective March 31, 2023, the Alberta Government added a requirement that employers fit test each employee who wears HPDs.[16] A trend towards recommending HPD fit-testing as a best practice is emerging in the European Union and the USA.[17][18]

Fit-testing methods

Fit testing is typically carried out using one of the available fit-testing hardware and software systems (also known as field attenuation estimation system (FAES).[19] Although all fit-testing systems measure the amount of sound reduction provided by hearing protection devices, different systems use different approaches to making this measurement.

The different methods[20] used to measure the attenuation provided by HPDs are as follows:

Real-ear attenuation at threshold (REAT)

NIOSH mobile laboratory for REAT measuring (sound thresholds & real attenuation of earplugs)[21]

REAT is the most commonly used type of fit-testing technology used in commercial systems. REAT systems are modeled on the "gold-standard" approach to measuring hearing protector attenuation as defined in the established standard ANSI/ASA S12.6. This approach measures the difference in auditory (hearing) thresholds without hearing protection (unoccluded) and with hearing protection (occluded). Differences in occluded and unoccluded thresholds across one or more test frequencies are used to calculate the noise reduction. REAT systems rely on the subjective response of the person being tested to determine auditory thresholds much like a hearing test where the subject indicates when sound is heard at various frequencies.

REAT testing of earplugs For earmuffs this must be tested in an acoustic chamber, however for earplugs, headphones can be used, making the test easier for commercial use.[22] For noncritical screening, REAT can be performed using a web browser and simple audio devices.[23]

Loudness balance

This method first has the subject listen to tones with headphones and "match" loudness between both ears until tones sound equally loud on both sides. Then an earplug is placed in one ear while the baseline procedure is repeated to match loudness in both ears. The increase in loudness required to balance represents the attenuation achieved in that ear. The second earplug is then placed in the other ear and the procedure is repeated a third time. The required increase in loudness this time represents the noise reduction achieved in the second ear. The loudness balance fit-testing approach provides individual personal attenuation ratings for each ear.[24]

Microphone-in-real-ear (MIRE)

Earplugs with probes for MIRE measurements.

Also referred to as F-MIRE (field microphone in real ear). This method measures attenuation by placing a small microphone inside the ear canal while hearing protection is worn. Sound pressure levels (SPL) are measured inside and outside of the ear simultaneously and used to calculate a PAR.[24]

Fit test results

The effectiveness is typically measured as a personal attenuation rating (PAR) which is subtracted from the known noise exposure to estimate the total noise exposure a single person has when wearing the tested hearing protection device (HPD).[8][25]

The outcome measure generated by hearing protector fit-test systems varies from a simple pass/fail to a quantitative personal attenuation rating (PAR). and can be interpreted differently to determine the effectiveness of hearing protection or calculate total noise exposure.[22]

Personal attenuation rating (PAR)

Similar to a noise reduction rating (NRR) required on hearing protection devices in the United States, a personal attenuation rating (PAR) is obtained from an attenuation measurement at one or more than one frequency. The effectiveness is typically measured as a personal attenuation rating (PAR) which is subtracted from the known noise exposure to estimate the total noise exposure a single person has when wearing the tested hearing protection device (HPD).[8][25] However, the PAR is regarded as more accurate than the NRR because it is calculated per individual and per hearing protection device, while NRR is a generalized estimate of potential sound reduction based on the protection provided to a small population of people.[1] Therefore, PAR gives the evaluator an estimate of the total noise exposure an individual is receiving when wearing hearing protection.

PAR is subtracted from the known noise exposure to estimate the total protected noise exposure a single person has when wearing the tested HPD.[8][25] The method for estimating protected noise exposure based on the measured PAR may vary slightly across fit-test systems, so it is important to understand to use the PAR generated by a given fit test system[22]

Use of Fit-testing as a training tool

Evidence shows that including fit-testing as a part of employee training for correct hearing protection device use increases the user's ability to properly fit the device, and that this ability is often retained on follow-up.[9][26][13][27] Fit testing provides the individual with immediate feedback regarding the noise reduction achieved, which helps them understand how the device should feel when it is properly fit. Investments in fit testing and training have been shown to be effective at reducing the rates of standard threshold shifts in industry.[27]

See also

References

  1. ↑ Kah Heng Lee; Geza Benke; Dean Mckenzie (2022). "The efficacy of earplugs at a major hazard facility" (in en). Physical and Engineering Sciences in Medicine (Springler) 45 (1): 107–114. doi:10.1007/s13246-021-01087-y. ISSN 2662-4729. PMID 35023076. https://www.researchsquare.com/article/rs-807643/v1. Retrieved 2022-08-10. 
  2. ↑ Gong, Wei (2021). "Evaluating the effectiveness of earplugs in preventing noise-Induced hearing loss in an auto parts factory in China". International Journal of Environmental Research and Public Health 18 (3): 7190. doi:10.3390/ijerph18137190. PMID 34281127. 
  3. ↑ Berger, Elliott H.; Voix, Jérémie (2018). "Chapter 11: Hearing Protection Devices". in D.K. Meinke (in en). The Noise Manual (6th ed.). Falls Church, Virginia: American Industrial Hygiene Association. pp. 255–308. https://online-ams.aiha.org/amsssa/ecssashop.show_product_detail?p_mode=detail&p_product_serno=2719. Retrieved 10 August 2022. 
  4. ↑ "The use of hearing protection devices in South Africa: exploring the current status in a gold and a non-ferrous mine". Occupational Health Southern Africa 21: 10–15. 2015. https://www.researchgate.net/publication/275639377. 
  5. ↑ "Three Tips for Choosing the Right Hearing Protector". 2018-10-24. https://blogs.cdc.gov/niosh-science-blog/2018/10/24/hearing-protection/. 
  6. ↑ "Beliefs and attitudes among Swedish workers regarding the risk of hearing loss". International Journal of Audiology 43 (10): 585–93. 2004-11-11. doi:10.1080/14992020400050075. PMID 15724523. 
  7. ↑ "Are your ears really protected? Find out with NIOSH's QuickFitWeb". 2008-05-12. https://blogs.cdc.gov/niosh-science-blog/2008/05/12/quickfit/. 
  8. ↑ 8.0 8.1 8.2 8.3 "Fit testing of hearing protectors". Occupational Health & Safety 76 (10): 118, 120–2. October 2007. PMID 17972707. https://ohsonline.com/Articles/2007/10/Fit-Testing-of-Hearing-Protectors.aspx?Page=1. Retrieved 2018-12-28. 
  9. ↑ 9.0 9.1 "Hearing protector fit testing with off-shore oil-rig inspectors in Louisiana and Texas". International Journal of Audiology 55 (11): 688–98. November 2016. doi:10.1080/14992027.2016.1204470. PMID 27414471. 
  10. ↑ "Fit-testing hearing protectors: an idea whose time has come". Noise & Health 13 (51): 147–51. 2011. doi:10.4103/1463-1741.77217. PMID 21368440. 
  11. ↑ "Individual fit-testing of earplugs: a review of uses". Noise & Health 13 (51): 152–62. 2011. doi:10.4103/1463-1741.77216. PMID 21368441. 
  12. ↑ "Attitudes toward use of hearing protection devices and effects of an intervention on fit-testing results". Workplace Health & Safety 62 (12): 491–9. December 2014. doi:10.3928/21650799-20140902-01. PMID 25207586. 
  13. ↑ 13.0 13.1 "Evaluating the effect of training along with fit testing on foam earplug users in four factories in China". International Journal of Audiology 58 (5): 269–277. May 2019. doi:10.1080/14992027.2018.1563307. PMID 30880506. 
  14. ↑ OSHA (July 6, 2022). "OSHA Technical Manual (OTM) Section III: Chapter 5. Noise" (in en). US Occupational Safety and Health Administration. https://www.osha.gov/otm/section-3-health-hazards/chapter-5. "... has recommended HPD fit-testing as a best practice and valuable training tool that can help in training the worker to achieve an optimal fit" 
  15. ↑ NHCA/OSHA/NIOSH Alliance (2008). "Hearing Protection-Emerging Trends: Individual Fit Testing" (in en). NHCA Alliance Best Practice Bulletin: 3. https://www.hearingconservation.org/index.php?option=com_content&view=article&id=145:teaching-resources&catid=20:site-content&Itemid=167. Retrieved 18 January 2023.  PDF
  16. ↑ "Change highlights: Noise exposure – Part 16 in the OHS Code" (in en). Alberta (Canada): Government of Alberta. December 2022. pp. 3. https://ohs-pubstore.labour.alberta.ca/lh003. "A new requirement has been added for employers to ensure workers are fit tested for the hearing protection devices they use and wear. ... This change is intended to prevent noise induced hearing loss. The effectiveness of hearing protection is greatly reduced if the equipment does not fit correctly or is not inserted or worn correctly." 
  17. ↑ Technical Committee CEN/TC 159 “Hearing protectors” (17 November 2021) (in en). EN 17479-2021. Hearing protectors - Guidance on selection of individual fit testing methods. Brussels: European Committee for Standardization. pp. 46. ISBN 978-0-539-04746-2.  link
  18. ↑ Accredited Standards Committee S12, Noise (2018) (in en). ANSI/ASA S12.71-2018. Performance Criteria for Systems that Estimate the Attenuation of Passive Hearing Protectors for Individual Users. Melville, New York: Acoustical Society of America. pp. 54. https://webstore.ansi.org/standards/asa/ansiasas12712018. Retrieved 25 October 2023. 
  19. ↑ Voix, Jérémie; Smith, Pegeen; Berger, Elliott H. (2018). "Chapter 12: Field Fit-Testing and Attenuation-Estimation Procedures". in D.K. Meinke (in en). The Noise Manual (6th ed.). Falls Church, Virginia: American Industrial Hygiene Association. pp. 309–329. https://online-ams.aiha.org/amsssa/ecssashop.show_product_detail?p_mode=detail&p_product_serno=2720. Retrieved 10 August 2022. 
  20. ↑ John R. Franks, William J. Murphy, Dave A. Harris, Jennifer L. Johnson & Peter B. Shaw (2003). "Alternative Field Methods for Measuring Hearing Protector Performance" (in en). American Industrial Hygiene Association Journal (Akron, Ohio: Taylor & Francis) 64 (4): 501–509. doi:10.1080/15428110308984846. ISSN 0002-8894. PMID 12908866. https://www.protectear.com/wp-content/uploads/2010/10/AlternativeFieldMethods.pdf. Retrieved 16 February 2023. 
  21. ↑ Kwitowski, August J.; Carilli, Angela M.; Randolph, Robert F. (September 2010). "MultiFit4: An Improved System for Insert-Type" (in en). Spectrum (National Hearing Conservation Association) 27 (2): 17–25. https://www.cdc.gov/NIOSH/Mining/works/coversheet1119.html. Retrieved 6 January 2023. 
  22. ↑ 22.0 22.1 22.2 "ANSI/ASA S12.6-2016 – Real-Ear Attenuation of Hearing Protectors". 2016-11-21. https://blog.ansi.org/2016/11/ansiasa-s126-2016-attenuation-hearing-protectors/#gref. 
  23. ↑ Randolph, Robert F. (December 2008) (in en). QuickFit Earplug Test Device (Technology News 534). Pittsburgh: DHHS (NIOSH) Publication No. 2009–112. pp. 2. https://www.cdc.gov/niosh/mining/works/coversheet581.html. Retrieved 6 January 2023.  + online test tool
  24. ↑ 24.0 24.1 "Fit testing ear plugs". Occupational Health & Safety 75 (6): 38, 40, 42 passim. June 2006. PMID 16805277. https://ohsonline.com/Articles/2006/06/Fit-Testing-Ear-Plugs.aspx?Page=4. Retrieved 2019-02-19. 
  25. ↑ 25.0 25.1 25.2 "Suitability of commercial systems for earplug individual fit testing" (in en). Applied Acoustics 90: 88–94. 2015-04-01. doi:10.1016/j.apacoust.2014.11.010. 
  26. ↑ "Longitudinal evaluation of a hearing protector fit training program". La Medicina del Lavoro 110 (4): 304–311. August 2019. doi:10.23749/mdl.v110i4.8214. PMID 31475692. 
  27. ↑ 27.0 27.1 Sayler, Stephanie K.; Rabinowitz, Peter M.; Cantley, Linda F.; Galusha, Deron; Neitzel, Richard L. (2018-01-26). "Costs and effectiveness of hearing conservation programs at 14 US metal manufacturing facilities" (in en). International Journal of Audiology 57 (sup1): S3–S11. doi:10.1080/14992027.2017.1410237. ISSN 1499-2027. PMID 29216778. 

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