Editing Earplug (section)

=== Rating ===
{{main|Hearing protection fit-testing}}
The [[United States Environmental Protection Agency]] (EPA) mandates that hearing protection is rated and labeled. To be rated, hearing protection is tested under ANSI S3.19-1974 to provide a range of attenuation values at each frequency that can then be used to calculate a Noise Reduction Rating (NRR). Under this standard a panel of ten subjects are tested three times each in a laboratory to determine the attenuation over a range of 9 frequencies.

In the European Union, hearing protectors are required to be tested according to the International Organization for Standardization (ISO) acoustical testing standard, ISO 4869 Part 1  and the Single Number Rating (SNR) or High/Middle/Low (HML) ratings are calculated according to ISO 4869 Part 2. In Brazil, hearing protectors are tested according to the American National Standards Institute ANSI S12.6-1997 and are rated using the Noise Reduction Rating Subject Fit NRR(SF). Australia and New Zealand have different standards for protector ratings yielding a quantity SLC80 (Sound Level Class for the 80th percentile). Canada implements a class system for rating the performance of protectors. Gauger and Berger have reviewed the merits of several different rating methods and developed a rating system that is the basis of a new American National Standard, ANSI S12.68-2007

The various methods have slightly different interpretations, but each method has a percentile associated with the rating. That percent of the users should be able to achieve the rated attenuation. For instance, the NRR is determined by the mean attenuation minus two standard deviations. Thus, it translates to a 98% statistic. That is, at least 98 percent of users should be able to achieve that level of attenuation. The SNR and HML are a mean minus one standard deviation statistic. Therefore, approximately 86% of the users should be able to achieve that level of protection. Similarly, the NRR (SF) is a mean minus one standard deviation and represents an 86% of users should achieve that level of protection. The difference between the ratings lies in how the protectors are tested. NRR is tested with an experimenter-fit protocol. SNR/HML are tested with an experienced subject-fit protocol. NRR (SF) is tested with a naive subject-fit protocol. According to Murphy, et al. (2004), these three protocols will yield different amounts of attenuation with the NRR being the greatest and NRR (SF) being the least.

The experimenter-fit NRR should be adjusted per the guidelines of the National Institute for Occupational Safety and Health as the required NRR ratings differ greatly from lab tests to field tests.

The NRR(SF) used in Brazil, Australia, and New Zealand does not require derating as it resembles the manner in which the typical user will wear hearing protection.

==== Noise Reduction Rating (NRR) ====

[[Hearing protection device|Hearing protectors]] sold in the US are required by the EPA to have a noise reduction rating (NRR),<ref name="epa">{{cite web|url=http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr;rgn=div5;view=text;node=40%3A24.0.1.2.14;idno=40;sid=19269b8f1aa80c731d6cc056ae8f850c;cc=ecfr#40:24.0.1.2.14.2.17.14 |title=EPA Standard, Title 20, Part 211 |publisher=Ecfr.gpoaccess.gov |date=2012-10-09 |access-date=2013-06-22}}</ref> which is an estimate of noise reduction at the ear when protectors are worn properly.

Real-ear attenuation at threshold (REAT) measurements are performed multiple times with 10 to 20 subjects to determine the NRR.  Using the collected data, an average group attenuation is reported along with a standard deviation for attenuation on the hearing protector package.<ref name=":3" />

Due to the discrepancy between how protectors are fit in the testing laboratory and how users wear protectors in the real world, the [[Occupational Safety and Health Administration]] (OSHA) and the [[National Institute for Occupational Safety and Health]] (NIOSH) have developed derating formulas to reduce the effective NRR.

While the NRR and the SNR (Single Number Rating) are designed to be used with [[A-weighting|C-weighted]] noise, which means that the lower frequencies are not de-emphasized, other ratings (NRR(SF) and NRSA) are determined for use with A-weighted noise levels, which have lower frequencies de-emphasized. NIOSH recommended and the U.S. EPA mandated <ref name="epa" /> that 7-dB compensation between C and A weighting be applied when the NRR is used with A-weighted noise levels.

The OSHA training manual for inspectors says the adequacy of hearing protection for use in a hazardous noise environment should be derated to account for how workers typically wear protection relative to how manufacturers test the protector's attenuation in the laboratory.<ref name="osha">Occupational Health and Safety Administration, January, 1999. The OSHA Technical Manual, OSHA Publication,  [http://www.osha.gov/dts/osta/otm/noise/hcp/attenuation_estimation.html Section IV, Appendix IV: C.] {{Webarchive|url=https://web.archive.org/web/20061009005341/http://www.osha.gov/dts/osta/otm/noise/hcp/attenuation_estimation.html |date=2006-10-09 }}</ref> For all types of hearing protection, OSHA's derating factor is 50%. If used with C-weighted noise, the derated NRR will become NRR/2.<ref name="osha" /> If used with A-weighted noise, OSHA applies the 7-dB adjustment for C-A weighting first then derates the remainder.<ref name="osha" /> For example, a protector with 33-dB attenuation would have this derating:

: Derated NRR = (33 – 7)/2

NIOSH has proposed a different method for derating based upon the type of protector.<ref name="crit">Linda Rosenstock et al. {{cite book |title=Criteria for a Recommended Standard: Occupational Noise Exposure], NIOSH Publication, No. 98-126 |date=June 1998 |location=Cincinnati, Ohio |page=7 |url=https://www.cdc.gov/niosh/docs/98-126/default.html |access-date=10 August 2022 |language=en |edition= 2nd|chapter=1.6.4 Confirmation Audiogram, Significant Threshold Shift, and Follow-up Action |quote=When a significant threshold shift has been validated, the employer shall take appropriate action to protect the worker from additional hearing loss due to occupational noise exposure. Examples of appropriate action include explanation of the effects of hearing loss, reinstruction and refitting of hearing protectors, additional training of the worker in hearing loss prevention, and reassignment of the worker to a quieter work area.|doi=10.26616/NIOSHPUB98126}}</ref>   For [[earmuffs]], the NRR should be derated by 25%, for slow-recovery foam earplugs the derating is 50% for all other protection, the derating is 70%.  NIOSH applies the C-A spectral compensation differently than OSHA. Where OSHA subtracts the 7-dB factor first and derates the result, NIOSH derates the NRR first and then compensates for the C-A difference. For example, to find the derated NRR for an earmuff by using the NIOSH derating system, the following equation would be used:

: Derated NRR = (Original NRR x (1-.25)) – 7

Painful discomfort occurs at approximately 120 to 125&nbsp;dB(A),<ref>{{in lang|de|en}} [http://www.lima-wiederladetechnik.de/Schalldaempfer/Schalldaempfer.htm Schalldämpfer = Gehörschützer für Jäger, data collected on noise levels] {{Webarchive|url=https://web.archive.org/web/20090328141932/http://www.lima-wiederladetechnik.de/Schalldaempfer/Schalldaempfer.htm |date=2009-03-28 }}</ref> with some references claiming 133&nbsp;dB(A) for the threshold of pain.<ref name=":0">{{Cite web|url=http://www.earplugstore.com/morabshootea.html#|title=More About: Shooting/Hunting Hearing Protection|website=www.earplugstore.com|access-date=2017-03-03}}</ref> Active [[ear muffs]] are available with electronic noise cancellation that can reduce direct path ear canal noise by approximately 17–33&nbsp;dB, depending on the low, medium, or high frequency at which attenuation is measured.<ref>{{cite web |url=http://www.3m.com/3M/en_US/company-us/search/?Ntt=active+ear+muffs+with+electronic+noise+cancellation |title=Search results for "active ear muffs with electronic noise cancellation" |website=[[3M]]}}{{rs|date=October 2022|reason=primary corporate advertising source}}</ref> Passive earplugs vary in their measured attenuation, ranging from 20&nbsp;dB to 30&nbsp;dB, depending on the fit of the earplugs, whether the employee can and knows how to insert the earplugs into the ear canal correctly, and whether they are used correctly<ref name="AIHA-6-11">{{cite book |last1=Berger |first1=Elliott H.|last2= Voix |first2= Jérémie |editor=D.K. Meinke |editor2=E.H. Berger |editor3=R. Neitzel |editor4=D.P. Driscoll |editor5=K. Bright |title=The Noise Manual |date=2018 |publisher=American Industrial Hygiene Association |location=Falls Church, Virginia |pages=255–308 |edition=6th |url=https://online-ams.aiha.org/amsssa/ecssashop.show_product_detail?p_mode=detail&p_product_serno=2719 |access-date=10 August 2022 |language=en |chapter=Chapter 11: Hearing Protection Devices}}</ref><ref>{{cite journal |last1=Toivonen |first1=Markku |last2=Pääkkönen |first2=Rauno |last3=Savolainen |first3=Seppo |last4=Lehtomäki |first4=Kyösti |title=Noise Attenuation and Proper Insertion of Earplugs into Ear Canals |journal=The Annals of Occupational Hygiene |date=2002-08-01 |volume=46 |issue=6 |pages=527–530 |doi=10.1093/annhyg/mef065 |pmid=12176767 |url=https://www.researchgate.net/publication/11210051 |access-date=27 October 2023 |publisher=Oxford University Press |location=Oxford, UK |language=en |issn=2398-7308|doi-access=free }}</ref> and if low pass mechanical filters are also being used.

==== Double protection ====
The Canadian standard requires the use of two passive protective measures simultaneously at noise levels above 105 dBA. But the noise reduction does not increase very much. It is recommended to estimate the attenuation by adding 5 dB to the highest attenuation of one of the two HPDs. This recommendation does not take into account individual differences at all, and may lead to error.<ref>{{cite book |last1=Behar |first1=Alberto |last2=E.H. Berger, I.B. Bhunnoo |title=Z94.2-14. Hearing protection devices — Performance, selection, care and use |date=2014 |publisher=Canadian Standards Association (CSA Group) |location=Toronto, Ontario, Canada |isbn=978-1-77139-417-8 |pages=27–28 |edition=7th |url=https://www.csagroup.org/store/product/2701515/ |access-date=25 October 2023 |language=en |chapter=9.7 Double protection}}</ref>

Using both ear muffs (whether passive or active) and earplugs simultaneously results in maximum protection, but the efficacy of such combined protection relative to preventing permanent ear damage is inconclusive, with evidence indicating that a combined noise reduction ratio (NRR) of only 36&nbsp;dB (C-weighted) is the maximum possible using ear muffs and earplugs simultaneously, equating to only a 36 - 7 = 29&nbsp;dB(A) protection.<ref name=":0" /> Some high-end, passive, custom-molded earplugs also have a mechanical filter inserted into the center of the earmolded plug, with a small opening facing to the outside; this design permits being able to hear range commands at a gun range, for example, while still having full rating impulse noise protection.

Such custom molded earplugs with low pass filter and mechanical valve typically have a +85&nbsp;dB(A) mechanical clamp, in addition to having a [[Low-pass filter|lowpass filter]] response, thereby providing typically 30-31&nbsp;dB attenuation to loud impulse noises, with only a 21&nbsp;dB reduction under low noise conditions across the human voice audible frequency range (300–4000&nbsp;Hz) (thereby providing low attenuation between shots being fired), to permit hearing range commands.  Similar functions are also available in standardized earplugs that are not custom molded.<ref>{{Cite web|url=http://www.earplugstore.com/health-enterprises-acu-life-shooters-impact-ear-plugs.html|title=Health Enterprises ACU-LIFE Shooter's Ear Plugs (Sonic Valve II)|website=www.earplugstore.com|access-date=2017-03-03}}</ref>{{failed verification|date=June 2022}}

==== Derating in several countries ====
{| class="wikitable collapsible collapsed" style="text-align:center"
! Country, organization || Roll-down foam earplugs || Pre-molded earplugs || Earmuffs
|- style="text-align:right"
| USA, OSHA || 2 times reduction || 2 times || 2 times
|-style="text-align:right"
| USA, NIOSH || 2 times || 3.3 times || 1.33 times
|-style="text-align:right"
| Italy || 2 times || 3.3 times || 1.33 times
|-style="text-align:left"
| UK || 4 dB reduction || 4 dB || 4 dB
|-style="text-align:left"
| France || 10 dB || 10 dB || 5-7 dB    
|-style="text-align:left"
| Germany || 9 dB || 5 dB || 5 dB 
|}
The wide variation in recommendations<ref name="AIHA-6-11" /> may be due in part to the very large inter-individual variability in results that cannot be predicted; but can be taken into account by [[Hearing protection fit-testing|individual measurements]].

==== Expected updates ====
In 2007, the [[American National Standards Institute]] published a new standard for noise reduction ratings for hearing protectors, ANSI S12.68-2007. Using the real ear attenuation at threshold data collected by a laboratory test prescribed in ANSI S12.6-2008, the noise reduction statistic for A-weighted noise (NRSA) is computed using a set of 100 noises listed in the standard.<ref name="ansi">ANSI S12.68 (2007). American National Standard Methods of Estimating Effective A-Weighted Sound Pressure Levels When Hearing Protectors, are Worn, American National Standards Institute, New York.</ref> The noise reduction rating, rather than be computed for a single noise spectrum the NRSA incorporates variability of both subject and spectral effects.<ref name="ansi" />  ANSI S12.68 also defines a method to estimate the performance of a protector in an atypical noise environment.

Building upon work from the [[U.S. Air Force]] and the ISO 4869-2 standard,<ref name="iso">ISO 4869-2 (1994). ''Acoustics—Hearing Protectors Part 2: Estimation of effective A-weighted sound pressure levels when hearing protectors are worn,'' International Organization for Standardization, Geneva.</ref> the protector's attenuation as a function of the difference in C and A-weighted noise level is used to predict typical performance in that noise environment.  The derating may be quite severe (10 to 15 decibels) for protectors that have significant differences between low and high frequency attenuation.  For "flat" attenuation protectors, the effect of C-A is less. This new system eliminates the need for calculators, relies on graphs and databases of empirical data, and is believed to be a more accurate system for determining NRRs.<ref name="ansi" />