Editing Earplug (section)

==== 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.