Auditory Hazard Assessment Algorithm for Humans: Difference between revisions

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== Overview ==

[[Noise-induced hearing loss|Noise-induced hearing loss (NIHL)]] typically occurs when the auditory system experiences an elevation of [[Hearing threshold|hearing thresholds]] due to exposure to high-level noise, a phenomenon known as a [[Auditory fatigue|temporary threshold shift (TTS)]], and does not return to normal threshold levels.<ref>{{Cite journal|last=Ryan|first=Allen|last2=Kujawa|first2=Sharon|last3=Hammill|first3=Tanisha|last4=Le Prell|first4=Colleen|last5=Kil|first5=Jonathan|date=September 2016|title=Temporary and Permanent Noise-Induced Threshold Shifts: A Review of Basic and Clinical Observations|journal=Otology & Neurotology|volume=37|issue=8|pages=e271–e275|pmc=4988324|pmid=27518135|doi=10.1097/MAO.0000000000001071}}</ref> The damage to the auditory system can vary depending on the type of noise exposure. Unlike the continuous [[background noise]] often found in industrial environments, the impulse noise produced by weapons and [[Firearm|firearms]] demonstrates a very high pressure level within a very short duration of time, typically around a few milliseconds. As a result, near-field peak levels measured close to the muzzle of a weapon can range from 150 dB for handheld weapons and over 180 dB for [[heavy artillery]]. By comparison, noises from industrial settings were measured to have peak levels of 113 to 120 dB.<ref name=":3">{{Cite journal|last=Nakashima|first=Ann|last2=Farinaccio|first2=Rocco|date=April 2015|title=Review of Weapon Noise Measurement and Damage Risk Criteria: Considerations for Auditory Protection and Performance|url=https://academic.oup.com/milmed/article/180/4/402/4160429|journal=Military Medicine|volume=180|issue=4|pages=402–408|via=Oxford Academic|doi=10.7205/MILMED-D-14-00204|pmid=25826345|doi-access=free}}</ref>

In order to protect soldiers from hearing loss, the U.S. Army adhered to the [[United States Military Standard|Military Standard (MIL-STD) 1474]], which defined the maximum noise levels permitted to be produced by military systems.<ref name=":4">{{Cite journal|last=Amrein|first=Bruce|last2=Letowski|first2=Tomasz|date=January 2012|title=Military noise limits: How much is too much?|url=https://www.researchgate.net/publication/290297963|journal=Internoise 2012|volume=|pages=3981–3992|via=ResearchGate}}</ref><ref>{{Cite news|url=https://synergist.aiha.org/201611-noise-limits-for-warfighting|title=Noise Limits for Warfighting|last=Amrein|first=Bruce|date=December 15, 2019|work=The Synergist|access-date=January 7, 2020|url-status=live}}</ref> However, human volunteer studies demonstrated that the standard used since 1997, the MIL-STD-1474D, overestimated the hazard associated with impulse noise exposure.<ref name=":5">{{Cite journal|last=Patterson|first=James|last2=Ahroon|first2=William|date=December 2004|title=Evaluation of an Auditory Hazard Model Using Data from Human Volunteer Studies|url=https://apps.dtic.mil/docs/citations/ADA429771|journal=U.S. Army Aeromedical Research Laboratory|volume=|pages=|id=2005-01|via=Defense Technical Information Center}}</ref> The subsequent overprotection of the ears based on inaccurate evaluations of hearing loss risk was believed to potentially hamper verbal communication between military personnel on the battlefield and reduce situational awareness.<ref name=":3" /><ref name=":4" /> The AHAAH was developed to more accurately assess the hazard to the human ear from impulse noise by incorporating the acoustic and physiological characteristics of the ear in its analysis, which were not accounted for in previous metrics.<ref name=":5" /><ref name=":6">{{Cite journal|last=Price|first=G. Richard|date=July 2011|title=The Auditory Hazard Assessment Algorithm for Humans (AHAAH): Hazard Evaluation of Intense Sounds|url=https://apps.dtic.mil/dtic/tr/fulltext/u2/a550723.pdf|journal=Army Research Laboratory|volume=|pages=|id=ARL-TR-5587|via=}}</ref> The AHAAH was eventually used in 2015 to completely revise the MIL-STD-1474E and establish a new standard known as the MIL-STD-1474E.<ref name=":2" />