Auditory Hazard Assessment Algorithm for Humans: Difference between revisions

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Combatants in every branch of the United States’ military are at risk for auditory impairments from steady state or [[Impulse noise (audio)|impulse noises]]. While applying double hearing protection helps prevent auditory damage, the user is isolated from the environment and the ability to detect, identify and localize important environmental cues is impaired. With hearing protection on, a soldier is less likely to be aware of his or her movements, alerting the enemy to their presence. Hearing protection devices (HPD) could also require higher volume levels for communication, negating their purpose.<ref name=":0">{{cite web |last1=Amrein |first1=Bruce |title=NOISE LIMITS FOR WARFIGHTING Recently Revised Standard Addresses Noise from Military Operations |url=http://synergist.aiha.org/201611-noise-limits-for-warfighting |website=thesynergist |accessdate=3 July 2018}}</ref>

The [[United States Army Research Laboratory|US Army Research Laboratory]]’s developed the Auditory Hazard Assessment Algorithm for Humans (AHAAH) to evaluate the potential damage to a user when exposed to high level impulse noise. The model purports to be more than 94% accurate with regards to identifying safe and hazardous exposures based upon the Blast Overpressure Walk-up study conducted by the US Army.<ref name=Chan>{{cite journal |last1=Chan |first1=P.C. |last2=Ho |first2=K.H. |last3=Kan |first3=K.K. |last4=Stuhmiller |first4=J.H. |title=Evaluation of impulse noise criteria using human volunteer data |journal= J. Acoust. Soc. Am. |date=2001 |volume=110 |pages=1967–1975 }}</ref><ref name=Price>{{cite journal |last1=Price|first1=G.R. |title=Validation of the auditory hazard assessment algorithm for the human with impulse noise data |journal= J. Acoust. Soc. Am. |date=2007 |volume=122 |pages=2786–2802}}</ref> Over time the predictability of this algorithm has increased to 95% accuracy.<ref name=DePaolis> {{cite journal |last1=DePaolis |first1=Annalisa |last2=Bikson |first2=Marome |last3=Nelson |first3=Jeremy |last4=de Ru |first4=J Alexander |last5=Packer |first5=Mark |last6=Cardoso |first6=Luis |title=Analytical and numerical modeling of the hearing system: Advances towards the assessment of hearing damage |journal= Hearing Research|date=Feb 2, 2017 |volume=349 |pages=111–118 |doi=10.1016/j.heares.2017.01.015 |pmid=28161584 |url=https://europepmc.org/abstract/med/28161584 |accessdate=3 July 2018}}</ref> In almost every instance any error resulted in overcalculation of risk. By comparison the MIL-STD-147D was deemed correct in only 38% of cases with the same data.<ref name=DePaolis /> Originally developed from a cat animal model and later informed by human data, the AHAAH sums the basilar membrane displacements of 23 locations. The user inputs their noise exposure, protection level, and whether they were forewarned of the noise, to receive their hazard vulnerability in auditory risk units (ARU). This value can be converted to compound threshold shifts and the allowed number of exposure (ANE). Compound threshold shifts is a value that integrates both temporary and permanent shifts in auditory threshold, the latter being correlated to hair cell function.<ref name="DePaolis" />

The first military standard (MIL-STD) on sound was published in 1984 and underwent revision in 1997 to become MIL-STD-1474D. In 2015, this evolved to become MIL-STD-1474E which, as of 2018, remains to be the guidelines for United States’ military defense weaponry development and usage. In this standard, the Department of Defense established guidelines for steady state noise, impulse noise, aural non-detectability, aircraft and aerial systems, and shipboard noise. Unless marked with warning signage, steady state and impulse noises are not to exceed 85 decibels A-weighted (dBA) and, if wearing protection, 140 decibels (dBP) respectively.<ref name=":0" />