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Combatants in every branch of the United States’ military are at risk for [[Hearing loss|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 ([[Hearing protection device|HPD]]) could also require higher volume levels for communication, negating their purpose.<ref name="
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 (audio)|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><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 /> 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 [[Absolute threshold of hearing|auditory threshold]], the latter being correlated to hair cell function.<ref name="DePaolis" />
The first military standard ([[United States 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 [[United States 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 [[Decibel|decibels]] A-weighted (dBA) and, if wearing protection, 140 decibels (dBP) respectively.<ref name="
The AHAAH’s improvements in accuracy are often attributed to its sensitivity to the flexing of the middle ear muscle (MEM) and [[Annular ligament of stapes|annular ligament of the stapes]]. When someone is forewarned of a sound, the MEM flexes, which is associated with reduced ability of the sound waves to reverberate. When an impulse sound is produced, the stapes’s annular ligament flexes and strongly clips the sound’s oscillation peak.<ref name=Chan />
As the MIL-STD-1474 has evolved, technology and methods have improved the AHAAH model’s accuracy. AHAAH has been proven to be more accurate in cases of double protection but not always in unwarned impulse noise instances relative to the competitive metric LAeq8hr.<ref name="
== References ==
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