Auditory Hazard Assessment Algorithm for Humans: Difference between revisions

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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" />

The [[United States Army Research Laboratory|US Army Research Laboratory]]’s Auditory Hazard Assessment Algorithm for Humans (AHAAH) produced these numerical guidelines. Over time the predictability of this algorithm has increased to 95% accuracy.<ref name=":1">{{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=":1" /> 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=":1" />

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 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=":1" />