INTRODUCTION
N oise is acoustically made up of numerous sound waves with anarchically distributed amplitude and phase ratios, causing an unpleasant sensation1. Noise can be continuous - when there is no variation in terms of sound pressure nor sound spectrum; floating - when it presents variations in terms of acoustic energy in function of time; or impact noise - with acoustic energy peaks lasting for less than a second, at intervals greater than one second2.
Impact noises are usually produced by quick gas expansion, such as that produced by firearms or bomb explosions. These types of sound can reach intensities of 140 dB SPL (sound pressure level) in frequencies around 2 and 3 kHz and, for this reason; they are harmful for human hearing3.
When the human
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studied ear problems among Army personnel who were exposed to multiple traumas during eight years of war in Iran. Hearing loss, tinnitus, ear discharge, vertigo, tympanic membrane perforation, audiologic findings and the type of trauma were considered. Bone Conduction threshold over 15dB was considered as hearing loss. In the sample population, 21.5% complained of audiologic problems. 94.6% had hearing loss, 83.6% tinnitus without hearing loss, but there was a hearing loss on the audiologic findings. 80% of hearing loss was bilateral, 10.9% only on the right and 9.1% only on the left side. 89% of hearing loss was sensorineural (88% in high frequency). 6.4% of them had tympanic membrane perforation and none had complained of vertigo 32.
AUDIOMETRY
Pure Tone Audiometry (PTA) is the commonest test performed to assess hearing loss following exposure to noise from firearms. Standard technique for assessment of pure tone threshold at individual frequency is by modified Hughson-Westlake method33. Pure tone average is taken as average of pure tone thresholds at 500, 1000, 2000 Hz frequency.
Degrees of hearing impairment as defined by WHO (World Health Organization) is given in table below.
TABLE-