Abstract
Conscripts are exposed to various sources of impulse noise despite hearing protection recommendations. The aim of this study was to investigate the frequency of acute acoustic trauma (AAT) among conscripts after exposure to assault rifle noise in the Finnish Defence Forces (FDF). This nationwide population-based cohort comprised all conscripts (>220,000) in the FDF during the years 1997-2003 and 2008-2010. We included those who claimed to have AAT symptoms from assault rifle noise during the study periods. During the investigated 10 years, 1617 conscripts (annual variation, 75-276) experienced a new hearing loss due to AAT. Altogether, 1456 (90%) of all AAT-induced hearing losses were caused by rifle-caliber weapons and 1304 (90%) of them when firing a blank cartridge. There was no clear diminishing trend in the annual numbers of AATs. In 1277 (88%) incidents, no hearing protector was used. Tinnitus was the most prominent symptom. Hearing losses after AAT were typically mild, but serious deficits also occurred. In conclusion, we found that 0.7-1.5% of the conscripts experienced an AAT during their service in the FDF. Most incidents occurred when firing a blank cartridge with a rifle-caliber weapon and with no hearing protector in use.