Acute acoustic trauma in Finnish conscripts. Etiological factors and characteristics of hearing impairment

Etiological factors and otological and audiological findings were analysed retrospectively in 361 Finnish conscripts who had suffered acute acoustic trauma (AAT) from firearms shooting during their military service. The most common cause of AAT was shooting with hand-held weapons without ear-protectors (50%). Other common causal weapons were antitank guns (25%) and cannons (12%). Explosions had caused AAT in one-tenth of the cases. The tympanic membrane had been ruptured in 22 subjects (6%). The frequency at which hearing loss was severest was most commonly 6.0 kHz, followed by 8.0 kHz and 4.0 kHz in that order. Speech frequencies were involved in about 25% of the ears. A flat type of audiometric configuration was observed in about 20% and a rising type (low-tone loss) in about 5% of the ears. Impulse noise from large-calibre guns seemed to cause low-tone hearing loss more often than shooting with hand-held weapons.