Critical Peak Level for Impulse Noise Hazard: Permanent Hearing Threshold Shifts in Military Drill Squads Following Known Variation of Impulse Noise Exposure
From 1982 to 1983, new recruits of The Royal Norwegian Guards Ceremonial Drill Squad (n=32, males, 20 yrs), on their own initiative, changed from low horizontal to high vertical rifle positions during ceremonial firing. In addition, they used the more powerful brass Energa 7.62 mm blank ammunition when firing a simultaneous round which ended each of the 20 official ceremonial drill performances distributed over a 3 months period. The soldiers did not use hearing protection during these ceremonies. Permanent noise-induced hearing losses in the 1983 squad were substantially increased (Fig. 1). Apart from this change, routine and training programs were identical. This gave us the unique opportunity to make a retrospectively-designed, controlled study on the effects of known variations of weapon position and impulse noise exposure on permanent noise-induced hearing losses in man. This was accomplished by letting the 1984 Drill Squad (new recruits) go through the drill program with 1982 red blank ammunition and 1983 (vertical) weapon position under audiometric surveillance.
KeywordsHearing Loss Noise Exposure Impulse Noise Single Round Hearing Protection
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