MILITARY AVIATION NOISE Noise-induced hearing impairment and noise protection

This research on military aviation noise was conducted because the personnel working with military aircraft were concerned about noise induced hearing damage. In addition, comprehensive data on hearing impairments and occupational exposure of military pilots in the Finnish Air Force was not available. Moreover, data on the effects of overflight noise of military jets was necessary for the evaluation of noise induced hearing deteriorations of members of the public who might be exposured accidentally for the low-level jets' overflights. The averaged noise exposure levels of pilots varied during a flight from 97 dB(A) to 106 dB(A) in the cockpit and from 83 dB(A) to 100 dB(A) at the entrance of the ear canal. Radio noise was 4–10 dB higher than background noise inside the helmet. The attenuation provided by air crew helmets varied from10 to 21 dB(A) in the laboratory, and was at the same level during real flights. The attenuation measured in the laboratory and in working conditions was about 30 dB(A) for earmuffs. An active noise cancellation (ANC) device decreased averaged noise exposure (LAeq8min) 4–8 dB over the noise attenuation of the same helmets when the ANC system was off. The noise of overflights by military jets were measured and the noise levels were lower than those known to cause the permanent threshold shifts. However, noise induced hearing damages might be possible in certain conditions. In order to assess the hearing loss risk of pilots, hearing thresholds were measured before and after one flight using both conventional and extended high frequency (EHF) audiometry. Minor temporary threshold shifts (TTS) were revealed. The risk of noise-induced damage at the studied exposure levels is, in all probability, rather small. A novel NoiseScan data management system proved to be an interesting tool in assessment of the risk of developing hearing impairment on the basis of known risk factors. Due to the small number of risk factors, the hearing of pilots was shown to be at considerably less risk than that of industrial workers in Finland.