Balancing speech intelligibility versus sound exposure in selection of personal hearing protection equipment for Chinook aircrews.
BACKGROUND
Aircrews are often exposed to high ambient sound levels, especially in military aviation. Since long-term exposure to such noise may cause hearing damage, selection of adequate hearing protective devices is crucial. Such devices also affect speech intelligibility. When speech intelligibility and hearing protection lead to conflicting requirements, a compromise must be reached. The selection of personal equipment for RNLAF Chinook aircrews is taken as an example of this process.


METHODS
Sound attenuation offered by aircrew helmets and ear plugs was measured using a standardized method. Sound attenuation results were used to calculate sound exposure. Objective predictions of speech intelligibility were calculated using the Speech Transmission Index (STI) method. Subjective preference was investigated through a survey among 28 experienced aircrew members.


RESULTS
The use of ear plugs in addition to a (RNLAF standard) helmet may lead to a significant reduction of sound exposure. Using ear plugs that offer high sound attenuation, instead of using a less attenuating type, gives a little additional reduction of sound exposure, at the expense of a large reduction in speech intelligibility. Hence, it is better to use 'light' ear plugs. Better performance still is offered by Communications Earplugs, ear plugs featuring integrated miniature earphones. Results from the user preference survey correspond well with objective measurement results.


CONCLUSIONS
In the case of the RNLAF Chinook, the best solution is using Communications EarPlugs in combination with a standard helmet. The Chinook case clearly illustrates that hearing protection and speech intelligibility should be treated as connected issues.
Van Wijngaarden
S J
SJ
TNO Human Factors, Department of Perception-Speech Group, Soesterberg, The Netherlands. vanwijngaarden@tm.tno.nl
Rots
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D000337:Aerospace Medicine; D004430:Ear Protective Devices; D006317:Hearing Loss, Noise-Induced / Q000517:prevention & control; D006801:Humans; D008422:Materials Testing; D009784:Occupational Diseases / Q000517:prevention & control; D016272:Occupational Health; D013065:Speech Intelligibility