Noise Protection of the HGU-56/P Aircrew Integrated Helmet System Worn with Eyeglasses

The use of ancillary devices such as eyeglasses with a sound attenuating helmet can reduce the effectiveness of the helmet to protect the user from hazardous noise exposures. Three different eyeglass frame types bayonet, cable, skull were tested and the insertion loss sound reduction of the HGU-56p Aircrew Integrated Helmet System AIHS worn with the frames was measured across the frequency range from 25 Hz to 20 kHz. All three types of eyeglass frames reduced the effectiveness of the AIHS to protect the wearer from noise exposure. While the limits on operational capabilities resulting from the use of cable- or skull-style eyeglass frames were minimal, the bayonet-style frames can reduce by more than half the maximum allowable time in which an individual may be exposed to high-levels of environmental noise without the added protection of insert earplugs. It is recommended that earplugs be used when bayonet-style eyeglass frames are worn with the HGU-56p AIHS.