Noise Attenuation in HALO Vertical Wind Tunnel Training

摘要

The Vertical Wind Tunnel (VWT) at Ft. Bragg, NC is one of the Army's training grounds for High Altitude Low Opening (HALO) parachute jumpers. Due to the nature of the operation (i.e., jet engine and high wind stream) personnel using the VWT are exposed to steady-state noise levels in excess of 120 dBA SPL (sound pressure level). These levels exceed the safe noise exposure limits stipulated in DA PAN 40-501 even when double hearing protection is worn; therefore, time limits on noise exposure must be enforced. These time limits substantially curtail training efforts and impact military readiness status. Efforts have been made to increase the attenuation provided by the helmets worn in the VWT. An innovative approach was used to measure the at-the-ear noise levels under five different parachutist's helmets in the VWT. Subsequently, an estimate was made to determine the maximum allowable time of noise exposure. Results suggest that one of the helmets provides superior hearing protection to the others, thus allowing sufficient training time in the VWT. Application of these results and recommendations will be discussed.