Factors affecting sound exposure from firing an SA80 high-velocity rifle

Abstract

The effect of distance on the peak sound pressure level and sound exposure level from an SA80 rifle has been investigated. Sound pressure waveforms were measured in two directions from the gun: downrange, from 50m to 300m, and to the left-hand side, from 0.3m to 32m. Some additional measurements were made to the right of the gun. Measurements made downrange showed three distinct features of the waveform; the shock wave from the supersonic bullet, the reflection from the ground, and the muzzle blast. The time elapsed between the shock wave and the muzzle blast increased with increasing distance: 94ms for a distance of 50m, and 507ms for a distance of 300m. The highest peak sound level downrange from a single round was between 151dB(C) and 148dB(C) at distances from 50m to 300m, and varied little if at all with distance. To the left of the gun, the peak sound pressure level of 161dB(C) at 0.3m reduced to 128dB(C) at 32m. The peak sound pressure level was estimated to be 137dB(C) at a distance of approximately 20m to the left-hand side. Hearing protection must therefore be worn by anyone closer than 20m to a person firing. The peak sound pressure level was estimated to be 135dB(C) at a distance of approximately 25m and therefore hearing protection is recommended at distances of up to 25m. The sound exposure level of 98dB(A) at 20m indicated that an observer at this distance could hear about 1440 rounds without hearing protection before the noise exposure reached the upper exposure action value specified in the Control of Noise at Work Regulations 2005. Peak sound pressure levels were on average 2.4dB higher at the left ear compared with the right ear.