Occupational noise exposure on a Royal Navy warship during weapon fire

Measurements were made of the sound pressure levels on a military ship HMS Grimsby during firing of a Heavy Machine Gun (HMG) mounted on the starboard bridge wing. The measurement positions comprised three locations on the ship's bridge (the wheelhouse) and one location on the starboard bridge wing. Equipment and Procedure: The three locations on the bridge were the starboard door, centre and port door. A total of 255 burst firings were measured during the survey comprising 850 rounds with each burst encompassing from 1 to 10 rounds.

The data have been assessed and interpreted in accordance with the Control of Noise at Work Regulations 2005.

The highest peak sound pressure levels measured on the bridge wing and on the bridge were 160.7 dB(C) (2170 Pa) and 122.7 dB(C) (27.3 Pa), respectively. The highest sound exposure levels measured on the bridge wing and on the bridge corresponding to one round being fired were 127.8 dB(A) and 88.9 dB(A), respectively. The ship's structure provided about 40 dB attenuation in the transmitted noise.

The operator of the weapon would be required to wear some form of hearing protection. On the basis of the measured peak noise levels, there would be no requirement for bridge crew to wear any hearing protection during firing of a HMG. However, crew exposure to noise on the bridge is likely to exceed the upper exposure action value corresponding to 85 dB(A) after about 11,750 rounds.

Measurements made on the bridge wings are likely to be affected by reflections from the ship's structure.