Hearing damage risk to divers operating noisy tools under water.

During the measurement of noise generated inside a standard hard hat and the underwater noise level produced by a pneumatic rock drill and two different high-pressure water jet lances commonly used in underwater work, noise levels were recorded of up to 170.5 dB(A), in relation to a pressure of 1 muPa, in the water close to the diver's heads. Fortunately, the noise is attenuated by the hoods/helmets worn by the divers and the raised hearing threshold in water and compressed gas. The recorded temporary threshold shifts indicate, however, that lengthy exposure might be hazardous to divers' hearing. This possibility is confirmed by a comparison of the noise levels observed in the present study with hearing damage risk criteria.