Effects Of Low-Frequency Water-Borne Sound On Divers: Open Water Trial.

Abstract

Navy divers may be exposed to active sonar transmissions while underwater. Previous manned experiments to determine safe levels of exposure have all been conducted in enclosed settings characterized by standing wave sound fields. The purpose of this experiment was to determine if plane wave (open water) acoustics alters the physiological or subjective responses of exposed divers compared to standing wave exposures. 54 manned exposures to two low-frequency underwater acoustic signals were performed at depths of 30 and 60 feet in a fresh water spring. Two projectors were used to create a plane progressive traveling acoustic wave. Divers were exposed in both helmeted and unhelmeted diving rigs. Effects on hearing, vestibular function, cardiac rhythm, and a key-insertion task were measured. Subjective responses were also recorded. In addition, the effects of neoprene wet suits on sound attenuation were measured. Slight decrements in hearing acuity were detected, but these results were confounded by circumstances unrelated to the underwater sound exposures, such as ear squeezes from diving, and microphone feedback noise. No adverse effects in vestibular function, cardiac rhythm, or key insertion performance were detected. Subjective responses revealed that divers were moderately annoyed by the underwater sound, but overall found the exposures tolerable. Neoprene wet suits generally act to attenuate low-frequency sound exposures, but under certain circumstances may also accentuate a sound exposure, possibly through a resonance effect. There is no indication from the results of this study that low-frequency water-borne sound exposures in the open water present any additional risk to divers compared to similar exposures in enclosed environments.