Abstract:
A 30-month experimental and modeling study was conducted into the effects of low-frequency active (LFA) sonars on Navy divers. 453 dives using 87 subjects were completed with one symptomatic event. A variety of dive equipment, depths to five atmospheres, and three signal waveforms were used. Interim guidance for exposure to LFA signals was issued by the U.S. Navy Bureau of Medicine and Surgery. For exposures to nonimpulsive waterborne sound in the frequency range 160--320 Hz, the following set of parameters did not compromise the safety of a highly trained, fit, and informed diver (diver compromise refers to a diver who could become a casualty or burden to others in an operational setting): A maximum overall SPL of 160 dB for no more than 100 s continuous exposure on a 50% duty cycle, with a cumulative exposure limit of 15 min/dive-day, a total of 9 days of exposure in a 2-week period. SPL is measured at the diver's location. This guidance is generalizable only to those populations equivalent in medical health and fitness to U.S. Navy divers. [Work supported by U.S. Navy.]