Evaluation of an Impulse Noise Producing Underwater Explosive Device on Hearing in Divers

摘要

The diver Audible Recall Device (A.R.D) is a self-contained small explosive device designed with a 6.6 sec delay fuse ignited by pulling a lanyard. It is weighted by both sand and lead shot, allowing detonation approximately 3m (9.8 ft) underwater. At a distance of 7m (22.9 ft) from the device, detonating at 3m (9.8 ft) underwater, the peak sound pressure level (SPL) is 185.5 dB (re 20 uPa) in-water, equivalent to 5.44 psi. With a explosion duration of 1.0 msec, the impulse is 2 psi. msec. Five U.S. Navy divers were exposed to this R.A.D. at a peak SPL of 186.2 dB (re 20 uPa) in-water, equivalent to an in-air value of 151.2 dB, which is 11.2 dB over the current 140 dB safe exposure limit for impulse noise, in-air, established by OPNAVINST 5100.23B 18103a(4). No reduction in hearing sensitivity in all five diver-subjects was observed as demonstrated by no temporary threshold shifts (TTS) in their audiograms. The impulse was described as very loud, but not uncomfortable. With the frequency of the A.R.D. impulse being 200-300 Hz, there was no damage to the lungs of gastrointestinal tract which would have been expected at lower frequencies around 50 Hz with higher impulse levels above 10 psi. msec. The A.R.D. was reliably heard by all five divers as far away as 1006m (1100 yds) at a depth of 3.0m (10 ft) in 9.1m (30 ft) of water. However, due to severe shrapnel risk from the casing, end-cap, and from lead shot and sand used as ballast, the A.R.D. was determined to be hazardous.