Sound Attenuating Properties Of A Wetsuit Hood
Poster Presentation -- "Open ocean trials of the effect of depth on underwater sound attenuation of a neoprene wetsuit hood." Undersea and Hyperbaric Medical Society Annual Scientific Meeting, Sydney, Australia, May 26th -29th 2004. In: Undersea and Hyperbaric Medicine 31, 317, 2004.
NSMRL's Diving and Environmental Simulation Department returned on 5 Feb 03 from a 10 day diving operation in the Bahamas where they carried out human diving experiments to determine the effects of dive depth on the sound attenuating properties of a standard neoprene wetsuit hood. The diving experiments were conducted from a dive boat in the Tongue of the Ocean off the coast of the Southern Berry Islands and New Providence Island in the Bahamas. The warm clear waters of the Bahamas provided an ideal test site for open water validation of experiments recently conducted in NSMRL's Genesis hyperbaric chamber on manned and unmanned assessment of wetsuit hood sound protection. In all, over 65 open ocean dives were conducted in 10 and 60-foot depths. NSMRL's dive team was supported by diver subjects from Naval Submarine Support Facility, Naval Undersea Medical Institute, Military Medicine Clinic, USS Connecticut, Submarine Squadron Support Unit at Naval Submarine Base NLON, CT and by divers from Mobile Salvage and Diving Unit 2 in Little Creek, VA. The open water experiments will provide essential data on which to base future guidance for permissible sound exposure of fleet divers operating noisy underwater tools or diving in the vicinity of high powered sonar.
NSMRL is determining the amount of underwater sound attenuation afforded by various diver wet suit materials and thickness. Testing is being conducted within the frequency range of 100-20,000Hz.
Wet suit material test rig with hydrophone located inside hood.
Partial Test Results
Psychological Effects of Low Frequency Underwater Sound on Divers
NSMRL is assessing diver aversion and panic reaction to Low Frequency sonar signals at different sound pressure levels within the frequency range of 500-2500 Hz. NSMRL recently generated specific guidance for military/commercial/recreational divers for underwater sound levels.
Diver-Worn Sound Meter
NSMRL is developing a personal dosimeter which alerts divers to noise hazards across broad range of frequencies and intensities.
Dive Station Topside Underwater Sound Level Monitor
NSMRL is developing an underwater sound monitoring system to allow diving supervisors to determine sound level exposure for working divers.
|| < Packaged monitor ready to travel to dive site.|
The Diving and Environmental Simulation Team focuses on ways to optimize the performance and safety of Navy divers. Our goal is to increase mission effectiveness by reducing workplace hazard and providing underwater noise-protection tools. On-going direct fleet support regarding guidelines for operational limits due to underwater noise are a critical part of the program. We are a team of two research psychologists, two diving medical officers, and five research-support personnel, including diving supervisors and a biomedical engineer.
Underwater noise can impact the diver through hearing damage and damage to internal organs, such as the lung and brain. Three approaches to improving the safety and enhancing the performance of divers are:
- Underwater Noise Guidance - Provides the permissible exposure limits for underwater noise, ranging from continuous noise through blast.
- Underwater Noise Measurement - This includes an underwater sound-level meter for use by top-side personnel and an underwater noise dosimeter for noise measurements on an individual.
- Protective Measures - Techniques and garments that enhance the protection of the diver from underwater noise by reducing the noise-intensity at the diver.
Auditory facilities include:
- Ten double-walled sound-proof audiometric booths
- 1000 cubic meter anechoic chamber
- 145 cubic meter reverberant room
- Mannequins with acoustic ear simulators
- Underwater measurement devices
- Underwater sound projectors
Diving facilities include:
- Dive Locker
- Three hyperbaric chambers on-site:
- A chamber with a removable wet pot (saturation chamber/depths to 350 FSW)
- A treatment chamber (depths to 165 FSW)
- An instrumentation test chamber (depths to 1000 FSW)
- Access to local open-water diving facility with acoustic support
Our efforts are augmented by collaborations with a number of universities and diving organizations, and various agencies including:
- Navy Experimental Diving Unit
- Naval Undersea Warfare Center
- Naval Research Laboratory Underwater Sound Reference Division
- Naval Submarine Support Facility
- Naval Medical Center at San Diego
- Naval Medical Research Center
- Space & Naval Warfare
- Defence Environmental Research Agency at Alverstoke in the United Kingdom
We have access to divers through the submarine support facility and the escape trainer.