The Risk of Noise-Induced Hearing Loss During Simulated Dives in Canadian Forces Hyperbaric Facilities

Abstract : This study was conducted in response to a Support to Operations/Support to Development Engineering and Evaluation (STO/DEE) request from ADM (Mat) for information relating to Canadian Forces divers' risk of developing noise-induced hearing loss during simulated dives. During a simulated dive, high pressure air is transferred into the dive chamber of a hyperbaric facility. The mechanism is audible and sufficiently high in level in adjacent areas to warrant the use of hearing protection. There were two parts to the experiment, the assessment of hearing protector attenuation and the measurement of sound levels. In Part I, hearing thresholds were measured at frequencies from 250-8000 Hz in twenty normal-hearing males and females (1) with the head uncovered and ears unoccluded, (2) while wearing a wetsuit hood, and (3) while fitted with three hearing protection earmuffs, unvented and vented. Venting, the practice of drilling a small hole in earcups, is meant to prevent eardrum barotrauma. Attenuation was derived by subtracting the unoccluded from the protected thresholds. In Part II, sound level measurements were made at twenty-two positions within the Diving Research and Diving Training Facilities of Defence Research and Development Canada ? Toronto. Earmuff venting resulted in a decrease in attenuation of as much as 17 dB at 250 Hz and 500 Hz. Although it was determined that some of the protected sound levels might be unsafe, the exposure duration was sufficiently short to minimize the possibility of hearing damage.