Noise characteristics of the Kirby Morgan 37 surface-supplied diving helmet under simulated diving conditions.

Abstract

Divers are exposed to noise from a variety of sources, including their breathing apparatus. Furthermore, there is a significant body of information that suggests divers are susceptible to hearing loss that worsens faster than the general population. This study measured the noise characteristics of a commonly used diving helmet, the Kirby Morgan 37 (Kirby Morgan Dive Systems, Inc., Santa Maria, CA) under simulated diving conditions that included variations in depth, breathing rate, and breathing gas. Depth was varied from 0 to 165 feet sea water (fsw) and breathing rates were varied from 22.5 to 90 liters per minute (lpm). Air and an 80% helium/20% oxygen mixture (heliox) were considered as diving gases. Measured noise levels increased with increases in both diving depth and breathing rate. Using heliox as the breathing gas produced lower noise levels than air under the same conditions. It was observed that the spectral characteristics of inhalation and exhalation were considerably different due to different flow paths through the apparatus. Exhalation produced mostly low frequency noise (below 600 Hz), while inhalation was responsible for most of the noise between 600 Hz and 20 kHz.