Speech Intelligibility as a Function of Helium-Oxygen Breathing Mixture and Ambient Pressure

Abstract

Speech intelligibility was obtained on Navy divers at sea level (in air) and at 200 and 450 ft (simulated) in helium-oxygen breathing mixtures. Subjects were personnel in training for Sealab 3 at the Experimental Diving Unit, Washington Navy Yard. A total of 26 subjects were evaluated (11 at 0 and 200 ft, 11 at 0 and 0,50 ft and four at 0, 200, and 450 ft). The speech material used was the PB-25 word lists equated by Campbell for difficulty; the lists were read prior to descending and immediately upon reaching depth. The helium-nitrogen-oxygen mixtures were 79/17/4 at 200 ft and 90/8/2 at 450 ft. A relatively nonreverberent recording environment was provided by an enclosure fabricated from mattresses available in the chamber's sleeping compartment. Listeners were 15 University of Florida students trained for tasks of this nature. The combined efforts of HeO2 mixtures and high ambient pressures were extremely detrimental to speech intelligibility (scores of less than 20% were common at 450 ft). [The project was supported by the Office of Naval Research.]