Effects of using long breathing hoses upon mask pressure.

Effects of using oxygen breathing hoses from 0.9 to 8.2 m (3 to 27 ft) long and mask fit upon mask pressure during 0.75 to 12-s decompressions from 2,438 m (8,000 ft) to either 6,096, 10,668, or 15,240 m (20,000, 35,000 or 50,000 ft) were determined. Peak mask pressures and duration of high mask pressure were related to mask fit, mask and hose stretch compliance, pressure differential, decompression rate, and other factors, with mask pressure increasing with hose length. Peak mask pressures frequently exceeded 80 mm Hg, a high pressure associated with increased incidence of pulmonary damage. Cargo-type aircraft, however, have sufficiently large volumes so that they will not decompress rapidly enough to have high mask pressure, even with an 8.2-m long hose. Long breathing hoses should not be used in smaller aircraft since small cabin volume will result in rapid decompression rates and high mask pressure. Above a flight altitude of 2,438 m, oxygen should always be breathed if hoses longer than 2.9 m (9 ft) are used. This would help prevent hypoxia, associated with the need to deplete air in the hose before oxygen is breathed, should cabin pressure be lost at a high altitude. The fastest decompression rates compatible with preventing mask pressures from exceding 80 mm Hg during decompressions to different altitudes with different length breathing hoses are given.