Rapid Decompression from 8 to 45 kft: Experimental Results from 10 Human Trials

Abstract

Introduction: In case of pressure loss of an airliner's cabin the initiation of immediate emergency descent is the primary task of the flight deck crew, supported by quick-donning oxygen equipment. For very rapid decompression < 5 s prebreathing of oxygen enriched gas is necessary to prevent transient unconsciousness of pilots as only exhalation is possible due to the expansion of alveolar gas. Flying at e.g. 45,000 ft, a mixture of 52% oxygen before pressure loss will be necessary for this scenario. For large transportation aircraft, a typical time interval of 10 - 20 s minimum can be expected for depressurisation, which allows the top-up of alveolar oxygen by several breaths if pure oxygen is provided early after start of events. Material und Methods: 10 subjects aged 29-71 yrs were decompressed from 8,000 to 45,000 ft. cruising altitude within 20 s, initially breathed air via a modified cockpit mask. After start of depressurisation the mask was switched to 100% oxygen. Subject oxygenation status was monitored via pulse oxymetry and oxygen partial pressure in the mask. Results: Minimum values during decompression and stay at maximum altitude for 10 s were an end tidal oxygen partial pressure of 43 hPa (41-62) and an arterial saturation of 77% (62-92). Middle ear pressure equilibration was performed without problems, none of the subjects showed any incapacitation during runs. Conclusion: By immediate switch (t = 2 s) to pure oxygen in a 20-s depressurisation prebreathing of an oxygen enriched gas is not necessary. The data can be used for model validation in this highly dynamic process, as proposed in the SAE A-10 Aircraft Oxygen Equipment Committee, opening the way to estimate crew and passenger hypoxia protection with different types of equipment. Learning Objectives: To understand the role of depressurisation time in protection strategies for flight deck crew against the threat of hyper-acute hypoxia.