Abstract: An oxygen breathing apparatus for protection of aircraft passengers against aircraft depressurization has a pressurized oxygen storage and a distribution unit operated responsive to loss of pressurization at high altitude for feeding a pipe with pressurized oxygen from the storage. The passenger masks have a face cover which is formed with an inwardly directed circumferential flexible sealing lip and are each connected to the pipe by a flexible hose having a metering orifice. The distribution unit delivers pressurized oxygen under a pressure which increases up to a first value which is reached when loss of pressurization occurs immediately under a predetermined altitude (about 40,000 ft) and has a second value, of about two times the first value as long as the altitude exceeds the predetermined value. In a modification, the second pressure is delivered for a given period, typically about 3 mn.