ABSTRACT
It is a common conception that passenger aircraft allows a normal sea-level environment. This, however, is untrue, and most are pressurized to cabin altitudes of between 1829 m (6000 ft) and 2438 m (8000 ft), although this maximum may be breached in emergencies. At 8000 ft cabin altitude, the partial pressure of oxygen will be the equivalent of breathing 15.1% oxygen at sea level, and a healthy passenger will experience a fall in arterial oxygen tension (PaO2) to around 8.7 kPa. This would rise to about 10.0 kPa at 6000 ft, giving oxyhemoglobin saturation (SPO2) of between 89% and 94% respectively.
