At 12,000 metres (39,000 feet), oxygen pressure is so low that even breathing pure oxygen doesn’t transfer enough into your blood. This is why all airliner cabins are pressurised, and need an air supply pumped into them to maintain our most vital life process. If the cabin were to depressurise at this altitude, you’d have approximately 15 seconds to get your oxygen mask on before losing consciousness.
The cargo hold is also pressurised to prevent items within passengers’ luggage leaking, expanding or bursting. In a standard commercial air recirculation system, the air that’s pumped out is composed of 50 per cent outside air and 50 per cent re-circulated air. The recycled air isn’t simply pumped back around the cabin; it goes through a complex cleaning process to remove bacteria, fungi, dust, fibres and odours. This 50/50 mix ensures that the chance of germs spreading is kept very low while also guaranteeing optimal fuel economy for the plane.
The outside component of this mixture is provided by the engines, which take in some of the surrounding air as they fly and compress it. This compression heats the air, so it is cooled and then filtered before being mixed with the recycled cabin supply. Sensors regulate the rate at which outside air is added to the cabin in order to maintain optimum air pressure inside the plane, allowing passengers and crew to breathe easy.
The truth about air inside planes
People dread flying for a number of different reasons, whether it’s a fear of confined spaces or potential disasters. A surprisingly common aspect of flying that makes people nervous is the thought of getting ill, but is cabin air as rancid as people think?
Thankfully, the answer is no. Recent studies have shown that a crowded airplane is no more germ-filled than any other typical enclosed space; they are actually more likely to be cleaner. This is partly due to the underfloor, high-energy particulate air (HEPA) filters, which are said to be of hospital quality by their manufacturers. Boeing claim that as much as 99.9 per cent of airborne microbes are captured and removed from the air on their aircraft, and that the air is replaced much more frequently than in an office, classroom or cinema.
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