Humans aren’t supposed to fly – we weren’t born with wings. Well, at least anyone I know wasn’t. However, for the past century or so, we have been doing our best to fly and to fly safe. One of the things we have to take into account in modern aviation is the altitude we fly at. High altitude is great for the aircraft and the airline – the aircraft experiences less drag because the air is less dense and also burns less fuel – good for the airline. The thing is, humans need oxygen. That’s why you’ve (hopefully) been breathing since the day you were born!
At 30,000 feet there is a lower concentration of oxygen than at sea level. So low that, if you take a human from sea level to 30,000 feet in a matter of minutes, they’ll pass out and eventually…well…you know. To get around this problem, aircraft cabins are pressurised to keep the oxygen levels far closer to what we are used to. The pressure stays in the cabin throughout the flight until the descent to the destination airport. During the descent the aircraft systems equalize the pressure inside the cabin to the ambient pressure outside.
As you know, before every flight there is a demonstration by the cabin crew. They talk about oxygen masks as part of their presentation. These would be used if there was a decompression in the cabin and the inside pressure becomes equal to the outside pressure. These oxygen masks provide a limited supply and so the aircraft would descent to a lower altitude where the pressure is back to levels that enable us frail humans to take in enough oxygen.
The following video was referred to in class today. We didn’t get to see it so I looked it up. It’s both entertaining and informative. I didn’t have the time to watch it all the way through and so skipped to the part about air pressure which starts at around 13:00. For a greater insight into what happens during a rapid decompression it’s well worth watching. For those nervous about flying, go here instead.