So, when the cabin is sealed, the interior pressure is equal to the atmospheric pressure at sea level. When the plane lands, the exterior pressure is equal to the interior pressure. So why does the plane need to be pressurised for the duration of the trip?
In: Engineering
At those altitudes the pressure is insufficient for your lungs to inflate properly. A lot of people will say ‘there is less oxygen…’ but it is more right to say the lack of pressure makes creating sufficient gradient in your lungs impossible. If you simply pressurized the outside air (with a mask or something) the pressurization process would get enough molecules together for you to get enough oxygen. Same thing when you go under water, the air is *too* pressurized so you have to breath a tank filled at regular pressure.
EDIT –
For the inevitable people who read this and go “wait, I was always told…”, you were told wrong. Think about it, if there isn’t enough oxygen to breath, how in the hell is there enough oxygen for a jet engine to combust? Why does a turbine work at that altitude but a ICE engine struggles? It is *pressure,* a jet engine is little more than an air compressing machine. If you have a tool that can compress the air at 30,000 feet by vacuuming up air molecules from far ahead of the plane the makeup of that gas is the exact same as it is at sea level, the only difference is you had to vacuum it up. If your lungs were a powerful vacuum you could easily breath at 30,000 feet. The problem is your biology cannot vacuum up enough air at 30,000 feet and as a result despite breathing hard you won’t get any gas into the lungs. Hence pressurization.
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