This is why getting your oxygen mask sorted as quickly as possible is the most important thing you can do until the pilot is able to bring the plane to a breathable altitude.
However, nervous flyers needn't worry too much.
As Jason Rabinowitz explained to Travel + Leisure, the pressure difference between the outside and inside makes it nigh on "physically impossible" to open a door mid-flight, although that hasn't stopped some people from trying in the past.
Smith says: "At a typical cruising altitude, up to eight pounds of pressure are pushing against every square inch of the [aircraft body]."
As for the windows, they are designed to withstand a monumental level of pressure from the outside and could easily survive a human's force. They're made using a polycarbonate compound with several layers.
In a note issued by Airbus back in 2007, the company warned that the airline industry was unprepared and "untrained" for a decompression event.
"In one cabin decompression event, a cabin crew member was saved from ejection out of the aircraft, because a passenger was holding on to the cabin crew member's ankle."
While these rapid decompression events are extremely rare, it is always good to know what to do if one were to happen.
Make sure your seat belt is fastened correctly, you know where the oxygen mask is going to drop from, and where any vulnerable passengers are that may need your assistance once you are safe.
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