Stephen Swintek/Getty Images
Cailey Rizzo
January 17, 2017

Every airplane passenger knows the spiel: “Although the bag may not inflate, rest assured oxygen is flowing. Secure your own mask before assisting others.”

But even though passengers hear what to do if oxygen masks suddenly drop from the cabin ceiling, the details on what the masks are actually there to do are a bit more vague.

When you’re flying you’re (obviously) at a much higher altitude than normal. The air is thinner, which means there’s less oxygen. On board every plane is a sophisticated pressure system that ensures everyone can breathe normally, but if something happens where there’s a sudden loss in pressure, the effect could be dangerous.

A loss of oxygen to the body causes causes something called hypoxia, the effects of which are confusion, cough, nausea, rapid breathing, changes in skin color, and headaches. If oxygen deficiency continues over a long enough period of time, it can cause unconsciousness, permanent brain damage or even death.

So, in order to keep everyone maintained with enough oxygen, the masks fall down and provide a personal flow.

However, the aircraft only has enough oxygen to provide a flow for “several minutes,” which is a lot shorter time than most believed. The masks are only meant to keep passengers supplied with oxygen until a pilot is able to bring the aircraft down.

Up in the cockpit pilots get their own oxygen masks. Once they’re outfitted, they maneuver the plane to less than 10,000 feet in altitude, where passengers will be able to breathe more easily.

“If the emergency descent feels perilously fast, this isn’t because the plane is crashing: it’s because the crew is doing what’s it’s supposed to do,” Patrick Smith, a pilot and author of “Cockpit Confidential,” told The Telegraph.

Airplanes don’t carry oxygen tanks above every single seat—that would be far too heavy. Instead, the panel above each seat includes a mixture of all sorts of chemicals that, when burned, create oxygen. (Some passengers report smelling burning when the oxygen masks fall. Don’t worry: It’s not the plane, it’s the creation of oxygen.)

Tugging on the mask when it falls kickstarts the process and allows oxygen to flow through. But this isn’t what inflates the bag. The size of the bag is completely reliant on the rate at which the passenger is breathing. Heavy breathers will have thinner bags while people who breathe less will see their bags inflate.

Just remember: No matter what, don’t remove the oxygen mask until crew inform you that pressure has been stabilized.

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