• Airplane doors are impossible to open at cruising altitude, which is about 36,000 feet above sea level.
  • Cabins are pressurized to mimic conditions at 8,000 feet above sea level to keep passengers alive.
  • The lower the air pressure, the harder it is for people to breathe.
  • The pressure pushing against the average passenger door equals about 1,100 pounds per square foot.

Following is a transcript of the video.

Narrator: This is episode 123 of “The Twilight Zone,” “Nightmare at 20,000 Feet.” Arguably one of the most iconic episodes of the show ever made, it stars William Shatner as a:

Clip: Portrait of a frightened man: Mr. Robert Wilson.

Narrator: Bob sees a gremlin on the wing of the plane and decides the only possible solution to the problem is to steal the air marshal’s gun, open the emergency exit, and shoot the thing. Clearly, this scene is complete fantasy. And I’m not talking about the gremlin.

There are a couple of reasons why you can't open an airplane door mid-flight. The first being: It's locked. But there's another big factor that "The Twilight Zone" seems to ignore, and that's physics.

Let's consult our first completely reliable source, the episode's IMDb "Goofs" page. It says the plane Shatner's flying in is either a twin-engined Convair or a four-engined Douglas DC-6 or DC-7. All of which would have been pressurized.

The higher a plane flies, the lower the air pressure outside. And the lower the air pressure, the harder it is to breathe. That's because the air is thinner the higher you go. The molecules are literally farther apart. So there are fewer oxygen molecules in every breath you breathe and less pressure diffusing that oxygen into your bloodstream.

Over 18,000 feet above sea level, and our bodies just aren't able to absorb enough to keep us functioning. That's why planes are pressurized to mimic conditions about 8,000 feet above sea level. It's a nice middle ground that lowers the oxygen in our blood by only about 4%, which is not enough to really affect how we function.

Modern airlines fly at about 36,000 feet above sea level. If they weren't pressurized, it would cause delirium in seconds and knock you out in under a minute. And the difference between the inside of the plane and the outside can be huge. Which is exactly where the doors come in. Inside the cabin, 8 pounds of pressure push against every square inch of surface area. The typical passenger door is about 6 feet tall by 3 1/2 feet wide. So we're looking at more than 24,000 pounds of pressure bearing down on that exit.

The strongest man alive can deadlift only 1,102 pounds. "But wait!" you scream at your computer screen. "This nightmare was at 20,000 feet, not 36,000. The pressure would be lower!" You're right, but there's no need to yell.

Clip: Keep your voice down.

Bob: I'm sorry, I'm sorry.

Narrator: The pressure would be lower, but still too much for a person to overcome, even William Shatner. And the door flying out into the inky black? Practically impossible on a modern plane. Most passenger doors are tapered, the inner edge being wider than the outer. It's called a plug door, and it basically acts like a bathtub-drain stopper, corking the hole without falling through. But what if someone on your plane had Shatner's superhuman strength? It could cause something called "explosive decompression." And it's the one thing "The Twilight Zone" got mostly right.

During an Aloha Airlines flight in 1988, a piece of the fuselage tore loose at 24,000 feet, leaving "blue sky where the first-class ceiling had been," according to the captain. The chief flight attendant was instantly sucked out of the plane through that gaping hole.

Explosive decompression happens infrequently, but it does happen. A rip in the plane wall, a window cracks, it doesn't matter the cause. The huge pressure difference creates a vacuum capable of shooting anything up to 1,000 pounds out into the sky. And that vacuum effect would last until the pressure inside the cabin matched the pressure outside. So Shatner made a good call buckling himself in before opening that emergency exit.

If you don't live in the Twilight Zone, your chances of pulling open an airplane door mid-flight are just as good as seeing a gremlin on the wing. So the next time you start getting nervous about it, just remind yourself:

Bob: I'm gonna be all right.