How Long Would You Survive From Your Plane Seat to Space?

Imagine a teleporter beaming you straight up from your sofa at sea level, with no time to get used to anything. At each of nine stops, from an airliner seat to the International Space Station, a stopwatch shows how long you'd stay useful, meaning able to think and act, not just awake. The times are averages for a calm, healthy adult. Smoke or panic and your clock runs faster.

The airplane cabin: 8,000 feet

A sealed cabin isn't sea level in a tube. The rules let it sit as high as 8,000 feet, about the height of Machu Picchu, only with worse legroom and no llamas.

The first thing to know for the whole trip is that the air up there is still 21% oxygen. What it loses is the pressure that pushes that oxygen into you. Same fizzy drink, no fizz.

In a study of 500 people, blood oxygen dropped by more than four points at cabin altitude. The air trapped in your crisp packet now pushes harder than the cabin air around it, so the packet puffs up. Your gut does the same. Danish doctors wrote a real paper about it called "Flatulence on airplanes", and even suggested charcoal seat cushions.

The stopwatch reads infinity.

La Rinconada: 16,700 feet

Nobody lives this high, surely? By NASA's count, about 50,000 people do, mining gold in the highest town on Earth. Every breath here holds half the oxygen of a breath at sea level. It's like drinking a milkshake through a coffee stirrer.

Their bodies have adapted. Researchers measured blood that was up to about 80% red cells. Down in Lima it's 40%. That comes at a price, and researchers estimate that as many as one in four people here have chronic mountain sickness.

Arrive straight from the sofa and one flight of stairs leaves you needing a lie-down. Go up to 18,000 feet, where half of the whole atmosphere is below your feet, and the stopwatch finally starts. You get 20 to 30 useful minutes, about one sitcom episode, and you won't notice them going. In FAA tests, some volunteers felt euphoric while they couldn't write their own name. You'll feel like a genius the whole time, which is exactly the problem.

The death zone: 8,000 metres

People do climb Everest. In 1978, Reinhold Messner and Peter Habeler even did it without bottled oxygen. But climbers take weeks to get used to the height. The teleporter gave you a fifth of a second.

At 25,000 feet, the stopwatch gives you three to five minutes. On the summit, under three. Above 8,000 metres no human body can adapt, not even a climber's. Cuts barely heal and colds don't go away. When doctors took climbers' blood just below the summit, its oxygen level was 24.6. Normal is 75 to 100.

In an altitude chamber, a physics professor forgot how to add 2 and 1. In his words, "After a short while, I didn't care."

Cruising altitude: 35,000 feet

This is where your flight actually cruises. You're just on the wrong side of the window. You get 30 to 60 seconds. If the air goes all at once, that drops to 15 to 30 seconds, about one unskippable advert.

That's why the safety briefing tells you to put your own mask on first. Help a child first and you might pass out before their mask is on. The bag may not inflate even though oxygen is flowing, and that's normal. Your anxiety will inflate instead.

Pilots' masks must go on with one hand in five seconds. And if the plane suddenly dives, that's deliberate. The pilot is racing you down to air you can breathe.

The oxygen wall: 40,000 feet

Finally the mask is on, and it's 100% pure oxygen. You win? Not up here. The air is so thin that even pure oxygen has to be forced into your lungs under pressure. A professor who tried it says it tries to blow you up like a balloon, and to breathe out you have to squeeze. Without that, you get 15 to 20 seconds.

Engineers drew a line here. Airliners must be built so the cabin never goes above 40,000 feet, even after a serious failure. Concorde used to cruise at 60,000 feet.

The Armstrong limit: 63,000 feet

This one is named after Harry Armstrong, an Air Force general. Not Neil. Harry. The air pressure here is about a sixteenth of sea level, so low that water boils at body temperature. You could bring a pot of water to the boil just by holding it, and the pasta still wouldn't cook. Your spit, your tears and the moisture in your lungs all start to fizz. Remember the flat fizzy drink? Now you're the drink.

Your blood doesn't boil, because your heart keeps it under pressure. It's the only organ up here doing its job. And whatever films say, you don't explode. Your skin holds. In 1960, Joe Kittinger's glove failed on his balloon ride up, and his hand swelled to twice its size. He jumped anyway.

The stopwatch is down to about 10 seconds, and here it hits its floor.

The stratosphere jump: 128,000 feet

Picture the step of a tiny capsule 39 km up, under a black sky. Outside your suit, you'd get about 10 seconds.

In 2012, Felix Baumgartner did it for real, from a balloon over New Mexico. With hardly any air to slow him down, he reached Mach 1.25, or 843 mph, with no engine. He got through a dangerous spin and opened his parachute after 4 minutes and 16 seconds of freefall. More than 9.5 million people watched live.

On the radio was Joe Kittinger, the man with the swollen hand, whose 1960 record Baumgartner was breaking. Baumgartner fell faster than sound and landed on his feet.

The Kármán line: 100 km

Congratulations, you're officially in space. Time to float majestically? No. You fall. Gravity is still almost full strength up here. The Kármán line is a definition, and there's no wall. Up here a plane would need so much speed to get lift that it would basically be a satellite.

Astronomer Fred Hoyle said space is only an hour's drive away if your car could go straight upwards. A tourist rocket hop up to here and back takes about 11 minutes. The stopwatch still reads about 10 seconds, the same as at 63,000 feet. Once the air is gone, going higher can't make it any worse.

The space station: about 400 km

The highest stop should have the shortest stopwatch. Instead it lands on infinity. Inside, the station keeps the same air pressure as your living room, with about 21% oxygen, so nobody needs a suit.

Gravity hasn't gone, either. Up there it's still 90% of what you feel on the ground. Astronauts are falling around the Earth and missing, at 17,500 mph, which means 16 sunrises a day. Frank Rubio went up for six months and stayed for 371 days, the ultimate delayed flight.

Step outside without a suit, though, and you're back to about 10 to 15 seconds. In 1966, NASA test subject Jim LeBlanc's suit hose came loose in a vacuum chamber. His last memory was the spit on his tongue starting to boil. He woke up fine once they pumped the air back in.

So the highest stop has the longest stopwatch. It was never the height. It was the pressure, and cabins, suits and stations all just bring sea level along.

The short version

• High-altitude air is still about 21% oxygen. What runs out is the pressure that pushes it into you.
• A cabin can sit at up to 8,000 feet and about 50,000 people live at 16,700 feet, but above 8,000 metres no human body can adapt.
• At cruising height you'd have 30 to 60 useful seconds, or 15 to 30 if the air goes all at once, so put your own mask on first and then help others.
• From the Armstrong limit upwards, the stopwatch bottoms out at about 10 seconds.
• The safest places on the trip are the ones that carry sea-level pressure with them, like your sofa and the space station.