One of the genius moments in Kubrick’s 2001: A Space Odyssey comes when Dave Bowman, locked out of the Discovery in a ‘pod’, without his suit helmet, re-enters anyway, via the emergency airlock.
He’s unprotected in vacuum – but he doesn’t die instantly, or freeze, or explode the way people usually do in movies when vacuum intrudes. The writer of that scene, Arthur C. Clarke, had used the same trick in his 1955 novel Earthlight – and on very sound scientific principles. (There’s a crater on the moon named after this novel. Just saying). Vacuum exposure was done scientifically again in Battlestar Galactica, perhaps more so than Clarke – the two vacuum-breathers ended up afterwards in a hyperbaric chamber with bloodshot eyes.
So how does the science work? Let’s suppose the starting pressure is 1 atmosphere – sea level – 101,325 pascals (a force of 1 newton per square metre), or 760 torr, or (if you’re in America), 14.696 psi. That’s the pressure used on the space station, but spacesuits run at much lower pressures, meaning some of the effects wouldn’t quite be the same. Also, there are differences between slow decompression (which happened to the crew of Soyuz 11 on re-entry in June 1971, killing them) and explosive decompression, when the pressure drops very rapidly to zero. I’m describing explosive decompression. And I’m describing it in street clothes, which for vacuum purposes is naked. Mechanically, a human can survive such a pressure change easily – as Clarke pointed out, all you have to do is surface from 10 metres (30 feet) underwater to experience a 1-atmosphere drop. Of course that isn’t the only calculation, but for all that, there has been a lot of stupidity about what DOES go on in sudden vacuum.
- Silliness 1: instantly blowing up like a balloon. Sure you’ll blow up – but not until long after you’re dead from other causes. While you’ve still got 1 atmosphere pressure inside you, and outside is a big fat zero, skin’s tough and flesh isn’t very elastic. In fact your skin is a good space-suit and there have been proposals for skin-tight elasticised spacesuits that mechanically add enough pressure to keep you together. What WOULD happen is that all the air would rush out of your lungs. If you tried to hold your breath, you’d rupture them. You’d also be more flatulent than a band of cowboys on a baked bean frenzy, but don’t worry. In space nobody can smell.
- Silliness 2: instantly freezing solid. Vacuum insulates – energy only transmits through it as radiation. At Earth orbital distance, anything in direct sunlight is at 106 degrees celsius, anything in shadow is at 186 below. We don’t have that variation on Earth because the atmosphere and oceans moderate it (conductive, more than radiative, transfer). In vacuum, whatever unprotected part of you faced the sun would roast and whatever faced shadow would eventually freeze, except that in space, everything spins. Yah – balancing the temperatures a la rotisserie (push your arms out to slow down…) The Apollo moon missions spun the CSM/LM during the trans-lunar cruise, deliberately, to even out the temperature gradients. The astronauts called it ‘barbecue mode’. If you were on the night side of Earth, though – or stuck in shadow – you’d eventually freeze. But not instantly. Humans are mostly salty water, which has a very high specific heat of 1 calorie/gram per degree C, meaning it’s hard to change its temperature quickly (‘the watched pot never boils’ wasn’t an aphorism, it was physics.) In the first seconds of exposure, though, you’d feel cold. This is because the vacuum causes the water on your skin, eyes and inside your mouth to boil off, which you’d feel as cooling.
- Silliness 3: instant asphyxiation. As Clarke and Kubrick well knew, there’s oxygen already in your bloodstream. You get about 9-11 seconds consciousness, more if you’ve hyperventilated prior.
- Silliness 4: your blood instantly boils. A healthy human has a diastolic (lower) blood pressure of about 80 torr, at which blood boils at around 46.1 degrees celsius, higher than body temperature. That won’t change on initial exposure to vacuum. Only after your heart stops will your blood pressure drop to low-pressure boil.
That deals with the usual Hollywood tropes. But there’s more science to vacuum exposure. In an explosive decompression, if you’re in a cabin, the available space fogs because the thinning air dumps its water vapour. There’s a lot of noise, and the ‘surprise’ effect has been shown to reduce the period of consciousness. And there’s more, particularly if you’re cast into space. For instance:
- Sunburn. If you’re in space without a spacesuit, you’ll be exposed to the unfiltered rays of the Sun – including heavy ultraviolet. At the very least, you’ll be sunburnt. Clarke got that right in Earthlight.
- The Bends. While your flesh and skin stop you exploding instantly – and your blood won’t boil – there’s still a pressure drop with high risk of air embolism, including under the skin from water vapour. Among other medical reasons associated with vacuum exposure, that’s why the Galactica vacuum victims were seen in a hyperbaric chamber afterwards. The writers nailed the science.
- Capillary damage. There’s a high chance that capillaries in the eyes and other surfaces rupture. You’ll end up with bloodshot eyes at least.
How long will you last? There is, alas, data on that. Several people have been caught by space-suit test accidents in vacuum chambers. One, who survived, recalled feeling his saliva boiling off his tongue. The bottom line from those accidents is that you’ll lose consciousness after 10 seconds or so, and will die of anoxia within 2-3 minutes, ahead of freezing, expansion and all the rest. If you’re repressurised within about 90 seconds – and before your heart stops – you’ll probably survive. Survival and the nature of the injuries, on current information, seems to be on a per-case basis because the number of those caught by vacuum (mercifully) are minimal.
Still, vacuum exposure is nasty and not recommended. Don’t try it at home. Or anywhere else, for that matter.
Copyright © Matthew Wright 2016