So I’m a science fiction character who’s done something bad. They put me in the airlock - say 250x250x250cm filled with air at a pressure of one atmosphere - and open the door. Do I really blast out into space like in the movies with long-lasting hurricane-force winds, or does the air just puff out instantly, or what? Can I hang on to something and realistically remain inside the airlock?
I think it’s pretty standard for airlocks to open in the direction of the normally-greater pressure - so on submarines, that means opening outwards (so you can’t just accidentally open the door and let the water in) and on spacecraft, opening inwards, so that when pressurised, the airlock door seals itself and can’t be accidentally opened.
That’s not to say it’s impossible to have a Vogon-style airlock specifically built for the purpose of ejecting people, but that would be very bad news for anyone in the airlock when the door opens - even if they’re suited. Decompression is survivable, explosive decompression is big, bad news.
Heh, I just watched the movie the other night and thought of that scene too 
I often wondered that too, given that there’s so little air, is there really enough to impart such a force on you? On a windy day, with much air gusting past me, I can stand easily, if I had something to grab onto in the airlock surely I could remain inside.
And if I remain inside the problem remains the same, unless the airlock had controls on the inside to recompress the compartment.
That’s just a hatch. I think the OP is talking about an actual two chambered airlock that would be used to gain acces to the outside of the ship while in space.
To answer the op, it depends how big you design it and how fast the hatch opens. For the airlock you describem if the hatch opens relatively slowly sliding door style, air will start leaking out slowly at first and then more quickly as the opening gets larger. You will probably just experience a loud “whistling” until pressure equilizes, but you won’t get pulled out a pinhole crack like in Alien Resurection.
If your hatch is designed to just use the ambient pressure to swing open when released, everything would just blow out almost instantaneously.
In a real airlock though, they wouldn’t just blast you into space. Both chambers are closed, the air is evacuated from the chamber and then the outer door is opened to space so whoever or whatever can exit (presumably in some sort of craft or spacesuit).
The Sulacco from Aliens has the worst designed airlocks ever as both doors can apparently be opened at once. In reality, I don’t think Ripley would have been able to hold on as the contents of an entire hanger bay rushed past her at tornado speed.
Actually here’s an interesting link regarding psi and atomic bomb overpressure.
Normal atomospheric pressure is 15 psi IIRC, so according to the chart, you would experience 300-500 mph winds as the airlock explosively decompressed. Enough to destroy a building.
Don’t go to the movies for information on how things work. Their motivation is to make things look interesting.
If you had a hatch or airlock that could be opened to the outer vacuum without having problems with interlocks, there’d likely be a short burst as the pressure equalized, but once that was over with, there’d be no rush of air. Aliens was different ion that they had a huge chamber filled with air that was being exhausted. (And who, realistically, builds a spaceship with a single huge chamber full of air? This sort of thing is one reason why that’s a bad idea.) But if you look at 2001, for instance, I think you get a more realistic picture – Dave is blown into the airlock (whjich is in vacuum) by the air blowing out of his pod. Once that initial burst is over with, he’s not being tossed around anymore (although he is floating in zero-g).
It always bugged me that his pod didn’t go flying off in the opposite direction though. IIRC it stayed in place.
If untethered, yes (albeit a lot more slowly than Bowaman was propelled). I suppose it’s also possible that it could’ve used those attitude jets you see all over it (but never working) to maintain its position automatically. But that feels like fanwanking.
Thanks, because I totally didn’t know that, and accept everything I see in the movies, and it wouldn’t occur to me to, say, ask in this forum or anything.
Not a direct admonition to you, but I general comment. I can’t help myself. And, if it doesn’t get said, some weasel won’t realize that we all know it and will chide us for it.
I always assumed that a movie spaceship is programmed to keep the pressure in the airlock at 1 bar, and once it is opened to space it pumps in a lot of air in a futile attempt to equalize the pressure. Thus, stuff gets blown around. It helps in the suspension of disbelief anyway.
Sorry, I’m still a bit confused about the answer. Supposed I’m standing in a room like Priceguy describes, but the space-facing wall is a pane of glass (don’t ask who thought this would be a good idea). Somebody stumbles and shatters the glass.
In a pressure suit at the opposite end of the room, I see the event about to unfold and grab on to an inanimate carbon rod affixed to the wall. What happens to me? Does it matter if I am in the middle of the room? What if I have a kite (made of Kevlar or something). Will it fly for a second, couple seconds, get tugged and drop? How large would the room have to be for me to have to hold on for an extended period of time? Will I be able to hold on?
I don’t think those figures are directly applicable to this problem. If you had a pressurized space the size of a shoebox, instant depressurization wouldn’t cause 300-500mph winds. IANA physicist so I can’t explain exactly why it’s wrong.
Anyway, if nobody’s beaten me to it… the master speaks, and implies that so-called “explosive decompression” is largely a myth. You’d pass out from hypoxia in 10-15 seconds and then you’d still look more or less like you did before being decompressed.
What I wonder about, actually, is whether your body would freeze-dry instantaneously, or whether it would stay warm for a few hours in the thermos of space until all the heat radiated away.
(I was thinking the same thing on your behalf)
-FrL-
The thing to remember is that vacuums don’t suck. Air blows. So when you open the airlock, the only force acting on you is the air inside the airlock blowing out into space. And that force can only last until all the air has blown out. So movies where you get an instant hurricane when you open the airlock are just wrong. Where is all that air coming from?
Shouldn’t you be getting all your information from television?
I agree. That chart describes overpressures*, which is a different phenomenon than an ordinary pressure gradient. We can conceptualize this problem by thinking of popping a tire. A tire has a pressure of about 30 psig, while 1 atmosphere is about 14.7.
We’re not going to reach supersonic flow, but we’ll probably enter the choked flow regime, but only because we’re assuming the ambient pressure is 0. Choked flow occurs when the ratio of the chamber pressure to the ambient pressure is [(k+1)/2][1] where k is the specific heat at constant pressure divided by that at constant volume. matt directed me to a cite giving the Rasouli and Williams source model equation, which I’ll gladly run on a program I wrote in MatLab if anybody wants to supply the initial parameters (basically just size of champer and area of the leak. The program isn’t ready to calculate a rate of change, but I could add it easily enough). Given the constraints in the OP, the most useful thing the program would generate would be a plot of pressure in the chamber with respect to time.
*Which are huge, from my perspective. When I did testing of conventional explosives, I generally didn’t see readouts from the pressure sensors that got into the double digits)
k/(k-1) ↩︎
It was really more to illustrate how much power 16 psi can exert on something.
It would of course depend on the size of the opening and the pressure. And I would characterize it as more of a “burst” of air than a sustained wind.
I should also mention that people have been killed from the force of an explosing tire.
Bottom line, if a 6’ x 6’ hatch suddenly opens (say with explosive bolts), you’re probably going to get blown out the door. If you fire your space pistol through the outer hull, you’re not getting pulled out through the hole.
Do you have a cite here? I seriously doubt the truth of this, unless the tire propelled a foreign object directly into their eyeball. A tire inflated to 30psi does not equate to a shockwave with a 30psi overpressure. Neither does any kind of pressure venting. You’re really mixing 2 different concepts of pressure here.
Well, certainly no one is going to be killed by the overpressure itself. I don’t think that has been proposed in this thread. The question is how much force can the escaping air exert. Here is a cite describing serious injuries and one death from exploding tires. Obviously the opening was much smaller and the pressure was somewhat higher, but the idea is valid. There is enough energy in 15 lbs of overpresssure to move objects around.
http://www.osha.gov/dts/shib/shib042904.pdf.
Pretty much my thoughts. Yeah, I knows it’s TV/movies. But they have to be feasible on an elementary level. Consider that in the real world, you’d have to bypass all order of safety systems to eject a person from the air lock in the first place. It’s just one more push button to indicate, “keep filling chamber with air.” Possible safety systems? Don’t fill the chamber with air when the doors are open. Don’t open the doors until the air has been evacuated. Don’t open the internal doors until air has been put back in. Don’t open both sets of doors at the same time. Don’t open the outer doors if there’s a warm, breathing creature in the chamber.