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decompression venting

When the window blows out, get the air out as fast as you can
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I've only ever seen it in films (thank g*d), but cabin decompression seems to take ages and people and stuff go out the hole with the air. Seems like a Bad Thing(tm).

I assume the compressors get switched off when there's a fast leak (same trigger as the mask drop?), but what about opening a larger hole in the opposite side of the cabin, but with a grille across it to stop the people going too?

Hafta say, I'd rather be cold and hugging an O2 mask than in freefall.

maffu, Sep 17 2001

Mythbusters http://gadgetopia.com/post/2606
Thanks, internet! [DIYMatt, Dec 17 2010]

Decompression injuries http://en.wikipedia...ompression_injuries
Not at all nice. [8th of 7, Dec 17 2010]


       People and stuff departing prematurely through unauthorised exits is indeed a Bad Thing. At the back (usually) of the aircraft there are a number of big (think big pizza) sized valves letting the air out all the time. What happens when a shiney new hole appears, is these valves close up a bit, trying to keep the cabin pressurised. There is a switch in the pointy end which opens these valves fully, to ensure complete decompressurisation - used every time the aircraft lands. Landing with a pressurised cabin is also a Bad Thing, 'cos the doors won't open. Not sure about the grill - the pressure in the cabin would easily push you through it, so you would fall as chips.
drew, May 16 2002

       Why not just make people wear their seatbelts all the time to keep them selves from being sucked out of the airplane in case a big hole does appear in the wall.
jeffman, Jul 27 2003

       What about making a number of these things open at the same time? If there's enough of them, the pressure wouldn't be enough to deli-slice someone with the grill. also, the grill could be thick, rounded bars (as opposed to thinner ones which could "cut" with enough pressure)
Dickcheney6, Dec 17 2010

       Adding potential failure points to an aircraft? Just keep your seatbelt on.
DIYMatt, Dec 17 2010

       //I've only ever seen it in films//   

       Exactly. I am pretty sure that decompression is not remotely like that. There is only a finite volume of air in an aircraft, and it is only at 1 atmosphere (actually less). In the movies, people are sucked out from yards away, in a seemingly endless wind. This is, as my godmother would have put it, bollocks of the uttermost kind.   

       I'm guessing a real window blow-out would decompress the cabin in a matter of a few seconds, and wouldn't suck anyone out unless they happened to have their head up against the hole. And were quite thin.
MaxwellBuchanan, Dec 17 2010

       For 9 heartrending years maffu has been worrying about this while you chuckled to yourself, Max. About time you eased his mind.
bungston, Dec 17 2010

       He/she hasn't been around for quite a while. Perhaps he/she got sucked out.   

       No, wait...
MaxwellBuchanan, Dec 17 2010

       // Adding potential failure points to an aircraft? //   

       Defintion of an aircraft: "A large array of catastrophic failure points flying in close formation".   

       // decompression is not remotely like that //   

       No, it isn't. It's vary fast, very scary, and it hurts. A lot. And they don't tell you (or show you) the stuff about the loss of bowel control, involuntary urination, bleeding from the eyes and other mucous membranes, vomiting, convulsions, burst eardrums, nosebleeds and shock. And there are other nasty effects too.
8th of 7, Dec 17 2010

       I think, 8th, I would refer you to my godmother.
MaxwellBuchanan, Dec 17 2010


       "Barotrauma: an inability to equalize pressure in internal air spaces such as the middle ear or gastrointestinal tract, or more serious injury such as a burst lung"   

       We would refer you to the boffins at Farnborough, where knowledge of such things may be had.
8th of 7, Dec 17 2010

       /loss of bowel control, involuntary urination/   

       I dont think that happens to everyone. Just people who are scared. But bleeding from the eyes can be scary.
bungston, Dec 18 2010

       /loss of bowel control, involuntary urination/   

       I think that only happens to scaredy cats. Man up! A little bleeding from the eyes won't hurt you! OK, the burst eardrums do sting.
bungston, Dec 18 2010

       My godmother says the Borg suck. She also points out that barotrauma such as you describe happens only when decompression is faster than air can escape from the lungs and middle ear (other gaseous pockets are not such a problem), meaning a pressure drop on the order of 10 atmospheres (150psi) per second.   

       A window blowout in a typical passenger jet will cause near-total decompression (a drop of about 10psi, or 2/3rds of an atmosphere) in 0.5-1 second.   

       I would expect the Borg to have a better grasp of this kind of thing.
MaxwellBuchanan, Dec 18 2010

       There speaks the confident voice of a man who has never in his life experienced uncontrolled decompression, or seen and smelt the mess in the training chamber afterwards.   

       // Just people who are scared. But bleeding from the eyes can be scary //   

       The bowel movements occur because gas in the large intestine expands very rapidly, propelling the contents of the rectum out of the body. Urination is a consequence of this loss of sphincter control.   

       The same goes for vomiting; gases in the upper intestinal tract and stomach make a bid for freedom, and a lot of stuff can tag along for the ride.   


       The bleeding from the conjunctiva looks a lot worse than it actually is.
8th of 7, Dec 18 2010

       //vomiting// Intra-gastric pressure during a cough is about 200 cm H20, i.e. about 2.6 atmospheres, giving a pressure differential of 1.6 atm. across the cardiac sphincter. Which is 0.6 atm. more than it would be if cabin pressure dropped to zero, even assuming the cabin pressure had been one full atmosphere. So I'm not quite getting the pathophysiology here.   

       Also, why would decompression cause shock?
mouseposture, Dec 18 2010

       y'all might want to check out the Mythbusters episode on this.
FlyingToaster, Dec 18 2010

       what doesn't tally with what ?
FlyingToaster, Dec 18 2010

       Re Aloha 243: If sufficiently large portions of the plane are ripped out or peeled up, the decompression isn't going to be the problem, the 300+mph breeze is.   

       That being said, explosive decompression in orbit (the full 1 atmosphere) produces relatively minor burst blood vessels in the eyes. Admittedly, it's better if you breathe out before it happens, but the results are only uncomfortable, not dangerous.
MechE, Dec 18 2010

       //only uncomfortable, not dangerous// 65 people were injured in that incident and that was only going from 11psi to 6psi .   

       Basically anything that holds air is going to be pressuring out at the difference whether it wants to or not: Ears, sinuses, lungs, bowels.
FlyingToaster, Dec 18 2010

       I plugged "cabin depressurization" into YouTube and got the relevant portion of the episode.   

       recap for the lazy: they overpressurized a grounded DC9 carcass then did various things to it: a bullet fired through the skin or window was boring; realistically if that happened and you were nearby you could just put your hand over it and deal with the resulting skin rash later.   

       Blowing out the entire windowglass with det cord was impressive: the dummy didn't get sucked out only because it was bigger than the window opening, but it sure wasn't for lack of trying.   

       Think realistically: worst case going from 14 psi to 0 psi: if the window is 8x10" that's say half a ton differential: that's not enough to break all the bones necessary to squeeze a person through.
FlyingToaster, Dec 18 2010

       I should have said "not deadly" instead of not dangerous.   

       There definitely is some force involved, and someone standing near a large opening is at risk of getting blown out the opening. Not a significant risk of being pulled through a small opening. Likewise the entire pressure vessel is going to experience jet effects. If the opening is large enough, there is going to be a single large shove, sufficient to throw people around.   

       None of the injuries described in the wikipedia article, or in a quick pass over the relevant literature, are due to explosive decompression. Most are consistent with whiplash, falls, and flying debris (see above, RE: 300+mph breeze).
MechE, Dec 18 2010

       And as to holding a 5PSI differential. Seeing as human lungs during normal operation generate 8 (elderly) to 15 PSIG (young adult), the human body is more than capable of dealing with even relatively rapid pressure changes on that scale.
MechE, Dec 18 2010

       since the initial burst pushed one of the flight attendants to the ground; assumedly some of that flying debris was also from that.   

       wasn't me going on about lungs: there's another string of annos here dealing with a full atmosphere differential found in space as well as a 5-6psi difference (between 8,000 and 24,000 feet) of a low flying jetliner.
FlyingToaster, Dec 18 2010


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