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I recently envisioned a fight scene in which the three main characters are in a bar on a spaceship when about a dozen space marines ambush them. They take cover behind the bar, but without weapons or a back door their situation looks pretty grim. That is, until they find the fire alarm. It just so happens that the most drastic fire-extinguishing procedure for the bar is to open the windows (into the vacuum of space), essentially removing all oxygen from the room and thus suffocating the flame. In my fight scene, the decompression from this process is enough to stagger all of the space marines, (maybe) suck some of them out into space, and (definitely) suck out all of their weapons (let's assume they were dropped at the start, and thus were in the air when the windows opened). This gives the main characters a chance to jump out from behind the bar and use bottles and their fists to dispatch the remaining marines as the windows close again.

The part about this scenario I'm most worried about is that, since the main characters are the main characters, cliche dictates that they can't be wearing helmets. So, I want to know if I can get reasonably powerful decompression without knocking out the good guys. Headaches are fine, and are the bends so long as it's not immediately debilitating. If it is possible, some numbers would be appreciated for how fast the windows would open, and for how long decompression would actually be felt before all the air was evacuated (and how long until exposure to the ensuing vacuum would cause major problems).

Let's assume the room is about 100 feet square and 20 feet high. There are three windows about 3x15 feet, that open by sliding the pane up.

EDIT: As to the people who have a lot of confidence in these space marines, perhaps I should have specified: they are rookies, with little training, and zero training on space missions. As to why their guns are not attached with straps, I am handwaving that for now.

As to the danger of this firefighting system, the alarm is behind the bar, effectively inaccessible to anyone but the bartender. Plus, feel free to add any safety features you want, such as gas masks, nets over the window openings, etc.

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    $\begingroup$ Ah, the FTL solution to fire on your ship, lol. One thing, though, I'm guessing the space marines are not proper space marines and probably attended the stormtrooper marksman academy. Since, if they were properly trained, chances are they would be able to deal with a sudden decompression scenario (heck, actually, scratch that, if they were properly trained, there would already be a grenade behind the bar). Also, do you need to worry about gravity? $\endgroup$ – eharper256 Apr 16 '15 at 14:15
  • $\begingroup$ @eharper256 The marines are only there to destroy the humans, not the ship, so they're not likely to have grenades. And yes, they can be assumed to have little training. The ship has near-Earthlike gravity, either by artificial gravity or by hovering just above the atmosphere of a nearby planet. $\endgroup$ – DaaaahWhoosh Apr 16 '15 at 14:21
  • $\begingroup$ Hovering above the atmosphere? You're going to run out of delta-v pretty quick... $\endgroup$ – 2012rcampion Apr 16 '15 at 14:27
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    $\begingroup$ One would think Space Marines who, regularly fire weapons on board ships and stations, would be prepared for sudden decompression. $\endgroup$ – Schwern Apr 16 '15 at 16:41
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    $\begingroup$ I'm having a problem with the concept of a public place having a 'feature' that lets anyone kill everyone in the room by venting the atmosphere. Venting the atmosphere also won't get rid of the fire - it removes the flames, but everything is still hot. If you put O2 back into the room the combustibles will re-ignite. Also, marines would have slings on their rifles, especially 'space marines' who encounter zero g situations. $\endgroup$ – GrandmasterB Apr 16 '15 at 16:42
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As always, when dealing with space we can turn to the NTRS for info.

This document deals with speed of decompression, and effects on humans. It gives a formula for a time constant, $t_c$, which estimates the timescale on which decompression happens. For our case:

$$ t_c = \frac{V}{Ac} = \frac{100~\text{ft}\times 100~\text{ft}\times 20~\text{ft}}{3\times 3~\text{ft}\times 15~\text{ft}\times 343~\text{m}/\text{s}} = 1.32~\text{s} $$

For decompression into a vacuum, the total decompression time is huge, since it takes forever for the last couple moles of air to find their way out. However, most of the air will escape in around $t_{cr}\approx 1.5t_c\approx 2.0~\text{s}$ (for large pressure ratio $P_i/P_f$).

Note that the speed of sound appears in the formula: this is because the air will rush out at sonic speed. Since the blast is very short this is unlikely to throw anyone into space if artificial gravity is present. And since the windows are fairly narrow, I think it would be unlikely even in microgravity for anyone to be blown out.

Also fortunate is that the decompression time constant for the human pulmonary system is less than one second, so your characters are unlikely to suffer permanent lung damage due to pressure buildup. However, this does mean that all the oxygen in their lungs will be gone within a few seconds. Unlike someone holding their breath (or being choked) they can no longer use the 'stale' air in their lungs to maintain respiration. Unconsciousness will be almost immediate (in this case I would estimate $<5~\text{s}$).

We can compare this to the case of Jim Le Blanc (see page 3 in this NASA newsletter), who was exposed to vacuum for several seconds during spacesuit testing. In his case the decompression was much slower, around ten seconds, since his air was escaping through a relatively small disconnected oxygen hose. He lost consciousness only seconds after noticing the leak. The chamber was immediately repressurized; the inner hatch was opened only 17 seconds later, and a total of 85 seconds elapsed from the beginning of the incident to when the chamber was open to the atmosphere. He suffered no permanent injury. This means that if we limit exposure to only a few seconds and repressurize quickly, your characters should survive.

If the windows were slid open, it would have to be done fast. They would also have to be closed automatically (since the people are all unconscious) after the fire was extinguished, maybe around $10~\text{s}$, and the cabin would have to be repressurised. On Earth this is easy, you just open your vacuum chamber to the atmosphere. In space, you'd have to quickly vent air from the rest of the station to the now-evacuated cabin, putting the rest of the station at risk.


Realistically, the windows would probably not be slid open in an emergency. The aerospace industry tries to avoid mechanisms as much as possible, since they not only increase weight but are prone to failure. I would assume that the windows would either be installed with pyrotechnic fasteners or with plastic explosive embedded in the window itself, like some aircraft canopies. In that case your characters would die: there's no easy way to close a window that's now travelling away from you at several hundred meters per second. Unless...

...You give your characters oxygen masks. Likely mandated to be next to the panel that activates the emergency decompression sequence, they would be held tightly to the nose and mouth and emit a large flow of pure oxygen. Even one or two psi might be sufficient for a few extra seconds of consciousness, enough to make your way to an open airlock.

Picture the scene: your heros are crouching behind the bar, looking around for anything that might help them. One notices a stray shot has blown open a panel marked, "EMERGENCY FIRE SUPPRESSION," with three small gas cylinders inside. She jumps up and grabs one, tossing the other two to her compatriots. The stormtroopers realize what's about to happen and stop shooting as they look around for the second emergency panel, but it's too late: pressing the mask tightly against her face, our heroine pulls the lever. The sound of the explosive bolts is overwhelmed by the rush of air shooting out the window, the black of space briefly turning white as a flash of condensation escapes. The stormtroopers are thrown to the floor silently, as our heroes struggle to the door, the dark tunnel of anoxia closing in on their vision. Thirty seconds later, they wake up coughing and sputtering in the airlock between this compartment and the next. (One-liner, rimshot, explosions)

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