Explosive Decompression
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Basic Information

Explosive Decompression is a somewhat misleading term. Hollywood, in particular, has been mislead by it, and continues to mislead the viewing public with this speculative fiction trope. They like to show heads bursting, or at least eyeballs getting sucked from their sockets. Getting to that sort of situation takes a lot more force than "merely" being exposed to the vacuum of space.

Decompression in Aircraft

Explosive Decompression does happen to Aircraft. The Federal Aviation Administration splits decompression into three categories, only one of which is termed explosive:

  • Explosive Decompression happens faster than air can leave the lungs, often less than a tenth of a second. It exerts a force on the aircraft frame akin to a 500 pound bomb being detonated in the cabin.
    • The human body is pretty amazing in that regards. A metal plane frame might rapidly rip open from a pressure leak, and leave the crew inside merely bruised and slowly asphyxiating. Lung damage is almost guaranteed, and upon donning your oxygen mask you'll have to pressure breathe - that is, actively and forcefully exhaling because otherwise the injured lungs stay inflated. If you stayed in the airplane, and got oxygen in a timely fashion, you'll recover.
    • Immediately after Explosive Decompression, a thick fog may form in the cabin and behind the vehicle. Time for a piloting check with a hefty modifier.
    • Since it happens so quickly, there's no time to react. If you weren't strapped in, you may be skydiving without a chute - and you'd hate to be one of many naked falling bodies!
    • Important Note: Actual explosive decompression is very rare, and it takes a lot more to trigger this than you probably expect. A single bullet hole generally won't do it. The location and size of the hole does matter, but your aircraft or spaceship normally won't tear itself apart over a small hole or two, as they are engineered with safety systems and reinforcements designed to prevent exactly that. Most explosive decompressions are caused by metal fatigue on older craft, engineering failures on newer designs, or actual bombs going off inside the vessel.
  • Rapid Decompression takes longer than half a second, so you can breathe out before the craft looses all pressure. Lung damage isn't as severe, and you may escape it entirely. If you know there's about to be a decompression, exhale! For an explanation of why that's the smart move, see Space Exposure.
    • If the cabin depressurizes, you've got about 20 seconds before the oxygen deprivation leaves you stoned, and maybe double that before you pass out.
    • While you're scrambling to get your oxygen mask on, the entire plane will be shaking violently and dropping several thousand feet per minute. (Any actions/rolls taken during this time should be heavily penalized.)
  • Slow Decompression is gradual and hard to notice. If its gradual enough, and your Vehicle lacks good cabin pressure gauges, your first clue might be passing out from asphyxiation. Sucks to be you.

For more information on potential complications in an airplane emergency, see Air Disaster.

Decompression In Space

If you're at all interested in what actually happens to you if you end up outside the spaceship, visit our Space Exposure page. It's pretty thorough (and deadly).

While you're still inside the spacecraft, probably the most important point to note here as being different from what you see in movies and TV has to do with the rarity of full-on explosive decompression, and the ease with which you can avoid being pulled through a hole in a ship. While the pressure difference in space is greater than in the atmosphere and that does mean more force pushing the air out, some other forces are less in space: there's no wind blowing, no friction or air resistance, and minimal gravity. Normal earthly air pressure is just under 15 pounds per square inch, and that's about the amount of pressure you're likely to have inside your ship during normal operations. A hole in the hull will start to equalize that pressure with the nothingness of space, but it's not that hard to resist a pressure of just 15 PSI. Unless you happen to be very close to the hole when it is made, you can probably walk or crawl away from it. Make no mistake, the cold emptiness of space is trying to kill you, constantly. It's just that it is easier to avoid being sucked out than you'd think from the movies. This may be complicated by the usual problems of zero gravity if your craft wasn't accelerating when hole was made, and someone floating without a surface to grab hold of or push off of will be drawn towards the great void. If the thing that punched the hole in your vessel also coincidentally knocked you out, then you're probably in a lot of danger.

Also, sealing the hole is probably a lot easier than most movies make it out to be as well. Most ships would have some sort of patch kit onboard capable of making an air-tight seal, and that pressure differential sucking the air out will actually hold the patching material in place. If the walls around the hole are flat and featureless, you may be able to improvise a patch by putting plate or bowl over the hole. A well-engineered ship with bulkheads and compartmentalization will limit the likelihood of explosive decompression or the venting of all your oxygen. (All bets are off in a major head-on collision, of course, but space is so big that those should be ridiculously rare.)


2. Yahoo Travel article - "What they don't tell you in the plane safety video"
3. Youtube video explaining how the tv show The Expanse gets much more of the science correct than just about any other sci-fi show. It talks a good bit about explosive decompression along with all the other stuff.

Game and Story Use

  • Depressurized passenger flights are a good scare where the players can be heroes (by helping others put on masks) without being able to solve the ultimate cause themselves. That powerlessness can really punch home a horror theme or tension. Don't drag it out too long, or the players will resent it.
    • I'd run it like this: Start with the endurance roll to avoid fatigue or injury as the air is sucked out of their lungs. Then tell them that there's a hole in the fuselage, and ask for dex checks to keep from being flung out if anyone's not wearing a seat belt. Finally, the masks fall from the ceiling, and then you give them their first action. Anyone who does something other than grab a mask needs to make another endurance roll. One or two rounds later, fog forms and all attacks are penalized.
      • If this happens in the middle of a fight scene aboard a commercial plane, expect a TPK. A bullet causing an explosive decompression should happen on the same action / initiative number the gun was fired, since it can take less than a 10th of a second.
        • Excuse me. It's been brought to my attention the Mythbusters has demonstrated a bullet can't cause explosive decompression. The point about the explosive decompression happening faster than you can react is correct, but the idea that a single bullet hole will do it is apparently busted. I haven't seen the episode, so I don't know if it requires a bigger hole, or a whole clip on full-auto spray, or a seam coming apart, or whatever.
        • I do know that Federal Sky Marshals used to be issued glaser safety slugs and now carry hollow-point ammo. The later make large holes in things (as far as pistol bullets go), so I assume the Federal Air Marshal Service has done some testing to determine that a couple of bullets is no risk to the plane going down.
          • Unless, of course, you're playing a Conspiracy Theory game, in which case maybe the Marshals intentionally (or unwittingly) carry bullets that will take down a plane. Shooting down your own plane from the inside is better than being used in a new 9/11 scenario.
  • Or, you could go the creepy route. The plane that the players were about to embark on had a gradual depressurization, and half the passengers arrived dead. Departure is delayed, and the PCs get rerouted to a different flight. Of course, this is very tragic and alarming, and paranoid PCs will read plenty into it. The airline is unlikely to say immediately why they're moving you to another plane, and that will trigger some players conspiracy theory alarm.
    • Or the PCs are delayed and their flight takes off without them … and decompresses.
      • Even better, their tickets are stolen and the thieves (or their clients) get decompressed…
  • Panic is your worst enemy in any airline or spaceship emergency, especially a civilian passenger flight. People will panic and do the wrong thing nine times out of ten. Such circumstances are a spotlight moment for making the PCs look like bad-ass professionals, by contrasting them to the masses of people all around them who are fumbling ineffectively at the oxygen masks, life vests, seatbelts and emergency doors.
    • While we tend to think of such emergencies as being primarily a physical challenge, this may actually be a moment for a character with a social- or mental- focus to excel. It's hard to communicate with an oxygen mask on your face and a flaming wreck all around you, but PCs who exude confidence or authority may be able to prevent a mad riot at the emergency exits.
  • The above assumptions (and in particular the notion that it's less dangerous than in movies) assume modern human technology and environments. If your setting has aliens who are native to a world with a much denser atmosphere or higher gravity, ships built to house them may naturally operate with greater cabin pressure, and thus be more vulnerable to explosive decompression.
    • That might be an interesting way to balance/differentiate between space-faring species. One group might have some strong advantages (better weapons, better technology in general, more ships or just more resources, etc) but have ships that are more likely to rip themselves apart when hit. I'm not sure it's terribly realistic, but it's probably good enough for gaming.
    • Then again, the heavyworlder natives of a high-gravity densely-atmosphered planet are somewhat less likely to develop the technology to get off-world, simply because it takes more thrust to reach their native escape velocity.
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