Space Exposure
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Basic Information

Hard Vacuum

Your spaceship or spacesuit is punctured, and the air is quickly rushing out into the vacuum of outer space.

Rule #1: Don't hold your breath!

Exhale quickly! If you exhale in the initial seconds of exposure, your lungs will probably collapse with minimal injury. If you hold your breath, your lungs will likely rupture, sending molecules of air through your tissues. Trust me, the extra second or two of air isn't worth Internal Injuries.

Timeline of exposure

  • For the first 10 seconds, if you exhaled, you'll be uncomfortable, but can reasonably expect to keep your wits and effectiveness.
  • After about 10 seconds of exposure, your body begins to noticeably bloat up. The pain and discomfort gets worse.
  • Around 14 or 15 seconds, even astronauts in prime physical condition lose consciousness. Even if the GM gives you a saving throw to shrug that off, when parts of you balloon to double normal volume, the pain will be incapacitating.
  • After about 30 seconds of exposure, circulatory failure and flaccid paralysis set in. The fact that you're unconscious is probably merciful at this point.
  • It takes 90 seconds unprotected in space for your blood to reach a full-on "boil". Boiling is a misleading term. The water in your tissues turn to vapor because the boiling point is below room temperature in total vacuum. Rather than cooking, you radiate off you heat rapidly and can actually freeze. Your tissues bloat further, and bruising occurs, especially in the eyes. It is extremely unlikely that blood will actually leak out your eyes like you see in film.

Immediate recompression is needed to prevent death. Longer exposure than 90 seconds is almost certainly fatal.

Biochemical / Medical Effects of Vacuum

Listed in roughly the order of impending danger:

  • ebullism - The formation of gas bubbles in bodily fluids. Leads to the bloating.
  • hypoxia - Parts of the body (and quickly the whole body) are deprived of oxygen.
  • hypocapnia - Lack of carbon dioxide in the blood.
  • decompression sickness - Nitrogen bubbles form in the body. This causes severe joint pain, and so is commonly called "the bends".

The four items on that list will kill you long before any other dangers. Space is very cold as well, but you'll be too busy asphyxiating / swelling up / getting the bends to care about the gradual temperature change.

Other Dangers of Space Exposure

In addition to the effects of vacuum, many other hazards afflict you during space exposure.

Let's say your spacesuit remains pressurized, but suffers a partial power failure, or is otherwise unshielded from the dangers of space. Here's what else you have to worry about:

  • Eventual asphyxiation as your air supply runs out.
  • Extreme temperature variations. Whether this is more or less a danger than asphyxiation depends on where you are, how well insulated you are, and how much air the suit has left. See Temperature of Outer Space for full details.
  • Cellular mutation and destruction from high energy photons and sub-atomic particles. Not an immediate concern, but could cause cancer or other health problems down the road.
  • Potential for being hit by micrometeorites or space debris, depending mostly on where you are.

Recovery and lasting impact

Several astronauts have been exposed to Hard Vacuum over the years. Exposure of a minute or less will likely be recovered from, assuming you exhaled. 90 seconds of exposure is pushing the limits of the human body. Immediate recompression is needed to prevent death. Longer exposure than that is almost certainly fatal, as it was in the case of the Cosmonauts aboard Soyuz 11.

Most of the effects of brief exposure to vacuum are temporary. One real-life incident involved about 30 seconds of exposure. The astronaut passed out, but when the chamber was repressurized, he awoke uninjured. The bloating can take hours to dissipate. If just part of your body were exposed (by a partial suit failure), that bodypart alone might be painful and abnormally large for several hours. Bruising is also common, but otherwise there are no obvious physical symptoms the day after being repressurized.

Standard treatment for vacuum exposure involves repressurization (sometimes a long gradual process to prevent Decompression Sickness, but in a pinch getting the victim into a spacesuit is better than nothing), being put in a 100% oxygen atmosphere, and hydration to return circulation to damaged tissues.

If the fool held their breath, tissue trauma will be significant.

Sometimes even brief exposure can damage sinuses or eardrums, and this may have lasting impact on respiration and hearing. Steroids and decongestants will be applied as treatment, and the pressure in the sinuses may need to be actively pressurized.

Those who survive full space exposure (not just vacuum exposure) are advised to have frequent doctors check ups. Cellular damage from cosmic radiation could bring numerous long-term health risks, and detecting them early is important.

See Also


Game and Story Use

  • Space-faring PCs run the risk of space exposure if their spacecraft hits something or is attacked. The wind-tunnel effect as the air escapes is quite familiar.
  • During astronaut school or the academy, an accident in a pressure chamber exposes a character to hard vacuum, with effects very similar to space exposure.
    • As part of a character's back story, he might now have a phobia in regards to space or vacuum. Such a character might resign his commission, or insist on taking ludicrous precautions whenever in space. He might keep an extra emergency spacesuit in his bunk, or at his workstation.
  • One way to denote the veteran astronauts (from those who are just infrequent passengers onboard a spaceship) is by their instinctual response to depressurization. Those who know exhale quickly… others panic and hold their breath.
    • If the hull breach is quickly patched, those who panicked might be dead or coughing up blood, while those who exhaled are back to work in an hour or two.
  • Commercial space-flight, and/or problems during re-entry or landing can complicate or follow on to space diasters. The movie Pitch Black is an example of a plotline that starts with a spaceship crash and just gets worse. See Air Disaster for other plot ideas and likely troubles.
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