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Many science fiction stories, movies, and shows involve characters undergoing explosive decompression, the technical term for a rapid drop in pressure, usually all the way to a vacuum. Frequently, this is used as capital punishment, since shoving someone out the airlock without a suit is an efficient way of killing them in space. However, most of these depictions of explosive decompression, as well as most sources I have been able to find on the subject, disagree wildly on the specifics. Some involve the skin freezing and/or frosting over (probably wildly inaccurate, as a vacuum is actually the best possible thermal insulator), some describe blood boiling and eyeballs exploding, and some show no outward changes as the victim appears to suffocate.

The question is, what would actually happen to a person suddenly launched into space? Additionally, would the results change significantly if the victim is in sunlight, as opposed to shadow?

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This question asks for hard science. All answers to this question should be backed up by equations, empirical evidence, scientific papers, other citations, etc. Answers that do not satisfy this requirement might be removed. See the tag description for more information.

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    $\begingroup$ Copy and pasted your question in google and found the answer. I suggest you do the same. $\endgroup$ – Bewilderer Feb 8 at 3:33
  • $\begingroup$ There was a early space era test of an astronaut suit that had the wearer exposed to (artificial) vacuum for a very short period of time with no ill effects, so any "instant death" sort of thing is right out. Don't have time to look it up at the moment, though. $\endgroup$ – Andon Feb 8 at 3:34
  • $\begingroup$ "Several minutes" would seem to be the survival time, as long as recompression occurs. What sup @Gryphon ? $\endgroup$ – Agrajag Feb 8 at 3:41
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    $\begingroup$ @Bewilderer I did the same thing and found at least two contradictory answers. That's why I'd like a hard-science answer involving citations of reputable sources. $\endgroup$ – Gryphon Feb 8 at 4:02
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    $\begingroup$ "Hess explains that there's little medical study of what happens to a depressurized body because, well, it basically never happens." based on this, I am not sure you can get a hard science answer $\endgroup$ – L.Dutch Feb 8 at 6:05
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We actually have first-person testimony about what happens under these circumstances. In 1966 Jim LeBlanc was testing a space suit in a vacuum chamber when his supply line came detached and let his atmosphere out very quickly. This clip:

https://www.youtube.com/watch?v=KO8L9tKR4CY&feature=youtu.be

Includes some original footage as well as interviews with people involved. Jim lost consciousness very quickly - measured in seconds. The last thing he remembers was feeling the saliva on his tongue boiling. They were able to quickly re-pressurize the chamber and he regained consciousness shortly, without any permanent damage.

Passing out quickly is likely an unavoidable consequence. This is very similar to what happens with inert gas asphyxiation. In short, the extremely low pressures cause the lungs to lose oxygen with each "breath". As a result (in the case of inert gas asphyxiation) it is possible to pass out in even just a few breaths. In a vacuum of course "breathing" doesn't really make sense, but your lungs would still effectively leak oxygen out of your body, causing you to pass out rapidly (as happened to Jim in a vacuum chamber).

Given this, you might consider holding your breath to stop yourself from rapidly passing out. I'm not confident enough to say for sure what will happen if you do, but all signs suggest that it will be a bad choice even if is is possible (which it probably isn't). When scuba diving, holding your breath while surfacing is a very dangerous move and is virtually guaranteed to cause pulmonary barotrauma. A severe pulmonary barotrauma can cause injuries that lead to rapid fatality such as arterial gas embolism or tension pneumothorax. The risk of pulmonary barotrauma is related to the rate of relative change of air pressure, and for scuba diving is therefore most dangerous at the surface, when moving from, say, 2ATM of pressure to 1ATM. As a result I expect that going from 1ATM to 0ATM is equally, if not more, dangerous to someone trying to hold their breath.

It took about a minute and a half to re-pressurize Jim's chamber. He ended up with an earache, but otherwise no visible injuries. However, longer exposure could certainly have done more damage to his body. Unfortunately, I'm not sure what the longer term damage is myself, nor do I have any great references (pretty sure that study hasn't been done). Most of the immediate effects (such as Jim feeling his saliva boil) are caused by the lack of pressure. Technically his saliva was both boiling and freezing at the same time, which is what water does in a vacuum due to lack of pressure:

https://www.youtube.com/watch?v=2IOyJa8NSk0

The lack of pressure is the most dominant effect, although I'm not sure how quickly the body would actually freeze. Sunshine or shade won't matter immediately. He will freeze over regardless (due to lack of pressure), so the only effect of sunshine or shade will be to control the rate at which his ice escapes via sublimation. Warmer areas of space = faster sublimation and therefore quicker time to go from popsicle (aka frozen body) to mummy (aka dried body). For long-term results, I refer you to the relevant xkcd.

https://what-if.xkcd.com/134/

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What happens to the person is simple. What happens to their body involves a few more steps.

The first thing that happens is you scream. Well, you act to scream or the scream acts on you. The lungs are designed to withstand about 1/10th of an atmosphere of pressure, which is the typical delta occurring during breathing. You either scream all your air out of your lungs, or that air forces its way out, doing substantial damage along the way. This effect is probably not all that important for someone being executed by vacuum. For those who want to live, it matters greatly. Divers engaging in what is called a Controlled Emergency Swimming Ascent (CESA) learn to exhale while they are ascending to give the air in their lungs a way out. This decidedly unintuitive maneuver is essential for your survival.

The next thing happens is that you lose consciousness at around 15 seconds. The lungs are a powerful gas exchange mechanism, and you just exposed them to pure vacuum. The vacuum rips the oxygen right off of the hemoglobin, and then delivers that blood to the brain. 15 seconds later it reaches the brain, and you lose consciousness almost immediately after that. Death arrives soon after, as if the heart stopped beating (it may be beating, but it's not delivering oxygenated blood, so it's not helping at all).

You can survive like this for a while:

... one 1965 study by researchers at the Brooks Air Force Base in Texas showed that dogs exposed to near vacuum—one three-hundred-eightieth of atmospheric pressure at sea level—for up to 90 seconds always survived.

After that, the answer is a bit more boring. You do have issues with water boiling, but its not instantanious. Space is actually a very poor conductor, so it doesn't conduct any heat away. Your body radiates at a very low rate. Almost all of the cooling comes from evaporation, which is a very localized effect. Astronauts involved in accidents like this remember feeling the evaporation off of their tongue before losing conciousness. However, this takes a long time. At least as long as it takes to freeze in a cold weather environment. The cool needs time to work its way in (or, phrased the other way, the heat needs time to work its way out). Your eyes, however, do not typically "explode:"

Water in the soft tissues of your body vaporizes, causing gross swelling, though the tight seal of your skin would prevent you from actually bursting apart. Your eyes, likewise, would refrain from exploding, but continued escape of gas and water vapor leads to rapid cooling of the mouth and airways.

In fact, one of the new space suit designs, the Biosuit actually takes advantage of this. Human skin can actually hold its own against a vacuum on small scales. Obviously, large areas of skin suffer from expansion due to fluids entering the area, but if you compress the skin at a gross level, the microscopic structure can take the vacuum. The biosuit is actually not vacuum tight. The air can escape through the weave of the suit. The result? Your body can actually cool itself via presperation just like it does in the hot desert sun! Your body emits sweat like it usually does, and that sweat evaporates into the vacuum, cooling you off!

Not that that makes me any less disturbed at the idea of exposing my skin to the vacuum of space, but it has been done. One of the more famous leaks on the ISS was resolved by covering it up with a thumb. (the hole was obviously later fixed more permanently, first by Kapton tape, and later I believe it was cemented shut)

Once the effects of evaporation stop mattering and you become inert, what happens to the body is exactly what happens to an asteroid of similar size. If its in an environment that gets hot due to the sun, it gets hot. If it's in an environment that gets cold, it gets cold. This happens on a long timescale, at least compared to the 15 seconds of meaningful screaming.

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  • $\begingroup$ In the one accident he didn't feel evaporation - he felt the saliva on his tongue boiling. This is a natural consequence of being in a vacuum. Per the phase diagram of water, liquid water cannot exist in a vacuum and begins to both boil and freeze simultaneously. Liquid water can no longer exist below 1kPa (about 1/100th of an atmosphere). As a result you don't freeze due to cold - you freeze due to lack of pressure, which happens via a completely different process unrelated to radiative cooling. $\endgroup$ – conman Feb 8 at 17:33
  • $\begingroup$ "...first by Kapton tape..." Ah space-quality duct tape, the fixer of all problems. $\endgroup$ – rje Feb 8 at 20:37
  • $\begingroup$ Exhalation during CESA is used to prevent baryotrauma because the gasses in a divers lungs are going from multiple atmospheres of pressure to one atmosphere rapidly, which is very damaging to your insides. However, when suddenly exposed to a vacuum you are going from 1 atmosphere to 0 atmospheres. It is less clear to me if this is a sufficient change to cause damage if you attempted to hold your breath. This would be the equivalent of surfacing from a depth of 10 meters rapidly. $\endgroup$ – conman Apr 3 at 13:32
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    $\begingroup$ @conman 1 atm is enough to cause barotrauma, according to my instructors. From personal experience, 0.5 atm is enough to cause noticeable but (thankfully) temporary damage. The lungs are surprisingly low pressure devices $\endgroup$ – Cort Ammon Apr 3 at 14:23
  • $\begingroup$ @CortAmmon Sorry that you had to discover that personally! Therefore, note to self: do not try to hold your breath if suddenly in vacuum. You have seconds of useful consciousness and then you're out, and that is all there is to it. $\endgroup$ – conman Apr 3 at 14:35
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A. Man puts Arm In A Vacuum Chamber

This video shows what happens and, towards the end, shows facts and figures from NASA's Bioastronautics Data Book 2nd Edition - https://youtu.be/iWGGMchu6mQ?t=67

enter image description here


B. The Crew That Never Came Home: The Misfortunes of Soyuz 11

The mission ended in disaster when the crew capsule depressurized during preparations for reentry, killing the three-man crew. https://en.wikipedia.org/wiki/Soyuz_11

“They knocked on the side, but there was no response from within. On opening the hatch, they found all three men in their couches, motionless, with dark-blue patches on their faces and trails of blood from their noses and ears. They removed them from the descent module." http://www.spacesafetymagazine.com/space-disasters/soyuz-11/crew-home-misfortunes-soyuz-11/


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