In space, what would kill an unprotected human first?


Surely, there’s a good reason he’s wearing that suit…

This weekend, I was riding with some friends to a wedding about three hours from home. As the ride got longer, the conversation got more varied, and we eventually ended up wondering whether an unprotected human could survive in space for any period of time. We also wondered what would be the first thing to kill them (as opposed to the second thing to kill them) when they did eventually pass. You know, because that’s what you usually talk about on the way to weddings.

Several ideas were floated: perhaps the zero-pressure environment of space would make your body instantly explode. Perhaps you wouldn’t explode, but you would have tissue damage from expansion in your lungs, blood vessels, and pretty much anything else that traps air or liquid. Maybe you’d freeze? But then, there’s no matter to conduct heat, so maybe you wouldn’t? Alternatively, maybe you’d fry from all the radiation? There were plenty of theories.

So, what would actually happen to you? Read on to find out.


No, not that kind of vacuum.

Well, lucky for us (and terribly unlucky for the test subjects involved), NASA has looked into this very question! (Thanks for the help, Scientific American.) In a series of experiments during the early years of America’s space program, researchers put various animals into a vacuum in order to test the effects of exposure on the ability of bodily systems to function. The results were pretty gruesome…

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. During their exposure, they were unconscious and paralyzed. Gas expelled from their bowels and stomachs caused simultaneous defecation, projectile vomiting and urination. They suffered massive seizures. Their tongues were often coated in ice and the dogs swelled to resemble “an inflated goatskin bag,” the authors wrote. But after slight repressurization the dogs shrank back down, began to breathe, and after 10 to 15 minutes at sea level pressure, they managed to walk, though it took a few more minutes for their apparent blindness to wear off.

Chimpanzees exposed to the same conditions were also able to survive for limited amounts of time, though all animals succumbed after only a couple of minutes. Which answers a few of our questions from earlier:

  1. You wouldn’t instantly explode.
  2. You could survive for a couple of minutes, at least.
  3. Changes in pressure would definitely be a problem.
  4. It doesn’t seem like freezing/frying were too much of a concern in the research studies mentioned, so it’s probably safe to conclude that they’re not a big deal.

Former astronaut and Dartmouth Medical School Professor (now there’s a resume) Jay Buckley sheds more light on the situation.

In any system, there is always the possibility of equipment failure leading to injury or death. That’s just the risk you run when you are in a hostile environment and you depend upon the equipment around you. But if you can get to someone quickly, that is good. Often spacewalks are done with two spacewalkers and there is continuous communication. So if someone is having a problem, hopefully the other can go get them and bring them in… When the pressure gets very low there is just not enough oxygen. That is really the first and most important concern.

Ultimately, then, it seems that running out of oxygen (due to there being no oxygen in space and also due to all the weird things that would undoubtedly happen to your heart, lungs, blood vessels, etc.) is the primary threat to human life. But, obviously, surviving in space is something NASA has considered. Clearly, a human isn’t going to get thrown out there butt naked… but it’s entirely possible something might compromise their space suit and expose them to the vacuum of space. Thankfully, it seems like they’d have a few minutes to be rescued.

Leave a Reply

Your email address will not be published. Required fields are marked *