What happens to animals in the vacuum of space?

In the vast majority of modern shows, people sucked out into the vacuum of space freeze like popsicles in seconds. This is ridiculous. The reality is much more horrifying. In the 1960s there were several studies done on animals in high-grade vacuums that give us a real idea of exactly what would happen in the “oops, I forgot my spacesuit” scenario, and I’m going to walk you through the gory details, along with links to the original papers published in the 60s.

The first big thing to understand is how heat is transferred in space. You may remember that there are four main ways that heat can be bled off: conduction, convection, radiation, and phase change transfer (e.g. ‘enthalpy of vaporization’). When you’re in space, conduction and convection are out, because nothing cold is touching you (conduction) and there are no fluids to transfer heat away from you (convection). That leaves only radiation and phase changes that can cool you down. The infrared radiation leaving the human body is only about as much as a lightbulb, which is not going to drop your temperature extremely rapidly. You’ll also be cooled when the water in your skin boils away, but that’s only going to affect your outer layer. Your internals will be fine for a while, until they completely run out of oxygen.

So now that we’re clear that insta-freeze won’t happen, what are the actual steps in our grisly space demise? Here they are:

• As soon as you get into space, the air will be violently forced out of your lungs. Your lungs can’t take a one atmosphere pressure differential. In an experimental dog decompression study, most dogs also underwent “a high degree of subcutaneous emphysema and expulsion of gas from the stomach and lower bowel, often with simultaneous projectile vomiting, defecation, and urination”.
• Your fluids will start boiling away instantly. As pressure decreases, boiling point temperature also decreases until you reach the triple point (the point at which water, ice, and vapor exist at equilibrium). The triple point temperature for water is 32 degrees fahrenheit, well below body temperature. There was a NASA volunteer test subject, Jim LeBlanc, who was accidentally exposed to near-vacuum on camera while testing a space suit in 1966. He reported feeling the saliva boil away from his tongue before passing out.
• Generally speaking, you’ll pass out after about 10-15 seconds due to lack of oxygen. Since you can’t hold your breath, there’s not much wiggle room there. Your organs will continue to work for a while longer, but you’ll really want to get back to a pressurized environment as soon as you possibly can, because while all this is happening, you’ll also start bloating.
• Severe bloating will begin immediately, as water in your body turns to water vapor and the gases dissolved in your bloodstream start coming out of solution. It’s a good thing you’re passed out, because this is likely to be extremely painful.
• If you don’t get back to safety within about 2-3 minutes, the oxygen deprivation combined with organ hemorrhaging from lack of pressure will kill you. Animal studies with dogs and chimpanzees were conducted at near-vacuum (high altitude) to obtain those numbers, which I’ll discuss shortly.
• After death, your fluids will continue to outgas until your body is mummified. You’ll last quite some time at this point, if you can avoid gravity wells!

So how do we know the approximate point of irreparable damage? As I mentioned above, in 1964 an interesting (and disturbing) paper was presented called “Experimental Animal Decompressions to a Near-Vacuum Environment”, which contains descriptions of the rapid decompression of 126 dogs to near-vacuum (2 mmHg). Basically they decompressed batches of 6 dogs each for periods of time varying from 5 seconds to 180 seconds. At two minutes the dogs suffered 15% fatalities, and at three minutes the dogs suffered over 80% fatalities. Denitrogenated dogs (dogs that breathed pure oxygen for a period of time to remove most of the nitrogen from their bloodstreams) survived for slightly longer than non-denitrogenated dogs. The bloating was so bad that the dogs appeared inflated like balloons – in the words of the paper, “The water vapor effect and gas expansion were of such magnitude that the animals became completely immobilized with the extremities, neck, and body in an extended position, similar in appearance to an inflated goat-skin bag.” Many of the dogs died from heart failure long before recompression.

The dogs rapidly deflated once recompression commenced, and the dogs that survived quickly regained functionality in the majority of cases. To quote the paper, “During recompression to higher pressures, the subcutaneous gases were, of course, also recompressed and the animals quickly and dramatically deflated to their normal appearance, still remaining, however, in an obvious state of flaccid paralysis, unconsciousness, and apnea. This deflation process appeared to begin rather gradually with the onset of recompression. At 25 to 30 mm. Hg absolute, deflation became more rapid ; at approximately 70 mm. Hg the animals appeared to have returned to their normal size. At 45 to 50 mm. Hg, however, a major portion of the deflation is complete, suggesting that water vapor is probably the predominant gas concerned with the excessive distention of the animals.” Even in those decompressed for 180 seconds, lung trauma appeared to clear up in 24 hours.

Similar studies were done on chimpanzees, which were interesting because the chimps could perform complex tasks before and after the decompression. In one study, all eight chimps survived decompression, one of which was decompressed twice (the last decompression lasting 150 seconds). All the chimpanzees were able to perform at or above their pre-decompression mental levels, and in subsequent check-ins they displayed no noticeable long-term side-effects. In a subsequent study, one chimpanzee survived a 210 second decompression (subject 254, one tough chimp). I’m happy to report that S-254 demonstrated complete behavioral recovery after 199.25 minutes.

As you can see, reality is much more dramatic than fiction when it comes to rapid decompression in a vacuum. Try to keep your spacesuit intact.