It's a recurring horror in sci-fi: the hull is pierced, a human is trapped without equipment in an airlock about to open, a door needs to be opened in order to expel something undesirable. With no air and almost zero pressure, the human body isn't going to last long without some form of protection. But what does happen, exactly? Do your eyes explode outward while your blood evaporates?
Well, no. The truth is both less dramatic and far more fascinating -- as we have discovered through accidents in space and in test chambers, and animal experimentation in the s. The first thing you would notice is the lack of air. You wouldn't lose consciousness straight away; it might take up to 15 seconds as your body uses up the remaining oxygen reserves from your bloodstream, and -- if you don't hold your breath -- you could perhaps survive for as long as two minutes without permanent injury.
If you do hold your breath, the loss of external pressure would cause the gas inside your lungs to expand, which will rupture the lungs and release air into the circulatory system. The first thing to do if you ever find yourself suddenly expelled into the vacuum of space is exhale. The other things, you can't really do much about. Whatever you do, don't hold your breath! The vacuum of space will pull the air from your body. So if there's air left in your lungs, they will rupture. Oxygen in the rest of your body will also expand.
You'll balloon up to twice your normal size, but you won't explode. Your skin is elastic enough to hold you together. Any exposed liquid on your body will begin to vaporize. So the surfaces of your tongue and eyes will boil. Without air in your lungs, blood will stop sending oxygen to your brain.
You'll pass out after about 15 seconds. So if someone is having a problem, hopefully the other can go get them and bring them in. This is especially grave if you are holding your breath or inhaling deeply when the pressure drops.
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. Water and dissolved gas in the blood forms bubbles in the major veins, which travel throughout the circulatory system and block blood flow.
After about one minute circulation effectively stops. The lack of oxygen to the brain renders you unconscious in less than 15 seconds, eventually killing you.
That is really the first and most important concern," Buckey says. But death is not instantaneous. For example, one 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.
However, dogs held at near vacuum for just a little bit longer—two full minutes or more—died frequently.
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