Sometimes, sci fi gets it wrong. Sometimes, you don’t know. The movie “Outland” and “Total Recall,” for instance, show unprotected people blowing up like balloons when suddenly exposed to a vacuum. Other movies such as “2001” show people holding their breath and survive a few seconds of exposure. Others like “The Expanse” show people in space suits nonchalantly opening their faceplates for a few seconds to adjust things with no ill effects. So what’s the truth?
Until President Trump stops dicking around and turns over the federal prison system to the US Space Force and we can *finally* execute rapists and murderers and gang members and anti-nuclear activists and terrorists by shoving them out the airlock, we won’t know for sure just what the effects of explosive decompression really are on unprotected humans. But a few sub-scale experiments can be attempted. Standard latex balloons filled with water and air bubbles make a *fair* approximation of a body, and a simple vacuum chamber makes a *meh* approximation of the vacuum of outer space. So what happens? Well, “Outland” exaggerated the speed of the process… but, yeah, kerblam.
Holding your breath would be spectacularly useless, as well as potentially deadly. Human skin is stronger and less stretchy than latex rubber, so the effects shown here would be smaller and slower. What allows the water in the balloons to boil is that the air bubbles can expand because the latex is so stretchy, and as the balloon stretches the pressure within drops far enough for the water to boil. A better experiment would be to use something like very thin leather, actual animal skin, or some sort of other polymer, preferably something that simulates skins physical properties while also being transparent.
With an actual human, the skin would hold up reasonably well, at least for a while. But other exposed surfaces are less rugged. The interior of the sinuses and the lungs themselves are thinner, weaker, more porous; I suspect that within seconds an exposed person would be blowing bubbles of bloodfoam. As the heart continues to beat it will continue to pump blood through the lungs. Dissolved gases in the blood will readily pass through the membranes and be expelled to space, so the oxygen levels of the blood will plummet rapidly. And as the gasses disappear and the skin expands, blood pressure will drop… especially if the person starts bleeding out through the lungs and mucous membranes. As the blood pressure drops, especially with rapidly depleting oxygen levels, the heart will soon just plain quit.