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 1960s. 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.