Real-life action hero Felix Baumgartner plans to take a balloon up to the edge of space and then to jump out. In freefall he hopes to break the speed record for a human travelling without a machine, the needle, as it were, reaching speeds in excess of the speed of sound. In the BBC newsclip there’s a nice simulation of the event.
Of more concern was Pallab Ghosh’s claim that if Baumgartner gets a hole in his protective space suit his blood could begin to boil because of the very low pressure at that altitude. Wrong. He might get cold and could suffocate, his saliva might bubble in his mouth, but the pressure of your blood is sufficient to prevent it from boiling even if you are hurled into a vacuum.
This is what NASA had to say on the subject:
“If you don’t try to hold your breath, exposure to space for half a minute or so is unlikely to produce permanent injury…theory predicts – and animal tests confirm – that otherwise, exposure to vacuum causes no immediate injury. You do not explode. Your blood does not boil. You do not freeze. You do not instantly lose consciousness.”
UPDATE: The low pressure lowers the temperature at which blood and other body fluids boil, but the elastic pressure of blood vessels ensures that this boiling point remains above the internal body temperature. Although the blood will not boil, the formation of gas bubbles in bodily fluids at reduced pressures, known as ebullism, can cause pain although tissues are elastic and porous enough to prevent rupture. A flight suit will reduce the effects of ebullism. Shuttle astronauts wore a fitted elastic garment called the Crew Altitude Protection Suit (CAPS) which prevents ebullism at pressures as low as 2 kPa (15 Torr). More here.