What would happen to a astronaut if his space suit was accidentally tore in outer space?
In the Shuttle suit, an astronaut can survive 22 minutes with a 1/8″ hole in his suit. At that point the pressure will drop to where he is likely to suffer permanent brain damage, if he survives. The Shuttle suit has a secondary oxygen pack pressurised to 5,000 psi. If the primary system cannot maintain pressure in the suit (due, for example, to a 1/8-inch hole), the secondary oxygen pack will open its valve and attempt to maintain the pressure. If there is a large tear, the astronaut might have a few seconds to live. No matter what he does, severe vascular damage is certain, and the probability of permanent damage to the neural system (including the brain) is extremely high. However, as several notes here have pointed out, the outer layer of the space suit is very tough, and the probability of even a small puncture is low. Even if the external pressure drops to a vacuum, blood vessels maintain a high enough pressure that the body’s temperature remains below the boiling point of water
