The divers were experiencing 9 times atmospheric pressure in the chamber which would normally be what the pressure is in the water outside at approximately 200 feet. This is what enables you to just climb down a ladder into the water outside, since the pressure is equal the water doesn't come in. At this pressure your body and everything in it has dissolved gasses. Going from 9 atm to 1 (normal air pressure) instantaneously would make the body literally explode from the blood and other liguids would turn to a gas immediately.
This is also the cause of the bends in scuba diving where dissolved nitrogen turns to gas bubbles in your blood causing all sorts of problems or death.