"If we got a small hole [in our spacesuit], our oxygen would start coming out of the spacesuit, and the pressure would start to drop. If the pressure drops too far, then you'll get the bends, and if it drops below about 2.5 psi, then you don't have enough oxygen to maintain useful consciousness.
"Now, we have a device called the Secondary Oxygen Pack on the back of our backpack, and it's got a whole lot of oxygen in it, and it would be able to support a small leak for—depends on how small it is—but for at least 30 minutes. So for a small leak, we'd have our secondary-oxygen system kick in, and we'd be heading back to the airlock and repressurizing, and we'd be fine. A big leak—like a big hole in the suit, say a half-inch hole or something like that, or if your glove blew off—would pretty much be a real bad day for you."