Mark Mandell - Gone Round In New Jersey
1. As explained to me, PVC under pressure "ages" over time, more so with temperature changes, and will become brittle, fatigue and fail. This can happen with a water line as well, but there is a huge difference between 60-80psi in water as opposed to 100 psi with air. Water can be pressurized but not compressed so it doesn't "store" energy; break a water line and you get a squirt followed by running water. Break a PVC air line and the plastic shatters into shards and the stored energy in the compressed air sends it flying like an air gun (or nail gun, etc.). This is why OSHA prohibits its use in unshielded air line systems.
2. I have personal experience with the effect as a friend used 1" PVC lines in his garage air system. He called me one afternoon to come look at his garage. One of his PVC lines had ruptured and the plastic shrapnel had gone through the sheetrock on the opposite wall, 25 feet away. He said it sounded like a shotgun had gone off. Fortunately, nobody was in the shop when it happened as I have little doubt he or anyone else would not have survived.
He changed all his air lines out with copper. He has little sign on his shop wall with several shards glued to it. Sign says "Dear Death, Na Ha, Ya Missed Me!"