Corrected entry: When Mike and Sulley are falling through the door vault, they escape through the door they are holding onto. When the door hits the ground, it completely shatters, including the metal frame that surrounds the door. No matter how hard that door hit the ground, the frame wouldn't have broken like wood.
JC Fernandez
21st Sep 2008
Correction: You're assuming it's metal... clearly it wasn't. In any case, the laws of physics aren't the same in the monster world.
JC Fernandez