Hear me out on this one….after watching several videos of propane canister explosions both in outdoor and indoor settings, I’ve come to the conclusion that the library wouldn’t have collapsed had they gone off. Sure there would be significant shrapnel damage to the cafeteria as well as fire damage (not to mention a nice sized crater). I find it hard to believe both propane canisters would’ve damaged the load-bearing pillars (which were most likely iron beams covered in dry-wall) to the point that they would fail. The cafeteria ceiling/library floor was also most likely strengthened by metal beams as well, which is highly unlikely would be destroyed to the point that they would fail either unless they were allowed to burn for a significant amount of time. I think E+D were trying to copy the destruction caused by the ammonium nitrate bomb used in Oklahoma City and comparing the destructive force of that compared to a Propane bomb is like comparing apples and oranges.