Originally posted by: irishScott
Anyone stop to consider that maybe Al Quaeda planted a bomb as a failsafe? It would fit Occam's razor.
And if there is ever real, fact-based evidence to support a theory of a bomb in the basement, I no doubt would believe it was al-Qaida. It was attacked with a bomb at street-level (or the basement, forget the precise location) in 1993, so it's not all that hard to believe it could have happened again. However, I've yet to see any evidence of this happening.
First and foremost, is what happened (and watching the videos of the collapse fits this):
The planes, when they hit, tore into the buildings at a high level. They tore into the steel support columns, with the most important at the core of the building. The jet fuel spread and ignited fires on a few floors both above and below the main floors of impact. These fires, while not hot enough to melt steel, were hot enough to weaken support structures, and most importantly, severely weakened if not melted the non-steel support structures in-between floors. Take the concept of destroyed or compromised core support columns, and combine with that several floors of weakened floor support structures and material, and you have a big problem: a lot of weight from several floors above, resting on a few floors of severely compromised structure.
The buildings pancaked. No video has shown evidence of weakened supports caused by blasts at the base of the building (and these, if not properly controlled and calculated, would have likely led to a collapse to a particular side, and not what happened).
And watching the videos carefully, the buildings pancaked at the floors of impact. First, all the weight from the non-damaged floors above, forced a collapse of the compromised floors (and the damage was basically evenly distributed, since the main support systems were at the building's core, and the fuel, and thus fire, spread evenly across several floors). The momentum of this collapse, and now unsupported weight, forced the entirety of the next few lower floors to buckle under the pressure and continued a runaway pancake collapse.