( Skip to 17:41 ) An interview from an emergency worker recorded on 9/11 describes a sound like a "clap of thunder", a shockwave seen ripping through the building and busting out windows, the bottom floor that "caved out", and the building collapsing to the ground.
Here are videos of WTC7 collapsing:
For a building to fall symmetrically and in it's own footprint without falling over, the steel columns have to be removed symmetrically and within approximately 1/10th of a second of each other. It's impossible for fire to make this happen. So since fire can't be removing the column supports, something else must be.
However NIST said that a single column failure (column 79) caused the building to collapse, and also said that the falling debris or diesel fuel had almost no influence on the collapse. Could a single core column cause the rest of the columns to fail within 1/10th of a second? No, that's even faster than the human eye blinks.
WTC7 also fell at free-fall speed for over 100ft:
The once 47 story skyscraped was reduced to a 4 story pile of rubble: 4 & 5. Check.
While the collapse caused some damage to surrounding buildings, most of the debris was isolated to the buildings footprint. 6. Check.
There were dozens of witnesses who reported explosions. Ground Zero first responder Craig Bartmer and Airforce Medic Kevin McPadden reported hearing explosions during the collapse ( skip to 22:50 ). There are many more seen in in the following video, although these are witnesses to both WTC7 and the Twin Towers:
Skip to 0:45 in the following video and watch the cloud move hundreds of feet at a fairly fast rate:
Molten metal was seen in the rubble of WTC7 also. Skip to 25:20 to hear several witnesses describe it, or check out this and this website.
Thermal images also show extremely high temperatures: Keep in mind that's just the temperature on the surface. The 9/11 Commission, FEMA, and NIST reports all failed to address the molten metal. The temperature of this metal was much hotter than could have been produced by the fires, as structural steel melts at 2750*F and the temperatures of the fires were at the absolute maximum 1800*F: In the following video, Lead Engineer of NIST John Gross denies the existence of the molten metal:
Thermite, a combination of Iron Oxide and Aluminum, is an incendiary which sustains an extreme heat reaction, creating molten iron. Skip to 32:30 in the video to see some thermite reactions. Appendix C of the FEMA report described sulfur residues on the WTC steel. Sulfur slightly lowers the melting point of iron, and iron oxide and iron sulfide had formed on the surface of the structural steel. Thermite mixed with sulfur is called thermate, and produces a lower melting point and accelerated results.
Sec 12-4 of the NFPA: Guide for Fire and Explosion Investigations says that "unusual residues...could arise from thermite, magnesium or other pyrotechnic materials". However NIST didn't even look for this evidence.
edit on 11-9-2011 by TupacShakur because: To edit my post