No steel-framed building had ever collapsed due to fire. Due to the properties of steel, three conditions must be present for the collapse of a steel-framed building. Fires must be intense, long-lasting and large relative to the amount of steel in the building.
The corollary is that every previous total collapse was due to a controlled demolition. The Twin Towers, like WTC-7, exhibited all of the features of a controlled demolition. The official theory cannot account for any of them.
1) Sudden onset. Buildings are still, then suddenly the collapse starts as supporting columns are sliced by explosives. The Towers were motionless before they collapsed with no bending of the vertical steel columns and no video evidence of floors sagging.
A fire-induced collapse, if there were an example of one, would be gradual as floors would sag and vertical columns would bend.
2) Straight down. One of the hallmarks of a controlled demolition is the buildings fall in their own footprint so surrounding buildings aren't harmed. The Towers didn't land in their own footprint but came straight down centered around their vertical axes.
Again, due to the bending of steel a fire-induced collapse would asymmetric.
3) Near free-fall speed. According to NIST who authored the definitive government report on the collapses of the Towers, the North and South Towers fell in 11 and 9 seconds respectively. Free-fall from their height in a vacuum would be 9.2 seconds.
Because floors were pulverized from the top down, free-fall would not be necessary. The rate of collapse would be determined by the detonation timing.
Pancaking floors would be slowed by the resistance of the floors in accordance with the Law of Momentum Conservation .
4) Sliced steel. Explosives are used to cut through the vertical support columns into pieces. The steel is also generally cut into manageable lengths. Researcher Jim Hoffman observed most of the perimeter columns were sliced into 30 foot sections and the core columns sliced into sections a few stories high.
It takes high temperatures and directed energy to slice through steel.
5) Pulverization of concrete and non-metallic material. Explosives powerful enough to cut through steel can pulverize concrete. Virtually all of the concrete and non-metallic materials were pulverized into a fine talc-like powder while the building was falling.
Gravity can break the concrete into pieces but does not have the energy to pulverize it into dust. According to MIT scientist Jeff King this pulverization requires the breaking of chemical bonds, it is not a physical process.
6) Horizontal ejections. In controlled demolitions, there are horizontal ejections of dust and material from areas the explosives are set off. The ejections from the Towers were far more energetic, however. Massive steel beams were ejected in all directions at distances of up to 500 ft. and aluminum cladding was thrown up to 700 ft. away.
Gravity, of course, is a vertical force.
7) Total collapse. The Towers were reduced to rubble only a few stories high. Prior to and after 9/11 the only total collapses of steel-framed, high-rise buildings (aside from earthquakes where the building topples) were due to controlled demolitions.
Even if all the floors had pancaked, which they clearly did not, that would not account for the failure of the vertical steel columns.
8) Pyroclastic Flow. Controlled demolitions produce huge dust clouds when dust is ejected with great energy. Dust clouds were evident with a second of the buildings' collapse and expanded to many times the volume of each Tower.
Jim Hoffman calculated that the heat required for the dust clouds was over ten times the potential gravitational energy of the buildings.
9) Squibs, indicative of cutter charges. Horizontal ejections of white-grey smoke are seen below the collapsing areas. The location of the plumes corresponds to the location of the core columns.
Although it's been theorized the squibs were pressure releases from pancaking floors, the floors were pulverized with much of the debris thrown outside the fooprint of the building.
10) Molten metal in the basements areas. The high temperatures explosives generate to slice through steel produces molten metal. There were numerous accounts of molten metal buried under the rubble.
It requires temperatures of 5200 degrees F to liquify metal. The maximum temperature jet fuel reaches is approximately 1500 degrees F. Further, it quickly burned off leaving ordinary office fires that were relatively cool, oxygen-starved fires as indicated by the thick, black smoke.
11) Sounds produced by explosives. The 9/11 oral histories recorded by the Fire Dept. of New York (FDNY) contains numerous accounts of the occurances of explosives. One could perhaps argue that the explosive sounds were caused by gas lines. However, given that the collapses exhibited all the characteristics of a controlled demolition, it's clear that the sounds heard were caused by explosives. For example:
"There was just an explosion [in the South Tower]. It seemed like on television [when] they blow up these buildings."
- Firefighter Richard Banaciski
"It was [like] a professional demolition where they set the charges on certain floors and then you hear 'Pop, pop, pop.'"
- Paramedic Daniel Rivera
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