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The aeroplanes that flew into the Twin Towers contained 3Ot of aluminium. When their cracked fuel tanks burned intensely it caused the aluminium to melt. The molten aluminium streamed down to the lower floors and came into contact with water from the sprinkler system, which caused devastating explosions.
Two Boeing 767 aircraft hit the Twin Towers World Trade Center (WTC) 1 and WTC 2 on the morning of September 1 1 2001. Within an hour WTC 2 collapsed, followed by WTC 1 about 30 minutes later. The surrounding buildings were bombarded with projectile fragments in the process.
WTC I1 a 47-storey skyscraper, caught fire and collapsed late in the afternoon. Why did these buildings collapse?
The official report1 by the US government official commission, supported by other publications,2,3 concluded that the cause was overheating of steel girders in the centre of the buildings. Many people doubted this explanation, and claimed that it must have been a conspiracy4.
Many people had heard explosions immediately before the collapse of the buildings, leading them to believe that dynamite had been placed in the buildings. I will demonstrate on the basis of physics, thermodynamics and experimental studies carried out at Alcoa Ltd5 that the most likely explanation is otherwise.
According to my model of the event the collapse took place in four stages: the crash, the heating of the aircraft, the explosions and finally the collapse.
The crash
The Twin Towers are located side-by-side, and WTC 7 is only about 50m away (Fig 1). At 8:46am WTC 1 was hit between floors 93 and 101 by a Boeing 767 at a speed of 710km/h. A second plane crashed into WTC 2 20 minutes later at a speed of 820km/h between floors 77 and 85. Both aircraft were loaded with about 38t of fuel, and both were slowly descending.
Both finally halted close to the centre of the buildings, and several steel girders must have been cut during the crash. The aircraft must have passed through several floors before they stopped completely. They must have fragmented severely, and the fuel in the fuel tanks brought on a fierce fire.
It is clear that the airplanes crashed through the outer wall, cutting it like a Samurai sword and pushing that...