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Using a mathematical model Dr Keith Seffen has proved that once it was begun by the, well studied, structural failures caused by the planes impact and subsequent inferno the following collapse and pancaking were inevitable, his models showed that once begun the collapse would take around 9 seconds — only a little longer than a penny dropped from the top floor would take to fall to the ground.
Dr Keith sums up his experiment by saying
"In all senses, the collapse sequence was quite ordinary and natural. The World Trade Centre towers were designed to absorb an aircraft impact, but an accidental one with much less fuel and speed. It is widely acknowledged that the impacts on September 11th were extraordinary, which led to consequences well in excess of the design capacity for the buildings. The original design of both towers must be praised for standing as long as they did, saving more lives than might have been expected.""