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The study by a Cambridge University engineer demonstrates that once the collapse of the twin towers began, it was destined to be rapid and total.
His calculations suggest the residual capacity of the north and south towers was limited, and that once the collapse was set in motion, it would take only nine seconds for the building to go down.
This is just a little longer than a free-falling coin, dropped from the top of either tower, would take to reach the ground.
The controlled detonation idea, espoused on several internet websites, asserts that the manner of collapse is consistent with synchronised rows of explosives going off inside the World Trade Center.
This would have generated a demolition wave that explained the speed, uniformity and similarity between the collapses of both towers.
After reviewing television footage of the Trade Center's destruction, engineers had proposed the idea of "progressive collapse" to explain the way the twin towers disintegrated on 11 September 2001.
This mode of structural failure describes the way the building fell straight down rather than toppling, with each successive floor crushing the one beneath (an effect called "pancaking").
NIST’s findings do not support the “pancake theory” of collapse, which is premised on a progressive failure of the floor systems in the WTC towers