BBC: 9/11 demolition theory challenged

http://news.bbc.co.uk/1/hi/sci/tech/6987965.stm
<http://news.bbc.co.uk/1/hi/sci/tech/6987965.stm>
The University of Cambridge engineer said his results therefore
suggested progressive collapse was "a fair assumption in terms of how
the building fell".
"One thing that confounded engineers was how falling parts of the
structure ploughed through undamaged building beneath and brought the
towers down so quickly," said Dr Seffen.
[The south tower of the World Trade Center collapses, AP]
Conspiracy
theorists see evidence of a "controlled detonation"He added that his
calculations showed this was a "very ordinary thing to happen" and
that
no other intervention, such as explosive charges laid inside the
building, was needed to explain the behaviour of the buildings.
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.
Conspiracy theorists assert that these explosive "squibs" can actually
be seen going off in photos and video footage of the collapse. These
appear as ejections of gas and debris from the sides of the building,
well below the descending rubble.