Amanda Angelika wrote:

Well WTC 1 an 2 appear to have collapsed from the top, the collapse doesn't
appear to have started from the bottom. A collapse from the bottom wouldn't
make sense in any case because they had been attempting to fight the fires
in which case one would logically assume any potential softening of the
steel beams caused by heat above should have been cooled by falling water
from the fire fighting effort and sprinkler systems.

They were operating but not up to specification. When too many
sprinkler
heads are opened all at once the system depressurises and become
ineffective. Such systems are not designed to control fires starting on
huge
areas of many floors all at once. See :

http://www.architectureweek.com/2002/0515/news_1-1.html

Additionally, it is probable that some water lines were severred
by the plane impact.

There are eye witness
reports from people who managed to escape that the sprinkler systems were in
operation and there was water cascading down the stairwells.

The fact that WTC7 does appear to have collapsed from the bottom and so soon
after the fire people withdrew is somewhat puzzling though, the lower floors
should have been water logged which should have cooled the steel framework.

Water running down stairwells away from the fire is no indication that
water was necessarily running down structural beams in the middle
of the fire as well.