The stairwells in the two Towers

The following discussion was posted by a member of Yahoo news group "911insidejobbers" member ' toooldforthis21'

It concerns the stairwells in the WTC Towers, and speculates on whether the differing stairwell structures might account for which Tower was selected to be demolished first.
I wanted to run this by Christophera, in particular, since he has done a lot of detailed research work on the concrete cores of the Towers:
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From: "ron_winn" <ron_winn@...>
Date: Thu Mar 2, 2006 6:51 pm
Subject: The stairwells of the two towers.

Interesting. The History Channel has just shown a documentary on two
demolitions in Providence that went wrong and had to be brought down
by ball & chain. It was planned that both buildings that were close
together were to come down together but one fell sideways and the
other fell on to it.

By which time the demolition team had built up a large crowd of local
spectators. One of the team said how embarrassing that was.

But this wasn't all of it. The first attempt failed because it was
discovered that the stairwell was holding a building up.

I guess that the stairwells are formidable structures but there were
only three starwells in each WTC towers. However three of the
stairwells in the north tower were located inside the core. Only one
in the south tower was located inside the core.

It is noteworthy that the north tower was hit first with those in the
south tower having a head start of 18 minutes to evacuate this tower.

The north tower was hit first and had the stairwells inside the core.
An interesting thought.

A strange observation may be made here in that the first hit was
higher up the north tower than in the south tower. In theory more
people could have evacuated out of this tower in the stairwells
situated inside the core and the south tower with just the one
stairwell inside the core had an 18 minute envelope for people to
evacuate.

But what is more significant perhaps is what brought down the north
tower had to contend with not only the core but also all three
formidable stairwells inside the core.

May be this was the reason the south tower collapsed first. But it
still doesn't answer why the cores of both towers were just as easy to
bring down as the shells of the two towers.

That has to be down to something special.

Both WTC 1 and WTC 2 had three sets of stairwells. All six stairwells were inside the service core structure.

If the stairwells weren't inside the service cores, they would have to be outside in the open floor plan area, where they would have been taking up valuable rentable floor space. The stairwells would also have to be enclosed in some sort of fire protection - be it either concrete, concrete blocks, or gypsum firewall rated wallboard. The stairwells had to be enclosed, both by law and by the events of the bombing in the WTC basement several years before 9/11. One of the recommendations after the bombing was that the stairwells be pressurized in order to keep smoke out. This obviously could not be done if the stairwells weren't enclosed.

Anyways, the stairwells weren't substantial elements of the design. They were fairly lightweight metal pans, supporting the stairs and landings.