The cores themselves, basically, if you've seen diagrams of the building, there's a large, central rectangle in each of the towers that contain 47 columns, and these columns basically were the primary structural support of the building.  They were given the role of supporting the whole gravitational load of the building.  Since they were so strong, it would be reasonable to think they would have withstood, at least to some extent, the collapse, but in fact, as we see after the buildings' collapse, there was basically only little stubs of these things standing up a floor or two above the ground level.  The cores did not have much in them that would burn.  The cores basically were dedicated to things like elevator shafts, utility shafts, stairways.  So you have drywall material, you have a little bit of carpeting, you don't really have any inflammable material in the core itself.  The core was specifically designed so it could not function as a chimney.  They did not want, in case of a fire, for the fire to be able to travel through the elevators or for air to come in through the elevators.  So they were designed with what this architect Aaron Swarovski, I believe it was, referred to as a hermetically sealed system.  There were fire shutters that were designed to close off the core in an event like this and those, as far as we know, functioned properly, which means that there was a very limited amount of oxygen available.

Okay, as far as the issue of what failed and how?  Some of the initial suggestions, and these showed up in the NOVA documentary which is a good example of what I like to call proof by computer animation.  Thomas Egar, who was a materials scientist but not a structural engineer, who became a spokesman for these documentaries, indicated that the floors had somehow failed, the trusses supporting the floors had failed.  This was the theory that was put forward initially in the initial FEMA report.  Subsequently there have been basically complete contradictions of that.  Jim Hoffman has done quite a bit of research that is available on the Web concerning the problems with this idea that the floors would have simply fallen.  There was a study done by Weidlinger & Associates, the Chief Engineer there was Matthys Levy who is a very well known authority on building collapses.  He specifically disavowed the idea of pancaking or collapsing of the floors.  And the most recent official report we have on this, which is from the National Institute of Standards and Technology, NIST, rejected the idea that floor collapse was part of it.

And so, as a result, we have basically no sequential model at this point.  What NIST has suggested is that there was some kind of simultaneous collapse of the cores, but they have not attempted to give any kind of modeling as to whether those cores could have in fact been destroyed by the fires in the way that they claim.  And unfortunately, the material that would have allowed a detailed fire analysis, the actual physical evidence, is all gone.

One of the most significant things to my thinking that indicates that this could not have been the sort of collapse that were are told it was is the presence of the dust clouds.  And as you've seen in the pictures, and I'm sure that all of us have seen probably more than we would like, there were very, very large clouds of very thick dust that enveloped the area, that crossed the river, that made it almost all the way to New Jersey, from the pictures that I've seen.  This type of flow is something that we are familiar with in physics, it occurs in only two situations that we know of naturally.  One is in volcanic eruptions where a large amount of material is suddenly exploded into the air and basically forms small particles.  The other situation is something called turbidity currents.  These occur along the edges of continental shelves where mud or sediment will become suspended in water.  And the common thread is you have large amounts of a dense material that is suspended very quickly in the fluid, thereby creating another, denser fluid which is in effect the dust cloud.  And that fluid can achieve considerable velocities. 

The problem with creating this sort of this slurry of fine particles is that there really is no mechanism that has been proposed.  We have concrete floors with carpeting or flooring over them.  We have furniture.  We have floors basically that are coming together in a collapse but the concrete is basically protected under these layers.  Early in the collapse, in the very first moments, we see these thick clouds being ejected at very high speed.  They are clearly dense, because they flow downward and become part of this large, overall pyroclastic flow.  What we're basically being told is that the concrete sort of jumped up into midair where it exploded itself and was ejected as the floors came together.  Not a very plausible mechanism but I have yet to hear of anything else proposed to explain it. 

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