The story...

The expanding dust clouds seen at the WTC can only have been caused through an enormous amount of heat energy.

A second energy sink, that has apparently been overlooked, was many times the magnitude of the gravitational energy: the energy needed to expand the dust clouds to several times the volume of each tower within 30 seconds of the onset of their collapses... That leaves increases in gas temperatures and vaporization of solids and liquids, primarily water, to drive the expansion.
http://911research.wtc7.net/papers/dustvolume/volumev3.html

Our take...

Is it true that only heat energy could account for the dust clouds that we saw rolling down the New York streets? Maybe not: it could be one factor, but we suspect there are others.

Take the velocity of the debris, for instance, which would hit the ground doing 120 mph or more. What's going to happen to the dust as chunks of concrete shatter? Seems to us like it's going to be thrown outwards, enough to drive some kind of dust cloud even if there were no heat energy involved at all.

Think also about the air within the building, being compressed as it dropped. We already have accounts from survivors in the lower WTC stairwells to tell us what that was like.

Their tower was now disintegrating. Hundreds of thousands of tons of cement, steel, and glass began to melt away. And Ladder 6 was still in the stairwell.

Matt Komorowski: “The first thing I really felt was the incredible rush of air at my back. And maybe I felt it before everybody else, because I was the last guy.”

Stone Phillips: “Like a gust of wind, behind you.”

Matt Komorowski: “Gust of wind. Wind tunnel. It was the most incredible push at your back, that you can feel.”

Stone Phillips: “A rumbling sound, this gust of wind? And then what happened?”...

Sal D’Agostino: “I didn’t even make it to the doorknob. The door got blown open at me. Just missed my face. Hits my shoulder. And that’s when the gust of wind blew me backwards...”

Stone Phillips: “Tommy, what do you remember?”

Tommy Falco: “I remember I was on the stairs with Josephine. And I imagine we got knocked down the stairs...

Richie Picciotto: “We’re like rag dolls. Getting tumbled. And I had that feeling of falling, too.”
http://www.acfd.com/miracle_of_ladder_company_6.htm

And what's going to happen to this wind, like a "wind tunnel", "the most incredible push at your back that you can feel", when it reaches ground level? It's going to shoot out in all directions, again contributing to the initial momentum of the dust cloud.

We're not claiming factors like this could alone cause the dust clouds as seen at the WTC, but it seems reasonable that they played some part. If they did, then maybe the requirements for heat energy-driven expansion aren't as great as is claimed, and perhaps the clouds could have been created from a gravity-driven collapse, after all.