The Murrah bombing is relevant because it provides examples of what happens to concrete in a structural failure: It breaks up into chunks. If the WTC collapses were primarily structural, why did almost all the concrete turn to dust? Structural failure would have left a much greater proportion of large pieces.

The theory that the basement explosion was caused by falling fuel would fit the facts, except for the many witnesses who testified that it preceded the plane impact by several seconds. The sound of the impact took a scant second to reach those on the ground, while the jet fuel would have taken nearly eight seconds to fall from the impact point on the 90th floor, assuming it fell freely all the way to the basement. If the fuel squirted downwards its fall would have taken less time, but it was not supersonic, and even a split-second fall fails to account for the reported multisecond delay.

Regarding the claim that the the core columns were heated above 900 degrees: The few core columns that were not cut up and shipped to scrap obvlivion and were available for NIST to examine do not bear out that theory, as Griffin points out in my reference. And what evidence is there that the core, in fact, compromised to the extent necessary to support your blast-furnace airflow?

The Murrah building was not 110 stories tall, and was made with different materials using a different design. It fell not even one tenth of the distance and weighed less than one tenth of one of the towers. One of its primary load bearing walls was obliterated by several hundred pounds of ammonium nitrate and deisel fuel detonated at the base of said wall from a height of approximately 4 feet, resulting in the instant and catastrophic loss of structural integrity and immediate collapse. Again, there is no valid comparison to be made here.

OK, try and imagine this: Place a cinder block on the ground and drop another, identical cinder block on it from a height of 5 feet. The two will break into several chunks. Now, perform the experiment again, this time taping two cinder blocks together and dropping them on the bottom one from the same distance. Notice that the bottom one will be reduced to smaller chunks due to the greater kinetic energy imparted by the greater mass of the falling blocks.

Apply this principle to the WTC Towers. Each consecutive floor added more and more kinetic energy to to the fall due to increase of mass. 500,000 tons of falling concrete and steel would pack one hell of a punch. I am confident that it would be enough to reduce a 4 inch concrete slab to little more than dust and fist-sized chunks, which is exactly what we see in the ground zero photos. Not all of the concrete was reduced to dust. Much of it is visible in the debris pile. The concrete in the floors was not reinforced, either; it was ordinary concrete similar to that used in sidewalks and driveways. Breaking that stuff is easy in comparison with say, reinforced 6000 PSI fiber mix.

The fact that the elevator doors were blown off of their tracks is clear evidence that the core was compromised; the elevators were contained inside the core. Several stairwells were also heavily damaged, which would allow the fire to feed on fresh air being drawn up from the lower floors by convection. Ask anyone who has fought or been close to a forest fire; they will talk about winds in excess of 30 MPH trying to suck everything into the flames. This is caused by convection, and is the primary mechanism of a side- or bottom-draft furnace.

As for the explosion in the basement, the number of people who say the explosion happened after the plane hit far outnumber the two addled witnesses who claim it happened before.

Regarding the powder vs. chunks quesiton, note this cite from Griffin:
Hoffman (2003) reports, “nearly all of the non-metallic constituents of the towers were pulverized to powder.” www.mujca.com/textnewyork.htm

"Two addled witnesses":
“Two addled witnesses”: Elsewhere on this page, I've already named others who support Rodriguez' statements. Here are some items from Griffin's thoroughly-footnoted article
www.mujca.com/textnewyork.htm
showing that there are, indeed, plenty of eyewitnesses supporting the thesis of controlled demolition. Regarding specifically the explosion preceding the first impact in the North tower:

Teresa Veliz, on the 47th floor, reports that suddenly “the whole building shook. . . . [Shortly thereafter] the building shook again, this time even more violently."

Rodriguez states that he and the other 14 people in the office heard and felt a massive explosion below them. "When I heard the sound of the explosion,” he says, “the floor beneath my feet vibrated, the walls started cracking and everything started shaking. . . ." Seconds [later], I hear another explosion from way above. . . . Although I was unaware at the time, this was the airplane hitting the tower.” Then co-worker Felipe David, who had been in front of a nearby freight elevator, came into the office with severe burns on his face and arms yelling "explosion! explosion! explosion!" According to Rodriguez: “He was burned terribly. The skin was hanging off his hands and arms. His injuries couldn’t have come from the airplane above, but only from a massive explosion below.”

Mike Pecoraro, who was working in the north tower’s sixth sub-basement, stated that after his co-worker reported seeing lights flicker, they called upstairs to find out what happened. They were told that there had been a loud explosion and the whole building seemed to shake. Pecoraro and Chino then went up to the C level, where there was a small machine shop, but it was gone. "There was nothing there but rubble,” said Pecoraro. "We're talking about a 50 ton hydraulic press--gone!” They then went to the parking garage, but found that it, too, was gone. "There were no walls.” Then on the B Level, they found that a steel-and-concrete fire door, which weighed about 300 pounds, was wrinkled up "like a piece of aluminum foil." Finally, when they went up to the ground floor: “The whole lobby was soot and black, elevator doors were missing. The marble was missing off some of the walls”.

Regarding multiple detonations clearly reminiscent of controlled demolition, Veliz states of the North tower that, as she was finding her way out, “There were explosions going off everywhere. I was convinced that there were bombs planted all over the place and someone was sitting at a control panel pushing detonator buttons”. Numerous witnesses mention aspects of the South tower's fall that bespeak controlled demolition. Griffin cites at least fifteen witnesses to a series of explosions or flashes immediately preceding the collapse. Six of these witnesses explicitly mention the resemblance to a controlled demolition.

Now, how many witnesses can you cite whose accounts contradict this? How do you explain away eightteen witnesses (and there are more)?

Defendants in Rodriguez's suit might argue that the basement explosion and damage Rodriguez and other witnesses reported could be explained as a deformation wave from the impact travelling down through the structure at the speed of sound in steel and breaking at the building's foundation, chased by the fireball along with some debris and maybe an elevator or two; that the sound of impact, arriving simultaneously with the wave, might've been drowned by the rupturing of building materials below, and Rodriguez might've mistaken the first sound of subsequent damage above as the plane's impact. But the testimony alone regarding the South tower saps credibility from this facile hypothesis; if the South tower's fall resulted from preplanted explosives, then surely the North's did also.

Furthermore, there is much evidence beyond witness statements supporting the thesis of controlled demolition covered in Griffin's article. Most of it has not yet been mentioned in this discussion. To cite one example: The speed with which the buildings fell, once collapse began, shows that there was virtually no support for any of the structures after that initial moment, just as if such supports had been cut using explosives in a planned demolition. NIST's report fails to address the mysterious nearly-free fall, but instead models only the period between plane impact and the start of the collapse. Moreover, NIST declines to disclose the details of even this partial analysis.

The more I think about it, the better your idea sounds. (My own bro suggested it to me a few months ago.) It'd certainly make high temps more believable. It would've contributed a relatively clear component to the plume, and would've created an audible roar. My gut feeling is that explosives would still be needed to achieve the rapid fall, but we're really at the point where math or experiment is required.

Your comment that temperature is uncorrelated with smoke opacity is way off base. The reason thick smoke indicates a relatively low-temperature fire is simple and fairly obvious: It reveals that the combustion is incomplete. This is naturally true of dump fires. High-temperature combustion produces mainly gas, and thus a relatively transparent plume.