I think if you go with the supposition a nuclear bomb exploded beneath the tower, whose chief purpose was demolition (Dimetri goes as far to claim with certainty that this demolition protocol was mandated to exist underneath the towers back when it was built,) then we are dealing with unprecedented demolition (at least to the public.) For instance, you say "as the reaction went upwards" but I would think it would be more instaneous, at least the shockwave and heat will permeate through the entire building before gravity accelerates the building downwards.

And even then, I am having trouble explaining how the tower began to fall from the large hole in the building. One theory I can propose is that the explosion beneath was calculated not to "dustify" the steel, but to super-heat it to the point where it would fail at the large hole in the building. Then everything comes crashing down on itself and becomes, for the most part dust. I know some things need work, but I am just beginning to wrap my head around this, at first, seemingly ludicrous theory.

Note that this theory seemingly doesn't match these images of the spire seemingly turning to dust before the tower even accelerates much. But, I notice that this might be a time perceptual deception if the time frames aren't posted on all the images, as this is a no brainer (basic science presentation skills) when producing these types of images side by side. The last image, might be unequally spaced into the future. Regardless some dust seems to outline the spire, but it might not have completely dissolved, which would make the above theory more plausible.