I've read his explanation(s) before, and it's literally filled with stuff that can be debunked. I'm only going to cite two though. From his list of explanations:
1) -Fact which is undisputed by either side, both are not in the demolition business
(He's referring to Larry Silverstein and the fire department commander)
No one not in the demolition business, is going to call firefighters "it." No one.
2) The ominous looking smoke in the background can be just as easily applied to WTC 5 and WTC 6, both directly behind WTC 7 in one of the photos and they were flaming away. Scroll down to see both.