"Simensen **speculates** that the two commercial jets were immediately trapped inside an insulating layer of building debris .."

I 'speculate' that those planes were in little pieces..

"The debris -- especially plaster, which blocks the transfer of heat -- would have formed a shield protecting the rest of the building...."

Now, there is some wild 'speculation'....bits & pieces of plane & building went everywhere, they didn't form any shields!

"This molten aluminium could then have flowed downward through staircases and gaps in the floor, ..."

No one saw any molten stuff in stairs, and any metal - molten OR in chunks could just as easily fall thru or break off sideways...he is speculating on what would help his ideas

"
... consistent with the timing of the explosions and subsequent collapse of both buildings ."

Explosions? There were no "explosions"! It has been shown over & over that 'puffs of smoke" were that plaster & such mentioned as 'insulation'.

He may have an honest theory, but it is barely more than wild guessing.