BTW the "plane explosions can't melt steel" is one of the most easily debunked 9-11 "truther" talking points.
The idea is that jet fuel burns between 600C and 950C, but the melting point of steel is 1200C to 1370C, depending on it's purity. Those numbers don't add up, right?
Wrong.
You see, steel is not the same as ice. Water has clearly defined states. Above 0 Celsius it's a liquid, below that it's ice.
Metals on the other hand work a little differently. As you heat them up they soften and become fully liquid at the melting point.
When steel hits 1370C it flows like water, but at 900C it's still lost 60% of it's hardness.
You take a 1 inch thick steel crowbar, the sort that could easily apply almost a thousand pounds of force to a stuck door before breaking, heat that crowbar up to 900C and an average man could bend it in their... well not bare hands, because it would be hot but if they had fireproof gloves they could bend that crowbar without additional tools.
Now also remember your basic science that hot metal expands.
So you have that jetfuel burning along with wooden desks, polyester carpets, about a million boxes of copy paper. Those steel beams get nice and hot, they're all trying to expand against eachother. Rivets start popping out. A steel beam which once could hold 10 tons is now only up for holding 4 tons.
Softened and overexpanded one beam buckles free from the rest of the structure. Now the remaining beams have to support what that beam but they're heating up and expanding too.
Then, all of a sudden 100 tons of building on top are being held up by a soft, hot, middle which can only lift 99 tons. The floors below wee meant to hold the top of the building, but not the kinetic energy if that top of building is heading toward them at 32.1 meters per second-per second.