You don't need to reach melting temperature to affect a steel structure - you can weaken the steel and produce strange unplanned loads at lower temperatures and cause failure cascades.
Here is the NIST story about WTC7: https://youtu.be/PK_iBYSqEsc
Myles Power made a video about WTC7: https://youtu.be/7PpsCCTMP8w
I don't endorse him on other topics, but this particular video is good.
EDIT: You can see how a furnace is built on the Primitive Technology channel. It requires insulation, a source of air, and combustible material - all things the rubble contained. NYC is riddled with tunnels, so the air supply is not a problem. The building provided both insulation and material to burn.
You don't need to reach melting temperature to affect a steel structure - you can weaken the steel and produce strange unplanned loads at lower temperatures and cause failure cascades. Here is the NIST story about WTC7: https://youtu.be/PK_iBYSqEsc Myles Power made a video about WTC7: https://youtu.be/7PpsCCTMP8w I don't endorse him on other topics, but this particular video is good.
EDIT: You can see how a furnace is built on the Primitive Technology channel. It requires insulation, a source of air, and combustible material - all things the rubble contained. NYC is riddled with tunnels, so the air supply is not a problem. The building provided both insulation and material to burn.
I never said the words 'melting temperature' - you did.