The critical temperature for structural steel (the temperature where it loses all it’s strength) is
1300o Fahrenheit. The open air temperature of burning kerosene is 1800o Fahrenheit.
In a confined space the temperatures would undoubtedly be higher.
The energy density of kerosene is 130,000 BTU a Gallon. The planes had around 10,000 gallons.
Or to put it another way 1,300,000,000 BTU’s of heat. Enough to weaken the structures holding up the floor
deck and make the floors around the fire start to pancake and start a chain reaction.
As an aside, the space this fuel would occupy would be around 1,300 cubic feet. Or a cube 11 feet on a side.
Edit: Another aside; The design was criticized in trade journals of the period when the twin towers were being built as being unsafe in the event of fire.
