"Temperature required to produce significant strength reduction in steel is about 600C (check it out)
That equates to cherry red.
Can you raise a large mass of steel and concrete to that temperature using the fuel sources available"

My father was a farmer, not a blacksmith. But we had a small portable forge, god only knows just how old. It held just a few handfuls of coal, and had a small, crude, hand cranked fan attached to provide forced draft. It took just a few minutes to heat steel well past cherry red to a white hot very malleable state.

Also, I have never been a "firefighter", but I have helped contain a small woodland fire and have seen the kind of draft generated by a few burning tree; just wood and leaves burning.

Start a fire with thousands of gallons of spilled fuel, let the drafts develop as every imaginable sort of secondary fuel ignites, and I can hardly imagine why anyone would question whether you would
weaken steel substantially.