Burning Building Perf Issues

Edit: Just going to re-write this one entirely.

I set an office block on fire, and once the structure started to collapse, I hit a catastrophic slowdown issue as long as I am within line of sight of a very specific central part of the structure.

Not sure exactly what square it is, but my perf goes from normal to well under 1 tick/real second if I am in direct LOS of some specific square in the middle of the inferno.

Compressed save available if someone can point me to an upload location.