That would be a pretty good start.
A "fuel" rating for each tile because even painted concrete can burn... briefly.
It's probably not in the design specs of the tile editor so adding this value would take some effort...
In addition to that, each "application" of flamethrower adds 1-2 turns to that number.
Given that Chris' design includes a density, too, the center of the effect might burn a turn longer, having the cinematic effect of the fire shrinking, then going out.