I've alwayse thought that the amount of gasoline in the fuel system in the engine compartment is quite small - maybe a pint - it is inside hose that has stainless brading and/or fire shield normally.  If I have a fire, I assumed I'd be able to miminize it quickly by turning off the fuel pumps.    Lycomings with engine driven fuel pumps would have to have the fuel selector turned to off  and maybe the electric pump off also to reduce fuel avaliable for fire.

If I have a bad exhaust leak and it catches the fiberglass cowl on fire - that may be a little bigger problem.

Dennis H.