Hi Crab
As lelebebbel says, the EMER OFF SW / FIRE Button closes the fuel valve but this is located just above the fuel tanks so there is a reasonable amount of left in the fuel lines between the valve and the engine. This takes some time to burn off and for the engine to run down (I would guess about seven seconds, maybe longer at idle). The idea, I assume, is to burn as much fuel inside the engine rather than allowing it to feed an engine bay fire, once the engine runs down, the extinguisher will automatically fire if there is still a fire indicated.
There is no fan.
Cheers
TeeS