Refer to figure.

Fire Bottles in engine compartments are usually electrically operated after manual selection by the flight crew, usually by means of fire-handles, based upon automatic fire detection.

Each engine has two Fire Extinguisher bottles available, which are connected to the fire zones via piping. The containers will keep pressurized powder/fluid and release the content if the cartridge is broken by an electronic signal from the flight deck.

When the pilot pulls the fire handle upwards, the fire bottle squibs are armed and certain automatic actions take place to isolate the associated engine:

Closure of the fuel shut-off valve;

Closure of hydraulic shut-off valve;

Closure of engine bleed air valves;

Tripping of generator exciter control relay and generator breaker;

Disabling of engine thrust reverser.

Thereafter, the pilot can turn the fire handle left or right to release either of the two cartridges to the engine to which the handle belongs.