The fire extinguisher appears only (Until Doom VFR) in the Doom RPG. Its primary use is to put out fires. However, it is also useful against the Archvile and Lost Soul classes due to their fiery nature. It uses Halon canisters as "ammunition".
The Fire extinguisher makes a return in Doom VFR as well. After completing UAC Administration, It's only purpose was to clear out the fires that appears out of nowhere.