CO2 extinguishers are filled with non-flammable carbon dioxide gas under extreme pressure and lack a pressure gauge, which helps identify them.
They work by displacing the oxygen around the fire, effectively suffocating it.
They are highly effective on live electrical equipment because the agent is clean and leaves no residue.
The extinguisher is operated by pulling a pin, aiming the horn at the base of the fire, squeezing the lever, and sweeping from side to side.