Carbon dioxide fire extinguisher. Pressurized canister containing liquid carbon dioxide (CO2) for extinguishing a fire. Modern CO2 extinguishers are red with a black label. The pin (blue, top centre) is removed and the movable horn (upper left) is aimed at the base of the fire. Squeezing the trigger (top right) releases a cloud of CO2. The CO2 reverts to a gas at room pressure and cuts off the oxygen supply, smothering the fire. Unlike a water-containing fire extinguisher, this one may be safely used on an electrical fire. The horn must not be held during use as the rapid expansion to a gas greatly lowers surrounding temperatures.