A CO2 extinguisher is a type of fire extinguisher that uses carbon dioxide gas to put out fires. It works by displacing oxygen in the area of the fire, which is essential for combustion. This makes it effective for electrical fires and flammable liquids, as it does not leave any residue behind. These extinguishers are typically filled with liquid carbon dioxide, which expands into a gas when released. They are identified by their black label and are commonly found in offices, laboratories, and industrial settings where electrical equipment is present. Proper training is essential for effective use.