A carbon dioxide (CO2) fire extinguisher is a portable, active fire protection device that works by expelling carbon dioxide onto a fire. It works by displacing the oxygen the fire relies upon to continue burning, and it is primarily used to extinguish fires in which the source of the fuel is a flammable liquid or gas.

• CO2s are designed for Class B and C (flammable liquid and electrical) fires only.
• CO2s will frequently be found in laboratories, mechanical rooms, kitchens, and flammable liquid storage areas.

CO2s may be ineffective at extinguishing Class A fires because they may not be able to displace enough oxygen to successfully put the fire out. Class A materials may also smolder and re-ignite.