The four classes of fire extinguishers 
Class A extinguishers put out fires caused by paper, wood or plastic with a combination of water and foam that removes heat and oxygen from the fire. 
Class B extinguishers put out fires caused by flammable gases and liquids, like oil and paint, with cold CO2, which removes heat and oxygen. 
Class C extinguishers put out fires caused by electrical sources, like old or exposed wiring, with a multipurpose dry chemical that interrupts the chemical reaction between oxygen, heat and fire. 
Class K extinguishers put out kitchen fires caused by cooking oils and grease with a wet chemical that removes heat and interrupts the chemical reaction between oxygen and fuel.