Water Fire Extinguishers
Water extinguishers put out fires by removing the heat from the fire. Pressurized oxygen directs the fire from the extinguisher. Water is only effective on basic combustibles, such as wood and paper.
Dry Chemical Extinguishers
Dry chemical extinguishers are filled with foam or powder, generally, sodium bicarbonate or potassium bicarbonate. The bicarbonate smothers the fire and deprives it of oxygen. Chemical extinguishers are usually pressurized with nitrogen.
Carbon Dioxide Extinguishers
CO2 extinguishers work in two ways to extinguish fires. CO2 is a very cold gas and it quickly reduces the heat of the fire (fires need fuel, heat and oxygen to burn). Additionally, CO2 is a heavier gas than oxygen and its presence displaces the oxygen.