Cheap water fire extinguishers come in various types, depending on the type of fire they are intended for. Water based. An acid and bicarbonate react to produce carbon dioxide which propels the water out of a hose and on to the fire. Only for fires not involving chemicals (for example, in a chemistry lab, any alkali metal present would explode dangerously). Other non-water liquids. In the past, carbon tetrachloride was used in a class ball to throw into the fire, where the rapid expansion caused the gas to expel all the oxygen, so putting out the fire. Unfortunately, the heat created poisonous fumes, so it was fairly quickly outlawed. Powder. Carbon Dioxide is used to propel a fire smothering powder out of a “horn”. Used on electrical fires, and oil/fat fuelled fires. Gas. Carbon Dioxide (large extinguishers) or a variation of a halogen-carbon inert gas (small extinguisher can like a hairspray can); either smothers, or smothers/cools the fire and flammable item. Used on oil/fat fires and electrical fires in particular.