Carbon dioxide, is a non supporter of combustion, which means it does not burn itself and doesn't let burn(a burning matchstick will extinguish in a CO2 atmosphere). For this property, CO2 is widely used as a fire extinguisher. read more
According to How Stuff Works, fire extinguishers use carbon dioxide to displace the oxygen necessary for a fire to burn, extinguishing the blaze. Fires need oxygen, fuel, and heat to ignite, and removing any one of those three components can put out a fire. read more