CO2 fire extinguishers discharge CO2 gas, also known as carbon dioxide.  This is stored in the extinguisher as a liquid, and the gas is created under pressure when the handle of the extinguisher is squeezed.

This causes the CO2 gas to emerge at great speed, which is why CO2 fire extinguishers are not recommended for chip pan fires – they could literally blast the flames into surrounding areas.

Unlike water and faom extinquishers, CO2 fire extinguishers do not work by cooling the fire and so are ineffective on fires involving flammable solids.

C02 fire extinguishers

Instead, a CO2 extinguisher works by replacing the oxygen surrounding the flames with carbon dioxide, meaning the fire can no longer burn.