Carbon Dioxide is a specialised extinguishant for use on electrical equipment.
Being a gas, it seeks its way into equipment and will get at a fire in cabinets of equipment and switchboards. Being a gas, there is no clean up after use and is the only choice for server rooms, switchboards and computer suites.
CO2 achieves a very light flammable liquids rating, but will not extinguish a Class A fire as it only displaces the oxygen while it is being operated. Once the flow stops burning timber, paper or textiles will re-ignite.