In the US we utilize 5 Classes to describe the types of Fire A, B, C, D & K

A – Paper Rags and Wood
B – Flammable Liquids and Gasses
C – Electrical
D – Flammable Metals
K – Restaurant Kitchen Grease

CO2 fire extinguishers have B & C ratings so they are only tested and rated by Underwriters Laboratories to be effective on Flammable Liquids and Gasses and Electrical types of fires

They are not rated to be effective on Paper, Rags and Wood, Flammable Metals or Restaurant Kitchen Grease.

CO2 extinguishes a fire by removing or displacing the Oxygen in the air and by cooling the burning material. That being said, will a CO2 extinguish a fire in a Class A, D or K fire – maybe? But they are not rated to do so for the following reasons.

CO2 is stored under high pressure so using it on Class A fire can be ineffective since the discharging CO2 can spread or disperse the burning materials.

Many Class D materials “produce” or release oxygen while they are burning so CO2 is not effective on these types of materials. Many will burn even in the absence of oxygen.

Burning Restaurant Grease is often above its auto ignition temperature and although CO2 has some cooling effect the quantity required to keep it from dissipating quickly and effect the cooling of the grease to the point that it will not flash back is too large to be stored in a hand held fire extinguisher.

I hope this information helps

Tim Krulan
NJ Fire Equipment LLC
41 Pine St
Rockaway NJ 07866