Carbon dioxide extinguishers are rated for which fire classes?

• A. A
• B. A and B
• C. B and C
• D. A, B and C

Answer: (C)

The key idea is understanding which fire classes a carbon dioxide extinguisher works best on and why. CO2 extinguishers operate mainly by displacing the surrounding air and creating a dense, non-flammable blanket over the fire. This makes them effective for fires involving flammable liquids (Class B) because the vapor is smothered and the surface is deprived of oxygen, reducing flame spread. They’re also suitable for electrical equipment fires (Class C) because CO2 is non-conductive and leaves no residue that could damage electrical components.

They’re not effective for ordinary combustibles like wood or paper (Class A) because such fires often require cooling and prolonged contact with the fuel, which CO2 doesn’t provide well enough. They also aren’t appropriate for metal fires (Class D) or cooking oils (Class K). So carbon dioxide extinguishers are rated for Class B and Class C fires.