What is the primary way carbon dioxide extinguishes a fire?

What is the primary way carbon dioxide extinguishes a fire?

• A. Displacing the oxygen in the environment.
• B. Cooling the fuel to below its ignition temperature.
• C. Reacting with the fuel to form a stable compound.
• D. Diluting the heat with water vapor.

Answer: (A)

Fire needs a supply of oxygen to keep burning. Carbon dioxide extinguishes a fire mainly by blanket­ing the flame and displacing the surrounding air, which lowers the concentration of oxygen available for the combustion reactions. Because CO2 is denser than air, the gas pools around the flame in enclosed or semi-enclosed spaces, starving the fire of the oxygen it needs. The other ideas don’t describe the primary action of CO2: it isn’t acting primarily by cooling the fuel (that’s more the role of water), it doesn’t chemically react with the fuel to form a stable compound, and it doesn’t work by creating water vapor to dilute heat.

Fire needs a supply of oxygen to keep burning. Carbon dioxide extinguishes a fire mainly by blanket­ing the flame and displacing the surrounding air, which lowers the concentration of oxygen available for the combustion reactions. Because CO2 is denser than air, the gas pools around the flame in enclosed or semi-enclosed spaces, starving the fire of the oxygen it needs.

The other ideas don’t describe the primary action of CO2: it isn’t acting primarily by cooling the fuel (that’s more the role of water), it doesn’t chemically react with the fuel to form a stable compound, and it doesn’t work by creating water vapor to dilute heat.