Which firefighting agent should not be used by itself to combat a major fire?

• A. Water
• B. CO2
• C. Foam
• D. Dry chemical

Answer: (B)

Carbon dioxide is not effective as a stand-alone solution for a major fire because its primary action is to displace the surrounding oxygen, choking the flame. In a large or unfolding fire, simply starving the fire of oxygen doesn’t address the heat in the fuel or the continuing fuel supply. The heat in the fuel surface won’t be cooled, so once the CO2 dissipates or the space is vented, the fire can reignite or flash over.

CO2 is also hazardous to people in occupied or partially enclosed spaces, making it unsafe to rely on in a major incident where crew must operate or be rescued. Its effectiveness is strongest in small, confined electrical fires or very limited applications, not for large, uncontrolled fires where cooling, vapor suppression, and maintaining a safer environment for firefighters are essential.

For major fires, suppression generally requires cooling and/or barrier methods in combination with other agents (such as water or foam) to remove heat and separate the fuel from the air, rather than relying on oxygen deprivation alone.