Name a tertiary firefighting agent aside from water and foam.

The correct answer is carbon dioxide (CO2) because it acts as a firefighting agent by displacing oxygen in the environment, which is crucial for combustion to occur. Without sufficient oxygen, a fire cannot sustain itself, leading to its extinguishment. Carbon dioxide is particularly effective for fires involving flammable liquids and electrical equipment, which can be challenging to extinguish with water or foam due to the risk of spreading the fire or causing electrical hazards.

While sand can smother small fires and dry powder agents (often chemical extinguishers) can interrupt the combustion process, CO2 is considered a more versatile and effective agent for specific situations, especially in enclosed spaces where inhalation risks are minimized or in environments sensitive to water damage. Fire blankets are useful for smothering fires in limited scenarios, but they do not fall into the category of traditional extinguishing agents in the same way that CO2 does.