Under what condition should firefighters use foam during firefighting?

Using foam during firefighting is particularly effective in scenarios involving flammable liquid fires or preventing reignition in spill situations. Foam is designed to smother flames by forming a barrier between the fuel and the surrounding air, which is essential for extinguishing fires fueled by volatile substances.

When dealing with flammable liquids, traditional water cannot always effectively extinguish the fire, as it may not mix well with the liquid or can spread the fire further. Foam, especially class B foam, is formulated to create a blanket over the flammable liquid, inhibiting the release of flammable vapors, thus preventing reignition. This characteristic makes it an invaluable tool for firefighters responding to hazardous material spills or fires where flammable liquids are involved.

In contrast, other conditions outlined in the options may not align with the primary function and effective use of foam. For example, foam is not suited for electrical fires due to the risk of conductivity. Additionally, while foam can provide some cooling, its principal purpose in firefighting is to combat flammable liquids and not specifically for cooling structures or creating barriers against smoke.