Which extinguishing agent is both nonconductive and effective for cooling fuels in Class A and B fires?

The correct answer is clean agent. Clean agents are designed to be nonconductive and are particularly effective in suppressing fires involving Class A (ordinary combustibles) and Class B (flammable liquids) fuels. Their formulation enables them to interrupt the combustion process and allow for effective cooling of the fuels involved in these classes of fires.

Clean agents, like halon replacements, do not leave residues that can cause damage to electronic equipment and are safe for use in areas with sensitive systems. This makes them incredibly valuable in settings such as data centers and laboratories where maintaining equipment integrity is crucial.

Chemical foam, while being effective on Class B fires for creating a barrier between the fuel and the air, may not be considered nonconductive. Carbon dioxide serves as an effective agent for Class B fires but does not provide as much cooling as clean agents. Though wet chemical systems are designed primarily for kitchen fires (Class K), they do not perform effectively in the other classes noted. Thus, clean agents are the most suitable choice for their nonconductive properties and cooling capabilities for both Class A and B fires.