What type of fires requires the use of a foam extinguisher according to FA-1 training?

Foam extinguishers are specifically designed to combat flammable liquid fires, making them effective for materials such as gasoline, oil, and solvents. The foam works by forming a barrier between the fuel and the oxygen in the air, which suppresses combustion. This characteristic is crucial because flammable liquid fires can quickly escalate and spread if not handled correctly. In contrast, other types of fires require different extinguishing agents. For instance, electrical fires typically need a Class C extinguisher, while wood and paper fires are best controlled with water or Class A extinguishers. Metal fires, especially those involving combustible metals like magnesium or aluminum, require specialized extinguishing agents to avoid dangerous reactions. Therefore, the capability of foam to smother flammable liquid fires is what makes it the appropriate choice in this context.