Final Answer:
The primary method of foam as an extinguishing agent is by forming a thick blanket that suppresses the release of flammable vapors. The secondary method involves cooling the fuel surface and preventing reignition.
Step-by-step explanation:
Foam is an effective fire extinguishing agent, and it operates through two primary methods. Firstly, it forms a thick blanket over the fuel, preventing the release of flammable vapors and cutting off the oxygen supply essential for combustion. This smothering effect helps to rapidly control and extinguish fires involving flammable liquids.
Secondly, foam acts as a cooling agent. As it covers the fuel surface, it absorbs heat and cools the substance below its ignition temperature, preventing reignition. This cooling effect is crucial in scenarios where there is a risk of reflash or re-ignition after the initial suppression.
In summary, the primary method involves smothering the fire, while the secondary method focuses on cooling the fuel to prevent reignition.