After extinguishing a flowing fire, which type of agent should be applied to follow up?

Applying foam as a follow-up agent after extinguishing a flowing fire is beneficial because it helps to prevent re-ignition and can cool down the remaining heat in the area. Foam creates a blanket over the surface, smothering any potential fire activity and effectively sealing in flammable vapors that might linger after the primary fire has been put out. This is particularly important in airport firefighting scenarios, where flammable liquids are commonly involved, as foam specifically designed for fuel fires can help control and prevent the spread of any residual hazards.

The other agents listed may not serve the same purpose as effectively. Water, while useful, can sometimes cause flare-ups in certain situations, especially if the fuel is lighter than water. Dry powder agents are good for extinguishing fires immediately but may not provide the protective barrier that foam does afterward. Atrophine is a medication not used in firefighting contexts. Therefore, foam is the ideal choice as a follow-up agent in this scenario.