Which extinguisher agent is effective at forming a coherent blanket that seals off combustible vapors?

The effective use of foam as an extinguisher agent lies in its ability to form a coherent blanket over flammable liquids, which is crucial in suppressing fires involving combustible vapors. When foam is applied to a burning liquid, it tends to spread over the surface of the fire, providing a layer that effectively seals off the vapors from the oxygen in the air. This blanket of foam not only suppresses flames but also helps to prevent re-ignition by cooling the surface underneath and blocking the escape of combustible vapors.

Water, by contrast, is primarily effective in cooling down the material on fire but does not create a vapor-sealing layer. Dry chemical agents and carbon dioxide can extinguish flames by interrupting the chemical reaction or reducing the oxygen level, but they lack the capability to suffocate vapors as foam does. Therefore, for scenarios where controlling vapors is essential, foam is the optimal choice as an extinguishing agent.