What type of foam is most commonly used for extinguishing fuel spills and suppressing flammable vapors?

Low-expansion foams are specifically designed for extinguishing fuel spills and suppressing flammable vapors. They work by creating a stable foam blanket that effectively isolates the fuel from oxygen, thereby preventing ignition and minimizing flammable vapors. This type of foam adheres well to surfaces and is particularly effective on liquid fuels, making it ideal for situations like fuel spills.

Low-expansion foams have a lower density that allows them to spread over a larger surface area, forming a continuous film that directly contacts the flammable liquid. This film not only suppresses the vapors but also helps in cooling the surface, reducing the chances of re-ignition. The efficacy of low-expansion foams in both extinguishing fires and controlling vapors makes them the preferred choice in scenarios involving liquid fuel hazards.

In contrast, high-expansion foams are primarily used for flooding large areas or filling enclosed spaces, while medium-expansion foams serve specific applications. Dry chemical foams address different fire classes and are not designed specifically for fuel spills. This makes low-expansion foams the most suitable for the application described in the question.