Which type of foam contains a surface-active agent that produces a fast-spreading film?

The type of foam that contains a surface-active agent capable of producing a fast-spreading film is known as aqueous film-forming foam (AFFF). This foam contains specific surfactants that allow it to spread quickly over liquid fuel surfaces, effectively creating a barrier that suppresses flame and prevents re-ignition. The film that forms not only enhances the foam’s ability to cover and extinguish fires but also provides greater control over flammable liquid hazards.

Foams classified as fluoroprotein may provide some benefits in terms of film absorption and burnback resistance but lack the rapid spreading attributes associated with aqueous film formers. High expansion foam works best for certain situations, like filling a room with foam to displace air but does not produce a fast-moving film. Class A foam is designed primarily for combating ordinary combustible fires and does not focus on producing a film for spreading over hazardous liquids. Therefore, the characteristics of aqueous film-forming foam clearly distinguish it as the correct answer in this context.