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 to produce a fast-spreading film is specifically Aqueous Film-Forming Foam (AFFF). This foam is designed to create a film that spreads rapidly over the surface of flammable liquids, effectively smothering the fire and preventing vapor release. The surfactants in AFFF lower the surface tension of the water, allowing it to spread quickly and incorporate the flammable liquid, effectively forming a barrier that inhibits combustion.

Other types of foam may serve different purposes but do not exhibit the same rapid film-forming characteristics. High expansion foam, for example, is used for filling large spaces with foam but does not create a film. Fluoroprotein foam is beneficial for hydrocarbon fuels but does not spread as quickly as AFFF. Class foams can refer to a range of foams tailored to certain combustibles but again, lack the fast-spreading film property synonymous with AFFF. Therefore, the distinct formulation of AFFF makes it the correct answer, highlighting its efficacy in firefighting scenarios involving flammable liquids.