The white liquid from the vehicle-mounted fire extinguisher is foam extinguishing agent. According to the relevant public information, foam fire extinguishing agent can be an effective fire extinguishing agent for flammable liquids, which mainly produces a condensed foam floating layer on the surface of the liquid, which plays the role of suffocation and cooling. Foam fire extinguishing agent can be divided into chemical foam, air foam, fluoroprotein foam, water film foam and solvent-resistant foam. Wide application range.