Foam Fire Extinguishers
The dual rating for types 'A' & 'B' fires mark the Foam Extinguisher's ability to contain and put out fires from combustible materials and flammable liquids. The Foam Extinguisher contains an Aqueous Film Forming Foam (AFFF). As it reads, the foam made from nitrogen. When sprayed upon a flame the chemical foam spreads on the flame covered materials and liquids and forms a film on it which neutralizes the burning of the material. Since it is made of nitrogen the foam then cools the fires or materials on fire.
Since the types of fire the Foam Extinguishers may put out could happen anywhere, it is best to know how to use it effectively and not only wield it in ignorance. Fires on solid materials must have the foam aimed at the base of the origin. A sweep from side to side spreads the foam and little by little cools the surroundings. If the fire has started on liquid surfaces, aim the foam at a vertical surface, in doing so the foam falls over the fire origin. Aiming vertically position the foam as it falls at the surrounding, cooling around and work inward to the source.
In special cases, the fire originates from inside a container. Unless you'd want singed hair or brows, spray the foam at the inner edge of the container...cooling one side as the foam slips downward the inside of the container.
Please note that the possible containers that may catch fire are pails of paint, petrol drums etc. Foam Extinguishers MUST NOT be used on electrical or deep fat fryers.
To better pick a fire extinguisher best for you, it is best to lok around you and purchase several fire extinguishers according to the places at risk in your home or work. Dual type extinguishin is available but it may not be in th ecombination suited for you.