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    Extinguishers: Ideal Applications for Portable Foam Fire Extinguishers

    By Mark Conroy


    Flammable liquid fires are special hazards, necessitating the installation of the right extinguishers to ensure safety. While dry chemical is known for quick knockdown, foam will prevent re-ignition of the fire (provided the fire surface is completely covered and is left undisturbed). Here is what you need to know regarding selection of foam extinguishers where extinguishment and prevention of re-ignition is paramount.

    Dry chemical extinguishers are often installed as the inexpensive solution, where minimum compliance to code requirements is the prime objective. But they have their limitations. If the ignition source is available after initial fire knockdown, re-ignition might still occur. Also, if the flammable liquid has been burning for some time and the flammable liquid is over-heated, re-ignition could occur without spark or flame (auto-ignition). Additionally, where heating is part of an industrial process, and is no longer controlled (run-away thermostat), there is a potential for auto-ignition. Foam extinguishing agent is preferable for these situations, because it creates a blanket on the surface of the flammable liquid. That barrier prevents vapors from being released. Ignition will not occur where flammable vapors are prevented from contacting oxygen in the air.

    For many industrial applications, hand-held foam extinguishers are most appropriate. That is because the surface area of a potential fire area is within the capacity of these extinguishers, and surface area can be estimated with some accuracy. The following tables provide information that can be used for selecting foam extinguishers. The first table provides characteristics of the extinguishers. The second table shows the relative sizes of surface areas for the fires used for rating extinguishers. This information can be used as guidance when selecting the most appropriate foam extinguisher for a particular application.

    Hand-Portable Foam Fire Extinguishers (Including bracket)

    P/N Mfg Size Rating USCG
    AX250 Amerex 2.5 Gallon 3A:20B No
    23697B Badger 2.5 Gallon 1A:30B No
    AX254 Amerex 6 Liter 2A:10B No
    AX250CG* Amerex 2.5 Gallon 3A:20B Yes

    UL Fire Test Pan Size

    Extinguisher Rating Pan Size
    10-B 25 ft2
    20-B 50 ft2
    30-B 75 ft2

    * For marine applications, Amerex 2.5 gallon foam extinguisher AX250CG is provided with bracket AX810CG.
    This extinguisher is US Coast Guard (USCG) Approved when installed in bracket AX810CG.


    Foam extinguishers have special air-aspirated nozzles, which introduces air into the foam/water solution to create the foam as the agent is being discharged. Today’s foam extinguishers use AR-AFFF, which is a special formulation of a foam-extinguishing agent that can be used on most flammable liquid fires, including alcohols. Foam extinguishers are required to have the foam replaced every 3 years (NFPA 10, Table 7.3.3.1). Foam is also typically replaced at the 5-year hydrostatic test interval (NFPA 10, Table 8.3.1), rather than 1 year, after hydrostatic test. Amerex units are recharged with AR-AFFF Premix (P/N AX502AR) and the Badger AR-AFFF foam recharge is P/N 23702B.

    Foam secures the surface of flammable liquid fires; extinguishing flames, and preventing re-flash. Your customers will appreciate your knowledge of foam extinguishers and the safety they provide to extinguish fires and prevent re-ignition.


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    Mark Conroy is an engineer in our Boston office, specializing in fire extinguishers and their applications.
    © 2019 Brooks Equipment

    Disclaimer: The opinions expressed in the above Tech Series article are the author’s only and provide limited information. Although the information is believed to be reliable, Brooks Equipment Company, LLC expressly disclaims any warranty with respect to the information and any liability for errors or omissions. The user of this article or the product(s) is responsible for verifying the information’s accuracy from all available sources, including the product manufacturer. The authority having jurisdiction should be contacted for code interpretations.