The A’s and B’s of Foam of Foam Concentrate and Delivery Systems

Members of the Fire Apparatus Manufacturers’ Association (FAMA) are committed to enhancing the quality of the fire apparatus industry and emergency service community through the manufacture and sale of safe, efficient fire apparatus and equipment. As part of this goal, we are here to help fire departments select the apparatus and capabilities that will work for their needs.


Not true! Class A foam is now used by many fire departments in the United States and Canada. However, with such well-documented safety benefits such as faster knockdown time, fewer rekindles, smoke reduction, quicker cooling, and a reduction in water damage, some departments are refraining from use because of misunderstandings. Worse yet, some aren’t specifying Class A foam systems on their new apparatus.

On occasion I’ve asked a fire officer, “Do you use Class A or Class B foam in your department?” Many times, I’ve been told that the department uses Class A only to find out the label on the side of their buckets reads “AFFF” (a Class B agent).


It is important to understand that Class A and B foams function very differently. Class B foams are mainly used on two-dimensional hydrocarbon (petroleum-based) and polar solvent (alcohol-based) fires. Class B foam concentrates are available in both polar and nonpolar formulations. Polar concentrate formulations can be applied to both hydrocarbon and polar solvent fuels. Nonpolar concentrates can be applied to hydrocarbons only. Class B foam works by creating a skin/film over the surface of the combustible or flammable liquid, separating the fuel from the air. The fuel must be contained or diked for the film to form.


Class A foams, on the other hand, are used on three-dimensional fires of ordinary combustibles and are technically known as synthetic detergent hydrocarbon surfactants. A key component of these foams is their surfactant properties. Surfactants enhance water as an extinguishing agent in two ways. First, they reduce the surface tension of the water. This provides more surface area for better heat absorption and allows the water to penetrate further into Class A fuels. Second, surfactants are attracted to carbon. This holds the water in contact with Class A fuels longer, providing better extinguishment and protection of exposures. It also pulls the carbon particulates out of the smoke, reducing available fuel to ignite and improving visibility.

One of my favorite demonstrations of Class A foam’s effectiveness is to place two separate drops of water onto a piece of corrugated cardboard placed flat on a table. Place a drop of foam (or even dish soap) into the first droplet of water, and the solution immediately penetrates the cardboard. After five minutes or more, the nontreated droplet is still beaded up on top of the cardboard. Tip the cardboard, and 90 percent or more of the water rolls down (out the door).


There is also a significant difference in the solution or amount of concentrate mixed with water. Class B agents are most commonly applied at ratios of one, three, or six percent depending on the fuel and as directed by the concentrate manufacture. Class A, on the other hand, is generally applied at ratios between 0.3 percent for overhaul operations (wet foam) to one percent for exposure protection (dry foam), with 0.5 percent commonly used for initial attack. This means that Class A Foam is much less expensive to apply, and you can run longer on the same amount of concentrate.


Adding to the confusion have been questions about the environmental impact of Class B foams containing perfluorochemicals (PFCs) highlighted in recent news stories nationally and worldwide. In my home state, a foam concentrate manufacturer settled a lawsuit with Minnesota alleging that it manufactured products containing PFCs, which contaminated ground water in the Southeastern Twin Cities metro area. This led to additional investigations related to possible contamination sites involving Class B foam.

As a past chief of a suburban department that routinely uses Class A foam, this raised concerns with my city council. I assured the council members that the foam we used for structural firefighting (Class A) was not the same as the Class B involved in the investigations and didn’t contain PFCs. I was also able to use information published by the U.S. Forest Service (USFS) to support my position and gain acceptance. Its list of qualified USFS-approved products that have passed specific biodegradability, human body exposure, and toxicity testing can be found at Note that the qualified products lists (QPLs) contain three categories including Class A foam, retardants, and water enhancements (gels). The Web site also has a list of approved foam and gel safety data sheets that are printable or downloadable. In addition, another useful link leads you to the environmental studies performed.


Once it is decided that a foam system will be specified on your new apparatus, how can you obtain information surrounding foam and additive proportioning systems? At under the “Fire Resources” tab you will find buyers guides. The buyers guide titled “Fire Apparatus Foam and Water Additive Proportioning Systems” outlines very helpful things to consider when specifying a foam system.

The guide leads you through, step by step, by first understanding the local hazards you may encounter with your new apparatus. Next, it explains the differences between Class A, Class B foams, emulsifiers, wetting agents, and gels. Deciding what type of foam or additive to use will assist with determining the type and size of proportioning system to be specified. The guide provides an overview of the various systems available to be specified on your apparatus, including different use ranges, characteristics, benefits and restrictions.


Proportioning technologies range from simple manual types, such as eductors, to fully automatic systems that are in a “ready-to-go” status and only require opening a discharge valve to be flowing foam. It’s important to note that automatic proportioning systems have come a long way by incorporating high-tech, microcomputer-driven components and simple-to-use operator interfaces to simplify operations. In addition, many have integrated other functions that historically were standalone, further streamlining the operation. Once the type of proportioning technology is decided, the foam source must be determined. The most common is an onboard foam cell, although some proportioning systems provide for off-board pickup or even a combination of both. Although not standard in National Fire Protection Association (NFPA) 1901, Standard for Automotive Fire Apparatus, or NFPA 1906, Standard for Wildland Fire Apparatus, a foam refill system to allow concentrate tank reloading from ground level is a highly recommended safety component.

The use of foam in firefighting often leads to lively discussions, but a little education goes a long way toward calming the debate. Modern systems take the guesswork out of foam application, and the benefits can be significant. If attending major fire shows like FDIC International, the exhibit floor will offer an excellent opportunity to discuss both concentrates and proportioning systems directly with the manufacturers.

In summary, water additives are great tools that improve efficiency and safety. To realize the greatest benefits, it is critical to understand the differences and characteristics of not only the concentrate, but also the delivery systems.

FAMA is committed to the manufacture and sale of safe, efficient emergency response vehicles and equipment. FAMA urges fire departments to evaluate the full range of safety features offered by its member companies.