There are many Class A foam systems–aspirated low-expansion foam, aspirated medium-expansion foam, compressed air foam, and foam solution. For a fire department that wishes to minimize capital expense and training requirements, the easiest and cheapest way to enter the new technological era is to start with foam solution, since existing nozzles and techniques can be used. Later, more equipment and training can be added to employ other Class A foam technology, if desired.


Using foam solution is not a new idea. Something similar was first used decades ago, when it was known as “wet water.” This had surface tension-reducing (wetting) properties like the foam solution of today, but, unlike its modern counterpart, did not cause foam to form. Foam solution–a foam-water mix applied through conventional fire apparatus and nozzles–allows water to better wet and penetrate burning material more effectively than plain water.

A large percentage of the total gpm in conventional structure firefighting often is wasted because it runs off the burning material. By properly applying foam solution, less than 10 percent is wasted, making the water 90 percent effective. Since the major effort in firefighting is to get water to the fire, it is pointless to waste most of it after all the danger and trouble taken to get it inside the structure.

In the 1970s, frustrated at seeing wasted water lying on the floor and running out the door; unwilling to accept defeat at the hands of a fire; and recalling how much easier it is to wash socks, dishes, and hands by adding a little detergent to water, we applied the same logic to firefighting. Because it was relatively cheap and readily available, we poured liquid organic cleaner into the booster tanks at a low concentration of about 0.1 percent. It worked impressively, particularly when applied by a broken straight stream (moving the nozzle rapidly back and forth to break up the stream) or a narrow spray from a combination fog nozzle directly to burning material.

The combination of foam solution and a high-flow-rate/short-duration attack, coupled with a redesigned communications system and rapid-response tactics and training, dramatically improved our fire department`s record. Using the new systems, we rarely lost a building; that is to say, there never was any substantial loss after the alarm was called–we even saved a sawmill.

Other departments have used other liquid dishwashing detergents with good results. In recent years, new foam concentrates–specifically designed for fighting Class A fires–have been developed. They now are used routinely in wildland firefighting applications. Fire departments that have used foam solution and other Class A foam systems have experienced excellent knockdown capability on structure fires as well. They have found that when foam solution is applied, a darkened area tends to stay dark, thereby increasing firefighter safety by reducing the probability of “fire at your back” and saving buildings that otherwise would be lost.

Folllowing are some considerations and concerns for departments that wish to add or are considering adding foam solution to their firefighting capabilities.


There are several ways of preparing foam solution. The most straightforward way is to batch-mix concentrate with water simply by pouring the correct amount into the booster tank.

A better alternative for most applications is an automatic discharge-side proportioner. Such proportioners add concentrate to the discharge side of the pump, adjusting the concentrate to the gpm flow through the hose. The pump operator only has to set the desired concentration. The proportioner requires no other attention.

Manual proportioners also can be used, but they need constant operator attention and flow meters to measure both water and concentrate flow rates so the operator can calculate the required concentrate injection rate. The manual method usually is a hit-or-miss affair. Advantages and disadvantages of each system are shown in Table 1.

Once the foam solution is mixed, it is applied through standard hoselines and nozzles. Note, however, that unbroken straight streams applied by smooth-bore or combination fog nozzles for direct attack will diminish some of the effectiveness of the foam solution. The reason for applying an unbroken straight stream to burning material is that, without the help of a surfactant, plain water has to be forced hard against the material to penetrate. (You can demonstrate this by putting a drop of water on wood or cloth. It will stay as a drop because of its high surface tension; but if you press the drop with your finger, that force will overcome the surface tension and force the water into the material with the same momentum as a straight stream.) By applying a broken straight stream or a narrow spray from a combination fog nozzle to the burning material, splashing is diminished and the wetting/penetrating effects of the foam solution are more fully realized.


Foam solution should be prepared just before use and used within half a day. Because it biodegrades after mixing with water, solution cannot be kept premixed in a booster tank waiting for the next fire.


Compared with Class B foams, in which concentrations of up to six percent are used, Class A foam solution requires very little concentrate. Most products seem to work best at concentrations of only 0.3 to 0.5 percent. This means that between three and five gallons of concentrate should be added to 1,000 gallons of water. As little as 0.1 percent, or one gallon of concentrate per 1,000 gallons of water, will substantially improve the wetting ability of water; but 0.5 percent is considered optimum, unless the manufacturer specifies otherwise.


The cost of foam solution is roughly $10 per gallon of concentrate, or a penny per gallon of water at a concentration of 0.1 percent, an easy figure to remember.

I have found that a fully involved single-story house can be darkened down with less than 100 gallons of foam solution using a high-flow-rate, short-duration attack. At a 0.5-percent concentration, it would cost about $5 more to save someone`s home than to lose all or a large portion of it by using plain water.


Class A foam can be used with existing Class B foam eductors by diluting the concentrate on the fireground to whatever concentration is required by the eductor.1 Table 2 shows the proportions. Some eductors are designed for concentrations of one percent. Class A foam concentrates designed for use at one percent are available, eliminating the need for dilution.

The difficulty with small add-on eductors is the long time required to deploy them and their fixed flow rate of only 60 or 95 gpm. This small flow rate is inadequate for attacking all but the smallest structure fires. Also, these eductors require a high engine pressure, typically 200 psi, which reduces pumping capacity to 70 percent of the rating. Usually, this is a problem only at large fires.

Existing built-in Class B foam-proportioning systems will work well with correctly diluted Class A concentrates, but many of them suffer from the same inability to deliver flow rates higher than 95 gpm.


For small departments with tight budgets and only a few small fires annually, the most cost-effective way to proportion concentrate is to batch-mix it in the tanks. Have premeasured concentrate for each booster tank and each tanker used for nursing pumpers conveniently placed near the tank`s filling port.

For a 1,000-gallon tank, use a full five-gallon pail of concentrate for a 0.5-percent solution. For 500-gallon booster tanks, prepare by storing the premeasured 212-gallon quantities in jerry cans or other suitable containers. Table 3 shows the amount of concentrate to be added to tanks of various sizes for various concentrations.

Concentrate can be added at the fire station. It will mix en route. To prevent foaming in the tank, ensure that the tank is full before adding concentrate.

Alternately, the pump operator can add concentrate at the fireground while hose is being stretched. A paddle can be placed into the tank filling port and moved slowly for a few seconds to mix the concentrate and water. The advantages of mixing at the fireground are that concentrate won`t be wasted and the tank won`t have to be rinsed after false alarms.

To save time, the correct amount can be blown into the booster tank by connecting an air line to a small concentrate tank, with an air valve in the cab. As soon as fire is confirmed by radio, the air valve can be opened en route.2 Since the concentrate mixes readily, it will be well-mixed by sloshing in the tank.

If a tanker shuttle is used to fill portable tanks, add concentrate to the portable tank after it has been filled by the tanker. Never put concentrate into a tank before filling it with water. The resultant foaming might bury the tank and/or the truck. This is spectacular but not helpful.

Even if hydrants are available, the booster tank can be used for initial attack. If that fails, then plain water from the hydrant can be used while the tank is refilled. Another advantage of attacking from the tank and letting the second company supply the first pumper is that the time saved can save a building that would be lost through delaying attack by catching a hydrant. After flashover, damage to a $100,000 wood-frame house proceeds at about $4,000 a minute, so every second counts. Remember, however: Before committing to an interior attack based solely on booster water, make certain that the second engine is en route and will arrive soon to establish a continuous water supply.

After using foam solution, flush the tank, pump, hose, and nozzles carefully with plain water. The solution is a powerful detergent that will give you the cleanest tank and pump in town; but, if not thoroughly rinsed out, it can interfere with pump and valve lubrication and packing.

To analyze the cost of batch-mixing, suppose a fire department uses foam solution at a concentration of 0.3 percent for economy. If it responds to six working fires per year using a 500-gallon tankful at each fire and, in addition, uses two 2,000-gallon tanker loads for large fires, it uses a total of 5,000 gallons of foam solution, requiring 15 gallons of foam concentrate at a cost of roughly $150 per year. Perhaps 40 percent of this solution will not be used at the fire, wasting about $60 per year.


For a busy fire department with, say, 200 working fires a year, the cost of wasted foam solution becomes significant. For an average of 1,000 gallons per fire at 0.5-percent concentration, the cost of concentrate will be roughly $50 per fire, or $10,000 per year. If 40 percent of the solution is unused, this is a cost of $4,000 per year, which is roughly the cost of buying an automatic discharge-side foam proportioner.

Fire departments with many fires and/or large fires therefore may prefer to use a built-in automatic discharge-side proportioner. Getting the largest possible proportioner maximizes both cost-effectiveness and fire suppression capability since it can feed several handlines and apply foam solution at the highest possible flow rate to exceed the critical flow rate.3 Another advantage over batch-mixing is that the proportioner allows direct use of hydrant water.

Because concentrate is injected downstream of the pump, it and the booster tank do not need to be rinsed after each use, although the proportioner should be turned off after the fire so the hose and nozzles can be flushed with plain water.


Use foam solution for direct attack, indirect attack, and exposure protection on structure fires.

Use a narrow spray, preferably from a low-pressure fog nozzle, for direct attack to get solution to soak the burning surfaces. Because foam solution penetrates the burning material readily without great force, straight streams, with their consequent waste through splashing, are not needed to force the water into the burning material.

Use solution when overhauling; doing this dramatically reduces rekindles and minimizes overhaul time and water damage.

If concentrate is limited, ration it rather than use it all up at the beginning of the operation. A concentration of 0.5 percent is thought to be optimum, but foam solution will work down to a 0.1 percent concentration.

Treat concentrate and solution carefully, as you would any strong detergent. Read and follow manufacturer instructions for product safety and use.

To reduce foaming, always add concentrate to water rather than water to concentrate.

Refill tanks from the bottom inlet, where possible, to reduce foaming.

Always use freshly mixed solution.

Carefully rinse or flush any equipment that comes in contact with solution or concentrate, including pumps and tanks.

Remember that Class A foam solution is not a panacea and does not replace firefighter training and fireground expertise. It simply is a tool that can increase firefighting effectiveness.

Don`t use foam solution that is more that 12 hours old unless the manufacturer recommends it.

Don`t get concentrate or solution in your eyes–“no tears” Class A foam has not been developed yet.

Don`t let foam concentrate enter storm sewers or waterways, as it can harm aquatic life before it is diluted. n


1. Brown, M.L., “Class A foam,” Letter to the Editor, Fire Engineering, Nov. 1992, 26.

2. Burke, F. (Syracuse FD, ret.), personal communication.

3. Edwards, C.B., “Critical Flow Rate,” Fire Engineering, Sept. 1992, 97-99.


Colletti, D.J., “Quantifying the Effects of Class A Foam in Structure Firefighting: The Salem Tests,” Fire Engineering, Feb. 1993, 41-44.

Gerard, J.C. and A.T. Jacobsen, “Reduced Staffing: At What Cost?” Fire Service Today, Sept. 1981.

Rochna, R.R. and P.M. Schlobohm. An Operational and Tactical Guide to Ground Applied Foam Applications. Boise Interagency Fire Center, 1988.

C. BRUCE EDWARDS, consultant and research director of FireTech Engineering, Inc. in Vancouver, Canada, was appointed deputy chief of the Wabasca (Alberta) Volunteer Fire Department in 1978. He is currently coordinating a joint U.S.-Canadian research project to develop and quantitatively evaluate advanced structural and wildland fire suppression systems. He is a graduate of the Institution of Fire Engineers (Great Britain) and holds a bachelor of applied science degree in electrical engineering and a master of applied science degree in medical engineering, both from the University of Toronto.

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