Without question, the use of Class A foam has become more popular, given its advantages in knockdown time, firefighter safety and environmental impact compared with untreated water. Nevertheless, there are many departments that still are wondering whether

Class A foam is right for them. Let's examine some of the most common questions regarding Class A foam and its use in firefighting.

How has Class A foam changed over the years?

In its infancy, Class A foam concentrate was as primitive as the pine-oil soap first used in the Texas Snow Job — a foam system employed by the Texas Forest Service more than three decades ago — or, in many instances, household dishwashing soaps and powders. Initially, many major foam manufacturers were not enthusiastic about producing Class A foams, as the emphasis was placed on Class B or aqueous film-forming foams (AFFF).

The popularity of Class A foam was confined to the forestry and wildland-interface users back then. However, competition amongst foam manufacturers eventually throttled up with the advent of compressed-air foam and its eventual acceptance in the firefighting community. Today, almost all of the major foam manufacturers have one or more Class A foams available. In addition, many mom-and-pop operations have sprung up with their own versions of Class A foam, though it is prudent to advise that the buyer beware.

What is the biggest challenge for fire departments in selecting a Class A foam?

It is difficult to select a single challenge a fire department faces when it is time to select which Class A foam to use. First, the department must have a working knowledge of fuel classifications and the correct foam for that usage. Believe it or not, there are departments that mistakenly believe that AFFF is a Class A foam because of the "A" in the acronym.

Class A foams are simply surfactants that bond with carbon-based materials, and as such are classified as "oleophyllic." Class B foams conversely are surfactants that repel carbon- or hydrocarbon-based fuels, such as gasoline, and therefore are classified as "oleophobic." It is absolutely imperative then to differentiate a Class A foam from a Class B foam, as they are complete opposites.

Indeed, if someone tries to sell you "universal" Class A/Class B foam, you should know that it simply does not exist in pure chemical form, as the interaction of these polar opposites when mixed results in a product that congeals and simply will not educt or induct through foam-delivery systems. Most of the foams touted as such are either Class B foams that have a wetting ability at low induction rates, or emulsifiers/encapsulating agents.

What questions should a fire department ask a foam supplier when deciding on foam?

Ask how many types of foam are available. If the foam manufacturer or vendor supplies only one type of foam, this could be a red flag. Also ask the supplier how long it has been providing foam to the firefighting industry. Ask whether the foam is U.S. Forestry approved. Do not be deceived by gimmicks and outrageous claims. One guise is to place a UL-approved label on the bucket in which the Class A foam is supplied — the only thing UL-approved is the bucket itself.

When selecting a vendor, ensure that it represents more than one Class A foam company. This is only common sense, because a vendor that only has one supplier obviously is going to claim that it is the "best" foam that it carries. Again, buyer beware.

Does foam have a shelf life?

Any foam concentrate has a shelf life if exposed to air. In addition, the chemicals used in the foam itself may break down over time. This was more evident years ago with Class B foams, as many had components that were known carcinogens and therefore were not environmentally or firefighter friendly. Great headway has been made by major foam suppliers to overcome the environmental issues regarding Class B foams. As far as Class A foams go, most have been environmentally safe from the beginning, as this foam type has been introduced into our urban water treatment systems for years in the form of shampoos, dish-washing soaps and common hand soaps. The basic chemical components of a Class A foam concentrate will remain stable for long periods of time if left in the sealed container.

One of the biggest mistakes a department can make is to allow the foam cell on the apparatus to go below the full mark for an extended period of time. For example, if the foam cell were to be left in a half-full position for a period of time, the concentrate will be exposed to air. The result will be that the water used as the primary carrying agent will evaporate, leaving a film or crust of the concentrate chemicals to form on the walls of the foam cell. Over time the crust will harden and fall off into the foam concentrate. It eventually will work its way into the eductor or inductor and clog the filter — hopefully you have one in advance of the foam delivery system — and preclude the flow of concentrate.

The best way to avoid this is to simply keep the foam cell full and the lid to the fill tower closed. The amount of activity or call volume obviously has an effect, as the bumpy ride to the fire stirs the concentrate to some degree. Conversely, should the apparatus sit idle for prolonged periods of time, it is advisable to do a visual inspection of the foam cell and stir the concentrate. In addition, the compatibility issue always gives rise when it comes time to switch foams, or in situations where you are about to add a different brand of Class A foam to the concentrate tank.

A simple method of checking compatibility is to take a clear 12-ounce soft-drink plastic bottle for use as a test vessel. By simply taking a sample of your present Class A foam and adding to it an equal amount of the proposed foam, the user can visualize whether a compatibility problem exists. The best method is to take about four ounces of each foam and mix it in the container. Shake gently for about 10 seconds and then observe the contents after about 15 minutes. Repeat the exercise and let the contents sit for an hour, then repeat the process one last time, letting the contents sit overnight. If the foam concentrates do not congeal, they are safe to mix.

In an emergency situation where Class A foams are mixed, you do not have the luxury of time experimentation and thus you need to make sure that there is an inline filter system to protect the foam pump delivery system. Never mix Class A and Class B foams, as the result will be hours and perhaps days of clean up to the foam cell, foam supply hose and possibly the foam pump itself.

When should a department consider gels?

Fire gels have separate and distinct application methods and an entire article could be devoted to that subject alone. The basic fact is that gel application still remains most predominate in the wildland and forestry firefighting legion, but has not gained popularity for the structural firefighting. This does not mean gels are not effective; they just currently enjoy the same popularity that CAF did two decades ago. However, time and improved application techniques may change their acceptance for urban structural fire suppression.

Is there any other advice?

Simply be aware that Class A foam concentrate has allowed us to chemically treat water to vastly increase its efficiency. When a compressor to mechanically alter the bubble structure was added to the process, a new era of firefighting was launched with CAF systems. CAFS has brought new attention to the benefits Class A foam because it offers the suppression team reduced time on scene, less collateral damage and the potential for more effective suppression than ever before.

Fire Types and Foam Uses

Let's examine the various types of fires that a department will encounter, and the foam that is most effective for their suppression.

Class A fires:As the name implies, this is the most common application for Class A foams, which are effective on three-dimensional, organic materials such as wood, paper and rubber. Such fires represent 99% of what will be encountered in urban and interface firefighting.

Class B fires: These fires are fueled basically by hydrocarbons such as gasoline, kerosene, heptanes, diesel and ethanol-blended fuels. FFFP, AFFF, and ARFFF foams are effective for such fires, as their primary function is to smother the fuels and provide a self-healing blanket to prevent re-ignition. Typically, industrial firefighting crews use this type of foam. It also is possible that municipal or urban departments may encounter this risk, but it is important to view the application rates required by NFPA Standard 11 to see whether there is enough foam available for combating this situation. For example, a 50x50 gasoline fire would require an application of approximately 113 gallons of 3% AFFF; nearly 380 gallons of 6% ARAFF would be needed for an ethanol-based fuel fire.

Class C fires: These are electrically charged fires and there simply is no foam made to safely fight these fires.

Class D fires: Flammable metals such as magnesium react violently with water when superheated. Some limited success has been achieved by using very dry Class A foam in a CAF system. The blanketing action of the foam isolates the fuel from the source of oxygen and may suppress small fuel loads of this type, which are found in some vehicle fires.

Neal Brooks is a retired fire chief and currently serves as national sales manager for W.S. Darley Fire Apparatus. He is a guest instructor for the Texas Engineering Extension Service (TEEX), which is part of the Texas A&M University system, and created curriculum related to using Class A foam and CAFS for structural firefighting. Brooks is a member of the A Foam Authority.

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