Basic Foam Operations - Part 2

There are a variety of foam concentrates available to the fire service. Some are more specialized than others and some are more common. In order to give company members a working knowledge, we’ll give a brief overview of the different types of foam...

Remember that for fires involving polar solvents, the alcohol-resistant concentrate has a polymer additive that allows the finished foam to be of value in controlling such spills and fires. Failure to use an alcohol-resistant concentrate will mean that the foam application will break down quickly and mix with the spilled product. We have to use the correct concentrate for the fuel in question.

Aqueous Film Forming Foam or “A Triple F” (AFFF) and Alcohol-Resistant AFFF (AR-AFFF) are very popular concentrates in today’s fire service. They are synthetic concentrates that do not rely on any protein-based additives like those described. AFFF can be used successfully when attacking a flammable liquid spill or fire that is hydrocarbon based. It can be used with either fresh or saltwater and is compatible with dry chemical extinguishing agents. Like with the fluoroprotein and FFFP concentrates, the physical properties of plain water are altered when mixed with the foam concentrate and the result is an extinguishing agent that has the ability to float on top of a flammable or combustible liquid spill. Recall, for example, that water alone would sink to the bottom of a fuel spill involving gasoline. Gasoline has a specific gravity of less than 1, which means that it is lighter than water and will float on top. The aqueous film that is part of the finished foam forms a seal overtop of the fuel spill. The film prevents the mixture of air with the fuel vapors, thus limiting the chance of ignition. AFFF has a fast drain time, in other words, the finished foam blanket can degrade quickly especially if the fuel is hot, such as immediately after fire knockdown. This requires a re-application to prevent dangerous vapors from igniting. Always make sure that a supply of concentrate is readily available for a minimum application rate. Application rates will be explained in greater depth in a later article.

Not all of the responses we go to are as simple as the typical hydrocarbon spill. Fuels such as alcohols or the newer blends and additives such as ethanol in gasoline make for a potentially difficult situation. AR-AFFF is a close cousin to AFFF and can be of great value to us. Ethanol blended gasoline that has 10% or more ethanol should be handled with an alcohol-resistant foam concentrate. Consult the specific manufacturer for details as it relates to this topic. Some foam concentrates have specific details that differ from other manufacturers.

Due to polymer additives, this type of concentrate (AR-AFFF) has greater capabilities and can be used successfully on both hydrocarbon and polar solvent spills and fires. Like with the example we used a short while ago for polar solvents and the FFFP foam concentrate, it’s important that we also use an alcohol resistant (AR-AFFF) concentrate for fires and spills involving polar solvents. Using AFFF on a polar solvent will cause the foam to break down and mix with the fuel rather quickly.

The destruction of AFFF’s finished foam and its aqueous film on polar solvent spills allows for the release of flammable vapors and the danger of ignition or re-ignition. The answer to this scenario is the use of an alcohol-resistant concentrate. Stronger polar solvents also require a higher application rate; just take a look at the specific application rates required for different liquids for the foam concentrates you’re presently using. The additives in alcohol resistant foam (AR-AFFF) gives us a concentrate that when mixed with water and air delivers a finished foam blanket that seals the spill with a protective “polymeric membrane” that prevents the release of ignitable vapors from a polar solvent spill. This type of foam blanket is best applied with an air-aspirating nozzle that we’ll cover later on. The alcohol resistant concentrates are a thicker concentrate compared to the non-alcohol resistant concentrates.

Advantages of Today’s Concentrates

Recall that without oxygen, one side of the fire tetrahedron is missing. The ability of foam to separate the fuel (vapors in this case) from the oxygen allows us to prevent a fire from happening or to extinguish a fire that has begun.