The typical foam eductor is an excellent tool in the tool box, so long as its capabilities and limitations are known. This eductor shown is capable of proportioning foam concentrate to water at various ratios, which makes it an even more effective resource.
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 concentrate and some of the “buzzwords” associated with foam. If you want more information, the major manufacturers have an enormous wealth of information available for free on the web. Take a look at the references at the end of the first part of this series.
Chemical Foam was the mixing of powdered chemicals that together created a finished foam product. Sometimes these chemical additives were referred to as Chemical A and Chemical B. It’s important not to confuse this nomenclature with other vocabulary such as Class A and Class B foam concentrates.
With chemical foam there was no single concentrate that was easily added to a hoseline. The two chemical powders were added via a hopper directly into the hoseline. Because of its difficulty in use, and less than perfect quality, it is no longer used in today’s fire service. Chemical foam was replaced by mechanical foam decades ago.
Mechanical Foam is the common product we deal with on a daily basis. Mixing water, foam concentrate, and air in the proper ratios to produce a finished foam blanket creates foam. The three ingredients are mixed via a mechanical process and do not require a chemical reaction to achieve a finished foam blanket. Our studies will primarily be concerned with the correct mixing of these three ingredients and applying the finished product effectively.
There are a variety of foam concentrates on the market today. Depending on the manufacturer, you may find differences in the specific details associated with each concentrate, so make sure you know the specifics of what your department is using. In this series of articles, we’ll offer a very generic look at some of the more common types of concentrates and equipment that can be used, but for specific details, consult the manufacturers.
Protein Foam was an original type of liquid concentrate that was made up of organic materials and other additives. When used to attack a flammable liquid fire, it had a good resistance to heat, but its use was limited to hydrocarbon spills and fires. It is not in use in any great quantity in the municipal fire service any more. Other types of concentrates have replaced protein foam. These more modern concentrates have additional features such as greater fuel shedding properties and the ability to be used on both hydrocarbon and polar solvent spills and fires.
Film Forming Fluoroprotein (FFFP) and Alcohol-Resistant Film Forming Fluoroprotein (AR-FFFP) build upon the benefits of protein foam and protein foam’s successor, Fluoroprotein foam. With synthetic additives as part of the concentrate, these concentrates can be used on fires and spills involving hydrocarbon fuels. With additional additives, these foams can be designed as an alcohol-resistant type of concentrate allowing them to be well-suited to incidents involving polar solvents. FFFP foam has the added benefit of being able to apply a very thin film over top of the spill, thus preventing the release of flammable vapors from mixing with air. With proper application, these types of foam concentrates offer a finished foam that is longer lasting, has good fuel shedding ability, and has good resistance to heat.
It also has similar features to AFFF (see below) in that a film floats ahead of the spill to create a layer that separates the fuel from the air. This concentrate can be used with both fresh and saltwater for even greater versatility. Check with the manufacturer as it relates to freezing and thawing (some sources say the concentrate can be affected by freezing and thawing, while other sources say the opposite). This agent is also compatible with dry chemical extinguishing agent in the event a coordinated attack is required.
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.
Given today’s incidents that the typical municipal fire department responds to, it is critical that the department has the ability to adapt to a host of situations. The multitude of chemicals that are a part of our everyday lifestyle also means problems for the first responders. As such, a foam concentrate that is good on both hydrocarbon and polar solvent spills and fires would increase any department’s capability. Concentrates such as AR-AFFF are one type of foam that would offer this advantage.
Today’s foam concentrates are designed to be mixed in certain ratios with water. In the past, 3% and 6% were common settings. The directions on a typical 3% x 6% five-gallon pail of AR-AFFF foam concentrate, for example, directed that for hydrocarbon fuels, the mixture of concentrate to water was 3% (in other words 97 gallons of water and 3 gallons of foam concentrate), while for polar solvent spills the ratio was to be set at 6% (6 gallons of concentrate and 94 gallons of water).
Newer concentrates can be as low as 1% mixtures of concentrate to water. Take a look at some of the products available from the different foam manufacturers. Each of their product guides goes in-depth as to the ratio as well as application rates for different types of fuels and spills.
Today’s common foam concentrates can be mixed with both fresh water as well as saltwater. This further increases our advantages. The fire service responds to many different types of incidents and a shore-based community could very well find itself relying on out-of-the-ordinary water supplies for any number of reasons. A response attributed to a manmade disaster or a natural disaster could render the municipal infrastructure and water supply useless. Such a situation calls for out-of-the-box thinking and knowing that saltwater could be a key ingredient in making our strategy work would pay dividends.
During the application of foam, concentrates of the same family, such as AFFF, can be mixed together just prior to eduction, but to batch mix the concentrates of different manufacturers for extended periods of time could become problematic. Also batch mixing for extended periods of times with other types of concentrates can be problematic. Always check with the manufacturer to determine the limitations of your foam concentrate.
Foam is also mildly corrosive and after application it is important that all elements of the foam system (i.e., nozzles, eductors, appliances, etc.) be flushed for at least several minutes.
The shelf life of foam concentrate is another advantage. Most concentrates have lengthy shelf lives of 5 to 25 years, but depending on the manufacturer, type of concentrate, and the storage conditions (such as temperature and exposure to direct sunlight) can all affect the lifespan of the concentrate.
There are many types of concentrates on the market and there are many sources of accurate information readily available. Take a look at some of these additional sources starting with the foam you presently have. Know your equipment before the incident occurs!
The next article in this series will take our studies further into the topic of foam firefighting and how it relates to the typical engine company.
ARMAND F. GUZZI JR. has been a member of the fire service since 1987. He is a career fire lieutenant with the City of Long Branch, NJ, Fire Department and is the deputy director of the Monmouth County, NJ, Fire Academy where he has taught for over 20 years. He has a masters degree in management and undergraduate degrees in fire science, education, and business administration. View all of Armand's articles here. He can be reached via e-mail at email@example.com or firstname.lastname@example.org.