Selecting the Right Foam

Part of deploying an effective firefighting foam operation is selecting the right foam concentrate to use in the operation.
Part of deploying an effective firefighting foam operation is selecting the right foam concentrate to use in the operation.

On many fire scenes, when nothing else has worked, someone will speak up and say, “Why don’t we try foam?” Then inevitably everyone on scene starts to bring out buckets of foam and bubbles are made, in hopes that the fire will go out. Sometimes it helps, sometimes it doesn’t. When it helps, it was because someone knew how to select the right foam, or it was pure luck. When it doesn’t help, the problem is likely that the right foam was not used for the situation. Using the wrong foam will waste time, water, and the expensive foam concentrate as well as create a situation that may not be as safe as firefighters believe.


Class A Foam Delivery System Considerations

Wildland Fire Apparatus Foam Systems

Foam, Foam Concentrate, and Delivery

Being able to select the correct type of firefighting foam should be a pretty simple process. However, many firefighters believe if it makes bubbles, it’s all the same and will get the job done. Nothing could be further from the truth, as firefighters must be able to match the foam to the fuel for an effective foam operation. There are many different types of foam, but the most commonly used by fire departments across the country are class A and class B foams. Lesser known/lesser used foams are high-expansion foams and even blast mitigation (bomb) foams. If a department deploys one of the lesser known foams, it probably has a specific use predetermined or already has a more advanced knowledge of foams. For the rest of the fire departments, making a purchasing decision or an on scene decision of which foam to select can be a challenge. To meet the challenge of selecting the right foam for the job, firefighters must first understand how foams are designed to function.

Understanding Function

Class A foams are considered wetting agents, which work by breaking down the surface tension of the fuel, allowing the water to penetrate. Class A foams are proportioned at 0.1%-1%, with the lower end of the range effective for fire attack and the higher end of the range more for exposure protection. Having bubbles is not that important when using class A foam, as no film or membrane is formed and there are no vapors to hold back. Bubbles can be useful, as they store extra water that can be used for exposure protection or to allow much more of the water to soak into the fuel. If a thick enough layer of bubbles is applied, oxygen is also excluded, taking away one aspect of the fire tetrahedron and thus inhibiting combustion.

Class B foams are more complicated than class A foams. Class B foams were the first firefighting foams originally developed in the 1920s and 1930s and have evolved over the years. The two most commonly used class B foams today are aqueous film forming foam (AFFF) and alcohol resistive aqueous film forming foam (AR-AFFF). AFFF can only be used on hydrocarbon-based fuels, as the film applied to the surface will not keep the alcohol-based fuels from mixing with water in the foam and thus destroying the foam. AR-AFFF deploys a plastic-like membrane when there is the presence of an alcohol-based fuel to prevent the alcohol fuel from pulling the water out of the foam.

With the environmental concerns surrounding AFFF and AR-AFFF foams, a new class B foam has emerged in the past few years. This foam has no fluorine and has become known as fluorine-free foam. The fluorine is the source of the environmental concerns of firefighting foam, so it has been removed but not without consequence. Fluorine-free foams do not apply the film to hydrocarbon fuels (fluorine being the key ingredient for film formation) but rather use the weight of the bubbles to hold back ignitable vapors very similar to how protein foams worked. For alcohols, the plastic-like membrane is still formed, so fluorine-free foams are effective on alcohol-based fuels (so long as they are designed to be alcohol-resistive).

Some foam manufacturers make a combination foam designed for use on class A and B fires. Understanding how these foams work is critical to understanding if these foams are the right selection for your department or the situation at hand. These combination foams must be closely scrutinized to ensure they will work in all situations as claimed. Many of these foams are wetting agents, which are appropriate and the best choice for class A fuels but can only be used on hydrocarbon class B fuels and still do not do the same job as a class B foam.

Using a wetting agent on a class B fire is not as effective as using traditional class B foams. A wetting agent basically dilutes the fuel to the point that it can no longer burn. If it was not for the wetting agents, the water and class B fuel would just separate rather than mix to dilute the product. These wetting agents may produce a “blanket” of bubbles that is able to completely cover and knock the fire down, but flammable vapors are still able to move through the bubbles and seek out an ignition source.

Photo 1 shows a fire that has reignited after being extinguished by a class A foam or wetting agent. Note the fire burning above the foam blanket that is on top of the fuel. This occurred because wetting agents do not seal the surface of a fuel like a class B foam does. Wetting agents also generally require more water and product to achieve extinguishment compared with class B foams. Wetting agents are not effective on alcohol-based class B fuels because water and alcohol are very miscible—thus, the need for alcohol-resistive foams and the reason wetting agents are not effective on all class B fuels.

 Photos by author.

Class B foams are noted to be safe to use on class A fires. Class B foams may be safe, but they are not always effective. Class B foams will cover a class A fire with bubbles and ultimately exclude oxygen and cool the product. Class B foam does not penetrate down into a class A material as a class A foam does. An example of this is a structure burning to the ground with the heavy timbers or other materials still smoldering. On a windy day, it is not a good idea to leave any type of smoldering material, so in this situation a department may elect to cover the area in foam. Using class B foam ultimately covers the entire area and stops the smoke, giving a false sense of security. The first gust of wind blows all the bubbles away and smoke is again generated, meaning there is still combustion. The foam did not penetrate down to the source of the smoke where material is still burning. If class A foam is applied, water can penetrate the materials, and no smoke is visible after the next gust of wind.

The best way to determine if foam is going to work as advertised and if it will be effective as promised is to look for an Underwriters Laboratories (UL) listing or classification. The UL label ensures that the concentrate has been proven through testing as either a foam or a wetting agent. If the concentrate does not have the UL listing, it likely is not a dependable product for firefighters. Class A foams may have a listing or approval through the U.S. Forest Service, but it is important to note that this listing is not so much a performance listing but rather one that concerns environmental impact. Other listings firefighters may see are through the U.S. Coast Guard for use in maritime applications and U.S. Defense Department (MIL-SPEC) for use in military and aviation applications. Photo 2 shows examples of different listings found on foam concentrate containers.

What Foam to Use?

The question remains, what is the right foam to use? The answer to that question, like so many other questions, is, “It depends.” With the information firefighters now have about class A and class B foams, they must make an informed decision depending on the situation. When on an incident scene, firefighters must choose from what’s available or decide that foam is not a viable option because of the fuel burning and the foam available. If the available foam is not safe or effective, don’t put firefighters at risk with a false sense of security thinking the foam is capable of handling the job at hand. Firefighters must consider many factors to make the right decision in selecting foam concentrate for the given task.

Class A and class B fuels are everywhere, so departments must be prepared to respond to both. This would naturally lead firefighters to think that a combination foam is what their department needs. However, combination foams are not always effective in all situations. Almost all gasoline sold in the United States is at least a 10% ethanol blend up to 85% ethanol (E85) in some instances. This creates the need for all departments to have access to alcohol-resistive class B foams. While departments don’t necessarily need to have enough alcohol-resistive class B foam available to extinguish a large storage tank of a class B product, there should be enough available to attempt a rescue of someone trapped or endangered by a flammable liquid fire. There is also a need to cover smaller spills of flammable liquids to protect victims and firefighters at critical events like vehicle entrapments. Many class B foams can also be used to suppress vapors from other types of hazardous materials such as acids. These materials may not commonly be found in a response area but can easily be transported through the area, so responders must be prepared.

There are more factors firefighters must consider than deciding between AR-AFFF and fluorine-free foam that is alcohol-resistive. AR-AFFF is proven to be effective and handle most flammable liquid incidents a department can face, while fluorine-free foam is relatively new and untested on large-scale incidents. With groundwater contamination and cancer the hottest topics concerning firefighting foam, many states are starting to regulate fluorine-containing foams—preventing the use of the fluorine-containing foams in training or making it illegal to purchase them altogether. This regulation could cause departments to switch to fluorine-free foam no matter what they believe works best for their situation.

If firefighters on scene have the option of choosing between AR-AFFF and fluorine-free foam, the situation must dictate what works best. If there is heavy fire involvement, AR-AFFF is the best option to quickly get the fire knocked down and under control. Many AR-AFFFs can also be proportioned at 1% for hydrocarbons, which will allow the foam supply to go farther as compared to fluorine-free foams that are currently proportioned at 3%. The fluorine-free foams would be great to use on unignited events or for postfire security after a fire has been extinguished. Fluorine-free has shown to last significantly longer before degrading to the point that reapplication is needed. Fluorine-free foam is, of course, much better for the environment, but the areas where AFFFs have contaminated the groundwater are generally where foam training or testing was conducted, not where there was a one-time response that involved foam.

The decision to purchase and deploy class A foam is not as critical as having class B foam. Class A fires are what fire departments and firefighters are mainly prepared for and trained to handle and do so daily. Long before class A foams were invented, firefighters were able to extinguish fires, and it can still be done today without class A foam. Class A foam is, however, an effective tool that can make water more effective, especially in areas where water sources are not readily available. It is important to realize that class A foam does not decrease the needed gallons per minute but rather can decrease the time the nozzle stays open, thus reducing total gallons used.

Consider the foam other local departments and agencies use when selecting foam. In many incidents that foam is going to be used, neighboring departments will be providing automatic or mutual aid. If one department shows up with a combination foam, one with standard class B, and another with fluorine-free foam, an incident commander can face a daunting challenge of making the foam operation effective. Foams that work by a different process cannot be used in conjunction with one another or on top of one another in most instances. Doing so will lose any gains already made with the original foam, possibly intensify the fire, and ultimately have crews come up short on the amount of foam concentrate needed. It is important to note that the foam concentrates departments use in an area don’t necessarily need to be the same brand. The foam should be the same type and percentage to ensure a seamless, effective, and safe operation, as these generally can be combined on scene, allowing for an effective operation.

The foam available from neighboring departments or regionally is also a factor when selecting a foam concentrate or especially how much to purchase. If a neighboring department has foam concentrate readily available to quickly respond to a scene, does your department even need to use foam? Reach out to that neighboring department and ensure a plan is in place for response and reimbursement before an incident occurs. Having a plan to share a foam resource can save departments money and ultimately provide a higher level of service.

The bottom line is that firefighters must have a knowledge of foam to be able to select what is best for the incident and their department. Ultimately, firefighters must consider the pertinent factors to their situation and use their knowledge to select the right foam and not be influenced by a fast-talking salesperson or some fancy promotional material. What is right for one operation may not be right for the next operation. It all depends on the incident. What is right for one department to stock and deploy may not be right for another department because of regulatory issues, response area hazards, and financial implications. Firefighters must research the available foam options to determine what is best and ensure their foam operation is safe and effective—not just a bunch of bubbles that firefighters hope will solve the problem.

Jonathan M. Hinson is a battalion chief with Chesapeake (VA) Fire Department, serving as one of the leaders on the department’s Foam Team. He has been in the fire service for 24 years and worked with Chesapeake for 17 years. He has a bachelor’s degree in business management from Virginia Tech and a masters of public administration from Old Dominion University. He is certified through the Virginia Department of Fire Programs as a Fire Officer III and Instructor II. He has completed National Foam’s Technician I, II, and III programs as well as National Foam’s Flammable Liquid Firefighting School at TEEX in College Station, Texas. He teaches on foam-related topics and is chief of the Newsoms (VA) Volunteer Fire Department.

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