Class A And B: What You Need To Know About Foam

You’re on-board with the technology. You’ve seen the powerful knockdown capabilities of foam and realize it’s a valuable fire suppression tool. You know your department can benefit from installing a system, but how do you go about determining the proper use of Class A and Class B foam?

Like any technology that’s new to your department, you start with education. By increasing your knowledge about the two different types of foam, you’ll be confident in knowing when, where and how to use Class A and Class B foam to achieve fast, safe suppression for any type of fire situation.

It’s obvious that Class A foam is used to fight Class A fires, and that Class B foam snuffs out the Bs. What may not be obvious, however, is how their chemical composition enables Class A and Class B foams to be more suitable for one fire situation over another.

The basic difference is how the foams react to carbon: Class A attracts it; Class B repels it.

As a carbon-loving solution, Class A foam soaks into solid, combustible materials by breaking down the surface tension of the water. It helps the water penetrate the burning material to quickly suppress the fire and prevent rekindles.

Class B foam, on the other hand, repels carbon. When mixed with water, it forms a film that hovers over a spill or burning liquid, sealing the flammable vapors. In the case of a spill, a Class B foam blanket prevents vapor production and ignition, or, in the case of a fire, suppresses the blaze and prevents it from spreading or reigniting.

Naturally, most municipal departments rarely use anything but Class A foam. It’s the firefighters protecting refineries and tank farms that keep thousands of gallons of Class B on hand and understand the application techniques inside and out.

This doesn’t mean municipal fire departments are immune to Class B hazards, however. Industrial fires, tanker truck collisions and railcar accidents are B concerns for any department, and it’s important to have the right amount of Class B foam available for these types of emergencies. It’s also important to make sure your firefighters are knowledgeable about Class B foam properties and tactics.

Techniques Vary

Techniques for applying Class A and Class B foam vary greatly. It’s essential your firefighters know how to flow each one effectively, even if Class B use is the rarity.

Class A foam application techniques are typically straightforward – attacking with direct or indirect methods.

Class B methods, on the other hand, require strategic stream placement to “blanket” the flaming liquid and prevent dangerous vapors from escaping. Depending on the circumstances, banking the stream off a wall or other nearby structure that’s situated opposite the fire can help direct the flow to roll it over, or “blanket,” the fuel.

Simply put, Class B foam is more hazardous than Class A. This doesn’t mean it isn’t a valuable tool for municipal departments, it just means firefighters must be aware of the hazards, and know how to use Class B responsibly.

Environmental Concerns

Environmental concerns, in particular, arise with the chemical makeup of Class B foam. It just isn’t as green-friendly as Class A. Unlike Class A foams that are biodegradable and approved by the U.S. Forest Service, chemicals that make up many Class B foams include perfluorochemicals (PFOAs and PFOCs) that can soak into the groundwater as runoff and potentially contaminate the surrounding environment.

Fortunately, there are ways departments can combat the environmental dangers of Class B foam, such as using compressed air foam systems, which minimize runoff when compared to nozzle-aspirated foam. Additionally, most CAF systems allow pump operators to precisely control the foam expansion ratio for the given situation, reducing foam waste and runoff.

As well as being a hazard itself, Class B foam is also highly corrosive. Firefighters must thoroughly flush the foam out of their operating systems and apparatus after each use to avoid damaging equipment.

While Class B foam is generally more expensive than Class A, using several gallons for education and training is money well spent for municipal departments. Even if the last chemical blaze in your area was over 20 years ago, there’s nothing worse than arriving at a Class B blaze unprepared. Implementing Class B foam drills and practicing several times per year will keep your firefighters’ skills in shape so they can attack any type of B fire with confidence.

Understanding the differences between Class A and Class B foam is only the beginning.

Now you’re informed enough to ask the right questions and get some answers. Talk to manufacturers about their products. Talk to neighboring departments about their experiences. Know your fire problems and find solutions that work. Train, train and train some more.

With new developments in the fire service industry ever increasing, building your knowledge about foam and foam systems is imperative to keeping your firefighters up to speed on advancing technology, and making sure they’re confident when the siren sounds.

Editor’s Note: Geary Roberts worked for decades as a career firefighter and captain in Glendale, Ariz., and previously founded and owned Pneumax. Roberts is president of Waterous’ Arizona operations.

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