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?

Fire suppression foam is a powerful firefighting tool, but it's important to understand the difference between Class A and Class B foam. Class A foam is designed for use on fires involving ordinary combustibles, such as wood, paper, and cloth. Class B foam is designed for use on fires involving flammable liquids, such as gasoline, oil, and grease.

Both types of foam are effective at extinguishing fires and preventing re-ignition. However, each type of foam has different applications and should be used accordingly. The basic difference is how the foams react to carbon: Class A attracts it; Class B repels it.

With its high surface tension, Class A foam soaks into solid materials and breaks down the chemical bonds of fires to stop them from spreading. 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.

Techniques Vary

Applying Class A foam is generally a straightforward process - attacking with direct or indirect methods. Class B foam, on the other hand, can be applied in several ways, depending on the type of fire and the circumstances.

One common method is to simply apply the foam directly to the burning liquid. This works well for small fires, but is not practical for large-scale or industrial incidents.

Another common method is to mix Class B foam with water in a proportion of about 0.75% foam concentrate to 99.25% water. This creates what is known as an AFFF (aqueous film forming foam) solution, which can be applied with a hose stream or through sprinklers.

For larger fires, it may be necessary to use a CAFS (compressed air foam system). CAFS injects foam concentrate into a stream of compressed air, which creates a dense foam that can be applied directly to the fire.

Environmental Concerns

There are several environmental concerns with using foam fire suppression agents. One concern is the potential for foam to contaminate water supplies. Unlike Class A foams that are biodegradable and approved by the U.S. Forest Service, many Class B foams include perfluorochemicals (PFOAs and PFOCs) which soak into the groundwater and contaminate the surrounding environment. Foam can also damage natural ecosystems if it is released into waterways.

Fortunately, there are ways to 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.

It's important to consider these environmental concerns when deciding whether to use foam fire suppression agents in your department. Weigh the benefits and risks of foam before making a decision.

For more information on how Burner Fire Control can assist your team in determining the most effective fire protection arrangement for your offshore or land facility, please complete the Contact Request below or call 1-800-864-4073.

Read the full article from Fire Apparatus & Emergency Equipment here.

About Burner Fire Control

Burner Fire Control delivers complete fire protection for onshore and offshore operations as well as safety, construction, fabrication, and maintenance services. Each person on our technical management team has an average of 25 years in the industrial & marine fire safety field experience. 

These skills plus the industry’s most respected certifications, our growing list of client credentials, and expertise in both the offshore and onshore fields make us one of the most unique privately-held organizations in the oilfield services sector.