One of the most promising technological advances to occur within the fire service over the last 25 years was the technology associated with Class A foam and compressed air foam systems (CAFS). This technology, which primarily had its beginnings in wildland fire operations, represents a revolutionary...
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One of the most promising technological advances to occur within the fire service over the last 25 years was the technology associated with Class A foam and compressed air foam systems (CAFS). This technology, which primarily had its beginnings in wildland fire operations, represents a revolutionary breakthrough today for use in structural firefighting.
In the more than two decades that I have been involved in fire service training and education, I have seen a lot of innovations that held promise. Some worked and were adopted by the fire service; some worked and were not adopted; and others just didn't work. But few innovations have come along that represent such a significant step forward in our capability to control structure fires.
The intent of this three-part series is to share the basic concepts of Class A foams and CAFS and their benefits to the structural fire service, even though virtually all fire departments that must fight fires in other types of ordinary combustible fuel could reap the same benefits. For a much more comprehensive text about Class A foam and CAFS technology, obtain a copy of The Compressed Air Foam Systems Handbook at cafsinstitute.org.
In the past 25 years, Class A foam and CAFS have received a great deal of attention. Not since the start of the debate over which is the "best" nozzle — a smoothbore or a variable pattern — has there been such controversy over new technology in the fire service.
It would seem that today there are numerous opinions on the use of Class A foam and CAFS from many in the fire service. Since an opinion is nothing more than a statement unsubstantiated by fact (if an opinion were a "fact," it would no longer be an opinion), let's examine the facts about Class A foam and CAFS and see what they can do for your fire department involved in providing structural firefighting response and operations.
The concept of Class A foam and CAFS is simple: Add Class A foam concentrate to water, forming a foam solution that, when applied to the surface of a Class A fuel, will spread out, wetting the surface of the fuel and penetrating below the surface to absorb heat and cool the fuel faster than plain water. In a nutshell, adding Class A foam concentrate to water doubles the water's fire suppression effectiveness. Adding compressed air to Class A foam solution to make a foam bubble blanket makes the water up to five times more effective. How is this accomplished? Read on.
Surface tension and gravity impede firefighting water. When one gallon of water at 60 degrees Fahrenheit is heated to 212°F and vaporizes, it absorbs a maximum of 9,366 Btu of heat — or 100% efficiency. If each gallon of water applied to a structure fire achieved 100% efficiency, fire suppression would be much easier and cause far less water damage. However, such is not the case.
Walter M. Haessler's research in 1974 found that a solid stream of water achieved only 5% to 10% efficiency (The Extinguishment of Fire, National Fire Protection Association, 1974). This means that each gallon of water absorbed about 933 Btu, and that the majority of the water applied through a solid stream simply ended up on the floor and then ran out of the fire compartment. This was due to:
- The surface tension of water, and
- The force of gravity
Surface tension affects the ability of a liquid to spread across a given surface. This is why water tends to bead on horizontal surfaces and roll down vertical surfaces. Water's surface tension limits the surface area in contact with the fuel, as most of the water beads or runs off, limiting its ability to absorb heat under actual fireground conditions.
What Is Class A Foam?
While firefighting foams of various types have been around since the late 1800s, most of them have been designed for use on flammable liquids and other Class B fuels. The only foams that were intended for use on Class A fires were the high-expansion (200 to 1,000:1 expansion rates) types originally developed for fighting fires in coal mines. These foams are best used as smothering agents where they are forced into compartments to displace air. With such high expansion rates, they have little water within them to perform any significant cooling.