Class A Foam and CAFS Briefing: Structural Firefighting

Compressed air foam systems (CAFS) produce finished foam by injecting "compressed air" into the foam-solution stream. The term "high energy" is sometimes used when discussing CAFS because the energy of the air compressor that forces air into the foam-solution stream is added to the energy already provided by the fire pump to create the foam-solution stream. While CAFS technology represents a radical departure from the more traditional methods of foam generation, it provides significant tactical advantages in structure fire suppression.

Compressed air is injected into the foam-solution stream in the fire apparatus, where it mixes with foam solution in a mixing chamber and the discharge hoseline. A CAFS relies on the "scrubbing action," or turbulence, within the mixing chamber and hoseline to create finished foam. Foam bubbles produced in this way are very small and consistent through this highly efficient method of generating foam bubbles.

In a CAFS, approximately 90% of the foam solution is converted into foam bubbles. All that is needed for a discharge device is a ball valve or smooth-bore nozzle. The finished foam is ready for application as it leaves the last section of hoseline. Adjusting the amounts of water, air and foam concentrate entering the discharge alters the characteristics of the finished-foam produced. Foam can range from wet (milky consistency) to dry (shaving cream consistency) by varying the amount of air that is injected into the discharge. Wet foam is ideal for structural fire attack while dry foam is ideal for wildland structure protection applications.

In addition, the discharge distances of CAFS attack lines and monitors are dramatically increased with the addition of energy from the air compressor. In general, CAFS discharge is usually much farther and holds a much tighter pattern than plain water and conventional systems. The most noticeable difference between CAFS and nozzle-aspirated foam is in direct fire attack. CAFS attack lines dramatically reduce knockdown times, generate much less steam, and create virtually no runoff or water damage.

In operation, the apparatus pump pumps water from the water storage tank through a pipeline where foam concentrate is injected. From this point on, foam solution continues through the pipe to a point where air from the air compressor enters the pipeline to form the finished foam. From this point to the actual discharge device, finished foam is propelled.

The key difference in a CAFS is an air compressor that has the capability of delivering air in the order of 200 cubic feet per minute (cfm). The introduction of this air on the discharge side of the fire pump not only aerates the foam solution, but adds energy to propel the foam through hoselines to discharge devices and then onto the fire.

Class A Foam and the Structure Fire Attack

The advantages of using CAFS generated Class A foam in structural firefighting are:

  • As the finished-foam stream contacts the burning fuel, it immediately begins penetrating the material to slow and then halt the combustion process
  • Since combustion is stopped more quickly than it is when using plain water, the development of heat and toxic byproducts are reduced
  • Water applied in the form of a finished-foam absorbs heat more efficiently, causing temperatures to drop more quickly to reduce the likelihood of flashover
  • Keeps the water where it is needed — on the vertical surfaces of the fuel and compartment/structure — so all of the water applied can absorb heat
  • Since the penetrating ability of water is enhanced by the finished-foam, less water is required to knockdown the fire
  • Since the penetrating ability of water is enhanced by the finished-foam, less time is required for overhaul

Using CAFS, we can handle a much greater volume of fire than ever before. This know-how has redefined our perceptions of what we can do with initial arriving resources — our personnel and water supply. CAFS use can impact firefighter decision-making in regard to fire control strategies at potential large-loss structure fires. Without CAFS, in some severe fire cases, we would ordinarily choose a defensive water application strategy — stand back, let the main body of fire burn and protect exposures. When deploying CAFS, we are highly effective with an aggressive offensive fire attack with initial-arriving firefighting resources.


As an end-user of CAFS generated Class A foam for over two decades, I have come to expect quick knockdowns and reduced total water supply need, sometimes by as much as two-thirds, as compared to using water alone. Time after time, fire after fire, CAFS show significant benefits over straight water. These benefits include:

  • Fire extinguished in less time
  • Fire extinguished with less total water supply
  • Reduced personnel stress from advancing lightweight compressed air foam-filled hoselines
  • Reduced personnel stress due to quick extinguishment
  • Firefighters have to spend less time performing overhaul operations
  • Reduced personnel exposure to heat and the toxic products of combustion
  • Greater fire volume extinguishment from the initial exterior foam application point (when conducting an offensive attack on a fully involved dwelling) prior to the crew making aggressive entry
  • Reduced fire and water damage to structures
  • More effective exposure protection applications
  • Increased likelihood of victim survivability
  • Increased efficiency of personnel and available resources

A typical CAFS apparatus includes:

  • Water tank
  • Foam concentrate tank
  • Fire pump
  • Foam proportioner
  • Air compressor

DOMINIC COLLETTI is the foam systems product manager for Hale Products and the author of the books The Compressed Air Foam Systems Handbook and Class A Foam — Best Practice for Structure Firefighters. Colletti is a former assistant fire chief and serves on the technical committee of the National Fire Protection Association (NFPA) 1500 Fire Department Occupation Safety and Health Program. He is a fire instructor with over 20 years of CAFS tactical firefighting experience. Colletti may be reached at