By Keith Klassen
For years, the fire service has been embroiled in the “great compressed-air foam system (CAFS) nozzle debate”—a debate that focuses primarily on which nozzle is best for compressed-air foam (CAF). In reality, CAF can be pumped through any nozzle. However, that doesn’t mean fire departments should just pick a nozzle at random. Nozzle selection must be based on research into how CAF works and consideration of the various factors that make each department unique. With that in mind, let’s look at how various nozzles affect the foam bubble structure and which nozzle is the weapon of choice for CAF operations.
How CAF Works
Smooth-bore nozzles allow the bubbles to be discharged with little disruption and are therefore the most effective choice for CAF. Photo Keith Klassen
The tip size is relative to the line size. For example, a 1" line may utilize a ball valve with a ¾" to 1" waterway and tips. Photo Keith Klassen
CAF is made by injecting air into the foam solution as it leaves the discharge. The agitation needed to create bubbles takes place in the hose as the mixture travels through the line. As it moves, the foam is agitated into smaller and more uniform-sized bubbles. This consistent bubble structure gives CAF its durability and dramatically increased surface area. The key is the increased surface area of the bubbles, which can absorb more heat with the same volume of liquid. When the foam reaches the nozzle, the bubbles are formed and ready to fight fire. That said, the most appropriate nozzle is one that has minimal disruption of the bubble structure. Disruption of the bubble structure returns a portion of the finished product back to foam solution, decreasing surface area and firefighting effectiveness.Types of Nozzles
Smooth-bore nozzles allow the bubbles to be discharged with little disruption and are therefore the most effective choice for CAF. Selection of a smooth-bore nozzle typically includes a valve with a large-diameter waterway. On a 1¾" line, a 1⅜" waterway and a threaded tip with a 15/16" to 1⅛" orifice are utilized. The tip allows adjustments of the product by the firefighter at the end of the hoseline by adding or removing the tip. The smaller orifice size will break a portion of the bubbles, removing some air and changing the foam consistency. The tip size is relative to the line size. For example, a 1" line may utilize a ball valve with a ¾" to 1" waterway and tips down to about a half inch. On a 2½" line, a ball valve with a 2" waterway and a 1¼" tip work well. Tip:
In general, to create a wet foam for fighting fire, the tip size should be approximately one half of the line size.
Fog nozzles are designed to take a solid stream of water and break it into small droplets. Due to this design, fog nozzles will also break the bubbles, returning the product to foam solution. Some firefighters are comfortable with smooth-bore nozzles for water as well as foam operations, while others insist on having fog capabilities for personal protection.
In addition to smooth-bore and combination fog nozzles, several manufacturers are marketing other products with the CAF market in mind. Akron makes the SaberJet nozzle, which has two waterways. One is a smooth-bore through the center of the nozzle and the second is a fog nozzle around the outside of the smooth-bore. One version controls both by the bail. The other controls them separately—the bail controlling the smooth-bore and the bumper controlling the fog. This version can flow both waterways concurrently.
Elkhart Brass makes the Flex Attack nozzle, which is a smooth-bore nozzle with a variable orifice. By turning the bumper on the front of the nozzle, the orifice size can be adjusted from 15/16" to 1⅜". There is a detent at the 1⅛" setting. This design eliminates the need to remove a tip to make changes. TFT designed the CAFS-Force nozzle. This nozzle is a fog nozzle adjustable to two settings marked “water” and “CAFS.” The water setting has a higher internal spring pressure than the CAFS setting. The purpose of the lower pressure settings is to decrease the effect on the bubbles.
Other nozzles have been used with CAF. Two of these are piercing nozzles and cellar nozzles. Piercing nozzles can have a drastic effect on bubble structure because of their small orifice size. They can, however, deliver the resulting foam solution to some hard-to-reach areas. Cellar nozzles will cause less bubble disruption because they have larger orifices. They can work well to cover a space such as an attic or basement with foam.Choosing the Right Tool
When flowing CAF through master streams, whether mounted or portable, smooth-bore tips will produce the best product. Tip sizes will vary depending on the flow and the product desired for a specific tactical application.
The bottom line: Use the proper tool with the proper product. If you own a vehicle with a diesel engine, you’re not going to fill the fuel tank with gasoline and expect good results. Fog nozzles work well for use with water or a foam solution, but results when flowing CAF will not be optimal.
When making a nozzle selection, study each one and test it as it will be used prior to purchase. Determine the performance of the nozzle on actual fire attacks as opposed to just flowing the nozzle in the station parking lot. Foam out of two different nozzles may look quite similar on the ground but may perform differently in actual situations, particularly on interior fire attacks. Do your homework to ensure you get the best bang for your buck in these tight budget times.Keith Klassen is a career captain with the Summit Fire District, a rural combination department bordering Flagstaff, Ariz. He has 33 years of volunteer and career experience in both structural and wildland firefighting, and a background in mechanical and vocational education. Klassen is also an international fire service instructor and a member of the IAFC.
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