Bubble Structure Is Key To Selecting A CAFS Nozzle

Compressed air foam can be pumped through any nozzle on the market today, but some are far more effective than others.

The nozzle selection by a fire department must be based on research of how CAFS works and consideration of the factors that make each department unique. It’s important to understand how various nozzles affect the foam bubble structure because that determines which nozzles should be the weapons of choice for compressed air foam operations.

Compressed air foam 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 compressed air foam durability, as well as dramatically increased surface area.

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. The most appropriate nozzle is one that has minimal disruption of the bubble structure. If the bubble structure is disrupted, a portion of the finished product reverts back to foam solution, decreasing surface area and firefighting effectiveness.

Smoothbore nozzles allow the bubbles to be discharged with little disruption and are therefore the weapons of choice for compressed air foam.

A smoothbore nozzle typically includes a valve with a large diameter waterway. On a 1 3/4-inch line a 1 3/8-inch waterway and a threaded tip with a 15/16-inch to 1 1/8-inch orifice are utilized. Adjustments of the product are made by the firefighter at the end of the hose line 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 one-inch line may utilize a ball valve with a 3/4-inch to one-inch waterway and tips down to about 1/2 inch. On a 2 1/2-inch line, a ball valve with a two-inch waterway and a 1 1/4-inch tip work well.

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 smoothbore nozzles for water as well as foam operations, while others insist on having fog capabilities for personal protection.

Other Products

In addition to smoothbore and combination fog nozzles several manufacturers are making other products with the compressed air foam market in mind.

Akron has the SaberJet nozzle, which has two waterways. One is a smoothbore through the center of the nozzle, and the second is a fog around the outside of the smoothbore. One version of the SaberJet has both controlled by the bail. The other version has them controlled separately, the bail controlling the smoothbore and the bumper controlling the fog. This version can flow both waterways concurrently.

Elkhart has the Flex Attack nozzle, a smoothbore nozzle with a variable orifice. By turning the bumper on the front of the nozzle, the orifice size can be adjusted from 15/16-inch to 1 3/8-inch. There is a detent at the 1 1/8-inch setting. This design eliminates the need to remove a tip to make changes.

Piercing And Cellar Nozzles

TFT has 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 idea of the lower pressure settings is to decrease the effect on the bubbles.

There are other nozzles that have been used with compressed air foam. Two of these are piercing nozzles and cellar nozzles. Piercing nozzles can have a drastic effect on bubble structure due to their very 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 a basement, with foam.

When flowing compressed air foam through master streams, whether mounted or portable, smoothbore tips produce the best product. Tip sizes will vary depending on the flow and the product desired for a specific tactical application.

Use the proper tool with the proper product. If you own a vehicle with a diesel engine, you are not going to fill the fuel tank with gasoline and expect good results. Fog nozzles work well for use with water or foam solution, but results when flowing compressed air foam will not be optimal.

When making a nozzle selection, study each nozzle being considered and test it prior to purchase. Be sure to test it, as it will be used. Determine the performance on fire attacks rather than flowing the nozzle in the station parking lot.

Editor’s Note: Keith Klassen, who has more than 30 years in the fire service, is a career captain with the Summit Fire District bordering Flagstaff, Ariz. He is an Arizona State Fire Marshal Office certified instructor and instructor evaluator with over 20 years of foam experience. He is the CAFS instructional program manager for Waterous Company, overseeing domestic and international training with a staff of 12 Waterous-certified CAFS instructors. He is also a co-owner of inFOAMation associates LLC, which provides foam tactical training.

More Fire Apparatus Current Issue Articles
More Fire Apparatus Archives Issue Articles

No posts to display