Beware the Foam System That Answers the Question No One Asked

Using Class A foam and compressed air foam systems (CAFS) for everyday fire responses such as wildland, automobile and structure is the status quo in a number of departments across the United States.

Beware the Foam System That Answers the Question No One Asked
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Using Class A foam and compressed air foam systems (CAFS) for everyday fire responses such as wildland, automobile and structure is the status quo in a number of departments across the United States. As their use increases, specifying the right size and design foam hardware into new apparatus is an issue for the departments adding them to their fire suppression arsenal.
Apparatus committees involved in new apparatus specification need to thoroughly investigate the available foam agent and hardware choices on the market. The second step for the apparatus committee is to seek information that answers the question, "What type of foam system do I need to make the most out of what I have?" In other words, what type of foam system, foam concentrate and hardware will maximize fire combat resources (personnel, equipment and water supply)? The purpose of this question is simply that you do not end up with a foam system answering a question that no one asked!
As a fire officer engaged in specifying new fire apparatus, understanding the design and capabilities of foam systems is important. Foam system design must answer the call of day-to-day firefighting duties as well as the extraordinary job that occurs only once in a while — such as the growing inferno inside a large structure that has the potential to be a high-dollar-loss fire. For example, while 90% of fires might be extinguished with one or two 1¾-inch hoselines, the other 10% cause the majority of the dollar fire loss. When designing a new engine, it is important to not only plan for a foam system that will effectively stop the frequent minor fire, but equally important to stop the large, rapidly spreading, potential high-dollar-loss fire.
For an example of planning for the frequent and infrequent fire, let us look at one apparatus specification scenario where a few "tweaks" turned the foam system into a high performer. The objective of modifying the foam system specification is to increase foam system capability to make the most out of initial fire attack resources.
The scenario: A fire district in the Southwest with a population of 30,000 and a moderate wildland/urban interface (WUI) fire problem has decided to purchase a new engine designed to cover both structure fire and WUI responses. The officers have read and heard a lot about the attributes of Class A foam and CAFS for WUI and the structure fire attack. They request a foam product demonstration from a local vendor and see CAFS/Class A foam technology at work, first-hand, during live fire training in an acquired structure.
Impressed with the demonstration, they specify an engine with a 1,000-gallon booster tank, 1,250-gpm midship fire pump, 30-gallon Class A foam concentrate reservoir, five-gpm electronic foam proportioner and a CAFS with 200-scfm rotary air compressor. The foam system is connected to three compressed air foam-capable discharges — two 1¾-inch crosslays and a 1¾-inch front-bumper trash line. While this all sounds good, taking a closer look at the specification we find a few important foam system configuration details that have either been overlooked or neglected. By making some minor changes involving relatively minimal amounts of money we can dramatically improve the fire-suppression performance of this engine.
The first neglected detail is the tank-to-pump line diameter. While the tank-to-pump line is not a foam system component, its flow rate capability will impact foam system performance. The apparatus committee allowed the use of the truck builder's standard specification, which calls for a three-inch-diameter tank-to-pump valve and line. A three-inch tank-to-pump line will allow about 500-gpm water flow from the tank into the 1,250-gpm fire pump. By increasing the size of the tank-to-pump valve and line from three-inch to four-inch, we can double the flow rate to about 1,000 gpm. When this apparatus responds as an initial-attack engine to a structure fire and works from tank water, the increased water delivery rate — by a factor of 100% — provides greater fire suppression capability. This change is well worth the investment.
The second detail overlooked in the specification is a provision for a CAFS discharge outlet providing a hard-hitting high-flow pre-connected portable monitor. This is a portable monitor at the end of a 2½-inch pre-connected hoseline, usually 150 to 250 feet in length. One advantage of using compressed air foam is that hoselines are filled with about 30% compressed air and 70% foam solution (liquid) by volume. This makes them lighter and more maneuverable compared to hoses filled with water.
At a fully involved structure fire, the capability to deploy a hard-hitting portable monitor with limited initial attack personnel is a real advantage. Since the 2½-inch hoseline is partially filled with air, it feels, handles and advances more like a 1¾-inch line filled with water. Ease of repositioning makes the 2½-inch compressed air foam attack line a valuable fire-suppression tool. A minimal crew of two firefighters can deploy the monitor, apply foam, and shut down and reposition the charged hose to another location to best hit the fire. Adding a pre-connected portable monitor to the apparatus configuration is an excellent way to increase the firefighting capability of initial-arriving personnel at structure fires, or to quickly coat exposed structures during WUI incidents.
The third detail overlooked is the gpm rating of the foam system discharge manifold. The truck builder's standard discharge manifold flow rating specification provided is 750 gpm. This component can be upgraded to a 1,000-gpm manifold to provide higher foam solution delivery rate capability.
What is a foam system manifold? Electronic foam proportioners are discharge-side devices, meaning that they are installed in piping connected to the discharge side of the fire pump. This piping network is called a "foam system manifold" and typically has a double-check valve assembly to prevent the backflow of foam agent into the fire pump or booster tank. Every foam system discharge manifold has a specific gpm rating, such as 500, 750 or 1,000 gpm. The gpm rating is governed by the size pipe used, flow restrictions caused by check valves, 90-degree elbows and other piping turns.
Why have a 1,000-gpm manifold installed? Primarily because increased application rate equals superior fire suppression. The 1,000-gpm flow rate also dovetails in with other foam system component capability. For example, we already determined that the four-inch tank-to-pump line and valve will deliver about 1,000 gpm into the fire pump. The five-gpm electronic foam proportioner is capable of delivering 1,000 gpm of Class A foam solution at a 0.5% proportioning ratio. So, it makes good sense to install a 1,000-gpm foam system discharge manifold that complements the capacity of other foam system components.
To recap, by changing three apparatus specification items we have dramatically increased foam system performance and maximized initial fire attack capabilities. Some fire officers play devil's advocate, contending that the high-flow concept is not required and that today's engines have become too big — their sheer size and weights are huge — for the type of service that is being delivered, speaking about the high number of emergency medical service runs.
When discussing this phenomenon a number of years ago, a fire chief from the Southwest coined the analogy, "We are delivering pizzas with cement trucks." While this statement may be true, realize that when you need to pour concrete you need a cement truck. When you have a large, rapidly spreading structure fire, you need an engine with an appropriate-size water supply, fire pump and foam system to deliver the required delivery rate of foam solution to stop the fire.
Many volunteer and combination departments have found foam technology to be a valuable asset in enhancing firefighting capabilities of limited initial-arriving personnel at daytime working fires. If you are on a new fire apparatus committee, do your homework — know what you want to use the new foam system for; take the time to think through the needed system performance; specify and purchase the appropriate foam system. You will be glad you did.
DOMINIC COLLETTI is the author of The Compressed Air Foam Systems Handbook and Class A Foam — Best Practice for Structure Firefighters. He also is co-author of Foam Firefighting Operations 1 and The Rural Firefighting Handbook. Colletti is a former assistant fire chief and serves on the technical committee of NFPA 1500 Fire Department Occupation Safety and Health Program. He is the Global Foam Systems Product Manager for Hale Products and can be reached at dcolletti@idexcorp.com.
author: By DOMINIC COLLETTI




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