Apparatus

What Foam? The Principles And Practices Of Foam Applications

Issue 9 and Volume 11.

2.5-inch Class A CAFS attack line controls large volumes of fire during initial attacks.
A 2.5-inch Class A CAFS attack line is an excellent tool for controlling large volumes of fire during initial attack. Firefighters with a 2.5-inch line and a portable monitor launch an attack on a fully involved dwelling in Clinton, Conn.
Florida firefighters take part in a training and education program on the use of compressed air foam.
These Florida firefighters take part in a training and education program, a required and vital step when implementing the use of compressed air foam.
Less digging and pulling is required when compressed air foam is issued.
While less digging and pulling is required during an overhaul when compressed air foam is issued, a thorough overhaul of a room and contents fire will mean window and door moldings will have to be removed.
One of the advantages of using CAFS is producing a foam blanket that clings to threatened fire exposures.
One of the many advantages of using CAFS is the capability to produce a foam blanket that clings well to threatened fire exposures.

There is a lot to do for department officers planning to implement foam agents in fire operations for the first time. Decisions need to be made and activities must be coordinated relating to hardware specification, purchase and firefighter training. The objective of implementing a foam program is to reduce fire loss and increase firefighter safety. One of the required steps is creating a suitable training and education plan with the goal of taking the mystery out of what foam is, how it works and how to best use it.

What follows are some basic foam principles and practices that will help to reduce confusion and assist the troops in maximizing foam’s positive fireground effects.

Class A foams are intended to be applied for fire suppression of ordinary combustible type fuels, not on flammable liquids. Most Class A foam concentrates are synthetic, detergent-based products that are biodegradable and, when used according to directions, pose little environmental risk.

Class A foam works in several ways to increase firefighting capabilities when combating ordinary combustible fire. Similar to an industrial detergent, Class A foam concentrate reduces water surface tension. This allows the foam solution to penetrate exposed fuel cracks and crevices for more effective moisture penetration and fuel cooling.

Added to water at small ratios, typically between 0.3 percent and 0.5 percent, Class A foam concentrate is also a good bubble producer. The bubbles can be produced by using a variety of foam generating systems, including fog nozzle, air-aspirating nozzle, high-expansion foam generator and Compressed Air Foam Systems (CAFS).

Creating “bubbles” or a “finished-foam blanket” is highly desirable as it allows water contained within the foam blanket to stay in contact with hot fuel surfaces. When a foam blanket clings to horizontal or vertical fuels, two actions occur: the water in the foam blanket evaporates or drains out and the bubbles break. This both cools the fuel and allows moisture penetration. These actions first slow, and then stop pyrolysis, provided enough foam is applied.

Class A foam is not a chemical fire retardant. After a fuel surface is treated with Class A foam, the moisture provided will eventually evaporate from the fuel. When exposed to approaching fire conditions, fuels will subsequently reach ignition temperature and burn.

Remember that Class A foam is not chemical fire retardant and no long-term fire stopping action occurs after application.

There are significant gains when using Class A foam over water in that much less total water supply and/or time is required to protect a threatened fire exposure or to extinguish a given size fire load. Additionally, moisture penetrating wood fuels due to the reduced water surface tension raises the fuel moisture content.

As wood fuels get wet, a longer exposure to heat is required to bring them up to ignition temperature since moisture must first out-gas from the fuel. The result: a small amount of Class A foam concentrate mixed with water provides a big bang for the buck during fire suppression.

Class A foam concentrate, the concentrated agent we purchase from manufacturers in 5-gallon containers, 55-gallon drums, or large tote containers is not, however, a replacement for water.

Increased Suppression

Foam agents, used correctly, increase the fire suppression capability of a given size water supply. While fires have been extinguished with Class A foam using much less total water supply compared to the application of water alone, keep in mind that foam concentrate is not a replacement for an appropriate water supply.

Some departments capture a fraction of the benefit of Class A foam by only using Class A foam for mop-up and overhaul operations. They do not believe that there are any advantages to using it for initial fire attack.

Do not cut the product short. It brings many benefits for initial fire attack. Applied during initial attack, it clings to fuel surfaces and starts to immediately penetrate deep seated non-flaming fire and hot spots. This means less of a dig and pull overhaul will be required.

Class A Foam Applications

I have used Class A foam for interior structure fire attack, automobile interior, hay bale, tire, coal, plastic, dump, bog, wildland, brush, paper bale and many other types of fire.

Extinguishing these fires in less time means increased firefighter safety as crew exposure to heat and toxic products of combustion is lessened. There are many benefits to using Class A foam.

One benefit is seen in rural areas where tanker shuttles (tender shuttles on the West Coast) are used to transport water to the fire scene. One of the leading causes of firefighter fatalities is apparatus accidents on roadways. Reducing the total water supply required by using Class A foam – sometimes by up to two-thirds – means that tankers are on the road for less time and therefore there is less risk of firefighter injury from roadway accidents.

It’s important to keep in mind that Class A foam is not for flammable liquid type fires. Use an appropriate Class B foam concentrate to combat flammable spills and fire. Class A foam is not intended to be applied on flammable liquids. Class A foam may not provide the fuel vapor sealing action that Class B foams provide and therefore, firefighter safety could be compromised. The best practice in the fire industry is to use appropriate Class B foam on flammable liquids.

While Class B foams have been around in one form or another since the late 1800s, they are available today in a number of types and formulations. One of the most widely used formulations in North America today is Aqueous Film Forming Foam (AFFF).  The reason for the growing popularity of AFFF foam concentrates over the past 40 years is their excellent flammable liquid firefighting performance. In addition to AFFF placing a physical barrier or “cap” over a flammable liquid fuel in the form of a foam blanket, it also sheds an aqueous film over the fuel’s surface. This film starts suppressing vapors ahead of an advancing foam blanket, providing excellent flame knockdown characteristics.

AR-AFFF is becoming a staple in our tool arsenal. With the advent of alternative automotive fuels, like Ethanol 85 (E85), using Class B foams that can tolerate application on polar solvent fuel hazards is more important than ever.

Flammable liquid hazards break down into two broad categories: normal hydrocarbons and polar solvents. Fuels that are polar solvents (water miscible) must be secured with Alcohol Resistant (AR) Class B foam. Should non-AR foams be deployed, the polar solvent fuel will destroy the foam blanket since the alcohol fuel will mix with water in the foam blanket and cause blanket destruction.

Most AR foams work by forming a polymeric membrane (a physical barrier on top of the fuel surface) that separates the water in the foam blanket from the polar solvent fuel.

For any Class B foam to be effective in suppressing a flammable liquid spill fire, the rate of application discharged from hoselines and/or monitors must be much greater than the breakdown of the foam blanket from the fire’s heat. Inadequate application rates are often the major cause of failure to control flammable liquid fires.

Each Class B foam manufacturer specifies a minimum foam solution application rate expressed in gallons per minute of foam solution per square foot of spill area (gpm/sq.ft.).  Each manufacturer determines the minimum application rates for foam concentrate on specific flammable liquids.

Third-Party Testing

These application rates are verified through third-party laboratory fire testing. If a department plans on successfully attacking Class B fires with foam, it is critical that responding attack team members understand and follow the minimum foam solution application rates for the specific foam concentrate when used on the specific flammable liquid fuel challenge involved.

The latest advance in the world of foam generating systems is Compressed Air Foam Systems (CAFS). These systems use high-volume compressed air, typically from rotary air compressors, to provide air injection into a foam solution stream inside fire pump discharge piping. The advantage of using CAFS is that they produce a high-quality finished-foam product that knocks down flame and cools fuel more quickly than nozzle aspirated Class A foam systems. It is important to note that CAFS can also be used to generate Class B foam blankets for use on flammable liquids.

The big movement today with CAFS is their application with Class A foams for structure firefighting service. While not a cure-all for fireground problems and conditions, CAFS technology has shown to substantially increase the firefighting capability of initial fire attack resources – personnel, equipment, and water supply.

Lightweight hose line, quick flame knockdown, and reduced labor during overhaul. What does CAFS have going against it? The biggest problem with CAFS is that they are DIFFERENT. When I say they are different, the real issue is that adjustments to firefighting strategy and tactics are required. Training and education is an absolute necessity to harness their benefits.

The typical, full-size, new CAFS engine manufactured today has a five gpm foam concentrate proportioner and a 200-scfm rotary air compressor. This technology has improved in the last 20 years and is much more user-friendly today than ever before. Some systems are designed to be “hands-off” and operate automatically which reduces the burden on the pump operator under the pressure of severe fireground conditions.

CAFS Technology

One way to harness CAFS technology is to retrofit a system by using two DOT 440 cubic feet breathing air cylinders that provide enough air to expel the water in a typical size booster tank as compressed air foam.

The air cylinder concept is an idea for retrofits and can also save departments money over installing air compressor type systems when purchasing new apparatus.

In summation, the application of Class A and Class B foams can increase the capability of initial attack crews to extinguish fire. They should be a planned part of all new fire apparatus design.

If designing a new fire apparatus, invest the time to take a good look at what CAFS technology can offer a department and the public.

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