BY JEFF COTNER
ACHIEF CALLED ME LAST FALL, SAYING THAT HIS department had taken delivery of a new fire apparatus that was equipped with a discharge-side direct-injection foam system. He said he wanted to use Class A foam but his firefighters were reluctant to because “they don’t know what it is.” This is too often the scenario.
We must educate our personnel on the fundamentals of using Class A foam. They need to know what it is and how it works, become very familiar with the foam system or proportioner used, and know how to make foam in the structural world.
HOW IT WORKS
Class A foam is basically a surfactant, similar to dishwashing soap. You don’t wash your dishes in plain water; you add some soap. The same thing applies to Class A foam and firefighting. Not turning on the foam is like washing your dishes in plain water. It will take forever to clean the dishes; likewise, it will take a long time to put out the fire. Class A foam increases the water’s efficiency when extinguishing a fire. As a surfactant, it lowers the surface tension of water and allows it to penetrate Class A fuel.
To demonstrate this, try the following experiments. On a small piece of cardboard, put a drop of water on each half of it. Notice the water does not start soaking into the cardboard. Place a drop of Class A foam in one of the drops. The foam immediately reduces the surface tension and allows the water to soak into the cardboard (i.e., the Class A fuel) while the other droplet remains intact.
In another demonstration, fill two glasses about half full with dry peat moss. Add plain water to both, but add a drop or two of Class A foam to one. The glass with the foam additive allows the water to penetrate the peat (i.e., fuel) easily. Reducing that surface tension allows the water to penetrate the fuel and also allows the water to penetrate the dirt on our dishes. This sounds complicated, but Class A foam is very simple to understand.
An important characteristic of Class A foam is that it will bond with anything that is carbon-based. This is where Class A and Class B foams differ. Although Class B foam reduces the surface tension of water, it repels carbon. One reason Class B foam works on a liquid hydrocarbon fire is that it floats on top of the fuel. Because Class B foam doesn’t bond with carbon, it is not as effective on Class A fuel fires.
However, Class A foam can be effective on Class B fires if you use an air-aspirated nozzle or compressed-air injection system to apply the foam in a thick layer of bubbles. This will isolate the oxygen from the fuel just like Class B foam. Class A foams do not meet national standards for use with liquid hydrocarbon fires, which require them to be able to contain hydrocarbon vapors for at least 15 minutes. Because of this time factor, although applying Class A foam to a hydrocarbon-type fire will extinguish the fire, it will not suppress the vapors for long; they could reignite if a heat source is present. However, applying more Class A foam will work until the Class B foam operation is set up. When available, simply begin to apply the Class B foam on top of the Class A foam when adequate supply is established.
Firefighters have said that Class A foam will not work on car fires because of possible liquid hydrocarbons burning from the gas tank. However, Class A foam will extinguish a car fire with great success, even with hydrocarbons burning. However, remember that the Class A foam will not contain the hydrocarbon vapors for more than 15 minutes, so reapplication of Class A foam and application of Class B foam may be necessary.
KNOW YOUR FOAM SYSTEM
Firefighters must know how their particular foam system operates and be confident in its performance. Measuring the proper amount of foam to inject is essential. Assuming your system uses direct injection, it will be a balance pressure type that uses pressure differentials or an electronic type using a microprocessor and water flow to determine the proper amount of concentrate to inject. The proportioner will always add the foam on the discharge side of the pump for structural firefighting use. Depending on the manufacturer, these systems may operate differently at the pump panel. However, the result is the same-you are proportioning 0.1 percent to one percent of the foam concentrate into the hoseline. Most proportioners feature one-button operation and are preset to or can be programmed to 0.3- or 0.5-percent concentration.
Again, Class A foam is used at 0.1- to one-percent concentration, compared with Class B foam at between one and six percent, depending on the foam manufacturer. This is another one of those common operational errors. Some fire departments use Class A foam at Class B foam proportioning rates. Class A foam will not work better at rates higher than one-percent concentration. In fact, surface tension begins to increase at higher proportioning rates.
WHAT MAKES THE BUBBLES?
I have covered proportioning the foam concentrate and putting it into the hose stream. Foam concentrate and water mixed together are called solution foam; adding air makes finished foam or bubbles.
There are three ways to add air. Impact foam is created using a regular combination nozzle set on straight stream or a smooth bore nozzle; air is introduced on the stream’s impact when it deflects off the floor, wall, or ceiling and produces bubbles. An air-aspirated foam nozzle introduces air at the nozzle, which creates the finished foam when it exits the nozzle.
COMPRESSED AIR SYSTEM IS MOST EFFICIENT
However, the most efficient way of introducing air is the compressed air foam system (CAFS). Air is supplied from a high-volume air compressor or from mounted stored air cylinders. The CAFS adds the air right behind the foam solution at the pump. The air and foam are mixed together as they travel through the hose. Since the air is added at the pump, there is no need for any special nozzles. Full-flow smooth bore nozzles with tip sizes of 1 1/8 or 1 1/4 inches work well with the CAFS. Other types of nozzles tend to break down the bubbles created in the hose and are not as effective.
For initial attack, the CAFS is usually operated at 0.3 percent; impact and air-aspirated foams at 0.5-percent concentration. The 0.2-percent setting is most commonly used during overhaul, the one-percent setting during exposure protection. The CAFS is a high-energy system that uses the energy of the compressed air. This energy may cause a strong nozzle reaction when opening the nozzle, which is a safety issue of which firefighters need to be aware.
Using the CAFS makes hose much lighter because it is not just water that is being moved. The increased horsepower of the compressed air also extends the hose stream’s reach. The CAFS also decreases total water usage by nearly 50 to 75 percent compared with using just plain water, which reduces water damage and is advantageous in rural settings. Moreover, using the CAFS results in very low friction loss.
INCREASING FOAM USE CONFIDENCE
To raise operators’ confidence level in using foam, review the studies of foam use, such as “Quantifying the Effects of Class A Foam in Structural Firefighting: The Salem Tests” (Dominic Colletti, Fire Engineering, February 1993). Studies confirm that using Class A foam greatly improves firefighters’ operating effectiveness and overall safety.
Your fire department and community will benefit greatly from using Class A foam on your engine company. You just have to be willing to change and to learn a few new things. Although that can be a challenge in today’s fire service, an open and progressive mind is a must for a department that wants to use Class A foam to its fullest potential.
JEFF COTNER, a 23-year veteran of the fire service, has served the past 16 years with the Bloom Township (OH) Fire Department, where he is a lieutenant. He is vice president of the Ohio Society of Fire Service Instructors and a fire training officer II at the Ohio Fire Academy.