RURAL FIRE COMMAND

Quick Knockdown: Class A foam can make for a speedy attack on vehicle fires in rural areas
Story & Photos by Keith Klassen

Although vehicle fires are a common response for any department, they can be more challenging for rural departments where longer response times and distant water sources are common. In those situations, Class A foam can be an extremely helpful fire attack option.

Class A Advantages
Advantages to using Class A foam on vehicle fires include:
1. The increased reach of the stream enhances firefighter safety.
2. Foam provides a quicker knockdown with less water use due to the increased surface area of the foam solution and the resulting increased ability to absorb heat.
3. There’s a reduced chance of rekindle because the foam solution is much more effective in penetrating and wetting fuels.
4. The lightweight compressed air foam (CAF) hoseline is more maneuverable and, therefore, particularly helpful if you find yourself with limited personnel.

How It Works
Class A foam bubbles can be created by using either an aspirating nozzle or a compressed air foam system (CAFS). An aspirating nozzle is a low-energy system that adds air to the foam solution at the nozzle and creates bubbles as the mixture agitates through a screen. Aspirating nozzles can create a larger volume of bubbles at a lower pressure with a shorter stream reach.

CAFS is a high-energy system that injects air under pressure into the foam solution at the discharge and forms the bubbles in the hose. This creates a small, consistent bubble structure that’s lower in volume but has an increased stream reach due to the added energy of the air stream.

When fighting vehicle fires, it’s best to use both methods, starting with compressed air foam and then switching to aspirated foam.

From a Distance
Effective compressed-air foam for fire attack can be created through a 1 ¾" line using a smooth-bore nozzle with a 15/16" tip flowing 90–100 gpm and 40–45 cfm at 100 psi with 0.3 percent foam concentrate.

The purpose of using CAFS for the initial attack is to allow for an effective attack from a greater distance. Distance increases safety. Vehicle fires can create explosions and launch projectiles, including bumper struts, hatchback struts and air bags. Thus, you should make your attack at a quartering angle to the vehicle, as this location is most protected from launched projectiles.

The attack should begin at a distance where the stream just reaches the vehicle. It’s better to start farther away and advance than to start too close and have to retreat. At this distance, the compressed-air foam will quickly knock down the fire. Tip: Firefighters tend to waste product and create an ineffective application by bouncing foam off of surfaces, such as the hood and roof. Instead, direct the foam stream into the vehicle’s windows or other openings, toward the seat of the fire. You can also effectively attack a fire underneath the vehicle from a distance by bouncing the foam stream off the ground immediately adjacent to or under the vehicle.

You’ll be able to tell your fire attack is working when you see a change in the smoke from black (typical of a vehicle fire) to white. This change occurs because the foam is carbon-loving and will pull the carbon particulates out of the smoke.

Get Closer
When the fire has been knocked down and the heat quickly reduced due to the use of compressed-air foam, the likelihood of explosions and resulting projectiles is also reduced. At this point, you can advance your fire attack closer to the vehicle.

You can continue applying foam; however, the downside is the reach and energy of the stream—the same factors that were previously a benefit. This energy tends to blow the foam through the vehicle windows and out the other side with little effect or bounce the foam off surfaces, covering everything and everyone with bubbles. Tip: Reduce this effect by partially closing the ball valve at the nozzle. This will break bubbles, effectively making the foam wetter; however, this is a good consistency for overhaul.

A more effective tactic at this point is to switch from compressed-air foam to aspirated foam using a medium-expansion nozzle. This change can be made quickly and easily. The firefighter signals the engineer for the change, then removes the smooth-bore tip and screws the aspirating nozzle on the ball valve. The engineer closes the air valve to the discharge, increases the foam percentage and lowers the pump pressure.

Good medium-expansion foam for this application has an expansion ratio of between 30 to 1 and 50 to 1. This means that for every gallon of foam solution pumped through the nozzle, 30 to 50 gallons of bubbles will be produced. This foam can be made at approximately 60-psi nozzle pressure flowing 40–45 gpm and using 0.5 percent foam concentrate. Using this foam attack method, a typical four-door sedan can be filled to the point that foam is running out of the windows in approximately 30 seconds.

After the foam is applied, the water will begin to drain out of the bubble structure, effectively beginning the overhaul process. Steam popping up through the foam indicates locations that are still hot and will require further attention. If you can’t open the hood, use a Halligan or similar tool to pry up the hood midway down the side of the hood. You can then direct the foam can through the opening into the engine compartment.

If an investigation is needed immediately after fire extinguishment, the foam blanket can be quickly dissipated by switching to a low-gpm water fog stream to mechanically break the bubbles.

In Sum
As fire service professionals, we should constantly be researching and exploring safer, more efficient and more effective ways to do our job. The use of Class A foam on vehicle fires is one method that can aid rural fire services with the challenges they face.

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.

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