Flowin' Foam

By DOMINIC COLLETTI

Figure 1: This fire, which occurred on Long Island, N.Y., in 1995,
is a typical wildland/urban interface fire incident. Fueled by dry
pine trees, the fire quickly threatened roadways and structures.

Perhaps because the wildland fire service pioneered the technology, most wildland firefighters are familiar with the use of compressed-air foam systems (CAFS). Indeed, several wildland firefighting training curriculums around the country cover the application of nozzle-aspirated Class A foam and CAFS. However, many structural firefighters operating in the wildland/urban interface (WUI) have not been wildland cross-trained and are behind the curve in understanding the fire control benefits CAFS can bring to WUI incidents. These personnel could well use the advantages of the technology for their own wildland/structure fire problems, but have not been educated or trained in the strategy and tactics needed to make it work.

In this article, I'll review what makes CAFS technology superior to other methods, as well as tactics for employing CAFS in the WUI and the limitations of CAFS when applied to WUI fire challenges.

A Brief History

The growing use of CAFS in the United States and around the world  is a direct result of research and development work by the wildland fire service.

Although CAFS can be traced back to shipboard and aircraft rescue firefighting apparatus installations prior to the 1960s, it was the Texas Forest Service (TFS) that developed the technology that brought CAFS into the mainstream. In the 1970s and early 1980s, the TFS was instrumental in pioneering CAFS; it even developed hardware appropriately nicknamed "The Texas Snow Job." Through field-testing and real-world fire response, the TFS developed a good understanding of the product's benefits in wildland firefighting operations. News of the TFS' positive field results spread to other wildland agencies, such as the Bureau of Land Management (BLM), and eventually on to the structural fire service. As a result, more fire departments with structure responsibilities are adopting CAFS today than ever before. The bottom line: The technology works well and has the potential to save property, provide a bigger bang for your buck and increase the fire-suppression capability of fireground resources-our equipment, personnel and water supply.

Figure 2: Fire personnel tried but failed to prevent
this fire from jumping over them and the road. CAFS
could have provided the firefighters with a valuable
tool to slow fire progression or even stop the fire’s spread.

CAFS Basics

The first step in using CAFS is to understand how they work; to do this, you must understand some basic concepts about Class A compressed-air-generated foam.

Adding Class A foam concentrate to water increases water's ability to wet-and therefore cool-wood fuels. Typical CAFS consist of a fire pump, electronic foam proportioner and high-volume rotary air compressor. The foam blankets CAFS produce keep moisture in contact with vertical and horizontal fuels. Untreated water rolls off vertical fuel surfaces, but foam bubbles cling to fuels and keep the water contained within the foam in contact with burning or ready-to-burn fuels.

Using CAFS is more effective than using just air-aspirating nozzles to produce a finished-foam blanket, because most CAFS produce multiple foam consistencies by controlling the ratio of liquid (foam solution) and air discharged into a hose. Having a wide range of foam consistencies-from wet, milky solutions to dry, shaving-cream-type foams-allows us to choose a foam type that best utilizes our limited water supplies for a specific fire.

CAFS produce one of three types of foam: wet, fluid and dry. These foams provide us with options to control the drain time of the finished-foam blanket. "Drain time" is a measurement of the foam blanket's capability to give up the liquid contained within bubbles. Scientifically measured as "25 percent drain time," it is the measure of the amount of time it takes a given finished-foam blanket to drop 25 percent of the foam solution out of the finished-foam bubble mass.

Foam application is not a magic act, nor is it a silver bullet. Success in slowing or preventing ignition depends on three critical factors:
* Quantity of agent applied (total gallons of foam solution);
* Quality of application (coverage of entire tree foliage); and
* Time allowed for moisture absorption (from the point of foam application to when the fire finally meets the fuel).

Photo By Dominic Colletti
Figure 3: Engine 5-6-14 from Coram, Long Island (N.Y.),
applies wet-consistency compressed-air foam to scrub
pines during a demonstration.

In the Field

How does this information relate to foam application and using CAFS on the fireground?
Let's take a look at a WUI fire incident, such as the one that occurred on Long Island, N.Y., in 1995. Fueled by dry pine trees in an area notoriously known as the "Pine Barrens," this incident started in the late morning. After the fire jumped a four-lane divided highway, firefighters managed to get it under control the next day. The fire is shown in Figures 1 and 2. 

Take a look at Figure 2. Here we see fire personnel making a stand and fighting fire in the roadway, trying to prevent the flames from jumping over them and the road. This photo was taken on a sunny afternoon, with blue skies, under severe fire conditions. The fire passed over the firefighters and the roadway, and kept on going. Fortunately, there were no serious injuries, but this is a situation in which CAFS would have provided the firefighters with a much-needed advantage over the fire. Read on to see how.

Pretreating Fuels

CAFS can be used in a number of ways in the WUI. One fire-suppression strategy is to apply CAFS-generated foam to raise fuel moisture content prior to the approach of a running fire. Firefighters pretreat fuels with a coating of foam, allowing personnel and apparatus to relocate to an area of safe refuge prior to the fire reaching the foam-treated area. Effective foam application that raises fuel moisture content slows down, and in some cases even stops, an approaching flame front. For this strategy to succeed, fuels must absorb enough water to raise their moisture content past the "moisture of extinction," or the maximum moisture content a fuel can hold and still support flaming combustion.

Figures 3 and 4 show compressed-air foam-equipped wildland engines during a pretreating demonstration. In Figure 3, the Coram, Long Island (N.Y.) Engine 5-6-14 is applying wet-consistency compressed-air foam to scrub pines. During the late winter and early spring, it is commonplace for these pine trees, both dead and alive, to have a very low moisture content. Fuel moisture content is governed by atmospheric conditions-relative humidity and precipitation. Extended periods of low relative humidity, little rainfall and moderately warm temperatures support explosive fire growth.  

During pretreatment, it's best to use a formation of engines to maximize foam coverage and moisture penetration (see Figure 4, which illustrates a classic pump-and-roll pretreat operation). Applying wet-consistency compressed-air foam and allowing it to soak into the fuel for an adequate time provides superior moisture penetration. When treating pine trees, for example, the wet-finished foam hangs on fuel surfaces while the detergents draining from the foam blanket begin to break down the waxy follicle over the pine needles. The foam solution draining from the bubble blanket also easily flows into small, exposed wood cracks and crevices because it has a low surface tension from surfactants in the foam concentrate.

Once the firestorm begins to approach these foam-treated fuels, their temperature begins to rise. At 212 degrees F, the fuels begin to outgas water as steam. This process uses an appreciable amount of energy that would have otherwise been used to distill flammable vapors from the surface layers of the tree and to raise the temperature of its interior layers. The water outgassing from the fuel increases the time required to fuel ignition. The benefit for us: This process appreciably slows down the progression of a fast-moving fire and allows other, more conventional fire-control methods-such as a control line made by a ground crew or a bulldozer operator-to have a realistic chance to be effective.

Photo By Dominic Colletti
Figure 4: Using a pump-and-roll engine formation
can maximize foam coverage and moisture
penetration during pretreatment of fuels.

Structure Protection

The same methodology applies to using compressed-air foam for structure protection. We can raise a structure's fuel moisture content by applying Class A foam well in advance of an approaching conflagration, provided the building has exterior materials that can absorb water, such as T 1-11 wood siding and wood shake roof shingles.

After performing typical pre-fire approach structure-preparation tactics, the best CAFS strategy is to apply wet compressed-air foam to the entire structure-roof, siding and eves-following immediately with a coating of dry foam over the top of the wet foam. The dry foam has a longer drain time; its sole purpose is to act as a cap over the top of the wet foam, preventing moisture in the wet foam underneath from evaporating. The combination of wet and dry foam provides the best opportunity for available moisture to stay in contact with and be retained in the fuel, inhibiting ignition. Wet fuels do not burn well.

Although the application of compressed-air foam for exposure protection is not a cure-all for WUI fire operations, it has proved time and again to be a valuable tool in saving property. When used appropriately, it also enables firefighters to utilize tactics that can move them out of harm's way, conditions permitting. No empty structure is worth a firefighter's life. 

When we recall the California fires of 2003 that wiped out numerous subdivisions, it's easy to see that we must think differently about fire control and suppression in the WUI. Compressed-air foam can be a good fit. However, its benefits are directly proportional to an understanding of what it is, how it works and how to use it. Training and education are required-and well worth the investment.

Dominic Colletti is the author of Class A Foam-Best Practice for Structure Firefighters and co-author of The Rural Firefighting Handbook and Foam Firefighting Operations 1 with Larry Davis.  He can be reached at dcolletti@idexcorp.com.