Why Foam for Wildfire Protection

Why Foam?

Water has long been the universally accepted agent for suppressing fires. However, water is not the most effective agent in all cases. For example, water is typically not effective on an oil fire, and can be positively dangerous. The development of firefighting foams was a positive step toward solving the problem of extinguishing oil fires.

Class A Foam
Class A Foam is more effective than plain water on Class A type fires because plain water has inherent limitations in cooling and penetrating Class A fuels due to a naturally high surface tension. This high surface tension causes water to form into droplets, and consequently, the majority of the droplets roll off fuels, impeding water’s heat absorption potential.

Technically this foam is known as a 'synthetic detergent hydrocarbon surfactant' and, when mixed with water at the recommended ratios, is biodegradable. Because it is a hydrocarbon surfactant, it also has an affinity for carbons and causes the water (as foam solution) to penetrate deep into wood fuels.

Class A Foam has wetting and penetrating characteristics to reduce the combustibility of Class A fuels and makes water 10 times more effective. It can be used with fresh, sea, or brackish water and can be stored for up to 25 years in its original container. Pretreating an area with foam can greatly reduce the chance that the area will burn. Class A foam will adhere to vertical surfaces, increasing the protection it can give to a structure. After the fire threat is passed, clean off any foamed areas with water if desired.

Foam can be aspirated (entrained with air) through a fog or air aspirating nozzle, or a Compressed Air Foam System (CAFS) such as the one we use here at Consumer Fire Products, Inc. Different quality of finished foam blankets can be formed using these foam generation devices. Forming a low expansion, quick draining finished foam bubble blanket will yield additional fire suppression proficiency upon direct attack by enabling the foam solution to adhere to horizontal and vertical fuels. It can literally stick to the sides of a building, tree, or other vertical structure. The foam solution will remain on the fuel, penetrating or evaporating, until it is all gone. The net effect of using Class A foam in this fashion is that the available water supply is efficiently used to cling to and cool the fuel. This maximizes water’s ability to suppress the fire, rather than being wasted by running off of it. Penetration of Class A Foam into fuels will increase their moisture content and prevent them from burning. In addition, the Class A Foam will act as a barrier between any fire and fuel.

Click HERE to see how how foam compares to gels and fire retardant

History of Foam

In the late 1800s, a method of extinguishing flammable liquid fires by blanketing them with foam was introduced. The original foam was a mixture of two powders and water produced in a foam generator. It was called chemical foam because of the chemical action to create it. Chemical foam is a stable solution of small bubbles containing carbon dioxide with lower density than oil or water that exhibits persistence for covering flat surfaces. Because it’s lighter than the burning liquid, it flows freely over the burning liquid surface and extinguishes the fire by a smothering action. Chemical foam is considered obsolete today because of the many containers of powder required for even the smallest fires.

In the 1940s, Percy Julian developed an improved type of foam called Aerofoam. By using mechanical action, a liquid protein-based concentrate, made from natural animal protein, was mixed with water in either a proportioner or an aerating nozzle to form air bubbles with the free flowing action. Its expansion ratio and its ease of handling made it very popular. Protein foam is easily contaminated by some flammable liquids; therefore, care should be used so that the foam is only applied above the burning liquid. Protein foam has slow knockdown characteristics but it is very economical for post fire security.

In the 1960s, National Foam, Inc. developed fluoroprotein foam. It contains an active agent called fluorinated surfactant which provides an oil-rejecting property to prevent contamination. It is generally better than protein foam because its longer blanket life provides better safety when entry is required for rescue. Fluoroprotein foam has fast knockdown characteristics and it can also be used together with dry chemicals which destroy protein foam.

In the mid 1960s, the US Navy developed a fire fighting foam called AFFF which is short for aqueous film-forming foam. This is synthetic foam with low viscosity that spreads rapidly across the surface of most hydrocarbon fuels. A water film forms under the foam bubbles which cools the liquid fuel and will stop the formation of flammable vapors and provide a dramatic fire knockdown, an important factor in crash rescue fire fighting.

Class A foams were developed in mid 1980s for firefighting wildfires. Favorable practical experiences led to its increasing acceptance for fighting other types of class A fires, including structure fires. Class A foams facilitate wetting of the class A fuels, lowering the surface tension of the water and assisting with saturating them with water, which helps preventing the material from burning, suppressing an existing fire and preventing re ignition. This method of applying Class A foam breaks the fire triangle which shows that fuel, heat, and oxygen are needed for combustion and continuous burning.

Los Angeles County Fire Department Tests Foam (CAFS)

In July 2001, Los Angeles county Fire Department conducted tests of its own to see how effective Class A Foam was compared to water. Looking for hard numbers they conducted these tests and reported the results to Fire Chief Magazine in order to share the results with the fire industry. What they found was:

Low concentrations of Compressed Air Foam (CAF) contain more water and penetrated better than high concentrations of CAF which appears in a drier state.
Foam outperformed water in tests under the following conditions:
Structural fire fighting where suppression of an existing fire occurred. The foam knocked down the fire 4 times faster and cooled down the fuels and air temperature 4 times faster. Less water was used and less damage occurred to the contents of the structure with foam being used.
Foam testing was also conducted on a five acre pile of shredded tires. Smoke and flames were visible from 40 miles away. When water was applied it was completely ineffective. Using CAFS, 3 systems were dispatched, and after 6 hours using handlines the fire was knocked down.
Foam was used for Wildland/Urban interface structure protection – with wind driven wildfires advancing, an engine company protected a wood-sided house with a CAFS before evacuating. Two hours later, after the fire had burned through the area, a helicopter pilot observed what he thought was nothing but white ash from the air. The engine crew returned to the site and found the structure still standing, fully intact, with everything else in the area burned to the ground.