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Fire-Fighting Foams
Fire-fighting foam is an effective way to suppress wildland fire, but requires a source for water. PLI's Fire-Fighting Module uses Class A Foam for mop-up operations. A relatively small amount of water can generate a large amount of foam. Class B foam is used to put out fires with liquid hydrocarbon fuels, such as an aircraft fire. PLI's DWFD Module can generate both Class A and Class B foams. What is foam? Air, injected into the stream of water pumped onto the fire, forms bubbles. In order for the bubbles to last long enough to be useful, a foaming agent is added to the water. The foaming agent is a detergent and a surfactant. Its molecules migrate to the interface between air and water, forming the elastic film that holds the air. Eventually the water drains, the bubbles burst, and the foam collapses. How Foam Puts Out Fire Foam acts to rob heat from the fire, cut off the oxygen supply, and seal off the fuel; thus, acting on all three sides of the "fire triangle." [The Fire Triangle is a teaching concept, widely used to explain the principles of fire suppression.] Foam allows water to be converted to steam more easily. Forming steam requires energy, thus taking heat away from the fire. The white, opaque surface of the foam reflects radiant energy (heat) and protects the fuel underneath. The foam blanket acts as insulation, keeping heat away from the fuel underneath. Water in the foam drains down into the fuel, wetting the surface and making it hard to ignite. The detergent foam solution allows water to penetrate into the fuel where it is quickly absorbed. The foam blanket holds in flammable vapors and prevents them from igniting. When the foam blanket completely covers a pile of snags, it cuts off the supply of oxygen. Composition of Foam Concentrate Many detergents will generate foam; for example, the widely used sodium lauryl sulfate, but the concentration is typically 3%. This required too much chemical for wildland fire applications. Surfactants that produce good foams with concentrations of less than 1% were developed for fire-fighting applications in Canada in 1985 and placed on the market. Phos-Chek® 881 Foam Concentrate developed by Monsanto and currently marketed by Astaris, contains a surfactant, organic solvents, an additive to improve foam stability, and a small amount of orange peel extract to give it a distinctive aroma. The surfactant is alpha-olefin sulfonate. Organic solvents include trimethyltrimethylene glycol and hexylene glycol. Lauryl alcohol is the foam stabilizer. Other foam concentrates on the market contain various combinations of surfactants, organic solvents, foam stabilizers, corrosion inhibitors, and other additives. Expansion Ratio of Foams and Types of Application Foams are classified as low expansion (where the ratio of the volume of foam produced to the volume of water used is in the range of 1:1 to 20:1), medium expansion (20:1 to 200:1), and high expansion (200:1 to 1000:1). Once the concentration of the foam is set by the foam proportioner to the appropriate value-0.3% is a suggested starting value-the expansion ratio is controlled by the amount of air injected into the water stream. This, in turn, is controlled by the type of nozzle. For mop-up operations most of the time is spent using straight foam solution (with no foam) and a mopup wand or an air aspirating nozzle and wet, low expansion foam. Medium expansion foam with the appropriate nozzle is used to blanket a pile of snags underlain by a bed of coals. Environmental Considerations Because of the widespread use of foam to fight wildland fires, several organizations have studied the effects on the environment. (See links below.) Foam is applied as a highly diluted solution. The effects on vegetation are negligible; however, foam should not be directly applied to ponds, streams and rivers because of the impacts on aquatic life. Corrosion of plumbing is a problem with some foam concentrates. In the past anti-corrosion agents, added to concentrates for aerial drops, have included sodium ferri-cyanide. Only foam concentrates rated for ground use and approved by the US Forest Service should be used in PLI's Fire-Fighting Module. The Material Safety Data Sheet should be consulted before a particular product is used. Useful Links to Other Sites General Discussions of Foams and Foam Systems Wildland Fire Chemicals - introduction from US Forest Service List of USFS approved foams for fighting forest fires Commercially Available Foam Concentrates for Fighting Wildland Fires Class A Foam from Ansul Phos-Chek WD-881 Class A Foam from ICL Performance Products, LLC FireTrol Class A Foam from FireTrol Corp. Foam Systems and Foam Hardware Portable Foam Systems from Scotty Firefighter Foam Kits from Scotty Firefighter Foam Hardware from Angus Fire Nozzles and Foam Hardware from Task Force Tips Ecological Effects of Foam Ecological Effects of Forexpan S and Silv-ex Foams Ecological Effects of Silv-ex Foam Home Site Map Products Fire-Fighting Module Mop-Up Chemicals Gels Contact Us Orders |