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Chemicals to Fight Fires Long-Term Retardants, Foams, and Gels Protecting houses with PLI's Fire-Fighting Module in the arid Western U.S. poses special challenges; particularly as to the best strategy and the most appropriate chemicals. With temperatures during fire season in many areas greater than 90º F. and humidities in the range of 10 - 15%, water evaporates quickly. The length of time from when the chemical is applied until the fire arrives at the property is a major factor as to whether the protection will be adequate. The chemicals used to fight fires in forest, brush, and grasslands fall into two categories: long-term retardants and short-term retardants or suppressants. Long-term retardants are effective after the water evaporates. They remain effective until removed by rain or erosion. In the arid Western U.S. this may be weeks or months. They are used for "indirect attack" whereby a barrier zone is created to limit the spread of the fire. In contrast, foams are used to "directly attack" fires. These are short-term retardants. They are very effective in putting out fires, but they lose their effectiveness after a quarter of an hour or so as water drains from the foam, the air bubbles burst, and the foam collapses. Another type of product, gel, is suitable for protecting houses and other structures. It may last for a day under humid conditions, but only for an hour or less under extremely hot and dry conditions in direct sunlight with a wind blowing. The protective layer of polymer gel can be rehydrated by applying a fine mist of water droplets. The combination of creating a barrier zone around a house with a long-term retardant and covering the house with a protective coating provides additional protection. Fire Retardants and Barrier Zones The recommended barrier zone or defensible zone around a house is at least 30 feet wide if the site is level and up to 150 feet wide if the house has a steep slope with flammable material below it. Why use a long-term retardant to create the barrier zone? The wind driving the fire may die down, but come back hours or several days later bringing the fire. The long-term retardant will provide protection after the water evaporates. Also, the retardant works by creating a char. This is acceptable for vegetation on the outer perimeter of the barrier zone, but not suitable for the exterior of a house, if other alternatives are available. Retardant Chemistry and Combustion (Pyrolysis) The only long-term retardant approved by the U.S. Forest Service for application on the ground is Phos-Chek G-75, manufactured by Astaris LLC. It consists of 65% ammonium sulfate, 25% ammonium phosphate, 5% guar gum, and plus other additives. When flames reach a tree coated with this retardant, the retardant releases ammonia, sulphuric acid and phosphoric acid. The ammonia blocks the local oxygen supply. A major component in wood is cellulose, a polymer. The acids depolymerize the cellulose in the wood. The long polymer hydrocarbon chains are broken into smaller molecular fragments at temperatures far below normal combustion temperatures, producing char, rather than complete combustion. The reactions consume more energy than they generate. Thus, the treated parts of the tree are very slow to ignite. Treatment Dosage and Cost The recommended dosage ranges between 1 gallon per 100 square feet for grassland to 8 gallons per 100 square feet for dense vegetation with trees and brush. PLI's Fire-Fighting Module has a 400 gallon water tank, which can treat a 30 foot zone around most houses. Creating a larger zone may require additional water; either from a source on the property or another tankload brought in by helicopter. The cost of the chemical is less than $1 per gallon of mix. Environmental Impact Ammonium phosphate is commonly used as fertilizer. After the fire danger has passed, retardant should be hosed off of trees, shrubs, and other landscaping. Increased growth of grass and weeds can be expected as can minor "fertilizer burns" on certain shrubs and trees. As retardant is flushed into ponds, streams, and reservoirs there may be significant impact on aquatic life (due to the presence of ammonia). Useful Links to Other Sites Wildland Fire Chemicals - introduction from US Forest Service List of USFS approved chemicals for fighting forest fires Ecological effects of foams and retardants Ecological effects of foams and retardants Home Site Map Products Fire-Fighting Module Mop-Up Foams Structure Protection Gels Forest Fire Contact Us Orders |