Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Fires start when a flammable and/or a combustible material, in combination with a sufficient quantity of an oxidizer such as oxygen gas or another oxygen-rich compound, is exposed to a source of heat or ambient temperature above the flash point for the fuel/oxidizer mix, and is able to sustain a rate of rapid oxidation that produces a chain reaction.
Forest fires are uncontrolled fires occurring in combustible vegetation. A forest fire differ from other fires by its extensive size, the speed at which it can spread from its original source, its potential to change direction unexpectedly, and its ability to jump gaps such as roads and rivers.
Water is currently the most frequently used fire-fighting medium. The extinguishing properties of water are based mainly on its effect in cooling the combustible material to a temperature below the ignition point of the material, by absorbing heat through conversion of water to water vapor.
Use of water as an extinguishing agent has a number of disadvantages. For example, during the extinguishing process, large quantities evaporate or flow away unused and may cause unnecessary water damage.
Use of water is particularly disadvantageous in fighting forest fires, because such fires are frequently preceded by a period of drought, and, accordingly, the ground has a particularly high water absorptive capacity. The waste of water is a very important aspect of forest fire fighting because a forest fire typically consumes the dry undergrowth (e.g., grass, foliage, and heather) and leads to individual crown fires which then unite.
Furthermore, since most forest fires occur in remote areas, aircraft are often employed. Fighting forest fires with aircraft involves the dropping of large quantities of water on the fire. However, by this method, as much as 80% of the load is wasted due to erosion before reaching the target, such that the aircraft must make a considerable number of trips in order to get the required amount of water on the fire to cool the vegetation to below its ignition point.
Numerous attempts have been made to improve water as a fire extinguishing agent. Thus, for example, the addition of substances which increase the viscosity of water have been described. These include cellulose derivatives, alginates or water-soluble synthetic polymers, such as polyacrylamides. Use has also been made of non-flammable mineral additives to the extinguishing water, e.g. water-soluble inorganic salts or water-insoluble materials such as bentonite or attapulgite [C. E. Hardy, Chemicals for Forest Fire Fighting, 3rd edition, Boston, 1977].
In special cases, such as when fighting forest fires, use has been made of mineral additives such as bentonite, attapulgite and water-soluble salts, as well as extinguishing water formulations mixed with alginates, which, after special preparation are frequently ejected from aircraft. Disadvantages associated with use of such additives include the high weight percentages of mineral additives generally required in order to achieve a sufficiently high level of thickening (e.g. 10 to 20% by weight); the corrosive action of certain salts such as sulfates or chlorides; and the possibility of undesired environmental influences, such as on fertilizing agents. Furthermore, the preparation of such thickened extinguishing agents generally requires special apparatus, particularly with respect to the mixing process. These agents generally cannot be applied using conventional fire extinguishing syringes and, such as in the case of alginate gums, do not adhere well to the target surfaces following spraying, particularly under the action of heat. Additionally, they frequently change their characteristics after even a short storage period and, after drying, sometimes leaving behind residues which are difficult to remove.
Other fire-fighting compositions are known in the art, which are aimed at either decreasing water consumption or prevention of re-ignition of fire, or both.
For example, suspensions for use in fire-fighting are known, comprising insoluble particles dispersed in a water-soluble polymer solution. Two types of such suspension are known: solid-liquid suspensions and gel-liquid suspensions.
Solid-liquid suspensions are described, for example, in U.S. Pat. Nos. 3,984,334; 4,037,665; 4,226,727; 4,234,432; and 5,861,106.
U.S. Pat. No. 4,652,383 describes a solid-liquid suspension composition comprising solid particles of vinyl polymer gelling agent (preferably a polyacrylate) and an ammonium compound suspended in a gelled liquid. Such a composition is not suitable for application using aerial equipment, and the polyacrylates are non-biodegradable materials.
U.S. Pat. Nos. 5,332,524 and 5,422,330 describe a fire-extinguishing solid-liquid suspension comprising water soluble poly(ethylene oxide) polymer for extinguishing Class A fire, and in association with fluoro-surfactant for extinguishing Class B fire. The composition is applied as a foam. The flow properties of the composition, the application mode and efficacy of extinguishing action are not disclosed.
U.S. Pat. No. 5,518,638 describes the use of thickened synthetic amorphous silica in water as a fire extinguishing and protection agent, using water-soluble polymers such as polyethylene glycols, polypropylene glycols, and their derivatives as thickening agent.
U.S. Pat. Nos. 4,971,728; 6,322,726; and 6,019,176 disclose chemical concentrates adapted for dilution with water to produce long term fire suppressants specially adapted for aerial application to suppress wild land fires, using guar gum and its derivatives as thickeners and flow conditioners. Disadvantages of these compositions include the fact that the polysaccharides used are very expensive, and the preparation of the aqueous solutions is difficult, requiring specialized equipment.
Gel-liquid compositions include those in which the gel phase comprises cross-linked synthetic polymers, known as super absorbent polymers (SAPs). Gels function as short-term fire retardants, since their effectiveness is due to their water content, such that upon evaporation of all the water, the gels are no longer effective.
U.S. Pat. No. 3,758,641, describes the use of a water-swellable, water-insoluble polymer gel comprising a crosslinked polymer or crosslinked copolymer of acrylamide, an acrylate salt, vinyloxazolidinone, vinylpyrrolidinone, a methacrylate salt, or a styrenesulfonate salt, or a copolymer of styrene and maleic acid, which has been crosslinked by reaction with a glycol. The crosslinked gel is mixed with a water-soluble synthetic cationic polymer in order to promote adhesion to cellulosic material. The application mode of the composition is not specified.
U.S. Pat. No. 4,978,460 describes the use of solid polymer particles of polyacrylate gel encased in a water-soluble release agent to extinguish fires. The time taken for these solid granular particles to expand upon absorption of water is longer than practical for the water to be retained in a fire hose. Additionally, in order to achieve the desired water absorption, 200 grams of gel per liter of water is required.
U.S. Pat. No. 5,190,110 describes absorbent polymers comprising discrete particles of insoluble sodium polyacrylate dispersed in a water miscible medium to be incorporated into water.
U.S. Pat. No. 5,849,210 describe a method of preventing a combustible object from burning by contacting the combustible object, before or during burning, with an aqueous composition comprising a water-insoluble superabsorbent polymer (SAP) and water.
The above prior art gel-liquid compositions are not suitable for use against forest fires, since the compositions must be washed away after use, are not biodegradable, and do not prevent re-ignition of the fire after water evaporation.
Another problem encountered in fighting a forest fire is an inability to precisely determine which objects, or areas, have been sprayed and which have not. This is an especially difficult problem encountered in aerial fighting of forest fires. Effective fire fighting requires that all objects or areas of interest are sprayed, while minimizing double spraying of some objects or areas.
U.S. Pat. No. 7,670,513 discloses a fire-fighting composition comprising a superabsorbent polymer (polyacrylate sodium salt); a soluble or dispersible colorant; an additional opacifying agent; and water. The colorant is selected such that its color is in contrast to the color of the combustible objects being treated.
Due to the solid, granular nature of the absorbent polymer particles used in prior art firefighting compositions, it is difficult, if not impossible, to use these polymers in certain applications. For example, if a natural source of water, such as a creek or a river, is to be used as the water source, it is impossible to pre-mix the polymer and batch add it to the water source, as necessary in traditional applications, in order to draw it off to use to combat fires. By pouring the additive-into a stream or river, most of the additive will simply flow past the point of suction of the water for use in combating fires.
Likewise, because of the particulate nature of the known water-absorbent polymers used in firefighting compositions, use of such polymers in standard firefighting hoses with standard equipment is nearly impossible. The solid nature of the polymers promotes particle agglomeration and subsequent blockage of the flow of the water. Alternatively, it is also sometimes necessary to provide pumps and spray nozzles adapted for handling such solid granular particles (see, for example, U.S. Pat. No. 3,758,641).
Some of the disadvantages associated with use of SAP in gel-liquid firefighting compositions can be overcome by the use of emulsions.
U.S. Pat. No. 6,296,781 discloses a fire extinguishing emulsion containing emollient; emulsifier; dispersant; oxygen depleting substance; radical scavenger; and oxygen competitor, in water acting as a carrier.
U.S. Pat. Nos. 5,989,446 and 6,245,252 disclose a water additive containing a cross-linked, water-swellable polymer additive in a water/oil emulsion produced by an inverse phase polymerization reaction to be added to the firefighting water. The polymer is a co-polymer of acrylamide and acrylic acid derivatives.
We have observed that such formulations may include chemical combinations that are dangerous to plants, and that various compounds disposed in the formulations may be substantially non-degradable or insufficiently degradable, particularly at ambient conditions.
We have further observed that the formulations do not contain a long term flame retardant, such that the underlying vegetation may be disadvantageously re-ignited after the water is evaporated.
U.S. Pat. No. 7,033,526 describes a firefighting composition in the form of a gel containing urea or a urea derivative that retains water and releases CO2 upon heating. The composition also includes a rheology modifier. Disadvantages of these compositions are similar to those of the above-described emulsions.
U.S. Pat. No. 7,189,337 describes a fire-fighting additive having a cross-linked, water-swellable polymer and a vegetable oil dispersion. The additive is added to firefighting water to form a gel. The use of such an additive may have the same disadvantages as the use of various traditional synthetic polymers.
The inventors have perceived a need for further improvements in fire-fighting formulations and methods, and the subject matter of the present disclosure and claims is aimed at fulfilling this need.