Fire extinguishing system utilising fluorine-free foam formation delivered via axial-flow hollow-cone nozzle

Abstract

A fire-extinguishing system comprising: (i) a tank suitable for containing a fluorine-free foam-precursor liquid material; (ii) a fluorine-free foam precursor liquid material; and (iii) one or more axial-flow hollow-cone nozzle(s), and a method of extinguishing a fire comprising directing a fluorine-free foam derived from this fire-extinguishing system onto said fire or fuel thereof. The foam-precursor liquid material preferably is or comprises a composition derived from the reaction product (RP2) of a modified acid with one or more compounds selected from an ethyleneamine, alkali metals, ammonia and alkanolamines, wherein said modified acid is the reaction product (RP1) of a complex alkyl compound with an acid selected from polyphosphoric acid, phosphoric acid, sulfuric acid and sulfonic acid, and wherein said complex alkyl compound is selected from ethoxylated fatty alcohols, fatty alcohols, ethoxylated alcohols, ethoxylated phenol, ethoxylated alkylphenol, alkyl polyglycoside and alkyl aryl.

Description

Fire Extinguishing System Utilising Fluorine-Free Foam Formation Delivered Via Axial-Flow Hollow-Cone NozzleField of InventionThe present invention relates to fire-extinguishing systems for generation and delivery of fluorine-free flame-retardant foam via an axial-flow hollow-cone nozzle, and to methods of extinguishing a fire using the same. The invention may be used against any type of fire and is of particular utility against lithium-ion battery (LIB) fires and tire fires.Background of the InventionFire extinguishers are currently designed to be different for different types of fire class. Few people outside of the fire-fighting community understand the classes of fires and fire extinguishers and it is likely that a lay person responding to a fire will use the first fire extinguisher available without checking whether it is the correct extinguisher for the fire.UL Solutions is an organization which handles fire extinguisher testing and certification, including certification to all key standards pertaining to fire extinguishers, specifically for carbon dioxide, dry chemical, foam, halocarbon clean agent and water-type fire extinguishers. UL Solutions has defined the fire classes as A (such as wood, cloth, paper, rubber, and many plastics.), B (liquid fuels such as gasoline, alcohols, diesel, etc.), C (electrical), D (metals such as Li and Mg), and K (cooking oils). LIB fires are not classified in the UL Solutions classification system as they have characteristics of classes A, B and D. Tire fires are also unclassified as they have characteristics of mostly A and B. There is no test defined by UL Solutions or any other agency for extinguishing LIB fires and tire fires. LIB fires and tire fires are much more complex than a magnesium metal or a gasoline fire or diesel fire. In the field, firefighters often refer to LIB fires and tire fires as being class B fires. Typically, LIB fires and metal fires are usually fought with water by fire departments. The water method requires a lot of water resulting in secondary damage and pollution from run-off water fouled with various chemicals and debris.LIBs are responsible for initiating many large fires due to malfunctioning LIBs on many devices such as electric vehicles (EV), electric bikes (e-bikes) and cell phones. There are also reports that reignition is a major problem for EVs where reignition sometimes occurs the next day. Thus, there is a need to disarm the LIB to eliminate reignition. There is a need for a reliable way to extinguish a LIB fire and then be on standby while the LIB is disarmed. A LIB fire cannot be considered as extinguished until the LIB cells are disarmed. A LIB is most dangerous when fully charged or over-charged. A fully discharged LIB is less dangerous as it is difficult to ignite but may not be completely disarmed.International application WO-2023 / 009675-A from the present inventors discloses a fluorine-free foam (FFF) composition (also referred to herein as the "PNSF" foam composition) derived from the reaction product (RP2) of a modified acid with one or more compounds chosen from a group comprising an ethyleneamine, alkali metals, ammonia, and alkanolamines. The modified acid is the reaction product (RP1) of a complex alkyl compound (CA) with an acid chosen from a group comprising polyphosphoric acid (PPA), phosphoric acid, sulfuric acid and sulfonic acid. The complex alkyl compound is chosen from a group comprising ethoxylated fatty alcohols, fatty alcohols, alcohols, ethoxylated alcohols, ethoxylated phenol, ethoxylated alkylphenol, alkyl polyglycoside, and alkyl aryl. The composition may further comprise a thickener, glycerin and / or water. The PNSF foam composition was found to be effective on Class B fires when used with apparatus such as pressure washers, foam cannons and multiple-nozzle booms. The composition was found to have good foaming properties, to self-intumesce and to have good flame-retardant properties. It is also reported that PNSF foam compositions having surfactant and flame-retardant properties are applicable to the following applications: 1) flame retarding polymers which requires the compound to have little moisture sensitivity and melt into the polymer; 2) stopping a wildfire where the surfactant property promotes adhesion and spreading on class A fuel, and 3) foam for fuel fires where the foaming is essential to stop re-ignition or burn-back resistance once the fuel fire is extinguished.However, there remains a need to provide a fire extinguisher that is applicable to all classes of fires, as well as improving firefighters' ability to tackle LIB fires and tire fires.Against this background, a new method has been developed to deal with all fire types, and particularly to improve firefighting against LIB fires and tire fires.Summary of the InventionThe inventors have observed that the PNSF compositions of WO-2023 / 009675-A can have unexpectedly high expansion ratios when delivered via an axial-flow hollow-cone nozzle. The high expansion enables the foam to extinguish all types of fires. The present invention represents an unexpected improvement on the invention disclosed in WO-2023 / 009675-A. Thus, the pressure washer method disclosed therein which requires high pressures (1500-4000 PSI) may be replaced with lower pressure methods and equipment which utilize an axial-flow hollow-cone nozzle, such as a pneumatic atomization axial-flow nozzles that contains a swirl insert. These nozzles unexpectedly enable expansion ratios of at least 10 and preferably exceeding 30, which enable the PNSF foam technology to be applicable to all classes of fires, and particularly LIB fires and tire fires. The high expansion ratio allows the PNSF foam compositions to be much more effective in fire-fighting applications compared to the lower expansion ratios achievable with the existing technology. The high expansion ratio is a particular and unexpected feature of axial-flow hollow-cone nozzles when used to deliver the PNSF foam compositions.According to a first aspect of the present invention there is provided a fire-extinguishing system comprising:(i) a tank suitable for containing a fluorine-free foam-precursor liquid material,(ii) a fluorine-free foam precursor liquid material; and(iii) one or more axial-flow hollow-cone nozzle(s).According to a second aspect of the present invention, there is provided a method of extinguishing a fire comprising directing a fluorine-free foam derived from the fire-extinguishing system of the first aspect onto a fire and / or a fuel of a fire, wherein said fuel may comprise flammable and / or inflammable materials. Preferably, the foam is directed onto the bottom of the flames in closest proximity to the fuel.Detailed description of the inventionThe fluorine-free foam-precursor liquid materialThe fluorine-free foam (FFF) precursor liquid material is preferably selected from the foam precursor compositions disclosed in WO-2023 / 009675-A, the disclosure of which is incorporated herein by reference. Preferably the fluorine-free foam precursor liquid material is or comprises a composition derived from the reaction product (RP2) of a modified acid with one or more compounds selected from an ethyleneamine, alkali metals (particularly sodium or potassium), ammonia and alkanolamines (and preferably selected from an ethyleneamine). The modified acid is the reaction product (RP1) of a complex alkyl compound (CA) with an acid selected from polyphosphoric acid (PPA), phosphoric acid (PA), sulfuric acid (SA) and sulfonic acid.Ethyleneamines are defined here as ethylene diamine and polymeric forms of ethylene diamine including piperazine and its analogues. A review of ethyleneamines can be found in the Encyclopedia of Chemical Technology, Vol 8, pgs.74-108. Ethyleneamines encompass a wide range of multifunctional, multi reactive compounds. The molecular structure can be linear, branched, cyclic, or combinations of these. Examples of commercial ethyleneamines are ethylenediamine (EDA), diethylenetriamine (DETA), piperazine (PIP), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), and pentaethylenehexamine (PEHA). Other ethyleneamine compounds which are part of the general term ethyleneamine (EA) as defined herein include aminoethylenepiperazine (EAP), 1,2-propylenediamine, 1,3-diaminopropane, iminobispropylamine, N-(2-aminoethyl)-1,3-propylenediamine, N, N'-bis-(3-aminopropyl)-ethylenediamine, dimethylaminopropylamine, and triethylenediamine. Said ethyleneamine is preferably selected from EDA, DETA, PIP, TETA, TEPA and PEHA. ETA or DETA are particularly preferred, and particularly DETA.Alkanolamines are chemical compounds that contain both hydroxyl (-OH) and amino (-NH2, -NHR, and -NR2) functional groups on an alkane backbone, such as for example, triethanolamine (TEA) and 2-amino-2-methyl-1-propanol (AMP).The amount of said compound selected from ethyleneamine, alkali metals, ammonia, and alkanolamines is chosen such that 10% by weight of said reaction product RP2 in water exhibits a pH of at least 3.5 and less than 8.5 and preferably from 5.5 to 8.0.The polyphosphoric acid (PPA) preferably has a grade of from 105% to 118%. The PPA-containing FFF precursor materials exemplified herein were made using PPA having a grade of 115%. PPA is available in various grades, the naming of which can be confusing as the percentage can exceed 100%. One hundred percent phosphoric acid contains 72.4% P2O5 as calculated from the formula weight ratio P2O5 / H3PO4. Similarly, pyrophosphoric acid (H4P2O7) contains 79.8% P2O5 as calculated from the ratio P2O5 / H4P2O7. The ratio of these P2O5 contents provides a relative phosphoric acid content, which for pyrophosphoric acid is 79.8% / 72.4%=110%. Due to high viscosity, PPA is difficult to pour and stir at room temperature, and it is easier to work with at temperatures above 60°C. All grades of PPA are useful in the present invention regardless of how formed.The concentrations of the phosphoric acid and the sulfuric acid are preferably each at least 80%. The preferred sulfuric acid has concentration of 96% to 98%. The SA-containing FFF precursor materials exemplified herein were made using SA having a grade of 96%.It is preferred that 10% by weight of said modified acid in water has a pH of less than 2.2.The acid is preferably selected from polyphosphoric acid, phosphoric acid and sulfuric acid. The preferred acid is polyphosphoric acid, since it exhibits relatively greater self-intumescence in the compositions of the present invention.The term "complex alkyl" is used in US-6696399, and the disclosure of such complex alkyls compounds is incorporated herein by reference. The complex alkyl compound (CA) is chosen from a group comprising ethoxylated fatty alcohols, fatty alcohols, ethoxylated alcohols, ethoxylated phenol, ethoxylated alkylphenol, alkyl polyglycoside and alkyl aryl. Preferably, the complex alkyl compound is an ethoxylated alcohol, preferably an ethoxylated alcohol with length C9-C13 and the degree of ethoxylation (n) is at least 3 and as high as 9.Ethoxylated alcohols belong to the class of compounds which are synthesized via the reaction of an alcohol (ROH) and ethylene oxide (C2H4O): ROH + n C2H4O → R(OC2H4)nOH with n preferred to be 1-18. Where R is a fatty alcohol, the reaction produces an ethoxylated fatty alcohol, i.e. a molecule which contains a carbon-rich fatty alcohol part and a hydrophilic polyoxyethylene chain, for instance having formula ROCH2CH2OH or RO(CH2CH2O)nH. Fatty alcohols (or long-chain alcohols) are usually high molecular-weight, straight-chain primary alcohols, typically derived from natural fats and oils, and having as few as 4–6 carbons or as many as 22-26 (i.e. the carbon chain length may be C4-C26). The hydrophilic component of such ethoxylated compounds is based on ethylene oxide (EO) or poly(ethylene oxide) (PEO).Stepan Co. provides a series of ethoxylated fatty alcohols, including Polystep® TD series, Makon® UD series, Makon® DA series and Makon® TD series. Makon® UD5 (5EO; i.e. an ethoxylation of n=5) has an MW of 394 and is dispersible in water and soluble at concentrations less than 10% by weight. Makon® UD6 (6EO) and Makon® UD8 (8EO) are soluble in water at concentration greater than 10% by weight. In general, as the amount of EO (ethylene oxide) in the molecule increases, the water solubility increases. Solubility will also vary with the particular fatty alcohol being ethoxylated. The Makon® TD series is ethoxylated tridecyl alcohol, the UD series is ethoxylate C11 branched alcohol, the DA series is ethoxylated C10 isodecyl alcohol.Alkyl polyglycoside is a biodegradable ingredient, for instance derived from plant starch and fatty alcohol from coconuts.The term complex alkyl phosphate ester (CAPE) refers to the compound formed by reacting a complex alkyl compound and phosphoric acid. Correspondingly, the term complex alkyl polyphosphate ester refers to the compound formed by reacting a complex alkyl compound and polyphosphoric acid. The term complex alkyl sulfate ester refers to the compound formed by reacting a complex alkyl compound and sulfuric acid. The term complex alkyl sulfonic ester refers to the compound formed by reacting a complex alkyl compound and sulfonic acid. In the case of the phosphate ester, the mono ester is R-O-P=O-(OH)2 and the diester is (R)O)2-P=O-(OH). The R group(s) is derived from the complex alkyl compound.As will be appreciated by the skilled person, corresponding formulae may be written for the other acids.The ratio by weight of the complex alkyl compound to said acid is preferably at least 0.01 but less than 20, and preferably at least 0.25 but less than 4 by weight. This ratio may be adjusted to achieve the desired viscosity and the desired foam expansion ratio. It will be appreciated that the appropriate ratio to achieve those objectives will vary with the identity of the complex alkyl compound and acid.The composition preferably further comprises water. Thus, the composition is preferably an aqueous composition.The composition preferably further comprises a thickener.Thus, the composition preferably further comprises water and a thickener. In order to improve the dissolution of the thickener into water, the composition preferably also comprises one or more organic solvent(s), particularly wherein the organic solvent is glycerin (preferably vegetable glycerin), which improves the wetting of the thickener so that it dissolves easily into water and thickens the composition. Thus, the composition preferably comprises water, thickener and one or more organic solvent(s), preferably wherein the organic solvent is or comprises glycerin, preferably vegetable glycerin. Thus, the composition preferably comprises water, thickener and glycerin (preferably vegetable glycerin).The water is present in the FFF precursor liquid material composition in an amount of 50 to 98% by weight. The amount of water in the FFF precursor liquid material may be adjusted to achieve the desired viscosity and the desired foam expansion ratio. It will be appreciated that the appropriate amount of water to achieve those objectives will vary with the precise identity and amounts of the components of the liquid material composition.Thickeners (also referred to as thickening agents) are used to the increase the viscosity of the foam precursor liquid material and / or the stability of the foam precursor liquid material or the foam. Thickening agents are well known in the art, and include polyacrylamides, cellulosic resins and functionalised cellulosic resins, polyacrylic acids, polyethylene oxides and the like. One class of thickener that is preferred for use in the present invention is the class of water-soluble polyhydroxy polymers, especially polysaccharides. The class of polysaccharides includes a number of water-soluble, organic polymers that can increase the thickness, viscosity or stability of a foam composition. Preferred polysaccharide thickeners include polysaccharides having at least 100 saccharide units or a number average molecular weight of at least 18,000. Specific examples of such preferred polysaccharides include diutan, xanthan gum, scleroglucan, heteropolysaccharide-7, locust bean gum, partially-hydrolyzed starch, guar gum and derivatives thereof. Examples of useful polysaccharides are described, for example, in U.S. Pat. Nos. 4,060,489 and 4,149,599. These thickening agents generally exist in the form of water-soluble solids, e.g., powders. While they are soluble in water, in their powder form they can and typically do contain a small amount of adventitious or innate water, which is absorbed or otherwise associated with the polysaccharide. Xanthan gum is a microbial polysaccharide made from fermenting sugar with a bacteria called Xanthomonas campestris, which creates a gel that is dried and milled into a powder. The neutral-tasting gum acts as a powerful thickening, emulsifying, and stabilizing agent.Diutan gum (e.g. KELCO-VIST™ diutan gum) offers a new and versatile approach to formulating new, high-performance products with consistent quality and higher profitability. It is an exceptionally efficient stabilizer with strong pseudoplasticity and other unique properties that benefit a wide range of industrial applications such as liquid laundry detergent. Diutan gum is a polysaccharide used for applications that require very high suspending characteristics such as cement, gypsum, mortar, agricultural chemical applications, and oilfield drilling fluids, liquid detergent among others. Kelco-Сагетм diutan gum is a water-soluble biopolymer produced by fermentation designed specifically for use in cosmetics and other personal-care applications. Kelco-Care™ diutan gum has exceptionally good thermal stability, is compatible with high levels of alcohol and polyols, and is readily biodegradable.The thickener is preferably selected from xanthan and diutan.It is surprising that thickeners such as xanthan is not problematic with the FFF precursor liquid materials and axial-flow hollow-cone nozzles of the present invention, since thickeners such as xanthan have previously been observed to cause foam solutions sprayed with a MILSPEC nozzle or foam cannon to exhibit low expansion ratios and low spreading coefficient.Organic solvents useful in the present invention include but are not limited to glycols and glycol ethers including diethylene glycol n-butyl ether, dipropylene glycol n-propyl ether, hexylene glycol, ethylene glycol, dipropylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, propylene glycol, glycerin (or glycerol), polyethylene glycol (PEG) and sorbitol. Said one or more organic solvent(s) preferably comprises or consists of glycerin. Preferably the glycerin is vegetable glycerin (VG). The use of vegetable glycerin is preferred over synthetic glycol ethers, as used in WO-2023 / 009675-A. As described hereinabove, the organic solvent should be suitable as a wetting agent for the thickener in water. In practice, the method to prepare the compositions described herein is preferably such that the organic solvent (preferably VG) is mixed with the thickener to wet it before adding the thickener to water. Only a small amount of the organic solvent is needed, and preferably organic solvent is present in an amount which is no more than 5.0 wt%, preferably no more than 3.0 wt%, preferably no more than 2.0 wt%, preferably no more than 1.0 wt%, and preferably no more than 0.5 wt% by total weight of the foam precursor liquid composition.The amount of thickener depends on the desired concentration of the modified acid / ethyleneamine reaction product in the FFF precursor liquid material. Where relatively higher concentrations are desired, then relatively lower amounts of thickener are present in order to achieve a viscosity with the ranges described herein.The amount of organic solvent (preferably glycerin, preferably vegetable glycerin) is typically 0.5 to about 2.0 times the amount of thickener by weight. Where two or more organic solvents are present and / or wherein two or more thickeners are present, this weight ratio applies also to the total amount of organic solvent and / or the total amount of thickener.The FFF precursor liquid material may further comprise other agents and additives as known to those skilled in the art.The foam precursor liquid material optionally comprises a surfactant. Surfactants are compounds that lower the surface tension (or interfacial tension) between two liquids, between a gas and a liquid, or between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, and dispersants. In the present invention, surfactants are compounds that lower the surface tension (or interfacial tension). Surfactants are included in the foaming compositions to facilitate foam formation upon aeration, to promote spreading of drainage from the foam composition as a vapor-sealing aqueous foam over a liquid chemical, and, where desired, to provide compatibility of the surfactant with sea water. Useful surfactants include water-soluble hydrocarbon surfactants and silicone surfactants, and may be non-ionic, anionic, cationic or amphoteric. When these surfactants are dissolved in water, negatively charged particles (i.e. anions) are created. Particularly useful surfactants include hydrocarbon surfactants which are anionic, amphoteric or cationic. Preferred anionic surfactants have a carbon chain length containing from about 6 to about 12 or up to 20 carbon atoms. As used herein, an amphoteric surfactant is a molecule that contains both a positively charged atom and a negatively charged atom. Surfactant molecules may include polymeric components and may also include a counter ion(s) such as sodium and ammonium; however the counter ion is not considered to be one of the positively or negatively charged atoms that qualifies the molecule as being an amphoteric surfactant. The amphoteric surfactant may be a betaine surfactant.The FFF precursor liquid material preferably exhibits a viscosity from 10cP to 400cP, more preferably 75cP to 300Cp, and most preferably 150cP to 275cPto as measured with a Brookfield DVplus viscometer at 60 RPM, #2 spindle, and 70°F. Preferred viscosities are those which can be sprayed at the pressure (preferably 50-110 PSI, more preferably 65-110 PSI, most preferably 65-100 PSI) of the delivery apparatus used to deliver the fluorine-free foam to the fire. The viscosity of the FFF precursor liquid material is preferably controlled as described herein to achieve the desired foam expansion ratio.The expansion ratio of the foams of the present invention is at least 10, preferably greater than 15, preferably at least 20, preferably at least 30, preferably at least 35, and typically no more than 70. Thus, the expansion ratio of the foam is preferably 15 to 70, preferably 20 to 70. The high expansion foams of the present invention spread quickly over the target area, i.e. they have a high spreading coefficient. It is considered that the high expansion ratio enables quick spreading because the expanded foams are very light in weight. Foams having an expansion ratio of less than 10 have a lower spreading coefficient. Given that conventional fluorine-free foam compositions have previously been observed to exhibit poor spreading coefficients, it is unexpected that the foam compositions of the present invention were found to spread quickly. The inventors attribute the improved spreading coefficients to the higher expansion ratios. Preferably, the spreading coefficient in respect of the present invention is such that a 28 sq.ft. circular tank can be covered with foam to a thickness of 4 inches in less than 10 seconds when sprayed at a rate of 2-3 gallons per minute.The expansion ratio of the foam is calculated as VF / VLM X 100, where VF is the volume of the expanded foam and VLM is the volume of the foam precursor liquid material from which the foam is derived. The expansion ratio of the foams may be measured according to NFPA STD 412, as taught in MIL-F-24385F. Preferably, expansion ratio is conveniently calculated by filling a 19 L bucket with foam and measuring the weight of the foam in this volume. The density of the foam precursor liquid material is measured by conventional means. The initial volume VLM can therefore be calculated, thereby allowing the expansion ratio to be calculated. Typically, foam precursor liquid materials having a concentration by weight of 3% to 7% have a density in the range of from about 1.05 to about 1.1 g / ml.The foams may also be characterized by their "drain time”. As used herein, “drain time" means the time for 25% of the initial foam volume to collapse. The measurement is conducted by filling a 19L bucket with foam, and the time taken for the foam to collapse by about 25% of its initial volume is measured.While the parameter of "spreading coefficient" is given a quantitative definition in the context of the MIL F 24385F test referred to herein, the term is instead used herein in a qualitative sense. The inventors simply observe the relative speeds at which the tested foams spread. High expansion foam (particularly those with expansion ratios exceeding 35) floats well above the liquid and glides across the fuel. Medium or low expansion foams (particularly with expansion ratios of less than 8) do not spread fast. In a 28 sqft fire test, the difference is easily observable between low / medium expansion ratios and high expansion ratios.The FFF precursor liquid material is preferably a solution, preferably an aqueous solution.The FFF precursor liquid material is suitably formed by reacting said complex alkyl compound with said acid to form said modified acid. The reaction to produce said modified acid is preferably performed with heating, preferably at a temperature from room temperature to 400°F. Next a thickener (e.g. xanthan) is dispersed in an organic solvent (preferably glycerin, preferably vegetable glycerin). The ethyleneamine (such as DETA) is then added to the thickener / solvent mixture to form the base, which becomes quite warm. Water is then added to this mixture in amounts sufficient to cause the base to thicken, for instance to provide a consistency similar to molasses. The modified acid is then added to the base, the solution heats up substantially driven by the acid base reaction. Additional heat may optionally be supplied to drive the reaction forward but the inventors have not found the addition of heat necessary. More water is typically added to form the final FFF precursor liquid material at the desired concentration. Where relatively higher target concentrations of the modified acid / ethyleneamine reaction product are desired, it is preferred that relatively lower amounts of thickener be present in the mixture, in order to achieve a viscosity in the ranges described herein.The FFF precursor liquid materials described herein exhibit flame retardancy, foaming properties and surfactant properties. The FFF precursor liquid materials described herein preferably also exhibit the property of absorbing Li radicals and fluoride radicals.The FFF precursor liquid material is preferably formed from ethoxylated alcohol, an acid selected from PPA, PA and SA, and said ethyleneamine (preferably EDA, DETA, PIP, TETA, TEPA and PEHA, and preferably DETA). Such materials exhibit particularly good foaming property and flame retardancy.The PPA-containing FFF precursor liquid materials have a complex composition. The complexity is in part due to the composition of polyphosphoric acid which inherently contains some orthophosphoric acid as well as pyro, tripoly, and longer chains depending on grade. Substantial steric hindrance is likely during esterificaton of long-chain PPA and so it is likely that some of the phosphorous atoms are not associated with an ester bond. Long-chain PPA also has fewer bonds available for forming esters. The orthophosphoric fraction of PPA would be expected to form ester bonds. Commercially available ethoxylated alcohol phosphate esters have a pH of about 2.0 to 2.5, whereas the complex alkyl-polyphosphate reaction product described herein typically exhibits a pH of less than 1.95, indicating relatively fewer ester bonds. It is possible that the primary reaction for some complex alkyl compound is solvating the PPA. As such, the present invention encompasses liquid materials formed by dissolving complex alkyl compound in PPA with heat if necessary to form a solution with an unknown amount of formal ester bonds, which are likely mono-ester bonds, optionally with some di-ester or tri-ester bonds (although there may be no di-ester or tri-ester bonds).The inventors have found during fire-testing that the FFF precursor liquid materials described herein exhibit excellent fire-retardancy for a wide range of fires, including all of class A, class B, LIB fires and tire fires. For instance, a 7wt% (7wt% of chemical components and 93 wt% water) FFF precursor liquid material derived from a modified acid formed from 125g PPA or SA to 175g ethoxylated C12 alcohol (MW of 394 and ethoxylation n=5, MAKON® UD5) performs very well for class A, class B, LIB fires and tire fires. The optimum relative concentrations of each component may depend on the fire type. The inventors have observed that a fire extinguisher containing such a 7 wt% solution and equipped with the axial-flow hollow-cone nozzle described herein, and operated at a tank pressure of 50-110 PSI (preferably 65-110 PSI, most preferably 65-100 PSI), provides a foam expansion ratio of over 35 and is effective for a wide range of fire-types, including LIB fires and tire fires.As used herein:(i) The term organic solvent may mean one or more organic solvents.(ii) The term surfactant may mean one or more surfactants.(iii) The term thickening agent may mean one or more thickening agents.(iv) For the purposes of this specification, axial-flow hollow-cone nozzles have an insert. The terms insert and whirl insert are used interchangeably. An insert that does not create a rotation is not part of this invention.(v) Flame retardants are chemicals that are applied to materials to prevent the start or slow the growth of fire.(vi) The terms complex alkyl and complex alkyl compound are used interchangeably.(vii) Polyethylene glycol (PEG) is also known as polyethylene oxide (PEO) or polyoxyethylene (POE), sometimes depending on its molecular weight. The structure of PEG is commonly expressed as H-(O-CH2-CH2)n-OH and forms structure for ethoxylates.(viii) Alkyl phosphates belong to a group of organic compounds called organophosphates. They are esters of phosphoric acid H3PO4 and corresponding alcohol. Ethoxylated alkyl phosphates are formed with ethoxylated alcohols.(ix) Alkylphenols are a family of organic compounds obtained by the alkylation of phenols. The term typically refers to commercially important propylphenol, butylphenol, amylphenol, heptylphenol, octylphenol, nonylphenol, dodecylphenol and, optionally, related long chain alkylphenols.(x) A solution is a homogeneous mixture of two or more substances. A solution may exist in any phase. A solution consists of a solute and a solvent. The solute is the substance that is dissolved in the solvent.(xi) Soluble means the ingredient will dissolve and merge with the substance it is put into. In short, it will become a homogenous mass.(xii) Dispersible means the ingredient doesn't merge with the substance it is put into, but it can be dispersed (spread out evenly) if handled according to a specific method. A hazy solution forms but no separation occurs.(xiii) A gel is a semi-solid that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady-state.(xiv) A foaming agent is a material that facilitates the formation of foam such as a surfactant.(xv) A wetting agent is a chemical that can be added to a liquid to reduce its surface tension and make it more effective in spreading over and penetrating surfaces. As described hereinabove, the inventors use organic solvents such as glycerin to wet a thickener such as xanthan to promote its dissolution into water.(xvi) The pH of compositions will often be measured. Herein, the pH measurement is 10% by weight of the composition in water unless specifically indicated otherwise.(xvii) Compositions will be discussed and disclosed usually by %. It is always % by weight of composition and never by volume unless specifically indicated. The concentration of the compositions is calculated as the weight of the ingredients (for instance, the acid, the complex alkyl compound, the ethyleneamine (or alkali metal, ammonia or alkanolamine where present), the thickener and the organic solvent) divided by the total weight of the composition (i.e. said ingredients and water), multiplied by 100.(xviii) Intumescence of a coating, as used herein, refers to the swelling up when heated or subjected to flames, thus protecting the material underneath in the event of a fire. The identifying unique characteristic of the FFF foam precursor liquid materials referred to herein, particularly the polyphosphates, is that these compounds intumescence from heat or flames with no need for melamine or pentaerythritol; this property is referred to as self-intumescence.Fire ExtinctionAt a certain point in the combustion reaction, called the ignition point, flames are produced. The flame is the visible portion of the fire. If hot enough, the gases may become ionized to produce plasma. A flame is the visible, gaseous part of a fire. It is caused by a highly exothermic reaction taking place in a thin zone. Very hot flames are hot enough to have ionized gaseous components of sufficient density to be considered plasma. The high temperature of the flame causes the vaporized fuel molecules to decompose, forming various incomplete combustion products and free radicals, and these products then react with each other. Sufficient energy in the flame will excite the electrons in some of the transient reaction intermediates such as the methylidyne radical (CH) and diatomic carbon (C2), which results in the emission of visible light as these substances release their excess energy. As the combustion temperature of a flame increases (if the flame contains small particles of unburnt carbon or other material), so does the average energy of the electromagnetic radiation given off by the flame. The chemical kinetics occurring in the flame is very complex and typically involves a large number of chemical reactions and intermediate species, most of them radicals. A fire is an example of a chemical chain reaction. A burning candle or other fire is an example of a chemical chain reaction.The military MILSPEC test (MIL-F-24385F) is performed on a fire derived from 10 gallons of E0 gasoline in a 28 sq. ft. round tank and 15 gallons E0 gasoline in 50 sq. ft. round tank and also contains one inch of water. Ten gallons of gasoline added to a 28 sq. ft. tank will form a layer only 0.57 in thick. Gasoline is not soluble in water. Gasoline is a complex mixture of non-polar compounds such as long chained hydrocarbons etc. Water is a polar molecule. The general solubility rule is that "like dissolves like", meaning polar dissolves polar and non-polar dissolves non-polar.The fire performance is defined more specifically by U.S. MILSPEC MIL-F-24385F, which is used to certify the performance of aqueous fluorine-free foams (AFFFs) for use in US Department of Defence firefighting applications and probably the most stringent compared to other standards of performance (e.g., International Civil Aviation Organization-ICAO, Underwriters Laboratories Inc.-UL) used in civilian applications. The test procedure also defines a MILSPEC nozzle that is a foam Venturi nozzle. This nozzle will be referred to herein as a "MILSPEC nozzle" and is used in some of the comparative tests presented herein.Figure 1 illustrates the Venturi effect. From the upstream side (shown on the left-hand side of the figure), a relatively high pressure and relatively low velocity liquid (1) is forced from a relatively wide channel into a narrower channel, which reduces the pressure and increases the velocity of the liquid (2). The diameter of the restricted flow region (3) determines the magnitude of the change in the flow velocity and pressure.Figure 2 shows the conventional MILSPEC nozzle referred to hereinabove. This nozzle is not part of the fire-extinguishing system of the present invention. On the input side of the nozzle (left-hand side of the figure), a high pressure and low velocity liquid is forced from an input channel (4) into a channel (5) of narrower diameter, thereby reducing the pressure and increasing the velocity of the liquid. As the liquid flows out of the region of restricted diameter and into the larger downstream chamber shown in the figure, the pressure increases and the velocity decreases. Such flow causes a vacuum to be generated in the low-pressure region, which causes air to be sucked in from the air intake holes (6) of the MILSPEC nozzle which are located in said region of restricted diameter in which low pressure has been generated. The larger downstream chamber contains an element (7) which mixes the air and the liquid material (the solution) and form foam which is then expelled from the discharge orifice of the nozzle (on the right-hand side of the figure). The dimensions of the input channel, the narrower diameter channel and the downstream chamber determine the magnitude of the pressure and velocity differentials. The foam cannon and pressure washer apparatus discussed hereinabove operate on similar principles.Thus, high-velocity, low-pressure liquid in a narrow tunnel creates a vacuum pull when expanded into foam in a large chamber and re-converted to high-pressure, low-velocity flow.One of the tests performed under new U.S. MILSPEC is a fire extinction test that specifies that a 6-ft diameter gasoline pool fire (28 sq. ft.) be extinguished in less than 60 sec sprayed at a rate of 7.8 L / minute. After spraying foam for 90 seconds, a burning one ft diameter pan with one gallon of E0 gasoline is placed in the center of the tank. For burn-back resistance, one then measures the time before one half of the tank has ignited by gasoline fumes escaping through the foam barrier. The flame from the burning one ft diameter pan with one gallon gas contributes to degrading the foam so that fumes feed the flames. The flames from the pan are small at first but then get higher and more intense as the fumes from beneath the foam feed the flames. The test is passed if the time to ½ burning tank is less than 360 seconds. This test is called back-burn in that the foam layer needs to protect for 6 minutes from full reignition for 28sqft test. MILSPEC drain time is the time for 25% of the foam to collapse to liquid.The MILSPEC nozzle does not spray a large footprint. By the term "footprint", it is meant the size of the area covered by the sprayed foam solution. The nozzle sprays droplets that must coalesce together to form a blanket over the fire for extinguishment.Axial-Flow Hollow-Cone NozzlesWO-2023 / 009675-A reports that the compositions disclosed therein had exceptional properties in extinguishing gasoline fires when applied with a 4000 PSI pressure washer and foam cannon, as used in washing cars. The foam spray pattern looks like a fine mist. In the earlier invention of WO-2021 / 061677-A, it was demonstrated that similar compositions (i.e. similar to those in WO-2023 / 009675-A) applied as a fine mist had exceptional ability to react with flames. In the present work, the inventors sought obtain foam using a lower pressure, for instance at around 100 PSI, and in the form of a mist. However, using the standard MILSPEC nozzle referred to herein above and 100 PSI tank pressure, many varieties of the compositions disclosed in WO-2023 / 009675-A were attempted, but the inventors were unable to identify a formulation which could be applied at the lower operating pressure of 100 PSI but which reproduced the pressure washer / foam cannon results on 28 sq.ft.The present inventors tested over 50 different nozzle designs and unexpectedly identified a subset of nozzles which generated surprisingly advantageous fire-fighting performance in combination with the FFF precursor liquid materials defined herein, producing created high-expansion foam. The inventors made the following observations during the course of their experimental work:(i) The foam behavior does not resemble a mist of foam, and has an appearance which is very different to that produced by the pressure washer / foam cannon method of WO-2023 / 009675-A. After being expelled from the nozzles, the foam produced according to the present invention instead forms a large mass that spreads into a thick blanket, travelling quickly over the fire and extinguishing the fire, with excellent spreading coefficient.(ii) The foam produced according to the present invention was found to have exceptional performance in extinguishing a 28 sq.ft. gasoline fire, which was superior to that of the 4000 PSI pressure washer / foam cannon system reported in WO-2023 / 009675-A.(iii) The present invention generated a foam which exhibited a very high expansion ratio exceeding 40 at pressures in the range of 65 PSI to 100 PSI.(iv) The new subset of nozzles did not produce high expansion foam even with the FFF precursor liquid materials described herein when these nozzles and liquid materials were used with high pressure systems, such as the pressure washer / foam cannon system. It is thought that the high pressure causes the residence time within the nozzle to be too short.Thus, the high expansion foam generated by the present invention was found to be more effective in extinguishing a gasoline fire than the lower expansion foam obtained with a MILSPEC nozzle. The high expansion foam generated by the present invention is more effective and generates a larger footprint compared to the low expansion foam obtained with a pressure washer / foam cannon system.As used herein, the term “low expansion foam" is a foam with an expansion ratio of less than 7. A "medium expansion foam" has an expansion ratio from 7 to 15. A "high-expansion foam" has an expansion ratio of greater than 15, preferably at least 20, preferably at least 30, preferably at least 35, and typically from 20 to 70. The inventors have observed that the expansion ratio is sensitive to the pressure at the nozzle, the concentration of the foam precursor solution (i.e. the FFF precursor liquid material), the ratio of the components of the modified acid (i.e. the ration of the alcohol component to the acid component). For arrays or banks of multiple nozzles, the expansion ratio is sensitive to the number of nozzles. The expansion ratio may also vary with the spray rate.Normally, creation of foam requires an air aspirator or addition of compressed air to a stream of aqueous liquid flowing very rapidly through an aspirator to form foam. Such devices are often called Venturi pumps or eductors and are specially constructed to create foam. An eductor is a device that uses the Venturi effect to introduce foam concentrate into the water stream. Water coming in the inlet of the eductor is directed through a tapered section and out through a small orifice (often referred to as a Venturi orifice) into a larger chamber thus creating a low-pressure area within the chamber. A metering valve is attached to an inlet to this chamber and when open allows the higher atmospheric pressure outside the chamber to push the foam concentrate into the chamber. The foam concentrate then mixes with the water coming out of the Venturi orifice and the mixture travels out the reverse tapered section in the discharge end of the eductor. Compressed air foam (CAF) consists of adding compressed air to a solution of water and foam concentrate and then expelled from a hose at high volume. Foam cannon is used in the car wash industry to create foam with a pressure washer and uses the Venturi effect.These systems do not easily accommodate a boom. A foam solution containing substantial air does not travel long distances within a pressurized hose. The pressure washer / foam cannon approach at 4000 PSI allows only a small boom to be constructed (typically no more than a 12x6 inch array). The inventors observed that even such a small boom did not work with the MILSPEC nozzle operated at 100 PSI, i.e. did not produce adequate foam or firefighting performance with the fluorine-free foam precursor compositions described herein.The MILSPEC nozzle and the foam cannon are similar in that both have a conventional Venturi-type design. They differ in the dispersal cone and pressure of operation.The nozzles which are the focus of the present invention are axial-flow hollow-cone nozzles. A hollow-cone nozzle sprays fluids in a ring-like pattern around a given radius. Hollow-cone nozzles produce a good interface between air and the surface of the droplets. The axial-flow hollow-cone nozzle enables high expansion foam without the use of a conventional Venturi pump (eductor), compressed air, or a pressure washer and foam cannon. The axial flow hollow-cone nozzles which are the focus of the present invention do not contain an air intake hole located within the walls of a restricted-flow channel through which the foam-precursor liquid material passes at a relatively lower pressure.The axial-flow hollow-cone nozzles convert foam-precursor liquid materials (particularly aqueous solutions) to fine uniform atomization or fine mist. Atomization can be considered as the process by which a liquid flow is made to disintegrate into fine droplets or mist. Thus, the liquid forms atomized small droplets with maximized surface area embedded in air, which are then expelled from the nozzle as a mist. The skilled person understands that mists are typically defined by average droplet size, as discussed in WO-2023 / 009675-A (the content of which discussion is incorporated herein by reference). The inventors believe that the fine mist expands into foam bubbles upon being released at the nozzle. It is believed that larger droplets would not expand into such bubbles as effectively as small droplets, and there would be fewer such bubbles.A hydraulic nozzle is a spray nozzle that uses only liquid pressure to atomize and distribute a liquid (such as water or aqueous solution) by forcing it through a small orifice at high pressure, creating a spray pattern without the need for additional air or gas; essentially, it's a single-fluid nozzle used for spraying liquids in various applications like cleaning and cooling. Hollow-cone hydraulic nozzles have been found to produce the smallest average droplet size of any purely hydraulic nozzle. Such nozzles have been found to be suitable for applications where fine uniform spray is required, such as cooling and cleaning of gases, absorption processes, dust control and air humidifying. Axial-flow hollow-cone cones have been found to create the smallest droplets of any type of hollow-cone nozzle. The swirl inserts and spiral grooves of the preferred nozzles described herein ensure an efficient whirling of the liquid which creates uniform droplets throughout and maximizes the total exposed surface area. It was unexpected that such nozzles could form high-expansion foam from a foam-forming composition. Indeed, one of the objectives of the inventors' initial experiments was to create a fine mist of the foam precursor solution of WO-2023 / 009675-A using the hollow cone hydraulic nozzles, from which the inventors expected a decreased expansion ratio.In the fire-extinguishing system of the present invention, the axial-flow hollow-cone nozzle is suitable for receiving an axial pressurized input flow of the foam-precursor liquid material. Thus, the FFF precursor liquid material (not containing air) enters the top of the nozzle, most preferably at a pressure of 65 to 100 PSI, and then exits at the orifice as high-expansion hollow-cone foam, preferably with an expansion ratio of greater than 35. In the nozzles which are the focus of the present invention there are no additional holes for air intake as found in conventional Venturi-pump foam nozzles such as the MILSPEC nozzle described hereinabove, in which air intake holes are located in the outer walls (usually in the outer walls of the restricted-flow channels of narrower diameter). The preferred axial-flow hollow-cone nozzles which are the focus of the present invention do not therefore rely on a conventional Venturi nozzle of the sort shown in Figure 1. Instead, the inventors believe that the air needed to generate the high-expansion foam enters primarily at the downstream discharge orifice at the same time that the foam having the hollow-cone pattern exits the discharge orifice. It will be appreciated that foam expanded to a high expansion (for instance to an expansion ratio of greater than 35) could not be accommodated within the relatively small dimensions of the nozzle described herein.In general terms, the nozzle preferably comprises, in the following sequence (following the passage of the liquid material through the nozzle): an entry orifice, a flow-restriction section adapted to reduce the volume and pressure of the input flow of the foam-precursor liquid material while increasing its velocity, a swirl chamber and a discharge orifice.The entry orifice is preferably situated within a threaded stem section of the nozzle through which the foam-precursor liquid material enters the nozzle.The foam-precursor liquid material is preferably transferred into the entry orifice at an input pressure of 50-110 PSI.The flow-restriction section is preferably adapted to rotate the axial flow of the foam-precursor liquid material about the central axis of said nozzle.The flow-restriction section preferably comprises two or more grooves or channels (preferably offset channels) in a spiral or helical arrangement relative to the central axis of the nozzle. The grooves or channels are adapted to cause rotational flow of the liquid material relative to the central axis of the nozzle. Preferably the grooves or channels are adapted to further reduce the volume and pressure of the flow of the foam-precursor liquid material while increasing its velocity. Preferably the flow-restriction section comprises two grooves or channels. Alternatively, the flow-restriction section may comprise more than two grooves or channels, particularly four grooves or channels, and such a configuration is particularly suitable as the dimensions of the nozzle increase.In a preferred embodiment, the conduit(s) of the flow-restriction section comprises an upper part and a lower part, and optionally a middle part. The upper part is in fluid communication with the entry orifice and is adapted to reduce the volume and pressure of the input flow of the foam-precursor liquid material while increasing its velocity. It will be appreciated that the upper and lower parts are in fluid communication, optionally via the middle part where present. The lower part is in fluid communication with the swirl chamber and is adapted to cause rotational flow of the liquid material relative to the central axis of the nozzle as the liquid material flows through the nozzle. The lower part is preferably adapted to further reduce the volume and pressure of the flow of the foam-precursor liquid material while increasing its velocity. It will be appreciated that said grooves or channels are preferably located in said lower part of the nozzle. The (optional) middle part is adapted to initiate or promote rotational flow of the liquid material relative to the central axis of the nozzle and preferably further reduces the volume and pressure of the flow of the foam-precursor liquid material while increasing its velocity.The flow-restriction section opens into said swirl chamber. In particular, said grooves or channels are located in the flow-restriction section such that said grooves or channels open into said swirl chamber.The swirl chamber suitably has a wider bore than that of the flow-restriction section. The swirl chamber suitably has a wider bore than that of each of the grooves or channels. It will therefore be appreciated that the swirl chamber is adapted to increase the volume of the material flowing into it from the flow-restriction section.Preferably, the swirl chamber is adapted to propagate the rotational flow of the material relative to the central axis of the nozzle as it flows through the nozzle, thereby transmitting the material through the swirl chamber in a direction having both tangential and axial components relative to the cross-section of the swirl chamber. As described elsewhere herein, it is the inventors' understanding that the liquid material is converted into foam in the swirl chamber.The propagated rotational flow in the swirl chamber is entrained with air, wherein the air is derived from air drawn in from said discharge orifice. The discharge orifice preferably has a diameter which is no smaller than the diameter of the grooves or channels. A discharge orifice diameter which is smaller than that of the grooves or channels would cause some pressure build-up before the foam is expelled via the discharge orifice.It is the inventors' understanding that the foam-precursor liquid material becomes atomized in the swirl chamber. The atomization of the liquid which begins in the swirl chamber requires some air intake via the discharge orifice and more air intake upon exiting the discharge orifice.Preferably, the nozzle comprises a housing and a swirl insert, wherein the swirl insert comprises or constitutes or forms said flow-restriction section. Preferably the interior surface of a portion of the housing and the exterior surface of a portion of the swirl insert are threaded such that said nozzle comprises said swirl insert located in threaded engagement within said housing.In a particularly preferred configuration of the housing and swirl insert embodiment, the swirl insert comprises two or more grooves or channels in a spiral or helical arrangement relative to the central axis of said nozzle. Preferably, the grooves or channels are disposed in the exterior surface of the swirl insert, particularly such that the grooves or channels become enclosed along their longitudinal axis (but not at each end of the groove or channel) when the swirl insert is located within the housing, i.e. a groove in a portion of the exterior surface of the swirl insert together with a portion of the interior surface of the housing create the longitudinal boundaries of the groove or channel. This particularly preferred embodiment relates to axial-flow hollow-cone nozzles of the type manufactured by Lechler, and in particular the Lechler Series 216 nozzles.In a further preferred configuration of the housing and swirl insert embodiment of, the housing comprises two or more grooves or channels in a spiral or helical arrangement relative to the central axis of said nozzle. Preferably, the grooves or channels are disposed in the interior surface of the housing, particularly such that the grooves or channels become enclosed along their longitudinal axis (but not at each end of the groove or channel) when the swirl insert is located within the housing, i.e. a groove in a portion of the interior surface of the housing together with a portion of the exterior surface of the swirl insert create the longitudinal boundaries of the groove or channel. This preferred embodiment relates to axial-flow hollow-cone nozzles of the type manufactured by Spraying Systems, and in particular the TX Series nozzles.Thus, in a preferred embodiment, the housing and swirl insert together constitute said grooves or channels of the flow-restriction section.Thus, the preferred nozzles contain an integrated swirl insert which, when located in the housing, create one or more spiral or helical grooves or channels. The grooves or channels generate or contribute to the rotary flow of the liquid material within the nozzle, and preferably also reduce its volume and pressure and increase its velocity as described hereinabove. It is the inventors' understanding that the spiral or helical grooves create a liquid whirlwind effect, thereby generating small uniform droplets that can be absorbed faster, cool quicker and moisturize better. The spiral or helical grooves ensure an efficient rotation of the liquid, which creates uniform droplets in a ring pattern.The preferred axial-flow hollow-cone nozzles comprise three elements:1) A stem section (preferably a stem section which is threaded on part of its exterior surface) containing an entry orifice through which the foam precursor liquid material enters the nozzle under pressure and into a swirl insert. The stem section is screwed into the housing after insertion of the whirl insert into the housing.2) A housing (preferably a housing which is threaded on part on its interior surface) adapted to engage and contain a swirl insert (preferably a swirl insert which is threaded on a part of its exterior surface), wherein the housing contains a foam discharge section with an orifice.3) A swirl insert (preferably threaded on a part of its exterior surface) which is adapted to cause the foam precursor liquid material to swirl / rotate about the central axis thereof powered by the input pressure of the liquid material and adapted to convert the liquid material to a high-speed atomized liquid, wherein within the swirl insert the liquid material achieves a low-pressure compressed state and passes through a plurality of grooves in a spiral or helical arrangement relative to the central axis of said nozzle which are adapted to release at an angle into a larger volume (the swirl chamber) where rotation continues, with air intake from a discharge orifice, from which the foam is expelled as a hollow cone.The nozzles are sensitive to the viscosity of the FFF precursor liquid material, which may be adjusted as described herein.Advantageously, these nozzles enable foam precursor liquid materials to be sprayed within a multi-nozzle or boom configuration to generate sprays with large footprints. Moreover, these nozzles offer the ability to generate foam with large expansion ratio and to form large booms without high pressure.Preferred axial-flow hollow-cone nozzles include those made by Lechler company and Spraying Systems.In the inventors' extensive experimental work, the fire-fighting performance of the axial-flow hollow-cone nozzles (such as the Lechler Series 216 nozzle) was unexpectedly better than full-cone nozzles (e.g. Lechler Series 490 nozzle) and tangential-flow hollow-cone nozzles (e.g. Lechler Series 302 nozzle), particularly in combination with the FFF precursor liquid materials described herein. It is the inventors' understanding that all of these nozzles were designed to apply water as a mist.It will be appreciated that the nozzle is suitably made from metal (typically stainless steel) so that it has the thermal stability necessary to withstand firefighting applications. Plastics materials are unlikely to have the requisite thermal stability.The bore diameter of the nozzle (defined herein as the diameter of the orifice of the nozzle) is preferably at least 1.0 mm, preferably at least 2.0 mm, preferably at least 2.5 mm, preferably at least 3.0 mm, preferably at least 3.5 mm, preferably at least 4.0 mm. The bore diameter is preferably no more than 6.0 mm, preferably not more than 5.0 mm, preferably not more than 4.5 mm. Preferably the bore diameter is in the range of 2.0 to 6.0 mm, preferably 2.5 to 4.5 mm, preferably 3.0 to 4.5 mm.The flow rate of the axial-flow hollow-cone nozzle is preferably at least 2.0 l / min of water, preferably at least 3.5 l / min of water, preferably at least 5.0 l / min of water, and typically no more than 8.0L / min, typically no more than 6.0 l / min, as measured at a supply pressure of 5.0 bar (approx. 72 PSI).The flow rates typically vary with the size of the nozzles. It will be appreciated that flow rates increase as the bore diameter increases. Larger nozzles may contain more grooves / channels (e.g. four grooves / channels) and / or grooves / channels with larger diameters, thereby providing higher flow rates.The Lechler Series 216 axial-flow hollow-cone nozzles are most preferred for use in the present invention, and particularly the Lechler 216.566 nozzle. The Lechler Series 214, 218, 220, 226 and 2TR axial-flow hollow-cone nozzles are less preferred.Of the Spraying Systems nozzles tested in the present work, the inventors observed very good results with the TX Series nozzles, particularly the TX-10 and TX-26 nozzles. While these axial-flow hollow-cone nozzles produced foam with high expansion ratios, the expansion ratios was relatively lower than those obtained with the Lechler 216 nozzles for a given FFF precursor liquid material. For instance, expansion ratios of about 20 were achieved with the TX-10 and TX-26 nozzles for liquid materials which produced expansion ratios of over 30 with said Lechler nozzles. Both nozzles extinguished an 8 sq.ft gasoline fire in similar times.The combination of these nozzles with the preferred FFF precursor liquid materials having the preferred viscosity characteristics described herein generates surprising and advantageous performance resulting in foams of high expansion ratio. This advantageous technical effect is less pronounced with other materials. For instance, the present inventors sprayed SolbergTM RF3 foam solution (Perimeter Solutions Inc.), a leading commercial firefighting foam, using the axial-flow hollow-cone nozzles described herein (in particular the Lechler Series 216.566 nozzle). While expanded foam was generated, the expansion ratio was less than 10, and with inferior burn results compared to the preferred liquid materials having the preferred viscosity characteristics of the present invention.Axial-flow hollow-cone nozzles (e.g. series 216 nozzles) were originally designed for liquids such as water that do not form foam. It is believed that the creation of foam, particularly for firefighting, is a new application for these nozzlesFire-fighting applicationsThe fire-extinguishing system of the present invention comprises one or more axial-flow hollow-cone nozzle(s).The fire-extinguishing system of the present invention comprises a tank suitable for containing a fluorine-free foam-precursor liquid material. The tank is preferably a pressurized tank, preferably pressurized to 50-110 PSI, preferably 65-110 PSI, preferably 65-100 PSI. This pressure is referred to herein as the operating pressure of the fire-extinguishing system. Preferably the tank has a volume of at least 1.5 gallons, or at least 2.5 gallons. It will be appreciated that the fire-extinguishing system suitably further comprises a hose connecting the tank to the nozzle(s).The fire-extinguishing system of the present invention may comprise an array of two or more axial-flow hollow-cone nozzles. An array of nozzles may be arranged on a boom. The boom may be attached to a boom lift, a telescoping pole or a robotic arm. It is possible to design very large systems with many nozzles in order to apply a large footprint or spray width.The fire-extinguishing system of the present invention may be in the form of a sprinkler system, a hand-held fire extinguisher, a foam cannon or a quadcopter drone. In the case of a sprinkler system, the system may be located in a fixed position (such as in a building) or may be mobile (for instance affixed to a helicopter or other aircraft or in the form of a boom for use on land or water). A single 2.5-gallon fire-extinguisher suitably contains a single nozzle or may have multiple nozzles particularly given that the preferred nozzles described herein have relatively small dimensions.Drones used to spread liquids over agriculture crops are of use in spreading the foams of the present invention directly over a fire. The foams of this invention may be spread over the class A fuel in front of a wildfire fire so that the fuel burns either slowly or not at all. The sprayed class A fuel has the property of not forming embers when subjected to a flame. There are many manufacturers of drones, for instance, the JDI Agras T40 drone. The sprayed high expansion foam forms an insulating blanket against the heat so that the drone can get near or even above the fire. Typical payloads of the drone are around 20 kg, i.e. about 5 gallons of solution.The high expansion foam generated by the present invention has been found unexpectedly to be applicable to any fire type chosen, particularly fires categorized as Class A, B, D, K, Li-ion battery (LIB) fires, and tire fires.In general, foam does not project far distances like water. For maximum fire extinction performance, it is necessary to position the boom close to the fire, for instance via helicopter, quadcopter, or boom lift. The fire-extinguishing system of the present invention can replace conventional nozzles in water sprinkler systems, and spray foam instead of water. The fire-extinguishing system of the present invention can also replace fire-suppression systems for battery storage systems used on the green energy grid.Best practice for dry chemical fire extinguishers is such that the dry chemical is applied at the base of the fire. In the fire extinction system of the present invention, the foam can be directed to the base of the fire or the surface of the fire. For very large fires with high flame height, it is important to apply near the base of the fire so that the foam lands on the fuel and is able to start forming a protective coating. For optimal performance, the foam is not applied in a such way that the foam gets consumed by the flames.This new technology is of technical benefit as high expansion foam can now be formed at much lower and standard operating pressures.Characteristics of the preferred nozzlesThe primary and unexpected observation made by the inventors in their experimental work is that the foam precursor liquid materials described herein enter the axial-flow hollow-cone nozzle and exit as high-expansion foam many orders of magnitude greater in volume than the nozzle itself. The volume of the foam precursor liquid material entering the nozzle is much larger than the entrance to the grooves or channels in the nozzle. The inventors present below their analysis of the axial-flow hollow-cone nozzles and their rationalization of their utility in the present invention. This analysis is not intended to be binding. The nozzles will now be described in greater detail, and with reference to the figures.Figure 3 relates to an axial-flow hollow-cone nozzle of the type manufactured by Lechler, and in particular the Lechler Series 216. Figure 3 shows a swirl insert (10) with a spiral groove (11). The upper part of the swirl insert in Figure 3 is 11.8mm by 11.8mm and has a coarse thread (12) which is used to screw the swirl insert into the housing. The upper part of the swirl insert also contains a rectilinear channel (13) about 3 mm wide into which the foam precursor liquid material is passed. The middle part of the swirl insert exhibits 4 rounded face sections (about 2 mm width) and 4 flat face sections (about 4 mm width) which are configured in an alternating arrangement with each other. Figure 3 shows two rounded face sections (14a, 14b) and one flat face section (15). Relative to the rounded face sections of the swirl insert, the flat face sections of the swirl insert generate a wider gap between the exterior of the swirl insert and the interior rounded face of the housing. A spiral groove (11) in the exterior surface of the swirl insert extends into one or more flat face sections of the middle part of the swirl insert (in the swirl insert in Figure 3, there are two grooves and hence two flat face sections into which a groove extends). Each groove also extends into the lower beveled part (16) of the swirl insert, which fits against the interior surface of the housing. One or more flat face sections (there are two such sections in the swirl insert of Figure 3) may not be associated with a groove, in which case that face forms a pocket with the opposing interior surface of the housing. The middle part of the swirl insert allows foam precursor liquid material to rotate around the outside of the swirl insert in a generally circular manner before passing into the spiral grooves. Thus, the design shown in Figure 3 enables the liquid material to rotate before entering the grooves. The groove angle relative to the central axis of the nozzle facilitates both rotational motion and axial flow. The groove angle of the swirl insert shown in Figure 3 is about 45° to the central axis of the insert / nozzle.The curvature of the swirl insert is such that the housing and the swirl insert fit together snugly, the spiral groove pressed snugly against the housing wall. It is the inventors' understanding that the fit between the housing and the swirl insert is not air-tight and is not intended to be so. The fit is such that some air may slowly “bleed in" especially if there is a vacuum force to facilitate or drive the air intake. Velocity of the liquid may create some vacuum to cause some air to bleed into the swirling liquid via the loose fit with the housing.The underside of the swirl insert has a discharge orifice through which the foam is expelled in a hollow-cone shape. There is a gap (about 2 mm in the Lechler 216 nozzle) between the bottom of the insert and the discharge orifice, and this gap is referred to herein as the swirl chamber. Within this gap (the swirl chamber), air is entrained into the liquid material, contributing to foam generation. Without intending to be bound by theory, the inventors postulate that air entrainment may also occur before the liquid material enters the grooves. Air enables atomization. The atomized foam precursor liquid expands into foam bubbles with high expansion ratio as it is expelled from the nozzle (rather than within the nozzle).The nozzle in Figure 3 is about 20mm in diameter and about 36mm long and weighs about 99g. Each groove in the spiral insert is about 2.5 mm wide and about 7.5mm long with a volume about 25 mm³. Using an input pressure of 100PSI, the flow rate of a preferred FFF precursor liquid material as described herein through the nozzle was found to be about 4.5 L / minute.Figure 4 shows the flow pattern for an axial-flow hollow-cone nozzle (20) with the swirl insert (10) of Figure 3. The liquid material flows into a channel in the upper part of the swirl insert (which is about 3 mm wide), then flows down into the gap between the housing (21) and the flat and rounded faces of the swirl insert, thereby creating rotational flow around the middle part of the insert, then flows into the spiral grooves, then swirls into the swirl chamber and then exits via the orifice as foam in a hollow-cone shape (22). It is the inventors' understanding that: rotational motion of the liquid occurs in the middle section before the liquid stream enters the grooves; that rotational motion is propagated by the grooves; that rotational motion continues in the swirl chamber; and that the atomized droplets then exit as a foam in the form of a hollow cone.While such entrainment of air doesn't conform to the conventional picture of the Venturi effect as shown in Figure 1, the inventors consider that the air entrainment observed with these nozzles can be considered as a Venturi-like effect. In other words, it is the inventors' understanding that the passage of the liquid material into the relatively smaller volume of the grooves is accompanied by a pressure drop and a velocity increase in accordance with the general physics of the Venturi effect.Figures 5a and 5b show the elements of the Spraying Systems TX-10 and TX-26 nozzles. The two nozzles have identical dimensions except for the orifice diameters. These TX nozzles are 12.6 mm in diameter and 15.6 mm in length. The volume of these TX nozzles is about one fifth the volume of the Lechler 216.566 nozzle. Figure 5a shows a plan view from above of the nozzle (30) with the insert (31) located in the housing (32). Figure 5b shows a plan view of the housing (32) without the insert, showing spiral grooves (33a, 33b). Figure 6 shows the insert (31) itself in more detail. Figure 7 shows a schematic of the nozzles.While the TX Series nozzles have a different visual appearance to the Lechler nozzles of Figures 3 and 4, it is the inventors' understanding that they are structurally related insofar as they operate by the same Venturi-like effect. In the TX Series nozzles, the groove for transporting liquid material and creating foam is located in the interior surface of the lower portion of the housing, and these grooves (33a, 33b) can be seen from Figure 5b. The essentially cylindrical swirl insert screws into the housing and covers the opening to the two grooves. The two grooves are in fluid communication with the volume adjacent the entrances to the grooves which is created by the swirl insert between the interior surface of the housing and the exterior surfaces of the insert below its threaded portion. This is because the essentially cylindrical section of the insert below its threaded portion includes cavities at that location which are in fluid communication with the entry orifice of the nozzle and in fluid communication with the grooves, thereby creating a volume for foam precursor liquid material to flow through before entering the grooves in the interior walls of the housing. The flow restriction created by this configuration gives rise to the Venturi-like effect discussed hereinabove.Thus, in the TX Series nozzles, the foam precursor liquid material passes through the cavities in the essentially cylindrical section at the lower part of the insert beneath its threaded section, and is then transported away via the two grooves in the housing, thereby generating rotational motion, and the liquid material is then expelled from the grooves into a larger volume (swirl chamber) which creates a vacuum sufficient to draw air through the center region of the orifice. The rotational movement continues in this chamber and the foam then exits the orifice as a hollow cone.The two types of axial-flow hollow-cone nozzle designs described hereinabove look different but the principle underlying both designs is the same. The initial speed of the flow-stream is provided by the input pressure into the nozzle. It is the inventors' understanding that the nozzle design causes the liquid material to rotate fast enough to lower the pressure so that the liquid material can be driven through narrow grooves. The high velocity solution is expelled into a larger volume which creates vacuum.The only location from which to add air into the flow to enable vacuum creation and to generate the foam is from the center region of the orifice. Neither of these nozzle designs have a dedicated air intake hole nor a solution / air mixing element (and hence are unlike the conventional MILSPEC nozzle of Figure 2), i.e. neither of these nozzle designs involve the liquid material passing across air intake holes in a low pressure region of restricted flow which causes air to be drawn in through the air intake holes, with the liquid material and air being mixed in a downstream mixing chamber to generate foam. For this reason, neither nozzle conforms to the conventional design of a Venturi-pump. In the inventors' experimental work, poor performance was observed for full-cone axial-flow nozzles, compared to hollow-cone axial-flow nozzles, which supports the inventors' understanding that air is being entrained intake via the exit orifice, because the full-cone nozzle design impedes the entrainment of air via the exit orifice.Thus, it is the inventor's understanding that air is introduced into the foam precursor liquid material within the nozzle, where the introduced air and liquid material are mixed under pressure and transformed into a fine mist which is then expelled as a hollow-cone foam spray. In the inventors' experimental work, tangential-flow nozzles were also tested but these do not contain the swirl inserts or spiral grooves and fail to generate foam with high expansion ratios.Detailed Experimental Work and ExamplesIn addition to the experimental results reported hereinabove, further discussion of the inventors' experimental work is provided below. Unless otherwise stated, the axial-flow hollow-cone nozzle(s) used in the experiments were the Lechler 216.566 nozzles.As already indicated, the axial-flow hollow-cone nozzles were tried with a pressure washer (approx. 4000 PSI) where the FFF precursor liquid material passes through the nozzles with a very short residence time, which generated only low expansions ratios and poor foam quality. Experiments with the same FFF precursor liquid material sprayed using the MILSPEC nozzle at about 100 PSI only obtained expansion ratios of 6-14. The same FFF precursor liquid material sprayed at 100 PSI via the axial-flow hollow-cone nozzles unexpectedly generated an expansion ratio of greater than 50. Expansion ratios lower than 15 were always observed with MILSPEC nozzle or pressure washer / foam cannon regardless of the composition of the liquid material.Using the FFF precursor liquid material sprayed at 100 PSI via the axial-flow hollow-cones according to the present invention, a 28 sq.ft. burn test was conducted with 3.5 gallons of gasoline, and a burn time of 13 seconds to extinction was obtained. In a second run, a burn time of 14 seconds was obtained. Excellent results were also observed in 8 sq.ft. burn tests on gasoline fires. These burn results exceeded those obtained with MILSPEC nozzle or pressure washer / foam cannon.Similar experiments were conducted with Class A, B, K, LIB fires and tire fires using the same FFF precursor liquid material sprayed at 100 PSI via the axial-flow hollow-cones as described above, and this system was also found to be effective in extinguishing these fires. Thus, a fire extinguishing system now exists that can be applied to a wide variety of fires.In the experiments described above the FFF precursor liquid material was a 7% by weight aqueous solution. The complex alkyl compound was a C11 branched ethoxylated fatty alcohol commercially available as Makon® UD5. The acid was polyphosphoric acid (PPA). The ethyleneamine compound was DETA. The liquid material further comprised xanthan and vegetable glycerin.The experiments were repeated with sulfuric acid (SA) substituted for PPA and similar results were obtained. The FFF precursor liquid material was derived from 300g SA, 450g Makon® DA4, 56g xanthan and 40g glycol ether dissolved in 4000g water. Then, 260g DETA was added to give a solution with a pH of 6.95. This concentrate was dissolved in 10700 g of water to give a concentration of 7% by weight. The tank containing this solution was maintained at a pressure 90 PSI for testing. Five axial-flow hollow-cone nozzles were arranged in a linear pattern and attached to a wand which was used to spray the foam into a fire. The expansion ratio was 60. To a 28 sq.ft. round tank containing one inch of water was added 2.7 gallons of E10 gasoline, which was then ignited. After 10 seconds, the foam is sprayed into the tank beginning at one side and staying on one side near the edge. The foam quickly forms a large connected mass that was found to spread very quickly across the tank and to form a foam blanket. After 5-6 seconds, the flames are only 2-3 foot tall and the fire has been taken under control. By about 12 seconds, the fire is out and there is a thick foam blanket covering the entire tank to protect against back-burn. It was unexpected that the foam spread so quickly across the tank. The width of the spray was about two feet, which is surprisingly large, and the resultant large footprint enable a foam blanket to quickly cover the whole tank. Thus, the advantage of such high expansion foam is that a very large volume spreads rapidly across the fire area. The high expansion foam was found to decompose to small bubble foam that had a specific gravity of about 0.7g-0.9g per ml, i.e. lighter than water and enabling the foam to float over the gasoline.The experiment described above with the SA-derived foam was repeated using vegetable glycerin instead of the glycol ether and similarly impressive and surprising results were obtained.For testing with LIB fires and tire fires, a modified water fire extinguisher was used. The hose with the conventional water nozzle was replaced with a hose with the axial-flow hollow-cone nozzle. The same PPA-based FFF precursor liquid material was used as described above. At 100 PSI tank pressure, the expansion ratio was observed to be 37. The whole tank is emptied with that initial pressure. While a single nozzle was used in these experiments, it will be appreciated that several nozzles could be used on one hose given the small size and light weight of these nozzles.The LIB fire test is conducted as follows. A BernzOmaticTM Propane Cane Torch with Trigger Start Ignition (39-inch length; available from Lowes) is used as the ignition source. The lithium battery is a lithium-polymer (Li-pol) battery commercially available under the name of HOOVO 6S LiPo Battery (22.2V 6200mAh 120C). The battery is tested in its fully charged state. A moderate flame from the BernzOmatic Torch is applied to the entire battery for about 10 minutes with a sweeping motion until the first cell caught fire. The cell starts burning briskly, with a flame about 24 inches in height being observed after about 3 seconds, at which point the foam is applied to the fire.When the PPA-based FFF precursor liquid material was applied to the fire at 100 PSI via the axial-flow hollow-cone nozzles as described above, the flame was extinguished in less than 5 seconds. A second cell in the battery then caught fire and was extinguished in less than 5 seconds. The other 4 cells failed to ignite but sequentially emitted large amounts of smoke without catching on fire due to the presence of the foam blanket disposed on the battery. A significant amount of char was observed on the batteries after the fire. The plastic that held the 6 Li-pol cells together had burned. At the end of the test, there were no burning embers from the plastic or the cells.It is likely that the incidence of LIB fires will increase, given the increasing uptake of electric vehicles, which may involve 7000-10000 batteries linked together. Any battery can malfunction and lead to a fire regardless of ventilation. Fires are most likely to occur in the fully charged state or when over charged. It is therefore critical that there exists a reliable fire extinction method for LIB fires.In an alternative method testing performance against LIB fires, a hot plate was used to cause the LIB to fail and catch fire. In this case, multiple cells failed simultaneously but, again, the PPA-based system described above completely extinguished the fires quickly. It will be appreciated that larger LIB fires may require a larger extinguisher with more nozzles to spray larger area.In a further LIB fire test, a 4-nozzle fire suppression system was suspended above the battery, wherein the axial-flow hollow-cone nozzles, operating pressure and PPA-based FFF precursor liquid materials are as described above. The hot plate remained on during the duration of the test. The hot plate caused one cell of the Li-Pol battery to fail (explode) and catch fire. The foam fire suppression system quickly extinguished the fire. It took 5 minutes for the remaining cells to fail under heat, i.e. the 6th cell failed 5 minutes after the failure of the 1st cell. A control experiment was conducted without the fire suppression system, and it was observed that the 6th cell exploded within only 2 minutes of the failure of the 1st cell The greater time period between the first and last failures of the 6 cells in this test using the fire suppression system is due to the foam blanket preventing the production of flames which increases the likelihood of the cell failing while heat is still being applied.The experiment described above was repeated, except that the xanthan and vegetable glycerin components were omitted from the composition, providing a lower viscosity liquid material. While the foam expansion ratio of 16 at a tank pressure of 60 PSI was still able to be categorized as "high", the expansion ratio was significantly lower than that observed for the system containing the xanthan and vegetable glycerin. The foam drain time of the xanthan-free foam was also relatively poor at about 3 minutes, whereas the xanthan-containing foam exhibited a drain time of over 10 minutes. It will be appreciated from the foregoing discussion that there are advantages for retaining longer foam drain times after application of the foam to a fire. The inventors believe that the relatively lower expansion ratio and shorter drain time of the xanthan-free foam relates to viscosity. The xanthan-containing composition had a viscosity of 227 cP, whereas the xanthan-free composition had a viscosity of 60 cP. Nevertheless, while low viscosity compositions may not inherently provide optimum fire-fighting performance, it remains the case that not only do they exhibit good flame retardant characteristics but they also exhibit other performance advantageous in that they can be sprayed easily with devices such as drones. Typically, drones need to minimize their weight and so do not usually incorporate the powerful pumps that may be needed for application of high viscosity compositions. Thus, the low viscosity xanthan-free compositions would be appropriate for tackling small fuel fires, or in in front of class A wildfires.The fire-extinguishing system of the present invention was also tested against a magnesium fire. A magnesium fire contains a lot of energy that is easily released, compared for instance to metals such as Al and Fe. An individual Mg shaving is quickly consumed and forms a white powder (which is likely magnesium oxide). In this test, 454g magnesium shavings were distributed in a 12 sq.in. pattern over an aluminum thin metal plate and placed on a concrete slab. The Mg shavings were set on fire with a propane torch. The magnesium quickly ignites into a very intense fire that looked like a single large bright-red ember. The fire was then attacked with a fire extinguisher containing the SA-derived composition (7% by weight concentration), axial-flow hollow-cone nozzles and operating pressure referred to above. Very intense light is given off and the fire is extinguished in about 15 seconds. The remains of the shavings were at a safe temperature in less than 2 minutes. Inspection of the remains revealed significant char as well as white powder in approximately equal amounts. Some Mg shavings had not caught fire. The aluminum plate also burned due to the intensity of the Mg metal fire.The Mg-fire test was repeated except that the FFF-precursor liquid material had a concentration of 50% by weight. The extinction time was approximately 10 seconds with intense visible light observed, as before. There was at least twice as much char as white powder.The results observed above can be compared with the following comparative experiment which involves the burning (without attempts at fire-extinction) of a 12 g sample of Mg shavings. The 12 g pile of shavings burned slowly with a moderate amount of light released. The fire burned for at least 30 seconds. During the fire, a cone forms over the pile of shavings. No char formation was observed. It is the inventors' understanding that the SA-derived FFF-precursor liquid material works by interrupting the cone formation by causing char to form. The char does not conduct heat and keeps the burning Mg from operating as a unit.Thus, the system of the present invention is also applicable to metal fires.These experiments also demonstrate that the FFF precursor liquid materials used in the present invention may be tailored for each class of fire. For instance, performance of the system against a magnesium metal class D fire is optimized by increasing the concentration of the active agents in the liquid material.The fire-extinguishing system of the present invention was also tested against a tire fire. Three different tire tests were done.(i) The first tire with rim from a golf cart had a diameter of 12 inches and 6 inches in width. It took about 15 minutes for the tire to ignite using two propane torches (BernzOmaticTM Soldering and Brazing Propylene Torch Kit (14.1-oz); available from Lowes). The SA-derived FFF precursor liquid material (7% by weight concentration) applied via the axial-flow hollow-cone nozzles extinguished the burning tire in less than 5 seconds. The foam expansion ratio was observed to be about 45, and the tires were completely engulfed in foam, which also stops reignition.(ii) Another tire of similar size with rim (18 in x 5 in) was caused to burn more fully caused with torches and the foam extinguished the fire in less than 5 seconds.(iii) The third test used a car tire with no rim. Gasoline was poured inside the tire and ignited. The fire is intense and not all the gasoline had been consumed when we started applying foam. The fire is more challenging to tackle because the gasoline also needs to be extinguished. Nevertheless, the fire took only 10 seconds to extinguish.In these tire fire tests, attempts were also made to reignite the tires after waiting a period of 24 hours after the initial fire had been extinguished. Despite using gasoline and propane torches, the tires would not reignite. The gasoline burns off and then the fire quickly stops. The inventors postulate that the foam has probably soaked into the tires, possibly via micro-holes formed during the burn tests, thereby preventing re-ignition.The fire-extinguishing system of the present invention was also tested against a.Class A fire. Testing for a UL 711 Class A fire extinguisher requires passing a "burning crib" test. For class 1A, the crib is made of 72 pieces of wood (2in x 2in x 20in) arranged in 12 layers of 6 pieces for each layer. The spacing is such as to form a square, each layer perpendicular to the next layer. The crib is placed on a metal grate. A tub with 1 gallon of gasoline is placed below the crib and ignited. After the gasoline is depleted and the crib completely on fire, the fire-fighting composition is applied. In the test conducted by the present inventors, as PPA-derived FFF precursor liquid material (7% by weight concentration) was applied via axial-flow hollow-cone nozzles at 100 PSI from an otherwise conventional fire-extinguisher until the 2.5 gallon tank was empty. The fire was completely extinguished, with the crib being completely filled with the high expansion foam. The fire is suffocated.The fire-extinguishing system of the present invention was also tested against a. Class K fire. A 7 sq.ft. tank was filled with one inch of water and then 1.5 gallons of cooking oil. The fire was ignited and allowed to burn for 10 seconds. The PPA-derived FFF precursor liquid material (7% by weight concentration) was applied via axial-flow hollow-cone nozzles at 100 PSI from an otherwise conventional fire-extinguisher, which quickly and completely extinguished the fire.Thus, a home-owner could utilise an extinguisher utilising the system of the present invention to a very wide range of fires that might occur in a home.The inventors have attempted to understand the mechanism by which the foam generated by the FFF precursor liquid materials and system of the present invention extinguishes any class of fire. It will be appreciated that the inventors do not limit the scope of the invention by the following discussion, and the results reported herein do not rely on any such theory, particularly given that these results were unexpected. Thus, the inventors postulate that the PNSF foam reacts with all flames regardless of which class of fuel is present, resulting in the emission of light and the formation of char which puts out the fire by depleting the fire of radicals and energy. No radiative heat is formed, which contributes to stopping propagation of the fire. The FFF precursor liquid materials of the present invention have a large endotherm (as shown by DSC and TGA) that absorbs a lot of heat as the foam is exposed to the flames / heat. The reaction of the foam with flames / heat results in formation of char and visible light to release the energy in a safe way. The visible light provides an alternative and harmless release of energy as compared to radiative heat. Char formation extracts a lot of energy. Char formation and light emission has been observed for fires wherein the fuels are wood, gasoline, cooking oil, magnesium metal shavings, tire and LIBs. The flames disappear as the foam absorbs the radicals, Li ions, Mg ions, wood radicals, gasoline radicals, etc. It is surprising that the same FFF precursor liquid material (particularly at concentrations in the range of 7%-14% by weight) was effective against such a wide range of fire classes. While the composition of the liquid material may be optimized for different fire classes, the same composition retains effectiveness against any fire class. It will be appreciated that a FFF precursor liquid material having a higher concentration may well be more effective against certain types of fire class than a lower concentration liquid material, for instance in a Class A fire where foam may not be essential, but the more relevant consideration is that is not desirable to have a different fire extinguisher for each fire class.To summarize, it was unexpected that the axial-flow hollow-cone nozzles described herein could achieve foam high expansion ratios of up to 70 using standard (low) pressures. The expansion ratio was found to vary with the composition (for instance, depending on its identity, concentration and viscosity and on the applied pressure). The inventors believe that this is the first method that delivers high expansion firefighting foam with high expansion ratios at standard pressure and without the use of a conventional Venturi-pump nozzle.

Claims

CLAIMS:

1. A fire-extinguishing system comprising:(i) a tank suitable for containing a fluorine-free foam-precursor liquid material,(ii) a fluorine-free foam precursor liquid material; and(iii) one or more axial-flow hollow-cone nozzle(s).

2. A fire-extinguishing system according to claim 1 wherein said tank is a pressurized tank, preferably pressurized to 50-110 PSI, preferably 65-110 PSI, preferably 65-100 PSI, and / or wherein said tank has a volume of at least 1.5 gallons, or at least 2.5 gallons.

3. A fire-extinguishing system according to claim 1 or 2 wherein said nozzle is suitable for receiving an axial pressurized input flow of said foam-precursor liquid material, wherein said nozzle comprises, in the following sequence: an entry orifice, a flow-restriction section adapted to reduce the volume and pressure of said input flow of said foam-precursor liquid material while increasing its velocity, a swirl chamber and a discharge orifice.

4. A fire-extinguishing system according to claim 3 wherein said flow-restriction section is adapted to rotate the axial flow of the foam-precursor liquid material about the central axis of said nozzle.

5. A fire-extinguishing system according to claims 3 or 4 wherein the flow-restriction section comprises two or more grooves or channels in a spiral or helical arrangement relative to the central axis of said nozzle, preferably wherein said grooves are adapted to cause rotational flow of the liquid material relative to the central axis of the nozzle and to reduce the volume and pressure of the flow of the liquid material while increasing its velocity.

6. A fire-extinguishing system according to any of claims 3 to 5 wherein the nozzle comprises a housing and a swirl insert wherein the swirl insert constitutes said flow-restriction section, preferably wherein the flow-restriction section comprises two or more grooves or channels in a spiral or helical arrangement relative to the central axis of said nozzle and the housing and swirl insert together constitute said grooves or channels, and / or preferably wherein the interior surface of a portion of said housing and the exterior surface of a portion of the swirl insert are threaded such that the nozzle comprises the swirl insert located in threaded engagement within the housing.

7. A fire-extinguishing system according to claim 6 wherein said swirl insert comprises two or more grooves or channels in a spiral or helical arrangement relative to the central axis of the nozzle, preferably wherein the grooves or channels are disposed in the exterior surface of the swirl insert such that the grooves or channels become enclosed along their longitudinal axis when the swirl insert is located within the housing.

8. A fire-extinguishing system according to claim 6 wherein said housing comprises two or more grooves or channels in a spiral or helical arrangement relative to the central axis of said nozzle, preferably wherein the grooves or channels are disposed in the interior surface of the housing such that the grooves or channels become enclosed along their longitudinal axis when the swirl insert is located within the housing.

9. A fire-extinguishing system according to any of claims 3 to 8 wherein said flow-restriction section opens into said swirl chamber, wherein said swirl chamber has a wider bore than that of the flow-restriction section, and wherein said swirl chamber is adapted to propagate the rotational flow of the liquid material thereby transmitting it through the swirl chamber in a direction having both tangential and axial components relative to the cross-section of said swirl chamber.

10. A fire-extinguishing system according to claim 9 wherein said propagated rotational flow is entrained with air derived from air drawn in from said discharge orifice.

11. A fire-extinguishing system according to any of claims 3 to 10 preceding claim wherein said entry orifice is situated within a threaded stem section through which said foam-precursor liquid material enters the nozzle.

12. A fire-extinguishing system according to any of claims 3 to 11 adapted to transfer said foam-precursor liquid material into the entry orifice of said nozzle at an input pressure of 50-110 PSI.

13. A fire-extinguishing system according to any of claims 3 to 12 wherein said fluorine-free foam-precursor material becomes an atomized liquid in the swirl chamber.

14. A fire-extinguishing system according to any preceding claim wherein fluorine-free foam is expelled from the nozzle in the form of a hollow-cone spray.

15. A fire-extinguishing system according to any preceding claim which comprises an array of at least two of said nozzles, optionally wherein the array of nozzles is arranged on a boom, optionally where said boom is attached to a device selected from a boom lift, a telescoping pole and a robotic arm.

16. A fire-extinguishing system according to any preceding claim which further comprises a hose connecting the tank to said nozzle(s).

17. A fire-extinguishing system according to any preceding claim wherein the system is selected from a sprinkler system, a hand-held fire extinguisher, a foam cannon and a quadcopter drone.

18. A fire-extinguishing system according to claim 17 wherein the sprinkler system is located in a fixed position (such as in a building) or is mobile (for instance affixed to a helicopter or other aircraft or in the form of a boom for use on land or water).

19. A fire-extinguishing system according to any preceding claim wherein said foam-precursor liquid material is in the form of a solution, preferably an aqueous solution.

20. A fire-extinguishing system according to any preceding claim wherein the viscosity of said foam-precursor material is from about 10cP to about 400cP, preferably 75cP to 300Cp, and most preferably 150cP to 275cP, measured using a Brookfield DVplus viscometer at 60 RPM, #2 spindle, and 70°F.

21. A fire-extinguishing system according to any preceding claim wherein said foam-precursor liquid material is or comprises a composition derived from the reaction product (RP2) of a modified acid with one or more compounds selected from an ethyleneamine, alkali metals (particularly sodium or potassium), ammonia and alkanolamines, wherein said modified acid is the reaction product (RP1) of a complex alkyl compound with an acid selected from polyphosphoric acid, phosphoric acid, sulfuric acid and sulfonic acid, and wherein said complex alkyl compound is selected from ethoxylated fatty alcohols, fatty alcohols, ethoxylated alcohols, ethoxylated phenol, ethoxylated alkylphenol, alkyl polyglycoside and alkyl aryl. and preferably wherein said fluorine-free foam precursor liquid material further comprises water, and preferably wherein said fluorine-free foam precursor liquid material further comprises a thickener and optionally one or more organic solvent(s).

22. A fire-extinguishing system according to claim 21 wherein said one or more compounds selected from an ethyleneamine, alkali metals (particularly sodium or potassium), ammonia and alkanolamines, is an ethyleneamine, preferably wherein said ethyleneamine is selected from ethylenediamine (EDA), diethylenetriamine (DETA), piperazine (PIP), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), and pentaethylenehexamine (РЕНА).

23. A fire-extinguishing system according to claim 21 or 22 wherein the ratio by weight of the complex alkyl compound to the acid is at least 0.25 and less than 4.0 by weight; and / or wherein the amount of said compound selected from ethyleneamine, alkali metals, ammonia, and alkanolamines is such that the foam-precursor liquid material exhibits a pH from 3.5 to less than 8.5 and preferably 5.5 to 8.

024. A fire-extinguishing system according to any of claims 21 to 23 wherein said thickener is selected from xanthan and / or diutan; and / or wherein said organic solvent is glycerin, and preferably wherein the foam precursor liquid material comprises said thickener in combination with said organic solvent, preferably wherein the ratio by weight of organic solvent to thickener when they are both present is in the range of 0.5 to 2.0.

25. A fire-extinguishing system according to any of claims 21 to 24 wherein the complex alkyl compound is an ethoxylated alcohol, preferably having a chain length C9-C13 and wherein the degree of ethoxylation (n) from 3 to 9.

26. A fire-extinguishing system according to any of claims 21 to 25 wherein the foam precursor liquid material comprises water in an amount of 50 to 98% by total weight of the material.

27. A fire-extinguishing system according to any of claims 21 to 26 wherein the ratio of said complex alkyl compound to said acid and / or the viscosity of the foam precursor material and / or the concentration of the foam precursor material is selected to obtain a foam expansion ratio of at least 10, preferably at least 15, preferably at least 20, more preferably at least 30, preferably at least 35.

28. A fire extinguishing system according to any preceding claim 21-27 which is suitable for extinguishing fire types selected from the group consisting of Class A, B, D, K, Li-ion battery (LIB) and tire fires.

29. A fire extinguishing system according to any preceding claim 21-28 wherein the foam has the property of absorbing Li radicals and fluoride radicals.

30. A method of extinguishing a fire comprising directing a fluorine-free foam derived from the fire-extinguishing system defined in any preceding claim onto a fire and / or a fuel of a fire, wherein said fuel may comprise flammable and / or inflammable materials.

31. A method according to claim 30 wherein the foam is directed onto the bottom of the flames in closest proximity to the fuel.

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