TECHNICAL FIELD

[001] The present disclosure is related to a firefighting composition comprising phospholipids, and to a method of forming a fire extinguishing foam in a fire extinguishing system using the composition.

BACKGROUND ART

[002] In fire truck carried fire-fighting foam systems and larger stationary fire-fighting foam systems, water and a concentrated foaming solution are mixed and a gas added to form a foam. The foam formulations intended for such use are often called AFFFs (aqueous film forming foam), as water is used to make a foam that forms a film over burning fuel. The role of the foam being to cool the fire and to coat the fuel, preventing contact of oxygen with the fuel, resulting in suppression of combustion and resistance to re-ignition after a fire has been put out.

[003] Fluorinated surfactants have for a long time been used as a critical component in high-performance fire-fighting foams applied against fires of liquid fuels. Common fluorinated surfactants have a perfluorocarbon tail and a hydrophilic head group (either ionic or highly polar). The tail giving the surfactant its unique and highly-desirable property, i.e. being simultaneously hydrophobic and lipophobic. A fluorinated surfactant gives the foam formulation a surface tension of about 18 mN/m, which is lower than for typical non- fluorinated surfactants (about 25 mN/m).

[004] In a typical standardized test of fire-fighting foams, the foam is applied to a burning jar of heptane. After the fire has been put out, a torch is placed in the middle of the foam bed, resting on top of the now extinguished fuel. The time until re-ignition (so-called "burn-back time") occurs is measured. It is very important that this time is long enough, e.g. to allow safe evacuation of an aeroplane after a fire.

[005] If the foam does not contain fluorinated surfactants (or possibly silicone surfactants), the foam will be "oleophilic", meaning that fuel can, and will migrate up into the foam lamellas via wetting and spreading mechanism, finally leading to a premature re-ignition. Likewise, when the foam is applied through so-called "forceful application" (meaning that the foam is plunged into the (burning) fuel liquid when the fire is extinguished) fuel will inevitably be emulsified or trapped inside the foam if fluorinated (or possibly siliconized) surfactants are not used, as the foam will then be "oleophilic"/will be wetted by the fuel. This will give poor (short) burn-back times meaning that the foam will not resist re-ignition for long enough time. [006] The fluorinated surfactant comprises perfluorinated alkyl chains that are stable, chemically inert, highly persistent in the environment, bioaccumulative and toxic. There is, hence, a need for finding alternative surfactants to replace the fluorinated surfactants in firefighting foams.

SUMMARY OF THE INVENTION

[007] It is an object of the present disclosure to provide a firefighting composition for, which composition comprises a more environmentally friendly surfactant than perfluorinated surfactants and which composition gives burn-back times in fire tests that are on the same order as for perflourinated foams. A further object is to provide a method of forming a fire extinguishing foam in a fire extinguishing system using the composition.

[008] The invention is defined by the appended independent claims. Non-limiting embodiments emerge from the dependent claims and the following description.

[009] According to a first aspect there is provided a firefighting composition. The composition comprises phospholipids, wherein the phospholipid has a phosphatidylcholine head group, and two saturated fatty acid chains having 12 to 20 carbon atoms in each chain. The composition comprises a spreading agent selected from a mono unsaturated and/or saturated fatty alcohol having 12 to 20 carbon atoms, wherein a mass ratio of phospholipids to mono unsaturated and/or saturated fatty alcohol in the composition is 4:1 to 15:1, and/or a surfactant protein, wherein a mass ratio of phospholipids to surfactant protein in the composition is 1000:1 to 10:1. The phospholipids and spreading agent together amounts to 80-100% by weight of the composition.

[0010] The present firefighting composition may be mixed with water and used in fire extinguishing systems where aqueous film forming foams are used, replacing the silicon based surfactants or hydrocarbon-based surfactants, such as fluorosurfactants, such as fluorotelomers, perfluorooctanoic acid (PFOA), or perfluorooctanesulfonic acid (PFOS), in these systems.

[0011] The present firefighting composition is based on phospholipids with a phosphatidylcholine head group and two saturated fatty acid chains and a spreading agent being a fatty alcohol and/or a surfactant protein. After mixing with water and gas to form a foam, the phospholipids are spread at the air-liquid interface of the formed foam film.

[0012] Common fluorinated surfactants have a perfluorocarbon tail and a hydrophilic head group (ionic or highly polar). The tail being simultaneously hydrophobic and lipophobic.

A fluorinated surfactant gives aqueous solutions with a surface tension around 18 mN/m, which is lower than normal surfactants (about 25 mN/m).

[0013] A foam comprising the composition comprising the phospholipids only spreads poorly on a hydrocarbon liquid. The spreading agent is present in the composition so as to allow a quick and spontaneous spreading of the phospholipids on the air/water interface in the foam.

[0014] The present firefighting composition is inspired by the function of the pulmonary surfactants in mammals, which achieve ultra-low surface tension, clearly below 18 mN/m and down to 0-1 mN/m, upon sufficient compression of the adsorbed surface layer. Pulmonary surfactants require compression of the surface of the lung (such as during exhaling) to exhibit a low surface tension of 0-1 Nm/m. Upon compression of a foam film comprising the composition along the film axis by shrinkage of the foam bubbles of the foam after their formation, the foam film exhibit a surface tension comparable to, or significantly lower than that obtained in a typical fire-fighting foam based on fluorinated surfactants.

[0015] Benefits connected to a low surface tension (lower than that of the hot burning fuel, e.g. heptane that has a surface tension of 20 mN/m at room temperature) are twofold: i) this allows spontaneous spreading of a foam liquid onto the burning fuel, and (more importantly) ii) this prohibits spreading and transport of fuel, after putting the fire out, from the underlying fuel reservoir, along the foam lamellas and up to the foam/air interface, which can lead to a catastrophic re-ignition at the surface after the fire has been put out (so called "burn-back"). The foam will, as opposed to a foam with a higher surface tension, display an overall "oleophobic" behaviour and so called "fuel-pickup" into the foam lamellas (that may also happen during so-called forceful application of the foam, when the foam plunges into the burning fuel liquid) will be avoided, giving obvious benefits as the foam cannot be re-ignited. [0016] The head group of the present phospholipid, the phosphatidylcholine head group, is polar and hydrophilic, and the two non-polar saturated fatty acid chains having 12-20 carbon atoms, or 12-18, or 14-18, or 16-18, or 18-20 or 16-20, or 18, or 16 carbon atoms in each chain being bound to the head group, are hydrophobic. The two chains may be of the same length, i.e. have the same number of carbon atoms. Alternatively, the two chains may be of different lengths having different numbers of carbon atoms. The composition may comprise only one type of phospholipid. Alternatively, the composition may comprise two or more types of phospholipids, for example differing in the length of the non-polar saturated fatty acid chains.

[0017] In a water solution or water-continuous dispersion, the present phospholipids have a normal surface tension. If an adsorbed surface layer of the phospholipid (the molecular monolayer at the air/liquid interface) is compressed along the direction of the film itself (in a bubble equivalent to shrinking the bubble), the phospholipids exhibit a surface tension as low as 0-1 mN/m, or 0-5 mN/m, or 0-10 mN/m, or 0-15 mN/m, or 0-20 mN/m, or 0-25 mN/m, or 5- 25 mN/m, or 10-25 mN/m, or 15-25 mN/m, or 5-15 mN/m, depending on the degree of compression. A degree of compression of a bubble such that the size of the bubble is contracted to about 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, or 90-5%, or 80-5%, or 70-5%, or 60-5%, or 50-5%, or 40-5%, or 30-5%, or 20-5%, or 40-10%, or 30-10%, of its original surface area. This results in a surface tension as low as 0-25 mN/m. Hence, it is clear that a contraction of the bubble is needed to obtain the low surface tension that is desirable and a prerequisite for the present composition to be used in fire extinguishing systems.

[0018] The surface tension obtained can be measured using for example a Wilhelmy plate or a Du Nouy ring using the pure foam liquid and compressing the adsorbed surface layer e.g. using a Langmuir trough setup.

[0019] The phospholipid can for example be a DPPC (dipalmitoyl phosphatidyl choline) or a hydrogenated lecithin. Lecithin typically has one unsaturated bond in one of the fatty acid parts of the molecule, which can be removed by hydrogenation to form two saturated fatty acid tails in the lecithin molecule. The phospholipid may be a natural pulmonary surfactant DPPC extracted from for example pig lungs. The phospholipid can be an artificial phospholipid. The lecithin may be for example be found in egg yolk, sunflower or soybeans.

[0020] The spreading agent may be a mono-unsaturated or saturated fatty alcohol having 12-20, or 12-18, or 12-16, or 14-18 or 16-18, or 16-20, or 18-20 carbon atoms or be a combination of such mono unsaturated and saturated fatty acids.

[0021] The spreading agent may, alternatively or in combination with the mono- unsaturated or saturated fatty alcohol, be a surfactant protein. The surfactant protein (SP) may be surfactant protein-A, surfactant protein-B, surfactant protein-C and/or surfactant protein-D. The surfactant protein is a low molecular weight hydrophobic protein. The SP proteins are believed to reduce the critical temperature of the phospholipid phase transition to a value lower than 37 °C, which improves its adsorption and interface spreading velocity. The compression of the interface causes a phase change of the surfactant molecules to liquid- gel or even gel-solid. Each SP protein, SP-A, SP-B, SB-C, SP-D, has distinct functions, which may act syne rgistica I ly.

[0022] The mass ratio of phospholipids to fatty alcohol in the composition may be 4:1 to 15:1, or 4:1 to 13:1, or 4:1 to 11:1, or 4:1 to 9:1, or 4:1 to 7:1, or 4:1 to 5:1, or 6:1 to 15:1, or 8:1 to 15:1, or 10:1 to 15:1, or 12:1 to 15:1, or 5:1 to 12:1, or 7:1 to 10:1, or 8:1 to 10:1.

[0023] The mass ratio of phospholipids to surfactant protein in the composition may be 1000:1 to 10:1, or 800:1 to 10:1, or 600:1 to 10:1, or 400:1 to 10:1, or 200:1 to 10:1, or 100:1 to 10:1, or 50:1 to 10:1, or 1000:1 to 50:1, or 1000:1 to 100:1, 1000:1 to 200:1, or 1000:1 to 400:1, or 1000:1 to 600:1, or 1000:1 to 800:1.

[0024] The mass ratio used of the spreading agent may depend on the spreading agent used or combination of spreading agents used. An optimal ratio of a spreading agent comprising both a mono-unsaturated or saturated fatty alcohol and a surfactant protein may depend on the exact composition of such a spreading agent and the ratio of mono- unsaturated or saturated fatty alcohol to surfactant protein.

[0025] The phospholipids and spreading agent together amounts to 80-100% by weight of the composition. In one embodiment the two components amounts to 100% by weight of the composition. In other embodiments other constituents, such as a stabilizing agent and/or a rheology modifying agent may amount to 0-20% by weight of the composition. Further additives known in the art of fire extinguishing foams may also be added into the composition. [0026] The phospholipid may be present in the composition in a range of 70-93, or 75- 95, or 80-90 % by weight of the composition.

[0027] The composition may be in dried form. The composition may be stored in dry form, as a liquid concentrate by adding some water to the composition or as an aqueous solution ready to be used and brought in contact with a gas to form a foam.

[0028] Upon compression of the foam, the foam will achieve the crucial oleophobic properties (fuel droplets or fuel itself does not spread spontaneously into this foam) which is directly correlated to good resistance to re-ignition (long burn-back times in a fire test as well as in a real-life scenario).

[0029] The composition may further comprise a stabilizing agent selected from non ionic liquid polymers, polyvinyl alcohol, non-ionic surfactants and ionic surfactants.

[0030] It is to be understood that the non-ionic and ionic surfactants also include so called amphoteric surfactants. This, as the pH of the solution determines the charge of such amphoteric surfactants. If the pH is at its isoelectric point, the amphoteric surfactant is uncharged.

[0031] The stabilizing agent may be added in the composition mainly to stabilize the composition and increase the storage stability of the composition if water is added and the composition is stored as a liquid concentrate or as an aqueous solution ready to be used. [0032] Stabilizers used could be so called steric stabilizers, which stabilize the composition in water solution by means of their bulky structure. Examples of such stabilizers are polymers. The polymers used should only lower the surface tension of a solution comprising the composition to a limited degree. A non-ionic liquid polymer may for example be tyloxapol. A polyvinyl alcohol with a relatively high degree of hydrolysis or a fully hydrolysed polyvinyl alcohol can be used (such that surface activity of the polyvinyl alcohol is not too large).

[0033] The stabilizing agent may also have a function as a foam-boosting additive, i.e. it may aid rapid foam generation of the solution through typical fire-fighting foam generating nozzles.

[0034] Non-limiting examples of such stabilizing agents are amidopropylhydroxysultaine surfactants, amine oxide surfactants, polysorbate surfactants, or alkyl aryl polyether alcohol type non-ionic liquid polymers. Such additives can be cocamidopropylhydroxysultaine, cocamidopropylamine oxide, lauramidopropylamine oxide, polyoxyethylene (20) sorbitan monolaurate(Polysorbate 20), polyoxyethylene (20) sorbitan monopalmitate(Polysorbate 40), polyoxyethylene (20) sorbitan monostearate(Polysorbate 60), polyoxyethylene (20) sorbitan monooleate(Polysorbate 80), orthyloxapol. The stabilizing agent may be cocamidopropylamine oxide and/or lauramidopropylamine oxide or lauramidopropylamine oxide.

[0035] The stabilizing agent may be present in the composition in an amount of 0.5-20 percent, such as 6-11 percent, or in an amount of 0.005 to 90 percent by weight of the organic components of the composition.

[0036] Foam-boosting effects can be obtained with stabilizing agents present in the composition in amounts of 0.005-90 percent, by weight of the organic components of the composition, or 0.05-90, 0.1-90, 1-90, 5-90, 10-90, 25-90, 50-90, 0.005-50, 0.005-25, 0.005-10, 0.005-5, 0.005-1, or 0.005-0.05 percent by weight of the organic components of the composition.

[0037] The composition may further comprise a rheology-modifying agent selected from polyvinyl alcohol, hydrophobized cellulose, lipopolysaccharides, hydrophobized starch, alkyl- substituted polyurethanes, water-soluble glycols, glycerol and ethylene oxide-propylene oxide block copolymers.

[0038] The hydrophobized cellulose may be e.g. hydroxypropyl methylcellulose (HPMC). The ethylene oxide-propylene oxide block copolymers may e.g. by Pluronics ^® . The water- soluble glycols may for example be diethylene glycol monobutyl ether, polyetylenglycol or propylenglycol.

[0039] The amount of the rheology-modifying agent in the composition may be 0.1-2% or 0.1-20% by weight of the composition. By adding the rheology-modifying agent it is possible to control the viscosity of a liquid formed from the composition in a range of 1-2000 mPas.

The drainage rate of the foam is related to the viscosity of the liquid formed from the composition, and drainage rate is an important parameter for foam stability. The rheology modifying agent, hence, may also contribute as a foam drainage retarding additive.

[0040] According to a second aspect there is provided a firefighting mixture comprising the composition above and further a scavenger component, wherein the scavenger component is a corresponding base of an acid having a pKa of at least 6.35.

[0041] The ratio of lipid to scavenger component in the mixture may be 1:2 to 1:75 000, or 1:2 to 1:10, or 1:10 to 1:100, or 1:100 to 1:1000, or 1:1000 to 1:10000 or 1:10000 to 1:75 000, or 1:2 to 1:50000, or 1:2 to 1:25000 or, 1:2 to 1:10000, or 1:2 to 1:1000 or 1:2 to 1:100, or 1:10 to 1:75000; or 1:100 to 1:75000, or 1:1000 to 1:75000, or 1:10000 to 1:75 000. [0042] The scavenger component may be selected from inorganic soluble carbonate, inorganic soluble monohydrogen phosphate, inorganic soluble sulphite, inorganic soluble hydroxide and/or ammonia.

[0043] With "soluble" is here meant that a scavenger component is dissolvable in water to a concentration of at least 0.025 M, or at least 0.1 M, or at least 0.25 M.

[0044] The scavenger component may be a corresponding base of an acid having a pKa of at least 6.35, wherein the acid is selected from one or more of HCO ₃ , NhV, H ₂ PO ₄ and HSO ₃ . Such corresponding base may then be CO ₃ ² , NH ₃ , HPC> ₄ ² and SO ₃ ² , respectively.

[0045] The inorganic soluble hydroxide may be NaOH, KOH and/or LiOH.

[0046] The mixture may be in dried form. The mixture may be stored in dry form, as a liquid concentrate by adding some water to the mixture or as an aqueous solution ready to be used and brought in contact with a gas to form a foam.

[0047] According to a third aspect there is provided a firefighting solution comprising the composition or the mixture described above and water, wherein a concentration of the phospholipids in the solution is 0.01 g/L to 300 g/L.

[0048] The water in the solution may comprise saline, such as 0.01-3.5% NaCI.

[0049] A concentration of the phospholipids in the solution may be 0.01 g/L to 300 g/L, or 0.02 g/L to 150 g/L, or 0.03 g/L to 100 g/L, or 0.04 g/L to 50g/L. A more diluted solution, e.g. having a concentration of phospholipids of 0.01 g/L to 100 g/L, may be used as is in fire extinguishing and brought in contact with a foam forming gas to form a foam. A more concentrated solution, i.e. having a concentration of phospholipids of 100 g/L or more, may need to be diluted with water before being used in fire extinguishing.

[0050] According to a fourth aspect there is provided a method of forming a foam in a fire extinguishing system, the method comprising to provide a solution comprising: phospholipids, wherein the phospholipid has a phosphatidylcholine head group, and two saturated fatty acid chains having 12 to 20 carbon atoms in each chain, and a spreading agent selected from: a mono unsaturated and/or saturated fatty alcohol having 12 to 20 carbon atoms, wherein a mass ratio of phospholipids to mono unsaturated and/or saturated fatty alcohol in the composition is 4:1 to 15:1, and/or a surfactant protein, wherein a mass ratio of phospholipids to surfactant protein in the composition is 1000:1 to 10:1, wherein the phospholipids and spreading agent together amounts to 80-100% by weight of the composition, wherein a concentration of the phospholipids in the solution is 0.01 g/Lto 300 g/L, and to bring the solution in contact with a foam forming gas such as to form a foam of the solution, and to contract the formed foam such that the size of foam bubbles forming the foam is reduced to 90% or less of its original surface area.

[0051] The method may comprises a step of, before the step of bringing the solution in contact with the foam forming gas, adjusting the concentration of phospholipids in the solution to a concentration of 0.01 g/L to 100 g/L.

[0052] If the phospholipid concentration of the solution already is at a desired concentration of 0.01 g/L to 100 g/L, this step of adjusting the concentration is of course unnecessary and can be omitted.

[0053] The solution may comprise a scavenger component as discussed above. The amount of this in the solution when used in the method may be 0.025 mole/litre to 10 mole- litre, or 0.1 mole/litre to 10 mole/litre, or about 0.5-2 mole/litre, or 0.25-10 mole/litre, or 1-10 mole/litre, or up to a saturation concentration in water of the component.

[0054] The foam forming gas brought into contact with the solution comprises at least one gas component that is incorporated in the foam bubbles during the formation of the foam. The gas component may a) react with another gas component in the formed foam bubbles, and/or b) react with a component in liquid phase in the formed foam bubbles, and/or c) be dissolved at least partially in liquid phase in the formed foam bubbles, and/or d) the gas component could condense. Alternatively, or in combination with any one or more of a)-d) above the gas contained in the bubbles could cool down. These alternatives results in a reduction of the volume of gas in the formed gas bubbles such that the formed foam bubbles are contracted.

[0055] The solution may be an aqueous solution, which may comprise saline, such as 0.01-3.5% NaCI, or the aqueous solution may be seawater.

[0056] The concentration of phospholipids in the solution may be 0.01-100 g/L, 0.5-20 g/L or 1-10 g/L.

[0057] When the solution is brought into contact with a foam forming gas, a bigger volume of foam than the volume of the foam forming solution is formed. Normally, for a typical fire-fighting foam of the "heavy foam" type, the volume of the foam formed is about 6- 8 times larger than the volume of the foam forming solution. Most common is a 7 times larger volume (i.e. a foam number of 7), but up to 10 times larger volume can also be obtained. [0058] The formed foam is contracted such that the size of foam bubbles forming the foam is reduced to 90% or less, 80% or less, 70% or less, 60% or less, 50% or less, or 90-5%, or 80-5%, or 70-5%, or 60-5%, or 50-5%, or 40-5%, or 30-5%, or 20-5%, or 30-5%, or 20-5%, or 40-10%, or 30-10%, of its original surface area. With such a contraction of the foam a surface tension of the foam bubbles is reduced to 0-20 mN/m. Preferably the surface tension is below 20 mN/m, i.e. below the surface tension of heptane (which is normally used in fire tests), and ideally below 18 mN/m (as low as possible to give generic oleophobicity regardless of fuel type - it is important that the surface tension of the foam is lower than the surface tension of the fuel itself). The exact reduction of volume is difficult to measure as contraction of foam bubbles may take place instantly as the foam is formed.

[0059] By reducing the volume of the bubble with about 90%, corresponding to a reduction of the bubble area with about 80%, a surface tension as low as 0-1 mN/m may be obtained (see for example Colacicco et a I, "pH, temperature, humidity and the dynamic force- area curve of dipalmitoyl lecithin" Respiration Physiology (1976) 27, p. 169-186., Fig 4 - here in a phospholipid concentration of 200 micrograms per millilitre, which is equal to 200 mg/L, for comparison with our experimental data below). The amount of compression needed to obtain a given surface tension may depend on the phospholipid concentration and spreading agent concentration in the solution. A higher phospholipid concentration may require less compression to give the same surface tension. Presence of a spreading agent being a surfactant protein may require less compression to obtain a certain surface tension.

[0060] By contraction of the foam bubbles the adsorbed surface layer of the phospholipids are compressed and a surface tension of 18 mN/m or lower of the bubbles is obtained, i.e. comparable to fluorinated foams. The contraction of the foam bubbles preferably takes place before the formed foam bubbles reach the fire or liquid to protect from re-ignition. Alternatively, the foam bubbles become contracted at the point of the fire or flammable liquid or shortly after landing on top of the fire.

[0061] If the solution does not comprise a scavenger component, the method described above may comprise an additional step of, before the step of bringing the solution in contact with the foam forming gas, of mixing the solution with a scavenger component being a corresponding base of an acid having a pKa of at least 6.35, such that the amount of said scavenger component in the solution ranges from 0.1 mole/litre to 10 mole/litre or up to a saturation concentration in water of the component.

[0062] The amount of the scavenger component in the solution may be 0.025 mole/litre to 10 mole/litre, or 0.1 mole/litre to 10 mole/litre, or about 0.5-2 mole/litre, or 0.25-10 mole/litre, or 1-10 mole/litre, or up to a saturation concentration in water of the component. [0063] The scavenger component may be selected from inorganic soluble carbonate, inorganic soluble monohydrogen phosphate, inorganic soluble sulphite, inorganic soluble hydroxide and/or ammonia.

[0064] The foam forming gas may comprise air, ammonia and/or carbon dioxide.

[0065] In a specific embodiment, the foam forming gas may comprise carbon dioxide and the solution may comprise a scavenger component being inorganic soluble carbonate. [0066] In a first alternative, the foam forming gas comprises ammonia. The foam forming gas may comprise at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80% or at least 90% or more of ammonia, the rest being air. Ammonia is a gas but is very soluble in water and will (at least partially) dissolve in the foam liquid before the foam lands on the fire or immediately after it has landed on the fire, thereby contracting the foam with about 10% or more in surface area. In one example, an amount of ammonia in the foam forming gas of 15% would result in a reduction of the surface area of the foam bubbles with about 10%, i.e. the area is reduced to about 90% of the original surface area. If the composition comprises a surfactant protein as spreading agent, such a contraction of the foam would be enough to obtain the desired surface tension if the lipid concentration is simultaneously high enough (e.g. 10 g/L or higher). In an embodiment where the spreading agent does not comprise a surfactant protein as spreading agent, and if the phospholipid concentration is simultaneously low in the formulation (e.g. 0.2 g/L), a larger reduction of the foam, to 20% or less of the original surface area may be needed to get the desired surface tension. In such a case an ammonia amount in the foam forming gas of 80% or more, may be needed. In this embodiment, no scavenger component is, hence, needed in the solution.

[0067] In a second alternative, the foam forming gas comprises carbon dioxide, such as at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80% or at least 90, the rest being air. The amount of carbon dioxide in the foam forming gas may be 10-100%, 20-100%, 30-100%, 40-100%, 50-100%, 60-100%, 70-100%, or 80-100% or 90-100%, the rest being air. As for the example above with the foam forming gas comprising ammonia, a lower of amount of carbon dioxide in the foam forming gas would result in a less contracted foam. If the spreading agent comprises a surfactant protein, and if the phospholipid concentration is simultaneously high (e.g. 10 g/L or higher), such a less contracted foam could give the necessary surface tension.

[0068] Carbon dioxide has a lower solubility in water than ammonia. Using carbon dioxide only or carbon dioxide mixed with air as the foam forming gas, without any scavenger component present in the solution, the volume of a foam bubble may be reduced but not to the same degree as when using ammonia in the foam forming gas. (At room temperature 1 ml CO2 per ml water can be dissolved. This means that if a foam with foam number 2 (e.g. 1000 ml water-based liquid and 2000 mL CO2 in the form of a foam) all CO2 would be able to dissolve in the water phase, giving a 100% contraction of the CC>2-bubbles in this foam. In a typical fire-fighting foam the foam number can be for example 7, which means that the amount of CO2 is 6 times higher than the amount of water present (e.g. a foam created from 1000 mL water-based liquid and 6000 mL C02). In such a foam the maximum absorption of CO2 into the liquid phase will be ca 1000 mL, and the CO2 bubbles will therefore contract from maximally from 6000 mL to ca 5000 mL, which is a volume contraction of 16% only. (Hence, not as large a contraction as with ammonia in the air.) In the presence of surfactant protein as spreading agent, and if the phospholipid concentration is simultaneously high (e.g. 10 g/L or higher), such a contraction may be enough to obtain the desired surface tension.

[0069] CO2 could for example be supplied to the foam forming gas by using CO2 from the exhaust pipe of the fire truck. Thereby, already heated CO2 is supplied. If the CO2 supply comprises pressurised CO2 of room temperature, the gas may have to be heated to compensate for adiabatic cooling, which arises when large volumes of CO2 are expelled during a short amount of time. Adiabatic cooling is an inherent limitation of using non-heated compressed or liquid CO2 as the CO2 source. If compressed CO2, e.g. in liquid form in a gas flask, is used as the CO2 source, external heating of the tube can be applied e.g. electrically or via waste heat from a fire-truck engine, e.g. via a conventional heat exchanger. A temperature of the gas when mixed with the solution should be 0-100°C. A temperature below 0°C could make the liquid freeze in the extinguisher nozzle. At a temperature above 100°C there is a risk that the foam forming solution starts to boil.

[0070] In a third alternative, the foam forming gas comprises ammonia and carbon dioxide, alternatively also mixed with air (without any scavenger component being present in the solution), which through a gas phase reaction in the foam bubbles form ammonium carbamate, which is dissolved in the water in the bubble forming ammonium hydrogen carbonate, thereby reducing the amount of gas in the bubble and, hence, the bubble is contracted. For a contraction of the volume of the bubble with about 90% at most 10-5% of the gas should be air, the rest should be a mixture of ammonia and carbon dioxide in a mole to mole relationship of 2:1 for optimum ammonium carbamate reaction to take place. If the spreading agent comprises a surfactant protein, and if the phospholipid concentration is simultaneously high (e.g. 10 g/L or higher), a lower contraction of the bubble is needed to obtain the desired surface tension, and the foam forming gas may comprise as much as up to 80% air.

[0071] In the embodiments described below, the solution comprises a scavenger component (as discussed above).

[0072] With CO ₃ ² present as the scavenger component in the solution and using CO ₂ as the foam forming gas, the formed foam bubble will contract due to the reaction between CO ₂ in the gas of the bubble and the carbonate ions in the foam liquid. The reaction is a neutralization reaction wherein HCO ₃ ions are formed and the CO ₂ gas is consumed.

[0073] Using NH ₃ as the scavenger component and CO ₂ as the foam forming gas, NH ₃ dissolved in the aqueous phase in the formed foam bubble will be compressed via the reaction of CO ₂ with NH3(aq) present in the aqueous phase and with any NH ₃ (g) present in gas phase inside the bubble due to the equilibrium with the solution. This reaction will form HCO ₃ and Nh via the first reaction and ammonium carbamate via the second reaction. Thereby, in both cases consuming CO ₂ and thus shrinking the bubble and compressing the surface film.

[0074] The solubility of NH3 in water is 31 wt%, corresponding to 310 g/L, the molar weight being 17 g /mol. The solubility of ammonia in water is, hence, 18 M. In seven litres of a foam having a foam number of 7 (the liquid expands 7 times), there is one litre of water solution and 6 litres of gas phase (CO2). In the one litre of water solution there may be 18 mole ammonia and the amount of CO2 in the foam (6 litres, ca 0.24 moles) may be fully neutralized. Theoretically, a 0.43 wt.% solution of NH3 in the liquid solution would be enough to take care of all CO2 in a typical foam. This corresponds to 0.25 M NH3.

[0075] With HPO ₄ ² as the scavenger component in the solution and CO ₂ as the foam forming gas, CO ₂ inside the bubble will react with the HPO ₄ ² in the aqueous phase in the formed foam bubble and HCO ₃ and PhPC will be formed. [0076] With SO3 ² as the scavenger component in the solution and CO2 as the foam forming gas, CO2 inside the bubble will react with SO3 ² in the aqueous phase in the formed foam bubble and HCO3 and HSO3 will be formed.

[0077] With OH as the scavenger component in the solution (e.g. accomplished by using NaOH, KOH or LiOH) and CO2 as the foam forming gas, CO2 inside the bubble will react with OH in the aqueous phase in the formed foam bubble and HCO3 or C03 ² and H2O will be formed.

[0078] In the method of forming a foam in a fire extinguishing system, the step of bringing the solution in contact with a foam forming gas such as to form a foam of the solution, may comprise to bring the solution in contact with a humid foam forming gas, such that during formation of the foam, gas in the foam bubbles has a dew point of 50-100°C.

[0079] In such a method, no scavenger component is necessary in the solution. The foam forming gas can be normal air. Other foam forming gases than air are of course also possible to use in this method. One such example is the exhaust gas from a combustion engine, e.g. the engine of a fire truck from which the fire-fighting shall take place. The humidity of this exhaust gas, consisting already to a large extent of steam (and CO2, which may be useful as discussed above) from the combustion of the fuel, will already be at least partially sufficient to fulfil the above described required humidity criteria. In this method, the necessary contraction of the foam is obtained by incorporating steam in the foam forming gas ( i.e . so that the gas has a dew point of 50-100°C, or 70-100°C, or 90-100°C, or 97-100°C). The humid foam forming gas may be formed by letting dry air bubble through warm/heated water-containing liquid/water before being brought in contact with the solution to form a foam.

[0080] The step of bringing the solution in contact with a foam forming gas such as to form a foam of said solution, may comprise to adjust the temperature of the solution and bring it in contact with the foam forming gas, such that during formation of the foam, gas in the foam bubbles has a temperature of 50-100°C.

[0081] By performing the foaming with a solution having a temperature of about 50- 100°C, or 70-100°C, or 90-100°C, or 97-100°C, the gas inside the formed foam bubbles will, at equilibrium, get saturated with respect to water vapour and reach the desired absolute humidity, e.g. a dew point of 50-100°C, or 70-100°C, or 90-100°C, or 97-100°C. [0082] The step of bringing the solution in contact with a foam forming gas such as to form a foam of the solution, may comprise to bring the solution in contact with a heated foam forming gas, such that during formation of the foam, the gas in the foam bubbles has a temperature of 50-100°C.

[0083] The solution may be brought in contact with a heated foam forming gas, such that during formation of the foam, the gas in the foam bubbles has a temperature of 50- 100°C, or 60-100°C, or 70-100°C, or 80-100°C, or 90-100°C, or 97-100°C.

[0084] Adjusting the temperature of the solution could for example be accomplished by heating the solution in the spray nozzle immediately before the thus heated solution is brought into contact with the foam forming gas. Alternatively, the foam forming gas may be preheated to a temperature such that the formed foam reaches a temperature of 50-100°C during foam generation.

[0085] Providing foam forming gas with a dew point of 50-100°C could for example be accomplished by bubbling the foam forming gas through water having a temperature of 50- 100 °C before the thereby humidified foam forming gas gets into contact with the solution. [0086] When the formed foam is ejected from a foam nozzle of a fire extinguishing system, the cooling as the formed foam travels through the air will cool the foam down resulting in condensation of the water vapour inside the foam bubbles into liquid water, giving a contraction of the bubbles as the water vapour passes from gas phase to liquid phase. As an example, to get a reduction in volume of the bubbles of about 25% (corresponding to a reduction of about 15% of the surface area of the bubbles) via this mechanism, the gas inside the formed foam bubbles should have a water content corresponding to an initial dew point of 70°C or higher directly upon formation of the foam in the nozzle. Such a low contraction in presence of a spreading agent being a surfactant protein, and if the phospholipid concentration is simultaneously high (e.g. 10 g/L or higher), may give the desired low surface tension.

[0087] Preferably, this dew point of the gas phase inside the foam bubbles, momentarily, as the bubbles are formed inside the nozzle, should be in the range of 90-100°C (giving around 67% volume reduction or more), or, most preferably between 97-100 °C (giving around 87-98% volume reduction).

[0088] In the method of forming a foam in a fire extinguishing system, the solution may be brought in contact with a foam forming gas in a container at a pressure of 85 kPa or lower, forming a foam at an underpressure, and contraction of the thus formed foam may be accomplished by ejecting the formed foam from the container into ambient air.

[0089] The underpressure used may be 85 kPa or lower, 35 kPa or lower, or 10 kPa or lower, or a pressure from 3 kPa to 85 kPa, or from 3kPa to 35kPa, or 25 kPA or lower. The foam bubbles formed in the container at this reduced pressure will thereafter, upon ejection from the container into ambient air (i.e. into air having atmospheric pressure or near atmospheric pressure (about 100 kPa) be compressed. This compression/contraction will activate the necessary low surface tension of the foam, which gives the foam its oleophobic, fuel-repellent character.

[0090] In one example, the foam is formed at a pressure of 85 kPa and ejected into the atmosphere for contraction. This results in a reduction of the bubbles to 90% of the original surface area. In the presence of a spreading agent being a surfactant protein, and if the phospholipid concentration is simultaneously high (e.g. 10 g/L or higher), such a contraction may be enough to get the desired surface tension. If no surfactant protein spreading agent is present in the solution, a larger contraction of the foam is needed (such as formed upon contraction at ambient atmospheric pressure of a foam formed at for example 10 kPa or lower).

[0091] In such a method, no special foam forming gas, no scavenger component, no heating of gas or liquids, and no moisture in the gas is necessary in the foam forming solution or in the foaming equipment setup. There are embodiments, however, in which presence of a scavenger component in the solution (or heating of the liquid or the gas, or introduction of humidity in the foam forming gas) may improve the contraction of the foam.

[0092] To bring about spontaneous contraction of the formed foam bubbles upon ejection of the foam from the container, the pressure inside the container when the foam is formed should be below atmospheric pressure. The low pressure may be obtained by sucking air out of the container. When the foam, after being generated at this low pressure, is ejected into ambient air the foam bubbles will be compressed. The foam may be ejected by adding a high air pressure to the container.

[0093] The method may for example be implemented by batch wise formation of foam at reduced pressure in the container, followed by ejection of the formed foam by applying a high pressure (e.g. 1 MPa). The process of alternating between applying a low pressure and a high pressure in the container, thereby altering between foam generation (at low pressure) and foam ejection (at high pressure, causing the foam to contract when reaching ambient air) may be repeated uninterruptedly, such that an even supply of fire extinguishing foam is provided from the container at the fire to be extinguished.

[0094] To form the foam and to bring about the necessary contraction of the formed foam after its generation to obtain the desired surface tension can be obtained by any combination of the above described techniques, where each technique contributes to the contraction with a given amount. Such a hybrid method is for example using a hot CO2- and steam-containing exhaust gas from a combustion engine and obtaining, simultaneously, bubble contraction as a result of i) a CO2 scavenger in the solution and ii) condensation of steam inside the foam bubbles as the foam cools down upon ejection from the container comprising the formed foam, and iii) gas volume contraction directly resulting from the gas cooling down (e g from 100 °C to 20 °C , which, according to the ideal gas law will make the gas bubbles contract with a factor 373K/293K e.g. from 0.10 mL to 0,079 mL, i e 21%).

[0095] The solution used in the method, may, as discussed above, comprise a stabilizing agent selected from non-ionic liquid polymers, polyvinyl alcohol, non-ionic surfactants and ionic surfactants.

[0096] The solution used in the method, may, as discussed above, comprise a rheology modifying agent selected from polyvinyl alcohol, hydrophobized cellulose lipopolysaccharides, hydrophobized starch, alkyl-substituted polyurethanes, water-soluble glycols, glycerol and ethylene oxide-propylene oxide block copolymers.

[0097] According to a fifth aspect there is provided a use of a composition in forming a foam in a fire extinguishing system, wherein the composition comprises: phospholipids, wherein the phospholipid has a phosphatidylcholine head group, and two saturated fatty acid chains having 12 to 20 carbon atoms in each chain, and a spreading agent selected from: a mono unsaturated and/or saturated fatty alcohol having 12 to 20 carbon atoms, wherein a mass ratio of phospholipids to mono unsaturated and/or saturated fatty alcohol in the composition is 4:1 to 15:1, and/or a surfactant protein, wherein a mass ratio of phospholipids to surfactant protein in the composition is 1000:1 to 10:1, wherein the phospholipids and spreading agent together amounts to 80-100% by weight of the composition.

[0098] The composition may further comprise a stabilizing agent selected from non ionic liquid polymers, polyvinyl alcohol, non-ionic surfactants and ionic surfactants. [0099] The composition may further comprise a scavenger component, wherein the scavenger component is a corresponding base of an acid having a pKa of at least 6.35.

[00100] The scavenger component may be selected from inorganic soluble carbonate, inorganic soluble monohydrogen phosphate, inorganic soluble sulphite, inorganic soluble hydroxide and/or ammonia.

[00101] The composition may be in a solution in which a concentration of the phospholipids is 0.01 g/L to 300 g/L.

DETAILED DESCRIPTION

[00102] Below is described a firefighting composition comprising phospholipids having a phosphatidylcholine head group, and two saturated fatty acid chains having 12 to 20 carbon atoms in each chain, and a spreading agent being a mono unsaturated and/or saturated fatty alcohol having 12 to 20 carbon atoms, and/or a surfactant protein.

[00103] The phospholipid can for example be a DPPC (dipalmitoyl phosphatidyl choline) or a hydrogenated lecithin.

[00104] The following phospholipids were used in the experiments described below, showing proof of the concept: a) LIPOID E PC-3, from Lipoid GmbH, (Hydrogenated Egg Phosphatidylcholine, Batch 527600- 2160021-01/921, Date of production 03/2016, Retest date 11/2021). 57% 18:0, 35% C16:0 (i.e. 57% of the phospholipids have fatty acid chains with 18 carbon atoms in each chain and no double bounds in the chains. 35% of the phospholipids have fatty acid chains with 16 carbon atoms in each chain and no double bounds in the chains). b) PHOSPHOLIPON ^® 90 H, from Lipoid GmbH, (Hydrogenated Phosphatidylcholine from Soybean, Batch 529400-2200078-20/902, Date of production 11/2020, Retest date 10/2023). 86% C18:0, 13% C16:0. c) LIPOID S 100, from Lipoid GmbH, (Phosphatidylcholine from Soybean, Batch 579000- 1190745-11/029, Date of production 07/2019, Retest date 06/2022).

[0124] The phospholipids were mixed with hexadecanol as the spreading agent in a mass ratio of 8.2:1 for hydrogenated lecithins:hexadecanol, and a mass ratio of 9.0:1 for non- hydrogenated lecithimhexadecanol, by dissolving the phospholipid and hexadecanol in 1/1 chloroform/methanol (V/V). [0125] Other spreading agents than hexadecanol are possible to use as long as they are a mono unsaturated and/or saturated fatty alcohol having 12-20 carbon atoms. They have low solubility in water, a polar head group and a non-polartail, and are amphiphilic.

[0126] The dissolved material was evaporated in a rotary vaccum evaporator at 37-40°C in a flask at a pressure between 100-300 mbar to a dry thin film to evaporate the chloroforom/methanol solvent.

[0127] A number of clean glass beads (5 mm in diameter) were added to the flask and the film together with a volume of saline was swirled under running hot water at 50-52°C until all lipid residues had been stripped from the flask walls and dispersed in the saline solution. The added volume of 0.9% saline to a 1000 ml round bottom flask was between 10-15 ml. [0128] The formed dispersion was transferred using a pipette to a 25 ml glass bottle and additional 0.9% NaCI was added to make a dispersion with a total concentration of 50-52 mg/ml of phospholipids.

[0129] A sonicator equipment (Sonicator 2 Vibracell VCX-750, probe 420-A) was used to further dipserse the hydrophobic phase and ensure that very small droplets were created. Sonication protocoil was 2 min at 40% amplitude, 1 min 60% amplitude, and finally 7 min 70% amplitude. The temperature at the end of the sonication was around 51°C. When the phospholipid was LIPOID S 100, an ultrasound bath (Retsch, setting=2) was used for 120 s (4ml) instead of the Sonicator 2 Vibracell equipment.

[0130] In the experiments discussed here, no stabilizing agent was added as the foam forming compositions were not stored for any longer time but used within a shorter time (days/weeks) after production. Further, no rheology modifying agent was added in these tests. [0131] The formed dispersions where evaluated for foam stability and oleophobicity using a Dynamic Foam Analyzer- DFA100 (KRLISS GmbH). A 40 mm diameter prism glass column and a G4 filter plate was used for sparging (pore size 10-16 pm). Further details about how the foams where created can be found below.

[0132] In addition to the formed dispersions discussed above, the commercial pharmaceutical Curosurf ^® was also evaluated for foam stability and oleophobicity. Curosurf ^® comprises a pulmonary surfactant extracted from porcine lung and is used to reduce surface tension at the air-liquid interface of the alveoli during for example mechanical ventilation. It is also used to treat infants with respiratory distress syndrome. Curosurf ^® comprises DPPC (dipalmitoyl phosphatidyl choline) (about 70% of the total phospholipid content) with a mass ratio phosphatidylcholine:hexadecanol of 9.3:1, and about 1% of specific low molecular weight hydrophobic proteins SP-B and SP-C in 0.9% NaCI.

[0133] The formed phospholipid dispersions were diluted to different concentrations with 1 M Na2CC>3. The volume of the phospholipd dispersions used was 25-50 ml. The content of ampoules of Curosurf ^® was diluted to a concentration of 2 mg/ml of phosphatidylcholine in a 1 M sodium carbonate solution (scavenger component being sodium carbonate).

[0134] The ratio of lipid to scavenger component in the mixture may be 1:2 to 1:75000. This interval is based on experiments performed for example with the phospholipid being Phospholipon ^® using Na2CC>3 as the scavenger, where a foam was formed and the wished oleophobic effect obtained over the whole range of the interval, i.e. using 40-10000 mg/L of the phospholipide in 1M Na2CC>3. For 40 mg/L of the lipid in 10 M Na2CC>3 the ratio of lipid:solid Na ₂ C0 ₃ x 10 H ₂ 0 (40 mg: 2860000 mg) is 1:72000. For 10000 mg/L of the lipid in 0.1 M Na ₂ C0 ₃ the ratio of lipid:solid Na ₂ C0 ₃ x 10 H ₂ 0 (10000 mg: 2860000 mg) is 1:2.9.

[0135] The gas flow rate was lL/min and the foam generation was stopped when the height of the formed foam reached 50-70 mm.

[0136] After foam generation the foam was allowed to equilibrate and in the case of using CO2 as blowing gas and sodium carbonate as CO2 scavenger in the liquid. Bubble contraction was seen in the form of a spontaneous contraction of the foam to ca 1/2-1/4 of the initial height, wihout any breakdown of the foam bubbles. When air was used instead of CO2, no compression and no breakdown of the foam was seen for any of the fomulations tested. All foams where very stable, and no lamella breakdown was seen for any formulation at any concentration tested.

[0137] After equilibration for ca 5-10 seconds, which in the case of CCh/carbonate also meant spontaneous compression of the foams, the foams were tested for oleophobicity, which is an important feature of fluorinated foams giving them good burn-back (anti-re ignition) properties. Oleophobicity was tested by dropping, or adding, liquid portions of ca 30- 150 pL heptane (colored red using the oil-soluble dye fat red bluish for microscopy from Fluka) onto the foam.

[0138] In case of an oleophobic foam, the droplets or liquid portions fell straight through the foam (quickly or more slowly reasonably depending on the viscosity of the formulation/foam) without any tendency to spread in the foam lamellas and laterally on the foam surface, just as could be observed for a commercial reference fire-fighting foam containing fluorinated surfactants (AFFF 3% S, diluted to a 3% solution with tapwater, Dafo Fomtech AB) generated in the same way as described above.

[0139] In case of a non-oleophobic foam, the added heptane droplets could be seen to spread laterally and vertically into the foam lamellas, finally coloring the foam red. This behavior could also be seen for a commercial non-fluorinated foam (Fomtec Enviro 3x3 Ultra, diluted to a 3% solution with tap water, Dafo Fomtec AB) and, in a separate test, with a foam created from a commercial hand dish detergent ("Yes" by Procter and Gamble)

[0140] 1 ml of the hand dish detergent was mixed with 50 ml tap water in a 100 ml glass flask. The mix was vigorously shaken by hand and the formed foam was poured into a glass beaker. Drops of red colored heptane was put onto the foam. Rapid spreading of heptane over the foam/air surface was observed. A red patch of heptane inside the foam also indicated rapid spreading inside the foam.

[0141] This form of spreading into the foam and red-coloring of the foam was never seen for the oleophobic foams. Table 1 below summarizes the results.

[0142] The observations are very central to the above described compositions comprising phospholipids and their use in forming a foam in a fire extinguishing system. The observations directly proves that fire-fighting foams generated in the above way, utilizing plant-based, non-fluorinated materials in low concentration combined with the described novel routes for spontaneous compression of the foam, will result in a foam with the crucial and desired oleophobic properties, which are directly correlated to good resistance to re ignition (long burn-back times) and to low or non-existent fuel-pickup in the foam.

[00105] As discussed above, other scavenger components than inorganic soluble carbonate can be used in the foam forming solution, such as e.g. NH ₃ , HPO ₄ ² , SO ₃ ² and NaOH. Alternatively, other foam forming gases than CO ₂ such as NH ₃ and/or air can be used. In other embodiments no scavenger is used and the foam may be formed and contracted as discussed in the summary section. The results thereof being similiar to the ones observed when using CO ₃ ² as scavenger component and CO ₂ as foam forming gas.

Table 1