FIRE EXTINGUISHING LIQUID

RELATED APPLICATIONS

This application claims the priority of UK patent application GB 2213580.0 filed on 15 September 2022, the contents of which are incorporated by reference herein in their entirety.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to fire extinguishing liquids, methods of manufacturing fire extinguishing liquids, and fire extinguishers containing those liquids.

BACKGROUND TO THE INVENTION

Some fire extinguishers are filled with liquid, herein referred to as ‘fire extinguishing liquid’. There are a number of properties which are desirable for the fire extinguishing liquid. Firstly, it must be effective at suppressing and extinguishing fires. This can be achieved in a number of ways, which are discussed in detail in the “Summary of the Invention” section below. The components contained in the fire extinguishing liquid are selected to maximize its effectiveness.

There is a need for further fire extinguishing liquids which are effective against a range of different types of fire. Different types of fire according to the European standard EN3 include Class A (fires involving organic solids, e.g. wood, paper), Class B (fires involving flammable liquids), Class C (fires involving flammable gases) Class D (fires involving combustible metals) and Class F (fires involving cooking oil and fat). It is rare for a given fire extinguishing liquid to be effective against multiple fire types.

At present, there is an increasing need for fire extinguishing liquids which are effective against lithium-ion (Li-ion) battery fires, particularly with the increasing prevalence of electric vehicles (EVs). A Li-ion battery contains an electrolyte between an anode and a cathode. The anode tends to be graphite and the cathode is a material having the ability to react with lithium ions. The electrolyte contains lithium salts and is flammable. Despite the name, lithium-ion batteries do not contain any lithium metal (although they do contain lithium compounds in the electrodes) and so fire extinguishing compositions which are tailored for metal fires are not suitable. Due to the flammability of the electrolyte, a Li-ion battery fire is akin to a liquid hydrocarbon fire. As such, Li-ion battery fires have more in common with a Class B fire, but in fact fall outside the criteria for both Class B and Class D fires. Li-ion batteries within EVs are particularly hazardous. EV batteries are designed to be lightweight with a high power-density, meaning that the walls of the cell are thin and electrolyte is pressurised. The electrodes also tend to be thin, composed of materials which could rupture and deposit fragments into the electrolyte upon impact, further increasing the flammability of the electrolyte. EV batteries are of course also prone to impact caused by traffic collisions. Such impacts could easily rupture the thin walls of the structural battery components and release the pressurised flammable electrolyte. This leads to a composition which could easily ignite and is potentially explosive, presenting a hazard to the occupants of the vehicle and any passers-by. One hazardous aspect of Li-ion batteries is that as you attempt to remove the wreckage, the debris moves through the pressurised electrolyte risking reignition. The potential for reignition in this way lasts for up to 14 days after the original collision.

Therefore, there is a need for fire extinguishing liquids which are effective in dealing with the unique challenges presented by a Li-ion battery fire in a manner which is safer and more efficient relative to known fire extinguishing compositions.

It is also desirable for fire extinguishing liquids to be effective over a wide range of temperatures. However, particularly in cold climates, the types of fire extinguisher which can be used are restricted. This is because the fire extinguishing liquid is often stored in pressurized containers, and there are safety risks associated with the liquid freezing. In addition to the safety risks, the low temperature can cause (a) freezing of the fire extinguishing liquid and (b) dissolved components in the liquid to come out of solution. Solid particulate matter inside the fire extinguisher can lead to undesirable consequences such as clogging of the nozzle.

SUMMARY OF THE INVENTION

Broadly speaking, the present invention provides a fire extinguishing liquid which demonstrates an improved ability to extinguish Li-ion battery fires quickly and safely relative to known compositions. The fire extinguishing liquid requires lower amounts of salt, making transport of the product more economical, and is cost-effective to manufacture.

In order to achieve this, a first aspect of the present invention provides a fire extinguishing liquid comprising one or more of a phosphate, hydrogen phosphate or dihydrogen phosphate salt, wherein the fire extinguishing liquid contains no, or substantially no, sulphate salts and no, or substantially no, hydrogen carbonate salts. The inventors found that such a fire extinguishing liquid is particularly effective in extinguishing Li-ion battery fires. The one or more of a phosphate, hydrogen phosphate, dihydrogen phosphate or polyphosphate salt has a suffocating effect on the fire as explained in more detail below.

It was found that by ensuring the absence or substantial absence of sulphate salts, the conductivity of the fire extinguishing liquid was reduced. This reduces the occurrence of electrical arcing when the fluid is used to extinguish a battery fire, thereby reducing the risk of sparking which might cause reignition of the Li-ion battery fire or lead to explosion. The liquid is therefore capable of extinguishing battery fires, for example Li-ion battery fires, effectively and with higher safety than existing fire extinguishing liquids.

In addition to this, the fire extinguishing liquid is able to prevent, contain and/or ameliorate thermal runaway in Li-ion batteries. Thermal runaway is the process whereby a fire or explosion is caused by a chain reaction within the battery. Thermal runaway occurs when a fault within a battery leads to an initial temperature rise, which triggers a chain reaction causing a very fast increase in temperature which can lead to fire and/or explosion. The liquid is able to extinguish a fire caused by thermal runaway within a cell of a battery, thereby preventing further thermal runaway in neighbouring cells. This is important because batteries may contain many cells, and limiting a fire to a single cell or a small number of cells can prevent irreparable damage to the battery and significantly reduce the risk of injury to people in the vicinity.

Furthermore, it was surprisingly found that by ensuring the absence or substantial absence of hydrogen carbonate salts, the amount of salt used per litre of liquid was reduced without jeopardising the performance of the fire extinguishing liquid. Since the amount of salt is lower and a reduced weight of ingredients is necessary to manufacture each litre of liquid, the economy of both manufacture and transport of the liquid are improved.

A second aspect of the present invention is a method of manufacturing a fire extinguishing liquid according to the first aspect comprising the step of mixing one or more of a phosphate, hydrogen phosphate or dihydrogen phosphate salt and a liquid vehicle.

A third aspect of the present invention is a fire extinguishing liquid made by a method according to the second aspect. A fourth aspect of the present invention is a fire extinguisher containing the fire extinguishing liquid according to the first aspect.

A fifth aspect of the present invention is a method of extinguishing a fire using a fire extinguishing liquid according to the first aspect.

First Aspect

In the following description, unless otherwise specified, percentages refer to weight percentages (wt%). By “weight percentage”, we mean the percentage by weight relative to the total weight of the liquid.

Herein, phosphate, hydrogen phosphate and dihydrogen phosphate salts are salts including the anions PC>4 ³ ', HPCL ² ' and H ₂ PC>4' respectively.

A hydrogen carbonate salt is a salt including the anion HCOa'.

A sulphate salt is a salt including the anion SCU ^2- .

Preferably, the salts present in the fire extinguishing liquid are each water-soluble. In some embodiments, each of the salts has a solubility in distilled water at 20 °C of at least 5 g / 100 mL, for example at least 6 g / 100 mL, for example at least 10 g / 100 mL, for example at least 15 g / 100 mL, for example at least 20 g / 100 mL.

The counter-ion to the above-mentioned anions may be selected from any suitable cation which combines with the anion to form a salt having the above solubility. Non-limiting examples of cations are alkali metal ions, alkaline earth metal ions, transition metal ions and organic cations such as ammonium ion (NH4 ⁺ ) or primary, secondary, tertiary or quaternary ammonium cations (NH ₂ R ⁺ ; NH ₂ R ₂ ⁺ ; NHR ₂ ⁺ or NR4 ⁺ respectively, wherein each R is independently selected from C1-4 saturated alkyl groups). Preferably, the counter cation is selected from alkali metal ions, alkaline earth metal ions and ammonium ion (NH4 ⁺ ).

In some embodiments, the one or more of a phosphate, hydrogen phosphate, or dihydrogen phosphate salt is a phosphate salt selected from trisodium phosphate (Na ₃ PC>4) and tripotassium phosphate (K3PO4).

In some embodiments, the one or more of a phosphate, hydrogen phosphate, or dihydrogen phosphate salt is a hydrogen phosphate salt, i.e. a salt including the anion HPCL ² '. In some embodiments, the hydrogen phosphate salt is selected from disodium phosphate (Na2HPC>4), dipotassium phosphate (K2HPO4) and diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ). In some embodiments, the hydrogen phosphate salt is diammonium hydrogen phosphate ((N ^HPC i).

In some embodiments, the one or more of a phosphate, hydrogen phosphate, or dihydrogen phosphate salt is a dihydrogen phosphate salt selected from monosodium phosphate (NaH2PO4), monopotassium phosphate (KH2PO4) and monoammonium phosphate ((NH ₄ )H ₂ PO ₄ ).

The fire extinguishing liquid of the first aspect contains no, or substantially no, sulphate salts. Sulphate salts are any salts including the anion SC>4 ² '. Thus, the fire extinguishing liquid of the first aspect contains no, or substantially no, SO ₄ ^2- anions. The term “substantially no sulphate salts” means that sulphate salts are present in an amount of less than 100 ppm (by weight), for example less than 50 ppm, less than 10 ppm, or less than 5 ppm. Examples of such sulphate salts are sodium sulphate (Na2SO4), potassium sulphate (K2SO4) and ammonium sulphate ((NF^SCU).

The fire extinguishing liquid of the first aspect contains no, or substantially no, hydrogen carbonate salts. Hydrogen carbonate salts are any salts including the anion HCCh'. Thus, the fire extinguishing liquid of the first aspect contains no, or substantially no, HCCh' anions. The term “substantially no hydrogen carbonate salts” means that hydrogen carbonate salts are present in an amount of less than 100 ppm (by weight), for example less than 50 ppm, less than 10 ppm or less than 5 ppm. Examples of such hydrogen carbonate salts are sodium hydrogen carbonate (NaHCCh), potassium hydrogen carbonate (KHCO3) and ammonium hydrogen carbonate ((NH4)HCC>3).

Particularly good fire extinguishing properties are observed for the fire extinguishing liquid when the one or more of a phosphate, hydrogen phosphate, or dihydrogen phosphate salt are each ammonium salts. Without wishing to be bound by theory, it is believed that this may be at least partly due to the increased quantity of ammonia produced through thermal decomposition of ammonium salts, which has a suffocating effect on the fire.

Thus, in some embodiments, the fire extinguishing liquid comprises diammonium hydrogen phosphate ((NH4) ₂ HPO4). In some embodiments, the one or more of a phosphate, hydrogen phosphate or dihydrogen phosphate salt consists of a hydrogen phosphate salt. In some embodiments, the one or more of a phosphate, hydrogen phosphate, or dihydrogen phosphate salt consists of diammonium hydrogen phosphate ((NH^HPCU).

In some embodiments, the liquid of the first aspect comprises at least 10 wt% phosphate, hydrogen phosphate or dihydrogen phosphate salt, for example at least 11 wt%, at least 12 wt%, at least 13 wt%, at least 14 wt%, at least 15 wt% or at least 16 wt%. In some embodiments, the liquid comprises up to 30 wt% phosphate, hydrogen phosphate or dihydrogen phosphate salt, for example up to 29 wt%, up to 28 wt%, up to 27 wt%, up to

26 wt%, up to 25 wt%, up to 24 wt%, up to 23 wt%, or up to 22 wt%. In some embodiments, the liquid comprises from 10 to 30 wt% phosphate, hydrogen phosphate or dihydrogen phosphate salt, for example from 15 to 25 wt%, from 18 to 22 wt% or from 20 to 22 wt%.

In some embodiments, the liquid of the first aspect comprises at least 10 wt% diammonium hydrogen phosphate, for example at least 11 wt%, at least 12 wt%, at least 13 wt%, at least 14 wt%, at least 15 wt% or at least 16 wt%. In some embodiments, the liquid comprises up to 30 wt% diammonium hydrogen phosphate, for example up to 29 wt%, up to 28 wt%, up to

27 wt%, up to 26 wt%, up to 25 wt%, up to 24 wt%, up to 23 wt%, or up to 22 wt%. In some embodiments, the liquid comprises from 10 to 30 wt% diammonium hydrogen phosphate, for example from 15 to 25 wt%, from 18 to 22 wt%, or from 20 to 22 wt%.

In some embodiments, the fire extinguishing liquid further comprises propylene glycol.

In some embodiments, the fire extinguishing liquid comprises:

(a) one or more of a phosphate, hydrogen phosphate or dihydrogen phosphate salt; and

(b) propylene glycol (C3H8O2).

In this way, the fire extinguishing liquid is able to operate at lower temperatures without freezing due to the presence of propylene glycol in the composition. In some cases, the fire extinguishing liquid may be able to operate at temperatures as low as -20 °C without freezing. As such, the liquid may enable liquid-based fire extinguishers to operate in colder climates, as described above.

Herein, the terms “propylene glycol” and “monopropylene glycol” may be used interchangeably to refer to the compound:

In some embodiments, the fire extinguishing liquid comprises: diammonium hydrogen phosphate ((NH^HPCU) and propylene glycol (C3H8O2).

In some embodiments, the liquid comprises at least 10 wt% monopropylene glycol, for example at least 10.5 wt%, at least 11 wt%, at least 11.5 wt%, at least 12 wt%, at least 12.5 wt%, at least 13 wt%, at least 13.5 wt%, at least 14 wt%, at least 14.5 wt% or at least 15 wt%.

In some embodiments, the molar ratio in the fire extinguishing liquid of the one or more of phosphate, hydrogen phosphate or dihydrogen phosphate anion to the propylene glycol, is from 0.3:1 to 0.8:1, preferably from 0.4:1 to 0.7:1.

In some embodiments, alongside the above components are dissolved in a liquid vehicle, preferably water, more preferably demineralised water, and even more preferably water which is both deionised and demineralised. The use of demineralised water further reduces the conductivity of the liquid, further improving its safety. The use of water which is both deionised and demineralised reduces conductivity even further, providing a very safe liquid for use in extinguishing battery fires.

Advantageously, the conductivity of the fire extinguishing fluid is further reduced by the presence of water which is both deionised and demineralised.

Therefore, preferably the fire extinguishing liquid is an aqueous solution of the above mentioned components. In other words, the fire extinguishing liquid comprises:

(a) one or more of a phosphate, hydrogen phosphate or dihydrogen phosphate salt;

(b) optionally propylene glycol (C3H8O2); and

(c) water.

In some embodiments, the liquid of the first aspect comprises at least 30 wt% water, for example at least 35 wt%, at least 40 wt%, at least 45 wt%, at least 50 wt%, at least 60 wt% or at least 70 wt%. In some embodiments, the liquid comprises up to 80 wt% water, for example up to 75 wt%. In some embodiments, the liquid comprises 30 to 80 wt% water, for example 50 to 80 wt%, 60 to 80 wt%, 65 to 75 wt% or 70 to 75 wt%.

In some embodiments, the molar ratio in the fire extinguishing liquid of the one or more of phosphate, hydrogen phosphate or dihydrogen phosphate anion to water, is from 0.01 :1 to 0.5:1 , preferably from 0.03:1 to 0.2:1, more preferably from 0.03:1 to 0.05:1.

Such ratios of components have been found to lead to enhanced firefighting abilities of the fire extinguishing liquid.

It has been found that a fire extinguishing liquid of the present invention demonstrates better fire extinguishing results than known liquids.

In order to better understand why the liquid displays these advantageous effects, the mechanism of combustion must first be understood namely the process of: heating decomposition (or gasification) ignition combustion extended chain of flame. Fire retardants or suppressants work by interfering with one or more of the steps in this mechanism. For example, they may work by blocking the oxygen supply or forming an oxygen blockade layer; controlling the production of combustion gas; lowering the temperature of the combustibles, or generating incombustible gas and diluting combustible gas.

Examples of fire extinguishing mechanisms are as follows:

(i) Suffocation, in which gases generated by the heating of components in the fire extinguishing liquid (i.e. gas which is vaporized and generated by heat energy of the combustibles), e.g. ammonia, carbon dioxide, nitrogen, or water vapour, have a dilution effect on the combustible gas, and a suffocation effect due to oxygen blockade.

(ii) Endothermic effects, wherein the sublimation, vaporization, decomposition or heating of components within the fire extinguishing liquid (or combustion residues) leads to a temperature fall, as the heat energy released by the fire is expended in heating/vaporizing components of the liquid, rather than stoking the fire.

(iii) Restraining effects, in which the fire extinguishing liquid confines the combustibles, and has a fireproofing effect on said combustibles (i.e. forming a protective layer), both restraining the outbreak of gas and preventing the underlying material from igniting. Alternatively, the non-combustible solid combustion residues may provide the fireproofing effect. Turning specifically to the components of the liquid of the present invention: without wishing to be bound by theory it is believed that when coming into contact with the heat of a fire, diammonium hydrogen phosphate decomposes according to: (NH^HPC i H3PO4 + 2NH3, producing ammonia gas. The ammonia has a suffocating effect on the fire, by replacing the oxygen in the surroundings. It also helps to cool the combustibles by its heat of vaporization (see the endothermic effect above). Furthermore, chemical agents which are not vaporized stick to any combustibles, and in so doing make them non-combustible, by the restraining effect described above.

Similar to the diammonium hydrogen phosphate, without wishing to be bound by theory it is believed that ammonium sulphate decomposes by pyrolysis according to (NH^SC i 2NH3 + H2SO4, followed by the decomposition of the H2SO4 product into SO3 and H2O. Treating a source of combustion with (NH ₄ )2SO4 lowers the threshold temperature for pyrolysis and combustion and provides an increase in the residue or char production, which further contributes to retardancy. However, char production is not relevant to Li-ion battery fires, and it has been found that in the absence of any sulphate salt, the suffocating effect of the remaining components of the fire extinguishing liquid is not significantly affected. The conductivity of the fire extinguishing liquid is reduced by the absence of ammonium sulphate and so the occurrence of arcing within the cell is reduced, reducing the risk of reignition when the liquid is used to extinguish battery fires, such as Li-ion battery fires.

Further, without wishing to be bound by theory it is believed that when coming into contact with the heat of the fire, ammonium hydrogen carbonate decomposes according to: NH3 + CO2 + H2O. The ammonia has the same effects as for the diammonium hydrogen phosphate. In addition, the CO2 and H2O also serve to have a suffocating effect on the flames. However, it has been surprisingly found that in the absence of any hydrogen carbonate salt, the suffocating effect of the remaining components of the fire extinguishing liquid is not significantly affected, and in addition the liquid contains smaller quantities of salt per litre and is more straightforward to manufacture.

When monopropylene glycol is present in the fire extinguishing liquid, this lowers the freezing point of the liquid. In doing so, it enables the liquid to be used in colder temperatures, specifically at temperature as low as -20 °C. Furthermore, in contrast to other “anti-freezing” agents, monopropylene glycol is advantageous since it is both environmentally friendly and non-toxic. Being able to operate at lower temperatures is especially useful, for example, in cold countries where prior art fire extinguishing liquid would freeze, greatly reducing its effectiveness. Prior to now, it was necessary to use powder or CO2 based extinguishers in such cold countries.

Preferably, at atmospheric pressure, the fire extinguishing liquid has a freezing point of at most 0 °C, for example at most -5 °C, at most -10 °C, at most -15 °C or at most -20 °C.

The fire extinguishing liquid may further include a firefighting foam component. Such a component both adds to the cooling effect of the liquid, and coats the combustible material, preventing oxygen contact and suppressing combustion. The foam component may include a surfactant, to lower the surface tension of the water in the foam. By lowering the surface tension, the water is able to better wet the surface of the combustible material, further reducing oxygen contact. In preferred embodiments, the firefighting foam component is a firefighting foam. In some embodiments, the firefighting foam component is an aqueous film forming foam (AFFF), such as FOMTEC® AFFF 3%. In some embodiments, the firefighting foam component is alcohol resistant aqueous film forming foam (AR-AFFF). The selection of firefighting foam component may depend on the particular intended application of the fire extinguishing liquid, as would be understood by the skilled person.

One example of a suitable AR-AFFF is Non-Newtonian 3x3% AR-AFFF manufactured by Aberdeen Foam.

In some embodiments, the firefighting foam component comprises diethylene glycol monobutyl ether, sulphuric acid mono-C6-C12-alkyl esters sodium salts, propan-1, 2-diol, alkyl polyglycoside and ethylene oxide polymer.

In some embodiments, the firefighting foam component comprises 2-methylpentane-2-4-diol, sodium decyl sulphate and sodium octyl sulphate.

In some embodiments, the liquid contains at least 2% firefighting foam component, for example at least 2.5%, at least 3%, at least 3.5% or at least 4%

In some embodiments, the liquid contains up to 12% firefighting foam component, for example up to 11.5%, up to 11% or up to 10.5%.

In some embodiments, the liquid contains from 2 to 12 wt% firefighting foam component, for example from 2 to 10 wt%, from 2 to 8 wt%, from 2 to 6 wt% or from 4 to 5 wt%. In some embodiments, the liquid contains at least 2% AR-AFFF, for example at least 2.5%, at least 3%, at least 3.5% or at least 4%

In some embodiments, the liquid contains up to 12% AR-AFFF, for example up to 11.5%, up to 11% or up to 10.5%.

In some embodiments, the liquid contains from 2 to 12 wt% AR-AFFF, for example from 2 to 10 wt%, from 2 to 8 wt%, from 2 to 6 wt% or from 4 to 5 wt%.

It has been found that liquids having compositions falling within the ranges set out above demonstrate improved fire extinguishing capabilities. For example, such liquids may provide reduced extinguishing time, reduced residual temperatures and/or a reduced quantity of liquid necessary to achieve extinguishment.

In some embodiments, the liquid of the first aspect comprises or consists of

10 to 35 wt%, for example 15 to 25 wt% or 20 to 22 wt% diammonium hydrogen phosphate; optionally 2 to 6 wt%, for example 3 to 5 wt% firefighting foam component; and balance water, to provide a total of 100 wt%; wherein the fire extinguishing liquid contains no, or substantially no, sulphate salts and no, or substantially no, hydrogen carbonate salts.

In some embodiments, the liquid of the first aspect comprises or consists of

10 to 35 wt%, for example 15 to 25 wt% or 20 to 22 wt% diammonium hydrogen phosphate; optionally 2 to 6 wt%, for example 3 to 5 wt% firefighting foam component; and 65 to 75 wt% water; wherein the amount of all components totals 100 wt%; wherein the fire extinguishing liquid contains no, or substantially no, sulphate salts and no, or substantially no, hydrogen carbonate salts.

In some embodiments, the liquid of the first aspect comprises or consists of

20 to 22 wt% diammonium hydrogen phosphate; optionally 3 to 5 wt% firefighting foam component; and balance water, to provide a total of 100 wt%; wherein the fire extinguishing liquid contains no, or substantially no, sulphate salts and no, or substantially no, hydrogen carbonate salts.

In some embodiments, the liquid of the first aspect comprises or consists of

20 to 22 wt% diammonium hydrogen phosphate; optionally 3 to 5 wt% firefighting foam component; and

65 to 75 wt% water; wherein the amount of all components totals 100 wt%; wherein the fire extinguishing liquid contains no, or substantially no, sulphate salts and no, or substantially no, hydrogen carbonate salts.

In some embodiments, the liquid of the first aspect comprises or consists of 15 to 25 wt% diammonium hydrogen phosphate;

2 to 8 wt% AR-AFFF; and balance water, to provide a total of 100 wt%; wherein the fire extinguishing liquid contains no, or substantially no, sulphate salts and no, or substantially no, hydrogen carbonate salts.

In some embodiments, the liquid of the first aspect comprises or consists of 20 to 22 wt% diammonium hydrogen phosphate;

3 to 5 wt% AR-AFFF; and balance water, to provide a total of 100 wt%; wherein the fire extinguishing liquid contains no, or substantially no, sulphate salts and no, or substantially no, hydrogen carbonate salts.

■ The liquid of the first aspect may contain 60% to 80% water, and more preferably 65% to 75% water, and more preferably still 70% to 75% water.

■ The liquid of the first aspect may contain 10% to 30% diammonium hydrogen phosphate, and more preferably 15% to 25% diammonium hydrogen phosphate, and more preferably still 20% to 22% diammonium hydrogen phosphate.

Second Aspect

A second aspect of the invention is a method of manufacturing a fire extinguishing liquid according to the first aspect comprising the step of mixing one or more of a phosphate, hydrogen phosphate or dihydrogen phosphate salt and a liquid vehicle. In some embodiments, the liquid vehicle is water, preferably demineralised water, even more preferably water which is both deionised and demineralised. In some embodiments, the method comprises the step of mixing diammonium hydrogen phosphate ((NH^HPCU) and a liquid vehicle. In some embodiments, the liquid vehicle is water, preferably demineralised water, even more preferably water which is both deionised and demineralised.

In some embodiments, the method further comprises mixing propylene glycol (C3H8O2) with the diammonium hydrogen phosphate ((NH^HPC i) and liquid vehicle.

In some embodiments, the method of manufacturing the fire extinguishing liquid comprises the steps of:

(A) heating water, preferably water which is both deionised and demineralised, to a temperature above room temperature; and

(B) adding diammonium hydrogen phosphate ((NH^HPC ) to the water.

In some embodiments the method further comprises adding propylene glycol (C3H8O2) to the water in step (B).

In some embodiments, the method further comprises the addition of the firefighting foam component described above.

In some embodiments, the method comprises mixing the solution after the addition of one or more of diammonium hydrogen phosphate ((NH^HPCU) and propylene glycol (C3H8O2). In some embodiments, after step (B) the method includes an additional step (C) of cooling the solution to below 25°C.

In some embodiments, after step (C) the method includes an additional step (D) of filtering the solution to remove undissolved residue. This filtering step may be carried out using any well-known filtration technique, including but not limited to passing the solution through filter paper or a sieve.

‘Room temperature’ refers to a temperature of around 21 °C.

In some embodiments, the water is first heated in step (A) to a temperature in the range 30 to 70 °C before any of the other components are added. This leads to improved dissolution of the other components of the composition. In some embodiments, the heating is carried out using an immersion heater, such as an electric element within the mixing tank. Other suitable methods of heating the water are known to the skilled person.

In some embodiments, diammonium hydrogen phosphate ((NH^HPO^ and optionally propylene glycol (C3H8O2) are added to the water separately. In some embodiments, diammonium hydrogen phosphate ((NH^HPO^ is added to the water in a first step, followed by the remaining components. In some embodiments, propylene glycol (C3H8O2) is added the diammonium hydrogen phosphate ((NH^HPOt) has been added.

In some embodiments, the method of manufacturing the fire extinguishing liquid comprises the steps of:

(i) heating water to a temperature above room temperature, preferably to a temperature in the range 30 to 70 °C;

(ii) adding diammonium hydrogen phosphate and mixing until dissolved; and

(iii) optionally adding one or more of monopropylene glycol and firefighting foam component, and mixing until dissolved.

In some embodiments, after optional step (iii) the method includes an additional step (iv) of cooling the solution of water and diammonium hydrogen phosphate to below 25°C.

In some embodiments, after step (iv) the method includes an additional step (v) of filtering the solution to remove undissolved residue. This filtering step may be carried out using any well-known filtration technique, including but not limited to passing the solution through filter paper or a sieve.

The amount of each component added to the water is preferably selected to arrive at a composition having:

■ 60% to 80% of water, and more preferably 65% to 75% of water, and more preferably still 70% to 75% of water.

■ 10% to 30% diammonium hydrogen phosphate, and more preferably 15% to 25% diammonium hydrogen phosphate, and more preferably still 20% to 22% diammonium hydrogen phosphate.

■ when present, 10% to 20% monopropylene glycol, and more preferably 12.5% to 17.5% monopropylene glycol, and more preferably still 15% to 17% monopropylene glycol.

■ when present, from 2 to 12 wt% firefighting foam component, for example from 2 to 10 wt%, from 2 to 8 wt%, from 2 to 6 wt% or from 4 to 5 wt% In step (ii) the component is preferably added to the mixture in their natural physical form, that is in solid form, preferably in the form of grains or a powder. Throughout these steps the diammonium hydrogen phosphate is preferably added while the mixture is being mixed or stirred. In optional step (iii) the monopropylene glycol is preferably added in its natural physical form, namely in liquid form.

The method may further include a step of adding a firefighting foam component as described earlier in the application. As above, the weight of firefighting foam component is preferably selected to arrive at an overall composition having 2% to 6%, for example 3% to 5% of firefighting foam component.

By heating the water first, in step (i), the dissolution of the components in steps (ii) to (iii) is improved. In preferred embodiments, the addition of the diammonium hydrogen phosphate is carried out in small increments. In this way, the chance of a rapid reduction in the temperature of the water is prevented, which may otherwise lead to a reduction in solubility. Specifically, in preferred embodiments, after a small amount of diammonium hydrogen phosphate is added to the water, that small amount should dissolve fully before a second small amount is added. In some embodiments, the total amount of diammonium hydrogen phosphate is added to the liquid vehicle in two or more batches, for example three, four or five batches, allowing for full dissolution, preferably with mixing, after each batch addition. In some embodiments, after all of the diammonium hydrogen phosphate is added, the mixture is mixed or stirred for 10 to 30 minutes to ensure an even distribution of the diammonium hydrogen phosphate throughout the mixture. Furthermore, throughout the addition step (ii), it is preferable that the water is maintained at a temperature from 30°C to 70°C, in order to aid the dissolution of the diammonium hydrogen phosphate.

After step (ii), the mixture may be mixed or stirred for 5 to 20 minutes, again to ensure uniform distribution of the diammonium hydrogen phosphate throughout the mixture. More preferably, the mixture is mixed or stirred for about 10 minutes.

In step (iv), it is preferable that the water is cooled to below 25 °C, for example below 24 °C, below 23 °C, below 22 °C, below 21 °C or below 20 °C. In some embodiments, the solution is left to cool naturally for a period of at least 5 hours, such as at least 6 hours, at least 7 hours or at least 8 hours. By cooling the mixture to a temperature which is approximately room temperature, the capacity of the water to hold the diammonium hydrogen phosphate in solution is decreased. As a result, a portion of any or all of these components may precipitate out of solution. Clearly, it is undesirable that this happens when the liquid has been packaged in e.g. a fire extinguisher. For example, such precipitation may cause the solid grains to block the extinguisher nozzle or any valves within extinguishers or aerosols, which risks reducing its effectiveness, or even rendering the fire extinguisher completely inoperable. So, the combination of the cooling in step (iv) and the filtering in step (v), which removes any diammonium hydrogen phosphate which may have precipitated as a result of cooling, and also any undissolved residues or impurities, ensures that the liquid does not contain any solid particulate matter which could block or damage a fire extinguisher in which the liquid may be contained.

The filtering may be performed using a mesh, the mesh size (i.e. the average size of the holes in the mesh) of which, is preferably selected to catch (i.e. filter out) particles whose dimensions are such that they risk damaging or blocking a fire extinguisher. For example, the mesh size may be 0.5 mm or less. More preferably the mesh size is 0.1 mm or less, and more preferably still, the mesh size is 0.05 mm or less.

The method may include a further step of filling a fire extinguisher with the liquid. Step (v), the filtering step, may take place as the fire extinguisher is being filled, in order to minimize the number of steps in the manufacturing process.

Third Aspect

A third aspect of the present invention provides a fire extinguishing liquid made by a method according to the second aspect of the present invention.

The liquid may include any of the optional features which have been set out above with respect to the first and second aspects of the invention, where compatible.

Fourth Aspect

A fourth aspect of the present invention provides a fire extinguisher (i.e., a fire extinguishing device) containing the liquid according to the first aspect of the present invention. The liquid may include any of the optional features which have been set out above with respect to the first, second and third aspects of the invention, where compatible.

A variety of fire extinguishing devices may be used to contain and deliver the fire extinguishing liquid according to the invention. For example, self-contained hand-held pressurised extinguishers may be used, wherein the liquid is delivered through a nozzle. The liquid may also be added to a sealed sachet, which could find use for example in fighting pan fires in a domestic environment. More sophisticated fire-fighting systems could also employ the fire extinguishing liquid of the invention, for example hose reel jets, high pressure hose reel jets, compressed air foam systems and ultra high pressure lance systems. Such systems are more suited for use by professional fire-fighters, such as fire and rescue service crew.

The liquid may be used in its concentrated form according to a composition as described herein, or may be diluted further with a liquid vehicle such as water. For example, the liquid may be diluted with water to provide a weight ratio of extinguishing liquid : water in the range of from 4:96 to 50:50, preferably from 6:94 to 30:70.

Other aspects

Another aspect of the invention is the use of a fire extinguishing liquid according to the first aspect of the present invention to reduce the risk of reignition when extinguishing a battery fire. Another aspect of the invention is the use of a fire extinguishing liquid according to the first aspect of the present invention to improve safety when extinguishing a battery fire. Another aspect of the invention is the use of a fire extinguishing liquid according to the first aspect of the present invention to reduce or eliminate the occurrence of arcing or sparking when extinguishing a battery fire. Another aspect of the invention is the use of a fire extinguishing liquid according to the first aspect of the present invention to prevent, contain and/or ameliorate thermal runaway in a Li-ion cell or battery.

EXAMPLES

Example 1

A fire extinguishing liquid was prepared according to the following method:

1) deionised and demineralized water was run into a mixing vessel, and heated to 40°C using an electric element located within the mixing vessel.

2) diammonium hydrogen phosphate was added slowly to the demineralized water in batches, allowing each batch to dissolve before making another addition. Thereafter, the solution was mixed for 15 to 20 minutes until the last of the diammonium hydrogen phosphate was dissolved.

3) AR-AFFF was added (Non-Newtonian 3x3% AR-AFFF manufactured by Aberdeen Foam), while slowly mixing (to avoid foaming). The mixture was allowed to cool to below 25 °C, and was then passed through a 20pm filter and the filtrate was passed directly into a fire extinguisher vessel.

The quantities of each ingredient were measured so that the amounts of each component in the final composition fell within the following ranges, based on the total weight of the overall composition: 20 to 22 wt% diammonium hydrogen phosphate; 3 to 5 wt% AR-AFFF; and 65 to 75 wt% deionised/demineralised water.

Comparative Example 1

A fire extinguishing liquid was prepared in the same way as Example 1, except that ammonium sulphate was added so that it made up about 2-3 wt% of the overall composition.

Conductivity Tests

Table 1

Table 1 shows conductivity data for Example 1 and Comparative Example 1 alongside some other common liquids. All conductivity measurements were carried out at 25 °C.

The data shows that the absence of sulphate salts in the fire extinguishing liquid of the present invention results in a lower conductivity of the liquid. It should be noted that, given the nature of the fire extinguishing liquid (i.e. a combination of phosphates and surfactants suspended in water), achieving 0 mS/cm is not possible. In the context of the invention, anything below 120 mS/cm represents an excellent value for conductivity of the fire extinguishing liquid when used to extinguish battery fires which would be expected to reduce the occurrence of arcing and reignition. Fire Tests

Battery fire tests

A 6-litre steel Commander Edge Extinguisher was filled with the liquid of Example 1 and nitrogen gas was added as propellant. The extinguisher included a foam rose nozzle.

The same was done with the liquid of Comparative Example 1.

The extinguishers were each used on a range of fire types and the results are provided in Table 2 below.

Table 2

The results show that the liquids perform equally well in the initial extinguishment of Li-ion battery fires, despite the absence of ammonium sulphate from the Example 1 liquid. The liquid of the invention is able to very quickly extinguish a fire fuelled by six large e-scooter batteries. Furthermore, the reduced conductivity of the Example 1 liquid can be expected to reduce the risk of reignition of the battery fires relative to liquids of higher conductivity.

The lack of any hydrogen carbonate salt produced a liquid of reduced mass without jeopardising its ability to extinguish the fires.

Scooter battery tests

Different sizes of standard P50 fire extinguisher cylinders were filled with the Example 1 liquid.

Different sizes of banks of cells from e-scooters were set alight and the fire was allowed to burn before the Example 1 liquid was applied using the extinguisher cylinders.

Table 3 shows the conditions used in the tests. Table 3

In all three tests the liquid was applied to the fire until the cylinder was empty. In all three tests the fire was fully extinguished and remained extinguished 5 minutes after the cylinder had emptied, showing that no reignition of the fire had occurred. This result amounted to a pass in all three cases.

Class A timber fire tests

Standard Class A fire tests were conducted using the Example 1 liquid.

The test involves constructing a wooden crib structure by stacking wooden batons in layers alternating between longitudinal and transverse directions, with 6 cm clearance between neighbouring batons within a layer. The cribs were all 700 mm high (14 layers of 50 mm thick batons: 7 layers longitudinal and 7 layers transverse) and the width was 500 mm. The length of the crib varies according to the rating of the test as shown in Table 4.

Table 4 Once constructed, the crib was ignited using a heptane fuel within a tray positioned beneath the crib. The fire is allowed to establish for 2 minutes before removing the trays and allowing the fire to burn for a further 6 minutes.

A P5 fire extinguisher cylinder containing the Example 1 liquid is then used to extinguish the fire. The test is successful if the entire fire is extinguished and no reignition is observed within 3 minutes following the end of the extinguishing procedure.

For example, an extinguisher rated 8A means that it is able to fully extinguish the 8A crib size with no reignition after 3 minutes (800 mm long, 500 mm deep crib), but is unable to pass the test on the next largest crib size (13A).

The results are set out in Table 5.

Table 5

The results show that the fire extinguishing liquid still works well against Class A timber fires when used in standard P5 extinguishers, despite the tailoring of the composition to be of lower density and deliver improved results specifically against lithium ion battery fires.

While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

All references referred to above are hereby incorporated by reference.