USE OF A FIRE EXTINGUISHING LIQUID

RELATED APPLICATIONS

This application claims the priority of UK patent application GB 2213898.6 filed on 23 September 2022, the contents of which are incorporated by reference herein in their entirety.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a new use of a fire extinguishing liquid, , and uses of 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.

It is 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.

Furthermore, 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) 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.

WO 2021/078381 describes a fire extinguishing liquid containing one or more of a phosphate, hydrogen phosphate or dihydrogen phosphate salt; a hydrogen carbonate salt; and a sulphate salt. The inventors have unexpectedly discovered that the liquid is particularly effective in certain applications.

SUMMARY OF THE INVENTION

Broadly speaking, the present invention provides the use of a fire extinguishing liquid as a flame-retardant treatment on a flammable entity. In particular, a first aspect of the present invention provides the use of a fire extinguishing liquid as a flame-retardant treatment on a flammable entity; the fire extinguishing liquid comprising:

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

(b) a hydrogen carbonate salt; and

(c) a sulphate salt.

A second aspect of the invention relates to the use of a fire extinguishing liquid as a flameretardant treatment on a flammable entity to reduce the flammability or ignitability of the flammable entity; the fire extinguishing liquid comprising:

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

(b) a hydrogen carbonate salt; and

(c) a sulphate salt.

A third aspect of the present invention provides the use of a fire extinguisher (i.e. , a fire extinguishing device) containing a fire extinguishing liquid to deliver a flame-retardant treatment to a flammable entity to reduce the flammability or ignitability of the flammable entity; the fire extinguishing liquid comprising:

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

(b) a hydrogen carbonate salt; and

(c) a sulphate salt.

Another aspect of the invention is a method of treating a flammable entity, for example vegetation, to reduce the flammability or ignitability of the flammable entity; the fire extinguishing liquid comprising:

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

(b) a hydrogen carbonate salt; and

(c) a sulphate salt.

The inventors have found that such a fire extinguishing liquid meets European standards for extinguishing at least fire types A and F. Furthermore it has been surprisingly found that, when used as a preventative treatment on a flammable entity which is at risk of ignition, the fire extinguishing liquid provides effective long-term protection from subsequent ignition or burning of the entity.

It has been found that the liquid is particularly effective as a flame-retardant treatment on vegetation which is at risk of setting alight and burning in a wildfire or bush fire. Thus in some embodiments, the first aspect provides the use of a fire extinguishing liquid as a flame retardant treatment on vegetation to reduce the flammability or ignitability of the vegetation; the fire extinguishing liquid comprising:

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

(b) a hydrogen carbonate salt; and

(c) a sulphate salt.

The prevention of ignition of vegetation is becoming an increasingly urgent problem as global temperatures rise and wildfires become more frequent in many locations around the world. The spread of wildfires leads to costly loss of crops, loss of wildlife habitat, huge CO2 emissions and a risk to life. The fire extinguishing liquid described herein can be used to treat vegetation, for example dry vegetation, as a preventative measure and the risk of subsequent ignition or burning of the treated vegetation is significantly reduced.

Herein, phosphate, hydrogen phosphate and dihydrogen phosphate salts are salts including the anions PO ', HPCU ² ' and H2POT respectively.

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

A sulphate salt is a salt including the anion SO

Preferably, the salts 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 (NHsR ⁺ ; NH2R2 ⁺ ; NHR ₃ ⁺ 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 (NH ₄ ⁺ ).

In some embodiments, the phosphate salt is selected from trisodium phosphate (NasPC ) and tripotassium phosphate (K3PO4).

In some embodiments, the hydrogen phosphate salt is selected from disodium phosphate (Na2HPO ₄ ), dipotassium phosphate (K2HPO4) and diammonium hydrogen phosphate ((NH ₄ )2HPC>4). In some embodiments, the hydrogen phosphate salt is diammonium hydrogen phosphate ((NF^HPC ).

In some embodiments, the dihydrogen phosphate salt is selected from monosodium phosphate (NaF^PC ), monopotassium phosphate (KH2PO4) and monoammonium phosphate ((NH ₄ )H2PO4).

In some embodiments, the hydrogen carbonate salt is selected from sodium hydrogen carbonate (NaHCOs), potassium hydrogen carbonate (KHCO3) and ammonium hydrogen carbonate ((NH ₄ )HCO3). In some embodiments, the hydrogen carbonate salt is ammonium hydrogen carbonate ((NH ₄ )HCO3).

In some embodiments, the sulphate salt is selected from sodium sulphate (Na2SO ₄ ), potassium sulphate (K2SO4) and ammonium sulphate ((NF^SC ). In some embodiments, the sulphate salt is ammonium sulphate ((NF^SC ).

In some embodiments, component (a) is a hydrogen phosphate salt, i.e. a salt including the anion HPC ² '.

Particularly good fire extinguishing properties are observed for the fire extinguishing liquid when the salts in components (a), (b) and (c) 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 ((NF^HPC ), ammonium bicarbonate (NH4HCO3), and ammonium sulphate ((NF^SC ). In some embodiments, component (a) (the phosphate, hydrogen phosphate or dihydrogen phosphate salt) consists of a hydrogen phosphate salt. In some embodiments, component

(a) (the phosphate, hydrogen phosphate or dihydrogen phosphate salt) consists of diammonium hydrogen phosphate ((NH^HPC ).

In some embodiments, component (b) (the hydrogen carbonate salt) consists of ammonium bicarbonate (NH4HCO3).

In some embodiments, component (c) (the sulphate salt) consists of ammonium sulphate ((NH ₄ ) ₂ SO ₄ ).

In some embodiments, the fire extinguishing liquid comprises:

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

(b) a hydrogen carbonate salt;

(c) a sulphate salt; and

(d) 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 ₄ )2HPO ₄ ), ammonium bicarbonate (NH ₄ HCC>3), ammonium sulphate ((NH ₄ )2SO ₄ ) and propylene glycol (C3H8O2). 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) a hydrogen carbonate salt;

(c) a sulphate salt;

(d) optionally propylene glycol (C3H8O2); and

(e) water.

Optional features of the invention will now be set out. These are applicable singly or in any combination with any aspect of the invention.

It has been found that a fire extinguishing liquids of the present invention demonstrate a surprisingly effective preventative effect when applied to flammable entities before ignition, in particular when applied to vegetation. In preferred embodiments, the components set out above are dissolved in a solvent, preferably water, and more preferably demineralized water.

Without wishing to be bound by theory, it is believed that the liquid may be particularly effective when used as a flame-retardant treatment on a flammable entity, to reduce the flammability or ignitability of the flammable entity. Due to the particular ratios of components employed the liquid having the composition described herein is particularly effective at being easily absorbed by a flammable entity, in particular dry vegetation, to create a coating on the surface of the entity which covers a relatively large proportion of the surface. In this way, when used as a preventative flame retardant, the liquid reduces the surface tension of a fuel source, releasing incumbent heat once a fire is ignited, preventing the build-up of flammable gases and thereby preventing ignition or reignition.

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. In some embodiments, the molar ratio in the fire extinguishing liquid of the phosphate, hydrogen phosphate or dihydrogen phosphate anion in (a), to the hydrogen carbonate anion in (b), is from 5:1 to 20:1, preferably from 6:1 to 15:1.

In some embodiments, the molar ratio in the fire extinguishing liquid of the phosphate, hydrogen phosphate or dihydrogen phosphate anion in (a), to the sulphate anion in (c), is from 3:1 to 15:1, preferably from 4:1 to 10:1.

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

In some embodiments, the fire extinguishing liquid also comprises water as a solvent, alongside the components mentioned above, such that the liquid is an aqueous solution of the specified components. In some embodiments, the molar ratio in the fire extinguishing liquid of the phosphate, hydrogen phosphate or dihydrogen phosphate anion in (a), to water, is from 0.01:1 to 0.5:1, preferably from 0.03: 1 to 0.2: 1.

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

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.

In some embodiments, the liquid 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%, up to 22 wt%, up to 21 wt% or up to 20 wt%.

In some embodiments, the liquid comprises at least 0.01 wt% ammonium bicarbonate, for example at least 0.02 wt%, at least 0.03 wt%, at least 0.04 wt%, at least 0.05 wt%, at least 0.1 wt%, at least 0.2 wt%, at least 0.3 wt%, at least 0.4 wt%, at least 0.5 wt%, at least 0.6 wt%, at least 0.7 wt%, at least 0.8 wt%, at least 0.9 wt% or at least 1.0 wt%. In some embodiments, the liquid comprises up to 5 wt% ammonium bicarbonate, for example up to 4.5 wt%, up to 4 wt%, up to 3.5 wt%, up to 3 wt%, up to 2.5 wt% or up to 2 wt%.

In some embodiments, the liquid comprises at least 0.01 wt% ammonium sulphate, for example at least 0.02 wt%, at least 0.03 wt%, at least 0.04 wt%, at least 0.05 wt%, at least 0.1 wt%, at least 0.2 wt%, at least 0.3 wt%, at least 0.4 wt%, at least 0.5 wt%, at least 1.0 wt%, at least 1.5 wt%, at least 2 wt%, at least 2.5 wt% or at least 3 wt%. In some embodiments, the liquid comprises up to 10 wt% ammonium sulphate, for example up to 9 wt%, up to 8 wt%, up to 7 wt%, up to 6 wt%, up to 5 wt% or up to 4 wt%.

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 liquid comprises up to 20 wt% ammonium sulphate, for example up to 19.5 wt%, up to 19 wt%, up to 18.5 wt%, up to 18 wt%, up to 17.5 wt% or up to 17 wt%.

In some embodiments, alongside the above components the liquid comprises balance solvent, preferably water, more preferably demineralised water. In some embodiments, the liquid comprises at least 30 wt% water, for example at least 35 wt%, at least 40 wt%, at least 45 wt% or at least 50 wt%. In some embodiments, the liquid comprises up to 70 wt% water, for example up to 65 wt% or up to 60 wt%.

In some embodiments, the liquid comprises

10 to 35 wt%, for example 20 to 30 wt% diammonium hydrogen phosphate;

0.01 to 5 wt%, for example 1 to 4 wt% ammonium bicarbonate;

0.01 to 10 wt%, for example 3 to 8 wt% ammonium sulphate; optionally 2 to 6 wt%, for example 3 to 5 wt% firefighting foam component; and balance water, to provide a total of 100 wt%.

In some embodiments, the liquid comprises

10 to 35 wt%, for example 20 to 30 wt% diammonium hydrogen phosphate;

0.01 to 5 wt%, for example 1 to 4 wt% ammonium bicarbonate;

0.01 to 10 wt%, for example 3 to 8 wt% ammonium sulphate; optionally 2 to 6 wt%, for example 3 to 5 wt% firefighting foam component; and 50 to 70 wt% water; wherein the amount of all components totals 100 wt%. In some embodiments, the liquid comprises

10 to 30 wt% diammonium hydrogen phosphate;

0.01 to 5 wt% ammonium bicarbonate;

0.01 to 10 wt% ammonium sulphate;

10 to 20 wt% monopropylene glycol; optionally 2 to 4 wt% firefighting foam component; and balance water, to provide a total of 100 wt%.

In some embodiments, the liquid comprises

10 to 30 wt% diammonium hydrogen phosphate;

0.01 to 5 wt% ammonium bicarbonate;

0.01 to 10 wt% ammonium sulphate;

10 to 20 wt% monopropylene glycol; optionally 2 to 4 wt% firefighting foam component; and

50 to 70 wt% water; wherein the amount of all components totals 100 wt%.

■ The liquid may contain 50% to 70% water, and more preferably 55% to 65% water, and more preferably still 58% to 60% water.

■ The liquid may contain 10% to 30% diammonium hydrogen phosphate, and more preferably 15% to 25% diammonium hydrogen phosphate, and more preferably still 16% to 20% diammonium hydrogen phosphate.

■ The liquid may contain 0.01% to 5% ammonium bicarbonate, and more preferably 0.5% to 3% ammonium bicarbonate, and more preferably still 1% to 2% ammonium bicarbonate.

■ The liquid may contain 0.01% to 10% ammonium sulphate, and more preferably 2% to 5% ammonium sulphate, and more preferably still 3% to 4% ammonium sulphate.

■ The liquid may contain 10% to 20% monopropylene glycol, and more preferably 12.5% to 17.5% monopropylene glycol, and more preferably still 15% to 17% monopropylene glycol.

In some embodiments, the weight ratio of diammonium hydrogen phosphate to ammonium bicarbonate in the extinguishing liquid is at least 2:1, for example at least 2.1:1, at least 2.2:1, at least 2.3:1, at least 2.4:1 or at least 2.5:1. In some embodiments, the weight ratio of diammonium hydrogen phosphate to ammonium bicarbonate in the extinguishing liquid is at least 3: 1 , for example at least 4:1, at least 5: 1 , at least 6: 1 , at least 7:1 or at least 8: 1.

In some embodiments, the weight ratio of diammonium hydrogen phosphate to ammonium sulphate in the extinguishing liquid is at least 2: 1 , for example at least 2.1:1, at least 2.2: 1 , at least 2.3:1, at least 2.4:1 or at least 2.5:1. In some embodiments, the weight ratio of diammonium hydrogen phosphate to ammonium sulphate in the extinguishing liquid is at least 3: 1 , for example at least 3.5: 1 or at least 4.0:1.

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%. 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.

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%, at least 4% or at least 4.5%. The inventors have found that the firefighting abilities of the liquid are dramatically improved when the composition comprises at least 6% firefighting foam component, for example at least 6.5%, at least 7%, at least 7.5%, at least 8%, at least 8.5%, at least 9% or at least 9.5%.

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%. It has been found that liquids having compositions falling within the ranges set out above demonstrate improved fire suppressant capabilities.

As explained above, the invention relates to using the above-described liquid as a flameretardant treatment on a flammable entity, and methods of treating a flammable entity with the above-described liquid. The treatment may reduce the flammability or ignitability of the flammable entity.

The flammable entity may comprise or consist of any entity which is susceptible to unwanted ignition or burning. The flammable entity may be a natural or synthetic entity.

The flammable entity is not already undergoing combustion during treatment with the fire extinguishing liquid. In this way, the treatment acts as a preventative measure and is not used merely to extinguish an existing fire.

In some embodiments, the flammable entity is not already undergoing combustion and has not already undergone combustion at any time previously at the time of treatment with the fire extinguishing liquid. In this way, the liquid is not being used on an entity which is already burning or has already burned, but on an unburned entity which is susceptible to future combustion.

In some embodiments, the flammable entity comprises or consists of vegetation which is at risk of burning in a wildfire or bush fire. In some embodiments, the flammable entity comprises dry vegetation.

The type of vegetation is not limited. The vegetation may include one or more of grass, plant matter, bushes and trees. The vegetation may be living or dead.

In some embodiments, the flammable entity comprises or consists of one or more of paper, cardboard, wood and plasterboard.

In some embodiments, the use of the fire extinguishing liquid comprises applying the liquid onto the flammable entity (e.g. vegetation) in an amount sufficient to slow or prevent the consumption of the vegetation in a wildfire. In some embodiments, the use of the fire extinguishing liquid comprises applying the liquid onto the flammable entity (e.g. vegetation) in an amount of at least 500 mL per m ² (for example, when the flammable entity is dry grass, per m ² of ground from which the grass grows), for example at least 600 mL per m ² , at least 700 mL per m ² , at least 800 mL per m ² or at least 900 mL per m ² . In some embodiments, the use of the fire extinguishing liquid comprises applying the liquid onto the flammable entity (e.g. vegetation) in an amount of up to 1500 mL per m ² (for example, when the flammable entity is dry grass, per m ² of ground from which the grass grows; when the flammable entity is a planar body such as paper, wood or plasterboard, per m ² of the planar entity surface), for example up to 1400 mL per m ² , up to 1300 700 mL per m ² , up to 1200 mL per m ² or up to 1100 mL per m ² . In some embodiments, the use of the fire extinguishing liquid comprises applying the liquid onto the flammable entity (e.g. vegetation) in an amount of 500 to 1500 mL per m ² (for example, when the flammable entity is dry grass, per m ² of ground from which the grass grows), for example 600 to 1400 mL per m ² , 700 to 1300 mL per m ² , 800 to 1200 mL per m ² or about 1000 mL per m ² . In this way, sufficient liquid is applied to prevent ignition while ensuring efficient use of the liquid and avoiding the application of more than is necessary.

In some embodiments, applying the liquid onto the flammable entity comprises spraying the liquid onto the flammable entity from a suitable container or vessel.

In some embodiments, the treatment of the flammable entity with the liquid is repeated periodically. For example, after an initial treatment, a further treatment may be applied after a period of from 1 hour to 7 days has elapsed since the initial treatment, for example from 1 hour to 2 days or 1 hour to 1 day. This ensures that the treated entity remains protected against ignition and reduces the risk of the treatment being washed away or otherwise removed from the entity.

Current wildfire containment procedures include the building of a firebreak in the path of the wildfire to contain the fire and prevent its spread to further vegetation beyond the firebreak. This is difficult manual work which may require the complete clearance of vegetation including bushes and trees in the path of the fire in order to effectively contain the fire. The use of the invention offers a much simpler and efficient alternative, since a section of vegetation in the path of the fire may be treated to provide flame retardancy, thereby effectively creating a firebreak without the need to manually clear vegetation.

In some embodiments the use of the fire extinguishing liquid comprises the localised application of the liquid to a section of vegetation in such a way as to contain a wildfire or halt the advancement of a wildfire through vegetation. In this way, the liquid is used efficiently only where needed and can provide an effective firebreak to prevent the burning of further vegetation. For example, a “band” of vegetation may be treated with the liquid, for example a band having a width of at least 1 metre, for example at least 2 metres or at least 5 metres. The band may have a width of up to 20 metres, for example up to 10 metres.

Alternatively, in some embodiments the use of the fire extinguishing liquid comprises a combination of vegetation clearance and treatment with the liquid, to provide a more effective firebreak. For example, after clearing a section of vegetation to create a physical firebreak, the cleared ground, which may contain some residual vegetation, may be treated with the fire extinguishing liquid to provide further resistance to ignition and a more effective firebreak.

The liquid may be manufactured by a method comprising the step of mixing (a) one or more of a phosphate, hydrogen phosphate or dihydrogen phosphate salt; (b) a hydrogen carbonate salt; (c) a sulphate salt; and a liquid vehicle. In some embodiments, the liquid vehicle is water, preferably demineralised water.

The method may comprise the step of mixing diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), ammonium bicarbonate (NH ₄ HCOs), ammonium sulphate ((NH ₄ )2SO ₄ ) and a liquid vehicle. In some embodiments, the liquid vehicle is water, preferably demineralised water.

The method may further comprise mixing propylene glycol (C3H8O2) with the diammonium hydrogen phosphate ((NH ₄ )2HPO ₄ ), ammonium bicarbonate (NI- HCO3), ammonium sulphate ((NH ₄ )2SO ₄ ) and liquid vehicle.

The method of manufacturing the fire extinguishing liquid may comprise the steps of:

(A) heating water to a temperature above room temperature; and

(B) adding diammonium hydrogen phosphate ((NH ₄ )2HPO ₄ ), ammonium bicarbonate (NI- HCO3) and ammonium sulphate ((NH ₄ )2SO ₄ ) to the water.

The method may further comprise adding propylene glycol (C3H8O2) to the water in step (B).

The method may further comprise the addition of the firefighting foam component described above.

The method may comprise mixing the solution after the addition of one or more of diammonium hydrogen phosphate ((NH ₄ )2HPO ₄ ), ammonium bicarbonate (NI- HCO3), ammonium sulphate ((NH^SC ) and propylene glycol (C3H8O2). After step (B) the method may include an additional step (C) of cooling the solution to below 25°C.

After step (C) the method include 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.

The water may first be heated in step (A) to a temperature in the range 50 to 70 °C before any of the other components are added. This leads to improved dissolution of the other components of the composition. The heating may be 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.

Each of diammonium hydrogen phosphate ((NH^HPO^, ammonium bicarbonate (NH4HCO3), ammonium sulphate ((NH^SO^ and optionally propylene glycol (C3H8O2) may be added to the water separately. Diammonium hydrogen phosphate ((NH^HPO^ may be added to the water in a first step, followed by the remaining components. Propylene glycol (C3H8O2) may be added after each of diammonium hydrogen phosphate ((NH^HPC ), ammonium bicarbonate (NH4HCO3) and ammonium sulphate ((NF^SC ) have been added.

The method of manufacturing the fire extinguishing liquid may comprise the steps of:

(i) heating water to a temperature above room temperature, preferably to a temperature in the range 50 to 70 °C;

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

(iii) adding ammonium bicarbonate and mixing until dissolved;

(iv) adding ammonium sulphate and mixing until dissolved; and

(v) optionally adding monopropylene glycol and mixing until dissolved.

After optional step (v) the method may include an additional step (vi) of cooling the solution of water, diammonium hydrogen phosphate, ammonium bicarbonate and ammonium sulphate to below 25°C.

After step (vi) the method may include an additional step (vii) 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:

■ 50% to 70% of water, and more preferably 55% to 65% of water, and more preferably still 58% to 60% of water.

■ 10% to 30% diammonium hydrogen phosphate, and more preferably 15% to 25% diammonium hydrogen phosphate, and more preferably still 16% to 20% diammonium hydrogen phosphate.

■ 0.01% to 5% ammonium bicarbonate, and more preferably 0.5% to 3% ammonium bicarbonate, and more preferably still 1% to 2% ammonium bicarbonate.

■ 0.01% to 10% ammonium sulphate, and more preferably 2% to 5% ammonium sulphate, and more preferably still 3% to 4% ammonium sulphate.

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

In steps (ii) to (iv), the components are 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, ammonium bicarbonate and the ammonium sulphate are preferably added while the mixture is being mixed or stirred. In optional step (v) 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 2% to 4% of firefighting foam component.

By heating the water first, in step (i), the dissolution of the components in steps (ii) to (v) 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 steps (ii) to (iv), it is preferable that the water is maintained at a temperature from 50°C to 70°C, in order to aid the dissolution of the diammonium hydrogen phosphate, ammonium bicarbonate and ammonium sulphate in steps (ii) to (iv) respectively.

After step (iii), the mixture may be mixed or stirred for 5 to 20 minutes, again to ensure uniform distribution of the ammonium bicarbonate throughout the mixture. More preferably, the mixture is mixed or stirred for about 10 minutes. For the same reason, after the addition of ammonium sulphate in step (iv), the mixture may be mixed or stirred for a further 20 to 40 minutes, and preferably for about 20 minutes.

In step (vi), 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, ammonium bicarbonate and ammonium sulphate 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 (vi) and the filtering in step (vii), which removes any diammonium hydrogen phosphate, ammonium bicarbonate and ammonium sulphate 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 (vii), 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.

A third aspect of the present invention provides the use of a fire extinguisher (i.e. , a fire extinguishing device) containing the liquid described above to deliver a flame-retardant treatment to a flammable entity to reduce the flammability or ignitability of the flammable entity. 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.

A variety of fire extinguishing devices may be used to contain and deliver the fire extinguishing liquid. For example, self-contained hand-held pressurised extinguishers may be used, wherein the liquid is delivered through a nozzle. 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.

Embodiments of the invention will now be described by way of example.

EXAMPLES

Example 1

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

1) 727 kg of demineralized water was run into a mixing vessel, and heated to 40°C using an electric element located within the mixing vessel.

2) 350 kg of 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) 30 kg of ammonium bicarbonate was added while mixing. After all of the ammonium bicarbonate was dissolved, the solution was mixed for a further 10 minutes.

4) 80 kg of ammonium sulphate was added while mixing. After all of the ammonium sulphate was dissolved, the solution was mixed for a further 30 minutes.

5) 50.75 kg of FOMTEC® AFFF 3% was added, 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.

Example 2

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

1) 727kg of demineralized water was run into a mixing vessel, and heated to 60°C using an electric element located within the mixing vessel.

2) 210kg of 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) 20kg of ammonium bicarbonate was added while mixing. After all of the ammonium bicarbonate was dissolved, the solution was mixed for a further 10 minutes.

4) 48kg of ammonium sulphate was added while mixing. After all of the ammonium sulphate was dissolved, the solution was mixed for a further 30 minutes.

5) 202.3 kg of monopropylene glycol was added while mixing, and the solution was stirred until fully dissolved.

6) 30.45kg of FOMTEC® AFFF 3% was added, while slowly mixing (to avoid foaming). The solution was then mixed and circulated for a further 30 minutes.

The mixture was allowed to cool to 18°C, and was then passed through a 20pm filter and the filtrate was passed directly into a fire extinguisher vessel. Example 3

In this Example, the fire extinguishing liquid made in Example 1 was tested for its ability to prevent ignition of dry hay.

1 m ² of dry hay was treated with 1 L of the liquid of Example 1 and left to dry for 24 hours. 1 m ² of untreated dry hay was placed next to and in contact with the treated hay. The untreated hay was set alight at the most distant point from the contact with the treated hay.

The untreated hay quickly caught fire and the fire advanced rapidly through the untreated hay towards the section of treated hay. The treated hay did not set alight and the fire naturally extinguished when it reached the point where the untreated hay met the treated hay.

Example 4

In this Example, the treated hay sample from Example 3 was tested for resistance to ignition under more intense conditions.

After the test of Example 3, a blowtorch was ignited and the flame was directed towards the sample of treated hay. The hay in the vicinity of the flame glowed red hot but did not ignite. The blowtorch was held in position for 8 minutes and the hay continued to glow red hot, but no ignition of the hay was observed.

Example 5

In this Example, the fire extinguishing liquid made in Example 2 was tested to determine its freezing properties.

The freezing point of the liquid was found to be -20 °C. The liquid is therefore suitable for use in low-temperature environments.

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.