WO2014195427A1

WO2014195427A1 - System and method for fire extinguishing through the use of water solutions of alkaline silicates

Info

Publication number: WO2014195427A1
Application number: PCT/EP2014/061749
Authority: WO
Inventors: Luca Patauner
Original assignee: BATTISTI, Giorgio; CORNELLA, Giuseppe
Priority date: 2013-06-06
Filing date: 2014-06-05
Publication date: 2014-12-11
Also published as: ITTN20130005A1

Abstract

The invention relates to a mixture for the extinguishing of a fire, the mixture comprising an aqueous solution of one or more alkaline silicates having a basic character, wherein the silicates form silica gel barriers when dispersed on burning material through the condensation and gelation of the silicate induced by carbon dioxide which is generated by the combustion of said burning material. The invention further relates to a method for producing a mixture for extinguishing a fire.

Description

SYSTEM AND METHOD FOR FIRE EXTINGUISHING THROUGH THE USE OF WATER SOLUTIONS OF ALKALINE SILICATES

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit and priority to Italian Patent Application No.

TN2013A000005 filed June 6, 2013, the disclosure of which is incorporated by reference herein in its entirety. BACKGROUND

Field of the Disclosure

The present invention relates a mixture and a system for extinguishing a fire. The invention further relates to a method for producing a mixture for extinguishing a fire and the use of such mixtures for extinguishing a fire. Related Art

Fire has always been present in the mankind evolution. In the human story, big fires destroyed entire towns. The industrial age, because of the strong request of materials (glass, metals) and energy (steam), brought a widespread use of fire, and the requirement of fire control became a must. The big energies developed in industrial boilers and in the blast furnaces, together with the introduction of new products that could not be extinguished by water, brought the birth of modern fire extinguishing technologies.

The fire extinguisher was born in 1816. As technology progressed, the use of chemical products incompatible with water (e.g., magnesium) as well as organic liquids such as oil (that are lighter than water and remain on surface and in which steam acts not as

extinguishing agent but as feeding agent) brought the need of new extinguishing agents that were different from water.

The first extinguishing agents used in a fire extinguisher were generally a water solution of potassium carbonate, followed by acid/alkaline solutions of sodium carbonate with tartaric acid that gave rise to foams. Carbon dioxide arrived later and was at first produced through carbonate and sulfuric acid reactions. An effective suffocating agent was carbon tetrachloride (CC14) or halon 104. Toxicity problems, however, brought the removal of these products from the market. Bromides were invented in Germany in the 1940's. In the 1950's ABC powders were developed and in the same year Halon 1211 (BCF) was developed, while the Halon 1301 (BTM) was synthesized by Du Pont de Nemorus for the U.S. Army. Fluobrene was patented by the Italian company Montecatini.

For a better understanding of the extinguishing mechanisms of the disclosure, a closer look may be undertaken at how combustion and fire extinguishing work. Included herein is a look at additional products available on the market and their features for a comparison and for the comprehension of the advantages of the new mixture.

Three basic elements are necessary in the combustion reaction process: a fuel, a combustive agent (oxidizer) and an effective ignition source. If only one of these elements is missing (or minimized), combustion doesn't happen.

The majority of the extinguishing agents operate on the combustion process through a physical action: choking or cooling. Recently, products have been developed that operate through a chemical action: chemical inhibition or negative catalysis. The extinguishing agents may also give rise at the same time to more effects, which means an improvement of the extinguishing effectiveness. Both chemical and physical effects operate on the combustion reaction speed (kinetic): the physical ones lower the temperature (cooling) and/or the reagents concentration (with oxygen depletion or with fuel gases dilution (choking)); the ones that have chemical action operate by intercepting and neutralizing the free radicals that are the active compounds for the propagation of the combustion chain. All the extinguishing agents may give rise to four classes of effects:

1. Dilution effect: this is realized when the fuel concentration in the combustion area is lowered. It can be realized by mixing water with a fired flammable liquid (water miscible) or with the dilution of a fired gas with an inert gas.

2. Cooling effect: this is realized by working on the fire thermal balance. The

effectiveness of this is given by the balance between the heat produced by the fire and the heat that is removed by the extinguishing agent. 3. Choking effect: this is realized with the removal of air (oxidizing agent) that gives rise to the stop of the combustion. If burning materials are covered with, e.g., a suitable blanket, air contact with the fuel may be prevented, thereby stopping combustion.

4. Negative catalysis effect: this is realized through the slowing down of the combustion reaction and may be done with chemical products that are able to neutralize the combustion reaction active intermediates (free radicals).

Often in fire extinction, the more effects that operate in synergy typically gives a better result for extinguishing the fire. It should be noted that not all the extinguishing agents can be used universally for any kind of fire which has resulted in the definition of different fire classes as a reference for the use of the extinguishing agents (from the European law UNI EN 2).

1. Class A: Solid materials fires

2. Class B: Liquid or fused solids fires

3. Class C: Flammable gases fires

4. Class D: Metals and chemical compounds fires

5. Class E: Energized electrical devices fires

What follows is a short description of the various up-to-date extinguishing agents and their operative zone, evaluated on the basis of the fired products and the fire size.

Water: it is the most used extinguishing agent because it is widespread, cheap, simple to use and not toxic. It is unique for fire control and the external protection of, e.g., buildings, tanks or the plants close to an active fire. The main characteristics of the extinguishing

effectiveness of the water are its great specific heat and the great vaporization heat. Both of these factors give rise to great heat absorption. A side factor in water use during fire extinction is its production of very big quantities of steam that act by moving air away and creating an inert atmosphere. In so doing, the water extinguishing effect is realized by cooling of the burning materials by heat absorption, choking (due to the separation between fuel and air caused by steam), dilution of water soluble flammable compounds (making them less able to combust) and by the breaking of the fuel-air contact provided by mechanical action of the water stream. Water, however, cannot be used on energized electrical devices, on devices that can be damaged by water, on chemical compounds that can react with it in a dangerous way, or on toxic compounds that can be dispersed in water (e.g., alkaline cyanides). Foams: As with water, foam is the most used extinguishing agent in industrial plants for the extinguishment of liquid fuels. It is typically a bubbled mass formed by an aqueous solution with a foaming agent expanded with air. Foam is lighter than the originating solution and all fuel liquids, so it floats on the surface forming a continuous layer that is not permeable to gases and that separates fuel from air. Foams are divided in two main groups: chemical foams and mechanical foams. In the case of chemical foam, the gas, usually carbon dioxide, is produced through a chemical reaction. In the case of mechanical ones, the gas, usually air, is mechanically emulsified with the foaming solution. Recently, "wetting foams" have been added to these two groups that are produced by the addition of surfactants. Due to their low cost and the ease of preparation, the mechanical ones are the most used today.

Powders: Powders are one of the more versatile extinguishing agents. The powders can be used in fires that involve different fuels such as, i.e., wood, paper and alkaline metals such as, e.g., magnesium. Each fuel requires the suited and specific powder for the best effect.

Generally, the powders are made with a mixture of solid particles of sodium bicarbonate, potassium bicarbonate, ammonium sulfate or ammonium phosphate, and various additives, that improve the storage, the fluidity, the hydrophobic proprieties which, in some cases, make them compatible with foams. Chemical powders are stable both at low and high

temperatures. Due to their reflecting proprieties, they may protect the operators from thermal irradiation. The powders components are typically "not toxic". The action mechanism of the powder is a combination of some contemporary effects that include: choking, due to the coverage actions or powder stratification over the burning material separating it from the air; cooling, due to the lowering of the fuel temperature under the ignition temperature and because of the heat absorption by extinguishing agent (endothermic decomposition of the powder); negative catalysis, due to the fact that the components of the powders interact with free radicals H+ and OH forming stable molecules with the break of the reaction chain, thereby stopping a fire.

Carbon dioxide: Carbon dioxide is an inert gas and a combustion product. Carbon dioxide is able, with its presence, to lower the air oxygen concentration under the limit where no combustion is possible. In addition to being a combustion product, carbon dioxide moves the chemical equilibrium of the combustion reaction towards the reagents limiting the

development of the combustion reaction. At environment pressure and temperature, carbon dioxide is a gas that is heavier than air that does not leave residues. Carbon dioxide is not toxic, but rather reduces the air oxygen content and under the 15% V/V can cause troubles, such as loss of consciousness and even death. Therefore, in enclosed areas where carbon dioxide has been released, breathing type equipment may be required if no previous ventilation has been provided. Carbon dioxide provides cooling action by absorbing heat and lowering the fuel temperature under an ignition temperature. The choking effect is realized by carbon dioxide taking the place of oxygen and lowering its percentage under the values required for the combustion (to about 18%). C02 is used mainly for class B and C fires and for the extinguishment of electrical devices under voltage. Carbon dioxide typically cannot be used as extinguishing agents for chemical compounds that contain oxygen (e.g., cellulose), on reactive metals such as, e.g., sodium, potassium, magnesium, titanium, zircon, or on metal, arsenic, phosphor hydrides, because it reacts chemically and may develop toxic gases.

Halogenated hydrocarbons: Halogenated hydrocarbons are produced through the

halogenation of saturated hydrocarbons when combined with chlorine, bromide, fluorine, or iodine atoms. These compounds have very good extinguishing properties and are stored in a liquid state. These compounds can be easily vaporized, are dielectric, not corrosive, unalterable, do not leave residue, and have very low freezing points, and in vapor state are heavier than air. Their extinguishing action is performed by negative catalysis because the halogens interact with free radicals depleting them from the combustion reaction stopping the reaction chain, by choking as their vapors take the place of the air and prevent the fuel-air contact and by cooling as the halogenated hydrocarbons moving from liquid state to gas state that lower the fuel temperature under the ignition temperature. Their effectiveness is due to their ability to diffuse quickly in the atmosphere and so to penetrate inside the obstacles; they are heavier than air and present high dielectric values that allow them to be used on electric devices under voltage. Some of these products are toxic and all are subject to the toxicity derived from decomposition products (e.g., gaseous hydrofluoric acid or hydrogen bromide) that are formed during the fire extinction. It has been demonstrated that the halons and especially bromine-based compounds such as, e.g., halon 1211, halon 1301, halon 2402, are to a large degree responsible for the ozone depletion from the atmosphere and so they are likely going to be dismissed. To overcome the ban of these products, the industry realized new extinguishing agents called "clean-agent", to replace the most problematic halons, which are compounds with a lower content in the halogens that are dangerous to the atmospheric ozone. Further extinguishing agents have been developed as an answer to the health dangers and the atmospheric ozone depletion (environmental risk). The research has been addressed mainly to the optimization of the spreading of known extinguishing agents such as, for example, atomized water, produced both in fixed and mobile structures through high pressure supply and, together with additives, that increase its effectiveness; water mists (i.e., water fogs with additives at high pressure that improve the effectiveness and reduce the water use). This technology is applied in fixed extinguishing plants. Twin agents are used in technology for the keeping of the foam effectiveness through the simultaneous actions of chemical powder on the flames both during the attack and maintenance phases. The alternative research has considered the evaluation of substances different from traditional ones as the "aerosols" that are pyrotechnical extinguishers. These come from a Russian technology connected with the aerospace fuels. The product for the generation of the aerosol is potassium nitrate that is combined with other auxiliary products. The extinguishing action is done mainly for negative catalysis of the potassium salts and carbonates, but can also be originated by choking on the base of the mode in which the aerosol has been produced. The toxic effects of this technology are still under study.

SUMMARY OF THE DISCLOSURE

A first aspect of the invention relates to a mixture for extinguishing a fire. The mixture comprises an aqueous solution of one or more alkaline silicates having a basic character, wherein the silicates form silica gel barriers when dispersed on burning material through the condensation and gelation of the silicate induced by carbon dioxide which is generated by the combustion of said burning material. In a further advantageous development of the invention, it is provided that the mixture contains the alkaline silicates in a percentage ratio of between 1% and 100% with regard to the water, in particular of between 10% and 30%. In other words it is envisaged that the ratio of the alkaline silicates with regard to the water is 1 %, 2 %, 3 %, 4 %, 5 %, 6 %, 7 %, 8 %, 9 %, 10 %, 11 %, 12 %, 13 %, 14 %, 15 %, 16 %, 17 %, 18 %, 19 %, 20 %, 21 %, 22 %, 23 %, 24 %, 25 %, 26 %, 27 %, 28 %, 29 %, 30 %, 31 %, 32 %, 33 %, 34 %, 35 %, 36 %, 37 %, 38 %, 39 %, 40 %, 41 %, 42 %, 43 %, 44 %, 45 %, 46 %, 47 %, 48 %, 49 %, 50 %, 51 %, 52 %, 53 %, 54 %, 55 %, 56 %, 57 %, 58 %, 59 %, 60 %, 61 %, 62 %, 63 %, 64 %, 65 %, 66 %, 67 %, 68 %, 69 %, 70 %, 71 %, 72 %, 73 %, 74 %, 75 %, 76 %, 77 %, 78 %, 79 %, 80 %, 81 %, 82 %, 83 %, 84 %, 85 %, 86 %, 87 %, 88 %, 89 %, 90 %, 91 %, 92 %, 93 %, 94 %, 95 %, 96 %, 97 %, 98 %, 99 %, or 100 %. Ratios of between 10 % and 30 % have proven to be particularly advantageous. Generally, ratios given in the present invention may comprise mass fractions (w/w), mass concentrations (w/v, v/w), and/or volume concentrations (v/v). Liquid ingredients like liquid silicate(s), solutions, and water are usually measured in volume units (v/v and/or v/m), while solid ingredients like solid alkaline silicate(s) and solid

fluorosilicate(s) are usually measured in mass units (w/w and/or w/v). For the preparation of the mixture it is generally possible to use solid alkaline silicate(s) and mix them with water and/or to use commercially available liquid solutions of silicate(s) in order to prepare the mixture. Liquid concentrated silicate(s) can be found as commercial products or can be produced by dissolving solid silicate(s) in water. The solution(s) may be concentrated and may for example comprise between 40% and 50% of solid alkaline silicate(s). It is also possible to dilute concentrated solutions to a desired lower concentration, e.g. to 10-30%. In a further advantageous development of the invention, it is provided that the alkaline silicates are Sodium Silicate and/or Potassium Silicate and/or Lithium Silicate.

In a further advantageous development of the invention, it is provided that the mixture contains alkaline fluorosilicates, in particular alkaline solid fluorosilicates.

In a further advantageous development of the invention, it is provided that the mixture contains the alkaline fluorosilicates in a weight percentage ratio of between 1% and 20% with regard to the mixture, in particular of between 0.2% and 1%. In other words it is envisaged that the mixture contains the alkaline fluorosilicates in a ratio of 1 %, 2 %, 3 %, 4 %, 5 %, 6 %, 7 %, 8 %, 9 %, 10 %, 11 %, 12 %, 13 %, 14 %, 15 %, 16 %, 17 %, 18 %, 19 %, or 20 % with regard to the mixture (v/v, w/v, v/w, w/w).

In a further advantageous development of the invention, it is provided that the alkaline fluorosilicates are Sodium Fluorosilicate and/or Potassium Fluorosilicate and/or Lithium Fluorosilicate.

In a further advantageous development of the invention, it is provided that the water based mixture further comprises one or more additives compatible with silicates and/or

fluorosilicates to optimize the extinguishing. In a further advantageous development of the invention, it is provided that the water based mixture containing the alkaline silicates creates a gel barrier on the burning material as an obstacle to combustion in use. A further aspect of the invention relates to a device configured to utilize the water based mixture of any one of the preceding claims for extinguishing burning materials.

A further aspect of the invention relates to a method for producing a mixture for extinguishing a fire, the method comprising providing water for creating a solution; providing one or more alkaline silicates having a basic character, wherein the silicates form silica gel barriers when dispersed on burning material through the condensation and gelation of the silicate induced by carbon dioxide which is generated by the combustion of said burning material; and mixing the water and the one or more alkaline silicates to create the solution. In a further advantageous development of the invention, it is provided that the alkaline silicates are mixed in a percentage ratio with regard to the water of between about 1% and about 100%, in particular of between about 10% and about 30%, with the water.

In a further advantageous development of the invention, it is provided that the alkaline silicate comprises Sodium Silicate and/or Potassium Silicate and/or Lithium Silicate.

In a further advantageous development of the invention, it is provided that one or more alkaline solid fluorosilicates are mixed with the solution. In a further advantageous development of the invention, it is provided that the one or more alkaline solid fluorosilicates are mixed in a percentage ratio of between about 1% and about 20%, in particular of between about 0.2% and about 1%, with regard to the mixture.

In a further advantageous development of the invention, it is provided that the alkaline fluorosilicates comprise Sodium Fluorosilicate and/or Potassium Fluorosilicate and/or Lithium Fluorosilicate. In a further advantageous development of the invention, it is provided that the method comprises adding one or more additives compatible with the silicates and/or the

fluorosilicates to optimize fire extinguishing. In a further advantageous development of the invention, it is provided that the mixture creates a gel barrier on the burning material as an obstacle to combustion in use.

A further aspect of the invention relates to the use of a mixture according to the previous aspect of the invention and/or of a mixture, which is produced by the method according to the previous aspect of the invention, for extinguishing a fire.

In a further aspect, a chemical mixture based on silicates may be used for fire extinguishing. This may comprise a water-based product made of alkaline silicate and/or fluorosilicate solutions that can be added with other compounds. Through synergy effects due to water, alkalinity and the physical chemical condition present in a fire, the dispersed product forms a silicon gel barrier on the burning material that, together with silicate and water, contains alkaline carbonates formed by alkalinity that reacts with the carbon dioxide formed in the combustion. When present, fluorosilicates generate hydrogen fluoride that has the effect of a negative catalyst for the combustion reaction through the action of the fluoride ion. The action of the product is due to various combined effects that are: water extinguishing effect

(evaporation, choking, and temperature reduction), silicate gel formation (formation of a local permanent barrier between fuel and oxidizer) and the presence of carbon dioxide,

concentrated in alkaline carbonates, formed in the gelation reaction, that are a localized reserve of C0₂, that is a well-known extinguishing agent. The extinguishing is essentially immediate and effective. The presence of carbon dioxide and water into the barrier acts as an effective obstacle to the restart of the combustion. The presence of fluorides is also a further obstacle to the combustion propagation reactions.

In one aspect, a water based mixture for the extinguishing of burning material that contains alkaline silicates, characterized by the fact to contain the alkaline silicates in a volume percentage ratio comprising between 1% and 100% and characterized by the fact to be added with alkaline solid fluorosilicates in a weight percentage ratio comprising between 1% and 20%. A ratio of between 1% and 100% generally means a ratio of 1 %, 2 %, 3 %, 4 %, 5 %, 6 %, 7 %, 8 %, 9 %, 10 %, 11 %, 12 %, 13 %, 14 %, 15 %, 16 %, 17 %, 18 %, 19 %, 20 %, 21 %, 22 %, 23 %, 24 %, 25 %, 26 %, 27 %, 28 %, 29 %, 30 %, 31 %, 32 %, 33 %, 34 %, 35 %, 36 %, 37 %, 38 %, 39 %, 40 %, 41 %, 42 %, 43 %, 44 %, 45 %, 46 %, 47 %, 48 %, 49 %, 50 %, 51 %, 52 %, 53 %, 54 %, 55 %, 56 %, 57 %, 58 %, 59 %, 60 %, 61 %, 62 %, 63 %, 64 %, 65 %, 66 %, 67 %, 68 %, 69 %, 70 %, 71 %, 72 %, 73 %, 74 %, 75 %, 76 %, 77 %, 78 %, 79 %, 80 %, 81 %, 82 %, 83 %, 84 %, 85 %, 86 %, 87 %, 88 %, 89 %, 90 %, 91 %, 92 %, 93 %, 94 %, 95 %, 96 %, 97 %, 98 %, 99 %, or 100 %. The alkaline silicates may be sodium silicate and/or potassium silicate and/or lithium silicate and characterized by the fact that the alkaline fluorosilicates may be sodium fluorosilicate and/or potassium fluorosilicate and/or lithium fluorosilicate. The water based mixture may be added with other additives compatible with silicates and fluorosilicates to optimize fire extinguishing. The water-based mixture may be characterized by the fact that it contains the alkaline silicates in a volume percentage ratio comprising between 10% and 30% and characterized by the fact to be added with alkaline solid fluorosilicates in weight percentage ratio comprising between 0.2% and 1%.

In one aspect, a method for creating a mixture for extinguishing burning material is provided. The method may include the steps of providing water for creating a solution, and mixing alkaline liquid silicate in a volume percentage ratio between about 1% and about 100% alkaline solid fluorosilicates in a weight percentage ratio of between about 1% and about 20% with the water to create a mixture. The alkaline silicate may comprise Sodium Silicate and/or Potassium Silicate and/or Lithium Silicate and the alkaline Fluorosilicates may comprise Sodium Fluorosilicate and/or Potassium Fluorosilicate and/or Lithium Fluorosilicate. The method may include adding other additives compatible with the silicates and fluorosilicates to optimize fire extinguishing. The alkaline silicates may have a volume percentage ratio of between about 10% and about 30%. The alkaline solid fluorosilicates have a weight percentage ratio comprising between about 0.2% and about 1%. BRIEF DESCRIPTION OF THE DRAWINGS

There are no drawings.

DETAILED DESCRIPTION OF THE DISCLOSURE

The disclosure and the various features and advantageous details thereof are explained more fully "with reference to the non-limiting examples that are described and/or illustrated in the accompanying drawings and detailed in the following description. It is noted that the features illustrated in the attachment are not necessarily drawn to scale, and features of one example may be employed with other examples as the skilled artisan would recognize, even if not explicitly stated herein. Descriptions of well-known components and processing techniques may be omitted so as to not unnecessarily obscure the examples of the disclosure. The examples used herein are intended merely to facilitate an understanding of ways in which the disclosure may be practiced and to further enable those of skill in the art to practice the principles of the disclosure. Accordingly, the examples given herein should not be construed as limiting the scope of the disclosure. The terms "including", "comprising", and variations thereof, as used in this disclosure, mean "including, but not limited to," unless expressly specified otherwise.

The terms "a", "an", and "the", as used in this disclosure, means "one or more," unless expressly specified otherwise.

The term "about" as used in this disclosure means within +/-10%, unless expressly specified otherwise. The term "solution" comprises solutions and/or dispersions.

Although process steps, method steps, algorithms, or the like, may be described in a sequential order, such processes, methods and algorithms may be configured to work in alternate orders. In other words, any sequence or order of steps that may be described does not necessarily indicate a requirement that the steps be performed in that order. The steps of the processes, methods or algorithms described herein may be performed in any order practical. Further, some steps may be performed simultaneously.

When a single device or article is described herein, it will be readily apparent that more than one device or article may be used in place of a single device or article. Similarly, where more than one device or article is described herein, it will be readily apparent that a single device or article may be used in place of the more than one device or article. The functionality or the features of a device may be alternatively embodied by one or more other devices which are not explicitly described as having such functionality or features.

From the previous discussion herein, one should be able to understand how the effects involved in fire extinction differ from each other as well as cooperate in synergy. The ideal extinguishing agent may be the one that is able to produce all the effects together, without causing damage to materials, is inexpensive and can be used universally. The target of the present disclosure is to describe the use of a family of chemical compounds capable to generate multiple extinguishment effects, is inexpensive and can be applied both for large and small fire extinction. It is well known from natural sciences that silicon is the second most abundant element on earth after oxygen, with which it easily reacts to form silicon dioxide Si0_2. From silicon dioxide thousands of structures are originated, generally known as silicates and

aluminosilicates (components of the most of the known minerals). Silicate structures are multiple and give origin to different proprieties if they are composed by the same base units. It is known that when silicates react with water it can hydrolyze and generate slightly acidic colloidal silicon dioxide solutions, commonly known as silicic acid.

Silicic acid originated by polymeric silicate structures and can also reversibly form new structures. From inorganic chemistry it is well known that the silicic acid tends to polymerize to form solid structures and gels. The acid alone is unstable and difficult to prepare and is stable only in dilute solutions. Differing from the acid, its alkaline salts are stable in water solution and also as concentrate products. Commonly known and used are sodium silicate, potassium silicate and lithium silicate.

Together with alkaline silicates are commercialized alkaline fluorosilicates and fluorosilicic acid. These differ from the silicate by the fact that the oxygen atoms are bonded to the silicon in the silicate and are changed with fluorine atoms.

Common silicates are available in strongly alkaline water solutions with a dry content of about 40%. They find multiple applications ranging from process industry to daily life, both alone and combined with other products.

From the chemical point of view, silicon in silicates and fluorosilicates is present at its highest oxidation number both with oxygen and fluorine and offer no possibility of further oxidation. This means that silicates cannot be oxidized and so are not flammable. This feature is already successfully used in the fire protection of materials as wood and paper (fireproof). In these applications, the silicate is typically used as a paint creating a permanent silicon dioxide coating on the substrate that can act as an obstacle to the combustion, thereby avoiding fire. Currently, there are no existing applications of liquid solutions of silicates and fluorosilicates as extinguishing agents for fire extinguishing and these solutions are described herein, according to principles of the disclosure.

It is known from common practice that an effective method to kill a fire is to cover the burning material with a blanket to separate the fuel from the air. The same principle is used in extinguishing agents based on powders and foams.

The target of the present disclosure is to use solutions based on alkaline silicates and fluorosilicates as extinguishing agents that are able to generate barriers of silicon gel and water "on site" on burning objects because of their extinguishing effect on the combustion. This system allows the flames to quickly die "on site" thanks to the contribution of multiple extinguishing effects, especially the choking derived by the barrier, with the use of the unique proprieties of the silicates and their gel formation mechanism.

It should be noted that in order to create the acidity necessary for silicate precipitation (i.e., gel formation), carbon dioxide is used as produced by the combustion; the high temperature of a fire provides an effect that accelerates this reaction.

From inorganic chemistry it is known that alkaline silicates are stable when pH > 9 and especially when it is higher than 10. Its water solutions are stable because of the presence of an excess of alkalinity which keeps it stable. These can be a solution such as ortosilicates

(Si0₄) 4-^", metasilicates (Si0₃) 2-^" and their mixtures with different hydrations. A similar discussion can also be done for fluorosilicates where there is a constant equilibrium presence of SiF₆ ^2" + 3H₂0 <=> (Si0₃)^2" + 6HF.

If the pH of these solutions is lowered under pH 9, the solutions tends to free the ortosilicic acid on the basis of the following simplified equation:

Na₂Si0₃ + H₂0 + 2H⁺→ Si(OH)₄ + 2 Na⁺ Once free, ortosilicic acid molecules begin to condense quickly, with water elimination, the process may be illustrated as with the following reaction:

Si(OH)₄ + Si(OH)₄ = H₆Si₂0₇ + H₂0 and successive condensations with other molecules may be represented by the following formulas:

OH OH OH OH

+ H₂0 HO Si OH + HO Si OH HO- -Si- ^■o- -Si- ^■OH

OH OH OH OH

+ HO Si OH HO Si O Si O Si OH + H₂0

OH OH OH OH At the beginning, oligomer silicic acids are formed then evolve into polymeric silicic acids. The polymeric silicic acids continue the growth, generating first spheroidal structures with a diameter in about the Angstrom size-range (also known as silicon dioxide primary particles), then higher structures that group primary silicon dioxide particles. In fact, the silanol groups (Si-OH) that are present on the surface of the spheres, when a certain diameter is reached, condensate with those present on other spheres and bring the spheres to condensate each other. Because of this condensation, the solution begins to thicken, forming a gel that strongly retains the water molecules of the solution. The three factors that control the gel formation are: concentration, temperature and pH. The condensation happens also when an alkaline silicate is left in contact with an atmosphere where carbon dioxide is present, as the latter (C0₂) dissolves in the solutions, thereby lowering the pH. In fact, carbon dioxide is an acid that slowly neutralizes the silicate alkalinity, lowering the solution pH to reach the gelification point. If the reaction is very slow, little silicate layers are able to form very strong glass layers. So, if a concentrated silicate solution is put in contact with a very concentrated carbon dioxide atmosphere (as is likely generated by a fire), the carbon dioxide quickly dissolves in the liquid following Henry's law where:

Pco₂=kC where P_Co₂ is the partial pressure of carbon dioxide in the atmosphere over the liquid solution, C is the carbon dioxide concentration in the liquid solution. As the C0₂ in water solution forms Carbonic acid (H₂CO₃), this, as acid, reacts immediately with the alkalinity of the silicate solution, and quickly forms alkaline carbonates and bicarbonates in the solution (e.g., KHC0₃, K₂C0₃, NaHC0₃, Na₂C0₃, LiHC0₃, Li₂C0₃). The fast formation of these compounds in the solution causes a decrease of the carbon dioxide concentration in the solution that require other carbon dioxide gas to dissolve from the upper atmosphere to keep the system equilibrium. The global effect is that the reaction between alkalinity and carbon dioxide causes a decrease of the pH, and the high temperatures that are present in a fire speed up the reactions thereby making them nearly instantaneous. It should be readily apparent that if one spreads silicate solution over burning materials layers of amorphous silicon gel will be created (because of the high reactions speed), that retains inside alkaline carbonates and bicarbonates. The final result is the formation of gel barriers containing water and alkaline carbonates, all of which are factors creating obstacles for combustion. Carbonates are carbon dioxide reserves, and as the CO₂ is a reaction product of the combustion following the law of the mobile equilibrium, its presence moves back the reactions, towards the formation of the reagents instead of the products, as per the general reaction: fuel + oxidizer = CO₂ + ¾0 + (at low extent SO_x, NO_x, and incombustible)

As one can see from the immediately above equation, water is one of the main products of the combustion reactions and so its presence in the gel is a further obstacle for the complete development of the reaction. Moreover, water absorbs a lot of heat with the result to cool down the system and slow down the reactions. It is further evident that the formation of a silicon gel layer over the burning materials can be an effective system for fire extinguishment that can use several effects to operate as with water (main extinguishing agent), one of the carbonates (choking), the barrier effect (interruption of the contact fuel/oxidizer caused by the silicon gel layer) and, if fluorosilicates are present, negative catalysis (negative catalysis induced by fluorides).

Sodium, Potassium, Lithium silicates features

Alkaline silicates mean a family of alkaline salts of the silicic acid with a certain

polymerization grade. Their main feature is the hydro solubility and most of them are commercialized as water solutions. These comprise a basic side (K₂O or Na₂0: potassium oxide or sodium oxide), an acid side (Si0₂: silicon dioxide) and water (H₂0). For a simple exemplary description consider the sodium ones; for the others the discussion is similar.

The general formula, in the case of sodium, can be written as:

Na₂0 · m Si0₂ ^« n H₂0 where the numbers m and n may have all of the values between 0 and infinite (∞). Limit cases are m = 0 and n = 1 for the sodium hydroxide (Na₂0 · H₂0 ); and m =∞ and n = 0 for the silicon dioxide anhydrous (Si0₂). The number m represents the molar ratio between Si0₂ and Na₂0. In the salts (made of an alkaline oxide and an acid oxide) R_m = mol acid oxide/mol basic oxide is an integer number. In the silicates, differing from salts, Rm may have all the possible values. In detail for the commercial solutions, Rm can have all the values, also fractions, between zero (sodium hydroxide) and 4 (tetrasilicate). At different values of R_m, different physical-chemical proprieties of the solutions should be considered, and for each application a suitable choice for this value is required. Commercially, for practical reasons, the weight ratio (R) may be used, instead Rm, as the Si0₂ (60) and Na₂0 (62) molecular weights have nearly the same values.

R = Na₂0 / % Si0₂

The sodium silicates can be seen as derived from the neutralization of the Silicic acid with sodium hydroxide (NaOH); as Silicic acid is very weak, to avoid hydrolysis and precipitation, the sodium (or potassium) silicate solutions have to be strongly basic, with a minimum value of pH of 10.5 for the ones more rich in Si0₂, and pH > 13 for the ones more rich in Na₂0. The only solvent for the sodium silicate is water. The solubility of sodium silicate in water has no limits, which means there is no saturation limits for it. This phenomenon is due to the massive presence of hydrophilic silanol groups (=Si-OH, similar to water composition H20) in their molecule. Therefore, the commercial stable solutions of silicates that can be pumped, have to respect precise concentration limits, R, impurities concentrations and temperature.

The first condition to store a silicate solution is that it is stable and can be pumped. The stability depends from R value that has to be between 1, 6 and 4. It is necessary to avoid the presence of compounds incompatible with the silicate as the ions H⁺, NH⁴⁺ and high valence cations that can form Si0₂ gel or insoluble silicates. Silicates have very low direct ingestion toxicity, as can be seen from the high value of LD₅₀ (dose for K_g of body weight that causes about 50% of deaths in animal tests). As indication for a silicate with R = 3,4 and a concentration of 35%, LD₅₀ is 3,5 g/Kg.

Silicate solutions have several applications in the building field; adhesives, water treatments, moulding, fireproof paper and wood. The silicate found applications as fire retardant in the wood materials, where silicate is used as paint to create surface barriers, is described in some patents such as, e.g., US 5,205,874, WO199400878A1, and EP0400162. It is also important to note that all these patents describe protection layers for the materials realized to protect them from the fire and chemicals, which is different from the fact of generating barriers on the burning materials in a burning fire through the formation of on-site gel barriers on the burning materials.

In fact, the principles of the present disclosure may include a liquid that can also be used for forest fire extinguishment, differing from what is described above in the above noted patents (e.g., US 5,205,874, WO199400878A1, and EP0400162) where a treatment is applied on the existing objects before the fire, as preventive protection, and not after the fire has started or during the fire.

In contrast to existing technologies, the silicate solutions of this disclosure provide advantages including: the synergy of different effects make them more effective; as they are alkaline solutions, they will not corrode steel tanks and are easily available on the market in large quantities; they are cheap; they are environmentally friendly (especially potassium silicates as they are the main part of most minerals and because potassium is involved in plant life and is absorbed by plants); they are not dangerous (excluding fluorosilicates) as LD₅₀ is high; the product is only irritating if dispersed in air (where it forms amorphous silicon dioxide that is not a cause of silicosis but only of temporary irritations). The product produced utilizing the principles of the disclosure is easily soluble in water and can be used successfully for the control of, e.g., forest fires, navy fires and on fixed installations (the solutions can be prepared at the required moment and produced

continuously). It can be said that if pure fluorosilicates were used, a low LD₅₀ would be achieved because of the high toxicity of fluorosilicates; it is a better solution, and this is also contemplated by the present disclosure - the use of mixed solutions silicates/fluorosilicates that also have the negative catalysis effect of the fluorides joined with other effects of the pure silicates but with a safer LD₅₀ that enables the use of these mixtures for forest and houses fire extinguishment.

Preferred configurations:

Silicate is effective both in solutions at 40%-50%, and in diluted water solutions of the products (to reduce the viscosity and make easier the gel formation), i.e. in solutions with less than 40% silicate(s). The preferred range to have the best compromise between cost, pumping, viscosity and effectiveness is the one where the concentrated product or solution is diluted from 3 to 10 times in the way to have solutions at the 10% - 30% v/v of the concentrated silicate solutions. If fluorosilicates are added, the presence of about 0.2% - 1% (v/v) of fluorosilicate as salt in the diluted solution is achievable.

Examples:

Tests have been performed under different conditions; distinguishing time (flame

disappearance has been taken as the measure of effectiveness): A variety of devices, such as home fire extinguishers, commercial fire extinguishers, industrial extinguishing equipment, or the like may utilize the mixture(s) as disclosed herein.

Test a)

An extinguisher has been charged with a water solution at 10% of the commercial product for a quantity of 6 liters as described in UNI EN3/7:2004; the material on fire was a big pile of wood impregnated with benzene; the erogation time of the product has been about 30 seconds. The fire has been killed in 20 seconds and a white layer remained on the wood and blocked the flames restart. After one hour, no sign of smoke from the wood was reported.

Test b)

A solution like test a) was prepared but this time using a garden sprayer fed by a pump for the extinguishing. A fire was created using a pile of dry forest wood along with a small quantity of paper and benzene which was then spread to encourage a fast start and growth of the fire. The extinguishment was accomplished in less than 20 seconds; because of the better nebulization, only 2.5 liters of solution was used for the complete extinguishment of the fire.

Test c) A solution like test a) was prepared with an added 1% of sodium fluorosilicate, and the same garden sprayer and pump of the test b). A fire was created using a pile of dry forest wood with paper and a small quantity of paper and 2 liters of gasoline was spread to have a fast start and growth of the fire. Extinguishment occurred in less than 8 seconds; it was evident that the addition of fluorosilicates was effective. For the extinction, about 3 liters of solution was used.

While the disclosure has been described in terms of examples, those skilled in the art will recognize that the disclosure can be practiced with modifications in the spirit and scope of the appended claims. These examples are merely illustrative and are not meant to be an exhaustive list of all possible designs, applications or modifications of the disclosure.

Claims

A mixture for extinguishing a fire, the mixture comprising an aqueous solution of one or more alkaline silicates having a basic character, wherein the silicates form silica gel barriers when dispersed on burning material through the condensation and gelation of the silicate induced by carbon dioxide which is generated by the combustion of said burning material.

The water based mixture according to claim 1, wherein the mixture contains the alkaline silicates in a percentage ratio of between 1% and 100% with regard to the water, in particular of between 10% and 30%.

The water based mixture according to claim 1 or 2, wherein the alkaline silicates are Sodium Silicate and/or Potassium Silicate and/or Lithium Silicate.

The water based mixture according to any one of claims 1 to 3, wherein the mixture contains alkaline fluorosilicates, in particular alkaline solid fluorosilicates.

The water based mixture according to claim 4, wherein the mixture contains the alkaline fluorosilicates in a percentage ratio of between 1% and 20% with regard to the mixture, in particular of between 0.2% and 1%.

The water based mixture according to claim 4 or 5, wherein the alkaline fluorosilicates are Sodium Fluorosilicate and/or Potassium Fluorosilicate and/or Lithium Fluorosilicate.

The water based mixture according to any one of claims 1 to 6, further comprising one or more additives compatible with silicates and/or fluorosilicates to optimize the extinguishing.

The mixture as described in any one of the preceding claims wherein the water based mixture containing the alkaline silicates creates a gel barrier on the burning material as an obstacle to combustion in use.

A device configured to utilize the water based mixture of any one of the preceding claims for extinguishing burning materials.

10. A method for producing a mixture for extinguishing a fire, the method comprising: providing water for creating a solution; providing one or more alkaline silicates having a basic character, wherein the silicates form silica gel barriers when dispersed on burning material through the condensation and gelation of the silicate induced by carbon dioxide which is generated by the combustion of said burning material; and mixing the water and the one or more alkaline silicates to create the solution.

11. The method of claim 10, wherein the alkaline silicates are mixed in a percentage ratio with regard to the water of between about 1% and about 100%, in particular of between about 10% and about 30%, with the water.

12. The method of claim 10 or 11, wherein the alkaline silicate comprises Sodium Silicate and/or Potassium Silicate and/or Lithium Silicate.

13. The method of any one of claims 10 to 12, wherein one or more alkaline solid

fluorosilicates are mixed with the solution.

14. The method of claim 13, wherein the one or more alkaline solid fluorosilicates are mixed in a percentage ratio of between about 1% and about 20%, in particular of between about 0.2% and about 1%, with regard to the mixture.

15. The method of claim 13 or 14, wherein the alkaline fluorosilicates comprise Sodium Fluorosilicate and/or Potassium Fluorosilicate and/or Lithium Fluorosilicate.

16. The method of any one of claims 10 to 15, further comprising adding one or more additives compatible with the silicates and/or the fluorosilicates to optimize fire extinguishing.

17. The method of any one of claims 10 to 16, wherein the mixture creates a gel barrier on the burning material as an obstacle to combustion in use.

18. Use of a mixture according to any one of claims 1 to 8 and/or of a mixture, which is produced by the method according to any one of claims 10 to 17, for extinguishing a fire.