WO2018015110A1

WO2018015110A1 - Powder composition for preventing and extinguishing fires

Info

Publication number: WO2018015110A1
Application number: PCT/EP2017/065704
Authority: WO
Inventors: Sretko Popadic
Original assignee: Savema Gmbh
Priority date: 2016-07-22
Filing date: 2017-06-26
Publication date: 2018-01-25
Also published as: DE102016113554B3

Abstract

A powder composition for fire extinguishing and preventing the spread of fire contains functional agents such as rheology modifiers, superabsorbent polymers and density increasing agents. When the powder composition is added to water, it forms a three-dimensional gel structure, and consequently causes an increase in viscosity. The resulting gel is intended for use in fire extinguishing but also in preventing the spread of fire. The three-dimensional gel structure exhibits a viscosity and fluidity that allow unimpeded gel flow through the standard firefighting equipment, and has the ability to retain on vertical and horizontal, including hanging surfaces. On the treated surface after evaporation of the water from the gel, due to the heat of fire, a firefighting crust is formed as an additional protective layer which prevents the spread of fire as well as the re-emergence of flame.

Description

Powder composition for preventing and extinguishing fires

Field of the invention

The present invention, in general, is related to fire extinguishing agents. Specifically, this invention discloses a powder composition for extinguishing and preventing the spread of fire, which when added to water, changes its properties, making it significantly more effective in firefighting. Moreover, the composition of the present invention is biodegradable and completely safe for human health as well as for the environment.

The present invention provides a composition which, when mixed with water, creates a three- dimensional network structure, a gel for fire extinguishing, which exhibits viscosity and fluidity that enable the uninterrupted flow of the gel through standard firefighting equipment, and thereby enable a prolonged retention of water on horizontal and vertical surfaces. These characteristics of the gel significantly increase efficiency in firefighting as well as in preventing the spread of fire.

Background

An uncontrollable spread of fire in the outdoors and indoors causes an enormous material damage, putting human lives at risk and taking them, too. Despite the existence of numerous modern methods for extinguishing fires, they still pose a great danger to the general population and for the property. With the development of economy, especially industry, agriculture, transport and tourism, as well as due to climate change, and above all, global warming, year after year the number and frequency of fires increases. Therefore, there is an increasing need for new, more efficient means for extinguishing fires.

Agents used for extinguishing fires desirably have the following characteristics: effectiveness in fighting fires, applicability to different materials, storage stability, absence of toxic by-products during the extinguishing process and simple use.

The most commonly used agent for extinguishing fires is water. Water is usually available in the vicinity of the fire location. Thus, widely used is treated water from water pipes and hydrants, fire engines or, in the case of forest fires, water from natural watercourses, rivers, streams, springs and lakes. The efficiency of water as a primary fire extinguishing media, is mainly based on the cooling effect, i.e. decrease in temperature of burning material below the ignition temperature, wherein the water molecules evaporate and heat drains. In addition, the steam blocks and removes the air which is necessary for combustion, thereby extinguishing the flame. Until recently, the water is considered as the most efficient and the cheapest agent for extinguishing fires. While it still has the highest importance in the field of fire protection today. However, despite the above mentioned advantages, water has a number of shortcomings that limit its use for fire extinguishing. The main disadvantage of the use of water for fire extinguishing is that most of the water remains unused, i.e. irreversibly flows, creating damage by flooding the premises located below the fire. In addition, the costs of water transportation, which is unavoidable when fighting forest fires, are high. When only water is used to fight the fire, it rarely reaches the center of the fire, as it quickly evaporates and turns into steam in the superheated air above the fire. The material to be quenched can absorb only a limited amount of water, which evaporates quickly. When under a threat, high risk objects (tanks of flammable substances, tanks, reactors), require fire prevention, which takes a lot of manpower and continuous water pouring over the facilities.

So far numerous firefighting methods have been developed. Use of water additives, in the form of powders, foams, etc, has been described in patent documents. When added to water, wetting agents increase the efficiency of extinguishing Class A fires. This concept is shown in U.S. Pat. Nos. 4,526,234 and 5,374,687. An effort has been made to develop compositions that can be used as additives in methods for extinguishing the fire which is already under way, ie. preventing the spread of fire by treating the vulnerable areas. This pretreatment may be applied to special structures, such as buildings or reservoirs, as well as the vegetation. Recently, substantial efforts have been made in the area of pretreatment with chemical retardants or suppressants. A number of these pretreatments have been developed and used for fighting rural forest fires. For example, antimony oxide and its complexes, borates, carbonates, bicarbonates, ammonium phosphate, ammonium sulfates, and other salts capable of being hydrated, have been demonstrated to have useful properties as firefighting chemicals. Representative prior art patents teaching the use of chemical retardants were granted in the early 1900's and continuing until more recent times. Such patents include; U.S. Pat. Nos. 1,030,909; 1,339,488; 1,813,367; 2,875,044; 3,537,873; 3,719,515; 4,021,464; 4,076,580 and 4,095,985. However, although the fire inhibiting properties of the borates, carbonates and bicarbonates have been established, the use of these materials for vegetation fires has been limited because of their tendency to inhibit plant growth when used in large quantities.

The use of gel-type formulations in firefighting is also known in the prior art. German Patent DE-OS 31 14 630 describes the use of gels that form a firefighting barrier on buildings with flat roofs. The material is designed so as to disable unwanted loss of water. However, this disclosure is related to high viscosity gels that cover and protect the surface exposed to fire, by forming a thick gel layer. The disadvantage of these gels is incontinence on vertical surfaces and thus bad fire extinguishing effect. In addition, due to the high viscosity of the gel it is necessary to use special firefighting equipment.

DE-PS 2,706,135 patent describes the use of superabsorbent polymers in firefighting. Namely, those are the copolymers of acrylic or methacrylic acid with acrylamide, acrylonitrile and ethacrylamide. The disadvantages of the abovementioned composition are relatively slow gel formation and particle agglomeration.

US Pat. No. 5,190,110 discloses an aqueous gel system consisting of mixture of water and a solid polymer which swells in the presence of water. Polymer particle size ranges from 20 μηι to 500 μηι. The polymer particles are dispersed in water by stirring or pumping, so that the final viscosity does not exceed 100 CPS. However, this procedure does not provide enough time for the particles to swell, and consequently, the viscosity is not increasing fast enough and thereby is not satisfactory.

U.S. Pat. No. 4,978,460 also discloses aqueous gel systems containing dry polymers for extinguishing and/or fire prevention, which swell in the presence of water. According to this invention, the polymer particles are coated with a water soluble agent which prevents particle agglutination. The time required for swelling of the encapsulated granular polymer particles varies from 10 seconds to several minutes. This time period, is too long for the retention of water in the fire hose. Therefore, when the encapsulated polymer particles are used together with the standard firefighting equipment, they do not have enough time to swell and thereby increase the viscosity of the water.

U.S. Pat. No. 3,758,641 also describes solid, granular polymer particles with high water absorption power which are used for firefighting. Because of the granular nature of the polymer particles, they absorb water very slowly. In addition, an agglutination of the particles takes place which further can cause the blockage of the flow of the composition through a fire hose. Therefore, the use of these polymer particles requires specific firefighting equipment, such as pumps and spray nozzles that are adapted for the use with such materials. In this case, it would be difficult to use the water from the natural springs, streams or rivers as most polymers would simply swell up after the addition of polymer additives in a stream or river.

US Pat. No. 5,264,251 discloses water-absorbing polymers in the form of stable water in oil emulsion. An important feature of these polymers, is a relatively low viscosity. However, the disadvantage of this composition is the absence of biodegradability and negative environmental impact. An additional problem in the development of fire extinguishing agents is the high price of compositions that are used as water additives. An important purpose of the present invention is also an appropriate choice of substances that can be used as an effective supplement to water for firefighting, which at the same are low-priced. Furthermore, the impact of these substances on the environment is very important. Absorbent particles that are currently used in various gel formulations have a detrimental effect on the environment, especially when used in large quantities, as in the case of extinguishing forest fires. For extinguishing forest fires, the use of cheap or waste materials that are widely available in sufficient quantity is of great interest. An example of such economical materials are lignosulfonates which are in fact waste obtained from the timber industry. The lignosulfonates are used as components in many formulations for fire extinguishing, as described in U.S. Pat. Nos. 3,464,921; 3,962,208; 3,915,911; 4,820,345; 5,112,533; 6,019,176 and 6,277,296.

Moreover, U.S. Pat. Nos. 8,192,653, 8,408,323, 8,734,689 and 8,961,838 disclose firefighting compositions containing starch, pseudo -plastic, high yield, suspending agent, paraffin or olefin and neutralizer. By using the compositions of these inventions, a gel structure is formed by the neutralization reaction which requires an intense mixing of powder components with water for at least 5 minutes. After the neutralization reaction, starch present in the mixture swells up, which may represent a technical difficulty. Firefighting crust described in inventions mentioned above is created at the beginning of exposure to the heat of fire on the outer surface of the gel where a solid shell protects the gel-like interior. However, this firefighting crust lasts only until the water from the gel evaporates which disables the protection from recurrence of fire.

Summary of the invention

Agent for extinguishing and preventing fires, which is described by the present invention is a powder composition comprising superabsorbent potassium polyacrylate polymer 50-90 wt %, and rheological modifiers and thickeners such as Acrylates/C 10-30 Alkyl Acrylate Crosspolymer 0,1-3,0 wt %, xanthan gum 1,0-10,0 wt %, guar gum 1,0-10,0 wt %, modified starch 1,0-10,0 wt % and carrageenan 0,1-3,0 wt %. This powder is added to the water at a low concentration (0,2- 2,0 wt %) to provide a gel-type composition.

This gel can be used as fire extinguisher for materials of class A, as well as for preventive fire protection. The advantage of the present invention compared to existing solutions described in the state of the art is the formation of three-dimensional gel structure that effectively extinguishes the fires and prevents outflow of water from the surface of burning material. In addition, the present invention provides a composition that can be used for gel formation without neutralization reaction and vigorous mixing, but immediately after mixing with water. Prolonged retention of the gel on a burning surface reduces the possibility of re-ignition. Specifically, the composition of the present invention provides the formation of a gel which retains on the protected surface for a period 6-36 hours depending on the environmental conditions (temperature, relative humidity, wind) as well as the nature of the material. Once the formed gel comes into contact with the heat of fire, the water incorporated in the gel evaporates. After evaporation of the water from the gel, on the protected surface remains a firefighting crust which represents an additional protective layer. Thus, the resulting firefighting crust prevents the spread of fire and the re-emergence of flame after the initial fire extinguishing.

Brief description of figures Figure 1 shows the application of firefighting gel on a vertical surface which is exposed to fire or needs to be protected from a potential fire.

Figure 2 shows the formation of firefighting crust after evaporation of the water from the gel which is caused by the heat released in fires. Detailed description of the invention

The composition of the present invention is a powder comprising a mixture of superabsorbent polymers, rheological modifiers, and thickening agents. The effect of this composition is based on the ability of these superabsorbent polymers to absorb a relatively large amount of water compared to the size and weight of polymer particles. Because of high hydrophilicity, the superabsorbent polymer particles have high water binding capacity, absorbing even 200 to 300- fold greater mass of water, compared to the mass of polymer particles. Superabsorbent polymers are well known in the field and are polymers of hydrophilic monomers, such as acrylamide, acrylic acid derivatives, maleic acid anhydride, itaconic acid, 2-hydroxyl ethyl acrylate, polyethylene glycol dimethacrylate, allyl methacrylate, tetraethyleneglycol dimethacrylate, triethyleneglycol dimethacrylate, diethylene glycol dimethacrylate, glycerol dimethacrylate, hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate, 2-tert-butyl amino ethyl methacrylate; dimethylaminopropyl methacrylamide, 2-dimethyiaminoethyl methacrylate, hydroxypropyl acrylate, trimethylolpropane trimethacrylate, 2-acrylamide~2- methylpropanesulfonic acid derivatives, and other hydrophilic monomers. Preferably, polymers are copolymers of acrylamide and acrylic acid derivatives and, more preferably, terpolymers of an acrylate salt, acrylamide, and a 2-acrylamide-2-methylpropanesulfonic acid (AMPS) salt. The salts may generally be any monovalent salt, but preferably are sodium, potassium, or ammonium salts. Many superabsorbent polymers are commercially available in the market and are used in cosmetic, pharmaceutical and agricultural products. As superabsorbent polymer of the present invention, potassium polyacrylate is used.

Potassium polyacrylate is a polymer having the chemical formula [-CH2-CH(COOK)-]n. Potassium polyacrylate particles have the ability to absorb 200 to 300-fold greater mass of water compared to the mass of polymer particles, and are useful as agents for increasing the density and gelation. Potassium polyacrylate is used in the composition of the present invention in the concentration range of 50-90 wt % and functions as a rheology modifier and agent for increasing the density and stability of the gel system. According to the European Chemicals Agency (ECHA), potassium polyacrylate is not classified in any of the hazardous classes according to Regulation EC No 1272/2008 (CLP / GHS Regulation). This is a great advantage compared to, commonly used sodium polyacrylate, which is, according to Regulation EC No 1272/2008 (CLP / GHS Regulation) classified as a substance dangerous to human health since it causes severe eye irritation.

Other ingredients of the composition of the present invention are rheological modifiers and density increasing agents which enable adequate gel density, improved swelling and efficient mixing of the composition with water. Within the scope of the present invention are natural, semi-synthetic and synthetic macromolecular substances which when mixed with water produce colloidal systems. These are long-chain polymers with molar masses from 10³ to 10⁶ Da which may be anionic, cationic, amphoteric and nonionic compounds. Combination of two or more agents in order to increase the density often provides improved effects on the increase of viscosity, density, gelation or stabilization of suspensions and emulsions.

Acrylates/ClO-30 Alkyl Acrylate Crosspolymer is a very powerful rheology modifier. It has a large molecular weight as a homo and copolymer of acrylic acid cross-linked with polyalkenyl polyether. The unique structure of the polymer enables fast moisturizing and high suspending capability even without mixing. The composition of the present invention has a good tolerance in the presence of electrolytes. These characteristics enable the use of Acrylate/ClO-30 Alkyl Acrylate Crosspolymer in products with a wide range of flow and rheological properties. In the composition of the present invention, it is used in a concentration of 1 -1 0 wt%, preferably in a concentration of 0.1 to 3.0 wt%, and works as a rheology modifier, a density increasing agent and a gel system stabilizer. Guar gum is obtained from the seeds of Cyanopsis tetrogonaloba L. Water soluble component is the galactomannan guar which consists of 35% galactose and 65% mannose. It also contains 5- 7% proteins, enzymes, etc. When dispersed in cold water, it swells up and forms a gel. It is 6 to 8-fold stronger gelling agent than starch. In the composition of the present invention it is used in a concentration of 1 - 10 wt% and has an effect on the rheological properties and stability of the gel system. The well-known guar gum derivatives are: Hydroxy and Carboxy Alkylated Guar gum, Oxidised Guar gum, Acetates of Guar gum, Cationic derivatives of Guar gum, Sulphated Guar gum, Guar gum formate, Guar gum acryl amide, Borate cross linked Guar gum, Reticulated Guar gum, Carboxy methyl hydroxy propyl Guar gum, Depolymerised Guar gum.

Xanthan gum is a polysaccharide obtained as a secretion product of a bacteria called Xanthomas campestris. It is composed of glucose, mannose and glucuronic acid in the ratio 2:2: 1 . Unlike other gums, it is very stable under a wide range of temperatures and pH. Moreover, there is almost no change in stability within the pH range 2 - 12. In addition, the temperature hardly has any influence on the viscosity of preparations with Xanthan Gum. One of the most remarkable properties of Xanthan gum is its ability to produce a large increase in the viscosity of a liquid by adding a very small quantity of gum, in the order of one percent. In the composition of the present invention it is used in a concentration of 1 -10 wt% and acts as a rheology modifier as well as a density increasing and gelling agent. In addition, Xanthan gum is fully biodegradable.

Carrageenan is obtained from red algae Gigartina stellata, Chodrus crispus, etc. It is located in the cell wall and intercellular matrix of the seaweed plant tissue. It is a high molecular weight polysaccharide with 1 5% to 40% of ester sulfate content. It is formed by alternate units of D- galactose and 3,6 anhydro-galactose (3,6-AG) joined by -1 ,3 and β-1 ,4 -glycosidic linkage. There are three main commercial classes of carrageenan kappa, iota, and lambda. The primary differences which influence the properties of kappa, iota and lambda carrageenan type are the number and position of ester sulfate groups as well as the content of 3.6-AG. Higher levels of sulfate esters cause decrease of the solubility temperature of the carrageenan and produce lower strength gels, or contribute to gel inhibition (lambda carrageenan). Carrageenans are large, highly flexible molecules that curl forming helical structures. This gives them the ability to form a variety of different gels at room temperature. They are widely used in the food and other industries as thickening and stabilizing agents. The carrageenan is used in the compositions of the present invention in a concentration of 0.5 to 5 wt%, preferably 1 -5 wt%, more preferably 0.5 to 3.0 wt%, and above all is involved in the formation of firefighting crust. Like Xanthan gum, carrageenan is also fully biodegradable.

Starch is a high molecular weight polysaccharide (C₆Hio0₅)n isolated from plant material and composed of amylose (linear polymer of D-glucose molecules joined by a-l ,4-glycosidic bonds) and amylopectin (polymer consisting of linear chains of glucose molecules linked by a- 1,4- glycosidic bonds and branches of the same structure as the linear chains to which they are bound by a-l,6-glycosidic linkages). Starch is a fine white or yellowish-white powder. In some plants, the starch particles have a characteristic shape and diameter of 2 μηι to 130 μηι. The starch is derived from two main sources: seeds (wheat starch, corn starch) and roots or tubers (potato starch, tapioca starch). The starch obtained from roots has longer amylose chains than the starch obtained from seed. Thus, the potato starch is better thickener than the corn starch. Starch can be modified by physical, enzymatic or chemical treatment of natural starch in order to improve its characteristics. The chemical reactions of starch modification include esterification, etherification, cationization, oxidation as well as combinations thereof. Modified starch can be used as a density increasing agent, stabilizer, emulsifier, or as a binding agent. Modified starch increases the stability of the system even during temperature and pH fluctuation, modifies the viscosity of the system, the texture of the final product, and affects the transparency. Gelation temperature of modified starch is significantly lower compared to the natural starch. Concentrated solutions of starch in water are prone to retrogradation, i.e. viscosity change during storage. This phenomenon was observed with each starch containing amylase except with starch potato. Starch modification provides reduced retrogradation and enhanced swelling capacity and gel transparency. Modified starch in the composition of the present invention is used in the range 1 to 10 wt%, and its main function is to form the firefighting crust. Such starch is fully biodegradable.

Other suitable rheology modifiers and density increasing agents that provide pseudoplastic properties to the system as a whole include modified casein, alginates, cellulose derivatives such as methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and carboxymethyl cellulose, polysaccharides, starches and gums, hydrated silicon derivatives (Bentonite), colloidal silicon dioxide (Aerosil), polyacrylic acid derivatives (Carbomer) and can be used individually or in combination. The combination of rheological modifiers can improve the rheological properties of the composition. Due to the synergistic effect of rheological modifiers and density increasing agents, it is possible to reduce their concentration in the product and by doing so achieve the desired applicative and economic effects. Should any of the above mentioned components of the composition of the present invention were to be used alone, the firefighting effect would be drastically reduced. When the individual components, potassium polyacrylate, starch, Guar gum, Xanthan gum are used as agents for increasing the density of water, high viscosity gel is formed which is not suitable for flowing through tanks, pipes and hoses. In addition, the gel formed from modified potato starch exhibits insufficient adhesion. Hence, it is not suitable for vertical surface application.

However, the fire extinguishing agent of the present invention is a powder additive which when mixed with water forms a gel, which acts as a non-Newtonian, pseudo-plastic system, with the property of thixotropy, ie. strength. The resulting gel can be easily applied on vertical and horizontal, including hanging surface, by spraying under low or high pressure using pumping equipment, with the aim of extinguishing Class A fires and preventing further spread of fire. After being applied, the gel cools down the burning surface and further prevents contact of the burning material with oxygen. During the movement of the resulting gel through hoses, by the action of external forces, the gel exhibits reduced viscosity, and upon the termination of the effect, the viscosity of the system rises again. The density of the resulting gel is very similar to that of water.

Water, which is commonly used fire extinguishing agent, lowers the temperature of the environment, ie. provides a cooling effect, but this effect is achieved only until the layers of water are retained on the burning surface. In practice, even 90-95% of the water flows down from the vertical surfaces due to gravity and disables the water to penetrate and retain upon the material. Thus, the water loses its ability to fight against fire as it runs down walls of objects or surface of forest vegetation in the land.

The powder composition of the present invention, containing the unique combination of superabsorbent polymers, rheology modifiers and density increasing agents, when added to water, forms a gel. The three-dimensional gel structure when exposed to heat of fire, remains on the surface to which it was applied due to its increased viscosity and stickiness. This allows up to 95% of water to remain on the burning surface.

When the gel applied to the treated surface comes into contact with the heat of fire, after a while the water from the three-dimensional gel structure will completely evaporate. After evaporation of the entire amount of water from the protected surface, a non-combustible char layer is formed. This creates a firefighting crust, as an additional protective layer which represents a thermal protection. The resulting firefighting crust acts as a barrier because the charred salts and char prevent the emergence of flame and the further spread of fire. This feature of the firefighting crust stems from the powder formulation containing superabsorbent polymers, rheology modifiers and thickeners described in the present invention. The overall effect of the gel and the firefighting crust contributes to optimal utilization of water as an extinguishing media. The firefighting crust produces fire-resistant layer which additionally protects the combustible material, prevents the emergence of flame, fire spreading and reduces smoke emissions. Moreover, there are no dangerous chemical reactions caused by contact of the gel or the firefighting crust with the flame. Furthermore, neither toxic nor corrosive by-products are produced.

By mixing the powder composition as disclosed in the present invention with water, the fire extinguishing properties of water, are improved. This ensures a drastic reduction of water required for firefighting. Moreover, the possible damage that occurs by shedding excess water in residential and commercial buildings and manufacturing facilities in industry is prevented. The composition of the present invention is very effective during fire extinguishing and controlling forest fires, which pose a great danger to human life.

The invention will be further described by the following examples, which are not intended to limit the scope of the present invention in any way.

Example 1

Powder composition Al Potassium polyacrylate 90,0 wt% Xanthan gum 3,0 wt% Modified starch 3,0 wt%

Guar gum 3,0 wt% Carrageenan 0,5 wt% Acrylates/C 10-30 Alkyl Acrylate Cross-polymer 0,5 wt%

The starting granular materials in accordance with the above mentioned recipe are placed into the mixer. Closed type mixing is performed for 10 minutes. The resulting homogenized material is loaded in moisture resistant containers made of polyethylene. Gel formulation Ml

Powder composition Al 0,5 wt%

Water 99,5 wt%

TOTAL 100,0 wt%

By gentle stirring 0,5 wt % of homogenized powder composition Al with water, in less than 10 seconds, the gel is formed and is ready to be used.

Example 2

Powder composition A2 Potassium polyacrylate 80,0 wt% Xanthan gum 6,0 wt% Modified starch 6,0 wt% Guar gum 6,0 wt% Carrageenan 1,0 wt%

Acrylates/C 10-30 Alkyl Acrylate Crosspolymer 1,0 wt%

The starting granular materials in accordance with the above mentioned recipe are placed into the mixer. Closed type mixing is performed for 10 minutes. The resulting homogenized material is loaded in moisture resistant containers made of polyethylene.

Gel formulation M2

Powder composition A2 0,5 wt% Water 99,5 wt% TOTAL 100,0 wt%

By gentle stirring 0,5 wt% of homogenized powder composition A2 with water, in less than 10 seconds, the gel is formed and is ready to be used. Stability testing of the powder compositions were performed, as well as examination of the properties, especially the stability and rheological properties, of the gel system formed by addition of the powder composition to water.

Stability tests

To assess the stability of the powder composition and the gel, commonly used accelerated aging tests were performed. The primary goal was to evaluate the stability and quality and to predict the shelf life under the regular storage conditions. The following tests were also performed: microbiological tests, centrifugation tests, temperature stress, rheological measurements, and measurements ofpH values.

Accelerated aging tests Samples of powder compositions Al and A2 were formed by mixing the starting components, filled into 50 ml PE containers and stored at room temperature, elevated temperature (40 ° C) and low temperature (2-8 °C) for 45 days.

Samples of gels Ml and M2, were filled into 200 ml PE containers and stored at room temperature, elevated temperature (40 °C) and low temperature (2-8 °C) for 45 days. Organoleptic tests

Monitoring of color, consistency and homogeneity changes of the samples of Al, A2, Ml and M2 stored in PE containers was performed. Visual evaluation of organoleptic properties of powder compositions and gels was performed immediately after preparation, as well as after 48h and 45 days in samples stored at room temperature. It is shown that the organoleptic properties of samples of both Al and A2 were unchanged after 48h and 45 days. In addition, the organoleptic properties of samples of both Ml and M2 were unchanged after 48h and 45 days.

Temperature stress tests 100g samples of Ml and M2 in the fully filled and well closed plastic box were stored in a thermostat (40 °C) and refrigerator (2-8 °C). The changes were observed.

Samples of both Ml and M2 gels remained stable after 90 days in the refrigerator and thermostat.

Microbiological tests Determination of total mesophilic and aerobic microorganisms, the total number of yeast and mold spores present in samples of Al, A2, Ml and M2 was performed. Samples of powders Al and A2 remained microbiologically safe after 90 days of storage. Samples of gels Ml and M2 remained microbiologically safe after 90 days of storage. pH measuring of the gel The pH value of the gel is measured by potentiometric, direct method, using a pH meter (pH meter HI 9321 "Hanna Instruments"), which is previously calibrated using standard buffer solution (pH 7.0 and pH 4.0). pH measured at 23 °C

From the data obtained by measuring the pH value of the gel, it can be concluded that there is no significant change in pH.

Determination of rheological parameters of the samples of Ml and M2 gels Rheological measurements were carried out (the apparent viscosity, voltage failure, flow curves, hysteresis area) using samples of the gels in order to assess the stability, ability to flow and possible applications.

The viscosity of non-Newtonian fluids (to which gels belong) is not constant at a given temperature and pressure, but changes with the speed gradient (shear rate). Therefore, the correlation of the shear stress and the speed gradient for non-Newtonian fluids is not a straight, but curved line. The testing was performed at constant room temperature, with increasing shear rate (D = 0-200 1/s). The rheological parameters describe the deformation of the system under the influence of the force. The maximum and the minimum of the apparent viscosity, r|_max and Tjmin are indicators of different states of the system. t]ma demonstrates the behavior of the structure at rest and is obtained at minimal shear rate; T|_mj_n is a measure of destruction of the structure obtained at maximum shear rate, by passing of the gel through the firefighting equipment.

Law shear rates provide information about the behavior of the gel in rest mode, while high shear rates are used to predict the behavior of the system during gel production, gel transportation through standard firefighting equipment, pipes and tubes, in order to extinguish or provide preventive care to the facilities threatened by the fire. All measurements were performed in a rotary viscometer Rheolab MC120 "Paar Physica", using the measuring cone-plate system. The tests were carried out 48h and 45 days after production of samples of Ml and M2 gels.

Sample Ml Umax (Pas); t|_min (Pas);

D=4,09 s^"1 D=200 s^"1

after 48 h 21,6 1,75

after 45 days 23,8 1,54

Sample M2 (Pas); T[_min (Pas);

D=4,09 s^"1 D=200 s^"1

after 48 h 32,8 4,83

after 45 days 36,4 5,43 In addition, flow curves and rheological characteristics of the samples were determined. Specifically, the effect of rheological modifiers and density increasing agents on the gel viscosity as well as their possible combinations in order to regulate the rheological properties of the gel were examined. All samples displayed pseudoplastic flow under the influence of shearing forces, with strong values of voltage failure and the emergence of thixotropy. Thixotropy is a consequence of the three-dimensional network structure that "crashes" during shear, and is renewed in resting state.

Thixotropy is a characteristic of gel systems with solvated asymmetrical or linear macromolecules in which the particles are bonded together by weak secondary bonds and hydrogen bonds, wherein the gel structure is formed within the system. Gel described in the present invention exhibits thixotropic properties. Therefore, while passing through a fire hose, the viscosity is reduced, and once applied on a vertical surface, the viscosity is reinstated. This allows smooth flow of the gel through the firefighting equipment (tubes and hoses), while at the same time enables the continuous retention of water in the form of gel on burning surface. More importantly, the viscosity of the pseudoplastic gel is not affected by temperature. Thus, the viscosity does not decrease even during extreme temperature events.

In order to determine the ability of the gel of the present invention to retain on a vertical surface and to minimize problems that occur during pumping and flow of the gel through hoses and tanks, gel formulations formed by mixing powdered composition with water at different concentrations were tested.

Gel formulation M3

Powder composition Al 0,75 wt%

Water 99,25 wt%

TOTAL 100,0 wt%

Gel formulation M4

Powder composition A2 0,75 wt%

Water 99,25 wt% TOTAL 100,0 wt%

Determination of the amount of water retained in the form of gel on a treated surface

In order to quantitatively determine the ability of powder composition to retain water on vertical, potentially combustible surfaces, mass of water as well as gel mass retained on vertical surfaces were measured. Tests were conducted with samples of gel formulations Ml and M2. Thin wooden slats (200 mm x 50 mm x 5 mm) were vertically dipped to the same depth of 50 mm in water or samples of Ml and M2 gels. The weight of wooden slats before and after immersion in water or a gel was measured, in order to determine the amount of water or a gel which is retained on a slat. The measurements were repeated three times and the average mass was calculated. Results were as follows:

The wooden slat dipped in water retains 0,18 g of water.

The wooden slat dipped in gel Ml retains 12,87 g of gel formulation.

The wooden slat dipped in gel M2 retains 13,50 g of gel formulation. These tests showed that a wooden slat dipped in gel Ml retains 71 -fold greater mass of water within the gel than a wooden slat which has only been dipped into the water, while wooden slat dipped in gel M2 retains even 75 -fold greater mass of water within the gel compared to a wooden slat that was dipped only into the water.

In addition, the effect of the fire protection achieved on combustible materials is determined by burning tests performed using cardboard and wooden slats.

Cardboard burning tests

Flame resistance measuring tests were carried out using gel samples, which were formed by applying the powder compositions of the present invention, in order to determine the ability of the gel to resist the spread of fire. The tests were conducted using a three-layer cardboard with the following dimensions: 200 mm x 70 mm x 3 mm and a propane-butane torch as a heat source (1300 °C), which was placed 10 cm away from the cardboard. During testing, the cardboard was held in a vertical position. The first test was carried out using the unprotected cardboard that kindled only after 2 seconds. Then another unprotected cardboard was submerged in water before heat exposure, and burst out in flames after 5 seconds. Another test was performed using a cardboard protected with a gel layer having different thickness: 1,0 mm, 1,5 mm, 2 mm, 2,5 mm and 3,0 mm. Each test was performed three times and an average time recorded from the initial heat exposure until the emergence of changes on the cardboard was calculated (Table 1), as described in Table 2.

Sample D 1 - Cardboard

Sample D 2 - Cardboard dipped in water Sample D 3 - Cardboard protected with 1,0 mm-thick gel layer

Sample D 4 - Cardboard protected with 1,5 mm-thick gel layer

Sample D 5 - Cardboard protected with 2,0 mm-thick gel layer

Sample D 6 - Cardboard protected with 2,5 mm-thick gel layer

Sample D 7 - Cardboard protected with 3,0 mm-thick gel layer Table 1 - The time measured from the initial heat exposure until the emergence of changes on the cardboard

Sample Time, s Sample Time, s Sample Time, s Sample Time, s of Ml of M2 ofM3 of M4

D 1 2

D 2 5

D 3 1,0 mm 23 1,0 mm 23 1,0 mm 25 1,0 mm 23

D 4 1,5 mm 28 1,5 mm 28 1,5 mm 40 1,5 mm 35

D 5 2,0 mm 35 2,0 mm 32 2,0 mm 62 2,0 mm 58

D 6 2,5 mm 60 2,5 mm 55 2,5 mm 90 2,5 mm 70

D7 3,0 mm 75 3,0 mm 67 3,0 mm 120 3,0 mm 94

Table 2 - Description of changes observed on cardboard

In all samples protected with the gel, after the evaporation of water from the gel, the firefighting crust that further prevented occurrence of flame was formed.

The tests for measuring fireproof features of gel samples which were generated from the individual rheological additives were also conducted, and the ability of the resulting gels to resist the spread of fire was measured. Gel samples were made as 1% aqueous solutions of individual rheological additives except of modified starch, which was used as 2% aqueous solution. Fireproof tests were carried out using the three-layer cardboard with the following dimensions: 200 mm x 70 mm x 3 mm. Ignition of the cardboard was carried out using a propane-butane torch as a heat source (1300 °C) which was placed 10 cm away from the cardboard. During testing, the cardboard was dipped in the gel and held in a vertical position. The average thickness of the gel that remained on a cardboard sample was 3 mm. Ignition of the cardboard was repeated three times and the average time recorded from the initial heat exposure until the emergence of changes on the cardboard was calculated (Table 3).

Table 3 - time required for appearance of changes observed on cardboard caused by the ignition

These tests showed that the significantly longer time period is required for initiation of ignition of the cardboard when the components are used in combination (Table 1), in the form of gel-type formulation, when compared to the use of solutions of individual components (Table 3).

Wooden slats burning tests

Wooden slats burning tests were performed using a propane-butane torch as a heat source (1300°C). Dry wooden slats (moisture content below 10 %) with the following dimensions: 300 mm x 70 mm x 30 mm, were placed in a vertical position and 10 cm away from the heat source. The tests were repeated three times and the average time recorded from the initial heat exposure until the emergence of changes on the slat was calculated. The first test was carried out using unprotected wooden slat that started to burn after 10 seconds. Then the wooden slat was moistened with water and started to burn 15 seconds after heat exposure.

Then a wooden slat was dipped in sample of gel M3. The average thickness of the gel retained on the slat was 3 mm. 120 seconds after heat exposure, evaporation of water from the gel occurred. After the water has evaporated, by further exposure to the heat, a firefighting crust was formed on the surface of the slat. The firefighting crust is an additional barrier that protects the material from burning and eliminates the possibility of ignition, as illustrated in the description of the observed changes of wooden slats given in Table 4.

Table 4 - Description of observed changes of wooden slats

Sample LI - Wooden slat (beech) immersed in the sample of gel M3 Sample L2 - Wooden slat (pine) immersed in the sample of gel M3

In all gel immersed samples, after the evaporation of water from the gel, the firefighting crust was formed. As described in Table 4, continuous exposure of wooden slats to the flame for a period of 20 minutes does not lead to combustion, occurrence of flame or smoke. After the heat exposure of wooden slats was terminated, in the next 5 minutes there was no occurrence of spontaneous combustion. Re-exposure of the treated samples to the flame for 5 minutes did not cause burning of the wood, occurrence of smoke or flame.

However, in all above described samples, permanent mechanical changes of the wood structure, like charring, weight and thickness reduction were observed. Thus, the resulting firefighting crust acts as a barrier because the charred salts and char prevent the emergence of flame and further spread of fire.

It is well Icnown that the biggest problem to be overcome in fighting fires is the recurrence of fire and flame on the site of previously extinguished fire, usually only a few minutes after the initial fire extinguishing. So, shortly after the evaporation of water at the site where the fire was extinguished, a relapse of fire often occurs. The present invention provides a solution to this technical problem, by providing a powder composition that enables retaining of water for a long time period on the material exposed to the flame and manifest effects of cooling and congestion. In addition, after the evaporation of water from the gel due to exposure to the heat of fire, the firefighting crust that prevents relapse after initial fire extinguishing is formed.

The formed gel as described by the present invention is intended for use in fighting fires as well as in preventive fire protection and satisfies all the criteria as the use of water. Even in combination with other firefighting agents (in the form of foam, powder, sand) there were no side effects that could diminish the efficiency of the gel. In firefighting, it is necessary to apply the gel by directed or dispersed spraying, onto a burning surface. For fire 1 prevention, gel 2 should be applied to the surface 3 in a thin layer, as shown in Figure 1. After the water from the gel 2 completely evaporated under the influence of heat, as shown in Figure 2, the firefighting crust 4 that provides a prolonged flame 3 protection is created. The powder compositions according to the present invention is mixed with water in a specially constructed mixer that is attached to a hose or hydrant. A resulting gel exhibits suitable viscosity and fluidity, which enables the smooth flow of the gel through a standard firefighting equipment. Because of its harmlessness, it is possible to apply the gel even to human skin. In addition, the gel may be applied to passages to be used during the retreat of vulnerable persons from the fire location. The applied gel will remain on the surfaces on which it is applied to, even in the event of strong wind. Polymers present during the hydration process can absorb water and swell, which leads to formation of millions of tiny droplets of water coated by a polymeric membrane. Stacking of these gel drops provides a thermal protection, by formation of so-called "thermal blanket" on the treated surface. In order to reach the treated surface, heat caused by the fire needs to eliminate all layers of gel drops. The polymer membrane of each gel drop and compact stacking of the layers prevent water evaporation. When the fire approaches the surface, the outer layer of gel drops closest to the fire absorbs the heat. The water contained in gel drops slowly evaporate while the next layer of gel drops absorbs heat, protecting the remaining inner layers. The process continues until water evaporates from all the layers of gel drops. After evaporation of the entire amount of water from the protected surface, a non-combustible carbonized layer, i.e. a firefighting crust is formed. Thus, it is provided an additional protective layer which represents a thermal protection and prevents the spread of fire and the re-emergence of flame.

LIST OF REFERENCE SIGNS

1 Flame

2 Gel

3 Fire-exposed surface

4 Firefighting crust

Claims

Sretko Popadic Patent Claims

1. A powder composition for extinguishing and preventing the spread of fire containing

Potassium polyacrylate 50,0 -90,0 wt%

Acrylates/C 10-30 Alkyl Acrylate Cross-polymer 0, 1 to 3 ,0 wt%

Xanthan gum 1 ,0 -10,0 wt%

Modified starch 1,0 -10,0 wt%

Guar gum 1 ,0 -10,0 wt% and

Carrageenan 0,5-3,0 wt%.

2. The powder composition for extinguishing and preventing the spread of fire according to patent claim 1, characterized in that it comprises

Potassium polyacrylate 90,0 wt%

Acrylates/C 10-30 Alkyl Acrylate Crosspolymer 0,5 wt%

Xanthan gum 3,0 wt%

Modified starch 3,0 wt%

Guar gum 3,0 wt% and

Carrageenan 0,5 wt%.

3. The powder composition for extinguishing and preventing the spread of fire according to patent claim 1, characterized in that it comprises

Potassium polyacrylate 80,0 wt%

Acrylates / CI 0-30 Alkyl Acrylate Crosspolymer 1,0 wt%

Xanthan gum 6,0 wt%

Modified starch 6,0 wt%

Guar gum 6,0 wt% and Carrageenan 1,0 wt%.

4. A gel for extinguishing and preventing the spread of fire, which is formed by addition of the powder composition, according to any of patent claims 1 - 3, to water in a concentration of 0,2 - 2,0 wt%.

5. The gel according to patent claim 4, wherein the concentration of the powder composition in water is 0,2 wt%.

6. The gel according to patent claim 4, wherein the concentration of the powder composition in water is 0,5 wt%.

7. The gel according to patent claim 4, wherein the concentration of the powder compositio in water is 0,75 wt%.

8. A firefighting crust for prevention of ignition and spread of fire which is formed by complete evaporation of the water from the gel according to any of patent claims 4 - 7.

9. A method for extinguishing and preventing the spread of fire, which includes:

- preparation of the powder composition by mixing the components according to any of patent claims 1 - 3

-addition of the formed powder composition to water in a concentration of 0,2-2,0 wt% to form a gel

-application of the resulting gel onto a burning surface or surface which needs fire prevention.

10. Use of the powder composition according to any of patent claims 1 -3 as a fire extinguishing or a fire prevention agent.