IL104758A - Fire extinguishing methods and systems - Google Patents

Description

EXTINGUISHING METHODS AND SYSTEMS FIRE EXTINGUISHING METHODS AND SYSTEMS FIELD AND BACKGROUND OF THE INVENTION The present invention relates to fire extinguishing methods and associated systems and, more particularly, to methods and related systems which do not involve halocarbons and which are highly effective in extinguishing fires, even when relatively small quantities of chemicals are used.

The present invention relates, in particular, to methods and systems for volume fire extinguishing. Volume fire extinguishing involves the temporary creation of an atmosphere which is incapable of sustaining combustion within the volume to be protected, typically a relatively confined volume.

One of the volume fire extinguishing methods in most widespread use at present includes the introduction of volatile halocarbons, such as Halon 1301, for example, into the volume to be protected. Halocarbons have excellent fire extinguishing capacity which is attributable to their being inhibitors of combustion. Halocarbons actively interfere with the chemical reactions taking place in the flame and effectively inhibit them.

Furthermore, halocarbons have a number of desirable properties such as low toxicity. In addition, halocarbons gases can be rather easily liquefied under pressure, making them easily storable in the liquefied state. Halocarbons do not adversely affect equipment and other materials with which they come in contact.

Nevertheless, halocarbons suffer from a fundamental disadvantage, namely, they are known to interact with ozone, which leads to the destruction of the earth's ozone layer. According to the 1987 Montreal Protocol, which prescribed a number of international measures for the protection of the earth's ozone layer, the use of halocarbons is to be completely banned by the year 2000.

It is thus quite urgent to find alternative volume fire extinguishing means which could successfully act as a replacement for halocarbons. A successful replacement for halocarbons would possess a volume fire extinguishing effectiveness at least equal to that of halocarbons, yet would be ecologically safe.

Two basic types of such ecologically benign fire extinguishing materials are presently known. The first includes inert gaseous diluents, such as carbon dioxide, nitrogen water vapor, and the like. The second type includes fire extinguishing powders based on mineral salts, such as carbonates, bicarbonates , alkali metal chlorides, ammonium phosphates, and the like.

As presently implemented, both types of materials suffer from serious disadvantages. Inert gaseous diluents are largely ineffective in disrupting the reactions taking place in the flame. Rather, inert diluents act by diluting the air in the volume being protected, thereby lowering the oxygen concentration below that required to sustain the combustion. An example of the use of inert diluents is disclosed in U.S. Pat. No. 4,601,344 to Reed which relates to a gas generating composition containing glycidyl azide polymer and a high nitrogen content additive generates large quantities of nitrogen gas upon burning and can be used to extinguish fires.

For relatively airtight volumes, the amount of diluent required roughly equals the amount of air already in the volume prior to combustion. If the volume to be protected is not airtight, the required volume of the inert diluent must be several times that of the protected volume.

Fire extinguishing methods based on inert dilution require relatively large amounts of diluent and are appreciably less effective and reliable than extinguishing with halocarbons.

Volume fire extinguishing with the help of powders is carried out by dispensing a powder aerosol in the volume to be protected. The aerosol envelops the flame thereby suppressing it. It is believed that powders chemically interrupt combustion by forcing the recombination and deactivation of chain propagators responsible for sustaining the combustion process in the focus of fire.

Such recombination is believed to occur both at the surface of the solid particles of the aerosol and, to some extent, also in reactions of the chain propagators with gaseous products of the evaporation and decomposition of powders in the flame. Chain propagators are gaseous atomic particles or radicals having a free valence, which serve to initiate and sustain the branched chain reactions characteristic of combustion processes in combustible substances containing carbon.

However, the efficiency of presently implemented volume fire extinguishing with the help of powders is also of limited efficacy because of the comparatively low dispersity of the fire-extinguishing powders. The particle size of presently used powders ranges from about 20 to about 60 microns. Such large particles have a relatively low surface to volume ratio. Since the desired reactions take place largely on the surface of the particles, a given amount of such powders has a limited capacity for interrupting the chain reactions and putting out the fire.

Further, it is difficult to prepare an aerosol of such powders which will distribute uniformly throughout the volume to be protected. It is, in addition, difficult to ensure that the powder particles, once formed, will stay in their original suspended state while stored for a sufficiently long period prior to use so as to maintain the viability of the product as a fire extinguishing composition. Finely-dispersed powders have a strong tendency to agglomerate, or cake, during storage. Such agglomeration greatly hinders the dispensing of the material from its storage container during use. Furthermore, whatever particles are able to leave the storage container and come in contact with the fire, are relatively coarse-grained powder particles, having a relatively low surface area to volume ratio and thus possessing reduced fire extinguishing capacity per unit weight .

Attempts have been made to solve the problems associated with the long-term storage of finely divided powders. Exemplary of such attempts is U.S. Pat. No. 4,234,432 to Tarpley, which discloses a powder dissemination composition in which the powder is contained in a thixotropic gel which prevents the agglomeration, sintering and packing of the powder material. The finely divided powder has at least a bimodal particle distribution size distribution encapsulated in a gelled liquid. The method appears to be complex, requiring the fabrication of a powder of well-defined particle size distribution.

In at least one case, attempts have been made to get around the storage problems by creating storing reaction precursors rather than the actual powders. U.S. Statutory Invention No. H349 to Krevitz et al. discloses reagent compositions which are chemically inert when solid and are chemically active when molten. The reagent compositions may comprise a first substance such as a high molecular weight wax or polymer and a second substance which is dissolved, dispersed, or encapsulated in a solid matrix of the first substance. The second substance is a highly chemically reactive compound such as a strong base or a strong acid. As solids, the reagent compositions are inert. When molten, the second substance is exposed and the resultant liquid solutions are highly reactive.

There is thus a widely recognized need for fire extinguishing methods and systems which are at least as effective as those involving the use of halocarbons but which are ecologically safe.

Specifically, there is a clear need for, and it would be highly advantageous and desirable to have, fire extinguishing methods and systems which use chemicals which do not adversely affect the earth's ozone layer and which are capable of putting out fires quickly and efficiently.

SUMMARY OF THE INVENTION According to the present invention there is provided a method of extinguishing a fire in a volume, comprising: pre-positioning a fire extinguishing device in communication with the volume, the device including a composition which includes: (1) a first reactant; and (2) a second reactant; wherein the medium is activated so as to cause the first reactant and the second reactant to react with each other to create products such that, when the products come in contact with the fire, the products chemically inhibit the chain reactions of the fire flame and bring about the extinguishing of the fire.

Also according to the present invention there is provided a system for extinguishing a fire in a volume, comprising: a fire extinguishing device pre -positioned in communication with the volume, where the device includes a composition which includes: (1) a first reactant; and (2) a second reactant; where the medium is activated so as to cause the first reactant and the second reactant to react with each other to create products such that, when the products come in contact with the fire, the products chemically inhibit the chain reactions of the fire and bring about the extinguishing of the fire.

According to the present invention there is also provided a method and a system wherein the device includes a slitted profile in which said composition is located.

According to further features in preferred embodiments of the invention described below, the device further includes a coolant material.

According to still further features in the described preferred embodiments the device includes a perforated tube in which the composition is located.

According to another embodiment according to the present invention the device includes a coolant material, which may be a granulated hydrophilic material.

According to yet another embodiment according to the present invention the device includes means for distributing the products to different locations.

According to still another embodiment according to the present invention the device is submerged in a liquid coolant and includes means for preventing entry of coolant into the device while accommodating the escape of the products into the coolant.

According to still another embodiment according to the present invention included in the device is a suitable filler material with fire extinguishing capabilities which aids in obtaining a controllable aerosol cloud.

The present invention successfully addresses the shortcomings of the presently known configurations by providing ecologically benign methods and associated systems for putting out fires which is highly effective and which requires relatively small amounts of chemicals per unit volume protected.

The methods according to the present invention are advantageous in that they facilitate the rapid and reliable liquidation of the focus of fire anywhere in the protected volume. The methods can easily be automated, so as to be activated automatically upon the sensing, for example, of a certain preset elevated temperature in the volume, or other parameters which may indicate the presence of a fire, such as radiation, gaseous products, change in pressure, and the like.

The compositions involved in methods according to the present invention act to extinguish the target in at least two basic ways. One way, which is common to presently known powder fire extinguishes, involves the absorption of heat by, and consequent heating of, the solid particles, amplified by the evaporation of various chemical species. A second, and much more significant way of extinguishing the fire, is through the chemical interaction of various species present during the activation of species present during the activation of a composition according to the present invention with the flame chain reactions, effecting the interruption of these chain reactions.

The present invention is suitable in the fire protection of various volumes, including, but not limited to, various compartments, machine rooms, cable tunnels, cellars, chemical shops, painting chambers, reservoirs, storage vessels for oil products and liquefied gases, pump rooms handling combustible substances, and the like, as well as diverse means of transportation, such as motor vehicles, aircraft, ships, locomotives, armored vehicles, naval vessels, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein: FIG. 1 is a configuration according to the present invention showing SFC material in solid or powder form placed in a profile; FIG. 2 is another configuration according to the present invention showing SFC material in solid or powder form placed in a perforated tube; FIG. 3 is a configuration as in Figure 1 but with a layer of cooling material placed over the SFC; FIG. 4 is a configuration as in Figure 2 but with a layer of cooling material placed around the SFC; FIG. 5 is another configuration according to the present invention showing an arrangement of SFC sandwiched between layers of hydrophilic material; FIG. 6 is another configuration according to the present invention showing a cooling system involving passage of the aerosol through a pipe surrounded by cooling liquid; FIG. 7 is another configuration according to the present invention showing a cooling system involving the injection of coolant into the aerosol; FIG. 8 is an exploded view of another configuration according to the present invention showing a compact unit including SFC and coolant injection; FIG. 9 is an assembled view of the configuration of Figure 8; FIG. 10 is a schematic depiction of a fire extinguishing system featuring SFC material and a distribution manifold for conducting the aerosol to various location following injection of coolant; FIG. 11 is another configuration according to the present invention featuring SFC material, cooling material and flame arrestors; FIG. 12 is another configuration according to the present invention designed for use immersed in a liquid; FIG. 13 shows the configuration of Figure 12 as it would appear when deployed in a liquid tank; FIG. 14 is yet another configuration according to the present invention designed for use immersed in a liquid; FIG. 15 shows the configuration of Figure 14 as it would appear when deployed in a liquid tank; FIG. 16 is yet another configuration according to the present invention, related to that of Figure 3, designed for use immersed in a liquid; FIG. 17 shows the configuration of Figure 16 as it would appear when deployed in a liquid tank.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is of methods and associated systems which can be used to effectively extinguish fires and which are not harmful to the ozone layer.

Specifically, the present invention relates to various means of storing two or more reactants which can be activated, directly or indirectly, and made to react upon the incidence of fire, forming products which, with or without the benefit of pre-cooling, tend to interfere with the propagation of the fire, thus serving to put out the fire .

Novel configurations for effecting methods for volume fire extinguishing are herein disclosed. A key feature of each of configurations according to the present invention is the in- situ formation of a very finely dispersed aerosol. The aerosol is not prepared ahead of time and stored, as in presently known systems. Rather, the aerosol is created or produced in situ during the fire accident, by combusting a solid-fuel composition or medium (hereinafter referred to as "SFC") , which includes at least two reactants capable of reacting with one another.

Preferably, one of the reactants is an oxidant while the other is a reducing agent. More preferably, the SFC further includes a filler, such as potassium chloride or ammonium phosphate. Upon reaction, the SFC forms gaseous products and solid aerosol particles in the combustion products. The gaseous products, and especially the solid aerosol particles, exert a strong inhibiting effect on the flame of the fire which is to be extinguished by promoting the recombination of combustion propagation centers, thereby inhibiting the continuation of the fire and extinguishing it.

In contrast with currently known powder volume fire extinguishing technologies, the systems according to the present invention obviate the need for storing an aerosol, usually stored as a powder and a separate pressurized propellant, such as air. As was described above, such storage leads to the gradual agglomeration of the particles, leading to dispensing difficulties and to reduced effectiveness brought about by the reduction of the particle surface areas.

The fire extinguishing capacity of an aerosol created in systems according to the present invention is greatly increased in comparison with known technologies since an aerosol according to the present invention is made up of particles of a much smaller size, typically on the order of one micron, and hence much larger surface to volume ratio, than has been heretofore known. The smaller particle size makes for a more highly dispersed and more highly effective aerosol .

As the particle size decreases, the extinguishing surface of the aerosol, on which heterogeneous recombination of the chain propagators takes place, increases. All other things being equal, the number of the aerosol particles per unit volume increases in inverse proportion to the cube of the diameter of the particles, whereas the surface area of the particles is directly proportional to the square of the diameter. Consequently, the total surface of the particles increases in inverse proportion to the diameter of the particles or in direct proportion to the dispersity of the aerosol.

Moreover, as the size of the particles diminishes, the rate of sublimation increases, and the extinguishing effect is augmented by homogeneous gas phase inhibition of the fire flame through the agency of gaseous products forming from the condensed part of the aerosol.

The ability of the aerosol to effect the recombination of the chain propagators depends to some extent on the chemical composition of the solid particles. It has been determined that the best fire propagation inhibiting properties are displayed by carbonates, bicarbonates , chlorides, sulfates, and oxides of metals such as, but not limited to, those belonging to Group IA of the Periodic Table, with the exception of Li and Fr. This is discussed, for example, on page 72 of in A. N. Baratov and L . P. Vogman, "Fire Extinguishing Powder Compositions", Moscow, Strojizdat Publishers, 1962, which article is incorporated herein in its entirety by reference as if fully set forth herein.

It has been further determined that the strongest inhibitors are strontium sulfates and cesium sulfates, with potassium chlorides and sodium chlorides being not quite as effective, and with potassium bicarbonates and sodium bicarbonates being somewhat less effective.

Taking into account the availability and cost, as well as the performance characteristics of these various inhibitors, it would appear that alkali metal chlorides may be commercially most suitable for use in fire extinguishing powders and aerosols.

According to the present invention these powders are created in situ in a finely dispersed form through the reactions of the SFC and are applied to the fire immediately following their creation. The SFC is combusted to produce the desired aerosol containing the compounds described above. Prior to combustion, the SFC includes at least two reactants which are capable of reacting with each other to form desired products.

Preferably, the SFC includes one reactant which is preferably an oxidant, such as potassium perchlorate, potassium dichromate, potassium nitrate, potassium chlorate, cesium nitrate or the like. The SFC further includes a second reactant preferably capable of acting as a reducing agent which may be one or more of various organic materials, such as rubber, polymeric materials, epoxy resin, phenol formaldehyde resin, and the like, or which may be phosphorus, sulfur, and the like. The SFC may also include a filler such as, but not limited to, potassium chloride. The filler serves the function of regulating the temperature of the aerosol by absorbing some of the heat of the oxidation- reduction reactions. Simultaneously, the filler serves as a source of potassium compounds which are used in extinguishing the fire.

It should be borne in mind that for extinguishing smoldering materials (fire accidents of Class A) , it is necessary not only to liquidate flame burning in the gaseous phase but also to isolate the surface of burning material from air. This can be accomplished, for example, with the further inclusion in the SFC of ammonium phosphates, which are known fire extinguishing compounds.

The precise composition and concentration of the SFC used in systems according to the present invention is selected with an eye toward the type of fire likely to be encountered and the cost, availability and ease of use of the various suitable components. The possible combinations of components making up the SFC and their precise concentrations are virtually limitless. What is critical to methods and systems according to the present invention is not the precise composition but the in situ reaction, preferably an oxidation- reduction reaction, of two or more components of the SFC to form an aerosol having very fine solid particles.

As illustrations of typical SFC compositions, and without in any way limiting the scope of the present invention, nine possible compositions are described below.

Composition 1: Potassium perchlorate 40-50 wt% Epoxy resin 7D-20 (with hardener) 9-12 wt% Potassium chloride 40-44 wt% Magnesium powder 0-4 wt% Composition 2: Potassium dichromate 20 wt% Gunpowder grade "H" 80 wt% Composition 3: g 25 wt% CSN03 75 wt% Composition 4: Mg 25 wt% KN03 75 wt% Composition 5; Iditol (phenol- formaldehyde resin) 30 wt% KN03 70 wt% Composition 6: Potassium chlorate 65-70 wt% Potassium chloride 16-20 wt Epoxy resin 12-18 wt% Composition 7 ·.

Potassium chlorate 37-45 wt% Potassium nitrate 37-45 wt% Epoxy resin 16-19 wt% Mg (or Al) 1- 3 wt% Composition 8: Potassium nitrate 70-80 wt% Epoxy resin 19-23 wt% Mg (or Al) 2- 4 wt% Composition 9 : Cesium nitrate 80-90 wt% Epoxy resin 10-20 wt% When selecting solid- fuel composition components, one should also ensure that both the initial composition of the SFC and its combustion products are non- toxic and explosion-proof . The explosion-proof compositions listed above were tested and were found to be characterized in that their combustion, while rapid, is incapable of becoming so rapid as to be become explosive. For illustrative purposes, it is believed that use of a combination of potassium perchlorate or potassium bichromate as the oxidant, rubber as a reducing agent, magnesium for enhancing the temperature and the rate of burning, and potassium chloride as filler provides an SFC which, upon combustion, produces an aerosol having a high inhibiting effectiveness, is harmless, and is explosion-proof .

Without in any way limiting the scope of the present invention, it may be instructive to briefly discuss the mechanisms believed to be responsible for the efficacy of methods and systems according to the present invention. For illustrative purposes discussion is limited to a system including potassium chlorate, an epoxy resin and potassium chloride.

Upon combustion of an SFC made up of potassium chlorate (68 wt%) , epoxy resin (16 wt%) , and potassium chloride (16 wt%) , without using magnesium, the following gaseous products, in the indicated mass fractions, were obtained: K 0.026 H2 0.017 H20 0.100 HC1 0.002 N2 0.160 CO 0.430 C02 0.183 KC1 0.082 The condensed phase is made up of solid particles of K2C03. The weight ratio of the gaseous phase to the condensed phase is 0.6 to 0.4.

During the cooling process of the aerosol in open air, KC1, KOH, KHC03, K2C03 and perhaps oxides of potassium, such as KO and K20, pass from the gaseous phase to the condensed phase. The solid particles thus formed have a diameter on the order of approximately one micron.

When the aerosol interacts with the combustion zone of the fire which is to be extinguished, such as a hydrocarbon fire, both homogenous and heterogeneous reactions take place. The heterogeneous inhibition processes, usually between solid and gaseous phases, take place at temperatures of up to about 1000°K. Above this temperature the predominant inhibition processes are homogeneous, typically between gaseous reactants.

The heterogenous processes may be described with the aid of the following reactions: A- + S - - -> AS (1) AS + A- > A2 + S (2) where A · is a radical active species from the fire to be extinguished, S is the surface of a solid aerosol particle and A2 is a molecular species.

From the above reactions it can be seen that the newly created AS can react with another active species to generate a stable molecular species while at the same time regenerating free aerosol particle surface which is available for further interaction with active species.

The homogenous inhibition processes taking place in the gaseous phase may be described by the following reactions: K + -OH + M - - -> KOH + M (3) KOH + ·0Η - - -> H ■20 + κο (5) where ·Η and -OH are radical active species and represents an energy input.

An SFC according to the present invention may be prepared in any convenient fashion. Three such methods will be described for illustrative purposes only without in any way limiting the scope of the present invention. in one process, the various components are dry mixed together. The mixture is then mechanically pressed to form pellets or tablets of desirable size and shape.

In a second process, the various components are mixed together to form a paste. The paste is poured into an appropriately sized and shaped form or mold and is dried, for example by heating, to remove any solvent and harden the SFC.

In a third process the components are mixed together to form a paste. The paste is simultaneously dried and shaken on a screen to form a dry powder. The powder is placed into tubes or shells suitably shaped and sized to facilitate the functioning of the SFC.

Various improvements of the methods and systems according to the present invention are possible. Two such improvements involve the confining of the flames of the SFC when undergoing combustion and the cooling of the combustion products prior to their release to the fire to be extinguished.

When the SFC is ignited an open flame of the burning charge is created. Also, the aerosol formed on combustion of the SFC is at elevated temperatures. The presence of an open flame, may, in specific situations, have detrimental effects. This is the case, for instance, when the fire to be extinguished involves a hydrocarbon reservoir, or where individuals are found in the vicinity and may be forced inhale flames into their lungs. Similarly, the high temperature of the aerosol militates against its uniform distribution in the volume being protected. The latter difficulty arises since a hot aerosol tends to first rise by natural convection toward the ceiling of the premises, reaching the focus of the fire to be extinguished only after the aerosol has cooled down sufficiently to descend onto the fire. Such circuitous movement of the aerosol may further lead to the escape of a portio of the aerosol from the space where it is intended to stay, with the attendant reduction in fire extinguishing efficiency and with possible adverse environmental effects on the surroundings, including personnel.

It is thus generally desirable to confine the flame produced in the combustion of the SFC while at the same time cooling the hot aerosol formed during the combustion of the SFC.

The confinement and cooling may be effected by any number of suitable methods. The approaches can be broken into physical cooling and cooling involving chemical reactions. Examples of various such techniques are described below.

One such method is to allow the SFC to combust intensely with the subsequent combination, as by ejection, of the hot aerosol with a coolant. Another method involves the dispersal of the SFC through the intensive intermixing of the air medium with the aerosol formed in simultaneous combustion of the entire rated quantity of compounded mixture, the mass of which is distributed in the volume being protected.

In the first method of cooling, it is possible to use as a coolant air, nitrogen, carbon dioxide, water, aqueous solutions of sodium salts and potassium salts, and the like. Experiments have demonstrated that the application of water or aqueous solutions of salts is preferable, since these coolants have high heat capacities and heats of vaporization.

Two basic methods of carrying out the intermixing of gases and liquids are offered, by way of illustration. The first involves the displacement of the liquid into a mixing chamber with the gas flux. A second involves the ejection of the liquid by the gas flux into a mixing chamber where the pressures and temperatures of the two fluxes become uniform. The latter method offers a number of advantages over the first. Primarily, the method does not require a reservoir operating under pressure, and is of simpler design.

Procedures for designing gas -liquid ejectors are set forth in the monograph of E. Ya. Sokolov and N. M. Zinger "Fluidic Apparatus", Moscow, Gosenergoizdat Publishers, 1984 (in Russian) , which is incorporated in its entirety by reference as if fully set forth herein. The gas -liquid ejector designs disclosed in the above-referenced monograph are largely inapplicable to the cooling of an SFC aerosol. This is because the flame or high- temperature aerosol is likely to break through into the mixing chamber and even into the volume being protected immediately after the ignition of the SFC cartridge due to a delay in the supply of the coolant flux.

The underlying principles of systems according to the present invention were disclosed and illustrated in Israeli patent applications Nos. 101298 and 101802, which are incorporated by reference as if fully set forth herein.

The present invention is of a series of novel and unique configurations which can be used to practically implement the underlying principles. Specifically, the configurations disclosed and claimed herein are intended to implement fire extinguishing techniques which overcome the difficulties which are encountered when a basic SFC-based system is implemented. In particular, the embodiments which are described below incorporate various means of cooling the aerosol so as to reduce its temperature and increase its density in order to decrease or eliminate adverse effects to surrounding personnel and property and in order to direct the aerosol to the base of the fire without waste of material or delay. The configurations further deal with ways of increasing the rate of aerosol formation so that the . aerosol is made available to extinguish the fire earlier than would otherwise be possible .

The principles and operations of the various configurations according to the present invention can best be understood with reference to the drawings and accompanying discussion.

Referring now to the drawings, Figure 1 illustrates a basic embodiment of a fire extinguishing system according to the present invention. Here the solid, granulated, powdered or gelled SFC 10 is packed or molded into a profile 12 of suitable size and shape and of any desired length, typically made of metal. An igniter 14 is used to activate the SFC and may be connected via an igniter cable 16 to a flame or heat detector, and the like. Upon activation, the SFC reacts to form a wall of aerosol which is uniformly discharged through the slotted opening of profile 12. Two or more units such as those shown in Figure 1 can be connected end -to -end to form a unit of any suitable length and can be installed in corridors or along the walls of a room or other enclosure.

To control the rate of aerosol formation, it is desirable to control the size of the SFC particles. It has been found that over a certain size range as the SFC particles are made smaller and their surface to volume ratio increases the rate of aerosol formation increases as does its fire extinguishing effectiveness. It was further found that when the SFC particles are made too small, the aerosol formation rate is too large, resulting in a lowered fire extinguishing effectiveness and possible explosions in closed spaces. In many fire extinguishing applications it is desirable to have all the aerosol formed within 10 or 20 seconds from the onset of aerosol formation. It has been found that suitable SFC reaction rates are those which result in the penetration of the reaction front into the SFC cartridge at the rate of from about 0.65 to about 1.35 mm/sec, with an optimum being approximately 1.1 mm/sec.

It is further important to design the SFC tablet, cartridge, and the like so that it has the proper geometry for optimal fire extinguishing effectiveness. Specifically, it should be noted that while the volume of SFC used controls the total amount of aerosol which is, in theory, available for extinguishing the fire, the exposed surface area of the tabled, cartridge, and the like, plays a leading role, along with particle size, in determining the rate of aerosol formation. Thus, the larger the gross surface are of the tablet, cartridge, and the like, the higher the rate of aerosol formation. For example, very high rates can be achieved where the SFC is "painted" in a thin layer onto a large surface, such as a wall, as is described below.

Another configuration is shown in Figure 2. Here SFC, preferably cylindrical in shape, is located inside a perforated tube 20. Upon activation, the SFC reacts to form an aerosol which escapes through the perforations 22 into the space to be protected.

Variations of the two embodiments of Figures 1 and 2 are shown in Figures 3 and 4, respectively. Here a suitable cooling material 30 is placed over the SFC (Figure 3) or around the SFC (Figure 4) . in these embodiments the aerosol which is formed upon activation of the SFC is forced to pass through cooling material 30 which results in the cooling of the aerosol prior to its release into the space to be protected.

Various means of cooling the aerosol are possible. One way is to effect heat exchange between the aerosol and a suitable heat absorbing medium, such as water, solutions of water and ethylene glycol or water and acetone, solid granulated dry ice (C02) , and the like.

Another means of cooling the aerosol is by allowing the aerosol to chemically react with a suitable material in an endothermic, or heat -absorbing, reaction or by bringing about the creation of water molecules which have a large heat capacity and which are capable of absorbing significant amounts of heat.

Examples of a suitable chemical coolants is boric acid (H3BO3) and similar acids which react with the basic intermediate potassium hydroxide (KOH) , created during the ignition of the SFC, to form water. The reaction is believed to be: H3BO3 + 3KOH ---> K3BO3 + 3H20 Additional materials which may be suitable in this context include, but are not limited to, NaHC03, KHC03, H2C03, and the like.

Depicted in Figure 5 is an illustrative embodiment of a honeycomb configuration wherein each of the voids of the honeycomb includes a layer of SFC 10 which is covered, preferably both at the top and at the bottom, with a layer of material 30 which will bring about the cooling of the aerosol, by physical and/or by chemical means. Any of the materials described above may be used for material 30. In addition, it may be useful to use as material 30 a granulated bed of perlite, vermiculite, or similar hydrophilic minerals which are capable of absorbing and keeping moisture for long periods of time. When the aerosol is discharged through the granulated bed the aerosol interacts with the moisture over the considerable surface area of the granulated particles and is cooled in the process.

Another configuration according to the present invention is shown in Figure 6 wherein the SFC is reacted in a burning chamber 40 from which the aerosol passes to a displacement chamber 42 where it contacts a suitable cooling liquid 44. Aerosol leaves the system through a tuyere 46 which runs through cooling liquid 44, thereby serving to further cool the aerosol prior to its exit from the system and its entry into the space to be protected.

A related configuration is shown in Figure 7 where aerosol formed upon the activation of SFC 10 enters a stopper 50, which serves to immobilize the SFC cartridge and prevent the blocking off of the opening, prior to its passage through an exhaust pipe 52 and its exit from the system. During its passage through exhaust pipe 52 the aerosol is cooled by the addition of a suitable coolant from a reservoir 54 which enters exhaust pipe 52 through a pipe 56.

A similar configuration is shown in exploded and assembled views in Figures 8 and 9, respectively. The compact SFC generator shown in Figures 8 and 9 features a combustion chamber 60 which houses SFC 10. A coolant pump 62 injects coolant through a tube 64 into the aerosol.

The various configurations discussed can be modified so as to channel the formed aerosol, after cooling if desired, through a manifold to various locations. Such a system is depicted schematically in Figure 10. Here, combustion chamber 60 includes SFC 10. Exhaust pipe 70 leads the hot aerosol away from combustion chamber 60. Coolant pipe 72, which is preferably equipped with an appropriate nozzle 74, is used to introduce coolant into exhaust pipe 70. A valve 76 may be used to control the flow of coolant. The cooled aerosol then enters a distributor 78 from where it is distributed to two or more locations . Such an arrangement may be useful where adjoining but separate chambers are endangered by a fire in one of the chambers such that a fire in one chamber preferably triggers fire extinguishing means in several chambers. An example of such a situation are the storage compartments of a commercial aircraft.

Yet another configuration according to the present invention is presented in Figure 11 which, in contrast with the previously discussed embodiments, features flame arrestors 80, between which is preferably located suitable cooling material 30. Flame arrestors 80 serve to break up the flame, preventing the flame from reaching the outside of the unit where they could trigger undesirable combustion of the surroundings, and further serve to enhance the contact between the aerosol and cooling material 30.

Systems according to the present invention may also be used immersed in a liquid, such as oil, which serves as the cooling medium upon activation of the SFC. Two such configurations are shown in Figures 12-15.

The device depicted in Figure 12 includes a combustion chamber 40 which houses SFC 10. Combustion chamber 40 is completely closed except for one or more exhaust pipes or tuyeres 80 which are so angled as to prevent the ingress of water into combustion chamber 40 when the device is submerged in an oil tank 82 (Figure 13) . When the SFC 10 is activated, the aerosol produced has sufficient pressure to exit the device through exhaust pipes 80 and to enter the oil reservoir where the aerosol is cooled as it rises through the oil to the vapor space at the top of oil tank 82, where the fire to be extinguished is typically located. A similar device, but one configured slightly differently, is shown in Figures 14 and 15. Here, the exhaust pipes 90 of Figures 12 and 13 are replaced by a cover 100 which preferably features an outwardly extending rim 102. When SFC 10 is activated, the aerosol formed leaves combustion chamber 40 through the space between combustion chamber 40 and cover 100 and is dispersed radially outwardly into the oil to a degree determined largely by the geometry of rim 102.

Yet another similar device is shown in Figures 16 and 17. Here use is made of a device similar to that of Figure 3 but further including a special cover 200, which unlike the cover of the embodiment shown in Figures 14 and 15, extends for relatively large distances, perhaps several meters. Cover 200 is shaped such that when SFC 10 is activated, the aerosol formed leaves as shown in Figure 17 throughout the length of cover 200 to form a screen, or curtain, of aerosol. It has been found that suitable SFC reaction rates are those which result in the spread of the reaction front along SFC face at the rate of about 12 cm/sec .

Another configuration effective in the extinguishing of fires in a specified space involves "painting" the interior walls, or some other surface, of the space to be protected with SFC in the form of a paint -like paste or quick -drying liquid. Such a configuration may preferably incorporate the benefits of cooling the aerosol by "painting" over the SFC a layer of suitable coolant material 30.

While the invention has been described with respect to a number of preferred embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made.

Claims (14)

31 104758/3 WHAT IS CLAIMED IS:

1. A method of extinguishing a fire in a volume, comprising: pre-positioning a fire extinguishing medium in communication with the volume, said medium including a composition which includes: (1) a first reactant; and (2) a second reactant; wherein said composition is activated so as to cause said first reactant and said second reactant to react with each other to create solid particulate products having a diameter of about one micron or less such that, when said products come in contact with the fire, said products chemically inhibit the chain reactions of the fire and bring about the extinguishing of the fire, and wherein said medium further includes means for cooling said products.

2. The method as in claim 1 , wherein said device is submerged in a liquid coolant and wherein said device further includes means for preventing entry of said coolant into said device but accommodates escape of said products into said coolant.

3. A method as in claim 2, wherein said means for preventing 32 104758/2 entry of said coolant includes at least one downwardly directed tuyere hydraulically connected at or near the top of said device.

4. A method as in claim 2 wherein said means for preventing entry of said coolant includes a downwardly directed covering hydraulically connected at or near the top of said device.

5. A method as in claim 1 wherein said pre-positioning includes coating said composition on a surface located in or around the volume.

6. A system for extinguishing a fire in a volume, said system comprising: a fire extinguishing device pre-positioned in communication with the volume, where said device includes a composition which includes: (1) a first reactant; and (2) a second reactant; where said composition is activated so as to cause said first reactant and said second reactant to react with each other to create solid particulate products having a diameter of about one micron or less such that, when said products come in contact with the fire, said products chemically inhibit chain reactions of the fire and bring about the extinguishing of the fire, 33 104758/2

7. The system as in claim 6, wherein said device is submerged in a liquid coolant and wherein said device further includes means for preventing entry of said coolant into said device but accommodates escape of said products into said coolant.

8. A system as in claim 7 wherein said means for preventing entry of said coolant includes at least one downwardly directed tuyere hydraulically connected at or near the top of said device.

9. A system as in claim 7 wherein said means for preventing entry of said coolant includes a downwardly directed covering hydraulically connected at or near the top of said device.

10. A system as in claim 6 wherein said pre-positioning includes coating said composition on a surface located in or around the volume.

11. A method of extinguishing a fire in a volume comprising: pre-positioning a fire extinguishing device in communication with the volume, said device including a composition which includes: (1) a first reactant; and (2) a second reactant; and activating said composition so as to cause said first reactant and 34 104758/2 said second reactant to react with each other to create solid particulate products having a diameter of about one micron or less such that, when said products come in contact with the fire, said products chemically inhibit chain reactions of a flame of the fire and bring about the extinguishing of the fire, wherein said products pass through cooling material and flame arrestors in said device.

12. A method as in claim 11 wherein said pre-positio ing includes coating said composition on a surface located in or around the volume.

13. A system for extinguishing a fire in a volume comprising: a fire extinguishing device pre-positioned in communication with the . volume, wherein said device includes a composition which includes: (1) a first reactant; and (2) a second reactant; wherein said composition is activated so as to cause said first reactant and said second reactant to react with each other to create solid particulate products having a diameter of about one micron or less such that, when said products come in contact with the fire, said products chemically inhibit chain reactions of the fire and bring about the extinguishing of the fire, wherein said products pass 35 104758/2 through cooling material and flame arrestors in said device.

14. A system as in claim 13 wherein said composition is coated surface located in or around the volume. Mark M. Friedman Advocate and Patent Attorney Beit Amot Mishpat 8 Shaul Hamelech Boulevard 64733 Tel Aviv