Background of the Invention

Field of the Invention (Technical Field)

The invention is related to prevention of unwanted fire by inhibiting ignition of a flammable mixture and preventing propagation of a flame as well as prevention of an explosion caused by the rapid escalation of the fire. These are accomplished by installing a fire quenching structure that is a three dimensional network of mesh structure made of various metallic or non- metallic solids in a critical region. The mesh structure provide the quenching effects needed for the fire prevention. The quenching structures are used in preventing fires for (a) fuel tanks of moving vehicles including motorcycles, automobiles, aircrafts, helicopters, boats and ships, etc., (b) tank cars and tank ships for transporting fuels, petrochemicals and other chemicals, and combustible solids, (c) storage tanks and pipe lines for fuels and chemicals, (d) silos used for storing combustible solids such as wheat, grains and other agricultural products, (e) buildings, (f) warehouses, and (g) processing vessels such as distillation column, reactors and heat exchangers.

Brief Description of Prior Art

In a fire, an existing flame supplies heat to either vaporize and/or decompose the neighboring liquid or solid, performing a continuous process of vaporization-combustion and/or decomposition-combustion cycles to thereby continue or escalate the fire. Free radicals play major roles in the process. When chain branching steps take place at a very high rate, the process becomes an explosion. In general, it is known that fuel combustion involves chain mechanisms that include chain initiation steps, chain branching steps, and chain termination steps. The main chain carriers are free radicals that include free atoms. Fires have been classified into Type A fires, Type B fires, Type C fires, and Type D fires. Type A fires refer to fires caused by burning of combustible solids such as wood, paper, fabrics, rubber etc.; Type B fires refer

to fires caused by combustion of liquids and vapors; Type C fires refer combustion in an area where electric power is on; Type D fires refer to combustion of metals such as potassium, sodium, magnesium etc. A fire is sustained under a condition in which (a) there is a supply of fuel, (b) there is a supply of oxygen, (c) high enough temperature is maintained, and (d) sufficient amount of free radicals exist to propagate a flame. Water, foam, carbon dioxide, halogenated hydrocarbons and various dry powders have been used for extinguishing fires. For extinguishing Type A fires, water, foam type extinguishers and certain types of dry powder extinguishers have been used. For extinguishing Type B fires, foam type, carbon dioxide, halogenated hydrocarbons and certain types of dry powder extinguishers can be used. For extinguishing a Type C fire, one can use carbon dioxide, halogenated hydrocarbons and certain types of dry powder extinguishers until the electric power is turn off and then treat the fire as Type A or Type B fire. For extinguishing a Type D fire, one has to use a special dry powder extinguisher. Flame retardants are used to inhibit burning of fabrics and plastics. In most cases, flame retardancy is believed to result from the presence in the retardant of one or more key elements, such as phosphorous, nitrogen, chlorine, or bromine is believed to convert organic matter to char and thus decrease the formation of flammable carbon containing gases. Chlorine and bromine remove hydrogen free radicals from flaming gas.

Compare with the prior arts, the methods and apparatuses of the present invention are based on the quenching effect provided by a three dimensional network of meshes.

Brief Description of the Invention

The present invention introduces methods and apparatuses for preventing unwanted fire by installing a fire quenching structure that is a three dimensional network of meshes made of various metallic or non-metallic solids in a critical region which is occupied or would be occupied by a flammable mixture. The invention is based on experimental observations that a three dimensional network of meshes have a quenching ability for inhibiting ignition and/or suppressing and/or preventing flame propagation. In theory, the

quenching effects may be partly due to heat dissipation through the network and partly due to termination of free radicals on the solid surfaces.

The key factors to be considered are: (a) nature of the solid surface in regard to quenching of free radicals, (b) thermal conductivity of the mesh solid, (c) surface area per unit apparent volume of the fire quenching structure, (d) surface area per unit mass of the mesh solid, (e) permeability with respect to flow of gas or liquid through the structure, (f) amount of liquid retained by the mesh structure upon draining the stored liquid, (g) the design of the three dimensional structure, and (h) manufacturability of the structure.

The fire quenching mesh structures are used in preventing fires for (a) fuel tanks for moving vehicles, aircrafts, and ships, etc., (b) tank cars, and tank ships, (c) storage tanks, and pipe lines, (d) silos, (e) buildings, (f) warehouses, and (g) processing vessels such as distillation columns, reactors and heat exchangers.

Brief Description of the drawings

Figures 1 and 2 illustrate the equipment and operations used to demonstrate that a three dimensional network of meshes can inhibit ignition of a combustible mixture and thereby protect a vessel containing liquid fuel. Figures 3, 4, 5a through 5c, 6, 7, and 8a through 8c illustrate experiments conducted to demonstrate that three dimensional networks of meshes can prevent propagation of flames. Figure 3 illustrates that a flame over burning fuel can not penetrate into a zone protected by a three dimensional network of meshes. Figure 4 illustrates that a three dimensional network of meshes can isolate a flame over burning fuel within a confined region. Figure 5a illustrates that, when a torch flame is directed toward a three dimensional network of meshes, it appears that the flame is prevented from penetrating into the network. There is no combustion taking place within the network but there is a gas-air mixture or a gas-liquid-air mixture passing through the network. This phenomenon is referred to as "filtration of a flame." Figure 5b shows that the mixture that has passed through the network of meshes contains fuel and can

be ignited by a match. Figure 5c shows that when the final surface of the network of meshes is heated to a high temperature, the mixture that has passed through it is re-ignited, but no flame is observed within the network. Figure 6 shows that the fuel in a vessel with a three dimensional mesh above it does not burn when the fuel vapor above the mesh has been ignited and burning.

Figure 7 illustrates that, when a mass of fuel in a vessel with a network of meshes is heated and ignited above the network, the liquid fuel is protected from the flame and does not burn. Figures 8a through 8c illustrate that a flame over a burning fuel in a vessel with a network of meshes above it can be extinguished by raising the fuel level so that the liquid level enters into the network.

Figures 9 through 16 illustrate various types of structures that can be used for fire quenching structures that are also referred to as networks of meshes and three dimensional meshes. Figure 9 illustrate a structure made of multiple layers of thin sheets; figure 10 illustrates a honeycomb or lath structure made of thin sheets; figure 11 illustrates a multivoid cubical step structure made of thin metal sheets; figure 12 illustrates a structure made of a set of parallel wires; figure 13 illustrates a structure with multiple layers of two dimensional wire meshes; figure 14 illustrates a structure that is made of multiple layers of two dimensional wire meshes interconnected by wires; figure

15 illustrates a structure made of wire meshes folded into zig-zag forms and stacked together; figure 16 illustrate a structure made of wire meshes folded into square wave forms and stacked together. It is further observed that many other types and forms of three dimensional meshes can be constructed with various types of solid materials for the prevention of ignition and propagation as well as explosion of the fire.

A fire quenching structure has a limited capacity for inhibiting ignition.

The structure can inhibit an ignition when the intensity of the ignition is lower than the inhibiting capacity of the structure. A quenching structure has cages and the cages have characteristic size, referred to as cage size Vc, and surface area per unit apparent volume, S. Figure 17 schematically illustrates how the capacity of a quenching structure to inhibit ignition, defined as the maximum

intensity of ignition that the quenching structure can inhibit, is related to the cage size and the surface area per unit apparent volume. A fire quenching structure also has a limited capacity to prevent propagation of flames and the capacity is also related to cage size and surface area per unit apparent volume. The relations are illustrated by figure 18.

Figure 19a and 19b illustrate various ways of installing fire quenching structures into fuel storage vessels. Figure 20 illustrates a way of installing fire quenching structures within a pipe line. Figures 21a through 21d illustrate the structure and use of a fire suppressing blanket made of a three dimensional net work of meshes. Figure 22 illustrates that fire quenching structures can be used in walls, doors and ceilings in buildings, such as houses and warehouses to prevent an unwanted fire.

Description of the preferred Embodiments.

The present invention introduces methods and apparatuses for preventing unwanted fires by inhibiting ignition of a combustible mixture and or suppressing and/or preventing propagation of a flame as well as prevention of an explosion caused by the rapid escalation of the fire. It is based on experimented observations that three dimensional networks of meshes of various solid materials have quenching effects for the inhibition of ignitions and suppression of flame propagation. Therefore, such a network serves as a quenching structure. In theory, the quenching effect of a three dimensional network of meshes may be partly due to heat dissipation effect and partly due to termination of free radicals on the solid surfaces. However, the present invention is not based on any speculation on the theory of the quenching effect.

A series of experiments have been conducted to demonstrate the quenching effects of three dimensional networks of meshes under various condition. Based on these experiments, uses of these dimensional meshes of the present invention have been developed.

Figures 1 and 2 illustrate that a three dimensional network of meshes, (denoted as 3-D mesh) has an inhibiting effect on ignition of a combustible

mixture. Referring to Figure 1, there is a container 1 that contains gasoline 2 to the level 3 indicated. A propane torch 4 placed above the fuel liquid level and a 3-D mesh 5 filling the vessel. The 3-D mesh is made of steel wire screens interconnected by steel wires 5. Upon lighting the propane torch, the gasoline does not ignite. This is in a striking contrast to an ordinary experiment without the 3-D mesh. Without the 3-D mesh, vigorous burning of gasoline takes place immediately upon lighting the propane torch. This experiment demonstrates dramatically the inhibiting effect of the 3-D mesh to ignition. Figure 2 illustrates experiments conducted in a system similar to the system of Figure 1. In this system a 3-D mesh fills only the gas mixture above the fuel level and only a top layer of the liquid fuel. Again, upon lighting the propane torch 4, no burning of the fuel takes place. These experiments demonstrate that the 3-D mesh has sufficient inhibiting effect to ignition even when the propane torch, which has a rather high energy intensity, is use to induce burning of the combustible gas mixture, viz. the gasoline vapor-air mixture.

Figures 3, 4, 5a through 5c, 6, 7, and 8a through 8c illustrate that 3-D meshes prevent propagation of flames. The system of Figure 3 has a vessel 6 containing gasoline 7 to the level 8 indicated. A 3-D mesh is placed to occupy a left portion of the vessel and thereby dividing the vessel into a first zone 10 and a second zone 11. The first zone is an unprotected zone; the second zone is a protected zone. Upon ignition by a match, vigorous burning with a high intensity flame 12 takes place in the first zone 10 immediately, but no burning in the second zone 11 takes place. This demonstrates dramatically that the 3-D mesh in the second zone has prevented the flame in the first zone from propagating into the second zone. The system of Figure 4 has a circular vessel 13 that contains gasoline 14 to the level 15 indicated. It contains a circular ring of 3-D mesh 16. The 3-D mesh ring divides the vessel into a central region 17 and an outer region 18. Upon bringing a match into the central region, a vigorous burning with a strong flame 19 takes place immediately in the central region, but no burning in the outer region. This demonstrate that the 3-D mesh ring has successfully isolated the flame and the flame is prevent from penetrating into the outer region through the 3-D mesh ring.

Figures 5a, 5b, 5c illustrate some observations made in a simple system containing a flat 3-D mesh 20 and a propane torch 21. Referring to Figure 5a, when the torch is lit and brought close to the 3-D mesh, there is a luminous flame 22 in the region in front of the 3D mesh but no luminous flame in the regions within the 3-D mesh nor in the region behind the 3-D mesh. The flame mass contains fuel, air and luminosity. The fuel in the flame has passed through the 3-D mesh but the luminosity has not. That fuel in the flame has passed through the 3-D mesh can be demonstrated by showing, as shown in Figure 5b, that the mixture that has passed through the 3-D mesh can be ignited by a match to form a new flame 23 at the back of the 3-D mesh. We may refer to this phenomenon as "filtering a flame." It means that while gas and fuel matter in the flame have passed through the 3-D mesh, the luminosity has not. Figure 5c shows that, when the intensity of the propane torch is increased, the 3-D mesh becomes red hot and a luminous flame 23 is seen at the backside of the 3-D mesh. Even under this condition, there is not a major flame within the 3-D mesh zone. The mesh surface at the back is at such a high temperature that the fuel that has passed through the 3-D mesh has been re- ignited by the high temperature mesh surface at the back side. To summarize, combustion of fuel has been suppressed within the 3-D mesh zone.

Figure 6 illustrates a system that contains a vessel 24 and a mass of gasoline 25 within, the vessel to the level 26 indicated and a layer of flat 3-D mesh 27 above the fuel surface. The gas space is divided by the 3-D mesh into an upper region 28 and a lower region 29. When the fuel is maintained at a proper temperature the fuel vapor in the upper region 28 burns with a luminous flame, but no burning takes place in the lower region 29. Again, the 3-D mesh has prevented propagation of flame into the lower region. Figure 7 illustrates a system that contains a vessel 30, a mass of gasoline 31 to the level 32 indicated and a 3-D mesh within the vessel. The 3-D mesh occupies both the liquid fuel region and the vapor region above. In the experiments performed with this system, the fuel in the vessel is heated to a high temperature to cause vaporization of the fuel at a high rate and the vapor above is ignited. A very vigorous burning takes place above the 3-D mesh region. But no burning takes place within the 3-D region. This is a very dramatic demonstration that the 3-

D mesh has prevented flame propagating into the region protected by the 3-D mesh.

Figures 8a through 8c illustrate experiments that demonstrate (a) compressing the burning zone of a flame by use of a 3-D mesh and (b) extinguishing a flame by further compressing the burning zone of the flame by use of a 3-D mesh. Referring to the figures, the system comprises a vessel 34, a mass of fuel 35 within the vessel up to the level 36 indicated and a 3-D mesh 37 above the fuel. The 3-D mesh separates the system into an inner region 38 and an upper region 39. Upon ignition, fuel burns with a flame in the inner region. The inner region is a burning zone. However, there is no flame in the 3-D mesh region and there is no flame in the upper region. Referring to Figure 8b, by introducing more fuel or some water through the bottom of the vessel, the liquid level of the fuel is raised, the burning zone is compressed to a smaller volume 38. Referring to Figure 8c, when the top liquid level of the fuel is raised farther and the level meets with the 3-D mesh, the flame is extinguished. One may also lower the 3-D mesh to meet with the top liquid level and thereby extinguish the flame. These experiments show that flame volume, defined as the volume of the burning zone, can be compressed and that the flame can be extinguished by reducing the flame volume to zero.

Figures 9 through 16 illustrate various structures of 3-D meshes that can be used. The material used in constructing 3-D meshes may be metal, glass, and polymers; the starting material may be in wire forms, wire meshes, flat sheets, and strips. Figures 9 illustrates a set of parallel sheets of metal 40 that forms a 3-D mesh. Figure 10 illustrates a vertical honeycomb or lath structure 41 made of thin sheets that can be used as a 3-D mesh. Figure 11 illustrate that a multivoid cubical step structure made of thin sheets can be used as a 3-D mesh. A set of fins with or without louvers that are used in constructing a water cooler of an automobile can be used as a 3-D mesh in a similar way.

Figure 12 illustrates a 3-D mesh made of a set of wires properly spaced.

One may identify a repeating pattern as a unit cell or a cage as illustrated by the shape a-b-c-d-e-f-g-h and define a cage volume per unit length as the volume of the shape a'-b'-c'-d'-e'-f-g'-h' where a'-e', b'-f, c'-g', d'-h' are unit

length. One may use a mass of steel wool, copper wool, aluminum wool, glass wool, or polymeric fiber as a 3-D mesh. Figure 13 illustrates that a set of flat wire mesh. 44 may be placed together properly spaced and be used as a 3-D mesh. Figure 14 illustrates a 3-D mesh made of a set of flat wire meshes 44a and a set of wires 45 that connects the wire meshes together properly spaced. Figure 15 illustrates a 3-D mesh made of a set of wire meshes 46, each being folded into a triangular zig-zag form, stacked together. Figure 16 illustrates a 3-D mesh made of a set of wire meshes 47 each being folded into a square zig¬ zag form, stacked together.

It has further been observed that many other types and forms of three dimensional meshes can be constructed with various types of solid materials for the prevention of ignition and propagation as well as explosion of the fire.

In a fire, the flame existing at a given time transfers heat to a mass of liquid and or solid fuel to either vaporize and/or decompose the fuel to thereby produce a combustible gas mixture and the gas mixture, in turn, burns to generate more heat to vaporize and/or decompose additional mass of liquid or solid fuel. Therefore, a combustion process comprises repeating cycles of vaporization-combustion and decomposition-combustion, resulting in a continuation or escalation of the fire. Free radicals play the major roles in a combustion process. In general, a combustion process involve chain mechanisms that include chain initiation steps, chain branching steps and chain termination steps. The main chain carriers are free radicals that include free atoms. In a chain termination step, the free radicals involved are deactivated. An explosion takes place when the rate of chain branching far exceeds the rate of chain termination.

The quenching effect provided by a quenching structure of the present invention may be partly due to heat dissipation through the structure and partly due to termination of free radicals on the solid surfaces. There may be other unknown reasons also.

A 3-D mesh of a given construction has a limited capacity to inhibit ignition and a limited capacity to prevent flame propagation. The 3-D mesh to

be used in a fire quenching structure has to be able to inhibit ignition of a substantial intensity that is expected in an accident and to be able to prevent propagation of a flame of a substantial intensity that is expected in an accident.

The ability of a 3-D mesh to inhibit ignition depends on (a) the nature of the solid surface and (b) the surface area per unit apparent mesh volume, designated as S. The surface area per unit apparent mesh volume is defined as the ratio of the solid surface area and the apparent volume of the 3-D mesh. Since a 3-D mesh is of a cage structure, the apparent volume of a 3-D mesh is defined as the volume of the envelope that encloses the 3-D mesh. One may also divide a 3-D mesh into a set of repeated pattern of cages and define the cage volume Vc, and the cage size of a unit cage. Although uniform cage size is preferred, it is not required for the 3-D mesh structure to inhibit ignition or prevent propagation of the fire. But minimum surface area is required. It is obvious that, as the cage volume Vc or cage size decreases, the surface area per unit apparent volume S increases. The first line 48 and the second line 49 in figure 17 respectively and schematically illustrate how the capacity of a 3-D mesh to inhibit ignition, defined as the maximum intensity of ignition that the 3-D mesh can inhibit, is related to the surface area per unit apparent volume and to the cage volume or cage size. A 3-D mesh can inhibit an ignition when its intensity is lower than the capacity of the 3-D mesh illustrated.

A 3-D mesh has a limited capacity to prevent propagation of flames. The first line 50 and the second line 51 in Figure 18 respectively and schematically illustrate how the capacity of a 3-D mesh, defined as the maximum intensity of flame that the 3-D mesh can prevent propagation, is related to the surfaces area per unit apparent volume of the 3-D mesh and to the cages volume or cage size of the 3-D mesh. A 3-D mesh can prevent propagation of a flame when its intensity is lower than the capacity of the 3-D mesh illustrated.

Referring to line 51 in figure 18, a flame of intensity X can propagate in a 3-D mesh of a cage size greater than Y, but can not propagate in a 3-D mesh of a cage size smaller than Y. Therefore, we may call the critical cage size Y as the cage size or cage volume for flame survival for the flame of intensity X.

To summarize, a fire quenching structure should be a 3-D mesh where surface area to apparent volume ratio is large enough, or cage size is small enough, so that (a) the maximum intensity of ignition it can inhibit is greater than the ignition intensity expected in an accident by a safe margin and (b) the maximum intensity of flame it can prevent propagation is greater than the flame intensity expected in an accident by a safe margin.

Referring to a 3-D mesh of a construction illustrate by Figure 13, it has been found that when the wire size is 0.07 cm, the cage volume is 0.061 cm**, and the surface area per unit volume is greater than 2.3 cm^/cm^, ignition of a gasoline-air mixture by a propane torch can be inhibited. The 3-D mesh can also prevent propagation of a flame of a substantial intensity. It is noted that, because a 3-D mesh is of a cage structure, it allows a gas mixture or a gas-liquid mixture to pass through rather freely.

Some ways of using the fire quenching structure of the prevent inventions are illustrated by Figures 19a and 19b and Figures 20 through 22. illustrates a fuel storage vessel 52 containing a volatile liquid fuel 53 to the level 54 indicated. There is a 3-D mesh fire quenching structure 55 and an inlet/outlet pipe line and a vent port. It shows that the quenching structure 55 fills the entire vessel including the space filled by fuel vapor and the space filled by the liquid fuel. It is also shown that there is a valve 56 and a 3-D mesh 57 in the inlet/outlet pipe line and there is a small 3-D mesh even in the vent port 58. This arrangement represents the most complete protection of the fuel storing vessel. The critical region in the vessel is the vapor space wherein flammable fuel vapor-air mixture exists. For the fuel storing vessel of a moving vehicle, the fuel level varies. therefore, a complete protection described is recommended for fuel tanks used in moving vehicles such as motorcycles, automobiles, boats, ships, aircrafts, and helicopters. Figure 19b illustrates a system similar to that illustrated by Figure 19a. In this system, however, the 3- D mesh used only fills the vapor space and a top portion of the liquid fuel space. This arrangement may be use for some stationary storage tanks and tank cars. In these cases, fuel levels are maintained substantially at high levels most of the time. Figure 20 illustrates a pipe line 59 with a valve 60. It shows

that 3-D meshes 61 are installed within the pipe line to minimize losses caused by a fire. *

Figure 21a through 21d illustrates a system with an open vessel 62 containing combustible organic substance 63 to the level 64 indicated and a 3-D mesh fire quencher 65 above the vessel. When the organic substance catch fire, the space 66 above the liquid organic becomes a burning zone. The way to extinguish the fire is to simply lower the 3-D mesh fire quenching structure down. As the 3-D mesh is lowered the burning zone 66 becomes smaller and smaller. As the mesh touches the liquid surface or is partially submerged into the liquid, the fire is extinguished.

Figure 22 illustrates one floor of a building protected by 3-D meshes. It has an outer wall 67 and compartments 68a through 68h, partitioning walls 69 and doors 70a through 70h and ceilings (not shown). An effective way to protect the building from fire is to incorporate 3-D mesh fire quenching structures in the partitioning walls, doors and ceilings. When it is so protected, a fire started within one compartment is confined within the compartment and is prevented from propagating into neighboring compartments.

It has been described that a fire quenching structure made of a 3-D mesh may be installed within a storage vessel or a processing vessel. "A storage vessel" is used either in a narrower sense or in a broader sense. In a narrower sense, "a storage vessel" refers only to a storage vessel proper. In a broader sense, "a storage vessel" refers to a combination of a storage vessel proper, any conduit, any flow controlling device such as a valve, a pump, a blower, or a compression connected to the vessel. Similarly, in a narrower sense, "a processing vessel" refers only to a processing vessel proper and, therefore, refers only to a reactor proper, an evaporator proper, a condenser proper, a heat exchanger proper, a boiler proper, a dryer proper, a refrigerator proper, etc. In a broader sense, "a processing vessel" refers to a combination of a processing vessel proper and accessories connected to it. The accessories may include one or more conduits, one or more valves, one or more pumps, one or more blowers, and one or more compressors, etc. Therefore, in a broader sense

"a processing vessel" refers to a reactor system, a condensing system, a heat exchanging system, a boiler system, a refrigeration system, etc.

It is noted that a none aqueous medium, such as ammonia, has been used in a low temperature power generation system. Such system can be used in Ocean Thermal Energy Conversion (OTEC) system and waste heat utilization system. The medium use is a combustible medium. A fire quenching structure of the present invention may be used to prevent unwanted fire in such a system.

Furthermore, there are needs to prevent unwanted fires outside of processing vessels and storage vessels containing flammable liquids. When there is a leak from a vessel containing a flammable liquid, the liquid that has leaked out together with air become a flammable mixture. Upon an ignition, this mixture becomes an unwanted fire. This unwanted fire may be a serious fire by itself or it may lead to a more serious situation such as " Boiling Liquid- Expanding- Vapor-Explosion" (designated as BLEVE). The BLEVE situation arises when the liquid inside of the vessel is heated so that

(a) the liquid temperature becomes higher than the boiling point under atmospheric pressure or the set pressure of the vessel, and/or

(b) the strength of the vessel is weakened by the higher temperature.

Under this condition, a vapor or a liquid-vapor mixture rushes out of the vessel and ignited to cause an explosion. The subject on "BLEVE Hazards" has been described in "Quantify BLEVE Hazards" in Chemical Engineering Progress, pages 66-70, February 1992.

There are two things that can be done to prevent or lessen the damage caused by an unwanted fire outside of a vessel containing a flammable liquid. These are:

(a) install a fire quenching structure made of a 3-D mesh on the critical region of the outer wall and bottom cover of the vessel;

(b) provide a pit protected by a fire quenching structure to collect the leaked liquid. The fire quenching structures help preventing an outside fire from starting or preventing an outside fire after it has started to become a serious fire and preventing it from causing a BLEVE situation.

It has been described that it is desirable to use a quenching structure that has (a) a high surface area per unit apparent volume, (b) a high surface area per unit mass (c) a low liquid retention per unit apparent volume. A bed of sand or any granular matter may be used as a fire quenching structure. However, such a bed does not meet the desirability criteria described and is not suitable for use inside of a processing or storing vessel. For use as a fire quenching structure in a liquid collecting pit or floor of a warehouse, a bed made of sand or a granular matter is adequate, because of the low cost and because the desirability criteria described can be relaxed greatly.

It has been described by referring to Figure 5c that when a 3-D mesh is heated to a high temperature, a gas-fuel mixture that has passed through the 3- D mesh is re-ignited. In order to avoid re-ignition, one may spray water on the 3-D mesh to prevent re-ignition. As an additional measure of safety. The spraying can be accomplished by a sprinkler device. This sprinkling system is of great use in preventing unwanted fire in a house or a warehouse. A sprinkler system may also be used on a fire quenching structure that is installed outside of a processing or storing vessel.