Method And Apparatus For Quenching Fires And Suppressing Explosions

Abstract

A method and apparatus for quenching fires and suppressing explosions is provided in which a deluge of fluid is released all at once onto the fire or combustion associated with the early stages of an explosion. A sensing device detects the fire or combustion and detonates a blasting cap, which detonation creates a shock wave which travels through the fluid in the vessel, to actuate a valve and release the fluid.

Description

This invention relates to a method and apparatus for quenching fires and suppressing explosions, and more particularly, to a method and apparatus for quenching a fire in its very early states and thus preventing or suppressing an explosion, using a deluge of a nonflammable fluid such as water.

In the processing and drying of explosives and other highly combustible materials, it is extremely important that a fire be extinguished immediately, before an explosion can result, with substantial damage. Fire-extinguishing systems which release a torrent of water on a fire to quench the fire are well known. These systems employ a heat-sensitive device which detects the presence of the fire, and initiates a mechanism for releasing the water.

In the case of explosive materials, however, fires quickly turn over to explosions, and the problem is somewhat more complicated. Explosions normally reach peak intensity instantaneously or in a matter of milliseconds; thus, an explosion can hardly be suppressed, once it has begun. However, explosions are normally preceded by a brief but very rapid combustion of the explosive material, which can be in a relatively confined space. Such combustion results in a rapid rise in temperature and pressure, which create the conditions initiating the next phase, in which the destructive forces of the explosion are released.

The time lapse between the ignition of the explosive material and the temperature and pressure buildup resulting in an explosion can be as low as 35 milliseconds. This interval, brief as it is, affords an opportunity for a quickly enough acting fire-quenching system to quench the combustion, and thereby prevent or suppress the initiation of an explosion. The problem is to design a quenching system that can respond effectively in such a short time.

Apparatus heretofore developed to cope with explosions do not respond quickly enough. Most employ a photoelectric or infrared sensing system to detect the initial combustion. The output of the photoelectric sensing system (which may or may not be amplified) is connected to an electric squib, exploding bridge wire or other detonating, or explosive device hereafter called a blasting cap, which when detonated opens an outlet valve of a water supply, releases a deluge of water to quench the fire. One typical system is shown in U.S. Pat. No. 3,235,860 to Vassil. Other typical systems are shown in U.S. Pat. Nos. 3,090,197 and 3,139,143 to Lapp et al. and Renda, respectively.

The weak link in these devices is the valve mechanism provided to release the deluge of water. The heat-sensitive detecting system can detect and signal the combustion quickly enough, but the mechanical valves employed are subject to failure, and also respond comparatively slowly. Fast-acting mechanical valves are known as in U.S. Pat. No. 3,187,499 to Holt, but the fast-acting valves are relatively expensive, and are subject to damage by the explosive force of the blasting cap used to open them.

Frangible plug or disc valves have been provided, which are ruptured by detonation of the blasting cap to release the deluge of water. Such discs or plugs are fast acting and reliable, but the mounting of the blasting cap to ensure rupture of the frangible member is a problem. If the blasting cap is quite close to the frangible member, or in contact with it, so that the force of the detonation of the blasting cap acts either directly on the disc or through the walls of the container to rupture the disc, a mounting block or the like is provided to support the disc and accommodate the blasting cap. Such mounting members can be damaged by the detonation of the blasting cap, and must be replaced frequently. The detonation of the blasting cap against a metallic mounting member can cause sparks, and even independent ignition of any combustible atmosphere which may surround the extinguishing system before the deluge is released. This can result in the initiation of the explosion before release of the deluge, rather than in its extinguishment by the deluge.

This invention provides a method and apparatus for the very rapid quenching or extinguishing of fires and the preventing or suppressing explosions. The apparatus has an extremely rapid response, and employs a frangible or rupturable valve member which is ruptured by detonation of a blasting cap without any danger of initiating combustion or explosion in a combustible atmosphere around the system, while minimizing damage to the structural members of the system.

In the apparatus of the invention, the blasting cap is mounted in the container for the deluge fluid such that at least a portion of the blasting cap is immersed in the fluid. The blasting cap is not placed in contact with the frangible valve, and the force of the detonation of the blasting cap is transmitted to the valve through the deluge fluid. Thus, there is little or no possibility that anything will be damaged other than the valve. Moreover, any sparks or heat are developed inside the fluid and inside the container, so that it is possible also to provide a primer explosive in association with the blasting cap to increase the force of the shock wave established in the fluid. This in turn increases the speed of response, and increases the force applied to expel the fluid from the vessel.

In accordance with this invention, an apparatus for extinguishing fires and suppressing explosions is provided comprising, in combination, a container for holding a supply of deluge fluid for quenching a fire and suppressing an explosion; an outlet in said container; a frangible valve closing off said outlet and retaining the fluid in the container; a blasting cap in the container and spaced from the valve in a position to establish upon detonation a shock wave in the fluid sufficient to rupture the frangible valve; and sensor means operatively associated with the blasting cap, for detecting a fire or explosion in its early stages, and detonating the blasting cap thereupon.

This invention further provides an improvement in the process for extinguishing fires and suppressing explosions by releasing a deluge of fluid from a container by detonating a blasting cap to burst a frangible valve which comprises, transmitting through the fluid in the container a detonating shock wave sufficient to burst the valve developed upon detonation of the blasting cap.

As indicated, the blasting cap is located in the container spaced from the valve and in a position so as to transmit the force released upon detonation of the blasting cap through the fluid in the container to the valve. This can be accomplished by positioning the blasting cap such that the force of the detonation of the cap is directed principally into the fluid in the container, thereby causing the shock wave created to travel through the fluid to the valve to burst the valve rather than through the walls or support structure of the container or to the valve directly. If desired, the blasting cap can be located in close proximity but yet spaced from the frangible valve and can be supported in a fitting or mounting block located adjacent the outlet of the container. However, this is not necessary. It is also possible to position the blasting cap in a remote portion of the container since the rate of transmittal of the shock wave through the fluid in the vessel is normally quite rapid and there is no significant effect on the speed of response of the apparatus due to the positioning of the blasting cap in the vessel. For example, if water is used as the deluge fluid, the rate at which the shock wave travels through the water is approximately 5,000 feet per second. Thus, it can be appreciated that the blasting cap can be located several feet from the frangible valve member without any significant loss in the rapidity of response of the apparatus. It is preferred that the blasting cap be at least partially immersed in the fluid in the vessel since this positioning of the blasting cap ensures that the force released upon detonation of the cap will act on the fluid in the vessel. However, it is also possible to position the blasting cap in the vessel above the fluid level so long as the cap is positioned such that the major component of the force released upon detonation is directed into the fluid in the vessel to be transmitted thereby to the valve.

The blasting cap, as indicated, can be mounted in or on a support fitting or mounting member or block fixed at or adjacent to the outlet of the container with the end of the cap extending into the interior of the container, and is preferably immersed in the fluid in the container. It is to be noted that in the specification and claims hereof, the term "outlet" of the container refers to the opening or line that is closed off by the frangible valve. The interior of the container is the entire interior space closed off by the valve, whether within the walls of the container itself, or within a line or fitting attached to the container.

The blasting cap fitting or mounting member can be combined with a support for the frangible valve in a single assembly. This construction has been found quite convenient, since both the detonated blasting cap and the frangible valve member can be replaced at the same time with a fresh valve and blasting cap by merely disassembling the support fitting and replacing the used valve and blasting cap.

If the blasting cap is not located in the same mounting block as the valve, the container is provided with an additional support fitting which engages the walls of the container and permits entry of the blasting cap into the fluid in the container without leakage of the fluid from the container. In both of the instances referred to above, the blasting cap is mounted in or through a portion of the container and extends or protrudes into the interior thereof. It is also possible for the blasting cap to be located entirely within the container mounted or suspended from a support structure therein.

The container itself comprises a vessel, tank, or other reservoir adapted to hold a supply of deluge fluid. The vessel preferably is capable of holding the fluid under pressures of the order of 100 to 300 p.s.i. or more, since pressures of this order are employed to burst the valve and force the deluge fluid from the vessel at a rapid rate. The container can take any desired shape. It can be cylindrical and can merely comprise fluid conduit or pipe containing the fluid under pressure.

The container can be of a size sufficient to accommodate enough fluid to quench the fire and suppress an explosion immediately upon opening. However, normally it has been found desirable to connect the valve and/or the container to a fluid line for supplying unlimited or very large volumes of deluge fluid, to ensure that no smoldering sparks or fire remain after the initial deluge. The flow of such fluid can be controlled by a pressure-actuated valve which is normally held in a closed position by the internal pressure of the fluid in the container. When the frangible member is opened by detonation of the blasting cap, the deluge of the fluid from the container rapidly reduces the internal pressure, herein to open the pressure-actuated valve and open the fluid line, thereby continuing the flow of fluid until shutoff.

The frangible valve, preferably, is a rupturable bowed disc of the type used throughout industry on pressure vessels, tanks, and in lines containing fluids under pressure. These discs are manufactured by such manufacturers as Fike Metal Products, Black Sivalls & Bryson, Engelhard Ind. and others, are installed in the pressure vessel, tank, and line systems as safety devices which upon some predetermined pressure rating will upon exceeding this pressure rating rupture, thereby protecting the system or systems in which they are installed from damaged because of over pressurization. Such discs as used for over pressurization application as stated are usually of the dished variety, but for this application the disc could be flat. Such discs are normally made of metal but can also, if desired, be made of plastic materials such as polyvinyl chloride, polyepoxides, polystyrene, urea-formaldehyde, melamine-formaldehyde, polypropylene, methyl methacrylate, and the like. Normally the concave side of the disc faces toward the interior of the container to resist the pressure of the fluid in he vessel. If cutting blades, as described below are employed, the disc is reversed to that the convex side of the disc faces toward the interior or pressure side of the vessel. The disc should be rupturable at pressures of the order of 150 to 250 p.s.i. Such pressure can be readily developed upon detonation of a blasting cap, and assist in driving the fluid from the container at a rapid rate. The disc can have score lines thereon, to facilitate its rupture at a predetermined location, and it is also possible to provide cutting blades or spears adjacent the disc such that upon deflection of the disc, the blades impinge upon the disc and cut the disc open.

The frangible valve need not be a disc, but can comprise a plug or plate that is rupturable by the shock wave developed in the deluge fluid upon detonation of the blasting cap.

The fluid in the container is normally maintained under a pressure of from about 5 to 75 p.s.i. less than the bursting pressure of the valve. The fluid is preferably under pressure in the tank for two reasons. Firstly, the pressure on the fluid increases the force under which the deluge fluid will be projected from the vessel, and thus speed the deluge. Secondly, by pressurizing the fluid in the vessel, the blasting cap need not supply the entire force necessary to burst the valve. The shock wave created by the blasting cap need only supply the 5 to 75 p.s.i. difference between the pressure already acting on the valve and the bursting pressure of the valve. This means that the fluid in the container is normally maintained at a pressure of from about 100 to about 175 p.s.i. One convenient method of establishing this high pressure is to provide a pressurized gas which fills the container above the liquid level in the container.

It is not necessary, however, to keep the deluge fluid under pressure, since all the pressure needed to burst the valve can be supplied by the blasting cap, either alone or in combination with a primer explosive, such as PETN or Pentolite, mounted on the blasting cap.

The sensing system employed to detect the combustion occurring in the early states of an explosion and initiate the blasting cap can comprise any of the heat and light sensors and transmitters known to those skilled in the art. The system shown in U.S. Pat. No. 3,235,860 to Vassil is preferred. Such systems are composed of a light and heat-sensitive element such as a cadmium sulfide or cadmium selenide cell that is sensitive to very small amounts of light and heat. Such cells respond photoelectrically, to immediately generate an electric current in an electric circuit connected to the blasting cap. The electric current can, if desired be amplified before it is transmitted to the blasting cap for detonation thereof. Other heat- and light-sensing systems can also be used, provided they have a rapid response.

The fluid used to extinguish the explosion is normally a liquid, and preferably is water. However, inert or relatively nonflammable gases can be used. These can be confined under pressure in the liquid phase, volatilizing when the valve is ruptured and pressure is released. Foam fire extinguishing materials such as carbon dioxide--generated compositions (sodium carbonate and sulfuric acid for example) and inert gases such as helium, nitrogen, and carbon dioxide can also be advantageously employed. It is also possible in certain instances to provide a deluge of granular or powdered materials such as sand to smother the explosion or fire.

In operation, upon the occurrence of the combustion associated with the first stages of an explosion, the sensing system generates an electric current, which detonates the blasting cap. The detonation of the blasting cap creates a shock wave in the fluid in the vessel, and raises the pressure inside the vessel to, in turn, rupture the frangible valve. This releases the fluid in the vessel, to quench the explosion. The total elapsed time from the initiation of the explosion until the fluid is released is less than about 20 milliseconds.

In the drawings:

FIG. 1 is a side view of an apparatus in accordance with this invention.

FIG. 2 is an enlarged view, partly broken away and partly in section, of a portion of the apparatus shown in FIG. 1.

FIG. 3 is a side view, partly broken away and partly in section, of another embodiment of the apparatus of this invention.

The embodiment shown in FIG. 1 comprises a pressure vessel 2, supported above a hazardous area by legs 16, and containing a quantity of water 3, introduced through an inlet 8 connected to a water line 10. A valve 12 is provided automatically to close off the water line 10 when the internal pressure in the vessel is above the line pressure. The valve can also be manually operated by a handle 15. The space above the water is filled with nitrogen gas 4, introduced through a gas inlet 6 to a pressure of 200 p.s.i.

The vessel 2 is formed with an outlet 18 at the base thereof, across which frangible valve and blasting cap assembly 20 is mounted, closing off the outlet 18. The blasting cap 42 as shown in FIG. 2 is connected via an electrical cable 21 lead wires 40 and a junction box 22 and via a further electrical cable 23 to a photoelectric fire detecting system 25, such as shown in U.S. Pat. No. 3,235,860 to Vassil.

The details of the blasting cap and frangible valve assembly 20 can best be seen by reference to FIG. 2. The assembly 20 is mounted on an annular flange 19 on the outlet 18, and is clamped tightly thereagainst by an annular mounting block 26 and bolts 48. The annular mounting block 26 is formed with a nozzle 28 through which the deluge of water from the vessel is released upon rupture of the valve.

The frangible disc valve 30 is made of metal and is of the type shown in U.S. Pat. No. 3,294,277 to Wood, and is supported in the assembly between an upper block 31 and a lower block 32, and has a hemispherically bowed portion 33. The lower block 32 is provided with knife blades 35, which make a clean cut in the disc 30 when it is thrust forcefully thereagainst, thus rupturing it. Above the disc 31, a blasting cap support 34 is provided, having an aperture 43 through which is placed a blasting cap mounting piece 36, supporting the blasting cap 42 in position.

As can be clearly seen by reference to FIG. 2, the blasting cap is immersed partially in the water above the frangible valve. The blasting cap mounting piece 36 and outer coupling nut 38 are constructed as one piece which is threadably engaged with the blasting cap support piece 34 through the aperture 43. An electrical conduit 21 which houses the electrical lead wires 40 of the blasting cap 42 is threadably connected to the outer connecting nut 38. The wires are run into the blasting cap 42 through a central passage 45 in the mounting piece 36. The coupling nut 38 is tightened against a washer 41 to prevent leakage of water from the pressurized vessel around the blasting cap mounting piece 36. Leakage around the blasting cap is prevented by O-rings 46.

In operation, upon the detection of a rise in temperature (which occurs in the first few milliseconds of an explosion), a current is generated by the sensing system 25 and flows through the cable 23, the junction box 22, and the lead wires 40, to the blasting cap 42. The electric current detonates the blasting cap, and a shock wave is established in the water. The valve disc 30 deforms, impinges against, and then ruptures against, knife blades 35, permitting a deluge of water to surge all at once from the vessel through the nozzle 28, to extinguish and suppress the explosion in the hazardous area. As soon as water pressure in the vessel is reduced below line pressure (which occurs almost immediately), the valve 12 opens, permitting additional water to flow from the line 10 into and through the vessel, and out nozzle 28. The total elapsed time from the occurrence of the first measurable increase in temperature producing infrared rays in the hazardous area until the deluge of water is released is about 18 milliseconds. No damage to the apparatus occurs due to the detonation of the blasting cap, due to the fact that the shock wave travels through the water.

It is a simple matter to reset the apparatus for reuse. The flow of water can be cut off to the tank by manually closing the valve 12 by means of handle 15. Upon replacement of a new blasting cap, and a new frangible disc valve in the valve and blasting cap assembly, the valve 12 can be manually opened permitting water to fill the tank to the desired level, and then manually closed until pressure is established in the tank, to hold the valve closed against the pressure of the water in the line 10.

The embodiment shown in FIG. 3 is similar to that shown in FIGS. 1 and 2. In this embodiment, however, the blasting cap support piece is located on the side of a vessel 50, and is separate from the valve assembly 52 at the bottom of the tank.

In the embodiment shown in FIG. 3, a sensor 55 is connected via an electrical cable 56 to a blasting cap assembly 60. The blasting cap assembly is similar to that described in connection with FIG. 2 with the exception that in this embodiment, a booster explosive 65 of PETN encased in a protective plastic wrapper 67 is positioned around the blasting cap to provide a greater explosive force and shock wave in the water 66 within the vessel. In this embodiment, the water is only under ordinary line pressure and the frangible disc valve 64 is set to burst at a pressure of 250 p.s.i. The detonation of the blasting cap and the PETN booster creates a shock wave in the vessel. The shock wave increases the pressure in the vessel to approximately 250 p.s.i., the rupture pressure of the valve 64, and also forces the water 66 from the assembly at a rapid rate. It is to be noted that in this embodiment (as in the case in the previous embodiment), the booster as well as the blasting cap are immersed in the water in the vessel so that the shock wave which bursts the valve travels through the water rather than through the walls of the vessel or the support structure associated with the basting cap and valve. Due to this fact, there is little or no possibility that the detonation of the blasting cap can itself trigger a further detonation on the outside of the vessel. Moreover, there is virtually no possibility of damage to any other part of the vessel or valve assembly upon detonation of the explosive. Nearly all of the explosive force of the detonation is carried via the shock wave transmitted in the water, and only a very small percentage of the force of the detonation is transmitted directly to the vessel or to the valve assembly.

Claims

Having regard to the foregoing disclosure, the following is claimed as the inventive and patentable features thereof:

1. A deluge apparatus for extinguishing fires and suppressing explosions comprising, in combination, a container for holding a supply of nonflammable liquid; a deluge outlet of reduced diameter in the container; a frangible valve closing off the outlet and the container; a blasting cap disposed at the outlet adjacent to and transversely with respect to the valve in a position to be immersed at least at the explosive end in nonflammable liquid held in the container and to direct the force of detonation of the cap principally into the liquid of the container and cause a shock wave to travel through the liquid to the valve to rupture the valve; and sensor means operatively associated with the blasting cap for detecting a fire or an explosion in its early stages, and detonating the blasting cap thereupon.

2. A deluge apparatus in accordance with claim 1, in which the blasting cap is mounted adjacent the frangible valve at the outlet.

3. A deluge apparatus in accordance with claim 1, in which the blasting cap is mounted at the side of the container.

4. A deluge apparatus in accordance with claim 1, in which the container is a pressure vessel.

5. A deluge apparatus in accordance with claim 1, in which the sensing means comprises a photoelectric sensor.

6. A deluge apparatus in accordance with claim 1, in which the frangible valve is a disc.

7. A deluge apparatus for extinguishing fires and suppressing explosions comprising, in combination, a container for holding a supply of nonflammable liquid; a deluge outlet of reduced diameter in the container; a frangible valve closing off the outlet and the container; a blasting cap in the container and spaced from the valve in a position to establish upon detonation a shock wave in the liquid sufficient to rupture the valve; a pressure responsive valve adapted to open a liquid line leading into the container up a drop in pressure in the container; and sensor means operatively associated with the blasting cap for detecting a fire or an explosion in its early stages, and detonating the blasting cap thereupon.

8. A deluge apparatus for extinguishing fires and suppressing explosions comprising, in combination, a container for holding a supply of nonflammable liquid; a deluge outlet of reduced diameter in the container; a frangible valve closing off the outlet and the container; knife blades mounted adjacent the valve to rupture the valve when thrust forcefully thereupon; a blasting cap in the container and spaced from the valve in a position to establish upon detonation a shock wave in the liquid sufficient to rupture the valve against the knife blade; and sensor means operatively associated with the blasting cap for detecting a fire or an explosion in its early stages, and detonating the blasting cap thereupon.

9. A deluge apparatus for extinguishing fires and suppressing explosions comprising, in combination, a container for holding a supply of nonflammable liquid; a deluge outlet of reduced diameter in the container; a frangible valve closing off the outlet and the container; a blasting cap in the container and spaced from the valve in a position to establish upon detonation a shock wave in the liquid sufficient to rupture the valve; a booster explosive associated with the blasting cap and detonated thereby; and a sensor means operatively associated with the blasting cap for detecting a fire or an explosion in its early stages, and detonating the blasting cap and a booster charge thereupon.

10. A deluge apparatus in accordance with claim 1, including blasting cap support means mounted on the container and having an aperture therethrough; a blasting cap support piece mounted in said aperture and holding said blasting cap in a position extending into the vessel; and connecting means for securing an electrical cable and lead wires to the blasting cap.

11. A deluge apparatus in accordance with claim 1, including sealing means to prevent leakage from the container at or adjacent the blasting cap.

12. A deluge apparatus for extinguishing fires and suppressing explosions comprising, in combination, a container for holding a supply of nonflammable liquid; an outlet line of reduced diameter leading from the container; a frangible valve across the line closing off the line and the container; a blasting cap disposed in the line in a position to be immersed at least at the explosive end in nonflammable liquid held in the container and to direct the force of detonation of the cap principally into the liquid of the container and cause a shock wave to travel through the liquid to the valve to rupture the valve; and sensor means operatively associated with the blasting cap for detecting a fire or an explosion in its early stages, and detonating the blasting cap thereupon.

13. A deluge apparatus for extinguishing fires and suppressing explosions comprising, in combination, a container for holding a supply of nonflammable liquid; a deluge outlet of reduced diameter in the container; a frangible valve closing off the outlet and the container; a blasting cap disposed in the container in a position before the entrance to the outlet to be immersed at least at the explosive end in nonflammable liquid held in the container and to direct the force of detonation of the cap principally into the liquid of the container and cause a shock wave to travel through the liquid to the valve to rupture the valve; and sensor means operatively associated with the blasting cap for detecting a fire or an explosion in its early stages, and detonating the blasting cap thereupon.