Abstract:
A blast compression wave absorbing device comprises a container filled with gas or air under pressure below ambient pressure (under vacuum). The device is positioned close to the facility or structure being protected, in atmosphere or under water. When a blast compression wave reaches the device, in accordance with various embodiments of the invention, the container collapses, ruptures, or its interior is being connected to the environment through rupturable diaphragm or fast-actuating valve. The ambient air starts to fill the internals of the container generating a negative pressure wave, which interferes with blast compression wave and produces a resulting pressure wave with reduced pressure and impulse affecting the facility or structure to be protected. The device can be used in a counter-terrorism operations, to protect high-risk facilities (nuclear and military installations, petrochemical plants, embassies), submerged structures, or to protect personnel in tunnels and bunkers from shock waves of fuel-air explosives.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not applicable 
     
    
     BACKGROUND OF THE INVENTION—FIELD OF INVENTION  
       [0002]     The present invention relates to blast effects suppression devices used to limit the damage associated with explosions, specifically, to reduction of impulse and overpressure of compression waves in order to minimize the damages in area being protected.  
       BACKGROUND OF THE INVENTION  
       [0003]     Terrorist bombings have always been a problem. In many instances, the bomb or explosive device is placed close to public buildings, embassies, sensitive (nuclear) installations, often in a parked vehicle. The damage associated with explosion is related to air compression waves (also known as pressure waves or shock waves). The duration of this overpressure may be milliseconds or more, and significant impulse associated with compression wave results in damages to structures (buildings) especially to buildings having large surface areas.  
         [0004]     Various means can be used to reduce compression wave effects: solid barriers (including blast mats), foams (foam glass, aqueous foams), plastic bags filled with water, mechanical venting, and chemical agents. Solid barriers and blast mats deflect shock waves or absorb wave energy from shock waves through momentum transfer to supporting structure; therefore, they cannot be used to protect the internal or external surface of the buildings or structures from the impulse associated with the shock wave. In addition, they are not effective in confined spaces.  
         [0005]     Foam glass, aqueous foams, and plastic bags filled with water are effective being close to the source of shock wave, if the location of bomb is known. They are not effective in protection of large areas or protection from remote explosions.  
         [0006]     Mechanical venting is employed to reduce the overpressure and associated stress in containment structures below the level allowable by design. Being effective in reducing the impulse, it cannot reduce the peak overpressure due to response time problem. Chemical agents suppress shock waves by extinguishing the combustion process, which generates them. Such agents are effective if used to suppress the explosion at a source. The examples of explosion and shock wave suppression devices are shown in the following patents granted in Canada:  
         [0007]     U.S. Pat. No. 2,284,694 John Donovan et al,  
         [0008]     U.S. Pat. No. 2,314,245 John Bureaux et al,  
         [0009]     U.S. Pat. No. 2,335,788 Donald Butz et al.  
         [0010]     The U.S. Pat. No. 2,284,694 discloses a method and apparatus for enclosing, controlling and suppressing the explosive destruction of munitions in an explosion chamber. Plastic bags of water are suspended within the chamber over the detonation area and filled with water.  
         [0011]     In U.S. Pat. No. 2,314,245, an apparatus for explosive blast suppression, and a method therefor, is disclosed. The apparatus comprises a hemispherical enclosure, positioning means associated with the enclosure, for positioning the explosive device substantially equidistant from any point on the wall. The enclosure is made of composite textile material, comprising one or several layers of a ballistic material.  
         [0012]     In U.S. Pat. No. 2,335,788, a blast suppression system is disclosed. The system includes a plurality of command-actuated units located in the immediate vicinity of a bomb. Each of the units has nozzles configured to disperse the suppressant material into the air surrounding the bomb. Preferably, the transmission occurs prior to the explosion of the bomb.  
         [0013]     The prior art does not address the issue of absorption and dissipation of peak overpressure and impulse of the compression wave from remote or internal explosions provided the position of explosive charge is unknown. If the impulse is absorbed, it is fully transferred to a supporting structure. Nor the prior art addresses the issue of protection from fuel-air explosives (FAE) and associated compression waves. The FAE shock waves are known as having lower peak pressure, longer duration and higher impulse. It is desirable to provide a device that absorbs the compression wave and reduce the structural and bodily injury caused by the blast over-pressure and associated impulse.  
       BACKGROUND OF THE INVENTION—OBJECTS AND ADVANTAGES  
       [0014]     Accordingly, several objects and advantages of the present invention are:  
         [0015]     (a) to provide a blast compression wave absorbing device which allows reduction of peak overpressure without transfer of impulse to supporting structure;  
         [0016]     (b) to provide a blast compression wave absorbing device able to reduce the impulse transferred to the structure to be protected being attached to the same structure;  
         [0017]     (c) to provide a blast compression wave absorbing device which can protect the large areas of building from distance;  
         [0018]     (d) to provide a blast compression wave absorbing device able to suppress compression waves from fuel-air explosives (FAE);  
         [0019]     (e) to provide a blast compression wave absorbing device with ability to reduce the overpressure and associated stress in containment structures where venting is not sufficient.  
         [0020]     Further objects and advantages of my invention will become apparent from a consideration of the drawings and ensuing description.  
       SUMMARY OF THE INVENTION  
       [0021]     The present invention provides a blast compression wave absorbing device, comprising means for generation of a negative pressure wave in predetermined area near the object to be protected. After explosion, the negative pressure wave interferes with a blast compression wave and reduces its peak pressure and duration. 
     
    
     DRAWINGS  
       [0022]     In the drawings, closely related figures have the same number but different alphabetic suffixes.  
         [0023]      FIGS. 1A and 1B  show a cross-sectional view of the blast compression wave absorbing device according to one embodiment of the present invention in a form of container, filled with gaseous matter.  
         [0024]      FIGS. 2A and 2B  show a cross-sectional view of the container shown in  FIGS. 1A and 1B , in collapsed form.  
         [0025]      FIGS. 3A, 3B , and  3 C show the blast compression wave absorbing device according to one embodiment of the present invention in a form of container having rupturable diaphragm.  
         [0026]      FIGS. 4A, 4B , and  4 C show a cross-sectional view of the blast compression wave absorbing device according to one embodiment of the present inventions in a form of collapsible container consisting of a plurality half-cylinders having rupturable diaphragms and welded to a flat metal sheet.  
         [0027]      FIG. 5  shows a cross-sectional view of collapsible containers attached to a wall and held in place by mounting means.  
         [0028]      FIG. 6  shows a cross-sectional view of a frame structure with collapsible containers to be placed on a ground level.  
         [0029]      FIG. 7  shows a cross-sectional view of a tunnel with collapsible containers attached to a ceiling and held in place by mounting means (mounting means are not shown).  
         [0030]      FIG. 8  shows a cross-sectional view of a hangar with collapsible containers attached to external surfaces of the roof and the walls.  
         [0031]      FIG. 9  shows a plan view of a building with collapsible containers attached to internal surfaces of the walls (mounting means are not shown).  
         [0032]      FIG. 10  shows a top-plan view of a high-risk facility (embassy, nuclear installation, etc) having a plurality of frame structures with collapsible or rupturable containers placed on the ground level around the building.  
         [0033]      FIGS. 11A and 11B  show a semi-diagrammatic view of the blast compression wave absorbing device having a container located under ground level, a rupturable diaphragm, a diffuser to direct a negative pressure wave to the wall of the object being protected, and a vacuum pump.  
         [0034]      FIGS. 12A and 12B  show a semi-diagrammatic view of the blast compression wave absorbing device having a container located under ground level, a rupturable diaphragm with small pyrotechnic charges and activation circuit, a diffuser to direct a negative pressure wave to the wall of the object being protected, and a vacuum pump.  
         [0035]      FIG. 13  shows a semi-diagrammatic view of the blast compression wave absorbing device having a container located under ground level, a valve with actuator and activation circuit, a diffuser to direct a negative pressure wave to the wall of the object being protected, and a vacuum pump.  
         [0036]      FIG. 14  shows a semi-diagrammatic view of the blast compression wave absorbing device having a container located under ground level, a valve with actuator and activation circuit, a diffuser to direct a negative pressure wave to the wall of the object being protected, and a plurality of gas ejectors.  
         [0037]      FIG. 15  shows a cross-sectional view of gas ejector having solid fuel gas generator as a source of compressed gas (activation circuit is not shown).  
         [0038]      FIG. 16  discloses a graph demonstrating the reduction in incident and reflected pressure of blast compression wave vs. capacity of blast compression wave absorbing device.  
         [0039]      FIG. 17  discloses a graph demonstrating the reduction in incident and reflected impulse of blast compression wave vs. capacity of blast compression wave absorbing device.  
         [0040]      FIG. 18  illustrates the reduction of incident pressure around protected facility when the device of this invention is in use. 
     
    
     DRAWINGS—REFERENCE NUMERALS  
       [0041]    
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                   
               
             
             
               
                   
                 101 container 
                 102 interior of container 
               
               
                   
                 103 diaphragm 
                 104 groove 
               
               
                   
                 105 mounting means 
                 106 wall 
               
               
                   
                 107 frame 
                 108 fence 
               
               
                   
                 109 pump 
                 110 check valve 
               
               
                   
                 111 duct 
                 112 pressure detector 
               
               
                   
                 113 amplifier 
                 114 igniter 
               
               
                   
                 115 pyrotechnic charge 
                 116 valve 
               
               
                   
                 117 valve actuator 
                 118 ejector 
               
               
                   
                 119 solid fuel gas generator 
                 120 diffuser 
               
               
                   
                 121 compression wave 
                 122 nozzle 
               
               
                   
                 123 ejector diffuser 
               
               
                   
                   
               
             
          
         
       
     
       DETAILED DESCRIPTION OF THE INVENTION  
       [0042]     Referring to  FIG. 1A  and  FIG. 1B  of the drawings, a blast compression wave absorbing device consists of a hollow thin-walled cylindrical container  101  having an interior  102  filled with a gas (for example, with air, nitrogen or carbon dioxide). The gas has a pressure below ambient pressure (below atmospheric pressure or, for submerged objects, below hydrostatic pressure at the depth of installation), for example, 1 psia (7 kPa abs). The container  101  has sufficiently thin walls designed to collapse or rupture at a predetermined external pressure, for example, at 4 psig (27.2 kPa gauge). The container  101  in collapsed form can be seen in  FIG. 2A  and  FIG. 2B . If the container  101  collapses, the ambient air (or water) starts to fill the void (the space previously being a part of container). This movement of air (or water) generates an area with reduced pressure around the container (a negative pressure wave). The negative pressure wave interferes with blast compression wave and effectively reduces blast compression wave peak pressure and associated impulse in predetermined area. The amplitude and the duration of the negative pressure wave depend on the container internal volume, the pressure difference between the gaseous matter inside the container and ambient pressure, and the contact area between container internals and the environment. If the container ruptures, the ambient air (or water) starts to fill the interior of the container. The movement of air (or water) generates a negative pressure wave, which interferes with blast compression wave and effectively reduces blast compression wave peak pressure and associated impulse in predetermined area.  
         [0043]     After explosion, the blast compression wave reaches the container placed between an object to be protected and a potential source of compression wave. The container collapses or ruptures when the pressure of compression wave reaches a predetermined value, for example, 4 psig (27.2 kPa gauge). The container generates the negative pressure wave until the air stops filling the void. As a result of interference of compression wave and negative pressure wave, the peak pressure of compression wave in the area around the container reduces.  
         [0044]     As can be seen from  FIG. 3A ,  FIG. 3B , and  FIG. 3C , the container  101  has a rupturable diaphragm  103  with a groove  104 . Similarly, the diaphragm  103  is designed to rupture at predetermined external pressure, for example, at 4 psig (27.2 kPa gauge). The container shown in  FIG. 4A ,  FIG. 4B , and  FIG. 4C  consists of a group of connected by welding half cylinders having rupturable diaphragms  103 . The container  101  can be provided with pressure indicator and nipple (not shown) to connect the container internals with vacuum pump in order to restore deteriorating internal pressure if required. The relatively long containers (longer than 2 m) can be provided with several diaphragms.  
         [0045]     As can be seen in  FIG. 5 , a plurality of collapsible or rupturable containers can be attached by mounting means  105  to a wall  106  of the building being protected (embassy, hangar, nuclear installation, or any other high-risk facility). The containers can be placed in the post-supported or freestanding frame  107  (see  FIG. 6 ) on the ground level around the building, or be attached to the external surface of submerged structure to be protected. After explosion, the compression wave propagates radially from the burst point. When the compression wave reaches the container  101 , it collapses (in case of collapsible container) or its diaphragm ruptures, the ambient air starts to fill the container generating the negative pressure wave. The collapsed cylindrical container can be seen in  FIG. 2A  and  FIG. 2B . The negative pressure wave interferes with compression wave and reduces its peak pressure and associated impulse in the area around the container. As a result, an object being protected is subjected to a resulting pressure wave with substantially reduced peak pressure and impulse. The required negative pressure wave parameters depend on maximum allowable peak overpressure and impulse of the structure (object) being protected. The containers can also be placed on the ceiling of a tunnel (see  FIG. 7 ) or in a bunker to protect from fuel-air explosives (FAE) and associated compression waves. As can be seen in  FIG. 8 , a plurality of collapsible containers  101  can be attached to the external surface of the wall  106  of the hangar. The containers can be attached to the internal walls of the building in the areas with insufficient venting capabilities and subjected to a highest impulse in case of internal explosion (see  FIG. 9 ). To protect the high-risk facility such as embassy or nuclear installation from large vehicle bombs, a plurality of freestanding or post-supported frames  107  with containers should be placed around the building within a fence  108  (see  FIG. 10 ).  
         [0046]     In case of building demolition involving shaped charges of explosives of known weights and power, the aforementioned embodiment of blast compression wave absorbing device can be used to prevent propagation of compression waves that cause a glass breakage in adjacent buildings.  
         [0047]     Another embodiment of the invention is shown in  FIG. 11A  and  FIG. 11B . The blast compression wave absorbing device is provided with container  101  having internals  102  filled with the gas at a pressure below atmospheric pressure, for example, in the range of 0.01 psia to 1.0 psia. In this embodiment, container  101  is located below the ground level. Rupturable diaphragm  103  covers an opening in a duct  111  connecting container  101  to the atmosphere. A suction of a vacuum pump  109  is connected to container  101 . A check valve  110  is installed upstream of the vacuum pump  109  to prevent an air ingress when vacuum pump  109  is not operating. Diaphragm  103  is positioned between a source of compression wave and the wall  106  of the building being protected. A diffuser  120  positioned at the end of the duct  111 . When a compression wave  121  having a peak pressure, exceeding predetermined pressure (for example, 4 psi (27.2 kPa)), reaches diaphragm  103 , it ruptures allowing the air between diffuser  120  and wall  106  of the building being protected to enter container  101 . The generated negative pressure wave propagates outside and interferes with moving compression wave  121  and reduces the peak pressure and impulse affecting the wall  106  of the building. Diffuser  120  directs the negative pressure wave to the wall  106 . After explosion, diaphragm  103  should be replaced, and vacuum pump  109  should be restarted to restore the vacuum in container  101 . Because the air ingress is always present in vacuum systems, the internal pressure detector or pressure switch (not shown) can be provided to start the vacuum pump when internal pressure in container  101  deteriorates.  
         [0048]     In addition to the elements shown in  FIG. 11A  and  FIG. 11B , the blast compression wave absorbing device as seen in  FIG. 12A  and  FIG. 12B  is provided with an external pressure detector  112  positioned between a potential source of compression wave and the building being protected, an amplifier  113 , an igniter  114 , and at least one small explosive (pyrotechnic) charge  115 . The pressure detector  112  is located outside container  101  and measures an ambient pressure. If the peak pressure or the impulse of the compression wave exceeds predetermined level, the pressure detector  112  changes its output (electrical current or voltage). Amplifier  113  generates an electrical signal sufficient to activate the igniter  114 . Igniter  114 , which can be of any well-known construction suitable for this purpose, provides a detonating electrical impulse and initiates an explosion of pyrotechnic charge  115 . The diaphragm  103  ruptures, connecting internals  102  of the container  101  with atmosphere and generating the negative pressure wave. When diaphragm  103  with pyrotechnic charge  115  is replaced, the vacuum pump  109  should be restarted to restore the vacuum in container  101 .  
         [0049]     The blast compression wave absorbing device as seen in  FIG. 11A  and  FIG. 12A  can be used if the second explosion immediately after the first one is improbable.  
         [0050]     Another embodiment of the invention is shown in  FIG. 13 . It differs from the blast compression wave absorbing device shown in  FIG. 11A  by having a valve  116  and a valve actuator  117 . The valve  116  is actuated by the valve actuator  117 , which is actuated by amplifier  113 . Amplifier  113  generates a signal sufficient to actuate the valve actuator  117  if the peak pressure or the impulse of compression wave  121  exceeds predetermined level as detected by pressure detector  112 . Valve actuator  117  can be of any well-known construction suitable for this purpose, for example, an electrical motor. Another example is a pneumatic actuator having a solenoid valve connected to a source of compressed air (not shown). The solenoid valve is electrically connected to amplifier  113 . Solenoid valve opens and allows compressed air to move valve actuator  117  and open the valve  116 . The opening time of valve  116  should be relatively short, for example, in the range of  200  milliseconds. The valve  116  opens, allowing the ambient air to move into container  101  and to generate negative pressure wave, which interferes with blast compression wave and reduces the peak pressure and the impulse affecting the wall  106  of the building. The valve  116  closes when the compression wave passes pressure detector  112  and the air pressure around pressure detector  112  drops below the predetermined level. The vacuum in the container  101  deteriorates due to air in-leakage or due to opening of the valve  116 . An internal pressure detector (pressure switch), which is not shown in  FIG. 13 , detects the higher pressure in the container than a set pressure (for example, 0.1 psia). Vacuum pump  109  starts in order to restore the set pressure in container  101 . When the vacuum is restored, the blast compression wave absorbing device is ready to suppress the compression wave generated by next explosion.  
         [0051]     In the embodiment of the invention disclosed in  FIG. 14 , the blast compression wave absorbing device is also provided with external pressure detector  112 , amplifier  113  and valve actuator  117 . It differs from the blast compression wave absorbing device shown in  FIG. 13  by having an ejector  118  to maintain a predetermined pressure (vacuum) in container  101 . Ejector  118  can be started either manually, by operator, or automatically, by well-known automatic pressure control means, for example, by pressure switch (not shown). Ejector  118  can use a high-pressure water, compressed gas, or compressed air as a motive fluid (the sources of motive fluid are not shown). When the vacuum in container  101  deteriorates and should be restored, one of ejectors  118  starts. The vacuum generated by ejector  118  evacuates the air from the internals of container  101  through appropriate check valve  110  connected to a suction line of ejector  118 . When the vacuum in container  101  is restored, the blast compression wave absorbing device is ready to suppress a compression wave generated by next explosion.  
         [0052]     The  FIG. 15  discloses a cross-sectional view of the ejector with a solid fuel gas generator as an example of ejector shown in  FIG. 14 . Ejector  118  is provided with a solid fuel gas generator  119  connected to a nozzle  122 , and an ejector diffuser  123 . The solid fuel gas generators are well known and widely used as solid fuel rocket engines, gas generation charges for various purposes, etc. The solid fuel gas generator  119  develops a high velocity flow of hot gas in the nozzle  122  of ejector  118 . Ejector  118  develops a vacuum in the suction line and removes the air from container  101 . Ejector  118  discharges the air to atmosphere through the ejector diffuser  123 .  
         [0053]      FIG. 16  discloses a graph demonstrating a reduction in incident and reflected pressure of blast compression wave vs. capacity of the blast compression wave absorbing device.  
         [0054]      FIG. 17  discloses a graph demonstrating a reduction in incident and reflected impulse of blast compression wave vs. capacity of the blast compression wave absorbing device. The capacity is measured by an ability of the blast compression wave absorbing device to generate the negative incident impulse (measured in psi-msec) at the standard distance from the device. In this example, if the incident impulse should be reduced from 22 psi-msec to 10 psi-msec, the blast compression wave absorbing device should have a capacity of 12 psi-msec. The calculated incident pressure of 6 psi at the surface of the facility being protected will be reduced to 2.7 psi (in this example). To do that, the blast compression wave absorbing device should be placed at appropriate distance from the wall of the facility.  
         [0055]      FIG. 18  illustrates the reduction of incident pressure around protected facility when the device of this invention is in use.