Abstract:
A container for containing an explosive device, including a mitigating layer defining an enclosure openable to insert the explosive device therein and closable to surround the explosive device, the mitigating layer reducing a force of a blast caused by an explosion of the explosive device, and a fragment-retaining layer substantially surrounding the mitigating layer, the fragment-retaining layer being resistant to a remainder of the force of the blast passing through the mitigating layer and retaining fragments propagated by the explosion of the explosive device, such as to reduce potential injury to a person in proximity of the container.

Description:
RELATED APPLICATION(S)  
       [0001]     This application claims priority on U.S. provisional application Ser. No. 60/713,740 filed Sep. 6, 2005, the entire specification of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to explosion containment, and more particularly to a container allowing safe transport of at least one small explosive device.  
       BACKGROUND ART  
       [0003]     Millions of small explosive devices such as detonators, detonating cord, airbag inflators and fuses are made and shipped every year. Detonators, detonating cord, uncased explosives, and other devices containing small explosive charges are widely used by many security and military agencies, for example for the destruction of suspect explosive devices, disposal of unexploded munitions, and wall breaching during hostage rescue operations. These devices are also widely used in the petroleum industry, the entertainment industry, the construction industry, etc.  
         [0004]     As a result, small explosive devices and charges often need to be carried in the presence of others, including the general public, usually in portable cases, such as when detonators and detonating cords are taken by security personnel to sites where operations require breaching walls and destruction of explosive materials.  
         [0005]     Upon detonation, rapid combustion processes produced even by a small explosive device compress surrounding fluid media so quickly that shock waves are produced. Also, the physical expansion of the hot blast combustion products adds to pressure loading of objects in its path, as well as generates radiation. The hot blast combustion products are typically capable of igniting combustible materials nearby and inflicting burns on exposed humans. Humans may be killed by intense blast pressure alone, as this causes lung damage above threshold levels. Below threshold conditions for fatal injury, blast pressure may cause damage to ears and lungs, and sudden accelerations that lead to spinal injuries. Moreover, fragments from exploding cased explosive devices may lead to fatal internal damage.  
         [0006]     Explosive effects dissipate rapidly in air as long as the blast is unconfined. Large obstructions such as buildings surrounding a street in which a blast occurs prolong pressure durations and lead to greater damaging capability. Complete or near-total confinement maximizes blast effect duration, as the blast pressure is prevented from being dissipated.  
         [0007]     In order to provide safe handling of small explosive devices, it is often desired to prevent detonation of one explosive charge from causing detonation of others nearby, an event widely termed “sympathetic detonation”, as mass detonation of large quantities of small explosive charges generates blast parameters equivalent to single-charge detonations of similar weight. A number of prior art small explosive devices containers are designed to prevent sympathetic detonation, but not to confine either blast effect or fragments. As a result, such containers are usually destroyed when the elements contained therein explodes, and components are hurled at significant velocities. As such, these containers would be unsuitable for transportation of small explosive devices next to people, as the components projected by the explosion could cause serious injury.  
         [0008]     For example, in U.S. Pat. No. 5,160,468, Halsey et al. disclose the use of a mitigating material, pumice, to surround hard plastic tubes to contain explosive devices. The hard plastic tube forms a barrier between the explosion and the mitigating material. If the plastic tube is omitted, the mitigating material attenuates the blast pressure but is not adapted to retain fragments produced by the blast.  
         [0009]     Accordingly, there is a need for an improved container allowing safe transportation of small explosive devices.  
       SUMMARY OF INVENTION  
       [0010]     It is therefore an aim of the present invention to provide an improved container allowing safe transportation of small explosive devices.  
         [0011]     Therefore, in accordance with the present invention, there is provided a container for containing an explosive device, the container comprising a mitigating layer defining an enclosure openable to insert the explosive device therein and closable to surround the explosive device, the mitigating layer reducing a force of a blast caused by an explosion of the explosive device, and a fragment-retaining layer substantially surrounding the mitigating layer, the fragment-retaining layer being resistant to a remainder of the force of the blast passing through the mitigating layer and retaining fragments propagated by the explosion of the explosive device, such as to reduce potential injury to a person in proximity of the container.  
         [0012]     Also in accordance with the present invention, there is provided a container for containing an explosive device, the container comprising an outer shell including a body and a cover relatively movable between an open position and a closed position, a fragment-retaining layer disposed against inner surfaces of the body and the cover such as to substantially define a first enclosure when the body and the cover are in the closed position, a mitigating layer disposed against inner surfaces of the fragment-retaining layer such as to define a second enclosure within the first enclosure when the body and cover are in the closed position, the second enclosure being adapted to receive the explosive device therein, wherein the mitigating layer reduces a force of a blast caused by an explosion of the explosive device, and the fragment-retaining layer resists a remainder of the force of the blast passing through the mitigating layer and retains fragments propagated by the explosion.  
         [0013]     Further in accordance with the present invention, there is provided a method of containing an explosion of an explosive device, the method comprising reducing a force of the explosion using a mitigating layer surrounding the explosive device, and containing the reduced force of the explosion and fragments projected by the explosion using a fragment-retaining layer surrounding the mitigating layer. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     Reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment of the present invention and in which:  
         [0015]      FIG. 1  is a perspective view of a container according to a preferred embodiment of the present invention; and  
         [0016]      FIG. 2  is a cross-sectional view of the container of  FIG. 1 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     Referring now to the drawings, a container or transport case  10  according to the present invention is shown. The case  10  comprises an outer shell  12  surrounding a fragment-retaining layer  14 , which surrounds a mitigating layer  16 .  
         [0018]     The outer shell  12  preferably has a rectangular cross-section, and includes a body  18  and a cover  20  which together define an enclosure, also preferably of rectangular cross-section. In a particular embodiment, the outer shell  12  protects the internal components and materials being transported from weather and incidental damage, and as such is made of a shock resistant plastic, for example a polypropylene copolymer such as Coroplast™. Alternate materials for the outer shell include wood or any appropriate type of metal such as for example steel or aluminum.  
         [0019]     In the embodiment shown, the cover  20  is pivotally retained on the body  18  through hinges  22 . The body  18  and cover  20  also include locking means  24  retaining the cover  20  in the closed position when engaged. Alternatively, the hinged cover  20  can be replaced by a cover completely separate from the body  18 , or by a guillotine-type door, a hatch-type door, a drawer, a plurality of doors, etc.  
         [0020]     In a particular embodiment, the case  10  is designed to handle small explosive devices (e.g. less than 1 kg total of TNT-equivalent explosive), and as such the hinges  22  and locking means  24  allow some gas to escape between the closed cover  20  and the body  18 , with the gas leakage and attendant shock waves mitigated to the extent required to prevent permanent injury to nearby people or prevent sympathetic detonation or burning of nearby energetic materials. In an alternate embodiment, the case  10  is used to contain explosive devices and other devices that may contain hazardous biological, radioactive, or chemical agents that could be dispersed under pressure, and as such the seal between the cover  20  and body  18  is adequate to prevent release of the hazardous material. The degree to which the seal is impervious to the transmission of gas can thus be varied through various closure modifications readily available to one in the art.  
         [0021]     A handle  26 , which may be fixed or extendable, is attached to the body  18  to facilitate transport of the case  10  either by hand or by a robotic device. It is also considered to provide the case  10  with more than one handle  26 , or alternatively with no handle at all.  
         [0022]     The fragment-retaining layer  14  is located within the enclosure defined by the outer shell  12  and is in contact therewith. The fragment-retaining layer  14  includes a bottom sheet  28  and four (4) side sheets  30  located in the body  18 , and a top sheet  32  located in the cover  20 . The bottom and side sheets  28 ,  30  preferably abut one another and the sheets  28 ,  30 ,  32  together define an enclosure within the enclosure of the outer shell  12 .  
         [0023]     The sheets  28 ,  30 ,  32  of the fragment-retaining layer  14  are made of a fragment-retaining material which minimize shock wave transmission as well as retains fragments propagated by an explosion of a size corresponding to the explosive device(s) to be transported in the case  10 . In a particular embodiment, the sheets  28 ,  30 ,  32  are made of polycarbonate, such as Lexan®, as this material has been proven to deform plastically to a great extent under explosive loading without rupture. Polycarbonate also features low acoustic impedance, which is desirable for shock wave attenuation. Alternatively, the sheets  28 ,  30 ,  32  can be made of a metal of similar properties and/or can comprise ballistic armor in order to protect the encased explosive devices from impinging projectiles or ammunition fragments. As such, the fragment-retaining layer  14  resists to a remainder of the blast force passing through the mitigating layer  16 .  
         [0024]     The mitigating layer  16  is located within the enclosure defined by the fragment-retaining layer  14  and is in contact therewith. A bottom panel  34  is located against the bottom sheet  28 , a side panel  36  is located against each of the side sheets  30 , and a top panel  38  is located against the top sheet  32 . The inner surfaces  56  of the panels  34 ,  36 ,  38  define an enclosure for the explosive device which will be contained in the case  10 .  
         [0025]     The panels  34 ,  36 ,  38  of the mitigating layer  16  are formed of a blast effect mitigating material which effectively reduces the strength of the blast of an explosive device in close proximity. Examples of such materials are disclosed by Gettle et al. in U.S. Pat. Nos. 5,225,622 and 5,394,786, which are both incorporated herein by reference. The mitigation mechanism of such materials is a combination of mechanical and chemical factors that stop the chemical reaction of the explosive before the entire explosive is consumed. A portion of the remainder of the explosive force is mitigated as it passes through the material. In a preferred embodiment, the panels  34 ,  36 ,  38  are made from lightweight honeycomb filled with attenuating filler material and sealed off on both sides with a thin relatively friable tissue. Other mitigating materials can also be used in the panels  34 ,  36 ,  38 , such as pumice, foamed plastic beads, etc.  
         [0026]     Although the mitigating layer  16  is shown as being formed of separate panels, it can also be integrally cast or otherwise molded to maintain an intended shape. Alternatively, the mitigating layer  16  can be tubular or in the form of amorphous bags of blast effect mitigating material so long as the bags are adequately secured to resist displacement when moved or disturbed.  
         [0027]     The inner surfaces  56  of the panels  34 ,  36 ,  38 , which define the enclosure where the explosive device will be contained, includes an interior lining that either provides negligible resistance to or delay in rupture, or permits transmission of the impinging blast wave into the blast effect mitigating material. In a preferred embodiment, the lining is perforated or otherwise permanently open to the unobstructed flow of gas between the space where explosive devices and materials are placed and the blast effect mitigating material.  
         [0028]     Alternatively, the lining can be a fabric or metal foil that prevents penetration of moisture or spilled fluids into the blast effect mitigating material, a frangible material resistant to the transmission of gas in ambient conditions but otherwise readily ruptured by the impingement of a blast in the event of a detonation inside the case  10 . Such a lining would be preferable when the blast effect mitigating material is a gel or fluid, or when powdered, liquid, or gaseous extinguishing agents are employed that assist in mitigating explosive effects or otherwise serve to suppress post-blast ignition of nearby flammable materials.  
         [0029]     In the embodiment shown, the case  10  includes at least one blast effect mitigating divider  40 , such that opposed exposed surfaces  58  of the divider  40  define together with the inner surfaces  56  of the panels  34 ,  36 ,  38  a plurality of separate compartments, in order to resist or inhibit the occurrence of sympathetic detonation when more sensitive explosive devices are carried. In  FIG. 1 , two such dividers  40  are illustrated, extending throughout the enclosure defined by the mitigating layer  16  in a perpendicular manner.  
         [0030]     Each divider  40  includes a middle sheet  42  sandwiched between two divider panels  44 . The middle sheet  42 , like the bottom, side and top sheets  28 ,  30 ,  32  of the fragment-retaining layer  14 , is composed of a fragment-retaining material such as for example polycarbonate. Like the sheets  28 ,  30 ,  32 , the middle sheet  42  can also include ballistic armor to prevent fragments and projectiles such as bullets from impacting explosive devices inside the compartment. The divider panels  44  are composed of blast effect mitigation material similarly to the bottom, side and top panels  34 ,  36 ,  38  of the mitigating layer  16 . The opposed exposed surfaces  58  of the divider panels  44  include an interior lining similar to the lining of the inner surfaces  56  of the panels  34 ,  36 ,  38 .  
         [0031]     In the embodiment shown, the case  10  also includes removable blast effect mitigating dividers  46 , one of which is shown in  FIG. 1 . The removable dividers  46  each include a middle sheet  48  similar to the middle sheet  42  of the divider  40 , sandwiched between two divider panels  50  similar to the divider panels  44  of the divider  40 . The removable dividers  46  also includes opposed exposed surfaces  60  including a lining similar to the lining of the exposed surfaces  58  of the divider  40 . The removable dividers  46  are sized such as to be snuggly slidable within a compartment of the enclosure defined by the mitigating layer  16 .  
         [0032]     In a particular embodiment, the dividers  40  and removable dividers  46  are intended to prevent sympathetic detonation between explosive devices located in separate compartments. However, prevention of sympathetic detonation is not essential. The critical requirement is that in the event of a detonation of one or more explosive devices within the case  10 , release of blast generated gas, from the case  10 , is so slight that no permanent injury is inflicted on humans in close proximity to the case  10 . Fragments from explosive device components, and components of the case  10 , are preferably completely confined. Extremely rapid cooling of hot gaseous products is also preferable such as to prevent possible ignition of case materials and other items kept within the case  10 .  
         [0033]     Alternatively, it is considered to provide a case  10  without the dividers  40  and/or without the removable dividers  46 . For example, the case  10  can provide a single compartment.  
         [0034]     In the embodiment shown, the body  18  includes an inspection port  54 , formed by aligned holes through the outer shell  12 , fragment-retaining layer  14  and mitigating layer  16 . The port  54  facilitates examination or characterization by various means so that inspection devices such as optical and other electromagnetic imaging devices, chemical sensors, and radiation detection probes may be installed in appropriate locations. Alternatively, the port  54  may be provided with an appropriate nozzle to inject various kinds of agents, such as aqueous foams for blast effect mitigation or neutralizing of chemical or biological agents, or cleaning material for scrubbing radioactive dusts. The port  54 , when not in use, is closed by an appropriate cover (not shown). Alternately, the port  54  can be omitted.  
         [0035]     In the embodiment shown, the body  18  also includes at least one vent  52 , which is defined by an aperture cut in one wall of the outer shell  12 , in order to release hot blast gases. Preferably, the vent  52  is located near explosive devices within the case  10  and is vented in a direction away from a person carrying the case  10 . The vent  52  is covered by the portion of the wall of the outer shell  12  removed to form the aperture (not shown), re-attached over the aperture in such a manner that the vent cover is easily dislodged under internal pressure.  
         [0036]     Alternately, the vent  52  could be located in other locations, for example in corners of the outer shell  12 . Also, alternate covers for the vent  52  include an elastic or flexible bag that expands under pressurization caused by an internal explosion. This expandable member may be substantially comprised of a fabric or plurality of fabric layers capable of catching debris and fragments from the detonation of a stored explosive device. Alternatively, the expandable member may be substantially comprised of a mesh that allows gradual release of internal gas, thereby reducing the loads imparted by the blast to the hinges  22  and locking means  24 . Any combination of such components for vent covers can be made by an individual skilled in the design of blast protection devices, such as bellows-type components combined with mesh and elastic “balloon” components.  
         [0037]     Although not shown, mountings or other provisions for cylindrical vessels, or other shapes of explosive devices, may be provided in the compartments. Straps or other similar components can be provided for additional restraint to the explosive devices within the compartments.  
         [0038]     In a particular embodiment, wheels (not shown) are attached to the outer shell  12  to facilitate movement of the case  10  by hand or robot. The wheels may be integral to the outer shell  12 , or be provided by detachable means enabling the wheel assembly to be removed when not needed. Alternatively, skids may be provided that also serve to facilitate movement.  
         [0039]     Moreover, explosive devices or other items may be placed in protective cartons or wraps within the compartments to provide additional levels of protection. Such wraps and cartons may be substantially comprised of high-strength materials that resist bullets and ammunition fragments from penetrating.  
         [0040]     The case  10  (as well as detachable wheels, if provided) may be provided with a bag enclosure that seals the case  10  when it is shut, to prevent release of dangerous materials to the external environment, for instance if the device within contains radioactive materials or potentially lethal pathogens. The bag enclosure may be part of the detachable wheeled or skid device, attached to the outer shell  12 , or incorporated with the internal compartments or linings of the case  10 . This bag enclosure may be coated or otherwise substantially comprised of materials that serve to neutralize the anticipated hazard.  
         [0041]     The case  10  can also include shielding against the transmission of electromagnetic radiation or interference (EMI), including the effects of electromagnetic pulse (generally designated as EMP) when the case  10  is closed. The case  10 , acting as a protection system, thus protects explosive devices kept therewithin from unintentional detonation or neutralization from radio waves or other electromagnetic events present outside the closed case  10 . Provisions for electrical grounding may also be placed in suitable locations of the case  10  in order to prevent the buildup of static electricity.  
         [0042]     Part or all of the outer shell  12  may utilize materials that facilitate external examination of the case contents, such as those permitting transmission therethrough of a desired portion of the electromagnetic spectrum. The fragment-retaining layer  14  and the mitigating layer  16  may be made of materials that are correspondingly similar.  
         [0043]     The outer surface of the outer shell  12 , the inner surfaces  56 , and the exposed surfaces  58 ,  60 , either alone or in combination, may be coated with fire-resistant materials in order to avoid ignition upon detonation of an encased explosive device. This is preferable when the case  10  is destined to contain energetic materials that may be capable of sustained burning with or without access to ambient air.  
         [0044]     Should vessels or containers storing radioactive, chemical, or biological agents be placed within cases where explosive devices are also kept, internal protective components that prevent piercing the agent container may be integrated within the second enclosure.  
         [0045]     The case  10  of the present invention thus minimizes the release of potentially hazardous phenomena under pressure above ambient to the environment external to it. Thus shock waves and pressurized gas leakage are mitigated to the degree desired by those who may be come into close proximity to the case  10  when explosive devices are contained therewithin.  
         [0046]     The mitigating layer  16  preferably provides substantial cushioning in order to protect explosive devices placed within the case  10  from shock and impact. Thus, the case  10  may be dropped, fall from a moving vehicle, stepped on, crushed by stacking with heavy objects, or struck by bullets with a reduced risk of explosion of the contained explosive devices or, in the case of an explosion, with limited risk of injury to people nearby. As it often is required to be carried by hand, the case  10  is preferably sized such as to be relatively light.  
         [0047]     The case  10 , sized accordingly, can safely contain a variety of small explosive devices, including, but not limited to, detonators, detonating cords, airbag inflators, fuses, small hand grenades, small anti-personnel mines, various recovered explosive devices, etc.  
         [0048]     Although the case  10  has been described as a portable case, it is also considered to integrate the case in a rolling cart, in a vehicle, in a building, etc. Where the case  10  is integrated in an enclosure of an existing structure, the outer shell  12  can be omitted. The case integrated in a rolling cart could be used, for example, in an airplane, where the rolling cart would be of a serving-cart type, to be rolled in proximity of a potentially dangerous device found, so that the device could be place within the case  10  with minimal handling. The case integrated in a vehicle could be used, for example, in a the cabin of a law enforcement vehicle, to transport small explosive devices destined to explode suspect devices, or to transport the suspect devices themselves away from the public.  
         [0049]     The embodiments of the invention described above are intended to be exemplary. Those skilled in the art will therefore appreciate that the foregoing description is illustrative only, and that various other alternatives and modifications can be devised without departing from the spirit of the present invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.