Abstract:
A water-based apparatus for mitigating the gas pressure loading and associated damage and injuries from a fully or partially confined explosion. The water-based apparatus comprises a water-blanket which rests on each pallet of ordnance to mitigate the gas pressure loading from an inadvertent explosion of the ordnance. The water-blanket includes a pair of storage modules, each module comprising a plurality of water storage compartments that store a predetermined quantity of water which is dependent upon the type and quantity of explosive in the ordnance on the pallet. The storage modules are joined by a zipper which allows the modules to be separated for ease in transport.

Description:
[0001]    This Application is a continuation of U.S. patent application Ser. No. 09/436,714, filed Sep. 18, 2001. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to apparatus for mitigating damage and injuries from an explosion inside a confined space, such as an explosion inside an ammunition storage magazine, a missile test cell, a missile maintenance facility, a bomb disposal vessel, a command and control center, or like structures. More particularly, the present invention relates to a water-filled blanket which may be deployed inside a structure to mitigate the gas pressure loading generated by an explosion inside the structure confining the explosion.  
           [0004]    2. Description of the Prior Art  
           [0005]    Explosive devices, such as projectiles, bombs, and missiles stored in an ordnance facility, will occasionally detonate accidentally, resulting in an explosion which may cause substantial damage and injuries. If the mass, strength and architecture of the structure are sufficient to fully or partially confine the explosion, then the by-products of the explosion will cause the buildup of high temperature gases. These high temperature gases, when expanding in a space with restricted venting, cause the buildup of gas pressures inside the facility. The magnitude of the peak gas pressure depends primarily on the type and weight of the explosive relative to the interior volume of the facility. The duration and total impulse of the gas pressure depend primarily on the degree of venting available for these gases to escape from the facility. The degree of venting, in turn, depends on the total area of openings in the building envelope, the volume of space in the building for the hot gases to expand into, the mass and strength of the building envelope, and the magnitude and location of the maximum credible explosion (MCE) inside the facility. The degree of confinement and venting in most weapons facilities is sufficient to produce a significant gas pressure loading inside the facility. Such a loading could cause a significant increase in the extent of damage and injuries inside and outside the weapons facility.  
           [0006]    Most ordnance facilities used for the production, maintenance, assembly and repair of weapons are conventional unhardened, above-ground buildings. These ordnance buildings must be located a large distance from nearby inhabited facilities in order to limit the risk of injuries and damage from hazardous debris produced by the maximum credible explosion (MCE) in the ordnance facility.  
           [0007]    Generally, the minimum safe separation distance from an ordnance facility encumbers a large area of land. For example, the minimum safe separation distance to inhabited facilities from an ordnance facility is 1,250 feet for an MCE (Maximum Credible Event)≦30,000 pounds NEW (Net Explosive Weight). Thus, an ordnance facility containing less than 30,000 pounds NEW, a typical situation, encumbers 112 acres of land which is the area of a circle with a 1,250 feet radius. The minimum safe separation distance and encumbered land area are, in turn, dictated by the maximum strike range of hazardous fragments and debris. At today&#39;s real estate prices, especially near the waterfront, the value of encumbered land often exceeds the acquisition cost of the ordnance facility.  
           [0008]    The minimum safe separation distance from building debris is also dictated, in part, by the gas impulse developed when the explosion is confined by the building envelope. This gas impulse contributes significantly to the launch velocity of building debris and the resulting maximum strike range of hazardous debris. Thus, any device or method that significantly reduces the magnitude of this gas impulse would significantly reduce the maximum strike range of hazardous debris and the corresponding encumbered land area needed for the safety of people and property.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention overcomes some of the difficulties of the traditional strategies for mitigating the effects of an explosion in that it comprises a relatively simple, yet highly effective water-based apparatus which mitigates the gas pressure loading developed inside the structure confining the explosion.  
           [0010]    One embodiment of the present invention is a water-blanket which rests on each pallet of ordnance to mitigate the gas pressure loading from an inadvertent explosion of the ordnance. Each water-blanket includes a pair of storage modules with each module comprising a plurality of storage compartments for storing a predetermined quantity of water. The storage modules are joined by a zipper which allows the modules to be separated for ease in transport. The quantity of water in the water-blanket depends upon the type and quantity of explosive on each pallet, the total number of pallets, and the structural and venting characteristics of the surrounding facility. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a perspective view of a water-blanket, constituting a preferred embodiment of the present invention when deployed on one or more pallets of ordnance;  
         [0012]    [0012]FIG. 2 is a detailed perspective view of the water-blanket of FIG. 1;  
         [0013]    [0013]FIG. 3 is a view, partially in section, of the water-blanket of FIG. 1;  
         [0014]    [0014]FIGS. 4A and 4B are graphs illustrating gas pressure versus time measured inside an unvented test chamber without water-filled blankets (FIG. 4A), and water filled blankets simulating three walls of a test cell (FIG. 4B);  
         [0015]    [0015]FIG. 5A is a graph illustrating the effect of a water-blanket on the maximum strike range of hazardous roof debris for a maximum credible explosion equal to 560 pounds NEW inside the facility illustrated in FIG. 5B;  
         [0016]    [0016]FIG. 6 illustrates a water-filled cradle mattress deployed on a missile assembly and maintenance stand;  
         [0017]    [0017]FIG. 7 illustrates a debris prediction model for the trajectory of debris from a building in which an explosion occurs;  
         [0018]    [0018]FIG. 8 is a graph illustrating the reduction in total gas plus shock impulse (i g +i s ) acting on the end walls of a building (FIG. 7) resulting from deploying water-filled cradle mattresses, as a function of net explosive weight (W) and weight of building envelope (γ);  
         [0019]    [0019]FIG. 9 is a graph illustrating the reduction (%) in the maximum debris distance (R d ) from deploying a water-filled cradle mattress, as a function of net explosive weight (W) and unit weight of building envelope (γ);  
         [0020]    [0020]FIG. 10 is a graph illustrating the reduction (%) in encumbered land area (R a ) from hazardous wall debris due to the water-filled cradle mattress, as a function of net explosive weight (W) of the MCE and unit weight of building envelope (γ) for the building described in FIG. 7;  
         [0021]    [0021]FIG. 11 illustrates a water-pillow which is deployed above a missile during an all-up-round test in a missile test cell;  
         [0022]    [0022]FIG. 12 is a graph illustrating the increase in explosive weight capacity of a missile test cell by deploying the water-pillow shown in FIG. 11;  
         [0023]    [0023]FIG. 13 illustrates a facility wherein water-blankets are suspended from the ceiling of the facility to enhance survivability against a penetrating weapon; and  
         [0024]    [0024]FIG. 14 illustrates a mobile bomb containment vessel enclosing a bomb basket wherein tubes of water are suspended from the outer rim of the bomb basket which contains explosives/bombs.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]    [0025]FIGS. 1, 2 and  3  illustrate a water-blanket, identified generally by the reference numeral  20 , which constitutes a preferred embodiment of the present invention. As shown in FIG. 1, a water-blanket  20  is draped over projectiles  24  stored on a pallet  22  to mitigate the effects of an explosion should one or more of the projectiles  24  on pallet  22  detonate.  
         [0026]    Water-blanket  20  includes a pair of storage modules  26  and  28  connected by a zipper  30 . Each storage module  26  and  28  has five water storage compartments with module  26  comprising water storage compartments  32 ,  34 ,  36 ,  38  and  40  and module  28  comprising water storage compartments  42 ,  44 ,  46 ,  48  and  50 . Attached to storage module  26  are four handles  60 ,  61 ,  64  and  65  which allow the user of water-blanket  20  to move storage module  26  from one location to another location within an ordnance facility after unzipping module  26  from module  28 . Similarly, storage module  28  has four handles  62 ,  63 ,  66  and  67  attached thereto which allow the user of water-blanket  20  to move module  28  from one location to another location.  
         [0027]    Water storage compartment  32  of module  26  includes a stem  52  which extends from compartment  32  and also communicates with a water storage chamber  70  formed within the interior of compartment  32  as shown in FIG. 3. The first pair of fluid passageways  56  and  76  connect water storage chamber  70  of compartment  32  to water storage chamber  72  of adjacent compartment  34 . In a like manner, there is a second pair of fluid passageways  57  and  77  which connect water storage chamber  72  of compartment  34  to water storage chamber  74  of adjacent compartment  36 .  
         [0028]    Although only one fluid passageway  78  is illustrated in FIG. 3 as connecting chamber  74  of compartment  36  to the chamber for adjacent compartment  38 , a second fluid passageway (not illustrated) also connects chamber  74  of compartment  36  to the chamber for adjacent compartment  38 . There is also a pair of fluid passageways (not illustrated) which connect the water storage chamber of compartment  38  to the water storage chamber of adjacent compartment  40 .  
         [0029]    Stem  52  of module  26  allows the user of water-blanket  20  to fill compartments  32 ,  34 ,  36 ,  38  and  40  of module  26  with water and also allows the user of water-blanket  20  to drain water from compartments  32 ,  34 ,  36 ,  38  and  40  of module  26 . Fluid passageways  56 ,  57 ,  76 ,  77  and  78  and identical fluid passageways (not illustrated) between adjacent compartments  38  and  40  allow for the transfer of water between adjacent compartments of module  26  of water-blanket  20 .  
         [0030]    Stem  54  of module  28  allows the user of water-blanket  20  to fill compartments  42 ,  44 ,  46 ,  48  and  50  of module  28  with water and also allows the user of water-blanket  20  to drain water from compartments  42 ,  44 ,  46 ,  48  and  50  of module  28 . Each of these adjacent compartments of module  28  also contain a pair of fluid passageways (not illustrated) for the transfer of water between the compartments.  
         [0031]    Based on the heat of vaporization of water and the heat of detonation of the explosive, such as TNT, the water-blanket  20  of FIG. 1 would require about 1.8 pounds of water for each pound of TNT explosive stored on pallet  22  to mitigate the effects of a confined explosion. For other high explosive materials, such as H-6, the water-blanket  20  would require about 3.8 pounds of water for each pound of H-6 explosive.  
         [0032]    It should also be noted that the length and number of water-blankets  20  to be used with each pallet  22  will vary depending on the type and net explosive weight of the explosive stored on pallet  22 . Water-blanket  20  will generally have a width slightly less than the length of any pallet of ordnance.  
         [0033]    The plot in FIG. 4A shows as a function of time the gas pressure measured inside an unvented test facility without water-filled blankets operating as walls simulating three walls of a missile test cell. The plot in FIG. 4B, shows as a function of time the gas pressure measured inside the same unvented test facility but with water-filled blankets simulating three walls of a missile test cell. Each test used 4.67 pounds of TNT. With 13.5 pounds of water, the gas pressure was reduced 89% from 51.3 psi (FIG. 4A) to 5.8 psi (FIG. 4B). There was a similar reduction in the total gas impulse.  
         [0034]    [0034]FIG. 5B shows a building  94  comprising a floor  108 , upstanding walls  100  and  102  extending from floor  108 , and a concrete roof  96  affixed to the top of upstanding walls  100  and  102 . Concrete roof  96  includes a chimney vent  98  having a vent area A V =68 ft 2 . The effective thickness of the concrete roof  96 , T e , is 18 inches. Pallets of ordnance stored in building  94  would utilize water-blankets  20  (FIG. 1) to mitigate the gas pressure environment generated inside building  94  by the maximum credible explosion  104 . As shown in FIG. 5A, water-blanket  20  substantially reduces the peak gas pressure and total gas impulse generated by the maximum credible explosion  104 . This reduction, in turn, reduces the maximum strike range of hazardous roof debris from about 124 feet (without a water-blanket, plot  90  of FIG. 5A) to about 13 feet (with a water-blanket, plot  92  of FIG. 5A). This is equivalent to a 90% reduction in the maximum strike range of hazardous debris.  
         [0035]    It should be noted that the shock wave from the maximum credible explosion  104  will aerosolize the water in water-blanket  20 , thereby allowing the water to absorb a substantial amount of heat energy in the hot gases of the explosion by changing the aerosolized water mist from a mist state to a vapor state. The capacity of the water to absorb heat energy in the hot gases (and thereby reduce the total gas impulse) depends primarily on the ability of the shock wave to aerosolize the water which, in turn, depends on the configuration and location of the water relative to the configuration and location of the explosive generating the maximum credible explosion.  
         [0036]    [0036]FIG. 6 shows a missile assembly and maintenance stand  112  which is used for maintenance of a missile  110 . Missile assembly and maintenance stand  112  includes four wheel casters  114  which allow for movement of the missile assembly and maintenance stand  112  from one location to another location within a missile maintenance facility; a main beam assembly  118  upon which missile  110  rests; an AFT trolley and restraining strap  120 , a forward trolley (not illustrated), and restraining straps  124  and  126  for securing the missile to the missile assembly and maintenance stand  112 . There is also provided a semi-circular shaped water-filled cradle mattress  116  which places water in proximity to the explosive components of the missile, thereby increasing the efficiency of the water to aerosolize and mitigate the gas pressure and associate effects of an accidental missile explosion.  
         [0037]    [0037]FIGS. 6, 7,  8 ,  9  and  10  show a missile maintenance facility which has four upstanding walls  132 ,  134 ,  136  and  138  and a roof assembly  140  mounted on the top of walls  132 ,  134 ,  136  and  138 . The missile maintenance facility deploys water-filled cradle mattresses  116  of the type illustrated in FIG. 6 to mitigate the effects of an accidental explosion  142  of a missile  110  when maintenance is being performed on the missiles. The building illustrated in FIG. 7 is 100 feet long, 50 feet wide, and 15 feet high. The maximum credible explosion  142  is located at the center of the missile maintenance facility, four feet above the floor of the facility. The unit mass of the building envelope (designated by the reference numeral  130 ) is γ which ranges from 25 psf minimum to 200 psf maximum. FIG. 8 illustrates the reduction in total gas plus shock impulse (i g +i s ) acting on the end walls  132  and  136  of the building if a water-filled cradle mattress  116  is located adjacent to each missile, as a function of net explosive weight W of the maximum credible explosion and the unit weight γ of the building&#39;s end walls. Plot  156  illustrates the reduction in total gas plus shock impulse on the end walls  132  and  136  if γ=200 psf; plot  154  illustrates the reduction in total gas plus shock impulse on the end walls  132  and  136  if γ=100 psf; plot  152  illustrates the reduction in total gas plus shock impulse on the end walls  132  and  136  if γ=50 psf; and plot  150  illustrates the reduction in total gas plus shock impulse on the end walls  132  and  136  if γ=25 psf.  
         [0038]    [0038]FIG. 9 illustrates the reduction in maximum debris distance, R d , for end walls  132  and  136  resulting from deploying the water-filled cradle mattresses  116 , as a function of net explosive weight, W, and unit weight, γ, of building&#39;s end walls  132  and  136 . Plot  166  illustrates the reduction in maximum debris distance, R d , for end walls  132  and  136  for γ=200 psf; plot  164  illustrates the reduction in maximum debris distance, R d , for end walls  132  and  136  for γ=100 psf; plot  162  illustrates the reduction in maximum debris distance, R d , for end walls  132  and  136  for γ=50 psf; and plot  160  illustrates the reduction in maximum debris distance, R d , for end walls  132  and  136  for γ=25 psf.  
         [0039]    [0039]FIG. 10 illustrates the reduction in encumbered land area for hazardous wall debris resulting from deploying a water-filled cradle mattress  116  adjacent to each missile in the building, as a function of net explosive weight, W, of the maximum credible explosion and unit weight of the building&#39;s walls, γ. Plot  176  illustrates the reduction in encumbered land area, R a , for hazardous wall debris if γ=200 psf; plot  174  illustrates the reduction in encumbered land area, R a , for hazardous wall debris if γ=100 psf; plot  172  illustrates the reduction in encumbered land area, R a , for hazardous wall debris if γ=50 psf; and plot  170  illustrates the reduction in encumbered land area, R a , for hazardous wall debris if γ=25 psf. The reduction in encumbered land area, R a , ranges from 75% to 90% for W=100 lbs NEW; from 20% to 75% for W=10,000 lbs NEW; and from 15% to 50% for W=30,000 lbs NEW.  
         [0040]    [0040]FIG. 11 shows a water pillow  182  which is deployed above a missile  180  undergoing an all-up-round test in a missile test cell (not illustrated). A bridge crane  202  is used to position and support water pillow  182  over a test restraint fixture (not illustrated) which restrains missile  180  during a missile test. Bridge crane  202  includes two bridge rails  184  and  185  upon which an I-beam  186  rides in the direction indicated by an arrow  188 . A carriage  200 , which has an I-beam  204  and mattress support structure  206  attached thereto, rides on I-beam  186  in the direction indicated by arrow  207 .  
         [0041]    Referring to FIGS. 11 and 12, FIG. 12 illustrates the increase in the safe explosive weight capacity of a missile test cell by deploying a water pillow  182  over missile  180  during test of the missile  180 . Comparing plot  230  (with water pillow  182 ) and plot  232  (without water pillow  182 ) shown in FIG. 12, the water pillow  182  reduces the total gas plus shock impulse by about 78% for W=100 lbs NEW; by about 37% for W=300 lbs NEW; and by about 27% for W=1000 lbs NEW. Also, if the safe impulse capacity of the walls and roof of an existing missile test cell is 15,300 psi-msec, as illustrated in FIG. 12, then the safe explosive capacity of the missile test cell is 300 lbs NEW without a water pillow (plot  232 , FIG. 12), but the safe explosive capacity of the missile test cell can be increased 163% to 790 lbs NEW (plot  230 , FIG. 12) by simply deploying the water pillow  182 . This example demonstrates that the water-based apparatus provides a very economical and effective scheme to substantially increase the safe explosive capacity of existing weapons facilities.  
         [0042]    [0042]FIG. 13 shows an underground command and control center  244  which has water-blankets  248 ,  252  and  256  deployed in rooms  250 ,  254  and  258 , respectively, to significantly enhance survivability of the command and control center  244  when the center  244  is under attack by a missile  240  which penetrates the ground  242  and roof  246  and then detonates inside room  258  of the command and control center  244 .  
         [0043]    When missile  240  carries a 100 pound NEW warhead, each water-blanket  248 ,  252  and  256  will be required to store about four cubic feet of water to reduce the peak gas pressure and total gas impulse in room  258  by about 90%. A water-blanket six feet long, four feet wide, and two inches thick would provide the required capacity of four cubic feet. The 90% reduction in total gas impulse now makes it practical and cost effective to blast harden the walls of each room, thereby limiting damage and injuries to the room penetrated by the missile.  
         [0044]    [0044]FIG. 14 shows a mobile bomb containment vessel  270  which is designed to fully contain the explosion effects from an explosive device  272  if the device  272  were to detonate inside the vessel  270 . Located inside vessel  270  is a bomb basket  274  fabricated from wire screen. Explosive device  272  is carried in basket  274  which holds explosive device  272  at a safe standoff distance from containment vessel  270 . Cylindrical water containers  276  are uniformly spaced along the outer perimeter of basket  274  and affixed thereto. When an explosion occurs inside vessel  270 , shock waves from the explosion aerosolize the water stored in the water containers  276 , thereby reducing the peak gas pressure and total gas impulse from the explosion by about 90% within vessel  270 . This 90% reduction in total gas impulse makes it possible to reduce the cost of the containment vessel shell  270 , or, alternatively, to increase significantly the safe explosive weight capacity of an existing mobile bomb containment vessel  270 .  
         [0045]    From the foregoing, it is readily apparent that the present invention comprises a new, unique, and exceedingly useful water-based apparatus for mitigating the effects from a fully or partially confined explosion. This water-based apparatus constitutes a considerable improvement over the known prior art. Many modifications and variations of the present invention are possible in light of the above teachings. It is to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.