Abstract:
A blast screen system for a framed opening including a mounting mechanism secured to the framed opening; and a flexible mesh panel secured by the mounting mechanism to cover the framed opening. The mounting mechanism includes a plurality of spring biased brackets, each having a first portion and a second portion, the first and second portions being joined by a pivot pin.

Description:
TECHNICAL FIELD 
     The disclosure is directed to a blast protection system, and more particularly, to an architectural mesh blast screen system configured to protect personnel and property from debris resulting from an explosion while still allowing for ventilation and light and providing a pleasing aesthetic appearance. 
     BACKGROUND 
     Government buildings, embassies, and other public areas are often times the subject of tenor threats and terrorist attacks. Many of these attacks involve the use of explosives that produce both large amounts of debris and a pressure wave. Debris from the explosion can be created from the surroundings of the explosion. Debris may also be augmented by the bomb maker by including ball bearings, nails, and other objects with the explosive. The debris is driven at high speed by the pressure wave from the explosion and may cause physical injury to property and people. 
     In a common security scenario, an explosive detonates outside of a building. The explosion generates both a pressure shock wave and a blast wind. The shock wave carries debris outwardly, damaging property and people. When the shock wave from the explosion encounters a window or other opening, broken glass shards of the window or other material covering the opening may also be carried by the shock wave. 
     In order to provide protection from such explosions, barriers of various types have been deployed in order to reduce the damage and injury resulting from these attacks. Typically, these barriers include solid structures that block the damaging debris resulting from the explosion, but they also reduce the ventilation and the light that reaches the protected area. These types of barrier are particularly unsuited for use with windows or other openings, and are not amenable to easy cleaning and maintenance. These barriers also often times do not have a pleasing aesthetic appearance and are typically large and unwieldy. It is also possible for a solid barrier to cause additional damage if the shock wave overwhelms the barrier and damages the barrier. 
     It would be desirable to have a blast protection system which provides protection from the debris resulting from an explosion while also addressing the drawbacks discussed above. 
     SUMMARY 
     A blast screen system for a framed opening including a mounting mechanism secured to the framed opening; and a flexible mesh panel secured by the mounting mechanism to cover the framed opening. The mounting mechanism includes a plurality of spring biased brackets, each having a first portion and a second portion, the first and second portions being joined by a pivot pin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       These and other objects, features, and advantages will become more readily apparent to those skilled in the art upon reading the following detailed description, in conjunction with the appended drawings in which: 
         FIG. 1  is a front view of a blast screen system according to an exemplary embodiment disclosed herein. 
         FIG. 2  is a fragmentary view of the mesh screen according to an exemplary embodiment disclosed herein. 
         FIG. 3  is a perspective view of a support tube according to an exemplary embodiment disclosed herein. 
         FIG. 4  is a schematic view of a mounting mechanism according to an exemplary embodiment disclosed herein. 
         FIG. 5  is a schematic illustration of the operation of the blast screen system according to an exemplary embodiment disclosed herein. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The blast screen system  100 , shown by exemplary embodiment in  FIG. 1 , preferably includes a mesh panel  10  which defines a blast screen having a predetermined width and height, upper and lower support tubes  22 ,  24 , and mounting brackets  16 . Top and bottom fascia guards (not shown) may also be provided. The mesh panel  10  is secured inside the support tubes  22 ,  24  which, in turn, are attached to the mounting brackets  16 . The mounting brackets  16  include tension springs  26  which are configured to normally keep the mesh panel  10  straight and in tension. In a preferred installation, the brackets  16  are installed on the floor and ceiling of the areas to be protected. 
     One preferred embodiment of the mesh screen  10  is shown in detail in  FIG. 2 . The mesh screen  10  preferably comprises a flexible mesh fabric, and more particularly, an architectural mesh. The mesh screen  10  is formed of a plurality of helically-wound spiral wires  12 , each of which is associated with two connector or crimp rods  14  positioned sequentially adjacent along the mesh screen  10 . The combination of a helically-wound spiral wire  12  and two associated crimp rods  14  define a spiral unit having a plurality of vertically adjacent open recesses that allow ventilation and light to pass through. The mesh screen  10  is thus formed from a plurality of mesh spiral units joined together by their respective crimp rods  14 , as depicted in  FIG. 2 . The ends of the crimp rods  14  may be fixed, preferably by welding, to make the assembly permanent. 
     The blast screen  10  is supported at the top and bottom by support tubes  22 ,  24 , as shown in greater detail in  FIG. 3 . The tubes are preferably manufactured from 1½″ schedule  40  tube (1.90 O.D.) in either grade T316 or T304 stainless steel. The mounting tubes  22 ,  24  have a plurality of apertures  18  cut along their length and sized to accept the spirals  12  of the mesh panel  10 . The end spirals of the mesh panel  10  are inserted into the apertures  18  of the support tubes  22 ,  24 . The spirals  12  are secured in the tubes  22 ,  24  by inserting a 10 gage straight rod (not shown) through the uppermost and lowermost mesh spiral to secure the mesh panel  10  in place. Tube caps  19  are attached to the ends of the tubes  22 ,  24  to secure the straight rods inside the tubes  22 ,  24 . The support tubes  22 ,  24  have sections of threaded studs  20  welded at predetermined locations which are used to attach the tubes  22 ,  24  to the mounting brackets  16 . 
     Referring also to  FIG. 4 , the mounting brackets  16  are preferably fabricated from ¼″ stainless steel plate in either T316 or T304 grades. The plates are cut and bent into final form defining first and second brackets  16   a ,  16   b , which are joined together with pivot pins  28  to form an enclosed space. The support tubes  22 ,  24  are mounted to the mounting brackets  16  by inserting threaded studs  20  from the support tubes  22 ,  24  into slots  17  in the upper portion of one of the brackets  16   a ,  16   b  through a compression spring  26  disposed within the space enclosed by the brackets  16   a ,  16   b , and securing with a fastening element  32 , such as lock nuts and washers. The brackets  16  normally hold the blast screen  10  straight by applying pretension on the integral compression springs  26 . This exerts a force on the support tubes  22 ,  24  keeping the mesh panel  10  under tension. The mounting side of the bracket  16  can be attached to the building structure B using appropriate mounting hardware  30 , such as concrete anchors or bolted connections into structural steel, as needed. 
     In a preferred embodiment, the mesh screen  10  is formed from 18 gage (0.047) stainless steel wire of either T316 or T304 grades, however, the mesh screen  10  can be made of any material and/or weave desired to match the particular safety requirements. More particularly, the mesh screen  10  may be configured for a specific application by varying the open area per square foot of mesh as desired. This is done by adjusting the spread, or loops per foot in the horizontal direction, the pitch, or spirals per foot, the gauge of the wire of the crimp rods  14 , or the gauge of the wire used to form the helically-wound spirals  12 . The mesh screen  10  may be woven from a combination of spiral wires made of the same material or of two or more different materials. The spiral wires of the mesh screen may be of the same shape or size, or they may have different characteristics. Factors that may determine the composition and construction of the mesh screen  10  include the safety requirements of the building, the window glass type, the use of safety laminations, the expected threat level, and other factors. 
     Alternative embodiments of the screen system  100  may use other materials that also allow light and ventilation to enter but provides protection to property and people. 
     The operation of the screen system  100  depicted in  FIGS. 1-4  will now be described. In the event of a blast, the pressure wave from the explosion will implode the window driving glass shards and debris inward toward the occupied area. As shown in  FIG. 5 , the pressure wave will also cause the blast screen  10  to billow inward pivoting the mounting brackets  16  in the direction of the blast wave. The bracket tension springs  26  will compress allowing additional movement of the mesh panel  10 . The open area of the screen  10  and flexibility of the system  100  will allow the blast pressure to vent while the close weave and strength of the mesh will trap glass shards and window debris. Thus, the pressure wave dissipates through the open area of the mesh screen  10  while the closed area of the mesh screen  10  traps the debris and prevents injury to property and people. 
     The above-described architectural mesh blast screen system  100  is designed to meet the standard established by the Department of State as outlined in performance condition  3 A described in the specification GSA TS-01, level C, the contents of which are hereby incorporated by reference. This performance condition allows for glazing cracks and fragments to enter the occupied area of a building. The window debris and glass shards, however, are to land no further than 3.3 feet from the window. The described combination of features is specifically designed to offer protection for large windows and open areas such as building entrances, vestibules, and security screening checkpoints. Other applications are of course possible and within the scope of this disclosure. 
     While the disclosure set forth herein has been described with respect to a particular embodiment, this is by way of illustration for purposes of disclosure rather than to confine the invention to any specific arrangement as there are various alterations, changes, deviations, eliminations, substitutions, omissions and departures which may be made in the particular embodiment shown and described without departing from the scope of the claims.