You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF THE INVENTION  
       [0001]     The present invention relates to an impact resistant glass structure and more particularly to an impact resistant glass structure having three spaced apart panes wherein an outermost pane is a monolithic glass sheet, a center pane is a plastic sheet such as a polycarbonate, and an innermost pane is a laminated glass having an annealed glass layer and a film layer such as polyester.  
       BACKGROUND OF THE INVENTION  
       [0002]     Exterior windows are part of a building envelope, which essentially includes those elements that comprise an exterior of a building. As part of the building envelope, exterior windows are subjected to a variety of weather extremes. Accordingly, an increasing number of localities are increasing the structural standards applicable to exterior windows. In particular, many localities are adopting laws and building codes which include strenuous impact standards. The impact standards often require the exterior windows to withstand an impact of a missile or projectile driven by the high winds of a hurricane or a tornado. Even in the absence of hurricane conditions, it is often desirable to have an exterior window having high strength and durability.  
         [0003]     Double-paned window glazing units are frequently employed in construction due to their favorable insulating properties. Such double glazed windows have advantageous thermal insulating properties because an air space exists between the two panes of glass. The air space acts as a thermal barrier. Such windows have a serious drawback however, in that they remain susceptible to being easily broken.  
         [0004]     It would be desirable to produce an impact resistant glass structure having three distinct spaced apart layers which militates against penetration of the vertical plane when impacted by a projectile.  
       SUMMARY OF THE INVENTION  
       [0005]     Consistent and consonant with the present invention, an impact resistant glass unit having three distinct spaced apart layers which militates against penetration of the vertical plane when impacted by a projectile, has surprisingly been discovered.  
         [0006]     The impact resistant glass structure comprises a generally planar glass first layer having an outer edge; a generally planar impact resistant plastic second layer spaced from and substantially parallel with the first layer, the second layer having an outer edge; a generally planar laminated glass third layer spaced from and substantially parallel with the first layer and the second layer, the third layer having an outer edge; a first spacer disposed between the first layer and the second layer adjacent the respective outer edges thereof; and a second spacer disposed between the second layer and the third layer adjacent the respective outer edges thereof, wherein the outer edge of the first layer, the outer edge of the second layer, and the outer edge of the third layer are adapted to be disposed in a window casing. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The above, as well as other objects, features, and advantages of the present invention will be understood from the detailed description of the preferred embodiments of the present invention with reference to the accompanying drawing, in which:  
         [0008]     The drawing is a schematic fragmentary sectional elevational view of a portion of an impact resistant glass structure in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0009]     Referring to the drawing, there is shown generally at  10  a schematic sectional view of an impact resistant glass structure in accordance with the present invention. The glass structure  10  includes a first layer  12 , a second layer  14 , and a third layer  16 . The first layer  12 , the second layer  14 , and the third layer  16  are spaced from and are substantially parallel with one another. In the embodiment shown, the first layer  12  is produced from an annealed glass having a low emissivity (low-E) material deposited on one surface thereof. It is understood that other glass types could be used without departing from the scope and spirit of the invention. An outer edge  18  of the first layer  12  is adapted to be installed in a window casing (not shown). In the embodiment shown, the space between each of the layers  12 ,  14 ,  16  is filled with a gas such as air, argon, krypton, or a blend of argon and krypton, for example, to militate against a fog or condensate forming on a surface of the layers  12 ,  14 ,  16 .  
         [0010]     The second layer  14  is disposed between the first layer  12  and the third layer  16 . In the embodiment shown, an outer edge  20  of the second layer  14  is spaced inwardly from the outer edge  18  of the first layer  12 . Typically, the second layer  14  is produced from a plastic having a greater impact resistance than glass such as a polycarbonate, a polymethyl methacrylate, and a polyethylene terepthalate, for example. One such plastic is sold by the General Electric Company under the trademark LEXAN MR10. It is understood that other plastic types could be used without departing from the scope and spirit of the invention.  
         [0011]     An outer edge  22  of the third layer  16  extends to substantially the same extremity as the outer edge  18  of the first layer  12 . Thus, the outer edge  18  of the first layer  12  and the outer edge  22  of the third layer  16  extend outwardly beyond the outer edge  20  of the second layer  14 . The third layer  16  is produced from a laminated glass having a film  32  disposed on an inner surface thereof. Preferably, the film  32  is a plastic material such as polyester, for example. However, it is understood that other film materials could be used. It is also understood that the third layer  16  could be coated the inner surface as shown, an outer surface, both inner and outer surfaces, or alternatively, the third layer  16  could be formed as a laminated structure having the film  32  sandwiched between two juxtaposed layers of glass. In the embodiment shown, the third layer  16  is produced from an annealed glass. It is understood that other glass types could be used.  
         [0012]     A first spacer  24  is disposed between the first layer  12  and the second layer  14  adjacent the respective outer edges  18 ,  20  thereof and a second spacer  26  is disposed between the second layer  14  and the third layer  16  adjacent the respective outer edges  20 ,  22  thereof. A first sealant layer  28  and a second sealant layer  30  are disposed around the first spacer  24  and the second spacer  26 . The first sealant layer  28  is produced from a polyisobutylene material and the second sealant layer  30  is produced from polyurethane. It is understood that other thermoplastic polymers could be used.  
         [0013]     In use, the first layer  12 , the second layer  14 , and the third layer  16  are installed in the window casing. The casing surrounds the outer edge  18 ,  20 ,  22  of the respective the layer  12 ,  14 ,  16 . The first spacer  24  maintains a separation between the first layer  12  and the second layer  14 . The second spacer  26  maintains a separation between the second layer  14  and the third layer  16 . The first sealant layer  28  and the second sealant layer  30  hold the spacers  24 ,  26  in place and also provide a vapor barrier between the interstitial space between the layers  12 ,  14 ,  16  and the atmosphere. A desiccant material (not shown) can also be disposed in the interstitial space to absorb moisture and militate against fog or condensate forming on of a surface of the layers  12 ,  14 ,  16 .  
         [0014]     The glass structure  10  provides a thermal insulating structure, as well as an impact resistant structure. In the event a projectile is caused to impact the glass structure  10 , the second layer  14  and the third layer  16  militate against a shattering and a complete failure of the glass structure  10 , and militate against fragments being caused to become airborne causing injury to a bystander. The glass structure  10  of the embodiment shown is sufficiently strong to militate against penetration in impact tests. The spacers  24 ,  26 , the first sealant layer  28 , and the second sealant layer  30  also militate against a separation of the layers  12 ,  14 ,  16  in impact tests.  
         [0015]     From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications to the invention to adapt it to various usages and conditions.

Summary:
An impact resistant glass structure having three spaced apart panes wherein an outermost pane is a monolithic glass sheet, a center pane is a plastic sheet such as a polycarbonate, and an innermost pane is a laminated glass having an annealed glass layer and a film layer such as polyester, the glass structure militating against penetration of the vertical plane when impacted by a projectile such as may occur during a wind storm.