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RELATED APPLICATION  
       [0001]     This divisional application claims priority to and the benefit of U.S. application Ser. No. 10/403,466, filed on Mar. 31, 2003, which, in turn, claims priority to and the benefit of United Kingdom patent application number 0207643.8, filed on Apr. 2, 2002, which applications are herein incorporated by reference in their entirety. 
     
    
     BACKGROUND  
       [0002]     The present invention relates generally to building components and, more particularly, but not exclusively, to building components for roofing, in the form of inflatable cushions.  
         [0003]     Inflatable cushions comprise two or more layers of a plastic foil material such as ETFE (ethylene tetra flouro ethylene) inflated with low pressure air. The ETFE foil cushion is restrained in a perimeter frame usually manufactured from extruded aluminium, which in turn is fixed to a support structure. As the ETFE foil cushion is inflated, the ETFE is put under tension and forms a tight drum like skin. ETFE foil cushions are sold under a number of trade names, for example “Texlon.” 
         [0004]     ETFE cushions of this kind are fixed to a support structure to form a cladding and are used to enclose atria or other enclosed spaces to provide a transparent or translucent roof or facade to the enclosure, as an alternative to and in a similar way to glass. A number of buildings have been built using this technology most notably the Eden project in Cornwall, England.  
         [0005]     Whenever a space is enclosed by a cladding system due consideration needs to be given to the effects of a fire should it break out in the building. In these circumstances, smoke and other products of combustion must be ventilated from the enclosure to prevent injury to the occupants and property. In some specialist buildings, other noxious fumes may also need to be ventilated from the enclosure to prevent injury to the occupants and property. In some specialist buildings, other noxious fumes may also need to be ventilated to atmosphere.  
         [0006]     To ventilate noxious fumes to atmosphere, two methods are primarily utilized. Firstly, the smoke, and/or fumes can be extracted by a mechanical extraction system usually consisting of fire-rated duct work and extraction fans. Alternatively, the smoke and/or fumes can be extracted by opening part of the roof or building facade and allowing the smoke to ventilate to atmosphere through the action of convection and/or wind.  
         [0007]     ETFE foil cushions can be used to ventilate smoke and/or fumes to the atmosphere in much the same ways as other cladding systems in that they can be fixed to a frame which opens automatically through a mechanical device in the event of fire. In addition, ETFE is a thermo-plastic material and therefore has the innate property of failing if the temperature reaches approximately 200° C., as the material loses its tensile properties as its temperature increases. When the cushion fails, it allows smoke and/or fumes to ventilate naturally to the atmosphere.  
         [0008]     The above methods suffer from a number of draw backs. The mechanical extraction approach is expensive and requires fire-rated machinery, regular maintenance and testing. Natural extraction requires expensive opening frames, which are complex to render, weather and watertight. They do not look the same as the adjacent cladding as they require a secondary opening frame, and mechanical operating parts which themselves require regular maintenance and testing. The failure of the ETFE due to high temperature does not occur if the building fire is located some way away from the ETFE, as the ETFE is not sufficiently heated by smoke and/or fumes to fail.  
       SUMMARY OF THE INVENTION  
       [0009]     It is an object of the present invention to provide an economical, visually unobtrusive, method of causing ETFE foil cladding systems to fail on demand in order to allow natural smoke ventilation from a building enclosure.  
         [0010]     It is a further object of the invention to allow the system to fail on demand in order to shed high loads such as snow or water ponding.  
         [0011]     Thus, according to one aspect, the present invention provides a building component in the form of an inflatable cushion comprising two or more sheets of plastics foil and a relatively rigid frame surrounding and supporting the foil sheets, the building component further incorporating a release mechanism in or adjacent to the frame arranged to release the foil sheets from the frame.  
         [0012]     Preferably, the sheets are made from ethylene tetrafluoro ethylene (ETFE). Preferably, the sheets define a space between them which is inflated with air and the frame restrains the sheets about their perimeters, thereby forming the cushion. The release mechanism may extend the entire periphery of the cushion. Alternatively, it may extend only part of the way around, for example, in the case of a polygonal cushion, it may extend around all sides except one. In the case of a rectangular cushion, therefore, it might extend around three sides.  
         [0013]     Preferably, the cushion has a bead formed around its periphery, and the bead is located within the frame. The bead may be a rope encapsulated by the sheet material. The bead may be held by a keder edge within the frame.  
         [0014]     The frame may be manufactured from extruded aluminium which, in turn, may be fixed to a support structure. The frame preferably incorporates a device which releases the ETFE foil cushion from the frame in the event of fire so allowing the smoke to ventilate to atmosphere.  
         [0015]     For releasing the ETFE foil cushion from the frame two exemplary means may be employed, namely, mechanically releasing the cushion or cutting it free.  
         [0016]     In the case of mechanical release, this may be achieved by either extracting the rope from the bead which restrains the ETFE foil cushion in the frame, or by hinging a part of the frame so that it releases the keder edge. Preferably, therefore, the release mechanism comprises a device which removes the rope from the bead on demand, releasing the ETFE foil cushion from the frame. Suitable means for removing the rope include, by way of example, a mechanical winch, or ram, block and tackle. This can be done via a turning wheel. Alternatively, the release mechanism may comprise a hinged member engaging the cushion, the hinged member being movable on demand to a position in which it does not engage the cushion, thereby releasing the cushion from the frame.  
         [0017]     In the case of cutting the cushion free, preferably, the frame incorporates a cutting device which either physically cuts or melts the ETFE foil along the edge of the cushion. Preferably, therefore, the release mechanism comprises an electrical resistance cable which causes the edge of the cushion to melt on demand, releasing the ETFE foil cushion from the frame. Alternatively, the release mechanism may comprise a cutting blade adjacent to the perimeter frame, and a means for moving the cutting blade so that on demand, the blade moves, cutting the ETFE foil cushion, thereby releasing the ETFE foil cushion from the frame. The cutting blade can be situated either above or below the inflated cushion. Suitable means for moving the blade include a mechanical winch, ram or block and tackle.  
         [0018]     Whichever mechanism is used for releasing the ETFE foil cushion from the frame, on release from the frame, the ETFE cushion moves away from the frame so allowing the products of combustion or other noxious fumes to ventilate to atmosphere. On operation of the release mechanism on one or more sides, the ETFE foil cushion may form a cylindrical or spherical shape due to retention of pressurised air in the cushion; flap or fall away from one or more sides of the frame; or flap or fall away from all sides of the frame. In any event, the removal of the cushion from all or part of the frame will allow smoke or noxious fumes to ventilate from the building. It will also allow any excessive water or snow loads to be released.  
         [0019]     A better understanding of the objects, advantages, features, properties and relationships of the invention will be obtained from the following detailed description and accompanying drawings which set forth illustrative embodiments which are indicative of the various ways in which the principles of the system and method may be employed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     For a better understanding of the invention, reference may be had to preferred embodiments shown in the following drawings in which:  
         [0021]      FIG. 1  is a plan of an exemplary ETFE cushion constructed in accordance with the present invention;  
         [0022]      FIG. 2  is a cross section through the assembly of  FIG. 1 ;  
         [0023]      FIG. 3  is a detailed cross section of the perimeter cushion frame showing one embodiment of an exemplary release mechanism;  
         [0024]      FIG. 4  is a detailed cross section of an alternative perimeter cushion frame showing a variant of the first embodiment of release mechanism;  
         [0025]      FIG. 5  is a detailed cross section of the perimeter cushion frame showing a second embodiment of an exemplary release mechanism;  
         [0026]      FIG. 6  is a detailed cross section of the perimeter cushion frame showing a third embodiment of an exemplary release mechanism;  
         [0027]      FIG. 7  is a detailed cross section of a perimeter cushion frame showing a fourth embodiment of an exemplary release mechanism; and  
         [0028]      FIG. 8  is an elevation of  FIG. 7 . 
     
    
     DETAILED DESCRIPTION  
       [0029]     Turning now to the figures, where like reference numerals refer to like elements,  FIGS. 1 and 2  show an exemplary ETFE cushion constructed in accordance with the invention. The cushion  11  comprises three rectangular ETFE foil sheets  12 ,  13 ,  14 , a support frame  15  and a plenum  16 . The frame  15  is located about the perimeter of the sheets  12 ,  13 ,  14  and incorporates a release mechanism. The space between the sheets  12 ,  13 ,  14  is inflated with air via the plenum  16 .  
         [0030]      FIG. 3  shows a first embodiment of an exemplary release mechanism. The overall arrangement comprises a cushion  21 , a support frame  22  and a building structure  23 . The cushion  21  has a bead  24  at its perimeter made from a rope  25  encapsulated by an extended portion of the sheets  26 ,  27 ,  28 . Between the bead  24  and the inflated part of the cushion  21 , there is an edge support  29 . The bead  24  is captured within a keder edge  31 , made from aluminium.  
         [0031]     The frame  22  comprises a housing  32  and a cap  33 . The keder edge  31  is clipped into the housing  32  and the cap  33  is bolted into the housing  32  to form a weather-tight seal. The housing  32  is itself bolted to the structure  23 .  
         [0032]     The edge support  29  includes a cable  34 , preferably electrically resistant, extending around the perimeter of the cushion  21 , or at least around three sides. When required, current may be passed through the cable  34  for the purpose of raising its temperature to a level where the ETFE foil  26 ,  27 ,  28  or the support  29  fails and the cushion  21  is freed from the frame  22 .  
         [0033]     A further exemplary release mechanism is shown in  FIG. 4  which is similar to that of  FIG. 3 , but in this case, the bead  44  of the cushion  41  is located in a compressible gasket  42  made, for example, of EPDM which is itself swaged into a retaining channel  43  forming part of the frame  45 . Again, there is a resistance cable  46  in contact with the foil of the cushion  41  which causes the foil to fail when current is passed through the cable  46 .  
         [0034]     A still further exemplary release mechanism is shown in  FIG. 5 . Again, the cushion  51  is located within the frame  52  by means of a peripheral bead  53  including a rope  54 , the bead being captured by a keder edge  55  which is clipped into the frame housing  56 . However, in this embodiment, there need not be a resistance cable. Instead, the rope  54  may be wound round a pulley  57  and connected to a winch (not shown). Thus, when required, the rope  54  is drawn by a winch, and the bead  53  collapses. As a result, the cushion  51  is released.  
         [0035]     Yet another exemplary release mechanism is shown in  FIG. 6 . In this case, the cushion  61  is located within the frame  62  by means of a peripheral bead  63  captured by a keder edge  54  clipped into the frame housing  65 . However, in this embodiment, a blade  66  may be provided on a carriage  67  which is arranged to be rotatable and to travel along a track  68  around at least three sides of the periphery of the cushion  61 , when required, cutting through the cushion foils to free the cushion  61 . Although the blade  66  is shown located below the cushion it could equally well be above. In the illustrated example, the blade  66  is shown in its deployed position, cutting through the foils. It is to be understood that in its normal position, the blade  66  would not make contact with the foils. When required, the blade  66  would be swung into the deployed position and moved along the cushion  61 . There may be a separate blade  66  for each side of the cushion  61 .  
         [0036]     Still further examples of a release mechanism are illustrated in  FIGS. 7 and 8 . In this case the cushion  71  is located within the frame  72  by means of a peripheral bead  73  captured by a keder edge  74  clipped into the frame housing  75 . However, in this embodiment, the foils, between the bead  73  and the inflated part of the cushion  71  are supported on and held along each edge by a hinged member  76  forming part of the housing  75 . Each hinged member  76  is pivoted about an axle  77 . Each hinged member  76  is held in its normal position, engaging the foils, by a series of levers  78  which are pivotally connected to the frame  72  by pins  79 . The levers  78  are connected together by connecting rods  81  and one lever is connected to a pneumatic or hydraulic ram  82 . When it is desired to release the cushion  71 , the ram  82  associated with each side is operated. This draws the levers  78  towards the ram  82 , rotating them clockwise about the pins  79  to the positions shown in broken lines. This in turn allows the hinged member  79  to pivot downwards about the axle  77  to the positions shown in broken lines, so releasing the cushion  71  from the housing  75 .  
         [0037]     From the foregoing, it will be understood, when the cushion is released, smoke can be ventilated and/or any accumulated excess snow or water loads can be released.  
         [0038]     While various embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. For example, it is to be appreciated that the arrangements shown in  FIGS. 6 and 7  could be combined, to allow the cushion to be released downwards to the blade. It will also be appreciated that, as with the earlier embodiments, the release mechanism illustrated in  FIGS. 7 and 8  can act on three sides or all four sides of the cushion. Accordingly, it will be understood that the particular arrangements and procedures disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any equivalents thereof.

Summary:
A building component for forming a roof. The component includes an ETFE foil cushion comprising sheets of ETFE foil which are held in a frame about their periphery, and which are inflated. The frame includes a release mechanism for releasing the cushion from the frame, for example, in the event of a fire.