13 14 and incorporates a release mechanism the space between the sheets 12 13 14 is inflated with air via the plenum 16 0030 fig3 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 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 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 a further exemplary release mechanism is shown in fig4 which is similar to that of fig3 but in this case the bead 44 of the cushion 41 is located in a compressible gasket 42 made for example of.