A collapsible-expandable lattice structure is described comprising a plurality of slats arranged in two panels. Each panel consists of first and second sets of parallel slats, the first set being arranged over and intersecting relative to the second set. Means is provided pivotally connecting slats of the first set to slats of the second set to form parallelogram linkages, the slats of one panel being located intermediate slats of the other panel, the first and second sets of one panel being parallel relative to the first and second sets of the other panel, respectively. Means is further provided for pivotally interconnecting slats of one panel to slats of the other to maintain a fixed pivotal relationship between slats of both panels.
A safety unit (11) in the form of a network or mesh for location across an opening to receive and restrain an object falling into the opening. The network or mesh is a trellis (12) comprising: a first array (13) of parallel rigid members (13A); a second array (14) of parallel rigid members (14A); and pivoting mechanism whereby each member (13A) of the first array (13) is pivotably attached to at least some of the members (14A) of the second array (14) so that the first and second array can be pivoted relative to one another between a first housed, configuration wherein the difference between the width (W') of the trellis (12) and the length (L') of the trellis (12) tends to a maximum; and a second, opened, configuration wherein the difference between the width (W) of the trellis (12) and the length (L) of the trellis (12) tends to a minimum. The trellis (12) is adapted for horizontal location in at least its opened configuration in a zone into or through which falling objects tend to pass by being supported at or near the periphery of the trellis (12) so as to restain falling objects contacting the trellis (12) in a region lying within the periphery.
