Security barrier structure

Abstract: A barrier structure for use e.g. in the walls and/or doors of safes, strongrooms and like penetration-resistant security enclosures comprises at least two layers of different materials selected for resistance to a combination of burglary tools, these being at least one layer of an elastomer material (7,10,13) reinforced with elements of hard material (8,11,14) and at least one layer of dense timber (3,6,9,12).

Description: The present invention relates to barrier structures for use e.g. in the walls and/or doors of safes, strongrooms and the like penetration-resistant security enclosures. More particularly, the invention is concerned with security barrier structures of which a constituent is an elastomer barrier material. Elastomers, and more especially polyurethane elastomers, have been proposed as a class of material useful for resisting burglarious attack upon safes and the like in GB-A-1427033 and GB-A-1513609, DE-A-3241526 and GB-A-2197362. The toughness and resilience of such materials make them difficult to penetrate using percussion-type tools, they have the tendency to clog and render ineffective the bits of abrasive tools, including the diamond drill, and they can render thermal attacks difficult particularly by the generation of thick and noxious fumes when burnt. Their natural vulnerability to edge-cutting tools can be overcome by incorporating the elastomer as the binding matrix in a composite barrier containing nuggets of an extremely hard materials such as sintered or fused alumina or zirconia. These barriers also have significant advantages in terms of weight and expense in comparison with more conventional metallic or concrete-based barrier structures of similar overall resistance values. In one aspect the invention seeks to enhance still further the security of elastomer-based barrier structures. That is to say it is possible, if equipped with breathing apparatus to overcome the effects of the attendant fumes, to soften the matrix of known elastomer barrier materials using an oxy-acetylene torch for example and thereafter to dig out a quantity of the barrier with a percussion tool. One aim of the invention, therefore, is to provide an elastomer security barrier structure with enhanced resistance to attack with this combination of tools, without sacrificing the weight and cost advantages of the elastomer barrier. Viewed from another perspective, it is known to construct low cost and lightweight demountable (modular) or prefabricated strongrooms from panels of which the security barrier comprises multiple layers of dense timber. With a sufficient density, this material has a surprising resistance to penetration with thermal tools, as well as useful resistance to axes and percussion tools. It is, however vulnerable to drills, saws and other mechanical cutting/abrasion tools, and another aim of the invention is to provide this kind of security barrier structure with enhanced resistance to attack with such tools, at reasonable cost and without a weight penalty. From NL-A-8501359 there is known an anti-explosives panel having five layers of different composition. From the outside to the inside of the panel these comprise a layer of reinforced concrete, a layer of a rubber-like material, a layer of wood-like material, a second layer of reinforced concrete and a layer of rubber. In such a construction resistance to drills and the like cutting/abrasion tools would be provided by the reinforced concrete layers. Reliance on that material, however, leads to an undesirably thick and heavy overall structure. Accordingly, the present invention resides in a security barrier structure comprising a plurality of layers of different materials selected for resistance to penetration by different burglary tools and arranged in the structure so as to be encountered successively in an attack from the outside of the structure, wherein at least one said layer comprises an elastomer material cast around elements of hard material and at least another said layer comprises dense timber. "Dense" in this respect implies a density of preferably no less than 0.6g/cm³, more preferably at least 0.85g/cm³, and most preferably no less than 1.25g/cm³, and the term "timber" is intended to embrace both natural wood and timber products such as the densified boards exemplified below. It has been found that the incorporation of a dense timber layer together with a reinforced elastomer layer in a structure according to the invention offers enhanced resistance to thermal attacks in comparison with a corresponding thickness of the reinforced elastomer alone, since dense timber is difficult to penetrate over a usefully wide area with tools such as the oxy-acetylene torch. This may be particularly so if the timber is backed with a layer of polyurethane or the like elastomer which will flare when the torch flame breaks through the timber layer and thus impedes widening of the breach in the timber by the torch. Furthermore, in tests it has been found that there is a quite dramatic increase in heat reflected back at the "operator" from an elastomer barrier incorporating a dense timber board in comparison with the elastomer barrier alone. In practical terms this may in particular mean that to conduct a torch attack on a barrier according to the invention a burglar will not only have to be equipped with protective clothing and breathing apparatus but will also need constant cooling with a water spray or the like. On the other hand, while the dense timber can be cut with drills and saws, resistance to the latter will be provided by the hard material in the reinforced elastomer layer. The combination of materials in a structure according to the invention therefore presents a formidable problem in terms of the resources required to achieve penetration over a useful area. At the same time, the incorporation of timber with the elastomer barrier, or vice versa , need not impose a significant weight or cost penalty in comparison with a respective prior art single-material barrier and in some embodiments may actually reduce the weight and cost of the overall structure. A preferred class of timber product for use in the invention takes the form of so-called "densified" or "converted" boards which comprise resin-impregnated, compressed ply boards such as those marketed under the trade mark DELIGNIT. Typical properties of such boards are a density of 1.4g/cm³, Brinell hardness of 160 N/mm², tensile strength of 125 N/mm², compressive strength of 270 N/mm² and bending strength of 170 N/mm². The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, Figures 1 and 2 of which are respective horizontal sections through the adjoining parts of two adjacent wall panels according to two embodiments of the invention for use in the construction of modular strongrooms. Referring to Figure 1, each illustrated panel comprises an inner steel plate 1 upon which are disposed, in order from the inner to the outer surface of the structure: an elastomer layer 2; a timber layer 3; an elastomer layer 4 incorporating an expanded steel mesh 5; a timber layer 6; a layer of elastomer 7 reinforced with hard nuggets 8; a timber layer 9; a layer of elastomer 10 reinforced with hard nuggets 11; a timber layer 12; and a layer of elastomer 13 the inner part of which is reinforced with hard nuggets 14 retained in a perforated metal cage 15 and the outer part of which is "straight" elastomer defining the exterior surface of the structure. The elastomer in the layers 2, 4, 7, 10 and 13 is typically a polyester-based polyurethane which in the cured state has a hardness in the range of 50-75° Shore D; an elongation in the range of 250-400%; a tensile strength in the range of 20-40 N/mm²; and a tear strength in the range of 60-110 kN/m. The nuggets 8, 11 and 14 may be of alumina, zirconia alumina ceramic or other hard and refractory material traditionally used for drill-resistance in security barriers, preferably with a hardness of at least 9 Mohs. The layers 3, 6, 9 and 12 are preferably composed of densified boards of which typical properties are given hereinbefore. The mesh 5 is provided to resist cutting into the inner timber layer 3 e.g. with a circular saw. In a typical panel structure with an overall thickness of 125mm, built on a plate 1 of 5mm thickness, the timber layers 3, 6, 9 and 12 may each be 15mm thick, the elastomer layers 2 and 4 may be 5 and 2mm thick respectively, the reinforced elastomer layers 7 and 10 may each be 13.5mm thick and the outer elastomer layer 13 may be 26mm thick overall, of which the nugget-reinforced thickness is 21mm. To construct a panel of the illustrated form, a sub-assembly of the four timber layers 3, 6, 9 and 12, together with the mesh 4 and cage 15, is first constructed, the boards forming these layers being screwed or bolted together with suitable spacers (not shown) to define spaces between them for the eventual elastomer layers 4, 7 and 10. This sub-assembly is then anchored by screws or studs (not shown) to the plate 1 and placed in a mould form which defines together with the plate 1 the overall profile of the finished panel including the illustrated stepped edge profile. The nuggets 8, 11 and 14 are placed between the layers 6 and 9, 9 and 12 and into the cage 15, and the mixed elastomer resin is then poured in to fill all the interstices remaining between the other components of the structure and the walls of the mould form, thereby forming the layers 2, 4, 7, 10 and 13 and bonding the whole structure together. The outer surface of the elastomer layer 13 can be moulded with a stippled or other decorative textured effect if desired. The grain in the layers 2, 6, 9 and 12 is preferably aligned alternately vertically and horizontally, in practice each timber layer being composed of a number of boards placed side by side (with vertical grain) or stacked one above the other (with horizontal grain). The presence of the intervening elastomer layers 4, 7, 10 and 12 will make the locations of the board edges very difficult to discover in an attack. The adjacent panels are connected together from the inside by rows of screws 16 passing through overlapping edges of the inner plates 1 and into welded-on tapping blocks (not shown). Turning to Figure 2, each illustrated panel comprises a fabrication in sheet steel defining stepped edge sections 20, 21 and a series of inner pans 23. The attached barrier structure comprises seven layers of timber 24-30 and an outer layer of elastomer 31 reinforced with hard nuggets 32. Pierced steel sheets 33-39 are disposed between each timber layer and between the outer timber layer and the reinforced elastomer layer. The timber, elastomer and hard nugget materials may be the same as those discussed above in relation to the Figure 1 embodiment. The exterior surface of the structure may be defined by "straight" elastomer with the nuggets 32 retained in a cage as described in relation to Figure 1 or, as illustrated in Fiqure 2, a steel finishing skin 40 may be applied. In a typical panel structure with an overall thickness of 175 mm, built between steel skins 23 and 31 of 2.5mm thickness, the timber layers 24-30 may each be 19mm thick, the reinforced elastomer layer 31/32 may be 25mm thick and the pierced steel sheets 33-39 may each be 1.75mm thick. To construct a panel of the form in Figure 2, the fabrication 20-23 is first made up, densified boards 24 forming the inner timber layer are fixed by screws 41 to the pans 23 with their grain running vertically, and the inner pierced steel sheet 33 is welded on to the edges of the pans. The next six timber layers 25-30 and pierced steel sheets 34-39 are built up successively onto this structure, being held together by numerous screw nails, the grain in the successive timber layers alternating between horizontal and vertical. The hard nuggets 32 are then placed in position with the outer finishing skin 40 welded on and the elastomer layer 31 is cast into this assembly, suitable filling and air-vent ports being provided for the purpose. The outer pierced steel layer 39 provides a good key to resist delamination of the elastomer 31, and the resin permeats between the edges of the boards in at least the outer timber layer 30. The adjacent panels are connected together from the inside by rows of screws 42 passing through the inner overlapping panel edges and into the timber layers 28-30 of the outer overlapping edges. Vertical steel channels 43 beneath the screw heads spread the clamping load and a snap-on trim 44 completes the assembly.

Claims: A security barrier structure comprising a plurality of layers of different materials (2-14;24-32) selected for resistance to penetration by different burglary tools and arranged in the structure so as to be encountered successively in an attack from the outside of the structure, whereby at least one said layer comprises an elastomer material (7,10,12;31) cast around elements of hard material (8,11,14;32) and at least another said layer comprises dense timber (3,6,9,12;24-30). A structure according to claim 1 comprising a said layer of elastomer material (7,10,13) cast around elements of hard material (8,11,14) disposed to the outer side of a said layer of dense timber (6,9,12), and a layer of elastomer material (4,7,10) disposed to the inner side of said layer of dense timber (6,9,12). A structure according to claim 1 comprising a plurality of said layers of dense timber (24-30) and a said layer of elastomer material (31) cast around elements of hard material (32) with the elastomer (32) thereof cast onto the outer side of said plurality of layers of dense timber (24-30). A structure according to claim 1 the outermost layer of which comprises a said elastomer material (13) the inner portion of which is cast around said elements of hard material (14) and the outer portion of which does not contain such elements (14) and defines the exterior surface of the structure. A structure according to claim 1 wherein the density of said timber (3,6,9,12;24-30) is at least 0.6g/cm³. A structure according to claim 1 wherein the density of said timber (3,6,9,12;24-30) is at least 0.85g/cm³. A structure according to claim 1 wherein the density of said timber (3,6,9,12;24-30) is at least 1.25g/cm³. A structure according to claim 1 wherein said elastomer material (4,7,10,13;31) has a hardness in the range of 50-75° Shore D and an elongation in the range of 250-400%. A structure according to claim 1 wherein said elastomer material (4,7,10,13;31) has a tensile strength in the range of 20-40 N/mm² and a tear strength in the range of 60-110 kN/m. A prefabricated strongroom constructed by assembling together a plurality of panels each comprising a security barrier structure as claimed in any preceding claim, the edges of adjacent panels being configured to provide overlapping barrier portions and adjacent panels being secured together by fastening means (16;42) applied from the inside of the assembly.

Inventors: SKELTON ANTHONY JOHN, SKELTON, ANTHONY JOHN
Applicants: CHUBB RESEARCH, CHUBB RESEARCH LIMITED
Application year: 1990
Main classification: E05G1
IPC codes: E05G1