SECURITY DOOR ASSEMBLY

Abstract: A barrier structure particularly for use in protective doors designed to resist explosive charges applied to their outer surfaces, comprises a layer of timber 5 located be­ tween the outer and inner door plates 2 and 4. The purpose of the timber is to absorb the shock and thermal energy of an explosion occurring at or near the outer plate 2 and thus shield the rearward portion 4 of the structure from the da­ maging effects of the blast. Preferably the outer plate 2 is readily detachable from the remainder of the structure un­ der the action of blast pressure transmitted to the interior of the structure, thereby permitting rapid dissipation of the blast and avoiding a concentration of pressure over a small area of the timber 5.

Description: Security Barrier Structure The present invention relates to security barrier structures and alms in particular to provide a structure having a high degree of resistance to penetration by the action of explosive charges applied to the outer surface of the structure. Barriers in accordance with the invention are intended especially for use in the construction of doors for buildings or other structures which are liable to come under explosive attack at the bands of burglars or saboteurs for example, although they may also find utilisation in the walls or other fixed boundaries of such structures. The prior art provides many barrier structures intended for use in, for example, the doors of bank vaults and the like security enclosures, which are designed to provide a high degree of resistance to penetration with drills, punches, fl##e-cuttiflg equipment and other mechanical and thermal tools coZmonly appropriated by burglars. Generally speaking, however, the materials and modes of construction employed in these structures are not well suited to resist the effects of high-explosive surface charges of even modest proportions. It is to the provision of structures providing protection from this kind of attack that the invention is principally directed, it being recognised that there is currently a demand for the protection of various kinds of building from explosive attacks which may be mounted not with burglarious intent but with the aim simply of causing damage to the structure and its contents or occupants. Any such structure clearly must be designed to withstand the physical shock of the blast. Furthermore, we believe that another significant factor contrIbutIng to the potential damage of a structure when an explosive charge is detonated at or near its surface is the near-instantaneous release of thermal energy in the explosion, which is not only per se destructive to material within its Influence but also exacerbates the blast pressure effects. Consequently, we believe that successfully to resist attacks of the nature indicated above a structure should be designed to withstand both the mechanical and thermal effects of an explosion, and one material which we have found to be of utility in such a structure both from the point of view of shock absorption and resistance to the transmission of heat is timber. Accordingly the present invention proposes an explosion-resistant barrier structure comprising a rearward portion adapted to provide a physical barrier between the two sides of the structure; a forward portion spaced- from the rearward portion and providing the exposed face of the structure; and a layer of timber located between said forward and rearward portions and adapted to protect said rearward portion from the effects of an explosive charge detonated at or near to said exposed surface. The purpose of the aforesaid timber layer is to act as a shock absorber to protect the structure behind it from blast effects and also as a thermal insulator to reduce the transmission of heat to the structure behind it, so that the rearward portion of the structure can be protected from the influence of an explosion occuring at or near to the exposed surface of the structure, and retain its integrity as a physical barrier notwithstanding the partial destruction or breaching of the portions of the structure in front of it. In structures according to the invention provided for thiefresisting applications, eg in bank vaults and the like, the aforesaid rearward portion of the structure will be constructed with materials chosen for resistance to penetration by the different kinds of tools likely to be found in the thieves' armoury. However, this is not an essential feature-of the invention and in other applications, where a high degree of resistance to attack with tools other than explosives is not necessarily required, the rearward portion may be of relatively simple construction sufficient for the purpose of providing a chosen degree of separation between the two sides of the structure (presupposing that the forward and intermediate portions might be breached by an explosive attack). In general, the forward portion of the structure need comprise little more than an outer finishing layer of the structure, eg a steel sheet, although in some embodiments this area of the structure may be developed to still further enhance resistance to explosive attacks or for other special purposes. It is desirable for this forward portion to he suitably mounted, such as by means of rivets, to enable it to become detached from the remainder of the structure relatively easily under the influence of an outward force exerted on the forward portion. With this arrangement, the forward portion may become detached under the influence of the blast pressure transmitted to the interior of the structure if the forward portion is breached by an explosion at or near its exposed surface. This detachment of the forward portion serves to dissipate the effects of the explosion and to allow the blast to be spread over a larger area of the timber layer than might be the case if the forward portion remained rigidly secured to the rest of the structure. The timber layer is therefore protected from a concentration of the blast in a relatively small area and may thus be better able to absorb its effects. The invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figures 1 and 2 are respectively horizontal and vertical sections through one embodiment of a blast-resistant door made in accordance with the present invention; Figure 3 is a front view on the outer face of the door of Figures 1 and 2; Figure 4 is a vertical section through another embodiment of a blast-resistant door made in accordance with the invention; and Figures 5 and 6 are respectively horizontal and vertical sections through a further embodiment of a barrier structure according to the invention for incorporation in a blastresistant door. Referring first to Figures 1 to 3, the door A comprises an internal frame 1 fabricated from tubular steel sections. Steel front plate 2 is mounted on frame 1 on one side thereof by means of rivets 3 in a manner to permit front plate 2 to become detached relatively easily from frame 1 by outward force exerted in the direction of arrow X on the inner surface 2a of front plate 2. Front plate 2 provides the outer, exposed face of the door. Steel back plate 4 is welded to frame 1 on the side opposite to front plate 2 to-provide a compartment between front plate 2 and back plate 4. A layer of timber 5 is disposed in this compartment between front plate 2 and back plate 4. It will be seen that front plate 2 is stood-off some distance from the intermediate layer of timber 5 to provide an air space 6 between front plate 2 and the timber 5. If the front plate 2 is penetrated when an explosive charge is detonated at or near its outer face, the blast pressure effects resulting from the explosion are dispersed in air space 6 over a large area of the timber layer 5, thereby to avoid or minimise a oncentration of pressure on a relatively small area of the timber. If a sufficient pressure force is exerted on the inner face of front plate 2 in the direction of arrow X in Figures 1 and 2, the rivets 3 will give to permit front plate 2 to be blown off the frame 1, thereby further to dissipate the blast and minimise its destructive effect on the timber layer 5. Timber layer 5 confers resistance to an explosive attack upon the door by acting to absorb physical shock and to reduce the transmission of heat through the door to the steel back plate 4 behind it. It is not essential to provide an air space 6 between front plate 2 and intermediate timber layer 5. As shown in Figure 4, two superimposed layers of timber 5a and Sb may be disposed between front plate 2 and back plate 4 in substantially abutting relationship therewith. The door A is hinged at 7 to an associated door frame B and can be provided with a suitable fastening mechanism comprising, for example, bolts (not shown) to be thrown into the frame B through the opening side edge of the door in response to manipulation of an external handle 8, together with fixed stud bolts 9 on the hinge side edge of the door. To demonstrate the efficacy of the above-described structures the following tests were conducted. A test door was constructed generally in accordance with Figures l to 3 hereof and having the following characteristics: plate 2 was 3mm thick mild steel; plate 4 was lAmm thick mild steel; the frame sections 1 were 50mm square, 2.5mm wall thickness steel tube; the internal space between the plates 2 and 4 was 50mm deep; and the timber layer 5 comprised 4amen thick maranti boards. This specimen was mounted in a typical frame and a limpet mine having a charge of 0.95kg of Tritanol explosive was applied to the surface of plate 2. When the charge was detonated the plate 2 was blown off and the timber 5 fell out, but the plate 4 attached to sections 1 remained intact and bolted to its frame, with some plastic deformation, so that the brrier as a whole was not breached. A similar test was performed with a door constructed generally in accordance with Figure 4 and where: plate 2 was 3mm thick mild steel; plate 4 was 16mm thick mild steel; the frame sections 1 were 75mm square, 2.5mum wall thickness steel tube; and the internal space between the plates 2 and 4 was 75mm deep and filled with successive layers of pine and maranti boards 5a,5b. This specimen was subject to the blast of a 2kg charge of TNT applied to the surface of plate 2 and the results were as in the previously described test, although somewhat less severe. Equivalent test specimens have also been found effectively to withstand high-velocity rifle fire from AK47 (Soviet), R1 (South African, equivalent to NATO G3) and R4 (South African) weapons. Turning now to Figures 5 and 6, these show a barrier structure for incorporation into a blast-resistant door which may withstand rather heavier charges than those of Figures 1 to 4 and which, in the illustrated embodiment, is designed also to be fire resistant. In this case, the barrier comprises essentially a double box-like structure. One "box" is composed of a steel plate 11 - which provides the outer face of the structure - attached to an intermediate steel plate 12 via framing sections 13, and stiffened by horizontal angles 14. The other "box" is compsed of a steel back plate 15 welded to the plate 12 via framing sections 16 and horizontal stringers 17. Within the first of these compartments there is a layer of timber 18 fronted by a layer of kieselguhr (diatomaceous earth) 19. In the completed door structure the rearward compartment between plates 12 and 15 will house a driving and locking mechanism (not shown) to throw door bolts into an associated frame, or alternatively the door may be locked by bolts thrown into engagement with sockets in the door (at the positions indicated at 20 in Figure 1) from a mechanism housed in the associated frame. The purpose of the timber layer 8 in this structure is, as before, to confer resistance to an explosive attack upon the door by acting to absorb physical shock and to reduce the transmission of heat through the door to the steel behind it. To demonstrate the efficacy of this type of structure the following test was conducted. A test specimen was constructed substantially in accordance with Figures 5 and 6 hereof and having the following characteristics: the overall thickness of the structure was 273mum, plate 11 was 3mm thick mild steel; plate 12 was 20mm thick mild steel; plate 15 was 10mm thick mild steel; the timber layer 18 was composed of 40mm thick maranti planks; and the kieselguhr layer 19 was 100mum thick. The specimen was supported in a rig to simulate its mounting to the associated door frame and a 3.33kg charge of type PE4 (cyclonite-based) plastic explosive (equivalent to about 5kg of dynamite) was applied to the surface of plate 11. When the charge was detonated the plate 11 was destroyed but both plates 12 and 15 remained intact and bolted to the frame, with some plastic deformation, so that the barrier as a whole was not breached. The timber 18 around the immediate area of the explosion was disintegrated as was the kieselguhr layer 19, but the steel plate 12 immediately behind this area of damage was only warm to the touch after the blast. In this particular example the kieselguhr layer 19 is provided to confer general fire resistance to the structure, and is not thought to make a significant contribution to blast resistance of itself. By replacing the layer 19 in this structure with further timber, therefore, resistance to even heavier charges of explosive may be obtained.

Claims: CLAIMS 1. An explosion-resistant barrier structure comprising a rearward portion (4, 12/15) adapted to provide a physical barrier between the two sides of the structure; and a forward portion (2,11) spaced from the rearward portion (4, 12/15) and providing the exposed face of the structure; characterised by a layer of timber (5, 5a/5b, 18) located between said forward (2,11) and rearward (4, 12/15) portions and adapted to protect said rearward portion (4, 12/15) from the effects of an explosive charge detonated at or near to said exposed surface. 2. A structure according to claim 1 having an air space (6) within it defined between said forward portion (2) and said timber layer (5). 3. A structure according to claim 1 or claim 2 wherein said forward portion (2,11) is mounted such as to enable it to become detached from the remainder of the structure (1/4, 13/12/16/17/15) relatively easily under the influence of an outward force (X) exerted upon said forward portion (2). 4. A structure according to any preceding claim wherein said forward portion is constituted by a first steel plate (2), said rearward portion is constituted by a second steel plate (4), and said first (2) and second (4) steel plates are interconnected peripherally by an internal steel frame (1). 5 A structure according to any preceding claim wherein there is disposed rearwardly of said timber layer (5, 5a/5b, 18) one or more layers of material resistant to penetration by non-explosive burglary tools. 6. A structure according to any preceding claim wherein there is disposed forwardly of said timber layer (18) a layer of fire-resistant material (19). 7. A structure according to any preceding claim in the form of an explosion-resistant door comprising a forward compartment defined between a front plate (11) and an intermediate plate (12) of the structure, and a rearward compartment defined between said intermediate plate (12) and a rear plate (15) of the structure; said forward compartment containing said timber layer (18) and said rearward compartment housing mechanism for fastening the door to an associated frame. 8. An assembly comprising a structure according to any preceding claim in the form of an explosion-resistant door (A), a frame (B) to which said door is hinged (7); and means (8,9) for fastening the door to the frame whereby said rearward portion (4, 12/15) of the door can remain fastened to the frame in the absence of said forward portion (2,11) of the door.

Inventors: BOWDEN, DARRYL WILLIAM, FIRTH, DAVID SIMPSON
Applicants: CHUBB SECURITY PROJECTS (PTY) LIMITED
Application year: 1985
Main classification: E06B5
IPC codes: E05G1, E06B5