EP0152881B1

EP0152881B1 - Security door assembly

Info

Publication number: EP0152881B1
Application number: EP19850101347
Authority: EP
Inventors: Darryl William Bowden; David Simpson Firth
Original assignee: Chubb Security Projects Pty Ltd
Current assignee: Chubb Security Projects Pty Ltd
Priority date: 1984-02-11
Filing date: 1985-02-08
Publication date: 1988-08-31
Also published as: EP0152881A3; EP0152881A2; GB2154639B; AU3859985A; DE3564718D1; GB8503134D0; GB2154639A

Description

The present invention relates to security door assemblies and aims 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 door. Assemblies in accordance with the invention are intended especially for use in the protection of entrances to buildings or other fixed constructions which are liable to come under explosive attack at the hands of burglars or saboteurs for example.
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, flame-cutting equipment and other mechanical and thermal tools commonly 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 concents 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 with this aim in mind the invention proposes a security door assembly comprising: a door frame defining a doorway; an explosion- resistant door mounted to the frame to close the doorway; and means for fastening the door to the frame in the closed position; said door comprising a rearward portion providing a physical barrier between the two sides of the doorway; a forward portion spaced from the rearward portion and providing the exposed face of the door; and a layer of timber located between said forward and rearward portions arranged to protect said rearward portion from the effects of an explosive charge detonated at or near to said exposed surface; characterised in that said forward portion of the door is mounted by means which enable it to become detached from the remainder of the door structure under the influence of an outward force exerted upon it by the transmission into the door of the blast pressure of a said explosive charge, and said fastening means are arranged to enable the rearward portion of the door to remain fastened to the frame following detachment of the forward portion as aforesaid.
The purpose of the aforesaid timber layer in the door 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 door can be protected from the influence of an explosion occurring at or near to the exposed surface of the door, and retain its integrity as a physical barrier notwithstanding the partial destruction, detachment or breaching of the portions of the structure in front of it. The use of timber for shock resistance in a bomb shelter door is known eg from US-A-3093098.
In general, the forward portion of the door need comprise little more than an outer finishing layer, e.g. 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. As stated, this forward portion of the door is suitably mounted, such as by means of rivets, to facilitate its detachment from the remainder of the door structure under the influence of an outward force exerted on it by the transmission into the door of the blast pressure of an explosive charge detonated at or near to the exposed surface of the door. This detachment of the forward portion if it is breached by an explosion 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.
In assemblies according to the invention provided for thief-resisting applications, e.g. in bank vaults and the like, the aforesaid rearward portion of the door will be constructed with materials chosen for resistance to penetration by the different kinds of tools likely to be found in 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 doorway (presupposing that the forward and intermediate portions of the door might be breached by an explosive attack).
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 assembly made in accordance with the present invention;
Figure 3 is a front view of 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 assembly 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 for incorporation in a blast-resistant door assembly according to the invention.

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 2 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 concentration 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 5b may be disposed between front plate 2 and back plate 4 in substantially abutting relationship therewith
The door A 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 1 to 3 hereof and having the following characteristics: plate 2 was 3 mm thick mild steel; plate 4 was 10 mm thick mild steel; the frame sections 1 were 50 mm square, 2.5 mm wall thickness steel tube; the internal space between the plates 2 and 4 was 50 mm deep; and the timber layer 5 comprised 40 mm thick maranti boards. This specimen was mounted in a typical frame and a limpet mine having a charge of 0.95 kg 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 barrier 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 3 mm thick mild steel; plate 4 was 16 mm thick mild steel; the frame sections 1 were 75 mm square, 2.5 mm wall thickness steep tube; and the internal space between the plates 2 and 4 was 75 mm deep and filled with successive layers of pine and maranti boards 5a, 5b. This specimen was subject to the blast of a 2 kg 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 composed 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 273 mm; plate 11 was 3 mm thick mild steel; plate 12 was 20 mm thick mild steel; plate 15 was 10 mm thick mild steel; the timber layer 18 was composed of 40 mm thick maranti planks; and the kieselguhr layer 19 was 100 mm thick. The specimen was supported in a rig to simulate its mounting to the associated door frame and a 3.33 kg charge of type PE4 (cyclonite-based) plastic explosive (equivalent to about 5 kg 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.
Reference is made to EP-A-0152880 in which the claims relateto a security door with liquid filled receptacles, rather than a layer of timber, between the forward and rearward portions of the door.

Claims

1. A security door assembly comprising: a door frame (B) defining a doorway; an explosion- resistant door (A) mounted to the frame (B) to closethe doorway; and means (9) forfastening the door (A) to the frame (B) in the closed position; said door comprising a rearward portion (4, 1215) providing a physical barrier between the two sides of the doorway; a forward portion (2, 11) spaced from the rearward portion (4,12/15) and providing the exposed face of the door; and a layer of timber (5, 5a/5b, 18) located between said forward (2, 11) and rearward (4, 12/15) portions arranged to protect said rearward portion (4, 12/15) from the effects of an explosive charge detonated at or near to said exposed surface; characterised in that said forward portion (2, 11) of the door is mounted by means (3) which enable it to become detached from the remainder of the door structure underthe influence of an outward force exerted upon it by the transmission into the door of the blast pressure of said explosive charge, and said fastening means (9) are arranged to enable the rearward portion (4, 12/15) of the door to remain fastened to the frame (B) following detachmentoftheforward portion (2, 11) as aforesaid.

2. An assembly according to claim 1 wherein the door has an air space (6) within it defined between said forward portion (2) and said timber layer (5).

3. An assembly according to claim 1 or claim 2 wherein said forward portion of the door is constituted by a first steel plate (2), said rearward portion of the door 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).

4. An assembly according to any preceding claim wherein there is disposed in the door rearwardly of said timber layer (5, 5a/5b, 18) one or more layers of material resistant to penetration by non-explosive burglary tools.

5. An assembly according to any preceding claim wherein there is disposed in the door forwardly of said timber layer (18) a layer of fire- resistant material (19).

6. An assembly according to any preceding claim wherein the door comprises a forward compartment defined between a front plate (11) and an intermediate plate (12), and a rearward compartment defined between said intermediate plate (12) and a rear plate (15); said forward compartment containing said timber layer (18) and said rearward compartment housing said fastening means.