Safes And Similar Security Structures

Abstract

A slab or panel for use in a safe or similar structure comprises a layer of material resistant to drilling and other forms of mechanical attack backed by a layer of material, preferably graphite, which melts and vaporizes but does not substantially react exothermically with oxygen at the temperatures generated by a thermic lance, i.e., of the order of 3,000.degree. C. The melting and vaporization involves the provision of such large amounts of latent heat thus taking several times as long to burn a hole through the slab. The material for resisting mechanical attack preferably comprises nuggets of heard material in a ductile metal matrix and a convenient form of construction there is a single layer of this material and a single layer of the vaporizable material. The vaporizable material is preferably in the form of blocks of triangular section fitted into compartments defined by metallic spacing members supported between a pair of steel plates.

Description

This invention relates to safes and similar security structures such as strong rooms and is particularly concerned with a construction of slab or panel for use either in the doors or walls of such structures. With the continued improvement in safe-breaking equipment it is necessary that corresponding improvements should be made in the structures themselves. One of the developments in this field is the thermic lance which is capable of developing very high temperatures of the order of 3,000.degree. C. associated with a high level of heat output in a readily controllable form. Such a device is capable of burning through any known material but the resultant hole is relatively small and it is necessary to burn a ring of such holes before it is possible to lift out a sufficient portion of a door or wall to gain access to the interior of a safe or the structure. If sufficient time and equipment is available there is no known form of structure which can entirely resist the action of such a device.

According to the present invention a slab or panel for use in a safe or similar structure comprises a layer of drill-resisting material which is backed by a layer of material which melts and vaporizes but does not react substantially exothermically with oxygen at the high temperatures involved of the order of 3,000.degree. C. as mentioned above. The outer layer provides the resistance to mechanical attack, which is not necessarily by drilling, but may be by punching, for example. The term " drill-resisting" is used for convenience to indicate resistance to any form of mechanical attack. The effect of the nature of the layer of backing material is that, in the oxygen-rich environment provided by a thermic lance, the material does not readily burn out but as just mentioned merely melts and vaporizes. This melting and vaporization involves the provision of such large amounts of latent heat that the operating temperature of the device is maintained only at the expense of increased consumption of lance and oxygen. The material is, of course, gradually removed in either a molten or vapor state and a hole will eventually be made right through the slab or panel, but it is found that this takes several times as long as it does to make a hole through a similar thickness of material at present used for such a slab or panel. The speed at which the material is removed is found to depend on a number of parameters including thermal conductivity, specific heat, latent heat of fusion and of vaporization, melting point and resistance to thermal shock.

Depending on the particular duty involved and costs consistent with this duty it is possible to calculate the necessary properties of the ideal material on the basis of these factors. In practice the material which best meets the majority of operating requirements is graphite but depending on the circumstances other materials such as tantalum, titanium or zirconium or compounds or mixtures of these elements or of the ores in which they naturally occur, having physical properties appropriate to the degree of resistance desired, may be used.

The layer of drill-resisting material is preferably in the form of nuggets of hard material embedded in a ductile metal matrix, e.g., nuggets of aloxite in a copper matrix. This layer provides the external protection against mechanical attack but offers little resistance to the action of a thermic lance. A hole can therefore be burnt in this outer layer comparatively rapidly but as soon as the hole extends as far as the backing layer the penetration is slowed down to a major extent for the reasons already described. The layer of drill-resisting material is, however, essential so as to protect the front face of the slab or panel from mechanical attack. Most simply a single layer of this drill-resisting material is backed by a single layer of vaporizable material and such a construction is found to be adequate for the majority of applications. Under some circumstances, however, for example, strong room doors of a greater than usual thickness more than one double layer may be provided with advantage. For example the double layer of drill-resisting material and vaporizing material may merely be duplicated and indeed any required number of such double layers may be provided. Alternatively intermediate layers of other materials may also be included, the only overriding requirement being that the face which is intended to define the front of the slab or panel is made of a layer of drill-resisting material while at some spacing to the rear of this is at least one layer of vaporizing material.

In a particular construction it may take 10 or 12 times as long to pierce a hole through the slab. This not only needs a correspondingly greater number of thermic lances together with associated equipment such as oxygen cylinders all of which is difficult to transport to the site, but the time required for the operation as a whole, i.e., the burning of a sufficient number of holes to obtain access to the interior of the safe is extended to such an extent that in the majority of cases it may well be unacceptable. In other words, although it is still possible eventually to gain access to the interior of the safe the time required is so much longer that in the majority of cases the operation as a whole becomes impracticable.

Particularly when graphite is used as the vaporizable material it is convenient for it to be fitted in the form of blocks which may be fabricated by sintering, fusing, casting and so forth. By making these blocks of a regular cross section they may be fitted together so as to form a virtually continuous layer with relatively small airspaces. For this purpose the individual blocks may be fitted into compartments at least partly defined by metal spacing members. The most convenient cross section for this purpose is triangular in which case the spacing members may be inclined to a plane perpendicular to the surface of the layer of the material. This enables the spacing members to perform a secondary function in impeding the burning of a hole through the layer. Since the spacing members are inclined to the direction of a hole which is burnt the heat impinging on a spacing member as soon as the graphite has been removed to a sufficient extent, tends to be conducted away by the spacing member, and owing the the inclination of the latter the direction of the hole itself tends to be correspondingly diverted. As a result the hole is forced to penetrate a greater thickness of graphite and moreover the fact that successive holes do not extend directly through the thickness of the slab makes it more difficult to obtain the necessary accuracy to remove a complete section of the complex construction of slab. For this reason it is generally necessary to burn a larger number of holes than would otherwise be necessary before the section as a whole can be removed and this makes the operation as a whole take even longer and entails the consumption of larger quantities of lance and oxygen.

A construction of complex slab or panel in accordance with the invention will now be described in more detail with reference to the accompanying drawings in which:

FIG. 1 is a cross-sectional view, and,

FIG. 2 is a perspective view to a reduced scale illustrating the manner of assembly.

The composite slab shown in the drawings comprises only a single layer of drill-resisting material and a single layer of vaporizable material. This is found to be adequate for a large number of general applications but as already described it may be desirable to provide a multilayer construction comprising a number of the double layer units shown in FIG. 1 or alternatively a combination of the individual layers shown in FIG. 1 with layers of other material. In FIG. 1 a layer of drill-resisting material is indicated generally as 1 while a layer of vaporizable material, graphite in this particular example, is shown as 2. The two layers are separated by a gap 3 which in the example shown is left empty to form an airspace. It is, however, possible to fill this gap with some other material to form the kind of multilayer construction referred to above.

Turning now to the details of the construction the layer 1 comprises a central portion 4 consisting of nuggets of aloxite in a copper matrix. The size of the nuggets is not critical but in a particular example in which the thickness of the copper matrix is approximately an inch and a half the average size of the nuggets may be approximately half an inch. The central portion 4 is bonded to a mild steel plate 5 by angle brackets 6 extending from the surface of the plate. On the front side of the layer 4 is a further mild steel plate 8 which is supported by sideplates 9 and 10 so that there is a narrow airgap between the plate 8 and the layer 4. The components 4, 5 and 8 together make up a composite drill-resisting layer.

The layer 2 is made up of blocks 12 of graphite of triangular section as shown, which are preformed and individually inserted into compartments defined by spacing members 13 and by front and backplates 14 and 15. Apart from the two blocks at the ends of the section the remaining blocks are all in the form of isosceles right-angled triangles so that the angles at the base of each triangle are 45.degree. and the spacing members 13 extend at 45.degree. to the plane perpendicular to the surface of the layer. During assembly the spacing members 13, which may be for example of mild steel or copper, are first welded to the plate 14 as shown by the welds 18. The plate 15 is then fitted subsequently and is secured to the apices of the triangles defined by the spacing members 13 by welds 19 made through corresponding holes in the plate 15. The preformed blocks of graphite are then inserted in the compartments thus defined, being slid in from one end as illustrated in FIG. 2. One end plate, not seen in the drawings, is first welded in position at the bottom as seen in FIG. 2, after which the blocks 12 are slid into position and the upper end plate 20 is fitted in position, being held by means of welds made through holes 21 connecting with the plate 5.

If the construction shown in FIG. 1 is acted on by a thermic lance the layer 1 is penetrated relatively easily. The gap 3 is then encountered and this allows the heat to spread laterally thus reducing the concentration of heat on the layer 2. The graphite will, however, eventually be heated to a temperature at which it melts and vaporizes but owing to the fact that it does not react exothermally with the oxygen present it does not readily burn and therefore is effectively removed only by the melting and vaporizing which as previously mentioned involves the provision of large amounts of latent heat. When the hole eventually reaches one of the spacing members 13 the spacing member tends to conduct the heat away so that the hole tends to deflect in the general direction of the spacing member, i.e., at an angle of about 45.degree.. This causes the hole to penetrate a greater thickness of graphite so that a further large quantity of latent heat has to be provided. Eventually, however, the hole will penetrate right through the composite slab.

A single hole will not, of course, be sufficient for purposes of access and it is necessary to burn a number of holes before the section as a whole can be removed. Owing to the devious and unpredictable courses of individual holes a considerably larger number is required than would otherwise be necessary. Difficulty of access is further increased by appropriate spacing of the welding points 18 of the spacing members 13 and it is found that the optimum distance between adjacent points 18 is approximately eight inches. This figure is independent of the other dimensions and is arrived at since it ensures that even when sufficient holes have been pierced to span the width of a complete block 12 and material in this region has been removed there is still not sufficient space for the entry of a tool to work further on the spacing members, particularly in view of the need to approach them via a suitable hole in the outer layer of drill-resisting material 1. Any spacing appreciable less than eight inches might enable complete section to be cut out more easily and an appreciably wider spacing might accommodate a handhole entirely within the width of one block. For this combination of reasons a spacing of eight inches is the optimum value.

Claims

We claim:

1. A safe having at least one wall including a slab comprising a continuous face layer, said face layer being of drill-resisting material and comprising nuggets having at least the hardness of fused alumina embedded in a ductile metal matrix, a backing layer of material which melts and vaporizes but does not substantially react exothermically with oxygen at temperatures of the order of 3,000.degree. C., and means additional to said face layer for supporting said backing layer behind said face layer.

2. A slab according to claim 1, comprising a single layer of drill-resisting material and a single layer of vaporizable material.

3. A slab according to claim 1 in which said vaporizable material is graphite.

4. A slab according to claim 1 in which said face layer comprises a ductile metal matrix and nuggets of hard material in said metal matrix.

5. A safe having at least one wall including a slab comprising a continuous face layer, said face layer being of drill-resisting material, and a backing layer, said backing layer including metallic spacing members defining at least in part a plurality of compartments of regular cross section, and a plurality of bars of a material which melts and vaporizes but does not substantially react exothermically with oxygen at temperatures of the order of 3,000.degree. C., said bars being of corresponding cross section to said compartments and being located in said compartments.

6. A slab according to claim 5, in which said blocks are of triangular cross section and said spacing members are inclined to a plane perpendicular to the surface of said backing layer.

7. A slab according to claim 6, including a pair of steel plates forming the outer sides of said compartments, said spacing members being supported by said plates.

8. A slab according to claim 7 in which said spacing members are secured to said steel plates at a spacing of approximately eight inches.