GB2293208A - Fire resistant safe - Google Patents

Abstract

A fire resistant safe 10 comprises a base 11 and lid 12 enclosing a chamber 13 adapted to receive material such as magnetic media. The base 11 and lid 12 are formed of the same layered construction which comprises: a metal box 17 surrounded by an inner insulating layer 16 of foamed concrete, an intermediate layer 15 containing or constructed from a foamed material containing water which changes phase at a suitable temperature, and an outer insulating layer 14 of foamed concrete. The intermediate layer 15 may be encased in a thin impermeable skin 18 to prevent loss of water. An outer surface of the skin may contain vent holes 19 closed by plugs of material which fuse at about 100 DEG C to allow steam generated in the intermediate layer 15 to vent to the exterior of the safe 10. The outermost layer may be coated with intumescent paint. <IMAGE>

Description

FIRE SAFE This invention concerns a fire safe for the protection of documents, valuables, and especially magnetic media against the effects of fire.

A number of design features for fire safes constructed to resist the effects of fire are known. A vital features is a well insulated case, to provide a barrier against the heat reaching the contents, and a waterproof seal, to protect the contents against the ingress of the water or vapour from the likely dousing of the site by the Fire Brigade. The acceptable limits for magnetic computer media generally are regarded as being 53"C and 80% humidity. Furthermore, there are many national standards against which the performance of fire safes is measured, which usually include the requirement to withstand a drop from a considerable height onto a hard surface, a test intended to simulate the effect of the safe falling through the floor of a burning building.

For any given external size of safe with any given quality of insulation, the rise in temperature of the contents under any given external heat conditions depends on the thermal mass of the contents. The ratio of surface area to volume of any given shape becomes less advantageous (from this point of view) with smaller size.

These factors are reflected in existing designs of fire safe on the market which tend to be massive in physical size and weight. This adversely effects the ease with which they may be accommodated, and increases their cost.

Alternative constructions for fire safes have been suggested, generally concentrating on either the particular arrangement of insulating layers for the purpose of improving the ease of production; or on details of design to avoid heat leakage paths through the insulation (such as via the water seals or latch); or to provide extra heat absorption capacity, usually by the provision of some material which will change phase at a useful temperature. Of these the latter is by far the most useful and is instanced by several authorities. For example US Patent Number 5069358 to Avery describes a fire safe constructed from a particular configuration of shell-like components making up the case. The housing is constructed of a conducting material, against which is located in intimate contact a mass of low-melting point material.On exposure to heat as in a fire, the temperature of the housing will not exceed the melting temperature of the lowmelting point material until such time as a quantity of heat in excess of the total latent heat of fusion of the low-melting point material has been transmitted through the exterior layers of insulation. By virtue of the relatively high value of the latent heat of fusion as compared to the ordinary specific heat of the material, this construction affords a better result than would have been the case without the use of phase-change material. Avery also describes the use of a water-loaded outer layer to produce a similar effect, in this case utilising the latent heat of vaporisation.

Solid materials which melt at a usefully low temperature are comparatively expensive compared to water in the outer layer described by Avery. It therefore makes commercial sense to make the use of water-bearing layers in the performance of the fire safe. In this respect the constructions previously described have serious shortcomings.

In the tests used by standards authorities for the purpose of assessing the efficacy of fire safes and supposed to represent a typical real fire, a safe under test is exposed to external temperatures which, depending on the particular test specification, vary typically between 850 and 1500 Centigrade. Given that the absorption of heat by a body depends inter alia on the relative temperature difference between the bodies giving and receiving the heat, the construction of a fire safe which by design maintains its external temperature at the boiling point of water makes little sense. A safe of otherwise similar construction, but which was so arranged to permit the exterior surface to rise to a far higher temperature would, when measured against the criterion of ensuring a lower chamber temperature, perform better.

According to the present invention there is provided a fire safe for the protection of documents, valuables, and especially magnetic media against the effects of fire, comprising: a housing for the items to be protected, the housing having a suitable thermal mass; an inner insulating layer shrouding the housing; an intermediate layer shrouding the inner insulating layer and adapted to bear water or other material chosen to change phase at an appropriate temperature; and an outer insulating layer shrouding the intermediate layer.

According to a first preferred version of the present invention there is provided in contact with the housing a body of material which changes phase at a temperature below 53"C.

According to a second preferred version of the present invention or the first preferred version thereof there is provided at least one extra layer of conducting material shrouding the outer insulating layer.

According to a third preferred version of the present invention or any preceding preferred version thereof the intermediate layer is partitioned into at least two parts.

According to a fourth preferred version of the present invention or any preceding preferred version thereof wherein access to the chamber is by way of a lid regulated by a spring-loaded closure. Typically the lid is latched to the chamber by way of a remotely-operable latch.

According to a fifth preferred version of the present invention or any preceding preferred version thereof at least the outer most layer is coated with an intumescent paint.

According to a sixth preferred version of the present invention or any preceding preferred version thereof the safe is adapted for fitting into a filing cabinet, drawer or trolley and incorporates means for supporting the safe within the cabinet, drawer or trolley.

The thermal mass of the housing can be taken to be the actual mass of the layer multiplied by its specific heat, or it can include an allowance for the thermal mass of the contents. It can also take into account the effect of any phase-change material that may be present.

The layers as described may be physically discrete layers made perhaps of different materials or by different production processes or stages, or they may be distinguishable only by their performance according to the description above.

In certain circumstances it may be advantageous for there to be an additional layer or layers in the construction, of conductive material, located outside any of the outer three layers already described (the housing already being conductive). This will depend primarily as to whether one small point or area on the safe surface is expected to be exposed to a concentrated heat source, or whether the whole safe is to be exposed to a widespread high temperature, and the particular shape of the safe.For example, if the safe is of spherical form (that is the shape whose surface area to volume ratio is the least for any volume) then providing a conductive layer between the inner and intermediate layers, or the intermediate and outer layers as described above would have the effect of making best use of a phase-change material provided in the intermediate layer in countering the effects of a localised heat source. If the overall shape of the safe were a flat rectangular block, in which the surface area to volume ratio were comparatively much greater, then an interposed conductive layer would possibly reduce the performance against a localised heat source, because this extra conductive layer would cause the insulating inner layer to be exposed to that temperature over its entire surface.

Consequently the effect and therefore desirability of such an extra layer depends on the particular conditions expected, and the calculated effect on the particular shape chosen. It may be advantageous that the intermediate phase-change layer is partitioned into two or more parts, so avoiding an uninterrupted path for the conduction of heat through the layer. The purpose of any such arrangement is directed to minimising total heat flow in to the inner layer under the expected service conditions.

Considerable care needs to be exercised in the detail of design of the safe to ensure that there are no short heat paths from the exterior to the innermost layer which will act to 'by-pass' the insulated layers provided in the constructions. In particular a latch, serving to hold closed an access panel of the housing (since this is of conducting material, needs to be operable from outside, and therefore presents a heat path from the outside of the safe through the layers of insulation.

To obviate this danger, the lid may sprung closed preferably by an 'over-centre' mechanism. Further a latch on the housing may be operated by remote means, for example by a magnet, from outside.

To provide a further level of protection against the effects of heat and especially from moisture, the safe may be finished in an intumescent paint, which when exposed to heat expands to provide a further layer of insulating material, and also will tend to close any gaps in the moisture seal of the safe.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing of which the sole figure is a cross section of a fire safe.

Fire safe 10 consists of a base 11 and lid 12 enclosing a plenum chamber 13 adopted to receive material to be protected such as magnetic media. Base 11 and lid 12 are of similar layered construction in which the outer layer 14 is of a heat resistant and heat insulating material, for example foamed cement. Intermediate layer 15 contains or is constructed of a phase change material which changes phase at an appropriate temperature, for example a foamed material containing water. Inner layer 16 is another heat insulating layer material, perhaps but not necessarily identical in composition to the outer layer 14. The innermost housing 13 is made of a conductive and physically strong material with a substantial thermal capacity. Typically it will be a metal box.

Intermediate layer 15 is completely encased in a thin impermeable skin 18 which prevents the loss of the water contained in layer 15. In suitable locations in skin 18 there is provided a series of vent holes 19 closed by plugs of material which fuse at or around 100"C. The locations of the vent holes 19 are chosen to allow any steam generated in layer 15 to vent to the exterior of the safe. The lid 12 is hinged to the base 11 along one long edge on the inner layer 17 by conventional means (not shown). A latch L is provided to close or maintain closed the lid 12 to the base (not shown). At interface 10 between base 11 and lid 12 is provided a moisture seal (which may be a single, multiple, labyrinth or other known type, not shown) which prevents the ingress of either steam or other phase-change vapour issuing from the vent holes 19, or externally applied water, in the event of a fire.

The dimensions of the fire safe are chosen and external hooks 21 located on opposite sides of the base 11 to allow the safe to hang on the hanging rails of a filing cabinet or drawer. This enables the safe to be readily located in a working office in a position most likely to encourage its routine use.

Claims (9)

1 A fire safe for the protection of documents, valuables, and especially magnetic media against the effects of fire, comprising: a housing for the items to be protected, the housing having a suitable thermal mass; an inner insulating layer shrouding the housing; an intermediate layer shrouding the inner insulating layer and adapted to bear water or other material chosen to change phase at an appropriate temperature; and an outer insulating layer shrouding the intermediate layer.

2 A safe as claimed in Claim 1 in which there is in contact with the housing a body of material which changes phase at a temperature below 53"C.

3 A safe as claimed in any preceding claim, in which there is at least one extra layer of conducting material shrouding the outer insulating layer.

4 A safe as claimed in any preceding claim, in which the intermediate layer is partitioned into at least two parts.

5 A safe as claimed in any preceding claim, in which access to the chamber is by way of a lid regulated by a spring-loaded closure.

6 A safe as claimed in any preceding claim, in which the lid is latched to the chamber by way of a remotely-operable latch.

7 A safe, as claimed in any preceding claim, having at least the outer most layer is coated with an intumescent paint.

8 A safe as claimed in any preceding claim, in which the dimensions are chosen to fit into a filing cabinet, drawer or trolley and means are provided for supporting the safe within the cabinet, drawer or trolley.

9 A fire safe substantially as described herein with reference to the accompanying drawing.