GB2161655A - Protector means for a cable - Google Patents

Abstract

A protector means 21, (24) for a service such as an electrical cable 12 passing through a fire barrier 11 incorporates both a good heat conductor and radiator such as aluminium or copper foil 23 or mesh (25, Fig. 3), and an insulating material such as mineral wool 22 or intumescent paint. The combination of insulating and heat conducting material enables heat to be dissipated from the service 12 without the surface temperature exceeding a predetermined value in the event of a fire. A penetration assembly 10 incorporating a silicone RTV foam sealant 19 and a frame of glass fibre reinforced cement 17 is also described in combination with the protector means. The insulating material can also be gypsum, vermiculite or perlite. <IMAGE>

Description

SPECIFICATION Protector means for a cable This invention relates to a protector means for a service such as an electrical cable passing through a penetration hole of a fire barrier.

Fire barriers may be found in many industrial and commercial buildings, particularly in power stations, factories, telecommunications establishments, oil refineries and chemical plant, and on ships and off-shore installations for example oil or gas platforms.

Cables and other services pass through penetrations in the fire barrier and are sealed in position.

Hitherto, it has been extremely difficult to do this in a satisfactory way which will prevent fire and hot gases breaking through the barrier at the penetration hole.

In particular, it is extremely difficult to protect against the spread of a "hydrocarbon-type" fire, in which a very high temperature is reached within a few minutes of the start of the fire. The intense heat especially affects thick cables having solid conducting cores of for example aluminium or copper but also affects multicore cables. When a fire breaks out, the heat from the hot side of the fire barrier is conducted through the fire barrier by such conducting cores and can cause an unacceptably high rise above ambient temperature at the "cool face" of the penetration through the fire barrier where cables project from the fire barrier penetration seal. Thus, the cable itself can provide a path for the fire to spread through the barrier, by creating sufficiently high temperatures to cause ignition.

Cables are frequently supported by metal racks which also provide a potential heat conduction path in the event of a fire and which themselves may be difficult to seal in place.

Some penetration systems, while potentially effective on installation may tend to deteriorate with time or in varying atmospheric conditions or may be too rigid to permit movements which occur in service or during fire conditions.

With these difficulties in view, it is an object of a first aspect of the invention to provide a new or improved protector means for services such as cables passing through a fire barrier.

According to the invention there is provided a protector means for protecting a service such as a cable passing through and locally sealed in a fire barrier, the protector means comprising a sleeve or similar enclosure surrounding the service from the fire barrier along part of the length of the service externally of the fire barrier and comprising, in combination, a heat dissipating material which is a good conductor and radiator of heat, and an insulating material, the materials being selected and combined so as to control the dissipation of heat from the service whereby, in the event of a fire, heat passing through the fire barrier and along the service is spread along the protector and dissipated therefrom at a controlled rate such that the maximum surface temperature of the protector does not exceed a pre-determined level.

The heat dissipating material should have good thermal conductivity and thermal radiation properties and for example may be aluminium or copper. It may be in the form of a continuous foil or of a reticulated material such as "expanded metal' or mesh.

The insulating material may be a fibrous material such as mineral wool or ceramic fibre; or a particulate insulation material such as vermiculite or perlite; or may be a low-density settable material such as gypsum plaster or a cement-based insulator; or an intumescent material such as intumescent paint.

In one preferred embodiment, the protector comprises a sleeve of aluminium foil packed with mineral wool and surrounding the service from the fire barrier along part of its length. In another preferred embodiment, the protector comprises a sleeve formed of expanded aluminium coated with a thick layer of intumescent paint.

The protector means specificed above may be used with any form of penetration through a fire barrier. However, the protector means may advantageously be combined with a fire barrier seal incorporating an elastomeric silicone foam.

It is an object of a further aspect of the invention to provide a combination with a penetration assembly which is particularly suitable for use with the cable protector means.

According to this aspect of the invention, there is provided, in combination, a penetration assembly, a service such as a cable and a protector means as set out above, the assembly comprising a penetration frame containing a first resistant elastomeric silicone foam through which the service passes and which seals around the service, the assembly projecting from at least one face of the fire barrier and the protector means extending from the penetration assembly along part of the length of the service.

The frame may be made of a fire resistant glass fibre reinforced cement such as that marketed under the trade name VELMAC.

Services such as cables passed through the penetration assembly, may be supported by a metal ladder rack which may pass completely through the penetration assembly, the silicone foam sealing the ladder rack into position.

A penetration assembly and two forms of protector means for services such as cables will now be described in more detail by way of example only with reference to the accompanying drawings in which: FIGURE 1 illustrates a penetration assembly in a fire-barrier, through which cables pass supported by a ladder rack; FIGURE2 is a longitudinal section through a cable passing through a penetration assembly and having a first form of protector; FIGURE3 is a longitudinal section through a cable passing through a penetration assembly and having a second form of protector.

Referring firstly to Figure 1 of the drawings, there is shown a penetration assembly generally indicated at 10 which forms part of a fire barrier generally indicated at 11. The penetration assembly 10 receives cables 12 supported by a cabling support or ladder rack 13.

The fire barrier 11 preferably comprises a pair of outer facing sheets 14 of fire resistant glass fibre reinforced cement (grc) and a pair of inner insulation layers 15 of mineral wool, separated by an air gap 16. However, the invention may be used with other types of fire barrier.

The penetration assembly 10 comprises a frame 17 of a fire resistant glass fibre reinforced cement material. A preferred material is the lightweight grc material marketed under the trade name VELMAC. It will be seen that the penetration frame 17 is allowed to project some distance from the face of the remainder of the fire barrier 11 so as to give extra fire protection to the cables 12.

The frame 17 is faced off with a facing board or "dammer" 18 of mineral wool orgrc,which is provided at each face of the frame in the example shown. Between the boards 18, a fire-resistant elastomeric silicone foam 19 is provided, a suitable material being that marketed by Dow Corning under the designation "Silicone RTV Foam". The foam 19 surrounds and seals onto the cable 12 and ladder rack 13 which supports it, and completely fills the frame 17 between the dammer boards 18.

Turning now to Figure 2 of the drawings, this diagrammatically illustrates a single cable 12 passing through a penetration assembly 10 which may be of the type shown in more detail in Figure 1.

No supporting ladder rack is shown for clarity.

The cable 12 passes through a hole 20 in the facing board or dammer 18 and through the foam 19. It will be appreciated that, in general, the same arrangement will be provided at each face of the penetration frame and therefore only one face is shown in Figures 2 and 3 of the drawings. In some circumstances it is possible that fire risk may only occur at one face of a fire barrier, in which case the protector generally indicated at 21 will only be provided at the other, ("cool") face of the barrier.

However, the use of a protector at the "hot" face serves to reduce the heat flux entering the cable and it is therefore greatly preferred to provide a protector at both faces.

The protector 21 shown in Figure 2 of the drawing comprises a mineral wool sleeve 22, surrounded by a metal foil sleeve 23. The length and thickness of the mineral wool sleeve and of the metal foil sleeve will be determined by application of relevant tests, according to the maximum permitted surface temperature of the cable at the "cool" face of the barrier. However, by way of a typical example, a mineral wool having a density of 45 Kg/M3 may be used for the sleeve which may have a thickness of 10 mm. The surrounding aluminium foil preferably has a weight of 2 Kg/M2 and forms a continuous sleeve completely surrounding the cable 12. The sleeve may be formed from a sheet of foil, the side edges of which are pop-riveted or crimped together.

As shown, only the cable 12 passes through the facing board 18 but it is preferred to insert the mineral wool and foil sleeves 22 and 23 through the hole 20 so that they extend into the dammer 18 of the penetration assembly 10 (as shown in dotted outline). In any case, it is essential that the protector 21 covers the cable completely from the face of the penetration assembly in the fire barrier.

The protector and cables can be installed before the foam is introduced into the penetration assembly, if this sequence of installation is possible.

The protector can be secured in position by a band clamp 30 tightened around an end portion of the sleeve 23. The foil from which the sleeve 23 is made is provided with slits or with cut outs so that it can be drawn against the cable 12 by the band clamp 30 to hold it in position. This also serves to enclose the mineral wool 22. It is particularly advisable to secure the protector in position where the installation might be subject to vibration, to prevent the protector from "walking" along the cable 12.

Using a protector 21 as shown in Figure 2, it has been found possible to meet the requirements of the so called "CEGB" test which simulates a hydrocarbon fire, without the surface of the cable or protector accessible on the cool face of the barrier exceeding 140"C.

Figure 3 of the drawings shows a further form of protector 24. The cable itself is firstly coated with a primer to permit good adhesion of an intumescent paint. The cable may be directly coated with intumescent paint.

Surrounding the cable is a sleeve 25 which is made of a reticulated high conductivity material.

The sleeve 25 is preferably made of aluminium or copper, either of which has a suitably high conductivity for heat. It is preferred that the sleeve should have small openings at closely spaced centres so as to have a large effective surface area.

However, it is also preferred that the metal sections between the openings should be of a substantial thickness so that the thermal conduction of the material is not adversely affected by the presence of the openings.

The sleeve 25 is thickly coated over at least part of its length with an intumescent paint which may even close the pores of the sleeve. In the event of a fire, the intumescent paint will expand and form an insulation layer keyed to the sleeve 25.

A suitable material for the sleeve 25 is an expanded metal mesh having strands approximately 0.5 mm thick by 0.5 mm wide and a pitch size for the mesh of between 0.5 mm and 2 mm. There is minimal current de-rating of the cable.

In order to meet the requirements for cables passing through a fire barrier, the surface temperature accessible at the "cool" face of the barrier must not exceed a certain level, typically 140"C. Where a hydrocarbon fire occurs at the hot face of the barrier, conduction through cables, particularly those having solid inneraluminium cores for example, may result in very high temperatures being achieved in the cable as it emerges from the penetration assembly.

The protectors described in relation to Figures 2 and 3 of the drawings operate by exerting a control on the heat loss from the cable.

It might be supposed that, in order to meet the necessary standards for the temperature at the cool side of the barrier, one need only put sufficient insulation around the cable to ensure that the surface temperature remains low. However, this gives rise to two problems.

Firstly, the quantity of insulation which may be required may be quite large so that the insulation projects a long way from the face of the barrier.

Over-insulating the cable in the region of the fire prevents heat from being dissipated from within the cable. Thus the temperature of the cable emerging from the insulation becomes proportionately higher than it would be in the same position on an uninsulated cable. Hence more insulation is required further down the cable, resulting in larger volumes of insulation being used.

Secondly, the heat flux on the hot face of the barrier, a proportion of which passes along the cable to the cool face, may be such that a build up of heat in the cable occurs, taking the temperature beyond the melting point of the cable. The cable will then collapse within the insulation since the heat cannot escape through the insulation. This collapse may then lead to the collapse of the insulation.

Thus, it has not been found satisfactory solely to insulate the cables.

However, without insulation, the surface temperature of the cable rapidly exceeds the permitted level. The present invention seeks to provide a means for dissipating the heat from the cable at such a rate that this temperature build up does not occur. Merely providing a heat sink is not in itself satisfactory since the surface temperature of the heat sink may again exceed the permitted level.

The present invention seeks to avoid the problems described above by combining a good conductor and radiator (which can conduct away and dissipate heat rapidly) and an insulator (which can prevent any localised rise in temperature beyond that permitted by the relevant standards).

Materials such as foils, meshes and so on are preferred for the conductor so as to improve its radiative surface area. Treatment with materials such as matt black paint to improve radiation may also be advantageous.

A proper balance needs to be found, in accordance with the materials chosen and the likely fire conditions, between the conductor and the insulator. It is desirable to ensure the maximum radial heat loss at each point along the protector without exceeding the permitted surface temperature. This means that the insulation is kept as thin as possible consistent with preventing this overheating, so that the heat reaching the outer conductor can be dissipated.

It is also desirable not to have to provide insulation along a substantial length of the cable so that the use of excessively thick insulation is again undesirable. A thick insulation tends to keep the cable hot and so the insulation needs to be longer as well as thicker. This is both uneconomical and undesirable in use.

Where an intumescent material is used, in the event of a fire this will create insulation at the hottest part of the protector.

It may be desirable that the protector should be thicker adjacent the fire barrier penetration assembly than it is at a position further spaced from the barrier. However, the use of a constant thickness sleeve permits easy mass production and also ensures that the protector is applied the right way round when being installed.

Claims (18)

1. A protector means for protecting a service such as a cable passing through and locally sealed in a first barrier, the protector means comprising a sleeve or similar enclosure surrounding the service from the fire barrier along part of the length of the service externally of the fire barrier and comprising, in combination, a heat dissipating material which is a good conductor and radiator of heat, and an insulating material, the materials being selected and combined so as to control the dissipation of heat from the service whereby, in the event of a fire, heat passing through the fire barrier and along the service is spread along the protector as dissipated therefrom at a controlled rate such that the maximum surface temperature of the protector does not exceed a pre-determined level.

2. A protector means according to Claim 1 wherein the heat dissipating material is aluminium.

3. A protector means according to Claim 1 wherein the heat dissipating material is copper.

4. A protector means according to any preceding claim wherein the heat dissipating material is in the form of a continuous foil.

5. A protector means according to any one of Claims 1 to 3 wherein the heat dissipating material is in the form of a reticulated material such as expanded metal or mesh.

6. A protector means according to any preceding claim wherein the insulating material is a fibrous material such as mineral wool or ceramic fibre.

7. A protector means according to any one of Claims 1 to 5 wherein the insulating material is a particulate material such as vermiculite or perlite.

8. A protector means according to any one of Claims 1 to 5 wherein the insulating material is a low-density settable material such as gypsum plaster or a cement-based insulator.

9. A protector means according to any one of Claims 1 to 5 wherein the insulating material comprises an intumescent material such as intumescent paint.

10. A protector means according to Claim 1 and comprising a sleeve of aluminium foil packed with mineral wool and surrounding the service from the fire barrier along part of its length.

11. A protector means according to Claim 1 comprising a sleeve formed of expanded aluminium coated with a thick layer of intumescent paint.

12. In combination, a protector means according to any one of Claims 1 to 11 and a fire barrier seal incorporating an elastomeric silicone foam.

13. In combination, a penetration assembly, a service such as a cable and a protector means according to any one of Claims 1 to 11, the penetration assembly comprising a penetration frame containing a fire resistant elastomeric silicone foam through which the service passes and which seals around the service, the assembly projecting from at least one face of the fire barrier and the protector means extending from the penetration assembly along part of the length of the service.

14. A combination according to Claim 13 wherein the penetration frame is made of a fire resistant glass fibre reinforced cement.

15. A combination according to Claim 13 or Claim 14 wherein the service passing through the penetration assembly is supported by a metal ladder rack, passing completely through the assembly, the silicone foam sealing the ladder rack in position.

16. A protector means for protecting a service such as a cable substantially as hereinbefore described with reference to and as illustrated in Figure 2 of the accompanying drawings.

17. A protector means for protecting a service such as a cable substantially as hereinbefore described with reference to and as illustrated in Figure 3 of the accompanying drawings.

18. The combination of a protector means according to any one of Claims 1 to 11 or 16 or 17, with a penetration assembly substantially as hereinbefore described with reference to and as illustrated in Figure 1 ofthe accompanying drawings.