GB2318975A

GB2318975A - Fire resistant duct

Info

Publication number: GB2318975A
Application number: GB9708850A
Authority: GB
Inventors: Arthur Peter Nelmes
Original assignee: Nullifire Ltd
Current assignee: Nullifire Ltd
Priority date: 1996-05-01
Filing date: 1997-04-29
Publication date: 1998-05-13
Anticipated expiration: 2017-04-29
Also published as: GB2318975B; GB9708850D0

Abstract

A fire-resistant duct for one or more cables and/or pipes comprises a frame and, within the frame, at least one blade for movably closing the duct, wherein: the blade comprises (i) a portion of intumescent material and (ii) flexible smoke retardant means to engage the cable or cables or pipe or pipes to thereby form with the blade a continuous barrier across the frame. Preferably the blade is arranged to be biased towards a closed position by a bimetallic strip, gravity or spring means. Two blades may be mounted adjacent to one another within the duct.

Description

FIRE RESISTANT DUCT The invention relates to a fire resistant duct for one or more cables and/or pipes.

Modern structures such as buildings, oil platforms and chemical plants, and transport systems such as oil tankers and other shipping, carriage trains and other rail transport, often contain many cables and piping which need to pass through walls or flooring between different parts of the structures. Such cable and pipe ducts provide a route for fire, smoke, gas and water to spread from one part of the structure to another in the event of fire. It is therefore desirable to provide a sealable duct.

Such ducts may be sealed with fire resistant mortar. However this has a disadvantage in that if further cables and/or pipes are needed to be fitted, holes must be drilled through the mortar. Similarly, intumescent coated mineral fibre board may be used to seal openings.

Cable and pipe ducts are also known which utilise pillows containing intumescent material or intumescent blocks to seal the duct. In the first case, pillows containing the intumescent material are packed around the cables and/or pipes within the duct to form a smoke- and fire-resistant barrier. In the second case, the cables and/or pipes are held in position by means of rubber cable blocks each of which define an orifice through which a cable and/or pipe is passed. Usually, the cable blocks are provided in several rows across the aperture of the housing, each row being held in place by means of a metallic stay plate which is required to maintain the structural integrity of the cable blocks and securely anchor the cable blocks within the frame of the duct.

There are several disadvantages associated with the latter two systems.

Firstly, when the cable duct is first fitted in position within the structure, a skilled specialist is required to ensure that cabling or piping passing through the duct is properly sealed. Secondly, if additional cabling or piping is passed through the duct at any time, the sealing pillows or cable blocks which form the smoke- and fire-resistant barrier need to be dismantled prior to fitting the new cables and/or piping. Furthermore, after the new cabling and/or piping has been fitted the smoke- and fireresistant barrier needs to be re-made in order to accommodate the new cabling and/or piping. In the inventor's experience, the re-building of a smoke- and fire-resistant barrier is commonly not carried out properly, resulting in serious and dangerous degradation in the smoke- and fire resistant properties of the structure in question.

The inventor has therefore designed a smoke- and fire-resistant duct which automatically adjusts itself to the size and number of cables and/or piping passing through it. Furthermore, the smoke- and fire-resistant duct of the invention also allows the fitting of further cables and/or pipes at a later stage without the need to dismantle the smoke- and fire-resistant barrier.

Accordingly the invention provides a fire-resistant duct for one or more cables and/or pipes comprising a frame and, within the frame, at least one blade for movably closing the duct, wherein the blade comprises at a first end: (i) a portion of intumescent material and (ii) flexible smoke retardant means to engage the cable or cables or pipe or pipes to thereby form with the blade a continuous barrier across the frame.

In use, the frame forms a duct through the wall or floor of the structure.

Cables and/or pipes are passed through the frame from one side of the wall or floor to the other. In use, the blade is movable from an open position, in which cables and/or pipes are passable through the duct, to a closed position, in which the first end of the blade rests upon the largest of the cables and/or pipes passing through the frame. The flexible smoke retardant means at the first end of the blade passes on either side of each of the cables and/or pipes to form a smoke-retardant screen. This helps prevent the passage of smoke along the gaps between cables from one side of the wall or floor to the other. If there is a fire in the vicinity of the fire-resistant duct the intumescent material at the first end of the blade expands to fill any gaps between the cables and/or pipes. This forms an effective smoke- and fire- barrier.

Intumescent material swell when subjected to high temperatures, e.g. in excess of 1500C, to form a char that may be up to fifty times the original thickness of the original material. This forms an insulating layer and also has the advantage that this kind of material fills any gaps around it. Such materials are well known in the art.

Preferably the blade is arranged to be biased towards a closed position.

This has the advantage that the fire-resistant duct is not left open by mistake. The blade may be arranged to be biased by means of a bimetallic strip which closes the duct in response to an increase in heat, by gravity or by spring means. The blade may be hingedly attached to the frame at a second end of the blade, for example in the manner of the flap of a letterbox. Alternatively the blade may be movable by translation from an open position to a closed position, for example in the manner of a vertical guillotine.

The blade may comprise two or more parts, hingedly attached at their adjoining edges. In such a device, when the duct is open, the blade parts may be folded about the hinge to lie adjacent to one another.

The flexible fire means may be in the form of a brush, for example of metal wire such as copper. Alternatively the flexible means may be in the form of one or more layers of glass fibre fire blanket which may be cut into strips to form a brush. In the latter case, the cuts in each of the strips may be moved transversely along the blade with respect to the previous layer so that none of the cuts overlap with each other, thus providing improved protection against smoke.

In an especially preferred embodiment the fire-resistant duct according to the invention comprises two blades mounted adjacent to each other. This has the advantage that the two blades significantly reduce the passage of heat through the fire-resistant duct until the intumescent material is activated by heat. Preferably intumescent material is mounted on at least a first blade on the surface of the blade facing the adjacent blade. This allows the area between the two blades to act as containment for the intumescent material in a fire, directing it towards the area around the cables and/or pipes. This prevents the intumescent material from spewing out of the fire-resistant duct with subsequent loss of intumescent material and failure to seal the cable-free area of the fire-resistant duct.

Preferably the frame is manufactured in two or more pieces. This has the advantage that, for example, a portion of the frame on which the cables and/or pipes are laid may be placed within the hole of the floor and/or wall of the structure to be protected, cable and/or pipes laid, and finally a portion of the frame with the blade(s) attached then fitted into place. This provides more room for the initial fitting of the cables and/or pipes.

Preferably the blade and frame are made from a metal such as aluminium or steel. The external surfaces of the frame and/or blade may comprise an intumescent coating of the sort known in the art to reduce the amount of heat transmitted through the wall and/or floor of the structure via the duct in the event of a fire.

The invention will now be described by way of example only with reference to the following figures: Fig. 1 shows a vertical cross-section through a fire-resistant duct according to the invention; Fig. 2 shows a front view of a fire-resistant duct according to the invention; Fig. 3 shows a cross-section through an alternative blade for use in a fire-resistant duct according to the invention; Fig. 4 shows a cross-section through a folding blade for use in a fire-resistant duct according to the invention; Fig. 5 shows a cross-section through a guillotine blade for use in a fire-resistant duct according to the invention.

Referring firstly to Figs. 1 and 2. The figures show a duct 10 mounted within a wall 12. The duct 10 has an aperture 14 which is defined by a rectangular frame 16. The frame 16 is mounted in wall 12 with the aid of a fire-resistant mortar 18 of the type known in the art. The duct 10 is shown with two cables 20 passing through aperture 14. In the preferred embodiment shown two rectangular blades 22,24 are shown mounted to the upper member of the frame 16 by means of hinges 26. This allows the blades 22,24 to pivot between the closed position (shown), in which the blade 22,24 lie across the aperture 14, to an open position (shown as ghost 28), in which the blades 22,24 are pivotted to lie adjacent the roof of the frame 16, to allow further cables to be inserted through the aperture 14.

Each blade 22,24 includes a brush 30 of three layers of a proprietary glass fibre fire blanket. Each layer is cut into strips and each layer is fixed to the overlapping strips layer by layer. From Fig. 2 it will be apparent that in use the blades rest upon the top of the cable 20 with the largest diameter. The brush 30 of glass fibre fire blanket hangs below the lower edge of the blade 22,24 and forms a smoke seal around the edge of both the larger cable and the smaller cable. Each blade 22,24 is rectangular and of the same width as the aperture 14 so as to close off the aperture 14.

An alternative to the use of glass fibre fire blanket will be the use of a brush of, for example, copper wire. This would advantageously be used in, for example, forming insulations where some degree of rigidity to the brush is required, such as in floor mounted ducts.

Fig. 1 shows a block of intumescent material 32 attached to the first blade 22. Preferably the intumescent material 32 is a graphite based proprietary intumescent material, for example supplied by Nullifire Limited, Coventry, United Kingdom. Such materials intumesce at approximately 1500C and expand to many times their original thickness forming a solid barrier of carbon foam.

Alternatively intumescent material may be attached to both blades on their facing surface. The material may cover substantially all of the facing surfaces.

In the event of a fire in the vicinity of the duct 10 the blades and brush form a smoke-resistant barrier against the passage of smoke through the duct. If the fire is close to the duct 10, the intumescent material 32 will expand and be forced between blades 22 and 24 to seal the gap between the lower part of the frame 16, the cables 20 and blades 22,24. The brush 30 on the end of each of the blades 22,24 will also help maintain the expanded intumescent material 32 around the cables 20 and prevent leakage.

The duct may also comprise further intumescent material 44, for example near to the hinges 26 to ensure a seal between the top of the blades 22,24 and the frame 16.

In the embodiment shown the blades 22,24, return to their closed position under reaction of gravity. The blades 22,24 may also be spring-loaded or, alternatively be maintained in an open position and closed upon an increase in temperature by a bimetallic strip of the sort known in the art.

Alternatively the blades 22,24 may be spring or gravity biased but may be held in an open position by means of a fusible link made of a metal having a low melting point. In the event of a fire, the fusible link melts and the blades 22,24 return to a closed position under reaction of the spring or gravity. Such fusible links are known in the art.

The blades 22,24 and/or frame 26 may be coated with an intumescent paint which expands upon exposure to heat. This reduces conductivity of heat through the frame. Furthermore, use of two blades also prevents conductivity of heat through the duct in a similar manner to the use of double glazing in windows because of the void between the blades 22,24.

In another embodiment the intumescent material can coat the entire surface of the first blade 22. In a further embodiment intumescent material may be provided on the inner surfaces of both blades 22,24.

Fig. 3 shows an alternative blade for use in a duct according to the invention. The figure shows a blade 40 having, at one end, intumescent material 44 within a housing 46 which extends along the full length of the blade. The housing comprises at its lower end an aperture 48 which extends along the full length of the housing and through which the intumescent material is guided when it expands due to heat. A depending fringe 42 is provided to each side of the aperture 48. This arrangement has the advantage that the intumescent material is guided in a controlled manner around the cables and/or pipes within the duct.

Fig. 4 shows a folding blade 50 comprising two portions 52,54. At one end of the first portion 52 is situated a brush 56 and intumescent material 58. The other end of the portion 52 is attached by a hinge 60 one end of to the second portion 54. The other end of the second portion 54 is attached by a hinge 62 to the frame of the duct.

In this embodiment the blade is therefore foldable and allows more access room for the fitting of cables etc. A guidance rod 64 is attached to portion 52 and is carried along a guide channel 66 in the wall of frame.

Such an embodiment has the advantage that the brush 56 and intumescent material 58 is moved to a position out of the way of any cables that are being fitted. In particular, if two blades are to be used it is preferable that they are arranged so that the brush and intumescent material on one or both of the blades are moved to an internal position with the brushes on each of the blades facing each other within the duct. Such a system may be spring or gravity biased.

Fig. 5 shows a blade 70 comprising a brush 72 and intumescent material 74, in which, in an open position, the blade is housed within a housing within the frame 76. Such a "guillotine blade" may be biased towards the closed position by either a spring within the housing or by gravity.

It is also envisaged that a flexible flame retardant means and a portion of intumescent material may be the same material. This would be the case where a rubber intumescent material is used on an end of the blade, the rubber intumescent material acting as both smoke-retardant means and fire-resistant means.

In conclusion, the invention provides a new smoke- and fire-resistant duct.

Such ducts have been successfully demonstrated by the applicants to achieve up to four hour fire resistance.

Claims

1. A fire-resistant duct for one or more cables and/or pipes comprising a frame and, within the frame, at least one blade movably closing the duct, wherein the blade comprises at a first end: (i) a portion of intumescent material and (ii) flexible smoke retardant means to engage the cable or cables or pipe or pipes to thereby form with the blade a continuous barrier across the frame.

2. A fire-resistant duct according to claim 1, wherein the blade is arranged to be biased towards a closed position.

3. A fire-resistant duct according to claim 2, wherein the blade is arranged to be biased by a bimetallic strip, gravity or spring means.

4. A fire-resistant duct according to any previous claim, wherein the blade is hingedly attached to the frame at a second end of the blade.

5. A fire-resistant duct according to claims 1 to 3, wherein the blade is movable by translation from an open position to a closed position.

6. A fire-resistant duct according to any previous claim, wherein the blade comprises two or more parts, hingedly attached at their adjoining edges.

7. A fire-resistant duct according to claim 6, wherein in the open position, the blade parts are folded about the hinge to lie adjacent to one another.

8. A fire-resistant duct according to any previous claim, wherein the flexible fire means is in the form of a brush.

9. A fire-resistant duct according to any previous claim, wherein the flexible means is made of one or more layers of glass fibre fire blanket.

10. A fire-resistant duct according to any previous claim, comprising two of said blades mounted adjacent to each other.

11. A fire-resistant duct according to claim 10, wherein intumescent material is mounted on at least a first blade on a surface of the blade facing the adjacent blade.

12. A fire-resistant duct according to any previous claim, wherein the frame comprises an upper piece and a lower piece.

13. A fire-resistant duct substantially as described herein with reference to the accompanying figures.