GB2364536A

GB2364536A - Fireproofing between wooden joists

Info

Publication number: GB2364536A
Application number: GB0114301A
Authority: GB
Inventors: Lionel Frederick Parks
Original assignee: SANDERS FIRE SYSTEMS Ltd
Current assignee: SANDERS FIRE SYSTEMS Ltd
Priority date: 2000-06-13
Filing date: 2001-06-12
Publication date: 2002-01-30
Anticipated expiration: 2021-06-12
Also published as: GB2364536B; GB0014417D0; GB0114301D0

Abstract

Sections of fire-resistant laminated mineral slab 16 are snugly fitted between wooden floor joists 12 and held in place from above by brackets 62 and helical fixings 54. A fire-resistant adhesive may be used to provide a better smoke and fire seal between adjoining panels 16.

Description

2364536 FIRE PROTECTION METHOD AND APPARATUS The present invention relates

to a fire protection method 5 and apparatus. In particular, the invention relates to improvements in a fire protection method and apparatus for timber floors.

It is desirable to restrict the possibility of the spread of fire within a building. Such restriction of the spread of 10 fire may, for example, provide any occupants of the building with sufficient time to evacuate the building. Such restriction may also reduce-the extent of damage caused by the fire before it can be extinguished.

The spread of fire within a building can be restricted by 15 sub-dividing the building into compartrzients, separated from one another by walls and/or floors of fire-resisting construction.

This is called "compartment at ion". The principles and applications of compartmentation are set out in Approved Document B, "Fire Safety" of the 1991 Building Regulations.

20 Floors of timber construction which are required to provide horizontal fire compartmentation can present particular problems.

This is especially true in existing buildings, which are either being upgraded to comply with current Building Regulations, or for which a change of use involves additional fire precautionary 25 measures.

Fire protection is added to timber floors with the aim of ensuring that the floor will retain structural integrity and insulation, under loaded conditions, for a stipulated period of fire resistance (see, for example, British Standard BS 476, pages 21 and 22). It is particularly preferable to protect the joists of the timber floor.

The required fire protection for the floor can be installed either from above or from below, depending on the circumstances.

When the timber joists of a floor in a building are readily accessible from the room below, the fire protection can be installed from''below. In this case, suitable fire protection boards can be fixed to the underside of the joists to form a continuous fire barrier across the top of the designated compartment area. When the fire protection can be installed from below, the solution is straightforward. However, it is often the case that access to the joists from below is not possible. This, particularly, can be the case in older buildings. Access to the joists from below is often not possible due to, for example, the need to preserve ornate plaster on the ceiling below the floor, multi-occupancy of the building or restricted ceiling height.

Fire protection can usually be installed from above when installation from below is not possible, and it is with this that the invention is concerned. Access to the joists is provided by removing the floorboards above the joists. The fire protection usually takes the form of rigid fire protection boards, or slabs 3 of mineral fibre, introduced between the joists. The purpose of this fire protection is to form a substantially continuous noncombustible infill in the space between adjacent joists. Furthermore, the fire protection should reduce the rate of combustion of the timber joists themselves.

The systems available for the fire protection of timber floors have inherent limitations. These limitations can render the fire protection systems ineffectual, to varying degrees, in the event of a fire.

Fire protection systems comprising rigid boards are intended for installation in squared-off and parallel joists. In practice,joists rarely fit the ideal scenario of being squaredoff and parallel. They usually have knots and joints, have been subjected to building structure movement and, in older buildings, may be hand-sawn timbers with uneven, wavy edges. It is desirable for the edges of the rigid boards adjacent to the cheeks (i.e. the vertical sides) of the joists to form a continuous fire seal with the cheeks of the joists. However, cutting the rigid boards to shape to follow the contours of the cheeks of the joists is extremely difficult and time-consuming.

Mineral fibre slabs are often preferred to rigid boards in fire protection applications. These slabs are usually made from sheets of mineral fibre, the sheets being made by coating the individual fibres with a resin binder to hold the mass of fibres together. The fibres then come to rest on a moving belt to form 4 a continuous laminated slab. The density, rigidity and compressibility of the resultant slab depends on the processing conditions and route chosen. Mineral fibre slabs can be cut to a precise shape with a sharp knife or with a fine-toothed handsaw.

A key element in the fire protection performance of a mineral fibre slabbased fire protection system is the retaining method used to secure the mineral fibre slab between the joists.

This is particularly the case where the ceiling below is a decorative plaster ceiling. Such a ceiling will usually break down and fall away in a matter of minutes, leaving the fire protection system fully exposed to the effects of the fire.

Fig 1 shows a schematic drawing of a first known system for the fire protection of timber floors. In this system, lightweight chicken wire mesh 10 is bent at several places into right angles to form a basket which is suspended between the joists 12,14. The mineral fibre slab 16 is held in the mesh basket between the joists, abovethe top surface of the ceiling 18 between the joists.

In practice, cutting and bending a roll of mesh in order to make the basket in Fig 1 is a difficult and slow process. The chicken wire is usually too flimsy to hold the mineral fibre slab rigidly in position between the joists. The action of pushing the slab down to the bottom of the space between the joists within the confines of the mesh tends to draw the mesh away from the cheeks of the joist. This leaves at least the lower part of the joist exposed to combustion in the event of a fire from below. In addition, there is no restraint on the mineral fibre slab to prevent it from being lifted up or dislodged in the event of a significant build-up of fire pressure from below. Furthermore, the wire mesh support 10 is exposed to the heat of the fire. This can result in a loss of structural integrity of the mesh and the slab could then fall away. In this system, slabs installed adjacent to each other along the length of the gaps between joists are usually simply pushed up against each other. The line at right angles to the joists along which two slabs abut is a line of weakness, allowing the passage of smoke and fire.

Fig 2 shows a schematic drawing of a second known system for the fire protection timber floors. In this system, steel angle brackets 20,22 are fixed as far down the joists 14,12 as is practically possible. Then a metal section 24 is laid across the gap between the joists, the metal section forming a cross-piece and resting on and supported by the angle brackets. The mineral fibre slab is then cut to a tight fit and pushed down to rest on the metal brackets 20,22 and cross-piece 24.

The system of Fig 2 is an improvement of the system of Fig 1, since it provides sturdy and rigid supports for the location of the mineral fibre slab 16. However, it shares a major limitation with the system of Fig 1 in that, in the event of a build-up of fire pressure from below, there is no mechanical 6 restraint to prevent upward dislodging of the mineral fibre slab.

Also, the adjacent slabs are usually only laid down as a simple push fit against each other or against the metal cross-piece 24.

The metal supports 20,22 and 24 for the mineral fibre slab are exposed, in the event of a fire from below, to the heat of the fire. This can lead to a loss of structural integrity and the slab could then fall away.

From an installation point of view, it is awkward to locate and insert screws to hold the brackets at the bottom of the cheek of the joist, particularly where there is a fragile decorative ceiling immediately below.

Fig 3 shows a schematic drawing of a third known system for the fire protection of timber floors. In this system, instead of the mineral fibre slab just resting on the angle brackets, the long edges of the slab 16 are impaled onto the brac:<.ets 30,32. The brackets are then lowered with the slab and screwed to the joists.

The system of Fig 3 is an improvement over both the system of Fig 1 and the system of Fig 2. Here, the part of the metal support which impales the mineral fibre slab is protected from fire damage by the slab. Also, since part of the bracket is enclosed in the slab, the lifting of the slab in the event of fire due to pressure from below is substantially prevented.

Since the mineral fibre slabs are formed as laminates, pushing part of the bracket into the side of the slab can 7 delaminate at least that part of the slab. The slab can completely delaminate when it is pushed down into the gap between the joists after it has been partially delaminated by the brackets. If the slab is partially or completely delaminated, the fire protection afforded by the slab is reduced compared to one of the same thickness which is not delaminated. In addition, it is still quite difficult to attach the brackets into the joist during installation because the surface of the slab tends to get in the way.

This system does not completely overcome the problem of metalwork being exposed to a fire from below. Similarly to the systems of Figs I and 2, metalwork exposed to fire can lose structural integrity. Also, the heat of the fire can be conducted through the metalwork to the upper part of the joists, accelerating the spread of fire past the fire protection slab.

None of the systems of Figs 1 to 3 can provide a fire protection system which gives a substantially smoke- and firetight seal between the mineral fibre slab and the cheek of the joist.

Accordingly, in a first aspect the present invention provides a method of installing a slab of fire resistant material in a wooden floor of a building, the method including the steps of attaching a first portion of a bracket to an upper surface of the slab and attaching a second portion of the bracket to a joist in the floor, a side surface of the slab abutting against a cheek 8 of the joist.

Preferably, the second portion of the bracket is attached to the joist in a position not lower than the upper surface of the slab. More preferably, the second portion of the bracket is attached to the joist in a position above the upper surface of the slab. Since the fire-resistant material is supported from above, it is possible to form a substantially smoke-tight seal between the slab of fire-resistant material and the joist, because there is no bracket interposed between the side surface of the slab and the cheek of the joist, and yet the bracket is not exposed to fire from below.

Preferably, the step of attaching the first portion of the bracket to the upper surface of the slab is achieved by rotationally inserting corkscrewlike helical attachment means into th'eslab. Helical attachment means tend to bite into slabs of fire-resistant material better than, for example, conventional screws.

Preferably, the second portion is removably attached to the first portion. This may be, for example, by any suitable attachment means such as a friction fit, a screw fit, a nut and bolt fit or similar. Alternatively, the first and second portions of the bracket may be formed integrally. This may be the case where the bracket is formed from a single piece of material, such as steel, and the second portion of the bracket is formed by bending the material. Typically, the first portion of 9 the bracket may extend across substantially the whole width of the slab. In use, the first portion of the bracket therefore may extend substantially between adjacent joists, with second portions of the bracket being attached to respective joists.

Preferably, the first portion is attached to the slab in a plurality of attachment locations along the length of the first portion. In this way, it is possible to reduce sagging of the slab between adjacent joists.

Typically, the method may be suitable for installing slabs of fire resistant material between joists which are up to around 1.2m apart.

The method may further include the step of applying fire resistant adhesive between adjacent slabs of fire-resistant material retained in a gap between joists in the floor. This helps to make the seams between the adjacent pieces of fireresistant material substantially smoke-tight.

In a second aspect, the present invention provides a fire protection apparatus for installation in accordance with the inventive method, the apparatus including a slab of fireresistant material and a bracket, wherein a first portion of the bracket is attachable to an upper surface of the fire-resistant material and a second portion of the bracket is attachable to a joist.

Preferably, the first portion of the bracket is attachable to the upper surface of the slab via corkscrew-like helical attachment means.

Preferably, the first portion of the bracket includes an elongate slot through which the substantially helical attachment means is rotationally insertable. The elongate slot (rather than a conventional circular drilled hole, for example) allows the substantially helical attachment means to be inserted into the fire-resistant material with ease.

Preferably, the second aspect of the invention includes any feature referred to with the respect to the first aspect.

Preferably, in both aspects of the invention, the slab of fire-resistant material is a mineral fibre slab. More preferably, the mineral fibre slab is compressible so that it can tightly abut the cheek by being packed into posit.iQn under slight compression. Still more preferably, the mineral fibre slab has a low binder content. This improves the fire protection capability of the slab compared to mineral fibre slabs with higher binder contents.

The preferred embodiments will now be described in detail, by way of example only, with reference to the accompanying drawings, in which:

Fig 1 shows a schematic drawing of a first known system for the fire protection of timber floors; Fig 2 shows a schematic drawing of a second known system for the fire protection of timber floors; Fig 3 shows a schematic drawing of a third known system for the fire protection of timber floors; and Fig 4 shows a schematic drawing of a system for the fire protection of timber floors embodying the present invention.

Fig S shows a schematic perspective view of an embodiment of the invention.

Fig 6 shows a schematic view of an embodiment of the invention using an extended integral bracket.

Fig 7 shows a schematic view of an embodiment of the invention using an extended bracket with separable parts.

Figs 1, 2 and 3 have already been discussed since they show known fire protection systems.

In Fig 4, a mineral fibre slab 16 is held between joists 12 and 14 by brackets 40 and 42, respectively. No part of the bracket is interposed between the side surface 44 of the slab and the cheek of the joist. Therefore the side surface of the mineral fibre slab can urge against the cheek of the joist to form a smoke-tight seal with the joist.

The preferred mineral fibre slab for this application is determined by the resin binder content, the shot content and the quality of fibrization. There are no well-established parameters for determining the preferred ranges for these factors. Instead, all the factors are assessed together for a particular product by fire protection installers. The preferred product here is an Owens Corning product LR 128. This has a relatively low resin binder content, is fairly rigid (in use, it can support its own 12 weight substantially without sagging, yet with adequate degree of compressibility) and has a high quality of fibrization.

During installation, the mineral fibre slab is cut to size and shape (although most joists will at least be nominally parallel) using a knife or a fine-toothed saw. The width of the slab is made slightly greater than the width of the gap between the joists. When the slab is later pushed.into the gap between the joists, it is compressed slightly due to the size mismatch. This enables the formation of the smoke-tight seal between the side surface of the slab and the cheek of the joist.

once the slab has been placed in the gap between the joists in the desired position, as low down as possible, first portions of brackets 40 and 42 are attached to the upper surface of the slab. This attachment is achieved using helical attachment means, denoted schematically in Fig 4 as 46 and 48. These are known per se and typically are metallic fixing components, in a helical shape, similar in shape to a corkscrew. They can be made by bending a rod of a metal into a helix. They are dissimilar to conventional screws in that they are hollow along the axis of the helix.

It has been found that these helical fixing components, if screwed into a mineral fibre slab, bite well into the slab. This is in contrast to conventional screws which can be easily pulled out from a mineral fibre slab.

It has further been found that if the bracket has a 13 conventional drilled circular hole for screwing the helical fixing component through, then the helical fixing component will tend to precess around the hole. Consequently, the helical fixing component does not then bite well into the mineral fibre slab and the bracket is not securely attached. To address this, the bracket includes an elongate slot instead of a circular hole.

When the helical fixing component is screwed through this slot, it does not tend to precess and so the bracket may be secured firmly to the slab.

Once the brackets 40,42 are attached to the slab, the second portions of the brackets are attached to the joists using conventional screws. The brackets 40,42 are preferably angled brackets, more preferably rightangled brackets. The second portions of the brackets are each attached to the respective cheeks of the joists in a position above the level of the upper surface of the slab.

In a modification, the first portions of the brackets are attached to the slab before the slab is positioned between the joists.

The helical fixing components do not tend to delaminate the mineral fibre slabs since the helices are screwed down through adjacent lamellae. This development therefore addresses the problems of the system shown in Fig 3.

Mineral fibre slabs are usually sold in lengths shorter than the length of joists in a building. Therefore it is usually 14 necessary to fit one slab adjacent to another lengthwise along the gap between the joists. Any gap where adjacent slabs should abut can allow smoke and fire to penetrate the fire protection layer. Therefore the end surfaces of the mineral fibre slabs are coated with a fire-resistant adhesive. The adjacent ends of the slabs are then pushed together. When the adhesive dries, there is a substantially smoke-tight seal between the adjacent ends of the mineral fibre slabs. Typically, mineral fibre slabs 75 mm thick installed in place between the joists and anchored to the joists using this new system satisfy the maximum fire rating required for a timber floor of 90 minutes integrity and insulation.

In a full scale 5 m x 3.5 m fire test by the Loss Prevention Council, in accordance with BS 476, page 21, under standard loaded condition, this new systen! readily achieved 90 minutes rating without collapse or loss of insulation. There was no failure, nor collapse of the system even when the pressure of a cooling-down water hose was applied directly to the exposed underside of the specimen floor, at the end of the fire test period.

Fig 5 shows a schematic perspective view of a further embodiment of the invention. Again, mineral fibre slab is fitted between joists 12 and 14. However, the embodiment differs from the embodiment described above in that the bracketry used is different. Here, at least the first portion 50 of the bracket is, for example, a continuous length of slotted steel angle, for example, of dimensions 50mm by 50mm. Slots 52 provide locations along the length of the steel angle for attaching the steel angle member to the mineral fibre slab 16. Attachment is via the same helical attachment means described above.

Schematic cross-sectional views showing aspects of Fig 5 in more detail are shown in Fig 6 and Fig 7. Fig 6 and Fig 7 show alternative embodiments of the invention to each other. In Fig 6, helical attachment means 54 attach the first portion 56 of the bracket to mineral fibre slab 16. The advantage of using a bracket which extends between the joists is that the mineral fibre slab can be supported across its lateral width between the joists. This helps to reduce further the likelihood that the mineral fibre slab will sag during its lifetime. It is envisaged that the distance apart between adjacent helicai attachment screws along the length of the first portion 'S6 of the bracket would be around 300mm, but this would vary depending on the overall span between joists. This embodiment is ideally suitable for fitting mineral fibre slab fire protection to flooring where the joists are set up to around 1.2mm apart.

In Fig 6, the bracket is made from a single piece of slotted steel angle. Its ends (one of which shown as end 60) are bent to form a second bracket portions for attachment to joist 12, for example by conventional screw fitting 62.

Fig 7 shows an alternative embodiment to Fig 6. In Fig 7, 16 the first portion 58 of the bracket is removably attachable to the second portion 64 of the bracket. First portion 58 is a continuous length of slotted steel angle, again of dimensions around 50mm by 50mm, with a length slightly smaller than the spacing between adjacent joists. Second portion 64 is removably attachable to first portion S8 by, for example, a nut and bolt fitting 66. Second portion 64 of the bracket is attachable to the joist 12 again by conventional screw fitting 62.

The embodiments illustrated in Figs 5,6 and 7, have been assessed by the BRE Centre for Fire Resistance and have been confirmed to be in compliance with the fire tested performance of the system described above.

The above description of the preferred embodiments of the invention are by way of example only, and are not intended to limit the scope of the invention. Modifications and improvements will be apparent to the skilled reader, and these are within the scope of the invention.

Claims

1. A method of installing a slab of fire resistant material in a wooden floor of a building, the method including the steps 5 of attaching a first portion of a bracket to an upper surface of the slab and attaching a second portion of the bracket to a joist in the floor, a side surface of the slab abutting against a cheek of the joist.

10

2. A method according to claim 1 wherein the second portion of the bracket is attached to the joist in a position not lower than the upper surface of the slab.

3. A method according to claim 2 wherein the second portion of 15 the bracket is atta-::hed to the joist in a position above the upper surface of the slab.

4. A method according to any one of claims 1 to 3 wherein the step of attaching the first portion of the bracket to the upper 20 surface of the slab is achieved by rotationally inserting corkscrew-like helical attachment means into the slab.

5. A method according to any one of claims 1 to 4 including the step of removably attaching the second portion to the first 25 portion.

6. A method according to any one of claims 1 to 4 including the step of integrally forming the first and second portion of the bracket.

5 A method according to any one of claims 1 to 6 wherein the bracket extends between adjacent joists.

8. A method according to any one of claims 1 to 7 wherein the first portion of the bracket is attached to the slab in a 10 plurality of attachment locations along the length of the first portion.

9. A method according to any one of the claims 1 to 8, further including the step of applying fire resistant adhesive between 15 adjacent slabs of fire-resistant material retained in a gap between. joists in the floor.

10. A method according to any one of claims 1 to 9 wherein the slab of fire resistant material is a mineral fibre slab.

11. A method according to claim 10 wherein the mineral fibre slab is compressible so that it can tightly abut the cheek by being packed into position under slight compression.

25

12. A method according to claim 10 or claim 11 wherein the mineral fibre slab has a low binder content.

13. A fire protection apparatus for installation in accordance with the method of any one of claims 1 to 12, the apparatus including a slab of fire-resistant material and a bracket, 5 wherein a first portion of the bracket is attachable to an upper surface of the fire-resistant material and a second portion of the bracket is attachable to a joist.

14. A fire protection apparatus according to claim 13 wherein, 10 the first portion of the bracket is attachable to the upper surface of the slab via corkscrew-like helical attachment means.

15. A fire protection apparatus according to claim 14 wherein the first portion of the bracket incl'udes an elongate slot 15 through which the helical attachment means is rotationally insertable.

16. A fire protection apparatus according to any one of claims 13 to 15 wherein the first portion of the bracket is removably 20 attachable to the second portion of the bracket.

17. A fire protection apparatus according to any one of claims 13 to 15 wherein the first portion of the bracket is formed integrally with the second portion of the bracket.

i

18. A fire protection apparatus according to any one of claims 13 to 17 wherein the first portion of the bracket extends, in use, across substantially the whole width of the slab.

5

19. A fire protection apparatus according to any one of claims 13 to 18 wherein the first portion has a plurality of attachment locations for attachment of the first portion of the bracket to the slab.

20. A fire protection apparatus according to anyone of claims 13 to 19 wherein the slab of fire-resistant material is a mineral fibre slab.

21. A fire protection apparatus according to claim 20 wherein the mineral fibre slab is compressible so that it can tightly abut the cheek by being packed into position under slight compression.

22. A fire protection apparatus according to claim 20 or claim 21 wherein the mineral fibre slab has a low binder content.

23. A method of installing a slab of fire resistant material in a wooden floor of a building substantially as hereinbefore described, with reference to Figs.4 to 7.

24. A fire protection apparatus substantially as hereinbefore described, with reference to Figs.4 to 7.

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