GB2148972A - Fire barrier assembly - Google Patents

Abstract

A fire barrier assembly (10) is principally made up of sheets (28, 29) and blocks (19) of glass-fibre reinforced cement (grc) or glass-fibre reinforced gypsum (grg) and stainless or galvanised steel facings (20, 21). The frame members (11) of the assembly have refractory insulating material cores (19), with skin members (20, 21) of steel partly but not wholly enclosing them. The cladding of the assembly can include grc sheets (29, 30), which are so retained by the frame members (11) that the sheets have a limited degree of sliding movement in their own general plane. <IMAGE>

Description

SPECIFICATION Fire barrier assembly This invention relates to a fire barrier assembly intended for use primarily as a passive fire restraint where there is a risk of fire in locations such as factories, power stations, ships, oil installations both onshore and offshore, and other commercial and industrial buildings or installations. Its use is not, however, limited to these particular locations.

The fire barriers with which the invention is concerned are not, in general, structural parts of the building or installation, but are added to the main structure as necessary, to limit the potential spread of fire, smoke and hot gases.

At present, one method of construction of a fire barrier involves the erection of a framework of rolled steel sections, which are then clad using rockwool or similar insulation boards and steel facing sheets. Each barrier is individually made and, once in place, is not readily adaptable, for example to insert cables through the barrier or to add or move a doorway.

It is an object of the present invention to provide a new or improved fire barrier assembly.

According to the invention, there is provided a fire barrier assembly comprising a plurality of frame members and a cladding structure secured to the frame members, characterised in that a frame member comprises one or more core members of mineral based refractory insulating material and a plurality of external skin members of incombustible sheet metal, partly but not wholly enclosing the core member or members and unsecured to the core member or members.

The skin members may be secured to each other at spaced localised fixings only, to minimise heat transfer between the skin members.

The skin members may be separated by low conductivity material to reduce heat transfer by radiation at the points of fixing.

The skin members may be of thin gauge sheet steel, preferably either stainless steel or corrosion-protected mild steel, for example galvanised mild steel.

The frame members may further include cover elements adapted to conceal the skin members from direct contact with a fire. The cover elements may comprise cover elements of mineral based refractory insulating material and may further comprise outer metal capping elements.

The fire barrier may be characterised in that the cladding structure includes at least one sheet of -mineral based refractory insulating material so retained at its edges by frame members as to have a limited degree of sliding movement in its own general plane, relative to the frame members.

Preferably, the sheet is slidably located between an abutment on the frame member and a cover element.

The edge of the sheet may abut a projection of one of the skin members.

The cladding structure may include one or more further insulation sheets.

The mineral based refactory insulating material may comprise glass fibre reinforced cement (grc); glass fibre reinforced gypsum (grg); mineral wool, or other suitable material.

The suitability of a particular material can be determined by its resistance both to the normal environmental conditions in which it is intended to be used and its resistance to the anticipated fire conditions.

In a preferred construction, a grc sheet and a further insulation sheet of mineral wool are secured together using a fire resistant material such as sodium silicate adhesive, and are then secured to the skin member with the edges of the mineral wool and grc sheets supported by respective projections on the skin member. A similar cladding is applied to a skin member at the opposite face of the barrier assembly, with an air gap between the two mineral wool sheets.

The fire barrier assembly may be fitted with one or more penetration openings for services such as cables or conduits.

A penetration opening may comprise a frame of mineral based refractory insulating material such as grc through which the services pass, the frame being closed by fireresistant material surrounding the services.

The fire-resistant material may comprise fire-resistant boards and the services may be sealed in position therein by means of fireresistant sealant such as fire-resistant silicone foam.

A fire barrier assembly embodying the invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a front elevational view, partly broken away, of a fire barrier assembly embodying the invention; Figure 2 is a horizontal section on the line 2-2 through an upright frame member of the barrier assembly; Figure 3 is a horizontal section on the line 3-3 through an upright side of a penetration frame of the barrier assembly; Figure 4 is a horizontal section on the line 4-4 of a side frame of the barrier assembly secured to a structural member of a building or installation.

Figure 5 is a vertical section through a loadbearing beam which may be used in a fire barrier embodying the invention.

Referring firstly to Fig. 1 of the drawings, a fire barrier assembly is illustrated at 10. This assembly is merely typical of those which can be constructed using the present invention, and should not be taken as limiting the scope of the invention.

The fire barrier assembly 10 has been shown broken away in the drawings, to show the different layers of which it has been assembled. The top left hand corner of the drawing shows the fire barrier assembly in its complete state.

The fire barrier assembly is made up of upright and transverse frame members generally indicated at 11 and 1 2 respectively, which are clad by a cladding structure 1 3.

The precise details of the upright frame members 11 and transverse frame members 1 2 differ according to their location and function in the fire barrier assembly. However, certain general principles of construction apply to all the frame members, and these will be described later with specific reference to Fig. 2.

The fire barrier assembly 10 shown in the drawings includes a door 14 and several penetration openings 15, 16, 17 and 18.

Details relating to these penetration openings will be described with reference to Fig. 3.

The principal materials used in the construction of a fire barrier assembly according to the invention are sheet steel, and mineral based refractory insulating material in the form of sheets and blocks. The preferred mineral based refractory material used for insulation is glass fibre reinfored cement (grc). The following description by way of example refers solely to the use of grc but it will be appreciated that other suitable materials, selected for their resistance to the normal environment and for their fire resistant characteristics may be used. These other materials may include for example glass fibre reinforced gypsum (grg) or materials consisting of or including mineral wool.

The grc material chosen must have superior fire-resistant properties. One particularly suitable material is a low-density fire-resistant grc marketed by Tarmac Industrial Holdings Limited under the Trade Mark VELMAC.

The steel used may be either heat-resistant stainless steel or a corrosion protected (e.g.

zinc-galvanised or painted) mild steel sheet, to ensure that the fire barrier is corrosion resistant.

Referring to Figs. 1 and 2, a typical upright frame member 11 comprises a core 1 9 formed from one or more bars of grc, and a pair of skin members 20, 21 of sheet steel.

The skin members 20, 21 are of thin gauge metal and, alone, would not have sufficient resistance to thermal distortion (for example buckling or curvature) to be used in the construction of a fire barrier. However, when combined with an inner core of the substantially incompressible grc, the metal sections are supported against such distortion.

In a fire, the thin sheet steel on the hot face of the upright might be expected to lose most of its strength at a temperature in the region of 500 to 1,000"C. The grc will then support the steel and insulate the steel at the cool face of the upright. This will still retain most of its strength because it is not excessively heated.

As a result of its composite structure, the upright can be expected to retain its integrity at high temperature.

The metal skin of the frame member is divided into two (or more) skin members, which are not in substantial thermal contact with each other. This reduces conduction from one side of the fire barrier to the other, since the grc has much lower thermal conductivity.

One method of connection is shown between the two skin members 20 and 21, through spaced fixing screws inserted at 22 between opposed small lugs 23, 24 on the respective skin members. The lugs 23, 24 are separated by a grc block, to reduce the radiative transmission of heat from the hot to the cool face of the barrier in a fire. In an alternative, the skin members are connected by small localised straps without the intervening grc block. The straps may be pop-rivetted to the skin members. The core 1 9 may be slid into the skin assembly on the construction site.

The advantageous behaviour of the frame member of the invention in the event of a fire can be predicted by considering how it differs in structure from a conventional solid steel frame member subjected to heat from one face.

In an upright made of solid metal, such as those previously proposed, a thermal gradient is set up through the material from the hot to the cool face. The material at the hot face has a high temperature, and expands to a length determined by the coefficient of thermal expansion of the material and that temperature.

The material at the cool face has a lower temperature, and so expands to a lesser extent. The resultant effect on the whole upright is therefore to bend the upright, because its hot and cool faces have expanded by different amounts, while forming part of one member.

Where only thin gauge metal skin members 20, 21, are used, which are substantially out of thermal contact with each other, each behaves more or less independently. Thus, the skin members at the hot face (say the member 20) will expand considerably. The skin member 21 at the cool face will tend to remain as it is or expand only very little. Because the two skin members are independent, the substantial expansion of the hotter skin 20 does not greatly affect the cooler skin 21 because of limited stress transfer. The only factor affecting the cooler skin 21 is the amount of heating it undergoes, and that is reduced by the insulating effect of the grc core 1 9.

The main temperature gradient occurs through the grc core 1 9. However, the tendency for the hot face of the grc to expand is opposed by shrinkage of the grc due to loss of water of hydration from the cement.

It will be seen that there are no fixings of the steel skin members through the grc core.

Any curvature of the core during a fire is not directly transmitted to the steel skin members because of the absence of mechanical connection.

The result is that the structural integrity and stability of the fire barrier incorporating the frame member 11 is much less threatened than that of a solid frame member of conventional type because overall distortion of the frame members is diminished and hence they are better able to continue supporting the cladding structure 13.

This is very important in preventing the spread of fire, since (a) the fire barrier does not suffer a struc tural collapse and (b) the barrier does not allow penetration of flames, hot gases or smoke, which can cause breakthrough of the fire and danger to life from pollution of the atmosphere.

It will be seen, therefore, that the combination of metal skin members with a grc core can be regarded as synergetic, with the properties of the combination becoming greatly improved compared with those of either the metal or grc alone.

The metal skin member 20 is not in contact with the grc across the entire outer face of the core 19, but has a rib 25 formed in it by rolling or pressing. The other skin member 21 as shown has an alternative abutment 26, formed by welding on a channel section bracket.

The metal skin members therefore afford several stepped abutments. These are used to support the cladding structure, forming most of the surface of the fire barrier.

The innermost layers of the cladding structure are a pair of mineral wool boards 27, 28 or similar insulation boards or batts, which abut the lugs 23, 24 and are separated by an air space. These boards 27, 28 are held in place by outer grc sheets 29, 30, which are considerably stronger than the mineral wool boards and serve to improve the structural integrity of the fire barrier, as well as providing further insulation. The mineral wool boards are adhesively secured to the grc sheets by sodium silicate adhesive for example, before being fitted to the frame, to assist in speedy assembly.

The grc sheets 29, 30 abut against the skin members 20, 21 where the skin members are supported by the core 1 9 of grc. The edges of the grc sheets 29, 30 are constrained by the rib 25 or the abutment 26, but the sheets are not fastened to the metal skin members 20, 21. Instead, they are trapped by grc cover elements or strips 31, 32, which are themselves protected from fire damage by metal capping strips 33, 34. The cover elements 31, 32 and capping strips 33, 34 are secured by bolts, screws or other fasteners 35, 36, to the metal skin members 20, 21 respectively.

This arrangement has several advantages over directly securing the grc sheets and mineral wool boards to the frame members. Each of the cladding layers 29, 27, 28, 30, is held in place against displacement in a direction perpendicular to its own plane, but is free to make limited sliding movements in two dimensions in its own general plane.

This simplifies assembly because there is no need to align fixing holes in the cladding with holes in the frame members for example, or to drill the cladding members in situ. The tolerances allowable in the positioning of the frame members are greater than would otherwise be the case.

In the event of a fire, thermal expansion of the cladding structure can take place without transferring excessive forces to the frame members or to fastenings, which would tend to distort the fire barrier assembly.

Before leaving the description of Fig. 2, it should be added that the upright in this position is supporting a steel door frame 37.

This is clamped in place by a grc block, held in its turn by the grc cover element 32 and its fixing 36. The door frame does not form a thermal bridge between the opposite faces of the fire barrier assembly, since it only contacts the skin members 20, 21 at localised, staggered fixing positions, and is shielded to some extent by the VELMAC cover elements.

To allow for the penetration of services such as electrical cables, conduits, and pipework through the fire barrier, penetration openings are provided and these may take the form shown in Figs. 1 and 3 of the drawings. The openings 1 5 1 6, 1 7 and 18 are similar in construction and differ principally in size, so only one will be described in detail by way of example.

In Fig. 3, part of the cladding structure 1 3 of Fig. 1 can be seen, together with a section taken at the edge of the penetration opening 1 5. The mineral wool boards 27 and 28, and the grc sheets 29 and 30 are supported against external steps on a grc penetration frame 38. In the example shown, this is made as a one-piece frame of generally rectangular shape, but other types of frame are available to suit different penetration arrangements. The frame is made of fire-resistant VELMAC grc.

The cladding structure is held in place, again with a degree of sliding movement possible, by grc cover elements 31 and 32 and metal capping strips 33 and 34, using self tapping screws 39 fastened directly into the grc frame 38.

The opening inside the grc frame 38 receives the services, which are diagrammatically represented at 40. A refractory board facing 41, 42, is attached to the frame, surrounding the service 40 at both faces of the penetration frame. Alternative materials may be used, for instance a refractory or fireresistant putty. A fire-resistant sealant 43 is injected into the space around the service 40, to seal the service into the frame, and prevent flame or gas penetration in the event of a fire.

A suitable sealant is that marketed by Dow Corning under the identification "3-6548 Silicone RTV Foam".

Fig. 4 of the drawings shows a form of attachment used for attaching the fire barrier assembly to a structural part 44 of the building or installation in which it is positioned.

The part 44 may for example be a concrete, brick or blockwork wall or pillar of a building.

The core 1 9 of the upright is drilled at positions such as 45 to take a suitable fixing such as a expanding bolt assembly, which extends into the part 44. Only minor modifications are made to the sections of the metal skin members 20 and 21, to reduce the width of the upright to permit secure fixing to the part 44. The extreme edge of the fire barrier assembly is sealed to the part 44 by for example a fire-resistant sodium silicate putty (not shown).

The invention has up to now been described in relation to providing a vertical fire barrier assembly. It can, however, be adapted to form a barrier at any angle, for instance a horizontal fire barrier for use in the vertical service shafts of high-rise buildings, through which cables and conduits are led. In a major fire, breakthrough of fire into the service shaft is a considerable hazard, since it can lead to fire spreading through the entire height of the building.

The construction of a horizontal fire barrier is in principle the same as the construction of a vertical barrier, except that the weight of the barrier has to be supported across its area. To do this, load-bearing beams are provided, such as that shown in Fig. 5.

The beam, generally indicated at 46, comprises a lower section 47 of refractory stainless steel, supported against distortion by an inner core 48 of grc. The edges 49 of the lower section 47 are extended to provide a support for a pair of grc sheets 50, forming part of the cladding structure. An upper steel section 51 is stepped to support upper grc cladding sheets 52, and lugs 53 are provided at suitable positions along the beam to take fasteners to secure the upper and lower metal sections 57 and 51 together, partly enclosing the grc core 48. Additional insulation boards of mineral wool for example can be enclosed within the space between the grc sheets 50 and 52.

Under some circumstances, where fire protection is only required from one face of the barrier, the metal sections 47 and / or 51 could alternatively be of corrosion-protected mild steel.

The beam 46 can be supported from below for example on corbels at its ends, or suspended from above by hangers. The use of hangers is particularly useful to support the beam when fire protection is only required beneath the barrier.

In any form described, the fire barrier can be made suitable for use where only one face needs to be protected from fire, by providing only that face with the grc sheet and insulation boards, and protecting the supporting members (uprights or beams) appropriately.

The fire barrier assembly which has been described in relation to Figs. 1 to 4 of the drawings is adaptable, even after being in service for a period. Cladding sheets of grc and mineral wool can be removed quite readily by removal of the grc cover elements and metal capping strips. Uprights can be added or re-positioned, for instance to add a doorway, or a service penetration frame. The sizes of the various components are preferably modular, in accordance with the modular sizes of precast concrete building structures.

A fire barrier assembly as shown in Fig. 1 of the drawings, with a total of 89 cable penetrations, and with the facings and frame member cores of VELMAC was fire tested under standard conditions simulating a hydrocarbon fire ("CEGB Test"). The test was discontinued after 95 minutes, at which time the barrier still retained its structural stability and integrity. Standard insulation criteria were met throughout the test. After the barrier had cooled, it was found that the distortion was so slight that the VELMAC faced door could still readily be opened.

Claims (23)

1. A fire barrier assembly comprising a plurality of frame members and a cladding structure secured to the frame members, char acterised in that a frame member comprises one or more core members of mineral based refractory insulating material and a plurality of external skin members of incombustible sheet metal, partly but not wholly enclosing the core member or members and unsecured to the core member or members.

2. A fire barrier assembly according to claim 1 wherein the skin members are se cured to each other at spaced localised fixings only, to minimise heat transfer between the skin members.

3. A fire barrier assembly according to claim 1 or claim 2 wherein the skin members are separated by low conductivity material to reduce heat transfer by radiation at the points of fixing.

4. A fire barrier assembly according to any preceding claim wherein the skin members are of thin gauge sheet steel.

5. A fire barrier assembly according to claim 4 wherein the skin members are of stainless steel.

6. A fire barrier assembly according to claim 4 wherein the skin members are of corrosion-protected mild steel, for example galvanised mild steel.

7. A fire barrier assembly according to any preceding claim wherein the frame members further include cover elements adapted to conceal the skin members from direct contact with a fire.

8. A fire barrier assembly according to claim 7 wherein the cover elements comprise cover elements of mineral based refractory insulating material.

9. A fire barrier assembly according to claim 7 or claim 8 wherein the cover elements comprise outer metal capping elements.

10. A fire barrier assembly comprising a plurality of frame members and a cladding structure secured to the frame members, characterised in that the cladding structure includes at least one sheet of mineral based refractory insulating material so retained at its edges by frame members as to have a limited degree of sliding movement in its own general plane, relative to the frame members.

11. A fire barrier assembly according to claim 10 wherein the sheet is slidably located between an abutment on the frame member and a cover element.

1 2. A fire barrier assembly according to claim 10 or claim 11 wherein the edge of the sheet abuts a projection of one of the skin members.

1 3. A fire barrier assembly according to any one of claims 10 to 1 2 wherein the cladding structure includes one or more further insulation sheets.

14. A fire barrier assembly according to any preceding claim wherein the mineral based refactory insulating material is glass gibre reinforced cement (grc).

1 5. A fire barrier assembly according to any one of claims 1 to 1 3 wherein the mineral based refractory insulating material is glass fibre reinforced gypsum (grg).

1 6. A fire barrier assembly according to any one of claims 1 to 1 3 wherein the mineral based refractory insulating material is mineral wool.

1 7. A fire barrier assembly according to claim 14 wherein a grc sheet and a further insulation sheet of mineral wool are secured together using a fire resistant material such as sodium silicate adhesive, and are then secured to the skin member abutting one or more projections on the skin member.

1 8. A fire barrier assembly according to claim 1 7 wherein a similar cladding is applied to a skin member at the opposite face of the barrier assembly, with an air gap between the two mineral wool sheets.

19. A fire barrier assembly according to any preceding claim and having one or more penetration openings for services such as cables or conduits.

20. A fire barrier assembly according to claim 1 9 wherein the penetration opening comprises a frame of mineral based refractory insulating material such as grc through which the services may pass, the frame being closed by fire-resistant material adapted to surround the services.

21. A fire barrier assembly according to claim 20 wherein the fire-resistant material comprises fire-resistant boards and the services are sealed in position therein by means of fire-resistant sealant such as fire-resistant silicone foam.

22. A fire barrier assembly substantially as hereinbefore described with reference to, and as illustrated in, Figs. 1 to 4 of the accompanying drawings.

23. A fire barrier assembly substantially as hereinbefore described with reference to, and as illustrated in Figs. 1 to 4 as modified by Fig. 5 of the accompanying drawings.