Known intumescent strip assemblies encapsulate intumescent material within a strip-like holder which is mounted for example along an edge of a fire door.

In the event of a fire the intumescent material is activated and it intumesces to create an intumesced material which occupies a far greater volume than the intumescent material prior to activation. The holder is either rigid under fire conditions and so is provided with openings to permit the expanding intumescing material to escape or is softened/destroyed under fire conditions to enable the intumescing material to escape.

The purpose of the intumescent material is to expand under early fire conditions to seal gaps located between opposed faces within the structure in which it is housed.

In both cases, after intumescence, the intumesced material is not encapsulated but is directly exposed within the gaps which are being sealed.

The intumesced material is generally of a foam-like structure or possibly a particulate composition, of low density. It tends therefore to be friable and have limited inherent mechanical strength. Accordingly, under later high temperature fire conditions the intumesced material may be liable to deteriorate physically due to direct exposure to the high temperature fire conditions and/or may be physically fractured due to distortion of the structure or turbulence from the fire.

According to one aspect of the present invention there is provided an intumescent strip assembly including an intumescent material encased within an elongate expandable hollow container formed from a high temperature resistant material, the container defining a first internal volume for containing said intumescent material prior to intumescence and being expandable by expansion of the intumescent material on intumescing to define a second internal volume greater than said first internal volume so as to contain intumesced material formed after intumescence of said intumescent material.

Various aspects of the present invention are hereinafter described with reference to the accompanying drawings, in which:- Figure 1 is a schematic cross-sectional view through an intumescent strip assembly according to a first embodiment of the present invention prior to intumescence; Figure 2 is a similar view to Figure 1 showing the first embodiment after intumescence; Figure 3 is a schematic cross-sectional view through an intumescent strip assembly according to a second embodiment of the present invention prior to intumescence; Figure 4 is a similar view to Figure 3 showing the second embodiment after intumescence; Figure 5 is a front view of a fire resistant grille incorporating intumescent strip assemblies according to the present invention; Figure 6 is a sectional view taken along line VI-VI in Figure 5; Figure 7 is an end view of a slat assembly used in the grille of Figure 5; Figure 8 is a side view of the slat assembly shown in Figure 7.

Referring initially to Figure 1 there is shown an intumescent strip assembly 10 including an elongate container or casing 11 which contains a strip of intumescent material 14. The intumescent material may be any conventional pressure generating intumescent material such as PALUSOL (RTM) or INTUMEX (RTM) which when exposed to elevated temperatures in excess of 100°C intumesce to form an expanded intumesced material.

The container 11 is expandable between a collapsed condition whereat it defines a first internal volume (which is sufficiently large to contain the intumescent material 14 prior to intumescence) and an expanded condition whereat it defines a second internal volume which is greater than the first internal volume and contains the intumescent material after intumescence. The container 11 is expanded from its collapsed condition to its expanded condition by the expansion of the intumescent material during intumescence.

The container 11 in Figure 1 is formed from a flexible sheet material 15 which is wrapped about the intumescent material 14. In the illustrated embodiment of Figure 1, the sheet material 15 is wrapped about the strip of intumescent material 14 so as to have overlapping end portions 15a.

The end portions 15a are not connected to one another and so may move relative to one another during expansion of the intumescent material 14 when it intumesces. This enables the internal volume of the container 11 to increase to its second internal volume such that after completion of intumescence, the intumesced material 16 is still contained within the container 11. This condition is illustrated in Figure 2.

It will be appreciated that the sheet material 14 may be tubular in form and that the sheet material defining the walls of the tube may be pleated and/or folded so as to define the collapsed condition of the container; the pleats and/or folds unfolding during expansion of the intumescent material to permit the container to expand to its expanded condition.

As indicated above, the container 11 is expanded from its collapsed condition to its expanded condition by expansion of the intumescent material.

The internal volume of the container therefore progressively increases from the first volume to define an increasing second volume until further expansion of the container 11 is prevented by the structure in which it is housed, eg it has filled a gap between a door and door frame, or alternatively expansion of the intumescent material stops. Thus the first volume is predetermined at the time of manufacture and the second volume is dependent upon the amount of expansion which is permitted within the structure or which is undergone by the intumescent material.

Preferably the sheet material is formed from a heat conductive material such as a metal foil which has a melting point above the maximum temperature of exposure expected under fire conditions or when exposed to the standard heating conditions of internationally recognized fire test methods such as BS 476 Pt. 20. A suitable metal is copper or a copper alloy which will withstand in excess of 2 hours direct exposure to this heating condition. It will be appreciated that other metals could be utilized where design considerations are less demanding or even more demanding. Accordingly, under fire conditions, after expansion of the container to its expanded condition, the container retains its integrity and so protects the intumesced material from direct exposure to the fire conditions.

It is envisaged that the gauge of copper foils would fall within the range of 0.02 to 0.3 mm, more preferably 0.05 to 0.2 mm and that the gauge of steel foils would fall within the range of 0.02 to 0.2 mm, more preferably 0.05 to 0.1 mm Forming the container from a heat conductive metal foil is also advantageous in that the walls of the container conduct heat around the periphery of the intumescent material about its entire periphery substantially at the same time. This permits the intumescent material to respond more rapidly and predictably to fire conditions.

In addition, the provision of container 11 for retaining the intumesced material can act to form a stronger intumesced material which is mechanically stronger than the intumesced material which is formed with conventional strip assemblies. In this respect, during expansion of the intumescent material, the container is initially expanded to its maximum expanded condition as permitted by the structure and thereafter further intumescence of the intumescent material acts to pressurise the intumesced material (since further increase in the second volume is not permitted) and so causes its density, particularly within its outer region, to increase. This has the advantage of making the body of intumesced material mechanically stronger.

In addition, the metal foil is impervious to gas and so retains the gases which escape from the intumescent material during intumescence. This also has the effect of pressurising the intumesced material and thereby create a dense intumesced material.

It will be appreciated from the above that forming container 11 from a metal foil has several different advantages and that different materials may be used for forming container 11 which may only provide one or more of these advantages.

For example, it is possible to form the container 11 from a sheet material which is heat conductive but not impervious to gas. This would provide the advantage of earlier and more predictable intumescence of the intumescent material but would not necessarily provide the advantages derivable from increasing the density of the intumesced material. A suitable sheet material may be a perforated metal foil or a mesh or fabric made from metallic filaments.

Alternatively the container may be formed from a sheet material which is not a good heat conductor but has sufficient heat conductivity to enable the intumescent material to be activated. Such a sheet material may or may not be impervious to gas. A suitable sheet material could be a fabric made from non-combustible fibres such as carbon fibres.

Since a metal foil as used for container 11 is susceptible to mechanical damage, eg puncture, it is preferred to encase the container 11 within a tubular protective sleeve 25 when it is intended to incorporate the intumescent strip assembly in a position where it is directly exposed to the environment. The sleeve 25 is preferably formed from a material having a low melting point which enables unhindered expansion of the container 11 under fire conditions. A suitable material is a plastics material such as polyvinylchloride; the sleeve 25 being preferably extruded from this material.

In Figures 3 and 4 the container 11 is formed from two elongate casing portions 50,51 which are telescopically inter-engaged. The casing portions 50,51 are both rigid and are preferably extruded from a suitable heat conductive material such as a metal which has a melting point above the maximum temperature expected under fire conditions.

A suitable metal from which casing portions 50,51 may be made is a steel sheet having a gauge of between about 0.6 to 0.9 mm, preferably about 0.8 mm The telescopic inter-engagement between casing portions 50,51 enable the container 11 to expand from the collapsed condition (Figure 3) to its expanded condition (Figure 4).

A fire resistant air grille 60 incorporating intumescent strip assemblies 10 according to the first embodiment is illustrated by way of example in Figures 5 to 8. The grille 60 includes a mounting frame 61 which is of generally square form made up of elongate frame members 62 extending along each side of the frame. A centrally located frame member 63 is also provided.

A plurality of grille slat assemblies 65 are provided which are supported at opposite ends between frame member 63 and opposed frame members 62.

The slat assemblies 65 define therebetween grille gaps 67 which during normal use define air passages for air to pass through the grille.

Each slat assembly 65 includes an intumescent strip assembly 10 in which casing 25 is preferably omitted. The container 11 of each strip assembly 10 is retained within support rails 68 which, as more clearly seen in Figure 7, are each of generally U-shaped cross-section.

Opposite ends of each rail 68 are attached to the respective frame member 63 and opposed frame member 62.

As seen in Figure 7, formation of the container 11 from metal foil is different to that shown in Figure 1. In this respect, two sheets of foil 15 are provided which are folded to cover one edge of the intumescent strip 14 and extend over both side faces of strip 14 to form two pairs of overlapping portions 15a.

Under fire conditions, the intumescent material 14 in each strip assembly 10 expands in direction E (Figure 7) and so causes the container 11 of adjacent grille slats to expand toward one another and thereby close the gap 67 therebetween. After gaps 67 have been fully closed, containers 11 are in mutual abutment and so further expansion is not permitted.

Accordingly additional intumescence of the intumescent material increases the density of the intumesced material and thereby improves mechanical strength of each expanded slat.