The present invention relates to an intumescent locking system, and in particular an intumescent lock that can automatically latch, lock, restrain or secure a closure member in a substantially closed state across an opening in a wall in the event of a fire.

Closure members, such as doors, windows and hatches, are used in a building to provide openable and closable vents across openings in walls within a building. In many circumstances, these closure members are designed to reduce or slow down the spread of fire or smoke within the building, and thus form part of the building’s fire or smoke control system.

A known characteristic of closure members - particularly those with front and back faces formed of separate sheet materials, is that upon application of a heat differential across the front and back faces of the closure member, the closure member will tend to warp or bend out of plane. This occurs because the high temperature on one side of the door (for example due to a fire in the room on that side of the door) will cause the face of the door on that side of the door to try to expand relative to the face of the door on the (relatively cooler) other side of the door. The resulting expansion can happen very quickly, especially where the two faces are made of separate sheet materials, as the relatively cooler face offers little resistance to expansion of the hotter face.

As closure members are typically hinged to the opening on one edge, and latched to the opening at a central part of the opposing edge, these points of the closure member typically will remain static relative to the opening - usually within a frame that is fitted within the opening. However, the top and bottom of the door at the opposing edge are typically unlatched and thus free to warp out of plane. They can thus quickly bend to flex into the cooler room side of the door in response to that temperature differential across the thickness of the door, which can then create partial venting of the opening that the door was closing. This is undesirable with fire doors or doors for controlling/holding back smoke (with fire or smoke seals around their edges) as it quickly diminishes their effectiveness at holding back the fire or smoke.

This warpage of the free corners of a closure member can also occur in solid doors as again the door can warp as a result of the temperature differential across the thickness of the door. Furthermore, the warping can be in the opposite direction if the interaction with the fire is such as to scorch the door in a manner that causes the material of the door to shrink (e.g. with a wooden door).

I n the prior art, multi-point latches serve to resist this corner flexing on doors and windows as a latch can be positioned nearer (or in) each free corner of the door. However, multi point latches are complex to install, as they commonly need to be recessed into the whole free edge of the closure member, and multiple keeps likewise need to be installed into the frame.

The present invention seeks to provide an alternative solution to resist the partial venting of an opening in a wall due to temperature-differential warping of a closure member that is closed across that opening.

According to the present invention there is provided an intumescent locking system, or an intumescent lock, for a closure member, the intumescent lock comprising a metal sheet backed with one or more intumescent pad, and one or more fixing for affixing the intumescent lock to the closure member or a frame or opening therefor. The intumescent lock can be used to resist bending of the closure member, such as a door, relative to its frame, upon the occurrence of a fire, or some other extreme heating against the door, whereby the door can better maintain an effectively shut configuration - i.e. it can avoid partial venting, as can occur if it warps at its corners. This is particularly useful for fire or smoke doors and windows, or fire or smoke hatches. It can also prevent further bending if the bending commences before the intumescent lock activates, it thus acting as an intumescent brake or retainer/restraint to apply a brake against that continuing bending.

In another aspect of the present invention there is provided a locking system, or a lock, for a closure member, the lock comprising a latching bolt for affixing to the closure member or a frame or opening therefor and a spring, wherein, in use, the latching bolt is biased towards an extended position by the spring, and restrained from advancement to that extended position by at least one heat sensitive component, wherein the or each heat sensitive component will soften, deform, dissolve or degrade at a temperature of between 65 and 240°C, releasing the latching bolt upon such softening, deformation, dissolution or degradation. Preferably the heat sensitive component will soften, deform, dissolve or degrade at a temperature below 190°C. Preferably the heat sensitive component is made of a polymer.

In some embodiments the latching bolt comprises a metal sheet backed with one or more intumescent pad, and the heat sensitive component is additional to the intumescent pad. In use the metal sheet and the intumescent extend parallel to the surface to which they are attached.

In some embodiments the latching bolt is affixed with one or more fixing. In some embodiments the fixing comprises a screw, rivet or bolt and the heat sensitive component.

In some embodiments the first aspect of the present invention is combined with the second aspect of the present invention. For example, the present invention provides an intumescent locking system, or an intumescent lock, for a closure member, the intumescent lock comprising a metal sheet backed with one or more intumescent pad, the metal sheet and the one or more intumescent pad together forming a latching bolt for the lock, the lock further comprising a spring, and the latching bolt being for affixing to the closure member or a frame or opening therefor, wherein, in use, the latching bolt is biased towards an extended position by the spring, and restrained from advancement to that extended position by at least one heat sensitive component, wherein the or each heat sensitive component will soften, deform, dissolve or degrade at a temperature of between 65 and 240°C, releasing the latching bolt upon such softening, deformation, dissolution or degradation.

This arrangement may be to provide two stages of advancement of the lock, one triggered at a first temperature, or in response to heat exposure from a first direction, and the other at a second temperature, or in response to heat exposure from a second direction.

For example, the one of the temperatures - usually the first - may be the temperature at which the heat sensitive component will soften, deform, dissolve or degrade and the other temperature (usually the second) is the temperature at which the intumescent of the intumescent pad(s) will activate (expand). The first may be lower than the second, or vice versa. In another embodiment, one of the stages (usually the first) may be upon heat exposure at the back of the frame, which is preferably where the heat sensitive component is at or adjacent, whereas the other stage (usually the second) may be upon heat exposure at the front of the frame, which is preferably where the latching bolt is at or adjacent.

The two may “activate” at the same temperature or at different temperatures.

In some embodiments the heat sensitive component will soften, deform, dissolve or degrade at a temperature that is lower than the required temperature to activate (expand) the intumescent pad(s).

In accordance with each aspect of the present invention, or a combined version, in some embodiments, the one or more fixing is a screw, a bolt or a nail. It could instead be a spot weld or some other fixing for attaching it to the frame, opening or closure member.

In some embodiments, the closure member comprises one or more hole for the fixing. The hole may extend through both the metal sheet and the intumescent pad.

The or each fixing may be positioned to extend through the one hole, or through a respective one of the holes, so that the fixings can be used for affixing the lock to the closure member or a frame or opening for the closure member.

In some embodiments, the fixings are low profile pan head machine screws. In other embodiments, they may be countersunk screws, or screws with a low profile head. These, or flat-head nails, rivets, spot welding or projection welding are beneficial as they tend to sit flush or close to flush relative to the metal sheet, thus allowing the intumescent lock to readily fit between the edge of the door and the frame (or opening) without any need to adjust the door or frame - with fire or smoke doors, due to the presence of a sealing member, there is typically already a 2-6mm gap between the edge of the door and the facing edge of the frame or opening. Preferably, the height of the head is no more than 3mm, and more preferably no more than 2mm above the free surface of the metal sheet, before its deflection. In some embodiments, the holes are pre-drilled or pre-formed into the metal sheet. However, if the metal sheet is adequately thin or soft, it is likely going to be a simple matter to instead drive the fixing - usually a nail or a screw - through the metal sheet (and typically the intumescent too) for affixing the intumescent lock to the closure member or frame (or opening).

In some embodiments, the holes, or the fixings, are applied to or through the metal sheet between 2 and 10mm away from respective ends or sides of the metal sheet.

In some embodiments, the fixings are integral to the metal sheet - e.g. welded thereto or formed out of the sheet material.

In some embodiments, the intumescent pad is coterminous with the metal sheet.

In some embodiments, the intumescent pad is adhered to the metal sheet.

In some embodiments, the metal sheet is elongated, with a length at least twice as long as the width and a width of between 10 and 30mm.

In some embodiments, there are two spaced holes, one at (or adjacent to) each end of the metal sheet, and there are two fixings.

In some embodiments, the gap between two of the holes or fixings is at least 30mm.

In some embodiments, the gap between two of the holes or fixings is no more than 200mm.

In some embodiments, the metal sheet is an elongated piece of metal, with a length at least twice as long as the width of the elongated piece, and there are fixings or holes only at or adjacent to two ends of the elongated piece.

The intumescent pad preferably extends at least substantially the full distance between the fixings or holes. In some embodiments, it extends the full length of the elongated piece. In some embodiments, it has a width corresponding to the width of the elongated piece. In some embodiments, the metal sheet is thinner than the intumescent pad, even before the intumescent pad expands in response to exposure to heat.

In some embodiments, the thickness of the metal sheet is between 0.5mm and 2mm.

In some embodiments, the metal sheet is made of stainless steel, zinc coated steel, zintec or galvanised steel. It may be painted to match the colour of the frame or closure member.

In some embodiments, the holes are elongated to form slots through which the fixings can extend.

In some embodiments, the metal sheet has a first straight edge and an opposing second substantially straight edge, and two ends, the holes or fixings being at or adjacent to the ends.

In some embodiments, the metal sheet has a substantially straight edge and a sidewardly extending flange extending from it that interrupts the substantially straight edge. Preferably, the flange is between 10 and 30mm long (along the length of the substantially straight edge. Preferably it occupies no more than 30% of the length of that edge of the metal sheet.

Preferably the flange is between 2 and 10mm wide - extending away from that edge.

The lock of each aspect of the present invention is arranged in use on an edge of the closure member, or on a closure-member-facing surface of the frame or opening for the closure member. It functions to latch, lock, restrain or apply a brake to the closure member (relative to the opening or frame) upon the intumescent strip becoming exposed to elevated temperatures that signify the presence of a fire (or upon the heat sensitive component being so exposed, or both. Upon that exposure, the intumescent strip expands to deflect a part of the metal sheet into or against the other of the closure member or closure-member-facing surface of the frame or opening for the closure member, or the heat sensitive component softens, deforms, dissolves or degrades to release the restrained latching bolt. It thus then latches, locks, restrains, retains or applies a brake to, the closure member, which could otherwise move relative to the frame or opening at the location of the intumescent lock.

In some embodiments, the other of the closure member or closure-member-facing surface of the frame or opening for the closure member is provided with a recess or keep. Then the deflected part of the metal sheet or latching bolt can be deflected into that recess or keep to increase the locking effect of the intumescent lock.

According to a second aspect of the present invention there is provided a doorset, or a closure member in a frame, one of the closure member and the frame being fitted with an intumescent lock comprising a metal sheet backed with one or more intumescent pad, the intumescent pad being against the one of the closure member and the frame.

Preferably, the intumescent lock is as defined above.

According to another aspect of the present invention there is provided a doorset, or a closure member in a frame, it being fitted with a lock comprising a spring and a latching bolt affixed to one of the closure member and the frame, wherein the latching bolt is biased towards an extended position by the spring, and restrained from advancement to that extended position by at least one heat sensitive component, wherein the or each heat sensitive component will soften, deform, dissolve or degrade at a temperature of between 65 and 240°C, releasing the latching bolt upon such softening, deformation, dissolution or degradation.

In another aspect of the present invention there is provided a doorset, or a closure member in a frame, it being fitted with a lock comprising a spring and a latching bolt affixed to one of the closure member and the frame, wherein the latching bolt is biased towards an extended position by the spring, and restrained from advancement to that extended position by at least one heat sensitive component, wherein the or each heat sensitive component will soften, deform, dissolve or degrade at a temperature of between 65 and 240°C, releasing the latching bolt upon such softening, deformation, dissolution or degradation. In some embodiments the heat sensitive component will soften, deform, dissolve or degrade at a temperature below 190°C. Preferably the heat sensitive component is made of a polymer.

In some embodiments the latching bolt comprises a metal sheet backed with one or more intumescent pad, and the heat sensitive component is additional to the intumescent pad. In use the metal sheet and the intumescent extend parallel to the surface to which they are attached.

In some embodiments the latching bolt is affixed with one or more fixing. In some embodiments the fixing comprises a screw, rivet or bolt and the heat sensitive component.

In some embodiments the first aspect of the present invention is combined with the second aspect of the present invention. For example, the present invention provides a doorset, or a closure member in a frame, it being fitted with a intumescent lock for the closure member, the intumescent lock comprising a metal sheet backed with one or more intumescent pad, the metal sheet and the one or more intumescent pad together forming a latching bolt for the lock, the lock further comprising a spring, and the latching bolt being for affixing to the closure member or a frame or opening therefor, wherein, in use, the latching bolt is biased towards an extended position by the spring, and restrained from advancement to that extended position by at least one heat sensitive component, wherein the or each heat sensitive component will soften, deform, dissolve or degrade at a temperature of between 65 and 240°C, releasing the latching bolt upon such softening, deformation, dissolution or degradation.

In accordance with each aspect of the present invention, or a combined version, the other of the closure member and the frame is fitted with a recess or keep that is generally aligned over the latching bolt or the intumescent lock such that upon expansion or extension of at least a part of the intumescent pad, or release of the latching bolt, at least a part of the metal sheet or the latching bolt will deflect into the recess or keep.

With the present invention the lock will cooperate with the recess or keep to resist or minimise partial venting of the opening due to warping of the closure member as a consequence of temperature differences between opposing faces of the closure member, or due to combustion-based contraction or expansion of one face of the closure member compared to the other.

In some embodiments, the recess or keep is aligned relative to the lock to only partially overlie the width of the lock/latching bolt before exposure of the lock to an expansion/release triggering temperature. The inventors have realised that due to the positioning of the intumescent lock at or on an edge of the closure member (or at or on a closure member facing surface of the frame), it will not be initially exposed to the full heat of a fire, even if the face of the closure member facing into the room of the fire is already exposed to that heat. This is because the frame and the closure member, and particularly the butting of the closure member against a stop of the frame, will initially at least partially shield the intumescent pad from that heat. As a consequence, the door will start to warp before the lock can activate from exposure to the heat of the fire.

By arranging the partial overlap between the lock and the recess or keep therefor such that upon some initial warping of the closure member that overlap can become a full overlap, the lock can be provided to expand into the recess or keep after that warp has started, but before the warping is sufficient to open a gap big enough to allow partial or significant venting of the opening in the wall. After all, upon some initial warping, a space between the closure member and the stop will form, which in turn exposes the gap between the closure member and the frame to the heat, and thus also the lock to that heat (which lock is in that gap), thus allowing activation of the intumescent to deflect at least a part of the metal sheet into the recess or keep. This positioning likewise benefits the aspect of the present invention with the at least one heat sensitive component as the door may start to warp before the at least one heat sensitive component starts to soften, deform, dissolve or degrade.

In a preferred embodiment, the expansion of the intumescent causes the metal sheet to bow outwardly between two or more fixings of the intumescent lock, and that bow flexes into the recess or keep, or against the other of the closure member and frame, to retain the closure member in a closed state - with minimal, if any, venting of the opening, and resisting further warping of the closure member (or frame relative thereto).

In some embodiments more than one lock may be provided on the closure member or frame - for example there may be one at a top corner of the closure member, spaced from a closing edge of the door, and another at a bottom corner of the closure member, spaced from the closing edge of the door. A conventional latch or lock may then be provided in a central region of the same edge of the closure member (opposing the hinged edge). The door is thus then provided with an alternative - intumescently activatable - multi-point latching system.

In some embodiments multiple locks of the present invention are installed on the closure member or frame/doorset - for example more than one along a top edge of the closure member or frame/doorset, and/or more than two along a (or each) side of the closure member or frame/doorset. In some embodiments one or more may be provided on a bottom edge of the closure member or frame/doorset.

In some embodiments, the closure member is a metal closure member with a metal front face and a metal rear face, each face formed of a metal sheet separated from the other by a fire resistant or fire retardant material, such as rock wool, mineral wall or a phenolic resin foam. The recess or keep might then be formed in the edge section of the closure member - e.g. in a top or bottom edge or in a free edge - opposite a hinged edge.

In some embodiments, the metal sheet has a flange extending out a side thereof, the flange being arranged to be part of the deflected part of the metal sheet, and sized to fit into the recess or keep upon that deflection.

In some embodiments, the recess or keep has an overhang that aligns with the flange such that the flange will engage under the overhang upon further warping of the closure member (or the frame). This resists inadvertent release of the lock from the recess if the warping of the door continues far enough, whereby the lock, and particularly the deflected part of the metal sheet thereof, will offer a resilient resistance to that further warping of the door, thus securing the non-venting state of the door.

In some embodiments, the intumescent pad is flexible, and the metal sheet offers the structural strength to the intumescent lock.

In some embodiments, the intumescent pad is made of a substantially rigid material made of a graphite compound in a matric of epoxy resin, reinforced with mineral fibres. The intumescent pad, once expanded, further providing substantial structural strength to the intumescent lock.

The preferred material for the intumescent pad is Technofire ® 2000, made by or Technical Fibre Products Ltd or supplied by Lorient ®.

In some embodiments the intumescent material is chosen to activate at a temperature above 130°C. Technofire® 2000 activates at 190°C.

It is preferred that the intumescent pad exhibit a free-space expansion ratio of at least 10:1 between pre-expansion and post expansion. Technofire ® 2000 offers a 22:1 expansion ratio and thus can easily cause a beneficial deflection of the metal sheet upon activation. However, as the metal sheet will resist that expansion, the activation is unlikely to achieve the full free-space expansion of the chosen intumescent material. It is for this reason that at least a 10:1 free space expansion ratio is chosen so that the material has sufficient expansion capabilities to adequately deflect the metal sheet (or the deflecting part thereof).

The present invention also provides a method of latching, locking, restraining or braking movement of a closure member within a frame using an intumescent lock as defined above, the locking occurring upon activation and expansion of the intumescent of the intumescent lock

The present invention also provides a method of latching, locking, restraining or braking movement of a closure member within a frame using a lock as defined above, the locking occurring upon releasing the latching bolt upon softening, deformation, dissolution or degradation of at least one of the heat sensitive components.

With the preferred misalignment of the recess/keep with respect to the lock, the resulting partial overlap, which corrects as the closure member starts to warp, will result in an aligned overlap when the intumescent pad starts to expand or upon softening, deformation, dissolution or degradation of at least one of the heat sensitive components. Further, when the intumescent activates, or after release of the latching bolt, the lock will activate (e.g. into the keep) to prevent or resist further warping, and thus locks, restrains or brakes movement of the closure member relative to the frame at the intumescent lock. In some embodiments, the lock or latching bolt is positioned opposite an opening in a face or edge of the other of the closure member and the frame so as to only partially overlap that opening, and upon a fire or heat heating one side of the door, the door will start to warp or bend, wherein when that warping tends to move the closure member relative to the frame so as to move the relative positions of the lock/latching bolt and the opening in a direction that starts to open a gap between frame and the closure member, the overlap of the lock and the opening will increase.

In some embodiments that side of the door is the side closest to a stop of the frame.

In some embodiments, when warping of the closure member or the frame relative to one another opens a gap between the closure member and a stop of the frame due to a fire on one side of the closure member, that opening of the gap exposes the intumescent pad to the heat of the fire and the intumescent pad of the intumescent lock then starts to expand.

In some embodiments, that warping causes a partial overlap between the intumescent lock and a recess or keep therefor to become a full overlap, the expansion of the intumescent lock then forcing part of the metal sheet into the recess or keep after that warp has started, but before the warping is sufficient to open a gap big enough to allow partial or significant venting of the opening in the wall.

In some embodiments this instead, or additionally, coincides with the release of the latching bolt.

In some embodiments, the expansion of the intumescent pad causes the metal sheet to bow outwardly between two or more fixings of the intumescent lock, and that bow flexes into the recess or keep, or against the other of the closure member and frame. This is preferably timed to retain the closure member in a closed state - with minimal, if any, venting of the opening. It serves to resist further warping of the closure member relative to the frame.

The metal sheet of the intumescent lock may have a flange extending out a side thereof, the flange being arranged to be part of the deflected part of the metal sheet upon expansion of the intumescent pad, and is sized to fit into a recess or keep in the other of the frame and closure member upon that expansion.

The recess or keep may have an overhang that aligns with the flange such that the flange will engage under the overhang upon further warping of the closure member or the frame.

In some embodiments, the lock is provided in combination with a keep, wherein the keep has an opening that is longer and wider than the lock. The full length and width of the intumescent lock (measured transverse to the expansion direction of the lock) is thus designed to expand into the keep in such embodiments.

In some embodiments the fixing is one or more bolt that affixes the lock to the frame, the opening or the closure member. In some embodiments, the or each bolt comprise a screw, a nut and a washer, the washer being a heat sensitive component. In particular, the washer is made of a heat softenable, heat deformable or heat dissolvable/degradable material, such that it will soften, deform, dissolve or degrade at a temperature of between 65 and 240°C, and more preferably a temperature below 190°C, or more preferably at a temperature below that of the expansion temperature for the intumescent pad.

In some embodiments the or each heat sensitive component has a glass transition temperature between 65 and 240°C, and more preferably below 190°C. In some embodiments this may be at a temperature below that of the expansion temperature for the intumescent pad.

By being at a temperature below that of the expansion temperature for the intumescent pad, there will be a tendency for the heat sensitive component’s material to soften first - i.e. to allow an initial movement of the latching bolt, before expansion of the intumescent.

In some embodiments the nut is a self-clinch blind standoff as that provides a clean finish to the installed lock - with the blind end thereof facing the door’s edge (or the frame if mounted instead to the closure member).

In some embodiments the spring is a coil spring. It may be provided behind the latching bolt - preferably behind the metal sheet through a gap or hole in the intumescent pad or pads, to apply a spring bias against the latching bolt or metal sheet for biasing it towards an extended position.

In some embodiments the latching bolt (or the metal sheet) is adequately stiff to minimise or prevent bending thereof under the influence of just the spring, although expansion of the intumescent pad might bend it in some arrangements.

In some embodiments there are two fixings, one at each end of the metal sheet.

In some embodiments the spring assumes a compressed state until the heat sensitive component(s) soften, deform, dissolve or degrade, whereupon the latching bolt will thereafter be allowed to displace towards its extended state - preferably into the keep.

In some embodiments there is a two stage activation of the lock. In some embodiments the first activation starts before the closure member starts to warp in the heat. In other embodiments lock allows for some warping and a first stage of activation of the lock is to lock the closure member with respect to the frame to prevent further warping of the door while the intumescent expands, or to ensure entry of the latching bolt into the keep. The intumescent may then be chosen from options that include those that expand less quickly.

In some embodiments the ends and a middle region of the latching bolt all expand or displace into the keep.

In some embodiments the latching bolt is affixed to a flange of the frame. In some embodiments the flange has three holes, two of the holes being for the fixings for affixing the latching bolt to the flange and the third hole being for the spring.

In some embodiments a false bottom is provided for the third hole by a cover plate. The cover plate may be screwed, welded or otherwise affixed to a rear of the flange. In an alternative configuration, for example where the flange is thicker, a blind hole may be provided for the spring, or, for a flat compressible coil spring, for example a conical coil spring, no third hole may be needed.

In some embodiments the heat sensitive component is a tube of thermoplastic. In some embodiments the tube surrounds the fixing for affixing the lock to the frame, opening or closure member.

In some embodiments the heat sensitive component extends behind a flange of the frame to present an external surface thereof to the environment on a rear side of the flange (and the door/closure member). With this arrangement the heat sensitive component (i.e. preferably the tube or washer) will be quickly exposed to the heat of the room on the rear side of the door/frame in the event of a fire, and sooner than the intumescent pad which is on the other side of the flange. The lock thus may be activated (by the heat sensitive component being softened, deformed, dissolved or degraded) before the intumescent pad even if made with an activation temperature (or a glass transition temperature) slightly above the activation temperature of the intumescent of the intumescent pad.

In some embodiments the or each heat sensitive component (i.e. the tubes or the washers) are only located behind the flange - the holes for the fixings over which they fit may be smaller than the washers/tubes, for example.

In some embodiments the or each heat sensitive component is made of polyethelyne.

In some embodiments the intumescent pad is made of 1.3mm thick Technofire (RTM) 67152B material.

In some embodiments the metal sheet is 0.9mm thick stainless steel.

In some embodiments holes for fixings at the ends of the metal sheet are at 10mm centres from the free ends of the metal sheet.

In some embodiments the metal sheet has a flange extending from a side thereof, for the reasons discussed above and below with respect to the first embodiment.

With each embodiment of the present invention, therefore, the lock will activate and lock the closure member in the event of a fire. In some embodiments this is a two stage activation, and the two stages can be either in a specific order or simultaneous, depending upon the location of the fire relative to the lock, largely irrespective of the activation temperature for each stage, as the heat of a fire may reach either one of the two activators first - i.e. the intumescent pad(s) or the heat sensitive component(s).

These and other features of the present invention will now be described in further detail, and purely by way of example, with reference to the accompanying drawings in which:

Figure 1 is a cut-away section though an edge of a closure member in the form of a door, within a frame;

Figure 2 is an enlarged view of the top corner of the door from Figure 1 , showing how it closes into the frame against or close to a stop of the frame, and showing a non- expanded intumescent lock fitted to the frame;

Figure 3 is a front view of the top corner of the door of Figure 1 with a front skin of the door removed to show a keep fitted inside a top edge of the door;

Figure 4 is an enlarged view of the top corner of the door of Figure 3, again with the front skin of the door removed to show the keep fitted inside a top edge of the door, and the non-expanded intumescent lock fitted to the frame;

Figure 5 is a plan view of a metal sheet of an example of an intumescent lock with a pair of holes for each receiving a fixing for attachment thereof to a door or a frame and a flange extending to one side thereof;

Figure 6 is an enlarged view, similar to that of Figure 2, cut through the top corner of the door and frame of Figure 1 , but showing it after exposure to an activating heat source on the right side (as drawn) of the door (such as a fire), whereby the intumescent lock has expanded to enter a part thereof into the keep in the top edge of the door, and whereby the door has warped into a bowed shape - with the top of the door having deflected away from the stop of the frame due to expansion of the right face of the door relative to a left face of the door (as drawn);

Figure 7 is an enlarged view similar to that of Figure 4, but with the intumescent lock in its expanded configuration from Figure 6, showing how it adopts a bowed configuration due to the fixings at each end thereof and how the bowing deflects the part of the metal sheet of the expanded intumescent lock into the keep;

Figure 8 is a plan view of a second example of an intumescent lock, viewing the metal sheet thereof, the intumescent lock having a pair of holes in the form of parallel and aligned slots, each being for receiving a fixing for attachment thereof to a door or a frame, and a flange extending to one side thereof;

Figure 9 is an enlarged view of the top corner of a door and frame of a second embodiment, similar to that of Figure 4, and again with the front skin of the door removed to show the keep fitted inside a top edge of the door, but wherein the non-expanded intumescent lock fitted to the frame is the intumescent lock of Figure 8;

Figure 10 corresponds to the view of Figure 9 but after expansion of the intumescent lock, similar to that of Figure 7, but showing how the slots allow the metal sheet to relative to the fixings to achieve a greater amount of bowing, thus permitting a shorter metal sheet to be used;

Figure 11 is an exploded view of an intumescent component - metal sheet to be backed with one intumescent pad - of a third embodiment of the present invention for fitting to a door frame;

Figure 12 is an enlarged sectional view of the component from Figure 1 fitted to a frame and with an edge of a door positioned relative thereto, the door having a keep positioned facing the component, showing how it appears prior to activation - with a non-expanded intumescent pad;

Figure 13 is a view corresponding to that of Figure 12, but after activation - with an expanded intumescent pad and a deformed washer - usually two thereof - see Figure 14;

Figure 14 is an enlarged front view of the embodiment of Figure 12, prior to activation, with the position of the keep in the door’s edge shown for reference; Figure 15 is an enlarged front view, similar to that of Figure 14, but showing a first stage of activation - after it has been exposed to heat that is insufficient to activate the intumescent, but enough to soften the washers, whereby the washers can become deformed in response to a biasing force from a spring of the latch, thus displacing the metal sheet towards the door edge upon the deformation of the washers, and, in this embodiment, into the keep; and

Figure 16 is an enlarged front view of the embodiment of Figures 14 and 15 after secondary activation, in which the heat was sufficient to expand the intumescent, and, in this embodiment, in which there was further deformation of the washers.

Referring to Figure 1 there is shown a cut-away section though an edge of a closure member, in the form of a door 10, within a frame 12. The door is in a closed state and as such bears against a stop 14 of the frame 12. The door is shown in section and it can be seen to comprise a window 16, a pull handle 18, a pair of latch handles 20 and a latch mechanism 22. There is also a sprung door closure mechanism 32 attached to the frame 12 for maintaining the door in a closed state as typically the door will be a fire door, whereby under many building regulations around the world, the door will need to be fitted with such a door closure mechanism. Such door closure mechanisms are well known and although only a part of it is shown in this figure, a skilled person will be very familiar with various types of such surface mounted closure mechanism with a sprung closure arm (not shown). The skilled person would also realise that such surface mounted closure mechanisms can be replaced or supplemented by hinged-edge mounted ones too (with a spring mechanism sunk into the edge of the door or into the edge-facing surface of the frame).

The door in Figure 1 also has a front kick plate 24 and a rear kick plate 26 which rear kick plate 26 houses an automated smoke seal mechanism 28 (for example a sprung one) for sealing the bottom edge of the door 10 against the floor or a threshold 30 of the frame 12 when the door is closed. This automated smoke seal mechanism 28 can be one to automatically raise and lower a bottom door seal upon opening and closing the door, using, for example, a hinge-side trigger mechanism. Such automated smoke seal mechanisms, often referred to as drop seals, are produced by companies such as Lorient ®. They are usefully provided on the doors that utilise the present invention so that when the door is closed in the frame, the door seal drops against the floor or threshold 30, but when the door starts to be opened again, the hinge-side trigger mechanism releases to lift the sprung seal member back up off the floor or threshold 30. It will nevertheless be recognised, however, that the use of a drop seal is optional. For example, it is instead possible for the rear kick plate 26 simply to overlay the bottom of the door, rather than being mounted on a frame for accommodating the drop seal. Indeed, all these various items of door furniture are optional - the window, the handles, the latch, the kick plates, the door closure mechanism, and can be excluded or replaced with alternative forms thereof, as well known in the art.

Referring next to Figure 2, an enlarged view of the top corner of the door 10 from Figure 1 is shown. This Figure better shows how the door 10 closes into the frame 12 against or close to a stop 14 of the frame 12. Although this figure shows a gap 34 between the door 10 and the stop 14, it is possible for that gap 34 to be zero. Indeed, its size will depend upon how tightly the latch mechanism 22 (see Figure 1) and the door closure mechanism 32 force closed the door, and also on the flatness/parallellness of a rear side 36 of the door relative to the stop 14, and on the height of any connecting rivets 49 (or screws or the like) used in the construction of the door (or the stop onto the frame).

Because that gap 34 is either zero or relatively small compared to the height of the stop 14 (the amount the stop 14 extends laterally across the opening), heat from a fire in the room to the right of the door (as drawn) will heat a rear side 36 of the door 10 before it can heat the intumescent lock 40.

Figure 2 also shows a non-expanded intumescent lock 40 fitted to the frame 12 - to a door-edge facing surface of the frame.

Still referring to Figure 2, a keep 48 is shown at the top of the door 10. This keep 48 defines a recess or opening 56 at the top of the door 10 into which the intumescent lock 40 can partially expand upon activation of the intumescent lock 40. As shown, this keep is fitted to bear against the front side 38 and the rear side 36 of the door 10 and is sandwiched between the metal sheets that form those front and rear sides 36. Those metal sheets also have opposing flanges at their tops that fold over the top of the keep to retain the keep in that top edge of the door. The flanges also provide overhangs across the top opening of the keep, which can provide an important retention purpose - as discussed later on. Although this arrangement for the keep is shown, any recess in the edge of the door could work to receive the intumescent lock when it expands. For example, it could be a hole cut in the edge of the door.

Figure 2 also shows a fixing (bolt) 52 being used to attach the intumescent lock to the frame 12. For this purpose, the frame can have a threaded hole into which the bolt can be tightened

In this embodiment, the bolt is not centrally mounted relative to the width of the intumescent lock. This is optional.

The intumescent lock comprises a metal sheet 44 and an intumescent pad 42. The intumescent pad is located between the metal sheet 44 and the frame as the intumescent lock 40 is attached to the frame. In this embodiment, the intumescent pad contacts the frame directly.

The bolt 52 has a low-profile head 54 such that it can attach the intumescent lock 40 to the frame without also touching the top of the door - there is free space between its bottom and the topside of the flange 50. In this embodiment the head extends no more than 3mm beyond the outer surface of the metal sheet, and preferably it is either countersunk into it - so as potentially to be flush or recessed into it, or it extends between 0.5 and 2mm beyond that outer surface (e.g. if not countersunk, or not fully countersunk).

Instead of a bolt 52, other forms of fixing can be used, such as screws, nails, rivets or even glue/adhesive. Although glue/adhesive will not create a head sitting proud of the metal sheet 42, it remains less preferable as it is more likely to fail in the event of a fire. A mechanical connection to the frame is thus preferred.

Although the recess or opening 56 and keep 48 is shown in the edge of the door 10, and the intumescent lock 40 is shown on the frame 12, it is possible for this to be reversed so that the keep or recess is in the frame and the intumescent lock is on the door’s edge. Further, whereas it is positioned at the top edge of the door, it could instead be on the free edge of the door (opposite the hinged edge of the door), or elsewhere around the door’s edge. There can be more than one of these intumescent locks around the door - e.g. one on the top and one near the bottom on the free edge of the door, or two on the free edge of the door, one near the top and one near the bottom. In some embodiments, there can possibly be an intumescent lock in the middle of the free edge of the door, if, for example, the door does not have a latch mechanism for keeping the middle of the door firmly latched in a closed state.

The door need not be limited to 1 , 2 or three such intumescent locks either - if the door is big enough to accommodate more, there may be more.

Referring now also to Figures 3 and 4, the keep is shown this time from the front of the door 10, rather than through an edge thereof. As can be seen the keep 48 is a shallow bowl and it is positioned to overlie at least part of the length of the intumescent lock 40 when the door 10 is closed. Figures 3 and 4 also show that there are two bolts 52 - one at or near each end of the intumescent lock 40. These two bolts leave a majority of the length of the intumescent lock bridging between the bolts, and most of that aligns over the keep 48.

Referring back again to Figure 2 the position of the non-expanded intumescent lock 40 is shown to be arranged, when viewed end on, not to align fully over the opening between the flanges of the keep - i.e. such that if the intumescent lock expands before the door moves slightly more open, it will not properly enter the opening/recess of the keep. It will still enter the keep, but will foul against the edge of the keep (or the overhanging flange 50 that is located thereover). As such, the recess or keep’s opening only partially overlies the width of the intumescent lock before exposure of the intumescent lock and door to an expansion triggering temperature. As discussed above, because of the small gap 34, the intumescent lock 40 that is positioned between the door and the frame will not be initially exposed to the full heat of a fire when the fire is to the rear side of the door - instead the rear face of the door (i.e. the rear side 36) gets heated first. This is because the frame and the door, and particularly the stop 14 of the frame 12, will initially at least partially shield the intumescent pad 42 from that heat. As a consequence, the door will tend to warp before the intumescent lock can activate from exposure to the heat of the fire. In the case of heating the front side 38 of the door, the front side 38 will attempt to expand faster than the rear side 36 of the door, so there will be a tendency for the door to bow or warp at the middle - i.e. for the middle of the door to move towards the heat. However, the hinged edge is secured by the hinges and thus will minimally bow (or will pull the frame with it. As for the free edge (opposite the hinged edge), the latch mechanism 22 will resist the bowing/warping of the free edge into that room (towards the fire), or it will pull the frame with any bowing/warping, whereas the free top and bottom of that free edge will instead bear against the stop. As a result, the door remains closed despite any bowing or warping of the door in this circumstance.

However, if the fire is instead in the room on the rear side 36 of the door, the bowing/warping will instead be in the opposite direction - causing the top and bottom of the free edge to bend away from the frame and stop, as shown in Figure 6. Although the latch mechanism 22, being at the approximate centre of the free edge of the door 10, will hold the central part of the door 10 relative to the frame 12 and stop 14, there is nothing yet to resist the movement of the top and bottom of the free edge relative to the frame 12 and the stop 14. The door 10 will thus bow relative to the frame 12 and the gap 34 between the stop 14 and the door 10 at the top and bottom of the door 10 will grow. This then brings the keep 48 and the opening or recess 56 thereof into a correct alignment with the intumescent lock 40, as per Figure 6.

This “mis-alignment” of the keep 48 relative to the intumescent lock 40 therefore relies on the fact that the gap 34 needs to grow enough such that the intumescent lock 40 can be exposed enough to the heat of the fire for activating the intumescent pad 42 in order for the alignment to be correct when that activation occurs (for a fire on the right side (as drawn) of the door 10). That activation will thus then expand the intumescent pad 42 to push/deflect a part of the metal sheet 44 into the keep 48.

As shown in Figure 6, that timing is when the gap 34 is significantly larger at the top of the door (although it tapers as the latching mechanism 22 holds the middle of the door in the closed state - so the door is bowing relative to the frame).

For a fire on the other side of the door, however, the latching, locking, restraining/braking or retaining effect of the intumescent lock 40 is not required to prevent partial venting of the door as the bowing (which occurs in the other direction) is already resisted by the centrally positioned latching mechanism 22 and the frame 12, as discussed above.

Referring back to Figure 2, it can be seen that the bolts 52 are not centrally located on the intumescent lock 40. This is optional but locating them to a more distal side of the metal sheet 44 from the stop 14 of the frame 12 provides a further benefit. As the intumescent pad 42 expands, it will try to bend or deflect the metal sheet 44. Centrally positioning the bolts 52 will provide a more balanced or even bending of the metal sheet 44. However, putting the bolts 52 further away from the stop 14 (and thus the gap 34) means that the side or area of the intumescent pad 42 that first gets exposed to the heat of a fire on that right hand side of the door 10 (as drawn) is potentially resisted less by the positioning of the bolts 52. This then potentially allows the metal sheet 44 to start to deflect quicker in that area. Furthermore, the metal sheet 44 at that proximal side 60 thereof (proximal to the stop 14) is potentially more free to deflect further than the opposite side 64 of the metal sheet 44 as it is potentially restrained less by the bolts. This then allows, or even encourages, the metal sheet 44 to twist in a defined direction, rather than just flexing or bowing.

As shown in Figure 6, the bending of the metal sheet 44 as it deflects need not exhibit such twisting, as the flexibility and elasticity of the metal sheet, as dictated by the thickness of the metal sheet and the material chosen for the sheet, will dictate whether it just bends or twists. However, twisting, if it does occur, would ideally want to be in a clockwise direction (as drawn) - i.e. such that the side of the metal sheet 44 closest to the stop 14 deflects further than the side of the sheet 44 further away therefrom. This is why the bolts 52 are preferably displaced to a side area of the ends of the metal sheet 44. This then helps to encourage the proximal side 60 of the metal sheet 44 (i.e. the side closest to the stop 14) to enter into the keep 48 first. Thus it is more likely to have entered the keep 48 before the warping of the door 10 takes the opening 56 of the keep 48 beyond that proximal side 60 of the metal sheet 44. The intumescent lock 40 will then be more likely to function correctly in the event of a fire. If instead the opening 56 has already passed that proximal edge 60, the intumescent lock 40 will be less likely to be able to retain the door 10 in its closed state, and partial venting of the door may then be more likely to occur. Referring next to Figure 7, a larger expansion of the intumescent pad 42 is shown, compared to Figure 6. That larger expansion forces the metal sheet 44 deeper into the keep 48. As the two bolts 52 secure the ends of the metal sheet 44 relative to the frame 12, the deflection of the metal sheet 44 is a bowing of the metal sheet 44. Therefore it is a central part of the metal sheet 44 that engages with the keep 48. Because the two bolts 52 cooperate to prevent or resist excessive rotation of the metal sheet 44 about axes of the bolts 52, the metal sheet 44 will provide a strong resistance to further bowing of the door 10 at the location of the intumescent lock 40. The intumescent lock 40 thus effectively bears and latches or locks against the door to restrict or resist the bowing of the door 10, and thus to prevent partial venting at that location of the door 10.

Referring next to Figure 5, a plan view of the metal sheet 44 of another example of an intumescent lock 40 is shown. It has a pair of round holes 58 for each receiving a fixing, such as the bolts 52, for attachment thereof (along with an intumescent pad 42) to a door 10 or a frame 12. As discussed above for the bolts 52 in the previous embodiment, the holes 58 are positioned closer to one side 64 of the metal sheet 44. This is for the same purpose as discussed above. However, this embodiment additionally has a flange 62 extending from the other side 60 thereof (the side proximal to the stop, or the proximal side 60 thereof). This flange 62 is positioned to correspond with the part of the metal sheet 44 that deflects into the keep 48 so that the flange 62 is one of the first parts of the metal sheet 44 to enter the keep 48 upon activation of the intumescent pad 42.

This flange 62 has a further beneficial function. As it is highly likely to enter the opening of the keep, as it is the first part of the metal sheet 44 to do so, it will serve to hook under the flange 50 of the door 10 that lies closes to the stop 14 as the door attempts to bow further than that shown in Figure 6. It will be appreciated, however, that instead of the flange 50 being part of the right side skin of the door 10, there may be a similarly positioned flange (relative to the flange of the metal sheet) provided as an integral part of the keep 48. Alternatively it might be a part of a top sidewall of the door 10 (or of the relevant side to which the keep is fitted).

As it hooks under that overhang or flange 50, it will positively lock the metal sheet 44 to the keep, thus resisting even more strongly any attempts by the door 10 to further bow.

In this embodiment, the flange 62 on the metal sheet is centrally located on the proximal side 60 thereof as that positions it centrally relative to the pair of holes for the fixings. In other embodiments the flange may be repositioned. For example, if an end of the metal sheet is designed to flex into the keep in response to expansion of the intumescent pad, the flange 62 would instead be at that flexing end.

Referring next to Figure 8, an alternative embodiment of intumescent lock 40 is shown. As per that of Figure 5, it has a flange 62 on its proximal side 60, and it is again generally rectangular, with holes 58 at each end. However, instead of round holes the holes 58 are elongated slots. Further, they are centrally positioned between the two sides 60, 64 of a main body of the metal sheet 44. The use of slots is explained with reference to Figures 9 and 10.

In this embodiment, the flange 62 works in the same way as before. Furthermore, the metal sheet is likewise designed to bow as the intumescent pad expands. However, as shown in Figure 9 the metal sheet is significantly shorter than in the previous embodiment. As shown, it has a length roughly corresponding to that of the length of the keep. Although this is an optional similarity in length, it does make alignment of the keep and the intumescent lock very straightforward when fitting them to the door and frame.

Figure 9 shows the intumescent lock 40 positioned to align over the keep 48, but as with the previous embodiment it is desired that end-on it is misaligned, like that shown in Figure 2. This is so that the other side 60 of the metal sheet (the side to be positioned furthest from the keep) generally aligns with the distal edge of the door facing side of the frame 12. The width of the metal sheet 44 (including the extension of the flange 62) is also similar to that of the previous embodiment. This then positions the free end of the flange similarly to that shown in Figure 2 - such that it lies above the opening 56 of the keep, and clear of the flange 50 or overhang above the keep with which it can ultimately engage in the event of a fire. Ideally it is positioned such that the door can flex through up to 10mm of bowing before it no longer clears that flange 50 or overhang (or more preferably up to 8mm).

Referring next to Figure 10, the intumescent lock of this further embodiment is instead shown in a deflected or expanded state. As shown the metal sheet 44 has bowed fully into the keep 48. However, due to the use of slots 58 rather than holes, the metal sheet has slid relative to the two bolts 52 which in turn has allowed a greater percentage of the metal sheet to deflect into the keep 48. This can then provide significant resistance to further bowing of the door 10.

To allow this sliding of the metal sheet, the bolts start further away from the ends of the metal sheet - as shown in Figure 9. Then, as the intumescent pad 42 expands, the metal sheet can flex to draw those ends together, such that the bolts end up nearer the free ends of the metal sheet 44, as shown in Figure 10.

In Figures 9 and 10, the head of the bolts 52 can be seen to align with the top of the keep. This can be an extreme of positioning for the bolt heads. It is preferred that a greater clearance is provided to ensure that the bolts do not interfere with opening of the door during normal operations of the door. This may be achieved with a lower profile head on the bolts, by countersinking the bolts (perhaps with chamfered edges to the slots, just as the round holes of the previous embodiment may be chamfered), or by lowering the door slightly.

Referring next to Figures 11 to 16, there is shown a further embodiment of the present invention. In this embodiment there is again an intumescent latch or lock (latching bolt) 40 and a keep 48 in an edge of a door 10 within a frame 12 for selectively receiving a free end of the intumescent lock 40 therein. Further, the intumescent lock 40 has a metal sheet 44 and an intumescent pad 42, much like that in Figure 4, but the keep 48 is now longer than the intumescent lock 40 as the full length of the intumescent lock 40 is designed to expand into the keep 48 in this embodiment.

As shown in Figure 11, the intumescent lock 40 in this embodiment again comprises fixings 152 to attach the metal sheet 44 and the intumescent pad 42 to the frame 12, but in this embodiment the fixings 152 comprise a screw/bolt 70, a nut 72 and a washer 74. In particular, the washer is made of a heat softenable, heat deformable or heat dissolvable/degradeable material, such that it will soften, deform, dissolve or degrade at a temperature below that of the expansion temperature for the intumescent pad. For example, the glass transition temperature of the material may be below that of the temperature of expansion of the intumescent pad. The washer is preferably a thick washer - like a tube, perhaps having a length equal to or longer than its external diameter. In this embodiment the nut is a self-clinch blind standoff as that provides a clean finish to the installed intumescent lock - with the blind end thereof facing the door’s edge.

In addition to the provision of the heat softenable, heat deformable or heat dissolvable/degradeable washer or tube 74, a spring 76 is provided behind the metal sheet 44 to apply a spring bias against the metal sheet 44 for biasing it towards an extended position. However, because of the washers 74 on the fixings 152 (one fixing at each end of the metal sheet 44) and due to the inherent stiffness of the metal sheet 44, the spring will assume a compressed state until the washers/tubes soften, deform, dissolve or degrade, whereupon the sheet 44 will thereafter be allowed to displace towards and into the keep 48 as the washers soften, deform, dissolve or degrade.

The choice of a material for the washers with a glass transition temperature below the expansion temperature of the intumescent pad is a preferred arrangement. However, it is also permissible for the intumescent to activate first - i.e. for the glass transition temperature to be at or above the expansion temperature of the intumescent pad. In this latter configuration, upon activation and expansion of the intumescent pad, either the washers also soften, deform, dissolve or degrade, or the stiffness of the metal sheet 44 needs to be sufficiently weak such that the metal sheet 44 will bend under the forces presented by the expanding intumescent, as per the previous embodiments. It thus then creates an initial activation of the intumescent lock. Then as the temperature reaches that required by the washers’ material, the intumescent pad can be allowed to further expand at its restrained ends (by the washers) as the washers soften, deform, dissolve or degrade. A full extension of the latching bolt then occurs into the keep.

With this modified version of the present invention, in the event of full activation of the intumescent lock 40, a greater degree of location of the latching bolt 40 into the keep 48 is achieved as even the ends by the fixings 152 can engage into the keep, unlike in the previous embodiments, in which the fixings 52 restrained those ends even after full activation of the intumescent pad or pads 42.

The intumescent lock of this embodiment otherwise has many common features to that of the first embodiment, including the initial offset of the latching bolt relative to the keep, as shown in Figure 12, to allow the door 10 to bend into alignment therewith as shown in Figure 13. As for the arrangement for the spring 76, in this embodiment the frame 12 comprises a flange 78 which extends down, over or under a side, top or bottom edge of the door, and into which three holes 84, 86 are provided. Two of the holes 84 are for the fixings 152, but the third hole 86 is for the spring 76. A false bottom 80 is then provided for that third hole by a cover plate 82, which may be screwed, welded or otherwise affixed to a rear of the flange 78. In an alternative configuration, for example where the flange is thicker, a blind hole may be provided for the spring, or, for a flat compressible coil spring, for example a conical coil spring, no hole may be needed.

In the preferred arrangement of Figures 14 to 16, the washers 74 soften, deform, dissolve or degrade before the intumescent pad expands. Therefore, from the installation configuration of Figure 14, where the intumescent pad and the spring are both compressed, and thus in which the metal sheet 44 lies close to the frame and out of the keep 48, upon exposure to a temperature or heat that is enough to soften, deform, dissolve or degrade the washer, the washers will soften, deform, dissolve or degrade under the bias of the spring 76, thus allowing the metal sheet 44 to displace into the keep as shown in Figure 15.

Due to the chosen inherent stiffness of the metal sheet 44 (the thickness of that sheet 44 can be predetermined in accordance with known material properties) that first stage expansion involves minimal or no bending of the metal sheet 44, and thus the metal sheet is sized to fit into the opening of the keep 48.

After that first stage expansion, in the event of a fire the temperature will continue to increase in the surrounding environment, whereupon the intumescent will also eventually trigger into its own expansion. It thus will then expand rearwardly to backfill the gap formed between it and the frame’s flange by the first stage expansion of the intumescent lock 40. That intumescent’ s expansion can be such that it will impose a larger force on the metal sheet 44 than that of the spring alone, whereupon the metal sheet 44 may be further displaced into the keep 48, for example by further deforming the washers 74, and/or by bending the metal sheet into a curve - a similar effect to that of the previous embodiments. Where the metal sheet 44 is to be bent by the expansion of the intumescent pad 42, the first stage expansion might simply be to move the metal sheet 44 towards the edge of the door - to close the gap there between, rather than necessarily taking it into the keep, with the bending thereafter taking the metal sheet 44 into the keep. For this arrangement, the shorter keep of the first embodiment might again be utilised. However, it is preferred for the first expansion to create an engagement with the keep to prevent or resist further warping of the door thereafter.

In this illustrated embodiment the washers are tubes of thermoplastic. As illustrated they surround the nuts. In this embodiment the nuts extend the full length between the two heads of the fixing 152 to define a fixed length for the fixing - by screwing the screw fully into the nut thereof.

In the illustrated embodiment, the washers/tubes extend only behind the flanges of the frame to present an outer surface thereof to the environment on that rear side of the flange (and door). With this arrangement the washer will be quickly exposed to the heat of the room on the rear side of the door, and sooner than the intumescent pad. It thus may be activated before the intumescent pad even if made with a glass transition temperature above the activation temperature of the intumescent of the intumescent pad.

Preferably the washers/tubes 74 are only located behind the flange - the hole for the fixings being smaller than the washers 74.

Preferably the screw of the nut of the fixings are made of a heat transmissive material to allow heat exposure thereon to be quickly transferred to the washers around them, or through to the intumescent.

Preferably the washers are made of polyethelyne.

Preferably the or each intumescent pads 42 is made of 1.3mm thick (prior to expansion) Technofire (RTM) 67152B material.

Preferably the metal sheet 44 is 0.9mm thick stainless steel. Preferably the holes 58 for the fixings 152 at the ends of the metal sheet 44 are at 10mm centres from the free ends of the metal sheet 44. The metal sheet 44 may be as shown in Figure 5, for example with the flange 62 extending from a side 60 thereof, for the reasons discussed with respect to the first embodiment.

In some embodiments the intumescent pads and metal sheet are replaced with a single component latching bolt for expansion into the keep only by the spring, although the dual action of the washers and intumescent is preferred. The present invention has therefore been described above purely by way of example. Modifications in detail may be made to the invention within the scope of the claims appended hereto.