Fire door

Abstract

A fire door having a total thickness of between 34mm and 36mm including a door core and a framework joined via a tongue and groove connection. The framework includes a recess configured to receive an intumescent strip. The door core comprises multiple material layers including a fire-retardant liner positioned between wood-based layers. The fire door provides at least 60 minutes of fire resistance and is suitable for retrofit into standard door frames without modification.

Description

FIREDOORFIELD OF THE INVENTION

[0001] The present invention relates to a reduced profile fire door. More especially, the invention relates to a multi-layered fire door construction, including at least one fire-retardant layer, wherein the total thickness of the door does not exceed 40mm.BACKGROUND TO THE INVENTION

[0002] Fire doors are essential for preventing the spread of smoke and fire within a building. The most commonly used fire door in the United Kingdom (UK) is an FD30, which is designed to withstand fire exposure for a minimum of 30 minutes. In commercial and higher risk settings, FD60 fire doors are more commonly used, offering at least 60 minutes of fire resistance before structural failure.

[0003] Most fire doors have a solid core construction, which may include materials such as particleboard, flaxboard, magnesium oxide board (magboard) or solid timber. The assembly of a fire door can vary greatly, some have a timber framing around the core with a laminated veneer surface; others have a lipping (typically 5 to 20mm thick) around the core with a veneer on top; and in some cases, a plywood, veneer or medium-density fibreboard (MDF) facing is adhered to the core without framing or lippings. There is no preferred construction method, provided that the door achieves the desired fire-resistance rating.

[0004] Fire doors may be equipped with approved intumescent strips, which play a crucial part in achieving the fire door rating. When subjected to high temperatures, the intumescent strips expand and seal the gap between the door edge and the surrounding door frame or threshold, thus impeding the passage of flames and smoke. Intumescent strips can be installed either within the door frame or recessed along the door’s peripheral edge.

[0005] In addition to intumescent strips, fire doors may be treated with intumescent materials, for example, an intumescent paint or graphite powder, to enhance their performance under fire conditions.

[0006] Standard internal doors in the UK typically range from 35mm and 40 mm in thickness. The use of intumescent strips and / or treatment with intumescent materials alone is insufficient to confer the necessary fire rating on doors of this thickness. In the event of a fire, these thinner doors are prone to rapid structural degradation and bucking because of insufficient material mass.

[0007] To meet modern fire safety regulations, FD30 fire doors are typically 44-45mm thick, while FD60 fire doors are typically 54mm thick. However, doors of this thickness present challenges for retrofitting into existing buildings, as most traditional door frames and thresholds were designed to accommodate 35mm thick doors.

[0008] Since door frames and thresholds in existing buildings are often pre-constructed or integral to existing architecture, modifying them to accommodate thicker fire doors is impractical, cost prohibitive and / or architecturally undesirable. Consequently, building owners are often forced to use non-fire rated doors, despite being aware that they do not meet current fire safety standards.

[0009] EP1643075 A2 discloses a fire door comprising a timber stile extending generally vertically along each side of the door, a timber mullion extending generally vertically between and spaced from the two stiles, two outer timber rails extending generally horizontally one along the upper side and the other along the lower side of the door, a central third timber rail extending generally horizontally between and spaced from the upper and lower rails, and a panel comprising a laminate of three plywood panels retained by timber beads within each of the spaces bordered by one of the stiles, the mullion, the central rail and one or other of the outer rails. A sheet of glass fibre containing cloth is adhered to each inner face of the outer two plywood sheets of the panel, and an intumescent containing sheet is adhered to each surface of the inner plywood sheet.

[0010] EP1643075 A2 teaches a fire door constructed of various structural layers supported by rails and stiles with a typical thickness of 54mm. Consequently, the fire door taught in EP1643075 A2 would be unsuitable for retrofitting into buildings with standard sized door frames or thresholds designed for 35mm doors.

[0011] The present invention seeks to provide a fire door having a thickness of 40mm or less, preferably being between 34-36mm, that meets appropriate fire regulations and ratings and achieves a fire resistance duration of at least 60 minutes without structural failure.

[0012] The improved fire door according to the present invention acts to resist the spread of fire and smoke for significant periods of time to assist effective evacuation of a building and minimise building damage. More especially, the present invention provides an improved fire door which has straightforward and seamless installation in new building constructions and retrofit applications within existing buildings having standard sized doorframes and thresholds. This is particularly beneficial for older buildings being repurposed as rental accommodations, hotels, or similar facilities subject to stringent fire safety regulations.

[0013] Fire testing conducted to evaluate the effectiveness of a fire door constructed in accordance with the present invention has demonstrated that they achieve a FD60 fire rating, offering a significant advantage in fire safety for standard door configurations and building construction.STATEMENT OF THE INVENTION

[0014] According to a first aspect of the invention there is provided, a fire door configured to have a reduced thickness profile, the fire door comprising a door core and a surrounding framework, wherein the framework is engaged about the peripheral edge of the door core and includes a recess configured to receive an intumescent strip.

[0015] In a preferred embodiment, the framework engages the door core via a tongue and groove connection joint, the framework having a T-shaped cross-section comprising a root portion defining the recess and a laterally extending tongue portion received within a corresponding groove in the door core.

[0016] Preferably, the door core comprises a plurality of material layers, including at least one fire-retardant liner positioned between two wood-based layers. The fire-retardant liner may consist of a fire-retardant material layer or a paper card sheet with fire-retardant material layers adhered to each side.

[0017] Preferably, the fire-retardant material comprises a nylon or polyurethane substrate impregnated or coated with an intumescent material, such as graphite powder or a solution of intumescent material.

[0018] In a preferred embodiment, the fire door may include first and second plywood face layers, a plywood core layer, a fire-retardant liner layer and a hardboard layer.

[0019] Preferably, the door core and door framework are dimensioned to maintain a total door thickness of between 34mm and 36mm, defined as the distance between the front and rear faces of the door.

[0020] Preferably, the plywood face layers may include apertures for receiving plywood infill panels which have a thickness of 3mm.

[0021] Preferably, the fire door is constructed to provide a fire resistance rating of at least 60 minutes in accordance with BS EN 1634-1 :2014+A1 :2018 standards, offering a fire-rated solution compatible with standard 35mm door frames without requiring structural modification.BRIEF DESCRIPTION OF DRAWINGS

[0022] The invention will now be described by way of example only with reference to the accompanying diagrammatic drawings, in which: -

[0023] Figure 1 is a perspective front view of a fire door constructed in accordance with the invention;

[0024] Figure 2 is an exploded view of a fire door constructed in accordance with the invention;

[0025] Figure 3 is a cross-sectional view of the fire door of Figure 2;

[0026] Figure 4 is a cross-sectional view of the fire door of Figures 2 and 3, whereby the tongue and groove connection between the framework and the door core is highlighted;

[0027] Figure 5 is a top plan view of a fire-retardant liner constructed in accordance with one embodiment of the invention; and

[0028] Figure 6 is a cross-sectional view of the fire-retardant liner of Figure 5.DETAILED DESCRIPTION OF THE INVENTION

[0029] A fire door constructed in accordance with the present invention is illustrated in Figures 1 to 4. The fire door is specifically designed to have a total thickness, including all material layers, of between 34mm and 36mm, thereby meeting the dimensional requirements of standard internal door configurations commonly found in existing buildings.

[0030] The fire door comprises a framework 2 formed from a suitable timber or engineered wood material. The framework 2 engages with the peripheral edge of a central door core 3 via a tongue and groove joint, providing a secure mechanical connection and structural integrity to the door assembly.

[0031] In a preferred embodiment, the framework 2 comprises two vertical stiles and a top rail. In an alternative embodiment, the framework 2 may also comprise an additional bottom rail, thereby forming a complete rectangular structure around the door core 3.

[0032] The framework 2 components may be joined using any suitable means, for example, nails or other fasteners, adhesives, or mechanical connections such as tongue and groove joints. Preferably, an adhesive containing an intumescent material will be used to enhance the fire resistance of the joints.

[0033] As best shown in Figure 4, the framework 2 has a generally T-shaped cross-section, comprising a root portion 30 and a laterally extending tongue 32. The root 30 includes a longitudinal recess 4 that is configured to receive one or more intumescent strips 6 (see Figures 3 and 4). Preferably, the intumescent strip 6 is continuously located along the peripheral edge of the framework 2.

[0034] The recess 4 provides a channel for the intumescent strip 6 allowing it to sit flush with the edge of the fire door.

[0035] The intumescent strip 6 is positioned such that, in the event of a fire, it expands under exposure to heat to seal the gap between the fire door and the surrounding door frame or threshold. This sealing action prevents the spread of fire and smoke, helping to contain the fire and reduce oxygen supply.

[0036] In an alternative embodiment, the intumescent strip 6 may be located within the door frame surround or threshold rather than within the fire door framework 2 itself.

[0037] The tongue 32 of the framework 2 projects laterally from one edge of the root 30, on the side opposing the edge housing the recess 4. The tongue 32 is dimensioned for insertion into a corresponding groove 34 or recess formed in the edge of the door core 3.

[0038] The door core 3 is the central portion of the fire door, and functions as the primary barrier against heat, flames and smoke during the event of a fire. The door core 3 is enclosed either fully or partially by the framework 2.

[0039] Preferably, the door core 3 is constructed of various material layers. The layers of the assembly comprise, in sequence: a 9mm plywood panel 10A (forming the front face of the door), a 3mm hardboard layer 8, a 12mm plywood core 16, a fire-retardant liner 18, and a second 9mm plywood panel 10B (forming the rear face of the door).

[0040] One or both of the plywood panels 10A, 10B may include apertures 12A, 12B adapted to receive decorative or structural 3mm plywood infill panels 14A, 14B. The number, shape and location of these apertures are variable and can be modified for aesthetic or functional purposes.

[0041] The fire-retardant liner 18 preferably comprises a 1 mm thick polyurethane or nylon cloth material. This cloth may be impregnated or coated with an intumescent material of approximately 0.55mm thickness, forming a fire-retardant material 42.

[0042] The intumescent material may be, for example, graphite powder and / or a solution of material which intumesces in the presence of excessive heat. A suitable intumescent solution would be an intumescent paint, such as that manufactured by the Applicant under the HW System brand.

[0043] An appropriate fire-retardant material 42 would be a 440 g / m2 nylon cloth impregnated with graphite powder.

[0044] As illustrated in Figures 5 and 6, in an alternative embodiment, the fire-retardant liner 18 may comprise a composite sheet formed by sandwiching a 0.5mm thick paper card 44 between 1 mm thick fire-retardant material layers 42. This construction provides both fire resistance and structural stability, allowing the liner to span the door surface without reliance on fastening means. It also simplifies the assembly process and offers enhanced protection as in the event that one face of the door or the fastening means are compromised under fire conditions, the fire-retardant liner 18 maintains coverage across the entire door surface and is unlikely to detach due to its inherent rigidity.

[0045] The fire-retardant material layers 42 are adhered to each side of the paper card sheet 44 using an adhesive (not shown), which may itself contain or be impregnated with intumescent material for added fire protection performance.

[0046] A groove 34 is formed along the peripheral edge of the door core 3 and is configured to receive the tongue 32 of the framework 2. The groove 34 has sidewalls 36 and a base 38 which are dimensioned to correspond to the tongue 32 for a secure fit.

[0047] In a preferred embodiment, the groove 34 is positioned between the front and rear door plywood face panels 10A, 10B and is defined by a shortened plywood core layer 16, fire-retardant liner layer 18 and hardwood layer 8. However, it is appreciated that other configurations may be used.

[0048] The contacting surfaces of the tongue 32 and groove 34 may be bonded with a suitable fire-retardant adhesive to form a permanent joint.

[0049] As shown in Figure 3, the various core layers, including the plywood core 16, fire-retardant liner 18 and plywood face panel 10B may be secured together by 18mm countersunk (CSK) screws 20. Alternatively, or additionally, the layers may be bonded with adhesive containing an intumescent material.

[0050] The plywood face panels 10A, 10B may also be secured to the tongue 32 portion of the framework 2 using mechanical or adhesive means. Furthermore, the material layers of the door core 3 may be secured by mechanical or adhesive means through the top of the door framework 2.

[0051] The use of a tongue 32 construction on the door framework 2 offers several advantages. For instance, this configuration increases the structural integrityof the framework 2 as more material is retained in the framework 2 compared to if the framework 2 were to house the groove configuration.

[0052] Most importantly, this configuration allows for a fire door with a compact design, enabling the door core 3 to be built within the structural boundaries of the framework 2. Furthermore, this configuration allows for improved tolerance to thermal expansion, minimising structural damage to the framework 2 under fire conditions.

[0053] In the event of a fire, the intumescent content of the fire door rapidly expands to form an effective barrier against the passage of fire, heat and smoke.

[0054] The plywood face panels 10A, 10B may be substituted with other wood-based sheet materials such as MDF, blockboard, solid timber or similar wood materials, depending on design preferences and performance criteria.

[0055] The material layers of the door core 3 are preferably coated with a heat activated intumescent material, such as an intumescent solution that expands when exposed to elevated temperatures. A suitable example includes an intumescent paint, such as that manufactured by the Applicant under the HW System brand.

[0056] It is appreciated that the terms “front” and “rear” may be used interchangeably when describing the door side.

[0057] Fire testing to BS EN 1634-1 :2014+A1 :2018 standards conducted by the Applicant demonstrates that doors constructed with the described internal fire-retardant liner 18 can meet an FD60 fire rating even with a total thickness of between 34mm and 36mm.

[0058] Achieving such a fire performance at this reduced thickness enables standard internal doors to comply with fire safety regulations without necessitating alterations to existing door frames or thresholds.

[0059] The fire doors described herein are lightweight, compact and visually indistinguishable from conventional internal doors in terms of appearance, weight and handling characteristics, while offering superior fire protection. They provide a hassle-free, regulation compliant solution for retrofitting into buildings, including period and listed properties.

Claims

CLAIMS1 . A fire door configured to have a reduced profile, comprising: a door core; and a framework engaged about a peripheral edge of the door core; wherein the framework is engaged about the peripheral edge of the door core via a tongue and groove joint; and wherein the framework comprises a recess configured to receive an intumescent strip.

2. A fire door in accordance with claim 1 ; wherein the door core comprises of a plurality of material layers; and wherein at least one section of the layers includes a layer of wood material located either side of a fire-retardant liner.

3. A fire door in accordance with claim 2, wherein the fire-retardant liner comprises a layer of fire- retardant material.

4. A fire door in accordance with claim 2, wherein the fire-retardant liner comprises a sheet of paper card having a fire-retardant material layer adhered to each side thereof.

5. A fire door in accordance with claim 3 or 4, wherein the fire-retardant material comprises a nylon or polyurethane substrate impregnated or coated with an intumescent material.

6. A fire door in accordance with claim 5, wherein the intumescent material comprises a graphite powder or a solution of material which intumesces in the presence of excessive heat.

7. A fire door in accordance with any preceding claim; wherein the framework consists of a T-shaped cross-section including: a root and a tongue; wherein the root comprises the recess configured to receive the intumescent strip, and the tongue portion extends laterally from a face of the root opposite the recess; wherein the door core comprises a groove configured to receive the tongue portion of the framework.

8. A fire door in accordance with any preceding claim;wherein the fire door has a total thickness of between 34mm and 36mm; the total thickness being defined as the distance between a front face and a rear face of the fire door; and wherein the tongue portion of the framework is disposed between said front and rear faces.

9. A fire door in accordance with claims 2 to 8; wherein the plurality of multiple layers of the door core comprise: a first plywood face layer; a second plywood face layer; a plywood core layer; a fire-retardant liner layer; and a hardboard layer.

10. A fire door in accordance with claim 9; wherein each of the first and second plywood face layers have a thickness of 9 mm; the plywood core layer has a thickness of 12mm; the fire-retardant liner has a thickness of between 1 mm and 3mm; and the hardboard has a thickness of 3mm.

11. A fire door in accordance with claims 9 and 10, wherein at least one of the plywood face layers includes one or more apertures configured to receive plywood infill panels.

12. Afire door in accordance with claim 11 , wherein each plywood infill panel has a thickness of 3mm.

13. Afire door in accordance with any preceding claim, wherein the fire door is configured to provide fire resistance for at least 60 minutes in accordance with BS EN 1634-1 :2014+A1 :2018 standards.

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