Field of invention

The invention relates to a fire barrier and in particular a fire barrier for use with railway carriages.

Background to the Invention

Railway transport systems around the world are required to meet various standards of safety regarding protection in the event of a fire. Accordingly, trains are fitted with a variety of safety measures including fire doors, fire extinguishers, fire retardant seating and the like. However, a major risk specifically with rail travel is the possibility of a fire occurring beneath a train, for example due to fuel spillages during derailment. This is a particular pressing concern for underground trains.

In such situations, it is critical that passengers are able to evacuate a train as quickly as possible and that fire is kept at bay for a sufficient period of time to allow passengers to escape. To this end, many trains around the world are fitted with under- floor insulation which is designed to increase the time it takes for fire beneath a train to penetrate a carriage, thereby reducing the amount of smoke and heat present in the carriage during and shortly after a crash.

The majority of rail carriages comprise a thick layer of thermal insulation positioned between the base of the train (conventionally fabricated from aluminium) and the floor of the train on which the seating is attached. The conventional materials used include fibreglass, which to be effective must be of a substantial thickness, usually in the order of 100-200 mm. This combined with the supporting aluminium base plates adds weight to train carriages as well as decreasing the available space inside the carriage compartment which could otherwise be used, for example as further storage. The ultimate result of this weight and the expense of these materials is an increase in the cost of rail transport. Accordingly, what is required is a slim-line, lightweight system which offers at least comparable fire protection to existing systems. The invention is intended to overcome or at least ameliorate some or all of the above-mentioned problems.

Summary of the Invention There is provided in the first aspect of the invention, a fire barrier for a locomotive, or railway carriage, the fire barrier comprising a first layer comprising a synthetic fibre insulating material and a second layer comprising an intumescent material.

The provision of a fire barrier having both a synthetic fire insulating layer as well as an additional intumescent material layer allows for the aluminium base plates used in conventional fire protection systems to be dispensed with. This allows for a reduction in weight and it has been found that by using the second layer of intumescent material, the quantity of fibre insulating material required is lessened. Accordingly, this allows for thinner and lighter fire barriers to be prepared having at least comparable effectiveness as fire barriers.

Whilst the fire barrier may be used as a direct substitute for existing insulation material, i.e. positioned between the base plate of the railway carriage and the interior of the railway carriage, it is often the case that the fire barrier comprises only the first layer comprising the synthetic fibre insulating material, the second layer comprising an intumescent material and a means for affixing said layers to a locomotive or railway carriage. In other words, the fire barrier may be positioned on the outside of a railway carriage or locomotive, not sandwiched between a base plate or outer wall and the interior of the railway carriage or locomotive.

Typically, the synthetic fibre insulating material is a non-woven fabric and even more typically a synthetic fibre insulating material comprises one or more polymers. The term "polymer" as used herein is intended to refer to long macro molecular molecules consisting of a series of repeating monomer units, rather than materials such as glass, ceramics or stone that have been fabricated into fibrous structures. It may be the case that the first layer is directly adjacent to the second layer. This ensures that no thermally conducting layers or air gaps can be positioned between the first and second layers. This prevents the transfer of heat occurring through conduction via an interleaving conducting layer, which may extend around the sides of the fire barrier, or by convection due to heating and subsequent escape of air from the air gap.

As used herein the term "directly adjacent" is intended to mean that the first and second (or other) layers are positioned next to one another, without an intentional gap, space or interleaving layer between. The layers may be joined to one another using methods such as by gluing, mechanical retention (such as tacking, stapling, etc.), lamination, heat sealing, combinations thereof, or other means, but this is not essential in order for the two layers to be "directly adjacent" as defined herein. Where the layers are joined to one another this can help to reduce movement of the layers relative to one another which is desirable as this could reduce the effectiveness of the fire barrier and introduce the need for regular maintenance, to ensure that the components remain aligned.

It is typically the case that, in use, the first layer is positioned between the second layer and the floor of the railway carriage. This ensures that the intumescent material is on the outermost face exposed to the fire and the synthetic fire insulating material is positioned between the intumescent material and the railway carriage to prevent the transfer of heat. The second layer may be positioned directly adjacent to the floor of the railway carriage or some embodiments it may be the case that an air gap is provided between the second layer and the floor of the railway carriage.

The synthetic fibre insulating material often comprises one or more polymers and more typically the polymers comprise one or more polyamides. Even more typically the polyamide comprises an aromatic polyamide. Aromatic polyamides (or aramids) are particularly useful with the present invention as they form strong fibres that help to maintain the structural integrity of the insulation but they are also very lightweight and have excellent thermal insulation properties. The synthetic fibre insulating material used in the invention may be a material selected from: poly-/?ara-phenylene terephthalamide, poly-meto-phenylene isophthalamide or combinations thereof. Typically, the polyamide comprises poly- meto-phenylene isophthalamide. The polymer poly-meto-phenylene isophthalamide (commonly known as NOMEX ^RTM ) demonstrates exceptional thermal insulation properties and has been chiefly used in applications such as flame retardant clothing for the emergency services and the military. Furthermore, when made from the above mentioned polymers, the insulating material is flexible which allows the fire barrier to be transported more easily than conventional insulation, reducing costs.

Further, the water adsorbent properties of these materials mean that any moisture or water given off by an intumescent material is absorbed into the fiber insulating material thereby helping to maintain the temperature of the fire barrier below 100°C. This is advantageous as it increases fire protection time and insulating properties of the fire barrier.

The synthetic fibre insulating material may also comprise a polysilicic acid wherein the polysilicic acid comprises 85 - 99 wt% S1O2 and 1 - 10 wt% A1 ₂ 0 ₃ . The remaining content of the polysilicic acid may consist of other components such as water and various trace impurities.

Polysilicic acids are semi-ionic chains of silica molecules usually accompanied by an additional metal oxide that can be worked into fibres. These fibres demonstrate extremely low thermal conductivity and have exceptionally high melting points which, when used in the first layer, can increase the performance of the fire barrier by reducing heat transfer and adsorbing heat without (or with minimal) structural degradation. It may the case that the synthetic fibre insulating material comprises a polyamide and a polysilicic acid and typically the relative levels of polyamide to polysilicic acid by weight would be in the range of 5: 1 and 1:5. Even more typically, the ratio of polyamide to polysilicic acid by weight would be in the range of 1: 1 and 1:4, and even more typically still the ratio of polyamide to polysilicic acid by weight would be in the range of 2:5 and 2:7.

The inventors have found that adopting the relative levels of polyamide to polysilicic acid mentioned above, results in a great improvement in insulating properties of the fire barrier. Without being bound by theory, it is thought that the polyamide and polysilicic acid interact with one another to reduce thermal conductivity. This synergy between the different polymers, in the relative levels mentioned above, appears to improve the thermal properties of the fire barrier beyond that of equal amounts of each material used independently or in combination as separate layers.

However, there is no particular limitation on the relative levels of polyamide and polysilicic acid and the amount of polyamide present in the synthetic fibre insulating material may be as a wt%: 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 65%, 75%, 80%, 85%, 90% or 95% polyamide with the remaining material consisting essentially of polysilicic acid. So there may be in the range 5% - 95%, 10% - 90%, 15% - 85%, 20% - 80%, 25% - 75%, 30% - 70%, 35% - 65%, 40% - 60% or 45% - 55% polyamide as the synthetic fibre insulating material, or a range comprising any combination of the above.

The synthetic fibre insulating material may consist essentially of 25% poly-meto- phenylene isophthalamide and 75% polysilicic acid wherein the polysilicic acid comprises 85 - 99 wt% Si0 ₂ and 1 - 10 wt% A1 ₂ 0 ₃ (FABBLOC 45 Insulating Fabric, ^RTM ). By combining the any of the above mentioned polyamide synthetic fibre insulating materials with any of the above mentioned polysilicic acid synthetic fibre insulating materials, an extremely light weight and efficient insulation layer is produced. When combined with an intumescent layer in a fire barrier, it is possible to make thinner and lighter fire barriers which reduces weight, maximises railway carriage space and reduces the overall cost of fire proofing railway carriages whilst offering at least comparable resistance to fire.

Alternatively, the synthetic fibre insulating material may comprise 90% - 100% poly- meto-phenylene isophthalamide. Further, the synthetic fibre insulating material may be a non-woven material, and typically a needlefelt material. Alternatively, the synthetic fibre insulating material may be a woven (or scrimped) material in addition to, or instead of being a non-woven material. The synthetic fibre insulating material usually also comprises a finish, such as a pesticide, fungicide or mould resistant substance to increase the durability of the fire barrier. A variety of finishes can be used to accommodate for problem associated with specific railway carriage applications and environments as would be well appreciated by the skilled reader.

There is no particular limitation on the type of intumescent material used although it is typically the case that intumescent material is provided in the form of a coating applied to the first synthetic fibre insulating material. As the intumescent material heats up, it expands and evolves moisture which adsorbs heat and helps to maintain the temperature of the fire barrier at around 100°C or below. It is often the case that the intumescent material is an epoxy coating.

The intumescent material is typically an intumescent fire-resistant coating composition comprising hydrated alkali metal silicate and one or more rheology modifiers, selected from carbon, silicon, silicon carbide, a polysaccharide or a modified polysaccharide.

The alkali metal silicate used is typically sodium silicate, potassium silicate or lithium silicate or combinations thereof. Typically, a combination of alkali metal silicates is used, comprising sodium silicate in combination with potassium silicate. Typically the ratio of sodium silicate to potassium silicate is between 1: 1 and 10: 1, or may be 3 : 1 to 6: 1. Typically the ratio is about 4: 1.

The carbon used may be in the form of graphite, amorphous carbon or carbon black.

The polysaccharide is usually a gelling agent or gum. Polysaccharides typically include xanthan gum, guar gum, locust bean gum, alginate derivatives, scleroglucan gum, welan gum, starch and derivatives thereof. Chemically modified polysaccharides such as hydroxyethylcellulose and carboxymethylcellulose may also be used. It is often the case that the polysaccharide is xanthan gum. Xanthan gum is a naturally occurring polysaccharide from Xanthomonas campestris. It consists of a polymer backbone of β 1,4-D glucose units. At the 3 position of alternate glucose monomer units branches a trisaccharide side chain containing 1 glucuronic acid and 2 mannose residues.

The carbon may be used separately as a rheological modifier. Alternatively, it may be used in combination with one or more polysaccharides.

Typical combination of polysaccharides is xanthan gum in combination with guar gum or locust bean gum.

The rheology modifier is used at an amount of 0.5 to 10% of the content of aqueous silicate medium, preferably at 1 to 5% thereof, and especially 1.5 to 3.5%.

The intumescent coating may comprise a solvent, which is typically water. Alternatively, the solvent used may be an organic solvent such as glycerol, ethylene glycol, or Ci - C ₄ lower alcohols, or combinations thereof. Typically, the lower alcohol is methanol, ethanol or isopropanol.

Typically, the intumescent material used in the invention will comprise one or more diaryl alkane-diisocyanates and it is often the case that the intumescent material will comprise diphenylmethane-diisocyanate or a derivative therereof. It is typical for at least some of the intumescent material used in the invention to be Nullifire LP1205 (details of which can be found in UK patent application number GB2329389 A).

The fire barrier of the present invention typically comprises a synthetic fibre insulating material which has a thickness in the range of 5-50 mm, or more typically 5-35 mm, or even more typically 10-15 mm. It is usually the case that the second layer is a coating applied to at least part of one side of the first layer. This coating may be applied prior to incorporation of the fire barrier into a railway carriage or may be applied once the first layer of the fire barrier bas been fitted into position. Typically the fire barrier is orientated such that the second layer comprising the intumescent material is orientated towards the source of the fire, i.e. in use is orientated away from the railway carriage interior. The provision of an intumescent material on the outer face of the fire barrier means that during a fire this material chars and forms a protective coating over the synthetic fibre insulating material. Each material on its own would be insufficient to prevent the permeation of heat and fire into the railway carriage for a time 45 minutes or longer.

It is usually the case in the fire barrier of the present invention that the second layer has a thickness in the range of 1-15 mm, or more typically 1-10 mm, or even more typically 2-5 mm in thickness. This results in fire barrier of total thickness in the range 6 - 65 mm, or more typically 6-45 mm, or even more typically 12-20 mm.

It is usually the case that the fire barrier further comprises one or more fixing means arranged to secure the fire barrier to the underside of a railway carriage floor. As used herein the term "fixing" is intended to mean any method of retaining the first and second layers in position relative to one another. This could include friction, fitting, gluing, lamination, mechanical retention (such as tacking, stapling, etc.), heat sealing or combinations thereof.

By making use of the intumescent material or intumescent coating on the outer face of the synthetic fibre insulating material, it is not necessary to provide layers of sheet aluminium to shield the insulating material from fire. When exposed to fire and heat the intumescent material forms a protective coating which slows down disintegration of the synthetic fibre insulating material. Accordingly, the fire barrier can be fitted to the base of a railway carriage floor by a variety of fixing means. Examples of suitable fixing means for use with the fire barrier of the invention include heat-resistant adhesives, pins, clips or scaffolds to hold the fire barrier in position or combinations thereof. It is typically the case that the fixing means is a scaffold wherein the scaffold comprises a plurality of beams. Typically the beams are arranged in the same plane as one another and one or more of the beams is arranged to intersect or overlap to the other beams. This creates a "criss-cross" or "crosshatched" arrangement of beams which secure the fire barrier to the floor of the train. Usually, the beams are arranged in two sets. The beams in a first set being substantially parallel to one another and the beams in the second set being substantially parallel to one another wherein the beams of the first set are arranged perpendicular to the beams of the second set. Typically, the beams are narrow having a width in the range of 10mm to 100mm, or more typically 15mm to 50mm or even more typically 20mm to 30mm. The beams may further have and I-shaped, or H-shaped cross-section or may have a substantially rectangular cross-section.

The use of narrow beams rather than sheets of aluminium is particularly advantageous as this reduces the surface area of metal which is exposed to fire, aluminium is a particularly good conductor of heat and therefore large sheets of this material would transfer heat to the railway carriage, possibly around the insulating material used in prior art systems. By using beams, typically narrow beams, this surface area is reduced and conduction of heat through the beams is minimised. It is typically the case that the beams are made of metal due to the favourable mechanical properties and ease of manufacture. There is no particular limitation on the type of metal suitable for use in the invention, provided that the metal is sufficiently strong to support the weight of the fire barrier. However, it is typically the case that the beams are made from a metal having a thermal conductivity lower than aluminium and even more typically the beams comprise galvanised steel. Galvanised steel does not substantially warp or fail under high temperatures and while denser than aluminium, is a poorer conductor of heat.

The support structure may additionally comprise a plurality of wires or mesh-type material extending between the spaces defined by the beams. Typically, this is a galvanised steel mesh. This helps to prevent the fire barrier from sagging through the spaces defined by the beams and therefore prevents disruption of the structure of the fire barrier when the train is moving.

The fire barrier is typically of a substantially flat, sheet-like construction when deployed and is typically the case that the fire barrier is positionable under the floor of the railway carriage, substantially parallel to the floor. The fire barrier is intended to conform to the shape of the railway carriage and is therefore generally deployed in a position abutting substantially flat against to the chassis of the railway carriage. By adopting such configurations, this also minimises the amount of space taken up by the fire barrier and therefore maximises the available space within the cabin of the carriage. The fire barrier typically covers substantially all of the underside of the carriage. The fire barrier may cover in the range of 50% to 100% of the underside of the carriage, or more typically 60% to 95% or may cover in the range of 70% to 90% of the underside of the carriage.

Whilst the fire barrier is typically deployed as part of the floor of the railway carriages, the fire barrier may be incorporated into the walls and/or the ceiling of a railway carriage. Further, the fire barrier my be positioned between an outer and an inner wall of a railway carriage in order to provide thermal insulation and in the event that the outer wall of the railway carriage fails, either due to heat or mechanical failure, the fire barrier may provide further fire protection.

It is typically the case that the fire barrier provides fire protection for at least 60 minutes and it is even more typically the case that the fire barrier provides insulation for at least 45 minutes during a fire. The term "fire protection" as used herein is intended to refer to the prevention of fire from penetrating through the barrier. Further, the term "insulation" as used herein is intended to mean that the temperature on the non-fire side of the fire barrier does not rise above a mean of 140°C nor exceed a maximum of 180°C for the period of fire protection. The inventors have found that by employing the configuration described above, it is possible to achieve fire protections and fire insulations for periods of time longer than any existing products having the same slim-line configuration.

In a second aspect of the invention there is provided a railway carriage floor comprising the fire barrier according to the first aspect of the invention.

In a third aspect of the invention there is provided a railway carriage comprising the railway carriage floor according to the second aspect of the invention. In a fourth aspect of the invention there is provided the use of fire barrier according to the first aspect of the invention in railway carriages. Typically, the use of the fire barrier is used as a fire protection device in railway carriage floors.

Unless otherwise stated each of the integers described in the invention may be used in combination with any other integer as would be understood by the person skilled in the art. Further, although all aspects of the invention preferably "comprise" the features described in relation to that aspect, it is specifically envisaged that they may "consist" or "consist essentially" of those features outlined in the claims.

Further, in the discussion of the invention, unless stated to the contrary, the disclosure of alternative values for the upper or lower limit of the permitted range of a parameter, is to be construed as an implied statement that each intermediate value of said parameter, lying between the smaller and greater of the alternatives, is itself also disclosed as a possible value for the parameter.

In addition, unless otherwise stated, all numerical values appearing in this application are to be understood as being modified by the term "about".

The invention will now be described with reference to the following figures and drawings.

Brief description of the drawings

Figure 1 shows a perspective view of the fire barrier of the present invention.

Figure 2 shows a cross- sectional view of the fire barrier installed in a typical train floor.

Description

Figure 1 shows the substantially rectangular fire barrier 1 of the invention in a deployed, flat configuration. The fire barrier 1 consists of a first layer 3 formed from a composite mixture of synthetic fibre materials comprising 25% poly-meto- phenylene isophthalamide and 75% poly silicic acid, wherein the poly silicic acid comprises 85-99 wt% silicon oxide and 1-10 wt% aluminium oxide. In use, the first face 5 of a first layer 3 is orientated facing towards the train carriage. There is also provided a second layer 9 which is a coating of a intumescent epoxy coating (Nullifire LP1205) positioned on top of the second face 7 of the first layer 3. The first layer 3 has a thickness of 12 mm and the second layer 9 is applied as a wet coating and forms a layer having a thickness of approximately 2 mm. When dried the thickness of the second layer 9 typically reduces to around 1 mm. Attached to the a face 11 of the second layer 9 are two pairs of galvanised steel beams 13, 15. Both pairs of beams are substantially in the same plane, one set on top of the other, and are arranged substantially perpendicular to one another. The beams are I-shaped beams and whilst pictured in Figure 1 in an upright configuration, these beams may be deployed in a side-on configuration (H-shaped). The beams are attached to the first face 11 of the second layer 9 by means of a high temperature adhesive and in use the beams 13, 15 are usually fixed directly to the underside of a railway carriage floor 23 in order to sandwich the first layer 3 and second layer 9 firmly against the underside of the railway carriage floor 23.

Figure 2 shows a cross-section through a railway carriage floor system 21 including the fire barrier of the invention. The floor of the railway carriage 23 is typically furnished with either a carpet, rubber or other coverings 25 which may be present in intervals along the length of the floor 23. Such coverings 25 are typically attached by means of an adhesive or fixings at the interface 27 between the floor 23 and the covering 25. Beneath the floor 23 there is often a series of supporting struts 29 which assist in holding the floor 23 in place and spacing the floor 23 from the base 31 of the train. The upper face 35 of the first layer 3 of the fire barrier abuts against the base 31 of the train and a second layer 9 of intumescent fire resistant coating (Nullifire LP1205) is attached to the lower face 35 of the first layer 3. The first layer 3 and second layer 9 conform to the shape of the base 31 of the train and are held in place by means of galvanised steel beams 13, 15 positioned relatively below the second layer 9 in order to sandwich the first layer 3 and second layer 9 against the base 31 of the train. The skilled person would of course, understand that the number of galvanised steel beams 13, 15 required and the length and breadth of the fire barrier 1 can be adapted depending on the particular dimensions of the train carriage to which it is fitted. Further, whilst the fire barrier 1 is particularly suited to be incorporated into railway carriage floor system 21, the fire barrier 1 may be included to surround other parts of a railway carriage chassis in order to prevent fire penetrating the interior of carriage from other directions than from below. It would also be well understood that the configuration of railway carriage floor system 21 differs between different trains, and therefore the railway carriage floor system 21 may have more or less supporting struts 29 and may have very different structural configurations.

In an alternative embodiment, the fire barrier 1 may be directly pinned to the base 31 of the train, thereby removing the requirement of a supporting network of beams 13, 15.

It should be appreciated that the materials, methods and uses of the invention are capable of being incorporated in the form of a variety of embodiments, only a few of which have been illustrated and described above.