GB2157560A - Fire-protection material - Google Patents

Abstract

A thermal protection sheet material e.g. a fire blanket or weld-spatter protection sheet comprises a sheet of flame-resistant material e.g. glass fibre or ceramic fibre fabric either coated with a surface layer of pulverulent carbon or containing impregnated pulverulent carbon.

Description

SPECIFICATION Fire Protection Material The invention relates to a fire-protection sheet material and is particularly, but not exclusively, concerned with fire blankets, especially those for use in a domestic environment, and weld-spatter protection.

Fire blankets are in wide use, particularly in domestic environments, and with increased attention to fire safety over recent years are becoming used on an increasingly wide scale. As is known, the blanket has as its function the smothering of an area of fire and its isolation from surrounding areas. The blanket obviously must be made of non-combustible flame-resistant material and in the past asbestos has been the material almost exclusively used for fire blankets.

Over recent years, however, asbestos has become known to pose serious health hazards and a great deal of effort has been expended to provide alternative materials in response to legislative, governmental and market demands.

Various fire-resistant sheet materials have been proposed as an alternative. Fire-retarded plastics are one example but in large measure fibre glass textiles have been the materials used instead of asbestos since they provide the nearest alternative in terms of flame-resistance. Fibre glass cloths, however, offer far inferior flame-resistance to asbestos and despite efforts over a number of years no acceptable real improvement has been put forward. Increased cloth weights are, of course, one approach and cloths weighing 750 g/m2 and more do offer improved performance. However, this is at the expense of acceptable drape, these relatively high weight cloths normally being inflexible so as to render them useless as fire blankets in practice. In general, cloth weights of less than 500 g/m2 are needed to provide a serviceable fire blanket.

A typical fire blanket as now commercially available in the UK is a loomstate 400 g/m2 woven glass fibre cloth. This has acceptable drape properties. However, its fire-resistance properties are poor compared to asbestos. In combatting a chip pan fire (a typical domestic fire situation), for example, the cloth will withstand the flames from the burning oil for no more than about 7 to 10 seconds before the cloth becomes brittle and therefore unreliable as a means of smothering and isolating the flames. Melting commonly occurs after a few seconds more with the result that oxygen can gain access to the fire and flames may escape to threaten adjacent combustible materials.

The glass fibre cloth field has developed considerably over recent years and cloths are available in a large number of wide ranging different types. One form of heavy cloth is available in graphite-impregnated form (typically as a 1100 g/m2 woven cloth). The graphite impregnation is provided for lubrication purposes so that the cloth is more resistant to fibre-fibre attrition, a feature of heavy cloths which can otherwise cause the cloth to break down, particularly when the cloth becomes more brittle and rigid on heating during service.

It has now been found that graphite and other forms of carbon increase the flame-resistance performance of glass fibre and other forms of flame-resistant sheet material by a substantial amount which is totaily unexpected. In some cases, perforation of fibre glass cloth by melting takes 10 to 20 times as long as in the case of loomstate cloth.

According to the invention, there is provided a fire-protection sheet material comprising a sheet of flame-resistant material (e.g. glass fibre or ceramic fabric) either coated with a surface layer of pulverulent carbon or containing impregnated pulverulent carbon.

The flame-resistant sheet material will usually be made of fibrous material. Sheet glass fibre fabric is normally used in preference to ceramic fabric. The glass fibre (or other) fabric is generally of low weight, usually not more than 750 g/m2 in weight, and particularly 625 g/m2 or less so as to provide desirable drape characteristics. Although such fabric of weight from 500 to 750 g/m2 (e.g. 500 to 625 g/m2) can be used, a weight of less than 500 g/m2 is normally preferred since it has been found to provide adequate flame-resistance for normal applications (e.g. as a domestic fire blanket) and offers an obvious cost advantage.Fabric of weight between 100 and 500 g/m2will normally be the fabric selected, especially fabric having a weight in the range 150 to 450 gim2 in particular fabrics with weights ranging from about 200 g/m2 up to about 400 g/m2.

Although glass fibre fabric used in the invention may be non-woven, woven cloth is preferred. Woven cloth may be of plied yarn composition, and may be of weavelock construction if so desired. The weave in any of the woven glass fibre cloths referred to may be twill or plain. Loomstate (untreated) woven cloth is normally used. Monofilament type cloths are preferred in the case of both woven and non-woven cloths.

As an alternative to glass fibre or ceramic fabric, the flame-resistant material may be a high temperature-resistant aramid fibre cloth, for example a woven cloth sold under either of the trade names Kevlarand Nomex.

The carbon coating or impregnation with carbon (e.g. at least 10 g/m2 of cloth, for example 10-50 glum2, preferably 15 to 40 g/m2) has been found to increase the fire-resistance of the sheet material by a substantial amount. Melting of 400 g/m2 woven glass fibre cloth, for example, can be completely avoided during exposure to a butane gas flame for several minutes whereas the same cloth untreated melts after 10--15 seconds. The carbon used for coating or impregnation may be pulverized charcoal, carbon black or graphite, graphite being the preferred material.

Graphite can be applied to the sheet of fire-resistant material as a solid-in-liquid suspension. The continuous phase of such a suspension may be aqueous but will preferably be a volatile organic solvent such as a petroleum spirit. A graphite suspension sold under the trade name "Catalin" has been found to be especially satisfactory.

When applying a graphite suspension to the sheet of fire-resistant material, the liquid phase enters the interstices of the sheet material and carries graphite particles with it. Impregnation of varying degrees can be achieved by this means although commonly a relative concentration of graphite forms as a surface layer.

This has been found to have no real disadvantages and may even have some advantages.

Application of a graphite suspension can be accomplished by brushing or by spraying. Other means of application are envisaged and these may range from dipping to roller application (for example, by calendaring the sheet material between rollers at least one of which is supplied with suspension, for instance by running in a bath of suspension).

It has been found to be of advantage to seal the carbon coated/impregnated sheet material to prevent loss of carbon. Any of a variety of sealers may be used, a normal practical requirement being that, in their as-applied state, the sealers are non-combustible and preferably do not rigidize the sheet material or give rise to fumes. Sodium silicate is one example of a suitable sealer, although this can have the disadvantage of increasing cloth brittleness. Polytetrafluoroethylene is an alternative. A silicone such as that sold under the trade name "Dow Corning" is preferred and has been found further to increase the fire-resistance of the sheet material. PVA sealers are also suitable.

The sealer may be applied separately to the sheet material or may be applied by including it in a carbon-containing formulation for application to the sheet, for example a PVA/graphite blend optionaliy containing silicone.

In a preferred embodiment of the invention, a fire blanket comprises a sheet of woven glass fibre cloth having a weight of less than 500 g/m2 (e.g. 100 g/m2 to 450 glum2, preferably 150 g/m2 to 300 g/m2 or 200 g/m2 to 400 glum2), the cloth being impregnated and/coated with particulate graphite and a silicone or other sealer (e.g. a plastics), for example by it having had a graphite-in-liquid suspension applied to its surface and the sealer subsequently applied after substantially complete evaporation of the liquid phase of the suspension.

In tests, such a fire blanket has proved far superior to the untreated glass fibre cloth, having resisted cooking oil domestic fires and gas flames for at least ten times the exposure time before which the untreated cloth melts and rigidizes to the point of brittleness over the flame-contact area.

The following specific Examples are intended to illustrate the invention: EXAMPLE 1 Single Graphite Coating A 1 m by 1 m specimen of cloth was cut from a roll of woven loomstate 400 g/m2 glass fibre cloth. The specimen was placed on a flat surface and brushed with a single coat of a graphite suspension in petroleum spirit (sold underthetrade name "Catalin").

After preliminary drying for 20 minutes whilst flat, the specimen was hung for final drying at room temperature (approximately 18"C) for 35 minutes at which point drying was complete.

The specimen was then supported in vertical disposition on the work surface, a 25 mm thick ceramic blanket being placed immediately to the rear to reduce heat loss in testing and to concentrate the heat. A butane torch having an 18 mm nozzle was then ignited and the flame adjusted to maximum heat (approximately 950"C).

The flame was then applied to the cloth with the tip of the hottest (blue) region contacting the cloth. The results are tabulated in the Table.

EXAMPLE 2 Single Graphite Coating/Silicone Seal The procedures in Example 1 were repeated except that after complete drying, a coating of 100 ml silicone (sold under the trade name "Dow Corning") was applied by brushing and allowed to dry.

The results of testing are shown in the Table.

EXAMPLE 3 Double Graphite Coating/Silicone Seal The procedures in Example 2 were repeated except that after preliminary drying a second coat of graphite suspension was applied. Preliminary and final drying of the second coat was then proceeded with as described in Example 1.

The results of testing are shown in the Table.

EXAMPLE 4 Triple Graphite Coating/Silicone Seal The procedures in Example 3 were repeated except that a third coat of graphite suspension was applied after preliminary drying of the second. Preliminary and final drying of the third coat was then proceeded with as described in Example 1.

The results of testing are shown in the Table.

EXAMPLE 5 Control (Untreated Loomstate Cloth) The testing procedure described in Example 1 was repeated for a specimen of the loomstate cloth without applying any graphite or silicone.

The test results are shown in the Table.

EXAMPLE 6 Loomstate Cloth with Silicone Coating The procedures in Example 2 were repeated except that application of the graphite suspension was omitted.

The results of testing are shown in the Table.

As will be shown from the Table, the cloths treated in accordance with the invention have far superior flame-resistance both in terms of lack of perforation due to melting of the glass fibre material and in terms of the spread of brittleness from the epicentre of the applied flame. The degree of brittleness also differs with the material in the brittle areas of the cloths treated according to the invention comprising noticeably less brittle material.

It is thought that similar results could be obtained with 200, 250 and 300 g/m2 cloths so that effective fire blankets could be made, with materials costs savings, from these light-weight cloths.

Accordingly, in an embodiment of the invention, there is provided a fire blanket which comprises a glass fibre drapable cloth having a weight of 400 g/m2 or less, the cloth containing graphite or other form of carbon coated on a surface thereof and/or impregnated therein and the cloth preferably being sealed to prevent or reduce carbon loss by means of a silicone or other sealing substance. The silicone sealer alone produces a surprising increase in flame-resistance and the invention includes within its scope a fire blanket as above described (or a fire-protection sheet material of any of the other forms described hereinbefore) wherein the cloth is impregnated or coated with the sealer alone without the presence of carbon.

Flame Test (Seconds) First* Second* Third* Perforation2 Brittle Area3 Example Graphite Graphite Graphite Silicone No. Coating Coating Coating Coating Soil1 Test 15 30 240 15 30 240 1 40 - - - H N N N F F 10 2 40 - - V M N N N F F F 3 40 25 - V M N N N F F F 4 40 25 25 V M N N N F F F 5 - - - - L 7 12 X 15 27 X 6 - - - V L N N 25 F F 32 a a paper tissue was rubbed on the treated surface after drying: H=heavy soiling M=moderate soiling L=light or no soiling 2 N=no perforation; number=approximate diameter of hole (mm) 3 F=essentially no brittleness; number=approximate diameter of brittle area where material can be broken away with fingers (mm) * weight in grams X not measured.

Claims (19)

1. A thermal protection sheet material comprising a sheet of flame-resistant material comprised of glass fibre or ceramic fibre fabric either coated with a surface layer of pulverulent carbon or containing impregnated pulverulent carbon.

2. Sheet material as claimed in Claim 1 wherein the flame-resistant sheet material is glass fibre fabric having a weight of not more than 750 g/m2 exclusive of the carbon.

3. Sheet material as claimed in Claim 2 wherein the glass fibre fabric has a weight, exclusive of carbon, of from 100 to 500 g/m2.

4. Sheet material as claimed in any one of Claims 1 to 3 wherein the flame-resistant sheet material is woven glass fibre cloth.

5. Sheet material as claimed in any preceding claim wherein the flame-resistant sheet material is loomstate woven glass fibre cloth.

6. Sheet material as claimed in any preceding claim wherein the carbon coating or impregnation provides from 10 to 50 g/m2 of carbon.

7. Sheet material as claimed in any preceding claim wherein the carbon is graphite.

8. Sheet material as claimed in any preceding claim wherein the coated/impregnated flame-resistant sheet material is sealed to prevent or reduce loss of carbon therefrom.

9. Sheet material as claimed in Claim 8 wherein the sealer is sodium silicate, polytetrafluoroethylene, a polyvinyl acetate resin ora silicone.

10. Sheet material as claimed in any preceding claim and comprising a sheet of woven loomstate fibre glass fabric having a weight of from 150 to 450 g/m2, said fabric being impregnated and/or coated with graphite present in the fabric in an amount from 15 to 40 g/m2 and sealed by an application of a silicone sealer over the graphite-treated fabric.

11. Sheet material substantially as hereinbefore described in any one of examples 1 to 4.

12. A method of producing a treated thermal protection sheet material which method comprises applying to a sheet of flame-resistant material comprised of glass fibre or ceramic fibre fabric a solid-in-liquid suspension of carbon and allowing the liquid phase of said suspension to evaporate.

13. A method as claimed in Claim 12 wherein the liquid phase of said suspension is a petroleum spirit.

14. A method as claimed in Claim 12 or Claim 13 wherein the suspension is applied by brushing, spraying, dipping or by advancing the sheet material in contact with a roller supplied with a supply of said suspension.

15. A method as claimed in any one of Claims 12 to 14 wherein the suspension contains a material which seals the carbon to the sheet material.

16. A method as claimed in any one of Claims 12 to 14 wherein a sealer is applied to the carbon-treated fabric after application of the suspension.

17. A method as claimed in any one of Claims 12 to 16 wherein the suspension is a graphite-polyvinyl acetate blend containing a silicone.

18. A method as claimed in Claim 12 and substantially as hereinbefore described in any one of Examples 1 to 4.

19. Athermal protection sheet material whenever obtained by a method as claimed in any one of Claims 12to 18.