GB2519067A

GB2519067A - Fire guards and materials therefor

Info

Publication number: GB2519067A
Application number: GB1315891.0A
Authority: GB
Inventors: Edward Watson Haynes; Steve Wise; Andrew John Gorton
Original assignee: WILLIAMS GRAND PRIX ENG
Current assignee: WILLIAMS GRAND PRIX ENG
Priority date: 2013-09-06
Filing date: 2013-09-06
Publication date: 2015-04-15
Also published as: GB201315891D0

Abstract

A multi-laminar material for containment of heat and/or flame is provided; the material comprising a first protective layer comprising a ceramic material, and a second protective layer comprising a carbon material. The ceramic material may be alumina, silica or aluminosilicate, e.g. in form of one or more layers of alumina fibre paper; the carbon material may be a carbon felt made from pre-oxidized polyacrylonitrile (PAN). The material may further comprise a structural layer such as a metal alloy (e.g. aluminium alloy), a metal or a polyaramid material; the material may be in a cellular structure such as a honeycomb configuration. The material may be used in a fire-guarded battery pack chamber (12, fig 1) of a motor land vehicle containing a battery system (22), the chamber having a relief port (34) with a bust disk (36). The chamber may also be coated with a silver epoxy layer (60, fig 5) being provided for earthing and/or shielding.

Description

FIRE GUARDS AND MATERIALS THEREFOR

The invention relates to multi-laminar materials for the containment of heat and/or flame, fire guards incorporating such materials and apparatus such as vehicles which incorporate such fire guards.

Some known batteries can malfunction, for example by catching fire if overcharged. This can not only bc a problem in itself but can be even more problematic when such batteries arc located near to combustible material where there is scope for fire to spread to the combustible material.

The present invention aims to alleviate at Icast to a certain extent the problems of the prior art.

According to a first aspect of the present invention there is provided a multi-laminar material for the containment of heat and/or flame, the material comprising: a first protective layer comprising a ceramic material; and a second protective layer comprising carbon material.

In some embodiments, the first protective layer comprises an alumina, silica or aluminosilicate ceramic material. The ceramic material preferably comprises one or more layers of a ceramic paper. In a preferred embodiment, the first protective layer comprises one or more, preferably two, sheets of alumina fibre paper. The layer of ceramic material prefcrably has a thickness of about 2-10mm, preferably about 2-5mm.

In some embodiments, the second protective layer comprises a carbon material which may be a carbon felt or may be provided as a foam or a honeycomb structure. Preferably, the carbon material is a prc-oxidiscd polyacrylonitriLe (PAM) carbon material. Preferably, the second protective layer comprises a carbon felt.

In some embodiments, the second protective layer has a thickness of about 1-5 mm, preferably about 1-4mm.

In some embodiments, the multi-laminar material further comprises a structural layer.

preferably located adjacent the first protective layer. Thc structural layer may be formed from any solid material, for example comprising polymeric material, metal, metal alloy or any mixture thereof In some embodiments, the structural laycr is formed by a core material and a coating (such as a panel comprising a core material and a coating). The coating preferably comprises a thermoset resin. The thermoset resin coating may comprise carbon fibre reinforcement. The themioset resin may be an epoxy-or phenolic-resin, preferably an epoxy resin, preferably with carbon fibre reinforcement. The core material may comprise a metal or metal alloy, such as an aluminium alloy (preferably a 5000 series aluminium alloy). In an alternative embodiment, the core material comprises an aramid polymeric material, preferably a nwta-aramid. In certain embodiments, the core comprises a,neta-aramid polymer, preferably poly(m-phcnylcnc isophthalamidc). The aramid, metal or metal alloy material is preferably provided as sheets, arranged to form a cellular structure, preferably where the cellular structure is in a honeycomb configuration. The structural layer preferably has a sandwich structure, with core material sandwiched between coating.

In some embodiments, the thickness of the structural layer is about 5-12mm, preferably about 6-9mm.

In the preferred multi-laminar material, the first protective layer is positioned adjacent the second protective layer. In a preferred embodiment, where a structural layer is present, the first protective layer may be positioned between the structural layer and the second protcctive layer. In some embodiments, sealant and/or adhesive may be present between any of the structural, first protective and second protective layers, or external thereto.

In some embodiments, an electrically conductive and/or electromagnetic shielding layer may be provided as part of the multi-laminar material. ftc eLectrically conductive and/or electromagnetic shielding layer may be attached in the material more towards a side thereof which is adapted to face a potential source of fire during use and/or to face inwardly to the interior of a structure to be formed by the multi-laminar material than the structural layer and/or at least one of the protective layers.

The electrically conductive and/or electromagnetic shielding layer may be covered by an insulating layer, such as an epoxy spray layer. The electrically conductive and/or electromagnetic shielding layer may form a Faraday cage or part of a Faraday cage. An electrical connector, such as a bolt, may be provided electrically engaged with the electrically conductive and/or electromagnetic shielding layer for connecting the same to earth.

The electrically conductive and/or electromagnetic shielding layer may comprise a distinct layer.

The electrically conductive and/or electromagnetic shielding layer may he directly attached to the second protective layer, optionally more towards a side of the material which is adapted to face a potential source of fife during use and/or to face inwardly to the interior of a structure to be formed by the multi-laminar material than the second protective layer and/or the first protective layer.

In some embodiments, the ratio of the thicknesses of first protective layer: second protective layer is 2:1 to 1:1. In some embodiments, the ratio of thickness of structural layer: first proteciive layer; second protective layer is 6-3:2-1:1.

A frirther aspect provides a multi-laminar material for the containment of electrical equipment such as a vehicle battery, the material having a structural layer and an electrically conductive and/or electromagnetic shielding layer.

A further aspect of the invention provides a fire guard which includes a sheet of material in accordance with the above aspect of the invention.

A further aspect of the invention provides a fire-guarded chamber which includes a battery pack located in a chamber thereof, thc chamber including a fire guard as in the previous aspect hereof At least a top wall of the chamber may be formed of the sheet of material.

The chamber may be sealed or substantially sealed.

The fire-guarded chamber may include a port arranged to open from the chamber to an exterior space upon application of a predetennined pressure at the port, the port being located on an underside of the chamber, the port preferably comprising a burst disk.

A further aspect of the invention provides a fire-guarded chamber which contains a battery pack and includes a port arranged to open from the chamber to an exterior space upon application of a predetermined pressure to the port, the port being located on an underside of the chamber, the port preferably comprising a burst disk.

A further aspect of the invention provides apparatus including a fire-guarded chamber as in any of the aspects hereof set out above and a tank arranged to contain a combustible fuel.

The tank may be located adjacent or above the fire-guarded chamber.

The apparatus may comprise a motor vehicle, such as a motor land vehicle. Application in other cnviromncnts such as UPS systems, aircraft or spacecraft is also envisaged.

The battery pack may comprise a traction battery pack of the motor vehicle.

The traction battery pack may be arranged to supply electrical energy to (and/or receive power from) a powertrain motor (or generator) of the motor vehicle.

The generator is operable to supply electrical energy for charging the battery pack upon transmission of a signal indicative of a braking command issued within the vehicle.

The present invention may be canied out in various ways and preferred materials and apparatus in accordance with the invention will now he described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a schematic view of a motor vehicle which includes a preferred fire-guarded battery pack chamber using preferred multi-laminar material in accordance with a preferred embodiment; Figure 2 is a schematic view of the battery pack chamber; Figure 3 is a view of the battery pack chamber from underneath; Figure 4 is a view of the battery pack chamber with a lid thereof removed; and Figure 5 shows a section through a modified version of the multi-laminar material.

There now follows a non-limiting detailed discussion.

A ceramic material' as referred to herein is an inorganic crystalline material. It should be appreciated that where the ceramic material is an alumina, silica or aluminosilicate ceramic, other components may also be present within the ceramic crystalline structure. Thus, in an alumina ceramic, alumina is the predominant oxide present, but other oxides including silica may also be present.

A ceramic paper' as referred to herein is a type of ceramic material in the form of a flexible sheet comprising ceramic fibres and optionally a binder. The ceramic fibres should be refractory any may, for example, be refractory alumina fibres.

Carbon fibres may be derived from polyacrylonitrile (PAN). A "pre-oxidized polyacrylonitrile carbon material" is a material formed from pre-oxidized PAN carbon fibres which may optionally have undergone further processing, for example to form a felt. The pre-oxidized material may undergo oxidation or may, preferably, be present in a pre-oxidised form.

A carbon felt' as referred to herein is a non-woven, carbon-containing fabric, which may be formed by compression of carbon fibres. A carbon felt is preferably formed from pre-oxidized polyacrylonitrile (PAN) carbon material. This may be referred to as a pre-oxidized PAN carbon felt.

An aluminium alloy' as referred to herein is an alloy in which aluminium is present, preferably as the predominant metal (by weight). Other elements present may include, for example, Cu, Mg, Mn, Si and Zn. An aluminium alloy as used herein is preferably an aluminium magnesium alloy, for example, a 5000 series aluminium alloy.

An aramid' as referred to herein is an aromatic polyamide. An ararnid is preferably an aromatic polyaniide in which at least least 85% of the amide linkages are attached directly to two aromatic rings.

A honeycomb' structure or configuration comprises an array of hollow cells formed between walls. [he cells are generally hexagonal in shape.

EXAMPLES

Test Procedure The test procedure used to assess the suitability of the multi-laminar material for use in a containment system for a lithium-ion battery was based on FAA Advisory Circular 20-1 35:

POWERPLANT INSTALLATION AND PROPULSION SYSTEM COMPONENT FIRE

PROTECTION TEST METHODS, STANDARDS, AND CRITERIA.

A test material was mounted with a gas flame to impinge directly on to the test material surface at a distance of approximately 20mm. The temperature achieved in the test set-up was between 980°C and 1020°C, using a Propane gas cylinder. For the purposes of comparative tcsting, a 1000°C flame temperature was the target.

S

A propane gas torch was sct at a short distance from the face of the test material. A thermocouple set in front of the test material surface measured the "flame" temperature. On the other side of the panel a thermocouple was bonded in a central position with tape. The two temperatures were monitored throughout the test using the Fluke multimeter. Fine gas adjustments were made to maintain flame maximum temperature. In general, initial flame temperatures were approximately 960°C, climbing to 1020°C after ten or more minutes.

The requirements for a material suitable for use in a containment system of the invention are that the material has minimal thickness, minimal weight, is capable of resisting a flame with temperature 1000°C directly on the surface for 15 minutes or more, while maintaining structural integrity, and providing sufficient thermal insulation to protcct a fuel containcr which may be positioned in a vehiclc adjacent the containment system.

The multi-laminar material of the invention was found to perform remarkably well and meet the above criteria, in contrast to a large number of other combinations of materials which were not able to satisfy the above requirements.

Materials tested for the protective layers included pre-oxidised PAN carbon felt, titanium alloy foil, silica aerogel, ceramic sheets. polyimide foam (Solimide®), refractory alumina fibre paper (Kaowool 1600 Paper), and alumina-boria-silica fibre fabric (Nextel ® 312), in various combinations as shown in Table 1. Various sandwich panel materials were tested for the structural layer. Panel core materials included Nomex ® (poly(in-phenylene isophthalamide)), aluminium alloy, and a ceramic board (Cotronics 360-I).

Test Material Test end Test end outer Duration of Condition of No inner face face test outer face, _______ temperature temperature where not Combination (°C) (°C) (minutes) satisfactory 01 Nomcx+Ti+ 1050 243 6 C-felt xl 02 Nomex + C-felt 985 309 6 xl 03 Nomex + Ii + 1000 250 15 Blistered C-felt xl 04 Nomex + C-felt 972 286 6 Flames from xl -I-Ti edges.

Ccramic+Ti+ 1026 230 15 C-felt xl 06 Ceramic-I-C-1008 266 15 felt xl 07 Ceramie+ C-1016 214/230/ 15/28/40 feltx2 220 08 Ceramic + 973 276 9.5 Aerogel Aerogel degraded 09 Al-core + C-Felt 999 254 16 x2 Nornex+C-felt 1020 274/218 15/25 Fuelbag x2 (with friel material bag material degraded attached to outer face) 11 Nornex + 1008 282 15 Ceramic sheet Ceramic sheet degraded 12 Nomex+ 1033 189/197 16/30 Ceramic+xl C-felt 13 Nomex+ 1007 258 15 Seam intact, Ceramic but very weak ______ (machined to 3mm) + xl C-felt (stitched seam) 14 A1-core+ 1040 206 15 Ceramic + xl C-felt ( stitched seam) Nomex+3rnm 1031 226 15 Kaowool + C-felt 16 Nomcx+3mm 1041 232 15 Kaowool + Panther felt with glass 17 Nomex+ 1025 252 iS Kaowool FP + C-felt + Nextel 312 AFIO 18 Nomex panel + 1042 264 15 Evonik Pt Evonik + C-felt foam degraded + Nextel (used) -stuck to CFRP panel Table 1: Material combinations tested and test summary. The inner face is that closest to the gas flame.

The pre-oxidised PAN non-woven carbon felt was demonstrated to provide a superior flame barrier. In the most severe test, the felt suffered oMy minor degradation after 40 minutes of direct flame impingement with temperatures in excess of bOO °C. The titanium alloy foil performed badly when used as a direct flame barrier. Significant distortion and discolouration was observed, and the heat protection provided for the CFR-epoxy sandwich panel behind it was very poor. Ceramic sheet (Cotronics 3 60-1) was intact after 15 minutes exposure with direct flame impingement on the surface, but the top layers were significantly degraded. The results shown in Table I indicate that a ceramic and carbon felt combination provides advantageous protective properties in comparison to other materials.

A multi-laminar material taken forward to testing in a full scale test battery containment box comprised a combination of two layers of 1.4mm thick Kaowool 1600 ceramic papcr (88% alumina, 9% silica, 3% other oxides) and one layer of pre-oxidizcd PAN non-woven carbon fell at nominal thickress 1.8 mm. A structural layer was provided comprising a sandwich panel with an aluminium alloy (5052 alloy) honeycomb core (6.525 mm thick) and carbon-fibre reinforced epoxy matrix skins each side (0.6 mm thick each). An aluminium alloy was used in the tested material because of its higher strength as shown in stress analysis. For some applications, alternative core materials could be used. For example, an alternative and lighter core material is a Nomex® honeycomb core.

In testing of the test battery containment box, following ignition of Lithium ion battery cells, the fire was allowed to burn until cxhaustion. The external temperature did not exceed 50°C.

When disassembled, the structural integrity of the multilarninar material had not been compromised. It was concluded that this combination of materials is suitable for containment of a lithium ion battery.

As shown in Figure 5, a modification to the above tested multi-laminar material comprises the same combination of two layers of 1.4 mm thick Kaowool 1600 ceramic paper (88% alumina, 9% silica, 3% other oxides) 40 and one layer of prc-oxidizcd PAN non-woven carbon felt 42 at nominal thickness 1.8 mm,. as well as the structural layer 44 comprising a sandwich panel with an aluminium alloy (5052 alloy) honeycomb core (6.525 mm thick) 46 and carbon-fibre reinforced epoxy matrix skins 48, 50 each side (0.6 mm thick each). However, the modified multi-laminar material 52 is also provided with an inner skin reinforcement region 52 comprising two Kevlar (registered trade mark) or other para-aramid fibre reinforced layers 54, 56. Also, an inner face 58 of the inner skin reinforcement region 52, which is a face intended to face towards a region where fire may break out such as to be the inner surface of a battery containment box inwardly of the structural layer 44, is covered by an electrically conductive andlor electromagnetically-shielding layer 60 which in turn is covered by an electrically-insulating layer 62. The layer 60 comprises a silver epoxy spray such as Cho-shield 596 (registered trade mark) and the electrically-insulating layer 62 comprises an epoxy insulator layer such as an epoxy spray, e.g. white epoxy spray.

The layer 60 provides both an earthing function and a Faraday cage and/or electromagnetic shielding function. To achieve the earthing function, a stainless steel or other bolt 64 may be bonded through the material 52, a free end of the bolt 64 being engaged by an electrical connection washer tab 66, a lock (or other) washer 68 and a nut or lock nut 70. The electrical connection washer tab 66 has a connector hole 72 for connection to electrical equipment to be earthed and/or to earth of the equipment (such as a vehicle) with which the material 52 is to be used. The bolt 64 has a shaft 74 which engages the electrically conductive and/or electromagnetically-shielding layer 60 and thus connects the layer 60 to the connection washer tab 66. The electrically conductive and/or electromagnetically-shielding layer 60 provides good electrical shielding between componentry on the two sides of the material 52 and also enables a battery box 24, 28 to be constructed as discussed below (or another structure to be constructed) which will provide good electrical earthing functionality.

The advantageous preferred materials described herein may advantageously be incorporated in a containment system to give fire resistance in the event of battery ignition, due to over-charging, or some other malfimetion. Such containment systems have thus advantageously been found to be capable of limiting the spread of both flames and heat for a period of 15 minutes or more.

Figure 1 shows an example of a motor land vehicle 10 in accordance with one embodiment, the vehicle including a fire-guarded battery pack chamber 12 located below a fuel tank 14 for supplying combustible liquid or gaseous fuel via a fuel line 16 to a combustion engine 18 (such as an IC engine) for supplying tractive power to at least one ground drive wheel 20 of the motor land vehicle 10.

The battery pack chamber 12 contains a Lithium-based (e.g. Lithium-ion) traction battery system 22 which is ananged to power the vehicle along by fractive eleefric motor power together with or as an alternate power source to the engine 18, the traction battery system also being chargeable in a conventional mamicr such as by a generator (not shown) of the vehicle 10, e.g. drivcn from tile engine 18 and/or by regenerative braking functionality, the generator in one example being reconfigurable as an electric motor to provide the tractive electric motor power mentioned abovc.

As shown in Fig. 4, the battery system 22 is secured to a rectangular base 24 o the chamber 12 by supports 26. The chamber 12 also has a lid 28 which has a rectangular top surface 30 and four rectangular sidcs 32 (two of which are shown in Fig. 2), the four sides 32, lid 28 and base 24 forming a sealed or substantially sealed enclosure containing the battery system 22 when the lid 28 is secured down onto the base 24.

At least the top surface 30 of the lid 28 and preferably also at least parts of and typically all of the sides 32 of the lid 28 are made from multi-laminar tnatcrial comprising a carbon fibre is reinforced-epoxy skinned sandwich panel with an aluminium alloy honeycomb core, plus two sheets of alumina fibre ceramic paper, supplemcntcd with one layer of prc-oxidiscd PAN non-woven carbon felt, with the ceramic paper and carbon felt held in place with a covering comprising a one ply aramid-epoxy composite fabric. Optionally, the base 24 is also made of this material.

[he base 24 incorporates a relief port in the form of a circular aperture 34 formed thercthrough and positioned below the battery system 22, a circular burst disk 36 being located within the circular aperture 34.

In thc event of a malfunction of the battery system, such as overcharging, resulting in fire there is firstly a limited amount of oxygen available to feed the fire. In the event of continued fire and a pressure build-up within the chamber 12, the relief port 34, 36 may advantageously open at a predetermined pressure by means of bursting of the burst disk 36. Accordingly, a catastrophic pressure build is advantageously avoided so that the chamber 12 cannot explode or otherwise release pressure in an uncontrolled manner. Furthermore, the relatively small burst aperture 34 may allow a flow of fire combustion products out of the chamber 12 while restricting the counteriow of oxygen-containing air into the chamber 12. Furthermore, the combustion products are advantageously ejected downwardly out of the chamber and away from the fuel tank 14.

S Furthermore, while the fire is burning and if it continues to do so, the preferred laminate material used in the construction of the chamber 12 provides excellent flame guarding and thermal transfer restriction performance for a continued period which may exceed 15 minutes.

Even with the fUel tank 14 containing combustible fuel and positioned near to, next to or above the chamber 12, the excellent performance of the chamber 12 helps ensure that fire and/or heat do not easily cause fire to break out at or in the region of the thel tank or elsewhere in the motor land vehicle 10.

It is envisaged that in other embodiments a plurality of similar relief ports 34, 36 may be provided through the base 24 of the chamber 12.

Various modifications to the specifically described examples are envisaged and are considered to fall within the scope of the present invention as dcflncd by thc accompanying claims as interpreted under patcnt law.

Claims

CLAIMS1. A multi-laminar material for the containment of heat and/or flame, the material comprising: S a first protective layer comprising a ceramic material; and a second protective layer comprising carbon material.
2. A material as claimed in claim 1 in which the first protective layer comprises an alumina, silica or aluminosilicate ceramic material.
3. A material as claimed in claim 1 in which the ceramic material comprises one or more layers of ceramic paper.
4. A material as claimed in any preceding claim, wherein the first protective layer comprises one or more layers of alumina fibre paper.
5. A material as claimed in any preceding claim in which the layer of ceramic material preferably has a thickness of about 2-10mm, preferably about 2-5mm.
6. A material as claimed in any preceding claim in which the second protective layer comprises a carbon felt.
7. A material as claimed in any preceding claim in which the carbon material is a prc-oxidized polyacry]onitrile carbon material.
8. A material as claimed in any preccding claim in which the second protective layer has a thickness of about 1-5 mm, preferably about 1-4mm.
9. A material as claimed in any preceding claim, wherein the material further comprises a structural layer.
10. A material as claimed in claim 9 in which the structural layer is formed by a panel comprising a core material and a coating.
11. A material as claimed in claim 10, in which the coating comprises a thermoset resin.
12. A material as claimed in claim 10 or 11, whcrcin thc coating comprises carbon fibre reinforcement.
13. A material as claimed in any of claims 10 to 12, in which the thermoset resin is an epoxy-or phenolie-resin, preferably with carbon fibre reinforcement.
14. A material as claimed in any one of claims 10 to 13 in which the core material comprises a metal alloy, a metal, an aramid polymeric material, or a mixture thereof
15. A material as claimed in any one of claims 10 to 14 in which the core material comprises an aluminium alloy.
16. A material as claimed in any one of claims 10 to 15 lii which the core material is provided as sheets, arranged to form a cellular structure; preferably where the cellular structure is in a honeycomb configuration.
17. A material as claimed in any one of claims 10 to 16, in which the thickness of the structural layer is about 5-12mm, preferably about 6-9mm.
18. A material as claimed in any preceding claim in which the ratio of the thicknesses of first protective layer: second protective layer is 2:1 to 1:1.
19. A material as claimed in any one of claims 10 to 18 in which the first protective layer is positioned between the structural layer and the second protective layer.
20. A material as claimed in any preceding claim in which sealant and/or adhesive layers are present between any of the structural, first protective and second protective layers, or external thereto.
21. A material as claimed iii any preceding claim which includes an electrically conductive and/or electromagnetic shielding layer.
22. A material as claimed in claim 21 which comprises a spray material.
23. A material as claimed in claim 22 which comprises a silver epoxy spray.
24. A material as claimed in any one of claims 21 to 23 when dependent upon claim 9 in which the electrically conductive and/or electromagnetic shielding layer is attached in the material more towards a side thereof which is adapted to face a potential source of fire during use andlor to face inwardly to the interior of a structure to be fonned by the multi-laminar material than the structural layer.
25. A material as claimed in any one of claims 21 to 24 in which the electrically conductive andlor electromagnetic shielding layer is attached in thc material more towards a side thereof which is adaptcd to face a potential source of fire during use and/or to face inwardly to the interior of a structure to be fonned by the multi-laminar material than at least one of the protective layers.
26. A material as claimed in any one of claims 21 to 25 in which the electrically conductive and/or electromagnetic shielding layer is covered by an electrically-insulating layer.
27. A material as claimed in claim 26 in which the electrically-insulating layer comprises an epoxy spray layer.
28. A material as claimed in any one of claims 21 to 27 in which the electrically conductive and/or electromagnetic shielding layer forms a Faraday cage or part of a Faraday cage.29 A material as claimed in any one of claim 21 to 28 which includes an electrical comector, such as a bolt, provided electrically engaged with the electrically conductive and/or electromagnetic shielding layer for earthing.30. A material as claimed in any one of claim 21 to 29 in which the electrically conductive and/or electromagnetic shielding layer comprises a distinct layer.31. A material as claimed in claim 30 in which the electrically conductive and/or electromagnetic shielding layer is directly attached to the second protective layer, 32. A material as claimed in claim 3 1 in which the electrically conductive and/or electromagnetic shielding layer is aftached to the second protective layer more towards a side of the material which is adapted to face a potential source of fire during use and/or to face inwardly to the interior of a structure to be formed by the multi-laminar material than the second protective layer and/or the first protective layer.33. A multi-laminar material for the containment of electrical equipment such as a vehicle battery, the material having a structural layer and an electrically conductive and/or electromagnetic shielding layer.34. A fire guard which includes a sheet of material as claimed in any preceding claim.35. A fire-guarded chamber which includes a battery pack located in the chamber, the chamber including a fire guard as claimed in claim 34.36. A fire-guarded chamber as claimed in claim 35 in which at least a top wall of the chamber is formed of the sheet of material.37. A lire-guarded chamber as claimed in claim 35 or claim 36 in which the chamber is sealed or substantially scaled.38. A fire-guarded chamber as claimed in claim 37 which includes a port arranged to open from the chamber to an exterior space upon application of a predetermined pressure at the port, the port being located on an underside of the chamber, the port preferably comprising a burst disk.39. A lire-guarded chamber which contains a battery pack and includes a port arranged to open from the chamber to an exterior space upon application of a predetermined pressure to the port, the port being located on an underside of the chamber, the port preferably comprising a burst disk.40. Apparatus including a fire-guarded chamber as any one of claims 35 to 39 and a tank arranged to contain a combustible fuel.4!. Apparatus as claimed in claim 40 in which the tank is located adjacent or above the fire-guarded chamber.42. Apparatus as claimed in claim 40 or claim 41 which comprises a motor vehicle.43. Apparatus as claimed in claim 42 in which the battery pack comprises a traction battery pack of the motor vehicle.44. Apparatus as claimed in claim 43 in which the traction battery pack is arranged to supply electrical energy to (and/or receive power from) a powertrain motor (or generator) of the motor vehicle.45. Apparatus as claimed in claim 44 in which the generator is operable to supply electrical energy for charging the battery pack upon transmission of a signal indicative of a braking command issued within the vehicle.46. A material substantially as described herein with reference to the accompanyingexamples.47. A fire-guarded chamber substantially as described herein with reference to the accompanying drawings.48. A motor land vehicle substantially as described herein with reference to the accompanying drawings.