BS 476 – Parts 20 & 22

Fire tests on building materials and structures

Independent Assessment of Fire Resistance Under BS 476 Parts 20 & 22

BS 476 Parts 20 and 22 are long-established British Standards used to determine the fire resistance of building elements when exposed to fully developed fire conditions. Unlike reaction-to-fire tests, which focus on how materials contribute to ignition and flame spread, these standards assess how an element performs when subjected to a sustained heating regime inside a furnace.

Part 20 sets out the general principles of fire resistance testing, including the standard temperature–time curve, furnace pressure conditions, and the criteria used to evaluate performance. Part 22 applies this framework specifically to non-loadbearing elements such as partitions, doorsets, glazed screens and ceiling membranes, assessing their ability to maintain integrity and insulation during fire exposure.

Fire Cloak™ EV fire blankets have been tested using the heating and pressure conditions defined within BS 476 Part 20, providing independently generated data on their behaviour under sustained fire exposure. The results demonstrate the blanket’s ability to maintain fire containment for extended periods, supporting its role as a robust protective measure in scenarios where maintaining separation and controlling fire spread are critical.

How Fire Cloak™ Aligns with BS 476 Parts 20 & 22

Fire Cloak™ EV fire blankets have been assessed using the heating and pressure conditions defined in BS 476 Part 20, with evaluation aligned to the fire resistance principles applied to non-loadbearing elements under Part 22. These standards focus on how an element performs when exposed to a sustained furnace regime, rather than how a material reacts in the initial stages of ignition.

Under this framework, performance is considered in terms of defined fire resistance criteria. For non-loadbearing applications, the primary measures are integrity (E) — the ability to prevent the passage of flames and hot gases — and, where applicable, insulation (I) — the ability to limit temperature rise on the unexposed face. Testing is conducted against the standard time–temperature curve and controlled furnace pressure conditions specified in Part 20, providing a consistent basis for comparison.

Assessment of Fire Cloak™ under these conditions demonstrates its capacity to maintain physical separation and resist the formation of through-openings during extended fire exposure. This controlled containment behaviour supports its function as a temporary fire barrier, helping to isolate and manage EV fire incidents in environments where preventing fire spread and maintaining compartmentation are critical priorities.

BS 476 Parts 20 & 22 Test Reports

Fire Cloak™ EV fire blankets are supported by dedicated fire resistance test reports carried out using the heating and pressure conditions defined in BS 476 Part 20. These reports document the behaviour of the blanket when installed within a representative test frame and exposed to the standard furnace regime for a defined duration.

The testing records the applied temperature–time curve, furnace pressure conditions and detailed observations of specimen performance throughout the exposure period. Particular attention is given to the formation of through-openings, sustained flaming, deformation of the fixing system and the overall ability of the blanket to maintain separation under sustained thermal stress — criteria consistent with the integrity principles applied to non-loadbearing elements under Part 22.

Each report provides clear identification of the product tested, specimen dimensions and construction, fixing method, test date and the applicable clauses of BS 476 Part 20 referenced during the procedure. Temperature and pressure data, photographic evidence and behavioural observations are included to ensure full technical traceability.

For clarity and transparency, the complete BS 476 Part 20 fire resistance test reports for Fire Cloak™ are available below for download.

BS 476 Parts 20 & 22 Test ReportBS 476 Parts 20 & 22 Test Report
Specified and Recorded Furnace Temperatures
Time (mins)Specified Furnace Temperature (°C)Actual Furnace Temperature (°C)
02022
3502467
6603563
9663641
12705684
15739728
18766762
21789784
24809818
27826823
30842843
33856859
36869879
39881904
42892897
45902908
48912923
51921923
54930932
57938945
60945948
63953961
66960972
69966972
72973979
75979994
78985994
81990998
849961011
8710011010
9010061005
Furnace Pressure
Time (mins)Recorded Pressure (Pa)
00.00
321.50
621.70
919.90
1221.10
1522.00
1822.40
2121.30
2420.50
2721.20
3021.60
3320.50
3621.50
3922.10
4221.50
4522.00
4822.90
5119.80
5422.60
5722.80
6019.60
6323.40
6618.00
6922.90
7221.60
7523.10
7819.90
8119.60
8423.30
8722.80
9019.40
Individual and Mean Temperatures on the Unexposed Face of the Specimen
Time (mins)T/C 10 (°C)T/C 11 (°C)T/C 12 (°C)T/C 13 (°C)T/C 14 (°C)Mean Temp (°C)
0191818191818
199105105767792
2120124117108112116
3180190160130141160
4249256236180220228
5283288281222268268
6311313314252302298
7339337352278333328
8359355384302361352
9398394434345411396
10423426445373444422
11426432445399446430
12422425446422444432
13425424450*448437
14434437463*467450
15448453479*483466
16453466***460
17465473***469
18471481***476
19482489***486
20484495***490
21******
60******
90******

Specified and Recorded Furnace Temperatures
Time (mins)Specified Furnace Temperature (°C)Actual Furnace Temperature (°C)
02027
3502492
6603587
9663659
12705705
15739744
18766770
21789792
24809811
27826819
30842841
33856855
36869865
39881878
42892893
45902916
48912904
51921920
54930937
57938943
60945944
63953946
66960964
69966964
72973981
75979978
78985987
81990992
84996999
8710011004
9010061001
9110081011
Furnace Pressure
Time (mins)Recorded Pressure (Pa)
00.00
321.60
622.40
922.50
1221.50
1521.80
1820.60
2121.70
2421.00
2721.50
3021.10
3322.30
3620.40
3922.60
4223.10
4522.20
4820.80
5121.30
5423.00
5722.40
6020.90
6321.50
6621.40
6920.40
7221.80
7521.90
7821.60
8120.30
8421.70
8720.30
9023.50
9122.40

What This Means in Practice

Assessment under BS 476 Parts 20 and 22 provides practical, decision-ready information about how Fire Cloak™ performs when exposed to sustained, fully developed fire conditions in a controlled furnace environment. Rather than focusing on how a material reacts during ignition, these standards examine whether a barrier can maintain separation, resist burn-through and withstand prolonged thermal exposure.

Below is a sector-specific view of how this translates into real-world operational value.

Performance under BS 476 heating and pressure conditions demonstrates Fire Cloak™’s ability to maintain containment during extended exposure. This supports safer incident management by helping crews isolate an EV fire, reduce lateral fire spread and create a controlled environment while suppression or cooling strategies are deployed.

For roadside recovery and post-incident stabilisation, fire resistance performance data provides reassurance that Fire Cloak™ can function as a temporary containment barrier under sustained heat exposure. This is particularly relevant when handling thermally unstable or damaged vehicles awaiting transport or secure storage.

In enclosed or shared structures, maintaining compartmentation is critical. Fire resistance performance aligned with BS 476 principles supports the use of Fire Cloak™ to help contain an incident to a single vehicle footprint, reducing the likelihood of fire spread to adjacent vehicles or structural elements.

Where EV fleets, battery systems or lithium-powered equipment are present, the ability to demonstrate resistance to sustained fire exposure supports structured risk assessments. Fire Cloak™ can be integrated into fire response planning as a physical containment measure within larger fire protection strategies.

Workshops and battery-handling areas require controlled isolation procedures. Demonstrated performance under BS 476 furnace conditions supports the inclusion of Fire Cloak™ within workshop protocols as a means of isolating vehicles undergoing diagnostic, repair or quarantine processes.

In ferries, enclosed transport decks and rail depots, the ability to maintain separation during prolonged fire exposure is essential. Fire resistance data aligned with BS 476 principles supports contingency planning in confined transport environments where evacuation and structural protection are critical considerations.

Independently generated fire resistance data provides an additional layer of technical evidence when assessing EV-related fire risk. This supports informed underwriting decisions and structured mitigation planning across commercial, industrial and public environments.

Certified Proof & Next Steps

Fire Cloak™ performance under the heating and pressure conditions defined in BS 476 Part 20 is supported by formal fire resistance test reports issued by an independent UK fire-testing laboratory. Each assessment documents the specimen configuration, furnace regime, pressure control and observed behaviour throughout the exposure period, in accordance with the general principles set out in the standard.

Testing was conducted using the BS 476 Part 20 temperature–time curve and controlled pressure conditions, with performance considered against the fire resistance principles applied to non-loadbearing elements under Part 22 — particularly in relation to integrity and sustained containment. The reports record furnace data, specimen observations and photographic evidence, providing clear technical traceability.

The results demonstrate that Fire Cloak™ maintains separation under sustained thermal exposure, resisting the formation of significant through-openings and sustained flaming during the defined test duration. This provides a transparent and technically defensible basis for inclusion within risk assessments, operational procedures and insurer discussions where fire resistance performance is a relevant consideration.

The complete BS 476 Part 20 fire resistance test reports are available for download below.

Fire Cloak™ EV Fire Limitation Blanket (8 x 6m)

Fire Cloak™ XL – EV Fire Limitation Blanket (12 x 9m)

About BS 476 – Parts 20 & 22

This section provides a clear, practical overview of how BS 476 Parts 20 and 22 define fire resistance testing for building elements.

BS 476 is a multi-part British Standard covering fire testing of building materials and construction elements.

Part 20 establishes the general methodology used to determine fire resistance when an element is exposed to a controlled furnace environment. It defines the heating regime, pressure conditions, specimen preparation and the performance criteria used to assess results.

Part 22 applies this methodology specifically to non-loadbearing elements, such as partitions, doorsets, glazed screens and ceiling membranes. It describes how these elements are installed within a test frame and how their performance is evaluated during exposure.

Together, the two parts form a framework for assessing how well a construction element can maintain separation during a fully developed fire.

At the heart of Part 20 is the defined furnace heating regime, often referred to as the standard temperature–time curve.

This curve simulates the thermal conditions of a developed compartment fire by progressively increasing furnace temperature over time in a controlled manner. The curve provides consistency between laboratories and allows fire resistance performance to be expressed in minutes of sustained exposure.

In addition to temperature control, the standard specifies pressure conditions within the furnace to simulate fire-induced pressure differentials that influence flame and hot gas movement.

BS 476 Part 20 defines three principal performance criteria used in fire resistance testing:

  • Loadbearing capacity (R) – the ability of a structural element to continue supporting its applied load
  • Integrity (E) – the ability to prevent the passage of flames and hot gases through the element.
  • Insulation (I) – the ability to limit temperature rise on the unexposed face.

For non-loadbearing elements tested under Part 22, performance is typically assessed against integrity and insulation, as structural capacity is not relevant.

Failure is determined by clearly defined observable conditions, such as sustained flaming, formation of openings beyond prescribed dimensions, or excessive temperature rise.

Testing is carried out in a purpose-built furnace where the specimen forms one face of the furnace chamber.

During exposure:

  • Furnace temperatures are continuously monitored.
  • Pressure is controlled to defined tolerances.
  • The unexposed face is examined for flame passage or hot gas leakage.
  • Thermocouples measure temperature rise where insulation performance is assessed.
  • Deflection and physical changes are recorded.

The duration for which the specimen maintains compliance with the defined criteria determines its fire resistance performance.

Although European harmonised standards have gradually superseded parts of BS 476, it remains widely referenced within:

  • Existing building specifications
  • Legacy design documentation
  • Refurbishment and retrofit projects
  • Insurance and risk engineering assessments
  • Sectors where British Standard data continues to be recognised

The standard continues to provide a familiar benchmark for fire resistance performance within the UK and certain international markets.

BS 476 Parts 20 and 22 are published by the British Standards Institution (BSI).

The full, authoritative versions of these standards — including detailed clauses, formulae and procedural requirements — can be obtained directly from the BSI website or authorised distributors.

This overview is provided for general informational purposes and does not replace the official published standard.

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