Part 12: The fire testing regime

Part 12: The fire testing regime

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Chapter 111: Assessing the fire performance of external walls

Introduction

¶111.1 For many years a variety of tests has existed for measuring the performance of materials in response to fire, ranging from small-scale laboratory tests up to full-scale tests of the kind described in the BS 8414 series. We have referred in earlier chapters of our report to some of those that are most widely used. No tests were carried out specifically on the combination of materials used in the refurbishment of Grenfell Tower or on the proposed external wall system, but those responsible for the choice of materials and the design of the external wall relied indirectly on results of some of the standard tests because they were referred to in the BBA certificate relating to Reynobond. They also relied on a widespread misunderstanding, not helped by poor guidance in Approved Document B, that any material with a Class 0 surface was suitable for use in the external wall of a high-rise building.

¶111.2 In those circumstances we think it is appropriate to consider whether the established tests, in particular BS 476 Parts 6 and 7, the results of which support the Class 0 classification, the European classification system or BS 8414 Parts 1 and 2, which contain the test methods for full-scale testing of external wall systems, are capable of providing the information that is required to enable designers to assess compliance with functional requirement B4(1). Any discussion of that question calls for an understanding of technical matters of a kind that is possessed only by those who are experts in the field. We have had the benefit of receiving reports and hearing evidence from three leading experts, Professor José Torero,^22302230 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006}. Professor Luke Bisby,^22312231 Bisby, Phase 2 Report: Regulatory Testing and the Path to Grenfell {LBYP20000001}; Bisby, Phase 2 Report: BR 135 Desktop Assessment Report {LBYP20000004}. and Dr Barbara Lane,^22322232 Lane, Phase 2 Module 2 presentation: An explanation of the relevant Reaction to Fire tests and Classification methods to restrict the combustibility of external walls of high buildings {BLARP20000022}. all of whose evidence is available on our website. None of their evidence in relation to testing was challenged and we therefore feel justified in accepting it in full. It is lengthy and complex, but we would urge the government and any others who have an interest in or responsibility for testing the performance in fire of materials and products used in the construction industry to read it in full. For the purpose of this report, however, we have attempted to summarise in our own words those parts that are of particular relevance to the refurbishment of Grenfell Tower.

The testing regime in context

¶111.3 Every new building of any complexity, and certainly every high-rise building, should have a fire safety strategy created at the time of its original construction or as soon as possible thereafter. It is important to recognise that testing of materials for their performance in fire has to be related to the fire safety strategy for the particular building. It is the responsibility of those who design the building, including the external wall, to ensure that the information obtained from that testing is correctly used in the development of the fire safety strategy.^22332233 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/29} paragraph 4.2.7. In England and Wales the contents of the fire safety strategy are ultimately dictated by the functional requirements in Schedule 1 to the Building Regulations, which must be reflected in performance requirements appropriate to the building in question.^22342234 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/33} paragraph 6.0.1. It follows that the performance of the materials intended to be used will need to be assessed with the particular fire safety strategy in mind. Thus, in a building with a "stay put" strategy for responding to fire, no significant spread of fire beyond the compartment of origin can be tolerated,^22352235 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/38-39} paragraphs 6.2.7-6.2.8 and 6.2.11-6.2.16. whereas in a building with a controlled evacuation strategy some spread of fire can be tolerated, provided it is compatible with the ability of the occupants to escape.^22362236 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/34-37} paragraphs 6.1.3-6.1.23.

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Assessing the performance of an external wall system

¶111.4 The processes affecting the spread of flame vertically are complex and depend on a number of factors, including the properties of the materials exposed to the flame, the rate at which combustible gases are produced and their propensity to transfer sufficient heat to perpetuate the flame and ignite adjacent material.^22372237 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/49} paragraph 7.2.23. Two approaches to making such an assessment may be taken: one is to assess the likely velocity of flame spread; the other is to assess whether the flame is likely to be extinguished.

¶111.5 Fire engineers have tools at their disposal for assessing the speed at which flames are likely to spread over a building's external wall system. Simple methods can be used for the assessment of very simple systems and can be applied in a very conservative manner, although they may be better suited to ranking materials rather than to obtaining an understanding of how a system is likely to perform.^22382238 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/54} paragraph 7.3.27. Complex computational models can also be used.^22392239 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/54-55} paragraphs 7.3.30-7.3.33. In all cases some simplification is required and certain assumptions must be made and a high degree of skill and experience is required to use the tools effectively.^22402240 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/55} paragraph 7.3.35.

¶111.6 Although some external wall systems continue to support burning and the spread of flame after an external source of heat has been removed, others that exhibit only small differences do not, with the result that the fire goes out.^22412241 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/56} paragraph 7.4.1.

¶111.7 A good example is provided by small differences in the degree of exposure to flame of the polyethylene core of an ACM PE panel in an insulated rainscreen system. As demonstrated by the experiments conducted by Professor Bisby and his colleagues at Edinburgh University, the extent to which the core is exposed to flame, which in turn depends on the fixing arrangements, has a significant effect on whether the panels sustain continuous flaming or the flames die out.^22422242 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/56} paragraph 7.4.2; Bisby, Phase 2 Experiments Work Package 2: System Interactions {LBYWP200000001/79} paragraph 449; Bisby {Day291/9:18}-{Day291/12:19}.

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¶111.8 A material that is non-combustible will not catch fire, regardless of the temperature to which the surface is raised.^22432243 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/56} paragraph 7.4.7. It will not support ignition and therefore there will be no flames. A fire within a compartment can impose a heat flux in the order of 100kW/m² on the external walls. If the materials do not support ignition when exposed to a heat flux of that magnitude, they can be regarded as non-combustible.^22442244 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/57} paragraph 7.4.10.

¶111.9 It is very difficult to judge whether a combustible material will continue to burn when the source of heat is removed because it is necessary to assess whether sufficient heat is likely to be transferred ahead of the flame to sustain burning.^22452245 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/56} paragraphs 7.4.3-7.4.4. However, there are currently no models that will accurately predict that and therefore it is necessary to test individual samples. Precision is essential because small changes in materials or the system as a whole can have a significant effect on the outcome. That makes any assessment of whether, and if so when, extinction will occur much more difficult.^22462246 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/59} paragraph 7.5.6.

Encapsulation

¶111.10 Innovative techniques in the construction industry have added to the difficulty of assessing the fire performance of an external wall. One such technique is "encapsulation" in which a combustible material is enclosed in a non-combustible outer skin in a way that is intended to ensure that ignition cannot occur. It may involve full encapsulation, in which the combustible material is protected on all sides or partial encapsulation, in which the combustible material is exposed at the edges.^22472247 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/60-61} paragraphs 8.1.3-8.1.4 and Figure 6. Certain materials used for encapsulation, such as aluminium, have very high thermal conductivity and therefore will dissipate heat from an external source. If the heat is dissipated quickly, the combustible material may not reach the point of ignition and the exposed edges may not give rise to flaming.^22482248 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/61} paragraph 8.1.5 and Figure 6.

¶111.11 A number of factors influence whether encapsulation will prevent ignition and the consequent risk of flames spreading. They include:

¶a. the way in which the combustible material reacts to heat, including degradation, thermal expansion, deformation, melting and dripping;

¶b. the performance of the ensemble of which it forms part, including its relative deformation (splitting, cracking and peeling); c. the performance of any adhesive; and

¶d. temperature gradients, as they affect relative deformation, localised stress and similar behaviour.^22492249 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/61-62} paragraph 8.1.8.

¶111.12 Assessing the performance of an external wall incorporating materials of that kind is more complicated than just modelling the spread of flame because it must take into account all the factors affecting the spread of flame, as well as factors affecting the physical behaviour of the system. As a result, it is necessary to carry out detailed and comprehensive testing of the system to identify the different kinds of mechanical failure that may occur and the conditions which induce them.^22502250 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/62} paragraph 8.1.11.

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The role of the cavity

¶111.13 Although tools and models exist that can enable an assessment to be made of the spread of flames vertically over a flat surface, less attention has been given to the spread of flames within cavities. The width of the cavity plays an important part in determining the rate at which flames spread through it and increased rates at which flames have spread can be explained by the presence of open vertical channels which create chimney effects leading to increased burning of combustible material.^22512251 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/63} paragraph 8.2.2 and 8.2.4.

¶111.14 If the width of the cavity exceeds a certain size, however, the transfer of heat from one side to the other and an increase in the rate at which heat is transferred upwards both disappear. Flames then spread at a rate similar to that at which they spread over a flat surface. Conversely, if the width of the cavity falls below a certain size, thermal expansion of the gases interrupts the general flow of air and the flames cease to spread internally.^22522252 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/63} paragraph 8.2.3.

¶111.15 As Professor Bisby's experiments demonstrated,^22532253 See Chapter 109. an external wall system incorporating ACM PE panels contains many features that add to the difficulty of assessing its fire performance. They include:

¶a. the low melting temperature and high thermal conductivity of the aluminium skins, which result in a complex mechanism affecting the transfer of heat from the external flames into the combustible cores of the panels;

¶b. the melting of the aluminium leading to the loss of protection for the core;

¶c. the polyethylene core of the panels melting at low temperatures;

¶d. the temperature gradients between the inside and the outside of the panels resulting in differential deformations of the aluminium plates, the splitting of the plates and the involvement of the polyethylene core in the fire;

¶e. inside the cavity, the pyrolysing, charring and burning of the insulation and possible burn-out. There may also be a rapid spread of flame because of the low thermal inertia of the insulation,^22542254 The surface temperature of a material with a low thermal inertia will increase rapidly when heated and it will ingite more quickly – see Bisby Phase 1 Report {LBYS0000001/19} paragraph 121; Grenfell Tower Inquiry Phase 1 Report, Volume IV, page 522 paragraph 22.13. although its tendency to char reduces fuel production and flame lengths; and

¶f. the interaction during a fire of the panels and the insulation, each of which affects the way in which the other behaves.

¶111.16 Modern cladding systems include many other complexities, including cavity barriers, complex geometries and intumescent sealants, and very careful analysis is necessary to establish their probable fire performance.^22552255 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/64-65} paragraphs 8.2.6-8.2.9. It is misguided to think that the only way to assess their performance accurately is to conduct a large-scale test that is representative of the worst circumstances likely to be encountered in practice. Although there may be some value in tests of that kind, the results are extremely difficult to interpret and it is therefore important that those who are responsible for carrying them out have a detailed understanding of the processes involved and the means by which failure can occur before they are undertaken.

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¶111.17 The complexity of the processes involved in assessing the performance of an external wall was demonstrated by the simplified tests carried out by Professor Bisby and his team on aspects of the external wall system of Grenfell Tower.^22562256 Bisby Phase 2 Experiments Work Package 2: System Interactions {LBYWP200000001/4} page 4, paragraph 17. He was able to identify some of the features of the system that significantly affected its performance in fire, including the significant differences between the performance of riveted panels and that of cassette-fixed panels and between foil-faced and non-foil-faced insulation.^22572257 Chapter 109. We refer to the information obtained from those tests in a separate chapter,^22582258 Chapter 109. but for present purposes it is clear that it is possible for small- and medium-scale tests to yield useful results, provided their limits are properly understood.^22592259 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/65} paragraphs 8.2.12; {JTOR00000006/66-78} paragraphs 9.01-9.3.16; Torero {Day289/77:16}-{Day289/78:1}.

The Class 0 tests

¶111.18 Fire science and fire engineering are relatively new disciplines^22602260 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/81-83} paragraphs 10.1.10-10.1.20. and the development of the science of fire testing has been somewhat sporadic. Tests have often been developed in response to external events or the advent of new technologies,^22612261 Bisby, Phase 2 Report: Regulatory Testing and the Path to Grenfell {LBYP20000001/75} paragraph 356. rather than being driven by the desire for knowledge in its own right.^22622262 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/83-84} paragraphs 10.1.20-10.1.27. For example, World War II led to the development of a test method to measure the effectiveness of certain products at resisting fires caused by incendiary bombs. That led to a series of full-scale tests in corridors lined with different types of wall-board which evolved to become the BS 476-7 method for testing the surface spread of flame.^22632263 Bisby, Phase 2 Report: Regulatory Testing and the Path to Grenfell {LBYP20000001/58} paragraphs 259-261.

¶111.19 At the time of the Grenfell Tower fire, Approved Document B recommended that the external surfaces of the walls of high-rise buildings should meet the provisions of Diagram 40. In the case of Grenfell Tower Diagram 40e provided that, above 18 metres from the ground, the external surfaces of the walls should satisfy national Class 0 or European Class B. The main tests supporting the national Class 0 classification are BS 476-6 (fire propagation) and BS 476-7 (surface spread of flame). Despite our investigations, no one was able to explain how tests designed to determine the fire performance of wall linings were adopted in Approved Document B (and the antecedent versions of that statutory guidance) to assess the performance of the external walls of high-rise buildings.

¶111.20 We have explained in Chapter 5 how those tests are carried out and what information and data is obtained from them. As is clear from those descriptions, neither test is apt to provide relevant information about the performance of a material or product in a fire in the external wall of a building.

Test method BS 476-6

¶111.21 Fire propagation testing to BS 476-6 was developed as a method of testing the reaction to fire of internal wall linings^22642264 Bisby, Phase 2 Report: Regulatory Testing and the Path to Grenfell {LBYP20000001/32-33} paragraph 156. and is directed primarily to assessing the performance of the surface of the product being tested. The sample to be tested is board-shaped and mounted in the test apparatus so that the edges are not exposed. Consequently, if materials within the product are encapsulated in or simply covered by a flame-retardant coating, direct ignition of the underlying layer or core is prevented.^22652265 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/127} paragraphs 12.3.54-12.3.55. Unless the outer surface or coating of the product burns through, so that the underlying layer is exposed, the test will not detect the presence of any combustible material in the core or lower layers.^22662266 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/129} paragraphs 12.3.64.

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¶111.22 The test was designed to represent the development of a fire within a room and its transition to flashover.^22672267 Bisby, Phase 2 Report: Regulatory Testing and the Path to Grenfell {LBYP20000001/35} paragraph 162; Bisby {Day290/100:19}-{Day290/101:10}. It does not correspond to the development of a fire on the outside of a building^22682268 Bisby, Phase 2 Report: Regulatory Testing and the Path to Grenfell {LBYP20000001/35} paragraph 163; Bisby {Day290/109:24}-{Day290/110:8}; {Day290/118:3-23}. and does not provide information about the heating length or the speed at which flames will spread.^22692269 Torero {Day289/91:6-16}. The derivation of the fire propagation index is convoluted and it is not possible to relate the values obtained from the test to practical experience.^22702270 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/127} paragraph 12.3.57. The test standard itself makes clear that the test has been designed to give comparative information on the performance of products in the early stages of a fire and that it should not be used for assessing the fire hazard under actual fire conditions.^22712271 See Chapter 5; {CTAR00000016/11} paragraph 11(i); Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/129} paragraphs 12.3.58-12.3.60. It is not possible to calculate the heat flux to which the sample is exposed during the test, so its performance cannot be related to any particular design conditions, e.g. where assumptions are being made about the level of exposure to heat that can be accommodated in the external wall.^22722272 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/129} paragraph 12.3.62; Torero {Day292/28:7-16}. The small size of the sample also precludes any assessment of the thermo-mechanical behaviour of the product.^22732273 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/129} paragraph 12.3.65.

Test method BS 476-7

¶111.23 Testing in accordance with BS 476-7 for surface spread of flame was developed as a way of measuring the spread of fires within corridors, not the spread of fire over an external wall.^22742274 Bisby, Phase 2 Report: Regulatory Testing and the Path to Grenfell {LBYP20000001/30} paragraph 145; Bisby {Day290/109:24}-{Day290/110:8}. It was first published in 1971 and was revised in 1987 and 1997,^22752275 Lane {BLARP20000022/61}. There was also a change to the foreword in 2014. but its origins lie in World War II and the risks posed by incendiary bombs.^22762276 Bisby, Phase 2 Report: Regulatory Testing and the Path to Grenfell {LBYP20000001/58} paragraphs 259-261. The test measures the spread of flame horizontally rather than vertically. In a fire in the external wall of a building the spread of flame vertically is likely to be the primary mechanism of development and a material which may not easily support the spread of flame laterally could well be capable of enabling it to spread vertically, even in the absence of an external source of heat.^22772277 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/133} paragraph 12.3.80. That phenomenon was seen at Grenfell Tower. Fire spread rapidly up the east face of the building; the much slower spread of fire horizontally was driven primarily by a very particular feature of the building, namely the crown, which allowed molten polyethylene to drip down the walls.^22782278 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/133} paragraph 12.3.81; Grenfell Tower Inquiry Phase 1 Report, Chapter 23, page 558, paragraph 23.55.

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¶111.24 Heat fluxes of up to 120 kW/m² can occur in fires involving the external walls of buildings, which is very much higher than that imposed by the test (5-32.5 kW/m²).^22792279 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/133} paragraph 12.3.82; Torero {Day292/33:11-23}. The sample holder used for the test obscures the edges of the product, thereby ensuring that only the surface is exposed to the heat and that any materials below the surface are protected.^22802280 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/133} paragraph 12.3.84. In those circumstances, the results achieved in the test do not enable one to assess how an external wall incorporating the product would perform in response to a fire.^22812281 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/133} paragraph 12.3.83. Professor Torero also explains in his report how Professor Drysdale and others have concluded that the results of the test are strongly dependent on the particular apparatus used and therefore the test ought not to be used to assess the material properties of the product in a real-world situation, see Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/132-133} paragraphs 12.3.77-12.3.79 and see also Torero {Day292/30:20}-{Day292/32:11}.Show full note

¶111.25 Accordingly, neither the BS 476-6 test method nor the BS 476-7 test method provides any of the information needed to make an assessment of the suitability of a product for use in the external wall of a high-rise building and it is therefore inappropriate to use them as a measure of the performance of an external wall in a fire.^22822282 Torero {Day 292/32:12}-{Day292/33:9}, see also Bisby {Day290/114:3-5}. The tests are too simplistic for that purpose, particularly in relation to composite products, because they primarily assess the properties of the surface rather than what lies beneath it. For that reason they do not provide any information about the likely performance of ACM panels on external walls.^22832283 Torero {Day292/34:16-20}. As Dr Connolly of BRE concluded in 1994,^22842284 See Chapter 7. the tests do not accurately reflect the fire hazards associated with cladding systems.^22852285 {RCO00000001/46} 4th paragraph. It is unfortunate that the government did not take steps to remedy the situation in the years before the Grenfell Tower fire, in view of the fact that there were numerous opportunities to abandon reliance on national Class 0 as a standard by which the fire performance of materials proposed for use in external walls of high-rise buildings could be judged.^22862286 See Chapter 7.

The European classification system

¶111.26 The tests supporting the European system for classifying the reaction to fire of construction products were intended to enable designers to identify construction products that prevented or slowed the development of a fire in a compartment so that flashover and a fully developed fire did not occur.^22872287 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/136-137} paragraphs 12.4.17-12.4.19. The classification system was based on a test known as the "room corner test", which involved lining a full-scale compartment with a product, igniting it and monitoring the development of the fire.^22882288 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/137} paragraph 12.4.20; Bisby, Phase 2 Report: Regulatory Testing and the Path to Grenfell {LBYP20000001/35} paragraph 165. A smaller and less costly version of that test, known as the "Single Burning Item" test,^22892289 Bisby, Phase 2 Report: Regulatory Testing and the Path to Grenfell {LBYP20000001/35} paragraphs 165-166 and {LBYP20000001/114} paragraphs 595-596. was subsequently developed and now underpins classifications A2 to D of the European classification system.

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The Single Burning Item test

¶111.27 The single burning item test is a scenario test, that is, a test which seeks to reproduce a set of circumstances that are considered reasonably likely to be encountered in practice, in this case a fire in the corner of a compartment formed by the meeting of two walls.^22902290 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/150} paragraph 12.4.68. Unlike the national tests referred to above, the temperature and heat release measurements obtained during the test are potentially of some value to a fire engineer seeking information to assess the fire performance of the product when used on an external wall because they allow some assessment to be made of the way in which the speed of flame spread develops over time, together with the heat release rate.^22912291 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/151-152} paragraphs 12.4.79 and 12.4.85.

¶111.28 An important difference, however, between a fire in a room and a fire in the external wall of a building is the magnitude of the heat flux. The burner which is used in the single burning item test delivers a maximum heat flux of less than 40kW/m², which is much less than could be expected in the case of a fire in an external wall of a building, which can generate a heat flux of up to 120 kW/m². Consequently, although poor performance of a product in the single burning item test can indicate poor performance in a fire in an external wall, the converse does not always hold true. A material which has performed well in the test may perform badly in an external wall fire.^22922292 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/152} paragraph 12.4.81.

¶111.29 Moreover, the way in which heat develops in the structure created for the purposes of the test will inevitably differ significantly from that in which it develops in an external fire. As the test progresses the speed at which the flames spread will accelerate due to the increase of the heat flux operating on the sample. In practice, that means that the flame on the sample will usually spread over its full height. The remaining flame spread, which may be influenced by the increased heat flux, is likely to occur in a horizontal direction where burning is still to occur. That again is different from what would occur in a fire in the external wall of a tall building, in which flames spreading vertically will normally provide the dominant mechanism by which the fire spreads.^22932293 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/152} paragraphs 12.4.82-12.4.84.

¶111.30 For the purpose of the test the bottom and top edges of the product are clamped in place and therefore shielded from exposure to the heat. The junction between the panels is also held in place by a metal section. The only edges of the sample that are exposed are those which occur at any joints within the test specimen itself or at the sides (although they too may be shielded if that reflects the end-use application). Consequently, the test does not reproduce conditions encountered in practice^22942294 Torero Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/153} paragraphs 12.4.91-12.4.93; Torero {Day292/44:4}-{Day292/45:11}. and material enclosing a combustible core might survive the test but not a fire. In a real fire the product might burn vigorously, allowing a large amount of heat to be released instantaneously, thereby becoming a significant hazard.^22952295 Torero {Day292/44:25}-{Day292/45:11}. Moreover, the test is not intended to, and does not, produce any data that reflects the way in which the physical structure of the product responds to heat.^22962296 Torero Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/153} paragraph 12.4.93.

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¶111.31 It follows that the European classifications which emerge from the single burning item test (i.e. classifications A2 to D) are of little assistance when assessing the performance of external wall systems.^22972297 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/153} paragraph 12.4.90; Torero {Day292/41:2}-{Day292/42:17}; Bisby, Phase 2 Report: Regulatory Testing and the Path to Grenfell {LBYP20000001/116} paragraph 604.

¶111.32 We note that there was some disquiet within the fire community when the European classification system was introduced. Concern was expressed about whether the single burning item test could credibly classify some types of construction products. In particular, a steel-clad polystyrene sandwich panel was found to lead to flashover in the room corner test, but more than half the laboratories that carried out such tests reported a very low heat release rate in the single burning item test.^22982298 B Messerschmidt, The Capabilities and Limitations of the Single Burning Item (SBI) Test, Fire & Building Safety in the Single European Market, FireSeat, 2008 {INQ00014960} and see Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/153-154} paragraphs 12.4.94-12.4.96 and Bisby, Phase 2 Report: Regulatory Testing and the Path to Grenfell {LBYP20000001/37-38} paragraphs 175-177.Show full note That led to some adverse comments on the test^22992299 "FireSeat 08 - Presentation by Birgitte Messerschmidt. Part 3 of 4" (https://www.youtube.com/watch?v=wsQHKDUomSA) 00:03:02 – 00:03:14; Bisby, Phase 2 Report: Regulatory Testing and the Path to Grenfell {LBYP20000001/116} paragraph 608. Also Lane {Day68/61:22-62:}. and a warning that, when considering its use in the context of national regulatory systems, it was important that the link to the development of a fire in a compartment be maintained so that the test and the results obtained from it were used appropriately.^23002300 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/148} paragraph 12.4.67, with reference to B Messerschmidt, The Capabilities and Limitations of the Single Burning Item (SBI) Test, Fire & Building Safety in the Single European Market, FireSeat, 2008 {INQ00014960}. However, in the years before the Grenfell Tower fire the construction industry and those with responsibility for the regulations lost sight of that link.

Large-scale testing

¶111.33 From 2000 onwards the statutory guidance in England and Wales on the construction of the external walls of high-rise buildings referred to large-scale testing as a way of demonstrating compliance with functional requirement B4(1) of the Building Regulations and readers were told that advice on the use of insulation in external walls could be found in BR 135. Later, in 2006, Approved Document B referred to BR 135 (second edition) and stated that external walls should either meet the guidance or comply with the performance criteria in BR 135 using full-scale test data from BS 8414.^23012301 {CLG10000007/95} section 12.5. That guidance remained in place up to the Grenfell Tower fire.^23022302 A further version of BR 135 was published in 2013 {CLG00000224}.

The development of BS 8414 and BR 135

¶111.34 The first edition of BR 135, published in 1988, described the development of a research programme incorporating large-scale testing. That programme is best understood as a series of large-scale experiments rather than the methodical development of a means of assessing the performance of external wall systems in fire.^23032303 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/103} paragraphs 12.2.26 and 12.2.28 and see the evidence of Dr Connolly summarised in Chapter 7. The objective was to "identify the design principles on which constructional recommendations might confidently be based"^23042304 {BRE00001077/4}. and the primary focus was on the use of combustible insulation in a cladding system.^23052305 See the title to the document at {BRE00001077} and see e.g. pages 3, 5, 7. The problem addressed by the study was the risk of flames spreading over the surface of a wall and within cavities^23062306 {BRE00001077/4-5} under the heading "Regulatory Aspects". but that risk was wholly unquantified and was not related to any particular evacuation strategy. It was therefore necessary to assess the results of the test in each case and determine the extent to which the risk of flame spread was acceptable given the fire safety strategy for the building under consideration.^23072307 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/103} paragraph 12.2.29-12.2.30.

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¶111.35 Three particular cladding systems were assessed for the purposes of the first edition of BR 135, a system containing insulation between an external layer of render and a masonry wall, a system incorporating expanded polystyrene insulation fixed to a masonry wall with an external facing of aluminium sheets, and a system of timber cladding of the kind traditionally used for low-rise buildings,^23082308 {BRE00001077/4-6} see in particular pages 5-6 under the heading "Experimental Fires". and the recommendations reflected the structures and physical characteristics of those systems.^23092309 {BRE00001077/9}; Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/104} paragraph 12.2.33-12.2.34. Importantly, the exterior materials used in the first two systems were non-combustible (cementitious render and aluminium) and therefore no question of the spread of flame over the external surface of the wall arose.^23102310 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/105} paragraph 12.2.39.

¶111.36 The principal danger identified in the experiments was the elongation of flames within cavities and therefore many of the recommendations were directed to the provision of fire barriers within cavities.^23112311 {BRE00001077/9}. However, subsequent studies carried out by BRE showed that fire barriers were not completely effective.^23122312 Connolly's 10 Large-Scale Tests in 1994 {RCO00000001/46} section 4.2.3 second paragraph and see Chapter 7. In this country attention appears to have been concentrated on cavity barriers, although little effort has been made to understand their effectiveness.^23132313 Bisby {Day290/162:4-14}; Torero {Day292/68:5}-{Day292/69:20}. Despite that, later editions of BR 135 continued to focus almost exclusively on the threat posed by the propagation of fire through cavities.^23142314 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/105-106} paragraph 12.2.43; BR 135 2nd Edition {BRE00005554}; BR 135 3rd edition {BRE00005555}. The only direct reference to the risk of flames spreading over the external panels of external wall systems is to be found in one paragraph in the third edition of BR 135, published in 2013.^23152315 {CEL00000584/22} section 6.4.1 which states: "Combustible panels are typically based on vinyl or glass-reinforced plastic, although various new products are being developed in this area, some of which also contain insulation materials. These products generally have good surface spread of flame characteristics to prevent rapid fire spread across the surface of the system, but once the panels become involved in the fire, they have the potential to generate falling debris, add to the overall fire load, and provide a route for fire to propagate up the outside of the building."Show full note It seems clear, therefore, that the concentration on cavity barriers as a means of limiting the spread of fire over external walls had its origin in BR 135 but was not based on a proper understanding of their benefits and limitations.

¶111.37 BR 135 sets out the criteria by which an external wall system is to be judged acceptable. However, it contains no explanation of those criteria nor any indication of what they are deemed to represent^23162316 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/106} paragraph 12.2.48. and it is a striking fact that none of the witnesses was able to explain their basis.^23172317 See for example the examination of Dr Colwell (who was involved in Fire Note 3 and Fire Note 9 and co-authored both the second and third editions of BR 135) at {Day231/167:23}-{Day231/176:25}; Debbie Smith {Day236/107:20} -{Day236/113:18}; Martin {Day251/119:4}-{Day251/120:24}. See also Chapter 7. Moreover, BR 135 itself does not attempt to relate the criteria to the requirements of the Building Regulations or the guidance contained in Approved Document B^23182318 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/108} paragraph 12.2.58. and the relevance of the criteria to practical experience has never been clearly articulated.^23192319 Bisby, Phase 2 Report: Regulatory Testing and the Path to Grenfell {LBYP20000001/42} paragraph 207. As a result, it has been left up to those seeking to make use of the data derived from tests in accordance with BS 8414 to satisfy themselves that the system under consideration is suitable for the intended use.^23202320 Bisby, Phase 2 Report: Regulatory Testing and the Path to Grenfell {LBYP20000001/42} paragraph 209. That is made clear in the third edition of BR 135, which states that the classification applies only to the system as tested and described in the classification report.^23212321 {CEL00000584/27} left column.

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¶111.38 The BS 8414 test itself is unsatisfactory in other respects. Some materials, such as high-pressure laminate, do not reach their maximum temperatures until about 30 minutes after the start of the test; for such products the initial 15-minute assessment period is therefore too short to identify the risk they pose.^23222322 Lane, Phase 2 Module 2 presentation: An explanation of the relevant Reaction to Fire tests and Classification methods to restrict the combustibility of external walls of high buildings {BLARP20000022/257} where Dr Lane highlighted temperature readings taken in BS 8414 tests conducted by MHCLG of HPL panels over A1 insulation. See also Lane {Day68/115:15}-{Day68/117:21}. A system incorporating panels of that kind might satisfy the performance criteria in BR 135 but still not comply with the functional requirements of the Building Regulations.

¶111.39 BR 135 also has its defects. For example, it contains no criteria relating to mechanical performance. Although it says that mechanical performance of the system should be taken into account as part of an overall assessment,^23232323 {BRE00005555/29} section A2.4 and {BRE00005555/33} section B2.4. it offers no guidance on how to evaluate it, although it is possible to formulate effective criteria.^23242324 See e.g. the Loss Prevention Standard 1582 approved by the Loss Prevention Council which has performance criteria for mechanical performance - {INQ00013964/12} paragraph 4.1.5.

Relevance to high-rise residential buildings

¶111.40 Making use of BS 8414 and BR 135 to assess the performance of an external wall system involves the application of performance criteria based on the temperature reached at a level of two storeys above the fire compartment within 15 minutes of the start of the test. The main difficulty with that approach is that it is possible for a fire that has become established in the external wall of a building to spread in a way that poses a significant danger although the criteria are still met. A fire may therefore spread beyond the compartment of origin in a way that is incompatible with a "stay put" evacuation strategy even if the external wall system has satisfied the performance criteria in BR 135.^23252325 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/109} paragraphs 12.2.63-12.2.64.

¶111.41 That difficulty does not appear to have been recognised by any of the lay witnesses, including those from DCLG or BRE.^23262326 Colwell {Day231/175:11-24}; Smith {Day236/114:4}-{Day236/115:4}; Martin {Day251/96:19}-{Day251/98:19}; Burd {Day238/214:10}-{Day238/215:6}. We obtained the clear impression that many in the industry thought that if, following a test in accordance with BS 8414, a system satisfied the criteria in BR 135, the building when completed would inevitably satisfy functional requirement B4(1) of the Building Regulations. Indeed, many failed to appreciate that the BS 8414 test applies only to the system as a whole and does not tell one anything about its individual components. It is a matter of concern that no one appears to have considered whether the extent of flame spread that could occur while still satisfying the performance criteria in BR 135 was consistent with the adoption of a stay put evacuation strategy.

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¶111.42 Only a limited amount of information can be obtained from a BS 8414 test. In particular, it produces very little information that is relevant to important questions relating to external wall systems, such as the speed at which flames are likely to spread and whether they can be expected to die out naturally.^23272327 Torero {Day289/67:8-18}. In particular, the thermocouples forming part of the test equipment does not provide information about:

¶a. the likelihood that the fire will extinguish itself once the crib has been extinguished;

¶b. whether the ignition temperatures of any of the materials are so high that they can be considered non-combustible;

¶c. the rate of internal or external flame spread over the façade; or

¶d. other properties of the system, such as ignition temperature, thermal inertia and heat of combustion.^23282328 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/109} paragraphs 12.2.65-66.

¶111.43 At best the BS 8414 test can indicate only whether it would be wholly inappropriate to make use of a particular system when constructing the external wall of a building.^23292329 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/110} paragraph 12.2.68; Torero {Day292/77:8-17}; Bisby {Day290/143:1-8}; Torero {Day292/76:25}-{Day292/77:6}. It was not designed to and does not provide technical information which, taken in isolation, can enable the designer to be confident that a particular system will adequately resist the spread of fire over the walls of the building. Put another way, failure to meet the performance criteria in BR 135 will demonstrate that a given system is unlikely to comply with functional requirement B4(1) of the Building Regulations, but the converse is not necessarily true: a given system might meet the performance criteria of BR 135 and yet fail to comply with the functional requirement.

¶111.44 We think it important to recognise that only a limited amount of information can be obtained from a BS 8414 test. It can never accurately reflect the conditions the building will encounter in use because there will inevitably be differences between the large-scale test and the building itself.^23302330 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/110} paragraphs 12.2.69-12.2.73; Bisby, Phase 2 Report: Regulatory Testing and the Path to Grenfell {LBYP20000001/42-43} paragraphs 210-211; Bisby {Day290/138:22}-{Day290/141:13}. A significant responsibility therefore rests on the shoulders of the person charged with assessing the significance of the results.^23312331 Bisby {Day290/140:3}-{Day290/141:13}.

¶111.45 Until recently it has not been recognised as widely as should have been the case that the functional requirements of the Building Regulations alone determine the standards that have to be met. That may be due in part to the fact that the statutory guidance is framed in prescriptive terms and is therefore easier and more attractive to follow. One aspect of that was a widespread assumption that if a system met the criteria in BR 135, the building would comply with functional requirement B4(1) without any need to analyse the information obtained from the test itself or consider the conditions likely to be encountered in use. In our view the way in which the guidance in Approved Document B is expressed helped to perpetuate that assumption. However, there was and always has been an obligation on construction professionals to assess the results of BS 8414 tests and BR 135 classifications.

¶111.46 The deceptively simple terms of Approved Document B diverted attention from the fact that the information derived from large-scale tests needed to be analysed in conjunction with other relevant information in order to understand the likely behaviour of the external wall when exposed to flames and heat generated by a fully developed compartment fire.

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¶In our view an analysis of that kind calls for a level of skill greater than that possessed by many of the construction professionals who routinely relied on such tests.

The future of large-scale testing

¶111.47 It is possible to criticise the BS 8414 test as not representing conditions likely to be encountered in practice and as being liable to deliver differing results based on random variations in the systems tested.^23322332 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/111} paragraph 12.2.78 and see for example the paper by Schultz J, Kent, Crimi, Glocking, Hull, "A Critical Appraisal of the UK's Regulatory Regime for Combustible Facades," Fire Technology, 57, 261-290, 2021 {INQ00014943}. Moreover, it is essential to recognise that even if it can be made more realistic it will never provide all the information necessary to make a reliable assessment of the performance of an external wall. That will have to be derived from a range of tests, including small- and medium-scale tests, to determine the physical properties of the external wall that are likely to influence the spread of fire. The proper role of the BS 8414 test is to check the accuracy of assessments based on other methods.^23332333 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/111-112} paragraph 12.2.79; Torero {Day292/84:12}-{Day292/86:25}. It should never be the only basis upon which the performance of an external wall system is assessed.

¶111.48 The reaction to fire of the external wall of Grenfell Tower amply illustrates the point. Any competent designer should have appreciated that the presence of polyethylene in the ACM panels presented a very significant danger, given the amount of energy that could be released if it became involved in fire. It should also have been clear that the aluminium sheeting enclosing that polyethylene was likely to deform and delaminate in response to heating and that the exposed polyethylene was likely to melt and drip. The experiments carried out at the University of Edinburgh demonstrated that it was possible to design small- and medium-scale tests capable of identifying the thermo-mechanical processes that led to the deformation of the panels and the involvement of the polyethylene in the fire.^23342334 Chapter 109. It follows that any assessment of the likely performance of an external wall system calls for a methodical analysis of a range of data and cannot be based on a single test that may not adequately reflect conditions liable to be encountered in practice.

¶111.49 Finally, it is important to recognise that if large-scale tests are to be of any value, it is important to ensure that those who carry them out make the data derived from them fully available to the manufacturer and designer. That degree of co-operation was lacking on the part of many of those who were involved in large-scale testing before the Grenfell Tower fire.^23352335 See in particular Chapter 22 and Chapter 24.

Desktop assessments

¶111.50 In relation to external wall systems, so-called "desktop assessments" or "desktop studies" involve the use of data derived from (usually) large-scale tests of one or more systems to establish by extrapolation how the system being assessed would respond if subjected to the same or a similar test. In practical terms, it is a method of demonstrating by reference to data derived from a BS 8414 test carried out on another system that the system under consideration would, if it were to be subjected to the same test, satisfy the criteria in BR 135.^23362336 Bisby, Phase 2 Report: BR 135 Desktop Assessment Report {LBYP20000004/8} paragraph 41. Although no desktop study was undertaken in relation to the external wall of Grenfell Tower, by the time of the fire they had become commonplace,^23372337 See for example Lewis {NHB00003433/38} page 28, paragraph 148; Lewis {NHB00003433/53} page 53, paragraph 194; Evans {NHB00003020/70} page 70, paragraph 190(d); Evans {NHB00003020/77} page 77, paragraph 200(a). particularly after they had been recognised by the Building Control Alliance in its Technical Guidance Note 18 as a means of demonstrating compliance with paragraph 12.7 of Approved Document B.^23382338 {NHB00000760}.

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¶111.51 Although a desktop assessment can, in principle, constitute a valid means of providing some of the information needed to assess the behaviour of an external wall system in response to fire,^23392339 Bisby, Phase 2 Report: BR 135 Desktop Assessment Report {LBYP20000004/8} paragraphs 41 and 44; Torero Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/114} paragraph 12.2.93; Torero {Day292/91:17}-{Day292/92:3}. its value depends to a very substantial extent on the quality of the data available for that purpose and the competence of the person carrying it out. To carry conviction such an assessment will need to be the subject of peer review or other competent oversight.^23402340 Bisby, Phase 2 Report: BR 135 Desktop Assessment Report {LBYP20000004/2} paragraph 7; {LBYP20000004/39} paragraphs 288 and 289; Bisby {Day291/66:6-13}; {Day291/89:4-11}.

¶111.52 The value of any desktop assessment of that kind also depends on both the author's and the reader's understanding of the limitations of the BS 8414 test and the criteria in BR 135. Just as a BS 8414 test should be regarded as no more than one source of information, so a desktop assessment should be treated as only part of what is a complex exercise that requires information from various sources.^23412341 Torero, Phase 2 Report: Adequacy of the Current Testing Regime {JTOR00000006/115} paragraphs 12.2.96 and 12.2.97; Bisby {Day290/92:8}-{Day290/93:3}; {Day291/66:22}-{Day291/67:10}; {Day291/74:19}-{Day291/75:10}.

¶111.53 Moreover, whether a system has itself been subjected to a test or has only been the subject of a desktop study, it is still necessary to assess how it is likely to perform as part of a building.^23422342 Bisby, Phase 2 Report: BR 135 Desktop Assessment Report {LBYP20000004/8} paragraphs 45 and 46; {LBYP20000004/24} paragraph 170; {LBYP20000004/42} paragraph 305; Bisby {Day290/123:10}-{Day290/124:7}; {Day290/140:17}-{Day290/141:9}; {Day291/73:4-24}. For the reasons we have given, meeting the criteria in BR 135 does not of itself demonstrate compliance with the functional requirements of the Building Regulations^23432343 Bisby {Day291/69:2-6}. and was not intended to do so.

¶111.54 There was ample evidence that those matters were not properly understood by construction and building control professionals in the years preceding the Grenfell Tower fire. For example, desktop assessments were often accepted by NHBC as "proving compliance" not only with Approved Document B but with the requirements of the Building Regulations themselves.^23442344 Evans {NHB00003020/10} page 10, paragraph 28(a); Evans {NHB00003020/15} page 15, paragraph 42, second sentence; Evans {NHB00003020/22} page 22, paragraph 68; Evans {NHB00003020/24} page 24, paragraph 74(b); Evans {NHB00003020/38} page 38, paragraph 107, final sentence; Evans {NHB00003020/63} page 63, paragraph 173, final sentence; Evans {NHB00003020/66}, page 66 paragraph 183; Evans {Day220/15:11-18}; {Day220/64:20-23}; {Day221/163:15-21}; {Day221/170:7-13}; {BLM00000211/3} second paragraph in blue text; Lewis {Day224/45:19-24}; {Day224/74:3-14}; {Day224/128:15}-{Day224/129:11}. See also {NHB00001408/4} paragraph 1.1.1.Show full note

¶111.55 The need for a methodical and scientifically rigorous approach to assessing how a system that has met the criteria in BR 135 will perform in practice^23452345 Bisby, Phase 2 Report: BR 135 Desktop Assessment Report {LBYP20000004/24} paragraph 170. is of greater importance when the data that provides the basis for the assessment has been derived from one or more tests carried out on different systems.^23462346 Bisby {Day291/68:6-14}. That exercise necessarily introduces additional layers of complexity, because the person making the assessment must take into account the potentially complex variations between the different systems. Accordingly, the level of expertise and experience required to make the assessment are higher.^23472347 Torero {JTOR00000006/114}, Phase 2 Report: Adequacy of the Current Testing Regime paragraph 12.2.95.1 and {JTOR00000006/115} paragraphs 12.2.97 and 12.2.98. See also Bisby {Day291/67:16}-{Day291/68:5}.

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BS 9414:2019

¶111.56 BS 9414,^23482348 {BSI00001934}. which was published in 2019, offers guidance on the interpretation of BS 8414 test data and provides procedures and rules for the way in which such data can be extended to systems other than those tested.^23492349 {BSI00001934/9} first paragraph. It proceeds on the assumption that the BS 8414 test series is in itself a sufficient mechanism for establishing the fire performance of a system; the limitations of the information that can be derived from BS 8414 test data are not acknowledged. It does not explain how the effect of any differences between the system as tested and the system as built are to be assessed without a desktop assessment at each stage of the process identified as requiring an application evaluation. Instead, it attempts to simplify the process of assessment using a set of prescriptive rules instead of calling for an examination by a qualified fire engineer.^23502350 Torero {Day292/95:19-21}; {Day292/99:20}-{Day292/100:19}; {Day292/103:25}-{Day292/104:13}. It aims to standardise what is intended to be an individual assessment.^23512351 Torero {Day292/100:9-19}. In our view it should be used with great caution and with the considerations we have mentioned in mind.

Conclusions

¶111.57 It seems clear to us that the regime that existed before the Grenfell Tower for assessing the performance of external walls in fire was inadequate. It relied heavily on small-scale tests which did not provide the information needed to make a reliable assessment of how materials were likely to perform in a significantly different context. It also relied on a large-scale test which lacked coherent performance criteria and provided limited useful information. The assessment method in BR 135 was too simplistic, allowing for a simple pass or fail result, when the results of the test required a degree of interpretation that was beyond the competence of most in the industry. Moreover, guidance on how to carry out effective desktop assessments was lacking.

¶111.58 Although we recognise that some changes have been made to the regulatory system since that time, including a ban on the use of certain combustible materials on some tall buildings, we remain troubled by the fact that there is still no fire testing regime that delivers relevant information and by the failure to recognise the need for the application of competent professional judgement. We think that a comprehensive overhaul of the fire testing regime needs to be undertaken together with initiatives that will improve the number of fire engineers capable of carrying out complex assessments.

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