Chapter 109: Testing the materials

Chapter 109: Testing the materials

¶109.1 In his Materials Testing Report^20672067 Bisby, Phase 2 Materials Testing Report {LBYMT00000002}. Professor Bisby described the tests carried out under his supervision on a number of the important materials and products used in the external cladding system at Grenfell Tower. They included: a. Reynobond 55 PE ACM rainscreen panels (ACM PE); b. Celotex RS5000 foil-faced polyisocyanurate polymer foam insulation; c. Kingspan K15 foil-faced phenolic polymer foam insulation; d. Aluglaze extruded polystyrene polymer foam window infill panels.^20682068 Bisby, Phase 2 Materials Testing Report {LBYMT00000002/2} paragraph 4; Bisby, Phase 2 Materials Testing Report {LBYMT00000002/14} paragraph 79 and Table 1.

Aims and objectives

¶109.2 The purpose of the tests was to record fundamental physical information about the materials and products and to assess their key characteristics and properties in fire.^20692069 Bisby, Phase 2 Materials Testing Report {LBYMT00000002/2} paragraphs 6-8. In particular, the testing aimed to quantify the thermal responses of the materials and thereby to provide information that would be relevant to understanding the contribution of each material to ignition, fire growth and fire spread during the fire at Grenfell Tower.^20702070 Bisby, Phase 2 Materials Testing Report {LBYMT00000002/30} paragraph 135. The tests were undertaken both at the University of Edinburgh by Professor Bisby and, to a more limited extent, by BRE.^20712071 Bisby, Phase 2 Materials Testing Report {LBYMT00000002/2} paragraph 2; Bisby, Phase 2 Materials Testing Report {LBYMT00000002/7} paragraph 29; Bisby, Phase 2 Materials Testing Report {LBYMT00000002/30} paragraphs 138-142.

Methods

¶109.3 Four methods of thermal analysis testing were used.^20722072 Bisby, Phase 2 Materials Testing Report {LBYMT00000002/30} paragraphs 138-142. Each of them subjected a material or product to heat in a controlled environment and measured the changes that took place in various properties of the material during the heating process.^20732073 Bisby, Phase 2 Materials Testing Report {LBYMT00000002/30} paragraph 137. We explain briefly below the information provided by each of the four methods. a. Bomb calorimetry

This method measures the gross heat of combustion of a material, i.e. the total heat released.^20742074 Bisby, Phase 2 Materials Testing Report {LBYMT00000002/31} paragraphs 152-156.

¶b. Thermogravimetric analysis This analysis, undertaken in both reactive (air) and inert (with no oxygen) environments, measures the mass of a material and the rate at which mass is lost.

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¶c. Cone calorimetry This test calculates the heat release rate of a material. It can also measure the critical heat flux required for ignition, that is, the amount of heat that must be applied to the material in order to make it burn.^20752075 Bisby, Phase 2 Materials Testing Report {LBYMT00000002/35} paragraphs 176-179.

¶d. Dynamic Mechanical analysis This test measures the mechanical response of a material when subjected simultaneously to heat and mechanical stress. Data about changes in various mechanical properties of the material, such as stiffness, can be used to infer physical or chemical changes which have occurred in response to an increase in temperature.^20762076 Bisby, Phase 2 Materials Testing Report {LBYMT00000002/35-36} paragraphs 182-185.

The results

¶109.4 The tests disclosed no unexpected results, given the properties of the materials tested and the information available on similar materials.^20772077 Bisby, Phase 2 Materials Testing Report {LBYMT00000002/38} paragraph 191; Bisby, Phase 2 Materials Testing Report {LBYMT00000002/57} paragraph 276; Bisby, Phase 2 Materials Testing Report {LBYMT00000002/61} paragraph 288; Bisby, Phase 2 Materials Testing Report {LBYMT00000002/67} paragraphs 320-321; Bisby, Phase 2 Materials Testing Report {LBYMT00000002/68} paragraphs 326-331. Nothing in Professor Bisby's work was challenged and we accept the validity of his conclusions.

Regimes of Burning

¶109.5 In his report Work Package 1 – Regimes of Burning^20782078 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002}. Professor Bisby assessed how each of the four products used in Grenfell Tower's external wall responded to fire when tested in isolation. Over 150 separate experiments were carried out as part of that exercise.^20792079 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/4} paragraph 16. They were directed to demonstrating and understanding the complexity of the products' response to heating (both thermal and mechanical) under a range of heating and fixing conditions. The work was also intended to develop an understanding of the various thermal and mechanical factors that were relevant to the subsequent system experiments, to provide an understanding of how the different products burned under different conditions and to provide additional background information.^20802080 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/2-3} paragraphs 8-12; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/12} paragraphs 72-74. The tests were designed to answer questions relevant to quantifying the contributions of different products to the spread of fire at Grenfell Tower.^20812081 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/12} paragraph 75.

¶109.6 The report contains a detailed description of the responses of the four products to heating that we do not repeat here. (Those who are interested can read Professor Bisby's report on the Inquiry's website.) Instead, we list the important conclusions to be drawn from that work, taking each of the four products in turn. Again, nothing in Professor Bisby's work was challenged and we accept the validity of his conclusions.

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Reynobond ACM PE

¶109.7 Although Reynobond ACM PE was the most difficult of the products to ignite,^20822082 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/72-76} Tables 7, 8 and 9, Figures 28-29 and paragraph 391. once ignited it released energy more rapidly than any of the others and released more energy per unit area than any of the other products.^20832083 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/66-67} paragraphs 361-362, Table 4 and Figure 26. It had the highest heat of combustion^20842084 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/4} paragraph 18; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/63} Table 3, Figure 24 and paragraph 357. and was the largest potential contributor to energy release in the external wall system at Grenfell Tower.^20852085 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/4} paragraph 19; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/67} Figure 26. Of the four products, it had the greatest potential to contribute to fire growth and spread by a substantial margin, contributing up to 59% of the total energy available on any given floor of the tower, calculated by reference to the density of the different materials used, the energy they contained per square metre and their approximate area on each floor.^20862086 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/4} paragraph 19; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/65} Table 4.

¶109.8 In most of the experiments the bulk of the core of the product melted during heating and dripped downwards, flaming as it did so, collecting in burning pools on any available horizontal surfaces.^20872087 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/5} paragraph 26; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/58} paragraphs 331-332; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/50} paragraph 278.

¶109.9 The colour of the core did not affect the heat of combustion, with no material difference being observed between the products with clear and black cores.^20882088 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/63} Table 3 and Figure 24. Although the method of fixing in the tests did not materially influence the time it took for the panels to ignite,^20892089 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/73} Table 8; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/107} paragraph 627. it did significantly influence the rate of burning and the rate at which heat was released by the product.^20902090 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/108-109} Figure 36 and paragraphs 630-633 and 637; Bisby {Day289/144:20}-{Day289/145:4}. The method of fixing also had a substantial influence on the extent to which the core of the product burned in place within the panels or dripped and flowed downwards.^20912091 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/109} paragraphs 634-639; Bisby {Day289/145:4-9}.

¶109.10 Overall, Professor Bisby's tests confirmed that Reynobond ACM PE was the most influential product for promoting external fire spread across the system, in that the amount of energy released and the speed at which it was released were directly related to the rate and extent of external fire spread.^20922092 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/80} paragraph 453.

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Celotex RS5000

¶109.11 This product was tested both with and without foil facers and the presence of the facer made a major difference to the way in which the product burned.^20932093 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/93} paragraph 496; Bisby {Day289/146:20-24}; {Day289/148:16-21}. The foil facers provided protection to the core of the product,^20942094 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/100} paragraph 569; Bisby {Day289/133:18}-{Day289/134:3}. which was comparatively difficult to ignite when tested in that form. When tested without a foil facer, however, it displayed a very low time to ignition and was comparatively easy to ignite.^20952095 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/6} paragraphs 44-45; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/72-76}, Tables 7, 8 and 9, Figures 28 and 29 and paragraph 393. The foam core of the product itself displayed a substantially lower heat of combustion than either Reynobond ACM PE or the Aluglaze infill panels.^20962096 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/6} paragraph 41; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/63-64} Table 3 and Figure 24 and paragraph 357.

¶109.12 Once ignited, RS5000 had a much lower heat release rate per unit area than Reynobond ACM PE,^20972097 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/7} paragraph 47; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/89} paragraph 453; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/79} Figure 30; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/84}, Figure 33; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/86}, Figure 35.Show full note both with and without foil facers in place.^20982098 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/82} paragraph 427; Bisby, Phase 2 Experiments Work Package 1 Regimes of Burning {LBYWP100000002/88}, paragraph 445. That was due to the fact that thermosetting polymer foams, including polyisocyanurate foam, form a layer of char^20992099 Phase 2, Experiments Work Package 1, Regimes of Burning {LBYWP100000002/88} paragraph 448; Bisby {Day289/146:12-19}; {Day289/148:4-15}. and do not drip or melt.^21002100 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/58} paragraph 330; Bisby, Phase 2 Experiments Work Package 2, Systems Interactions {LBYWP200000001/22} paragraph 143; Bisby {Day289/149:9-11}. When tested, RS5000 showed a gradual thermal decomposition in response to sustained heat, with a layer of char forming that cracked^21012101 Bisby {Day289/148:6-15}; {Day289/149:23}-{Day289/150:5}. and a low heat release rate.^21022102 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/89} paragraph 454; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/94}, paragraph 497; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/100} paragraph 564. The periods over which that occurred were longer than those of external fire spread.^21032103 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/7} paragraph 46; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/89} paragraph 454. Nonetheless, of the four products tested, RS5000 was the second highest contributor (38%) to the available energy per floor at Grenfell Tower.^21042104 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/65-67} Table 4, Figures 25 and 26; Bisby {Day289/153:3-9}; Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/22} paragraph 141.

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Kingspan K15 289/150

¶109.13 When K15 was tested without its foil facers, it was relatively easy to ignite. With the foil facers in place, the time to ignition was significantly extended^21052105 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/8} paragraphs 58-59; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/72-76} Tables 7, 8 and 9, Figures 28 and 29 and paragraphs 394-395; Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/80} paragraph 460. but was still shorter than that of RS5000 with foil facers.^21062106 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/75} paragraph 394. That was due to the presence of tiny perforations in the foil facers of K15^21072107 Bisby {Day289/120:1-7}; {Day289/134:13-18}; {Day289/153:10-16}; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/75} paragraph 394; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/102}, paragraphs 588-589. that were not present in the facers of RS5000 and increased its reaction to fire^21082108 Bisby {Day289/134:19-23}. by allowing the release of flammable products.^21092109 Bisby {Day289/169:23}-{Day/170:3}.

¶109.14 The heat of combustion of the phenolic foam core of K15 was comparable to that of RS5000,^21102110 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/7} paragraph 54. and was substantially lower than that of both the Reynobond rainscreen panels and the Aluglaze infill panels.^21112111 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/63-64} Table 3, Figure 24 and paragraph 357. As in the case of RS5000, once ignited, K15 exhibited a far lower heat release rate than Reynobond, both with and without foil facers.^21122112 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/89} paragraph 455; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/79} Figure 30; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/84} Figure 33; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/86}, Figure 35. It also exhibited a sustained, gradual thermal decomposition,^21132113 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/80} paragraph 458; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/95} paragraphs 515-516; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/102} paragraph 584. with a layer of char forming^21142114 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/89} paragraph 456; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/119} paragraph 713; Bisby {Day289/151:2-9}. at a rate slower than external fire spread.^21152115 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/80}, paragraph 453. Unlike RS5000, K15 showed some glowing^21162116 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/89} paragraph 456; Bisby {Day289/151:10-13}; {Day289/152:5-10}. and spalling, the latter resulting in hot fragments of phenolic foam being ejected.^21172117 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/23} paragraph 150. If it had been installed on Grenfell Tower in place of RS5000, it would have been the second largest potential contributor to the available energy per floor (39%).^21182118 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/119} paragraph 709; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/65-67} Table 4, Figures 25 and 26. It is worth bearing in mind that K15 accounted for only some 5% of the insulation used in the external wall of Grenfell Tower. It is not known exactly where on the tower it was placed.

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Aluglaze window infill panels

¶109.15 Although the extruded polystyrene core of the Aluglaze panels was comparatively easy to ignite^21192119 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/75} paragraph 392. and had both a higher heat of combustion^21202120 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/63-64} Table 3, Figure 24 and paragraph 357. and a higher heat release rate^21212121 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/79-80} Figures 30 and 31; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/82} paragraph 426; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/84-85} Figures 33 and 34; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/89} paragraph 452.Show full note than either RS5000 or Kingspan K15, the maximum potential energy contribution from the Aluglaze panels was very small (2-3%).^21222122 Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/64-67} paragraphs 360 and 362, Table 4 and Figures 25 and 26; Bisby, Phase 2 Experiments Work Package 1, Regimes of Burning {LBYWP100000002/116-117} paragraphs 686, 689 and 693. For that reason, they were not used in the experiments^21232123 Bisby, Phase 2 Experiments Work Package 2, Regimes of Burning {LBYWP200000001/21} paragraph 138. to which we refer below.

The system experiments

¶109.16 The configuration of the equipment used for the system experiments was intended to represent, in broad terms, a ventilated cladding system such as that installed at Grenfell Tower.^21242124 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/3} paragraph 11. It is described in detail by Professor Bisby in his report entitled Work Package 2 – System Interactions.^21252125 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/38-57} paragraphs 244-345; Bisby {Day289/159:3}-{Day289/163:22}. It consisted of an open-sided ventilated cavity created by placing a Reynobond ACM PE panel opposite various different materials, mostly insulation products. The overall size of the panel was 50cm wide by 100cm tall, being the maximum size which could be safely accommodated in the laboratory at Edinburgh.^21262126 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/42} paragraph 261. A propane line burner, (essentially a metal pipe with small holes in it which allowed the size of the initial flames to be controlled)^21272127 Bisby {Day289/159:14-20}. was used to heat and ignite the polyethylene core of the panel before being removed. The fire was then allowed to grow or extinguish itself without further intervention and a range of data was collected from each experiment.^21282128 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/2} paragraph 4.

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¶109.17 The following figure taken from Professor Bisby's report shows the experimental equipment ready for testing.^21292129 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/39} Figure 5.

¶Figure 109.1 – Annotated photo showing experimental setup ready for commencing an experiment

Aims and objectives

¶109.18 The apparatus used in the experiments was designed to deliver consistent and repeatable results and to allow a systematic exploration of the relative contributions of the different products to the fire.^21302130 Bisby {Day289/158:15-21}. The main point of interest was how a fire involving the Reynobond developed and the factors that influenced it. There were two particular physical processes that it was thought would be of importance:

¶a. The melting of the polyethylene and its consequent escape from the aluminium skins; and

¶b. The detaching of the aluminium skins exposing the polyethylene to the flames.^21312131 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/24} paragraphs 162-164.

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¶109.19 Once the polyethylene begins to melt, flow and ignite a complex heat transfer process occurs within the system. Energy is conducted away from the localised source of heat due to the high thermal conductivity of the aluminium skins,^21322132 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/24-25} paragraph 167. leading to the melting and involvement of ever greater quantities of polyethylene that then becomes available to burn. The process continues to release more energy than is required to melt and mobilise the polyethylene, leading to the growth of the fire.^21332133 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/25} paragraph 168. However, energy is also lost from the system and it is possible that losses due to conduction, radiation and convection can mean that the temperature of the panels cannot rise rapidly or may decrease, leading to the extinction of the fire.^21342134 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/25} paragraphs 168-169. Understanding the factors that affect the release of energy is fundamental to understanding whether an ACM product will burn in any given situation.^21352135 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/25} paragraph 171.

¶109.20 The release of energy is also affected by two other important factors: (1) the size and shape of the rainscreen cavity and (2) other materials and products (whether combustible or not) in the system, including the insulation.^21362136 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/25} paragraph 171. In the case of a rainscreen cavity, the reduction in the area available for the entrainment of air typically results in longer flames than would be observed in a similar fire in the open air, which leads to the heating of a larger area with the potential for additional heat release and fire growth.^21372137 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/25-26} paragraphs 173-174. In addition, the particular properties of the material forming the internal face of the cavity opposite the rainscreen panel determines the amount of thermal energy transferred back to the panels, either by reflection (e.g. from a foil facer)^21382138 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/26} paragraph 182. or as a result of ignition and burning which contributes additional energy to the system.^21392139 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/26-27} paragraph 183.

¶109.21 The experiments were intended to answer a number of important questions, including:

¶a. Did the presence of the cavity itself cause the panels to burn so vigorously?

¶b. Did they burn so vigorously because they were very well insulated by the other products? and

¶c. Did the burning of the combustible insulation products cause the panels to burn so vigorously?^21402140 Bisby {Day289/158:1-11}.

¶109.22 It is important to emphasise that the purpose of the experiments was to study the physical processes that might be relevant to the spread of fire at the tower, not to reproduce the tower on a small scale or to rate the products.^21412141 Bisby {Day289/158:22}-{Day289/159:2}. The experiments were directed to the spread of flames in a vertical direction only and no attempt was made to assess the spread of fire horizontally or downward.^21422142 Bisby {Day290/62:4-5}. All the tests carried out by Professor Bisby were designed specifically for the purpose because none of the standard tests was capable of providing the information he needed.^21432143 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/28} paragraph 196; Torero, Phase 2 Report, Adequacy of the Current Testing Regime {JTOR00000006/77} paragraph 9.3.7.

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The products and the conditions under which they were tested

¶109.23 The experiments focused on testing the following four products: a. Reynobond ACM PE; b. Celotex RS5000 foil-faced PIR polymer foam insulation; c. Kingspan K15 foil-faced phenolic polymer foam insulation; d. Foil-faced mineral wool insulation. Mineral wool insulation was used both for comparative purposes and to establish the fundamental thermal and physical processes leading to the upward spread of fire over the external wall.^21442144 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/28} paragraphs 197-201.

¶109.24 Experiments were also performed with a water-cooled steel plate replacing the insulation (referred to in the report as a "heat sink cavity") and without any cavity at all.^21452145 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/28} paragraphs 202-204. Experiments were also carried out with different fixing arrangements for the panels. They included one with edge-routing to simulate cassette fixing and one with edge-routing and face riveting to simulate riveted fixing. Rivets passing through the panel were expected to hold the aluminium skins in place in the early stages of a fire.^21462146 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/28-29} paragraphs 205-209; Bisby {Day289/162:20}-{Day289/163:17}.

¶109.25 Professor Bisby did not include the Aluglaze window infill panels in his experiments because they were not part of any continuous ventilated cavity at Grenfell Tower and were not thought to have played an important role in the spread of fire.^21472147 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/21} paragraphs 137-138.

Important aspects of system behaviour

¶109.26 Initial experiments carried out at Edinburgh demonstrated the importance of five important matters that affect the development of fires in cladding systems and that Professor Bisby and his team subsequently set out to control and vary in order to understand the behaviour of the system as a whole. They were: a. The burning and dripping of the polyethylene core of the ACM panels, b. The mechanical response of the panels, c. Thermal feedback from the insulation, d. Burning of the insulation, and e. Heat losses from the cavity.

¶109.27 The important factors influencing the growth and speed of fire within a cladding system were found to be (i) the amount of downwardly mobile polyethylene, (ii) the locations where it could pool and burn and (iii) the surface area of the resulting pool fire and hence its heat release rate.^21482148 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/29} paragraph 212. In addition, a number of important forms of mechanical behaviour were observed when the panels were heated, including warping of the aluminium skins and partial or full separation of the aluminium skins leading to exposure of the polyethylene core.^21492149 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/30} paragraphs 213-214.

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¶109.28 The extent to which the insulation provided thermal feedback to the panels was another important factor leading to the growth and spread of fire within the cladding system.^21502150 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/30} paragraphs 215-216. When heated to above their pyrolysis temperatures both Celotex RS5000 and Kingspan K15 produced combustible products which would burn within the cladding cavity, increasing the overall heat release rate and also potentially contributing to surface flaming of the insulation. That, in turn, influenced the thermal feedback to the panels and the growth and spread of fire within the system. To understand that better, experiments were performed with insulation products both with and without their foil facers.^21512151 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/30} paragraphs 217-218.

¶109.29 The extent to which heat was lost from the cavity by convection, radiation or conduction heat transfer mechanisms was likely to influence the growth and spread of the fire and therefore some experiments were performed without a cavity.^21522152 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/30} paragraphs 219-220.

The results of the system tests

¶109.30 Over 50 separate experiments were conducted in total, producing a large volume of data.^21532153 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/58} paragraph 346. Each test was run twice to check the repeatability of the results – Bisby {Day289/181:9-11}. In his report Professor Bisby described one of the experiments (Experiment 21) in detail because it exemplified a number of important processes that had been observed in some of the experiments and were of critical importance for Grenfell Tower. He also summarised what the data showed, both generally and with reference to the thermal and physical behaviour associated with each product and constituent material and the interactions between them.^21542154 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/58} paragraphs 348-350. We have adopted the same structure in this part of our report, although readers should refer to the detailed information set out in Professor Bisby's report and in the accompanying videos for a full explanation of the results of the experiments.

Experiment 21

¶109.31 Experiment 21 was performed on a cladding arrangement using an ACM PE panel with a routed (i.e. cassette-type) fixing and foil-faced Kingspan K15 insulation.^21552155 Bisby {Day289/164:3-7}. A number of key observations were made during the experiments,^21562156 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/59-65} paragraphs 356-381; Bisby {Day289/164:3}-{Day289/172:13}. For a more detailed examination of the physical processes examined during the tests see Torero, Phase 2 Report, Adequacy of the Current Testing Regime {JTOR00000006/68-76} paragraphs 9.1.1-9.2.21. of which the following were the most important:

¶a. After 1½–2 minutes of flame impingement on the panels from the line burner, a small pool fire of burning polyethylene began to form in the drip tray (which simulated something similar to a window ledge).

¶b. After 2¼ minutes, lateral movement of the aluminium facing on the lower return part of the aluminium cassette occurred and at about 3¼ minutes the facing slid off the return ledge and fell into the drip tray. That exposed the polyethylene on the top of the return ledge, leading to surface burning of the polyethylene in that area.

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¶c. Between 2¼ minutes and 4 minutes the pool fire within the drip tray grew in size. The mass of polyethylene increased during this period and corresponding increases occurred in the total heat release rate, temperature and flame height in the cavity during that time. d. By 4 minutes the flames had extended to about three quarters of the height of the cavity.

¶e. At about 5¼ minutes the first flames were visible above the experimental rig and by 6 minutes there was consistent flaming above the rig.

¶f. From about 6½ minutes the inside main vertical face of the panel began to separate from the outside face and a void began to form between the two aluminium skins.

¶g. From about 9 minutes visible flaming was evident on the inside of the ACM panel and flaming was also observed on the surface of the insulation. The following figure from Professor Bisby's report was taken at 9.44 minutes:^21572157 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/64} Figure 20.

¶Figure 109.2 – Experiment 21 (time 9.44 minutes)

¶h. Just before 10 minutes into the experiment the aluminium foil was lost from the face of the Kingspan K15 insulation and there was considerable surface flaming. The heat release rate was more than 50kW.

¶i. At about 10 minutes flames could be seen coming out of the top of the panel between the two aluminium skins.

¶j. At 10½ minutes the inside aluminium skin detached itself, exposing the remaining polyethylene in the core. At that point the heat release rate rose from about 150kW at 10½ minutes to a peak of 496kW at 10 minutes 50 seconds. In other words, in just 20 seconds the heat release rate more than trebled. Professor Bisby described that as the full involvement of the panel.^21582158 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/67} paragraph 394. The following figure from his report shows the system at that time:^21592159 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/65} Figure 23.

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¶Figure 109.3 – Experiment 21 (time 10.50 minutes)

¶k. Beyond that point the panel rapidly lost mass as burning and the involvement of the polyethylene increased.

¶l. Fully involved burning of the system continued for 2-3 minutes before the heat release rate rapidly declined to about 50kW by 13½ minutes. At that point the fire was running out of the fuel from the polyethylene needed to be able to maintain high heat release rates. m. After 13½ minutes the insulation continued to burn locally and slowly to lose mass. n. Flaming from the combustion of polyethylene was last observed at 18.04 minutes.

¶o. The insulation continued to burn locally in what appeared to be a self-sustaining reaction until the end of the experiment, which was terminated after 20 minutes. The smouldering eventually consumed the full thickness of the insulation in some places. Continued smouldering was not observed in similar experiments using PIR insulation; in those cases, the foam stopped burning when the polyethylene had been consumed.^21602160 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/62} paragraph 381; Bisby {Day290/65:10}-{Day290/66:8}; {Day290/66:19}-{Day290/67:9}.

System test results – general

¶109.32 When considering the data from all 50 experiments, it became apparent that not all of the tests had resulted in the full involvement of the panels. For example, the experiments carried out without a cavity, those carried out with a heat sink cavity and those in which the panel was riveted at its base did not progress to full involvement. In those cases, the peak heat release rate, the insulation mass loss and the total heat released were much lower than in all those cases in which full involvement of the panel had occurred.^21612161 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/79} paragraph 449.

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¶109.33 In those cases in which the panel did become fully involved in the fire some differences were observed in the magnitude of the peak heat release rate, the times taken to reach peak heat release rate, the mass of insulation lost and the total heat released.^21622162 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/79} paragraph 450. Those differences are discussed further below.

ACM tested in isolation

¶109.34 In the absence of a cavity, the polyethylene core of the ACM panel melted, dripped and ignited locally while the line burner was in place. However, the resulting pool fire failed to release enough energy to ensure that the energy retained within the system was sufficient for the temperature of the panel to increase at a distance from its base. As a result, insufficient polyethylene was mobilised to sustain continued burning and the growth of the fire and the fire extinguished itself when the line burner was removed.^21632163 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/124-125} paragraph 665; {LBYWP200000001/81-85} paragraphs 467-479. That demonstrated that a source of energy additional to that provided by the ignition of the polyethylene was required before localised burning of the polyethylene would lead to the delamination of the panels and full involvement of the core.^21642164 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/83} paragraphs 471-472.

ACM tested in a heat sink cavity

¶109.35 The introduction of a cavity in which a heat sink formed the internal face of the system resulted in minor increases in the feedback of heat to the panel and only a slight increase in the melting and mobilisation of the polyethylene core. That was caused by a slight increase in the height of the flames when they were small due to changes in air movements as well as the reflection of radiant heat.^21652165 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/125} paragraph 666; {LBYWP200000001/85-88} paragraphs 480-486. However, in none of those experiments did the panel become fully involved in the fire. That showed that the presence of a cavity was not by itself sufficient to cause the fire to develop.^21662166 Bisby {Day289/175:14-16}. Insulation also needed to be present, either to retain energy in the system or to burn and contribute additional energy.^21672167 Bisby {Day289/175:21-24}.

ACM with mineral wool insulation

¶109.36 The incorporation into the system of non-combustible insulation in the form of mineral wool resulted in the growth of the fire to full involvement of the panel because the insulation retained sufficient energy within the system to raise the temperature of the panel to the necessary level. Once the panel became fully involved there was a rapid increase in the heat release rate and in the total heat released. That demonstrated that it is not necessary for the insulation to burn in order for a fire to grow to the point at which the panels are fully involved.^21682168 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/125} paragraph 667; {LBYWP200000001/88-91} paragraphs 487-494. It also suggests that the critical factor in the development of a fire is the extent to which energy is retained in the system. Energy transmitted back to the panels supports continued heating, melting and the involvement of the polyethylene core and the deformation of the aluminium skins, which in turn increases the surface area of the burning polyethylene.

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ACM with combustible insulation without foil facers

¶109.37 The experiments showed that, by comparison with mineral wool, combustible foam insulation, whether PIR or phenolic, did not significantly increase the heat release rate or peak heat release rate of the system or the total heat released. However, the time taken to reach full involvement of the panels was shorter in the case of foam insulation (between 5 and 7 minutes) than in the case of mineral wool (between 10 and 12 minutes),^21692169 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/78} Figure 32; {LBYWP200000001/92} paragraph 506. primarily due to the ignition and surface flaming of the foam insulation, which both released additional heat and caused more uniform heating of the panel. As a result, the inner skin of the panel failed earlier, exposing a larger surface of polyethylene to burning.^21702170 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/125} paragraph 668; {LBYWP200000001/91-103} paragraphs 495-547. The combustibility of PIR and phenolic foams can therefore be seen to play a role in influencing the growth and spread of fire, but its contribution is secondary both to the burning of the polyethylene and to the insulating properties of the insulation.^21712171 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/96} paragraph 517; {LBYWP200000001/100} paragraph 535; Bisby {Day289/178:2-17}.

¶109.38 In the experiments carried out using Celotex RS5000 the behaviour of the system did not appear to be affected by the thickness of the material, which varied between 80mm and 100mm.^21722172 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/125} paragraph 669. The behaviour of systems incorporating Celotex RS5000 (a PIR foam) was broadly similar to that of systems incorporating Kingspan K15 (a phenolic foam), although there were subtle differences in the amounts of spalling observed and Kingspan K15 continued to smoulder after the ACM had burned itself out.^21732173 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/125} paragraph 670. That propensity to continue smouldering differentiated the phenolic foam from the PIR foam^21742174 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/97} paragraph 528. and both the total loss of mass and the total heat release of the system were higher when it incorporated phenolic insulation.^21752175 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/100} paragraph 534.

The addition of foil facers

¶109.39 Adding a foil facer to the mineral wool insulation resulted in a significant reduction in the time required for the fire to grow to the full involvement of the panel, a slight reduction in the amount of mass lost by the insulation up to that point, an increase in the temperatures within the panel and a very slight reduction in the total heat released. The introduction of the foil facer increased the reflective properties of the insulation, resulting in more rapid heating of the panel at a distance from the burning polyethylene at its base. The introduction of the foil facer also changed the surface properties of the insulation, including by promoting heat transfer by convection into the cavity.^21762176 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/126} paragraph 671; {LBYWP200000001/108} paragraphs 559-567.

¶109.40 Adding foil facers to RS5000 and K15 resulted in a clear increase in the time required to reach full involvement of the ACM, a reduction in the peak heat release rate (but without a major reduction in the total heat released), a clear reduction in the rate at which the insulation lost mass and a reduction in the temperatures measured at the midpoint of the panel.^21772177 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/126} paragraph 673. Professor Bisby concluded that the addition of the foil facers prevented early surface flaming of the insulation, thus reducing the early heating of the panel at a distance from the polyethylene pool fire at its base. The absence of surface flaming also resulted in less uniform heating of the inside face of the panel, a less symmetrical fire plume within the cavity and a more gradual compromising of the panel's inside face. That tended to prevent the sudden exposure of a large area of polyethylene and promoted a more gradual release of energy as it burned.^21782178 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/126} paragraph 674; {LBYWP200000001/109} paragraphs 569-573.

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¶109.41 In the case of Celotex RS5000, the addition of a foil facer resulted in a small reduction in the total mass lost. However, contrary to what might have been expected, the foil facer on Kingspan K15 promoted smouldering after the panel had burnt out,^21792179 Local burnout means that the polyethylene is not burning any more whether inside the panel or the drip tray – Bisby {Day290/62:24}-{Day290/63:7}. which explains a slightly greater loss of mass than when no foil facer was present.^21802180 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/126} paragraph 675; {LBYWP200000001/109} paragraph 574; Bisby {Day290/66:19}-{Day290/67:19}.

¶109.42 Those experiments again demonstrate the complexity of the process of heat transfer in a rainscreen cladding cavity. They also suggest that an intuitive view of the factors that govern the initiation, growth and spread of fire in such situations may lead to incorrect conclusions.^21812181 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/109} paragraph 575.

Varying the method of fixing the panels

¶109.43 Professor Bisby's experiments showed that the method of fixing ACM panels is capable of fundamentally altering their response to fire.

¶109.44 The inclusion of aluminium rivets passing through both faces over the lower third of the panel prevented the fire reaching the point at which the panel became fully involved. The rivets held the aluminium skins together and prevented the panel opening up. That reduced the area of polyethylene exposed to the fire and also discouraged its mobilisation into the drip tray, slowing and reducing the supply of fuel to the pool fire burning at the base of the panel.^21822182 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/127} paragraph 679. However, if the rivets were placed higher up the panel they did not prevent the separation of the panels lower down, which led to a very sudden loss of integrity, exposure of the polyethylene and a high peak heat release rate.^21832183 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/112} paragraph 585. All this indicates that riveting ACM panels would be likely to improve their performance in fire under most (but not all) circumstances,^21842184 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/127} paragraph 680; {LBYWP200000001/112} paragraphs 583-585. but that the number and location of the rivets are important in enabling them to slow or prevent the growth of fire.^21852185 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/127} paragraph 680. The behaviour of the panel in riveted form is to be contrasted with that of the panel in simulated cassette form as demonstrated in Experiment 21, described above.

¶109.45 In the case of the panels in simulated cassette form, the creation of additional routing lines on the inside faces resulted in a reduction in the time taken to reach full involvement in the fire and higher peak heat release rates. Professor Bisby attributed that to the fact that the increased amount of routing provided additional opportunities for the polyethylene to become involved in the fire and increased the propensity of the skins to separate, thereby exposing a larger area of polyethylene to the flames. That resulted in an increase in the rate of fire growth and made its development to the point of the full involvement of the panel more likely and more rapid.^21862186 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/126-127} paragraph 677. Accordingly, the routing of ACM panels for the purpose of cassette fixing made their fire performance worse.^21872187 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/127} paragraph 678; {LBYWP200000001/111-112} paragraphs 581-582.

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¶109.46 The evidence obtained from Professor Bisby's experiments provides further support for our understanding of why systems incorporating cassette-fixed ACM panels performed far worse when subjected to the European single burning item test (BS EN 13823) than those incorporating rivet-fixed panels.^21882188 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/112-113} paragraph 586. As discussed in Chapter 20. The differences in fire performance between the two fixing types again emphasises the complex way in which even simple systems respond to fire and the potential significance of what appear to be minor changes in methods of mounting and fixing.^21892189 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/113} paragraph 587.

Revisiting the Phase 1 conclusions

¶109.47 The results of Professor Bisby's experiments support the main conclusion reached by the chairman in the Phase 1 report, namely, that the principal reason why the flames spread so rapidly up Grenfell Tower was the presence of ACM panels with polyethylene cores which had a high calorific value, melted and acted as a source of fuel for the growing fire.^21902190 Phase 1 Report, Volume IV, paragraph 23.52. It is clear from the experiments that the principal factor which led to rapid growth of fire was the presence of unmodified polyethylene in the cores of the ACM panels, with its propensity to melt, drip and act as the primary source of fuel for the fire.^21912191 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/114-117} paragraphs 597-604 and 620; Bisby {Day289/184:7-10}. It was the burning of the polyethylene, rather than the burning of the insulation, which by a considerable margin determined how the external wall of the tower performed.^21922192 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/128-129} paragraph 695. In the words of Professor Bisby, ACM panels represent an extreme fire hazard, given their intense burning properties. We were struck by his evidence that every time he ran an experiment which led to the full involvement of the ACM he was surprised and alarmed.^21932193 Bisby {Day289/185:15-22}.

¶109.48 The experiments also support the conclusion in the Phase 1 report^21942194 Phase 1 Report, Volume IV, paragraph 23.52. that it was more likely than not that the presence of PIR and phenolic foam insulation contributed to the rate and extent to which the flames spread vertically.^21952195 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/115-117} paragraphs 605-620. However, it is now possible to be more specific about the precise contribution made by the insulation. In particular, the results of the experiments suggest that, although the contribution made by the insulation (with foil facers) to the total heat released during the period before the full involvement of the ACM is comparatively minor, representing less than 15% of the total energy released,^21962196 Even if all of the mass lost from the burning of the insulation products is assumed to be converted into energy, the Celotex RS5000 insulation is unlikely to have contributed more than 20% of the total energy released, the mineral wool about 0.1% of the total energy released and the Kingspan K15 about 53% of the total energy released. The figure for K15 reflects its propensity to smoulder after the ACM has substantively burned out – Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/128-129} paragraphs 692-695.Show full note it is the ability of the insulation to retain energy within the system and promote more rapid heating of the ACM that is the decisive factor in promoting the growth of fire.^21972197 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/127-128} paragraphs 682-686. PIR and phenolic foam products are exceptionally good insulators, a property that made matters much worse once fire had entered the rainscreen cladding.^21982198 Bisby {Day289/184:14-17}. That is why the experiments involving mineral wool also led to the full involvement of the ACM, because it too retains heat within the system and promotes rapid and extensive heating of the panels. It is not necessary for the insulation to be combustible for it to be capable of promoting the rapid and extensive growth of fire.^21992199 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/128} paragraph 690; Bisby {Day289/184:21-24}.

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¶109.49 It should be noted that when they did not have foil facers, the contribution of the insulation products to heat release rates was much higher and was comparable to that of the panels. It follows that, in the absence of foil facers, the contribution to a fire of the energy released through the burning of the insulation may be significant.^22002200 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/128} paragraphs 688-689.

¶109.50 The answers to the questions posed by Professor Bisby, therefore, are that it was not the presence of the cavity that caused the panels to burn with such vigour^22012201 Bisby {Day289/178:21-25}. nor the burning of the combustible insulation products,^22022202 Bisby {Day289:179:5}-{Day289/182:20}. but the fact that the cavity was very well insulated.^22032203 Bisby {Day289/179:1-4}.

Conclusions

¶109.51 The information obtained from the experiments support the following conclusions about the fire performance of rainscreen cladding systems incorporating ACM panels with unmodified polyethylene cores of the kind used on Grenfell Tower:

¶a. The most important influence on the growth of fire through such systems is the extent to which the particular materials and products of which they are composed cause energy to be retained within the system. Insulating or reflective materials within the cavity play an important part in performing that function.^22042204 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/129} paragraph 696.

¶b. The transfer of heat within a ventilated rainscreen system is extremely complex, even in the case of relatively small and simple arrangements. Particular modes of heat transfer may work in different ways for different materials and products in different situations.^22052205 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/129} paragraph 698; {LBYWP200000001/24} paragraphs 158-159; {LBYWP200000001/4} paragraph 17; Bisby {Day289/157:7-16}; {Day289/183:23}-{Day289/184:6}.

¶c. Intuitive assessments of the way in which fire is likely to spread are dangerous. They may lead to false assumptions that can be contradicted by empirical evidence, if sufficient time, care, instrumentation and technical insight is applied to understand the performance of the system.^22062206 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/129} paragraphs 701-703; {LBYWP200000001/4} paragraph 17; Bisby {Day290/73:11}-{Day290/74:14}.

¶d. The conditions required for ignition and the self-sustaining spread of flame are much less onerous than those typically encountered in ordinary compartment fires.^22072207 Torero, Phase 2 Report, Adequacy of the Current Testing Regime {JTOR00000006/67} paragraph 9.0.11; {JTOR00000006/76} paragraph 9.3.3.

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¶e. Even small changes in the configuration of the system, its geometry, the nature of the ventilation and the early development of the fire can have a significant effect on the speed at which the fire develops and the eventual outcome.^22082208 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/130} paragraph 704. For example, the experiments have drawn attention to the effect of mechanical fixings.^22092209 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/129} paragraph 699.

¶109.52 Nothing we have said in this chapter affects the chairman's previous conclusions about how the fire escaped from Flat 16 or the particular materials or physical processes that may have enabled that to occur.^22102210 Phase 1 Report Volume IV paragraphs 22.36-22.40. Professors Bisby and Torero were not asked to investigate the nature, amount or toxicity of the smoke emitted by any of the materials they examined under any conditions of burning.^22112211 Bisby, Phase 2 Experiments Work Package 2, System Interactions {LBYWP200000001/5} paragraph 34.

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