Grenfell Tower – Fire Safety Investigation:
Phase 1 Report – Section 2
Conclusions and Next Steps
Dr Barbara Lane FREng FRSE CEng
Fire Safety Engineering
5th November 2018
2.9 The primary failure – the Rainscreen cladding system
2.9.1 A high degree of compartmentation forms the most important basis of the single building safety condition Stay Put.
2.9.2 Approved Document B (ADB) 2013 states there are two main objectives for compartmentation:
(a) to prevent rapid fire spread which could trap occupants of the building; and
(b) to reduce the chance of fires becoming large, on the basis that large fires are more dangerous, not only to occupants and fire and rescue service personnel, but also to people in the vicinity of the building.”
2.9.3 Compartmentation relied on the performance of the external wall at Grenfell Tower, because the external wall connected every flat, and every flat must be a separate compartment.
2.9.4 The external walls were required to comply with Regulation B4 External Fire Spread:
“The external walls of the building shall adequately resist the spread of fire over the walls … having regard to the height, use and position of the building.”
2.9.5 In Section 8 and 11, of my Expert Report, I have identified the materials forming the rainscreen cladding system, and assessed their compliance with the relevant statutory requirements.
2.9.6 Based on the relevant test evidence submitted to the Public Inquiry, the construction materials forming the rainscreen cladding system, when either considered individually or when considered as an assembly, did not comply with the recommended fire performance set out in the statutory guidance of ADB 2013 for a building with a storey 18m or more above Ground Level.
2.9.7 These materials as installed on Levels 4-23 were:
a) Aluminium windows supplied by Metal Technology Ltd;
b) Insulating core panels as infill between windows, formed of combustible Styrofoam (extruded polystyrene) supplied by Panel Systems Ltd;
c) Window fan inserts specified as the combustible Kingspan TP10 insulation;
d) 100mm thick Celotex RS5100 combustible PIR insulation board applied to columns;
e) 80mm thick Celotex RS5080 combustible PIR insulation board (two layers) applied to the spandrels between floors;
f) Kingspan K15 combustible phenolic foam insulation (two layers) applied to the spandrels between floors
g) Arconic Reynobond 55 PE Cassette system ACP (smoked silver metallic);
h) Arconic Reynobond 55 PE Cassette system ACP (pure white)- Level 3 only;
i) EPDM weatherproof membrane between the new windows and the existing concrete structure;
j) Siderise Vertical cavity barriers on the columns;
k) Siderise Horizontal cavity barriers;
2.9.8 Additionally, I conclude the entire system could not adequately resist the spread of fire over the walls having regard to height, use and position of the building. Specifically, the assembly failed adequately to resist the spread of fire to an extent that supported the required Stay Put strategy for this high-rise residential building. The assembly failed adequately to resist the spread of fire to an extent that supported the required internal fire fighting – Defend in Place fire fighting regime.
2.9.9 There were multiple catastrophic fire-spread routes created by the external wall materials, the arrangement of the materials, as well as the construction detailing of those materials.
2.9.10 In addition, as I have explained in Section 9, the construction detailing created to seal the gap between the old and new windows, in each flat, meant that the materials and the arrangement of those materials, increased the likelihood of a fire breaking out of the flat and into the large cavities contained within the cladding system surrounding those windows. Those cavities were formed of and contained combustible materials.
2.9.11 Attempts had been made to subdivide the column cavities, and to provide vertical and horizontal fire stopping at key compartment lines. However, both the horizontal and vertical fire stopping were defective in their installation, but more importantly there is no evidence these fire stopping products have ever been proven, by fire test, to perform in an ACP based rainscreen external wall system of the type installed at Grenfell Tower.
2.9.12 The window openings were not provided with fire resisting cavity barriers. These unprotected openings themselves were instead surrounded by combustible materials, which acted as a means of fire and smoke spread.
2.9.13 There were combustible lining materials located within the flats, above and below the window openings. These materials support the spread of fire and smoke, from an incident adjacent to a window, also.
2.9.14 Therefore, in the event of any internal fire starting near a window, there was a
disproportionately high probability of fire spread into the rainscreen cladding
2.9.15 This was also true in the event of a fire remote from the window, unless the fire brigade extinguished it early enough to prevent heating of the rainscreen system via the window openings or via the window opening surrounds; or the fire was prevented by some other means from developing into a scenario which could cause the heating of the window opening or the heating of the materials surrounding those openings in a flat.
2.9.16 The interface between the kitchen window, and the window reveal lining materials, in Flat 16 and (a) the column rainscreen system and (b) the above window horizontal rainscreen system, was the primary cause of the early stages of fire spread.
2.9.17 The type of window reveal lining materials and how they were arranged around the window provided no means to control the spread of fire and smoke, from the small kitchen fire which was the source of the fire.
2.9.18 In addition, the type of materials in the rainscreen system and how they were arranged around the windows in the kitchen, contributed to the speed at which the fire spread from the flat of fire origin to a multi storey external fire within the rainscreen system.
2.9.19 Once the fire entered the rainscreen system outside Flat 16 on the East elevation, the Reynobond 55PE rainscreen cladding panel coupled with the ventilation cavity backed by the Celotex insulation or Kingspan K15 insulation, incorporating defective vertical and horizontal Siderise fire stopping material, and missing cavity barriers around the window, failed to control the spread of fire and smoke.
2.9.20 The Reynobond 55PE contributed to the most rapid of the observed external fire spread.
2.9.21 There were also Aluglaze extruded polystyrene core insulating panels installed between every window, in front of the existing window infill panels. Polystyrene produces large quantities of black toxic smoke; and supports rapid fire spread as evidenced during the fire.
2.9.22 The assembly – taken together with the insulation material on the existing external wall, the missing and defective cavity barriers – became part of a successful combustion process. This process generated substantial fire spread over 6 distinct pathways. A full geometric grid was created by means of the construction materials, which connected (in the event of an internal fire, cavity fire or external fire) every flat on a storey; and every storey from Level 3 to roof Level. These pathways also supported the spread of external fire back into the building, through the windows, and created a series of internal fire events.
2.9.23 The consequence of this was that any individual flat of fire origin was no longer in a separate fire rated box as is required. The compartmentation required in the building was breached by the ability of the fire to spread on the external wall from that compartmented flat to the next.
2.9.24 I conclude that the required single building safety condition Stay Put, was not
provided for, as was required, as a result of the rainscreen system installed during the primary refurbishment.
2.9.25 As a result, the arrangement and type of construction materials in the rainscreen system caused:
(a) A rapidly advancing and continuous external flame front which impacted flats on multiple stories;
(b) The generation of large quantities of polymeric based smoke which entered many flats;
(c) The flame front caused additional internal fires, many of which underwent a flashover fire (this in general occurred where external firefighting was not possible by LFB); these internal fires also produced smoke;
(d) The external fire and internal fires then affected the active and passive fire protection measures in the building.
2.9.26 The rainscreen system, installed during the refurbishment in 2012-2016, was therefore non-compliant with the functional requirement of the Building Regulations.
2.9.27 In my Phase 2 report I will investigate how this state of affairs came to exist at Grenfell Tower.
2.10 The failure of the early external fire fighting activity
2.10.1 I do not consider it reasonable that in the event of the installation of a combustible rainscreen system on a high rise residential building, the fire brigade should be expected to fully mitigate any resulting fire event. That is particularly so in circumstances where the fire brigade had never been informed that a combustible rainscreen system had been installed in the first place. Further, there are so many combinations of events, that could fall entirely outside the reach of external firefighting activity. This is important when only internal firefighting arrangements are made for high-rise residential buildings by statutory guidance at this time.
2.10.2 I have found no evidence yet that any member of the design team or the construction team ascertained the fire performance of the rainscreen system materials, nor understood how the assembly performed in fire. I have found no evidence that Building Control were either informed or understood how the assembly would perform in a fire. Further I have found no evidence that the TMO risk assessment recorded the fire performance of the rainscreen system, nor have I found evidence that an LFB risk assessment recorded the fire performance of the rainscreen system. I await further evidence on these matters, which I will explore in my Phase 2 report.