Why Did This Fire At An English Tower Block With Combustible ACM(LD-PE) Cladding Lead To The Horrific Grenfell Tower Inferno?
[ Posted by Lara Keller 2/11/19 Updated 8/11/19] Blog Table Of Contents
Continuing articles on the terrible Grenfell Tower Fire of 14th June 2017 in London. This one focuses on the truth that the ACM cladding fire at Grenfell Tower in England, was one of many similar fires in tower blocks with similar combustible cladding in England. If the conclusions of the Grenfell Inquiry’s Phase One Report are correct, and the wide spread interpretation of the UK BRE tests in 2017 on different combinations of ACM cladding and insulation are correct, then there should have been many more horrific fires on this scale in England. Clearly there are reasons for this grateful outcome, which have not been investigated by the inquiry. Statistics in the UK are organized by component countries, so this article only considers the situation in England. (See for more articles: Grenfell Fire Articles Collection ).
Part 1: Calculating the number of high-rise buildings in England with ACM(LD-PE) cladding.
According to the latest UK government statistics of September 2019, there are 435 high rise buildings (defined as over 18m+ or six storeys or more) in the UK with cladding that fail building regulations (Building Safety Programme: Monthly Data Release Data as at 30 September 2019 and Table 5: descriptions of large-scale system tests undertaken by the BRE and the number of buildings with similar cladding systems – England, 30 September 2019 ). Just over a quarter have had remedial action on their cladding completed. In total 257 of these high rise buildings had or have ACM cladding of the worst kind that is rated as category 3.
This type of cladding has the potential to release over 35 MJ of heat for each kilogram of material. Aluminum plates do not burn, so the heat comes almost totally from the burning of the core material between the plates (there is also a small contribution from aluminum bonding and paint materials). Unmodified low density polyethylene (LD-PE) used on the Grenfell Tower rainscreen cladding, theoretically gives 45 MJ / kg when it burns. The rainscreen used has a 3mm LD-PE (unmodified low density polyethylene) core, which means 2.76 Kg of LD-PE per square metre (m2) of rainscreen, which gives potentially 124 MJ/m2. Given an 80% efficiency of combustion (the rest as smoke and unburnt volatiles) in a real fire scenario this means around 100 MJ/m2 is produced.
There is also the contribution of any insulation behind the rainscreen if it is combustible. The 100mm PIR (Polyisocyanurate) insulation layer used on Grenfell Tower had around half the heat release potential per square metre as the ACM(LD-PE) rainscreen cladding. This material forms a char layer (like wood) which slows or prevents combustion in real fire situations. The toxicity of this material is a huge problem, as it produces large amounts of toxic cyanide gas.
The fire spread risk therefore comes from the ACM(LD-PE) producing 100 MJ/m2 in minutes when exposed to fire. To put this in context the average UK home has an energy consumption of 150 MJ in electricity and gas in 24 hours. There are 257 high rise buildings in the UK with this type of ACM(LD-PE) cladding.
Part 2: Calculating the number of high-rise flats in England with ACM(LD-PE) cladding.
The report (Building Safety Programme: Monthly Data Release Data as at 30 September 2019) gives the number of self-contained dwellings (ie flats) for 339 of the 435 high rise buildings (defined as the usual 6 storeys or more, 18m+) being investigated (the other 86 buildings are student accommodation, hotels and a few government buildings). The average number of flats per high rise building being investigated is 84. There are 257 high rise buildings with ACM(LD-PE) rainscreen cladding under investigation, with therefore approximately 20,560 dwellings.
Part 3: Calculating the probability of a significant (fire service attended) fire in any high-rise flat in England.
The number of fires sufficiently significant to be attended by fire services (FRSs) in high-rise flats (defined as over 18m+, or six storeys or more) for 2016 to 2017 is estimated as 1638. This was calculated as follows. The number of fires in purpose built flats of 10 storeys or more was 714. In purpose built flats of 4 to 9 storeys there were 1848 fires. Assuming that half these flats were between 6 and 9 storeys, the number would be 924. Hence 1638 = 714 + 924. (See Fires in purpose-built flats, England, April 2009 to March 2017)
There are approximately 408,000 high rise (defined as over 18m, or six storeys or more) dwellings (ie self contained flats) in England. This means in the period 2016 to 2017, 0.4% of high rise flats had fires attended by the fire services. Calculated as follows 1638 / 408000= 0.004 = 0.4%.
Part 4: Calculating the number of extensive serious fires in high-rise flats in England that have ACM(LD-PE) cladding.
In the period 2016-2017 there were approximately 82 significant (attended) fires in high-rise flats with ACM(LD-PE) rainscreen cladding. Calculated as follows 20560 * 0.004 = 82.2 .
Of the 714 fires in all high-rise flats of 10 storeys or more in England in the period 2016-2017, 8% spread beyond the room of origin. So of the 82 fires in high rise flats (defined as the usual 6 storeys or more, 18m+) with ACM(LD-PE) cladding, there should have been about 7 which spread beyond the room of origin. Calculated as follows 82.2 * 0.08 = 6.58 .
It is not recorded how many of these fires broke through a window to interact with the cladding, so need to consider the reaction of modern double glazing to fire.
Part 5: The vulnerability of double glazing in flat fires.
Modern double glazing is vulnerable to residential fires, according to many studies including this one from UL Firefighter Safety Research Institute (FSRI) from 2009 (see Analysis of Changing Residential Fire Dynamics and Its Implications on Firefighter Operational Timeframes).
A typical modern double glazed unit with a plastic frame and two panes (assembly E) was mounted as part of the wall of a furnace (see UL Impact of Ventilation on Fire behavior in legacy and contemporary residential construction, by Stephen Kerber, 2008 updated 2010), where the internal (furnace) temperature then rose with the temperature curve below (red line):
The standard cellulosic temperature curve (purple line) for building material testing is also shown for comparison to the UL9 and actual furnace temperature curves.
Over 3 tests the window construction “assembly E” failed at an average of 312 seconds (just over 5 minutes).
Part 6: Calculating the number of high-rise flats in England that projected fire for a sustained period onto ACM(LD-PE) cladding.
Clearly only a few fires, in high rise flats (defined as the usual 6 storeys or more) with ACM(LD-PE) cladding, spread from the room of origin to other rooms or communal areas. It is highly likely that these fires caused double glazing to break and were able to project fire to the external cladding for a sustained period of time.
So in 2016-2017 of the estimated 82 fires in high rise flats (defined as the usual 6 storeys or more, 18m+) with ACM(LD-PE) in England, about 7 would have spread beyond the room of origin, and have been able to project fire to the external combustible rainscreen cladding for a sustained period of time.
Part 7: Calculating total number of flat fires in England that projected fire for a sustained period on ACM(LD-PE) cladding.
Aluminum composite panels have been used in the UK since the mid 1990s, with a surge in use since the mid 2000s. Assuming the number of buildings with ACM(LD-PE) combustible cladding has expanded approximately linearly over the last 15 years; the number of high-rise flat fires in England since the mid 2000s that projected fire for a sustained period onto combustible external ACM(LD-PE) cladding, is estimated as 49 fires. Calculated as follows (15/2) * 6.58 = 49.35 .
None of these fires have gratefully created in England (or the UK generally) a horrific inferno on the scale of the terrible Grenfell Tower fire of 2017, which was the largest residential fire in England (and the UK) since the horrific bombing blitz of the Second World War.
Part 8: Recent well known residential tower block fires in England.
There was a terrible fire at the 12 storey tower block “Lakanhal House” in July 2009 in South London, that killed six people, and injured over twenty. There were multiple failures of fire safety in this 1950s block, after decades of botched fire-stopping work. It had been renovated in 2006-2007, where major fire safety problems had been ignored. The “high-pressure laminate window panels (HPL)” spread fire on the outside of the building, there was also a lack of cavity barriers in suspended ceiling voids, doors without fire-stopping and timber stairs.
High pressure laminate (HPL) is essentially layers of paper impregnated with resins, and cured at high pressures. They have very little resistance to surface fire spread. This is the highly unsuitable type of material, that was used to make decorative formica kitchen table tops in the past.
Many years before this there was a serious fire at the 11 storey “Knowsley Heights” tower block near Liverpool in April 1991. The tower block had been over-clad with “limited combustibility” fibre silica cement rainscreen sheets (by now defunct Cape Universal). The external concrete walls behind this rainscreen were painted with flammable rubberized paint. There was a 90mm deep cavity behind the rainscreen and no horizontal cavity barriers (fire breaks) were fitted.
Rubbish was set on fire in a re-entrant wall area, which then spread to the flammable paint, with the cavity behind the rainscreen acting as a chimney. The fire spread rapidly to the top of the building, but mercifully no smoke or fire spread into the flats. Water applied by fire-fighters could not reach the fire raging behind the rainscreen.
A subsequent inquiry as a result of this fire and others eventually reported in 2000, and caused a change in building regulations in the UK (Approved Document B) in 2006, that mandated that there must be cavity barriers (fire breaks) in external cladding cavities, and that the external and internal surfaces of cladding must resist fire spread by being of limited combustibility (ie aluminum facings on foam insulation and aluminum plates around polymer cores in ACM rainscreen).
Neither of these notable fire incidents at Lakanhal or Knowsley Heights in England involved ACM(LD-PE) cladding.
Part 9: Recent well known residential tower block fires outside the UK that did involved ACM(LD-PE) cladding.
There have been major ACM(LD-PE) cladding fires in the Middle East, China and South Korea. In France the Mermoz Tower Block fire (2012) in Roubaix. In Australia the Lacrosse Tower Block fire (2014) in Melbourne. In the United States the 43 storey Borgata Water Club fire (2007) in Atlantic City. Many of these fires involved external curtain walling rather than overcladding. There are a lot of reports that make recommendations to avoid these types of high rise tower block fires. Mostly they focus on banning combustible cladding (ie ACM(LD-PE) rainscreen) and combustible insulation, mandating sprinkler systems and fitting cavity barriers.
There is little widely accessible information on the use of cavity barriers at the time of these cladding fires, but the Australian Insurance Council in November 2017 noted:
“The [UK,2017] BRE Global tests provide our best indication to date as to the fire behaviour of the three most common categories of ACP’s [Aluminum Composite Panels, ie ACMs] installed on Australian buildings. One very important difference however is that cavity barriers were provided in all tests, whereas the provision of cavity barriers is not required in Australia and hence typically not specified.
Thus, the expectation is that the fire performance seen in the BRE Global results in the table, would probably be considerably worse with no cavity barriers installed. This is a significant concern for the Category 2 (FR or Fire Rated) ACP’s with any sort of combustible/fire retardant insulation or sarking installed behind the ACP.”
Also the manufacturer of the combustible ACM(LD-PE) rainscreen panels that were involved in the Mermoz Tower Block fire in Roubaix in 2012, made this statement:
“A spokesperson for 3A Composites, manufacturer of Alucobond, reiterates this: ‘The fire in Roubaix is subject to a legal inquiry. The official technical experts… have confirmed that the renovation of the façade, including the cladding material, was compliant [with] the building regulations in place.’
He stresses that Alucobond as siding material is one component of external wall construction and that other factors need to be taken into consideration with regard to fire safety: insulation material; sub-constructions, in particular with respect to the depth of the cavity; fire barriers to block the fire spreading in the cavity; installation complying with tests; cladding material; and sprinklers and fire escape routes.”
Rainscreen manufacturers have been grossly negligent in their supply and advertising of combustible rainscreen ACM products, given that they are aware of the fact that there have been serious fires fueled by these products, and they are banned for use on high-rise buildings in many markets. The statement by Alucobond is both self-serving and may also be factually correct.
Part 10: Conclusion, All high-rise ACM(LD-PE) fires in England need to be scrutinized.
The number of high-rise flat fires in England since mid the 2000s that projected fire for a sustained period onto combustible external ACM(LD-PE) cladding is estimated as 49 fires. The Grenfell Tower fire of 2017 was an horrific inferno that incinerated people in their own homes, and gratefully there have been no other residential fire disasters on this scale in England (and UK in general) since the Second World War.
If the Grenfell Inquiry is correct that the combustibility of the ACM(LD-PE) rainscreen (and to a lesser extent the PIR insulation) is the almost sole determiner of the extent of the Grenfell Tower fire (as separate from the scale of causalities) then there should have been many similarly horrendous fires involving ACM(LD-PE) cladding in England before Grenfell. There have not been.
Clearly the great majority of these particular smaller flat fires were not widely reported in the media as they did not spread. Some of these limited fires can be explained because they must have started on floors near the top of tower blocks, while others impinged on unclad sections of their exterior. The Grenfell Tower fire disastrously started near the base of a block completely clad in ACM(LD-PE) cladding. (It must also be noted that aerial fire fighting platforms can allow fire fighters to reach 25-30 metres up tower block exteriors (8 to 10 storeys), thus making active fire-stopping more effective on some high-rise fires if they are available).
The rest of the fires must have failed to spread due to some combination of active (ie fire fighters) and passive (ie cavity barriers) fire-stopping measures. Given that the high-rise tower blocks with ACM(LD-PE) cladding have been identified, then there must be related fire service records and cladding repair records, that can be scrutinized to determine the nature of the spread of tower block ACM(LD-PE) fires. The Grenfell Inquiry has relied on (often media) reports of notorious fires in tower blocks with ACM(LD-PE) panels in curtain walling rather than rainscreen systems, with much wider cavities, and constructed to different building regulations and product standards, in other regions of the world.
The issue of getting information about cladding fires in tower blocks, came up during the UK Parliament Inquiry in 1999-2000 on the “Potential Risk Of Fire Spread In Buildings via External Cladding Systems”. A memorandum from the then Department of the Environment stated, “2.2 The Department has a call-off contract with the Fire Research Station [UK BRE] to investigate real fires and this highlights any areas of concern that affect Building Regulations.” A similar memorandum from the Fire Brigades Union stated “2.4 Fires involving fire spread via external cladding have occurred before however, in the short time available to create this response it has been impossible to obtain comprehensive details of dates, times and places. No doubt the Home Office—Fire and Emergency Planning Directorate (FEPD) and the Department of the Environment, Transport and the Regions—Building Regulations Division (BRD) will have the details.” No one was monitoring the potential risk of cladding fires in tower blocks, or the factors that limited these fires. Instead there was only investigative action after a serious event.
The Grenfell Inquiry needs to compile the data on all ACM(LD-PE) cladding fires of any size in tower blocks in England, to determine the actual rather than extrapolated behaviour of this type of fire. All the causes of the horrific Grenfell Tower fire need to be established. All the companies and organizations that failed the victims need to be identified.