At 1.16am on Wednesday 14 June, the police and fire brigade were called to a residential 24 storey tower block in north west London after reports of a fire breaking out.
The fire turned out to be one of the most deadly in recent history. Already 80 people have been confirmed to have lost their lives but the complexity of the recovery operation means that the final number may not be known until next year.
There is much assumed knowledge about the tower, and what has been done to it that may have exacerbated the fire spread.
What is known is that Grenfell Tower was built in 1974 with an insitu reinforced concrete frame. It is owned by the Royal Borough of Kensington & Chelsea (RBKC), and managed by its arms-length Kensington & Chelsea Tenant Management Organisation.
It is also documented that it recently underwent a £10.3M refurbishment to install a new insulated exterior cladding, new double glazed windows and a new communal heating system. Nine new flats were also created from unused space within the building.
Rydon Property Services was selected as preferred contractor for the work in March 2014 and was awarded an £8.6M construction contract on 2 June 2014. Work was completed in July 2016.
It is also documented that earlier estimates from the originally proposed contractor Leadbitter came in at £11.3M, which was £1.6M above the proposed budget. “Value engineering” was then sought to “maximise the delivery of key project outputs within the proposed budget,” according to a paper presented to RBKC’s housing and property scrutiny committee on 16 July 2013.
Grenfell PA 41
What is not clear from the council’s publicly available planning documents is what was actually constructed.
“What the planners are looking for, and are concerned with, is primarily how the building is going to fit into the urban public realm,” says chartered fire engineer and Council on Tall Buildings and Urban Habitat fellow Simon Lay.
“Anyone who works on large projects knows that what gets put on the planning drawings isn’t necessarily what gets built.”
Anyone who works on large projects knows that what gets put on the planning drawings isn’t necessarily what gets built
So what we do know? The cause of the fire has been identified as having started on the fourth floor as a result of a suspected faulty fridge freezer. This alone should not have resulted in a fire of this magnitude.
Leeds University director of MSc fire and explosion engineering, Herodotos Phylaktou, explains that the most fundamental defence against fire in residential buildings of this kind is fire compartmentation. This means enclosing each of the flats and escape routes with fire resisting walls, doors, etcetera to contain any fire and allow enough time for the emergency services to extinguish it.
But in the case of Grenfell Tower, the fire took hold within minutes and spread ferociously internally and externally across the building, leaving firefighters powerless to stop it.
Many people are thought to have died because they remained in their flats, in line with the building’s fire procedures.
This exceeded the fire strategy for the building
“What we’ve seen is a very fast and unexpected fire spread,” says Phylaktou. “This exceeded the fire strategy for the building – to ‘stay put’ – and the fire will be contained within the compartment of the building.”
So what went wrong?
Lay says the overcladding cannot simply be looked at in isolation, explaining that the thin line making up an external façade on many drawings is actually a complex build-up with many different parts to it. This includes an insulation layer fixed directly to the original concrete cladding in addition to the overcladding system itself.
The overcladding system is a product called Reynobond PE, manufactured by Arconic. It is a type known as aluminium composite material (ACM), a 2mm to 6mm thick sandwich of two coil-coated aluminium sheets with a core of polyethylene plastic which gives the panel rigidity. The insulation was a 50mm to 150mm thick foam-based rigid insulation board Celotex RS5000.
According to Approved Document B of the Building Regulations 2010, materials for buildings over 18m in height should be of “limited combustibility”, but it is clear that they did combust.
The Metropolitan Police has confirmed it is looking into the impact the overcladding system may have had.
“Preliminary tests show the insulation samples collected from Grenfell Tower combusted soon after the test started,” it said.
Arconic said: “Our product is one component in the overall cladding system; we don’t control the overall system or its compliance.”
A statement put out by Celotex after the blaze said: “Safety testing was undertaken on RS5000 as part of a particular rainscreen cladding system and this is described in documents available on our website. As noted in those documents, any changes to components of the cladding system or construction methods used need to be considered by the relevant building designer.”
According to the Celotex datasheet, it passes fire test BR135 (see p16) when sandwiched between fibreboard and plasterboard. It is not thought that this was the arrangement used on Grenfell.
The build-up of the façade may also have contributed to the fire’s spread. Within a façade, fire stops are typically installed on the edge of the floor slab at each level to prevent fire from progressing up the exterior of the building. These horizontal strips expand when heated to fill the air gap behind the external face of the cladding, creating a barrier.
Without fire stops, the gap can act as a chimney, drawing the fire upwards. Alternatively, if fire stops are installed incorrectly, for example, on the face of the insulation, rather than directly onto the floor slab and punching through the insulation, the compartmentation is compromised by allowing fire to spread through the insulation. When the inquiry examines the exact details of the build-up, it is expected that these questions will be addressed.
Experts also tell New Civil Engineer that flames could have spread through windows opened for ventilation earlier in the evening before the fire broke out.
In line with Building Regulations, penetrations such as building services through the concrete frame should be sealed to avoid the internal spread of fire from floor to floor or from compartment to compartment.
RBKC has stated that after the refurbishment works were completed, a fire assessment was carried out.
However, New Civil Engineer spoke to one expert who says the presence or otherwise of firestops can often be missed during these inspections, leading to breaches in the fire protection.
These factors alone should not have affected the ability of people to evacuate the building.
Reports from people who were in the building during the fire say the corridors filled with smoke making evacuation almost impossible. Compartmentation should have stopped this from happening. RBKC said fire doors – essential to keeping the compartmentalisation intact – were installed at all of the required locations, were all in working order and were checked on a weekly basis.
Gas pipes were also installed in corridors as part of the refurbishment. It is not known if gas within the pipes ignited, further fuelling the fire.
Documents linked to the refurbishment have now been seized by the police to be used in the investigation. Samples of the surviving façade will also be analysed for the exact build up and materials used.
“We are continuing to seize material on a daily basis and the number of companies and organisations that we know so far to have played a role in the refurbishment alone is over 60,” the Metropolitan Police said.
The final conclusions from what will be a very complex investigation may be a number of years away.
Grenfell | Refurbishment in spotlight as tower fire is probed