Grenfell Tower report: How the fire began on the fourth floor and spread throughout the block

One of the most extraordinary aspects of the BRE report into the Grenfell Tower disaster is that it hammers home how a fire in a single fridge-freezer can go on to consume a 24-storey building if adequate fire safety mechanisms have not been put in place to stop it.

This is an abridged version of BRE’s suggested narrative of how the inferno started and the route it took as it spread:

1 The fire began on the fourth floor

It started in Flat 16 in a fridge-freezer situated within one metre of the kitchen window. This window was in the tilt-open position. Construction of the window breached building regulations and failed to provide “any substantial barrier” to the fire taking hold in the facade outside.

2 The facade ignited

Once the flames breached the window, BRE suggests several options as to what happened next: that the flames ignited the “highly combustible” polyethylene core of the aluminium cladding; that they ignited the “combustible” foam insulation; or that they took hold of the “flammable” materials around the window frame. Or several of these things could have happened at once.

3 Flames fanned up, across and down the facade

BRE believes the fire spread up the column adjacent to the kitchen of Flat 16, assisted by “combustible components in the construction and lack of appropriate subdivision of this fuel to prevent one component involving the next”. Flames also spread laterally, aided by the same shortcomings. The impact of flames entering the cavity between the concrete and the facade was exacerbated by the lack of adequate cavity barriers. These failed to seal the gap and created what appears to be a calamitous chimney-like effect. Downward fire spread also occurred, “as a result of burning droplets of polyethylene falling and igniting combustible materials below”.

4 Fire entered the other flats

As flames fanned out across the facade they encountered windows of other flats. BRE believes the same deficient construction around the window that let the fire escape from Flat 16 now afforded it a route to spread back into the other apartments.

5 Fire burned within the flats

Once the blaze was in any one apartment, it would burn from room to room at a speed that depended on whether or not doors inside were closed. Any single flat, once caught up, “would be substantively destroyed, as a flat is normally designed to be a single fire compartment”.

6 Fire and smoke entered the lobbies and stairwell

As residents fled, the lack of door closers meant some front doors did not automatically close, allowing flames and smoke to billow out of flats into the central core, including the lobby and stairwell, impinging on the means of escape for residents further up the tower.

BRE do not provide a specific timeframe for this suggested sequencing.

Waste chute rooms could have been safe havens 

Devastation: A photograph of one of the ravaged lobbies, which shows (arrowed) how the exterior fire-resisting doors preserved all of the waste chute rooms

The report says: “It is worthy of note that every one of the waste chute rooms has survived intact, having been protected by the fire-resisting door”.

These rooms were accessed from the lobby on each floor and situated near the stairwell.

It raises the poignant possibility that if trapped residents had sought shelter in the waste chute room on their floor, they might have been saved.

The report shows photographs from the 13th floor which contrast the fire-damaged lobby and exterior of the waste chute room door with the barely blemished interior of the waste chute room itself.

Survived intact: The interior of one of the waste chute rooms at the tower

It says: “Bin chute rooms have been largely undamaged.

“Whilst the fire has been kept out of these rooms, it is unclear whether the atmosphere within these rooms would have sustained life [during the fire].”

Sprinkler system might not have made a difference

The fact that the tower had no sprinkler system means that, like many buildings erected in the Seventies, it did not conform to current building regulations which require that blocks of flats over 30 metres tall have sprinklers inside each flat. But what was the impact?

BRE says once the fire had taken hold across the facade and ignited more than four flats, a sprinkler system was “very unlikely” to have made “any appreciable difference”.

Sprinklers could only have altered the outcome if they had “prevented the fire from leaving Flat 16 and igniting the cladding”.

Yet if a sprinkler had been installed in the middle of the kitchen ceiling, they said, “it is possible the chassis of the fridge freezer might have shielded the fire from the sprinkler”. This will be tested by reconstructing the fire in Flat 16 off-site and testing a sprinkler system.

How close was the Tower to collapse? 

BRE says that the fire burned “at a level of severity which would significantly impact upon the fire resistance of the structure for between nine and 12 hours”.

The original tower block, built with reinforced concrete in 1972, had floor slabs 10 inches thick and walls 12 inches thick, which tapered to eight inches from above the 13th floor.

Standard fire resistance tests show that eight-inch walls provide only six hours of fire resistance.

However, the thicker lower walls and floors exceeded the girth for which tests have been conducted. This appears  to have saved the building  from collapse. BRE conducted independent tests to assess “spalling” (break-up and buckling) of the concrete and exposure of the building’s reinforced steelwork to determine how close to collapse it was.

It concluded: “The physical evidence confirms parts of the structure very close to their point of failure.” Had the building been built to the lower requirements of current building regulations, “it is likely the tower would have collapsed”.

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