Fire safety experts say Grenfell Tower’s exterior will be the main focus for investigators examining the rapid spread of the blaze, called “unprecedented” by London’s fire commissioner.
While no cause of the blaze has officially been determined, witnesses have described how flames lapped up and around the 24-storey tower block at alarming speed in the early hours.
One told Sky News it took just 15 minutes for the fire to climb 17 floors.
Others said recently erected cladding, which experts say is attached to the outside of a building to help with weather-proofing and improve its look, was falling to the ground in flames.
Fire Brigade Union safety expert David Sibert said that ordinarily tower block flats are designed to be like a “fire-resisting box”.
He said: “So you should be able to set fire to your own flat and leave it to completely burn out and it won’t affect anybody else in the building.
“What’s happened in this fire today is like nothing that anyone in this country has seen ever.
“It’s too early to say or speculate but it certainly appears as though the fire has spread up the outside of the building, much more quickly than it should have done, something has gone wrong.”
It is understood work refurbishing the tower, which included the new cladding shell, was completed just over a year ago – at a cost of £8.6m.
The specification of the new exterior, usually a coating or covering, is not known but residents say they were reassured by management company Kensington and Chelsea Tenant Management Organisation and fire officials that it was safe.
One local, Mohamed Bouya, who witnessed the fire take hold, told Sky News: “They’ve refurbished it with loads of plastic, loads of these plastic boards going down the sides of the thing to make the building look nice.”
Design specifications seen by the Press Association suggest the renovation work carried out at Grenfell Tower included a 50mm “ventilated cavity” next to 150mm of Celotex FR5000 insulation.
This insulation, according to Celotex, has a Class 0 rating under UK building regulations, meaning it has the highest rating for preventing the spread of flames and prevents the spread of heat.
Angus Law, of the BRE Centre for Fire Safety Engineering at the University of Edinburgh, said: “The UK’s regulatory framework for tall residential buildings is intended to prevent the spread of fire between floors and between apartments.”
Construction firm Rydon, which carried out the refurbishment of the tower, said in a statement that its work “met all required building control, fire regulation, and health and safety standards”.