The aluminium composite material (ACM) rain screen was the 'principle reason' why flames spread up the side of Grenfell Tower. The fuel source was the flammable polyethylene core within the panels.
This is one of the key findings in the leaked first stage report from the Grenfell inquiry, as reported first by the Daily Telegraph.
Further, in the months leading up to the fire, the tower's external walls were refurbished and an ACM crown added to the building. The work did not meet building regulations.
Martin Moore-Bick, the inquiry's chairman, added that there is “compelling evidence” that the walls did not “adequately resist the spread of fire”. The report adds that the fire's spread was accelerated by insulation boards and window surrounds, both of which included combustible materials.
Video evidence suggested the crown was 'primarily responsible' for the horizontal spread of the fire. Flames had only spread vertically before they reached the crown, the report says.
The fire started in a Whirlpool fridge-freezer, and escaped the flat by burning through a uPVC window frame into the space between the insulation and the rain screen.
Since the disaster, survivors and bereaved families have maintained that the building work did not meet UK building regulations.
The findings also reflect the position of the UK's building inspectors’ organisation, Local Authority Building Control. In 2014 the group issued a certificate allowing the use of PIR insulation panels and fibre-cement panels.
Fire service procedures are also criticised in the leaked report. It is understood that fire commanders did not realise the fire-proof compartments had failed, so no effort was made to evacuate the tower.
Grenfell Tower is in the Royal Borough of Kensington and Chelsea, a west London borough. In addition to the public inquiry, the Metropolitan Police are conducting a criminal investigation into the events of the night. The largest of its kind ever carried out in the UK, the publication date of this report is still unknown.