Grenfell Tower’s “stay put” fire advice was “unreasonable” once cladding had been installed during the building’s refurbishment completed in 2016, an expert has said.
Professor Luke Bisby said the dangers of the flammable polyethylene (PE) used in the panels have been known for decades.
He concluded the primary cause for the “rapid and extensive” spread of the blaze up and around the block of flats was the presence of the material in the building’s cladding system.
In a report prepared for the public inquiry into last year’s June 14 disaster, which killed 72 people, he said a “stay put” fire evacuation strategy relies on compartmentation being maintained.
The inquiry has heard compartmentation could have been breached when a small kitchen fire on the 24-storey building’s fourth floor spread to the outside of the building as little as 11 minutes after it broke out in Flat 16 at around 12.54am.
“On the basis that fire compartmentation was not a credible component of any fire safety strategy, once the refurbishment cladding had been installed at Grenfell Tower, it follows logically that a stay put policy was also not a credible component of any fire safety strategy once the refurbishment cladding had been installed,” Prof Bisby wrote in his report.
The Professor of Fire and Structures at the University of Edinburgh told the inquiry in central London on Wednesday: “If a fire is ignited in a cladding system such as this – made from these materials – under any circumstances we have to expect it to spread quickly and catastrophically because of the nature of these materials.
“On that basis, it is unreasonable to expect compartmentation to be maintained, and, on that basis it is unreasonable to have a stay put policy in place.
“Now that, of course, relies on someone recognising they have got these materials on their building, which, of course, is clearly not the case apparently here.”
The inquiry has heard the London Fire Brigade (LFB) did not implement a change in its stay put advice until 2.47am.
Prof Bisby concluded in his report: “In my opinion, the primary cause of rapid and extensive vertical and horizontal external fire spread was the presence of polyethylene filled ACM rainscreen cassettes in the building’s refurbishment cladding system and in the architectural crown detail.”
He said the PE, on exposure to heat, will “melt and drip – possibly flowing whilst burning or generating flaming droplets”, pointing out its reaction to fire is available in decades-old literature, including publications from 1975 and 1976.
“The general principle that a thermoplastic will melt and drip and burn quite vigorously is very clearly highlighted in any of the reference texts that one would expect a competent fire safety professional to have at least skimmed if not know quite well,” he said.
Counsel to the inquiry Richard Millett QC suggested there has been a body of opinion since 1988 “of the dangers of thermoplastic materials from a safety perspective”.
“Absolutely,” the witness replied.
The inquiry heard the Reynobond 55PE aluminium composite material (ACM) panels, also referred to as cassettes, which formed the outer shell of Grenfell’s cladding system following the refurbishment, left PE exposed by way of a cavity.
Mr Millet asked: “Does that mean any flame emanating from the window set could get up through that crack and melt or burn the exposed PE?”
The witness said: “Absolutely.”
Prof Bisby said he believes the fire spread to the cladding through a hole in the window or out though the materials in the side or around the surrounds of the windows.
He agreed it was “likely” that if there was a fire anywhere near the window it would break out of the window and into the cladding.
“At the end of the day there is a number of ways by which cladding of this nature could be ignited on the outside of the building and to focus too heavily on the specifics of what’s happened in these particular fire scenario, I think in a way diminishes the importance of recognising the clear risks that it presents under any scenario,” he said.
Video footage played at the hearing shows the blaze taking hold before spreading up the east side of the tower as debris rains down.
The London Fire Brigade said a jet of water was directed above the fire at 1.11am but it had “no effect”.
However, Prof Bisby said he had not seen any evidence of this, with the first video footage showing firefighters spraying a covering jet below the window of Flat 16.
He said he could not say whether a jet fired above the fire, if it had not been, would have extinguished the blaze.
But Prof Bisby added: “In the absence of any information it’s certainly worth a try.”