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Grenfell | One year on

grenfell tribute

A full year on from the horrific Grenfell Tower fire on 14 June 2017, our profession is starting to understand how deeply its decisions affected the events of that night.

On 4 June the Grenfell Tower public inquiry published five expert reports on the causes, origins and spread of the fire which killed 72 people.

Much focus was given to the cladding, which several of the experts reported had not been tested for fire resistance before it was installed during the refurbishment of the tower between 2012 and 2016.

Fire engineering consultant CS Todd managing director Colin Todd, one of the expert witnesses in the inquiry, that the cladding system should have undergone a full scale test to comply with British standard BS8414 which sets out test criteria. He said that “no BS8414 tests were carried out” on the cladding before the fatal blaze took place.

Another expert witness, University of Edinburgh School of Engineering professor of fire and structures Luke Bisby, added that materials in the cladding were to blame for the quick spread of the fire.

He said: “The primary cause of rapid and extensive external fire spread was the presence of polyethylene filled aluminium composite material (ACM) rainscreen cassettes in the building’s refurbishment cladding system.”

Arup fire engineer Barbara Lane, who is also an expert witness to the inquiry took a hasher tone in her report, claiming she had seen “no evidence yet that any member of the design team or the construction team ascertained the fire performance of the rainscreen cladding system materials, nor understood how the assembly performed in fire”.

She added: “In my view it is essential that there is renewed and proper understanding of relevant test evidence, and how it relates to performance, as already emphasised in ADB [Approved Document B] 2013. This is a critical change which is needed throughout the design and construction industry.”

Approved Document B is the government’s advice about how to comply with building regulations.

Lane also raised serious concerns about the Approved Document B guidance in her report.

According to Approved Document B, different fire safety tests – some of which do not expose a panel’s core to heat – can be used to determine whether or not a product is safe. It means products could fail some European test standards, but still meet requirements for some British standards. As Lane points out, Approved Document B does not offer guidance on which outcome should take priority.

Lane used her report to call for an urgent update of Approved Document B, suggesting that “the performance standard for an external surface, should be European performance classification A (in this context of high rise residential buildings)”.

This is because under the European testing regime, a whole panel must be tested, including its core.

Lane also suggested definitions for “filler” and “external surface” should be included when they apply to a rainscreen cladding outer layer when formed using ACP with a combustible core.

The government is currently consulting about the need for an overhaul of Approved Document B.

Later in her report Lane acknowledges there is “a body of professional opinion” which believes a suppression system such as sprinklers might have prevented the fire from spreading, and recommends more research on sprinkler systems in tall buildings be carried out.

“Regarding the specific complex fire scenario here — ie an external cladding system fire, caused by an internal fire event breaking through the construction detailing in and around a window opening — I am of the opinion there is a useful body of research work needed here to resolve this matter,” she wrote.

“I am not aware of any body of work with this focus as yet, and do recommend that it is carried out.”

Several industry experts have told New Civil Engineer that sprinkler systems should be retrofitted in tall buildings which are18m high or more.

Lane also identified plenty in the tower which failed to comply with existing building regulations.

Unsurprisingly the cladding system, insulation panels and cavity barriers at Grenfell Tower failed to meet requirements set out in Approved Document B or the Building Regulations 2010. As Lane wrote, the cladding system was ultimately the reason the fire was able to spread so rapidly around the building envelope and back into individual flats.

Residents were advised to “stay put” in their flats because the system of compartmentation – where a fire is supposed to be contained in the flat of origin – should have worked. But compartmentation failed and the fire spread around the building envelope, putting much more pressure on the active and passive fire-stopping measures in place at the tower.

The lobbies and the stairways were supposed to have been kept free of smoke through smoke ventilation systems and firestopping doors.

But even though these were not designed to cope with such a fierce blaze, they had already failed to meet standards set out in Approved Document B and Building Regulations 2010.

“It is my opinion that the conditions of the stairs and lobbies would have created intense fear amongst the residents which is likely to have affected the ability of many of them to leave their flat and descend the stair, even when they were eventually instructed to do so,” says Lane’s report.

“The ability of residents to escape from Grenfell Tower was entirely dependent upon the performance of the sole means of escape route provided to them within the building.”

But the lobbies and stairs filled with smoke, whose temperature reached 150°C on some levels. This was partly due to failure of the smoke ventilation system to work properly.

“I consider that this system under the control of the fire service could have provided some assistance to improving conditions for means of escape and firefighting within the lobbies and therefore the stair,” says Lane’s report.

But fundamental problems with tower’s design also contributed to dangerous conditions during the fire.

The stairs, at 1040mm wide, were acceptable by the standards in place when the tower was designed and built, which required a minimum width of 900mm.

However, modern building requirements say 1100mm is the minimum width. The width of the stairs had a profound impact on the firefighters and their ability to tackle the blaze; several described the cramped conditions in the stairwells, the difficulty passing other firefighters and residents while wearing breathing apparatus and the difficulty of walking two abreast up the stairs.

The inquiry continues.

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