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By Danielle Aumord.

Expert witnesses analyse Grenfell Tower’s smoke control system

Grenfell Tower had a new smoke control system fitted in 2016 – designed by company PSB UK – due to the old one being broken “beyond repair”. But this system wasn’t standard because the columns in the tower were too thin. Designer Hugh Mahoney told the public inquiry into the fatal disaster that because of this, he was forced to use a “bespoke design” to make the new system fit.

But the new system designed by Mr Mahoney didn’t meet basic standards and was untested elsewhere. Mr Mahoney accepted this but continued to defend it by stating that refurbishment work to an existing building only requires “betterment” – ie, the new system is only required to be better than what was there before, not necessarily compliant with modern standards.

Simon Lay, a chartered engineer who has long experience of preparing fire strategies for high-rise residential buildings, was called to the inquiry to discuss this. He was questioned on the findings of a report he wrote for the British firm PSB.

The public inquiry heard this new smoke system was only ever expected to deal with a fire on one floor, not multiple fires burning simultaneously throughout the building.

But Mr Lay said that the system “operated as intended” when the fire broke out in flat 16 on the fourth floor of the tower and that it was likely it “operated beyond its expected parameters despite the failure of other provisions that it relied upon”.

The system, which focused on keeping smoke out of the stairway rather than clearing it from the lobbies, “was the most appropriate design response” to the constraints of the tower, he added.

“I have not been able to identify any appropriate smoke control system design capable of installation within the constraints of the tower which could have explicitly addressed both the lobbies and the stair maintaining tenable conditions in both at the same time,” he also told the inquiry.

However, Mr Lay did criticise industry practice when he said designers didn’t generally run computer modelling simulations of their systems to test the smoke flow, adding that this has become the “norm” in the industry and that there’s a “prevalence of poor practice in that area”. 

Dr Barbara Lane also gave evidence as an expert witness. She was far more critical of the smoke control system and said that she didn’t accept the idea that the regulations accepted ‘betterment’ alone as an acceptable performance standard.

“That is a slightly prevailing culture in industry: that if it’s generally slightly better, you know, the job is done. And I, long before this inquiry, have never shared that [view]. I don’t believe that’s how that regulation was written,” she said.

Dr Lane also criticised PSB’s design for only modelling its performance on circumstances where the only open door was the one that led to the stairs. On the night of the Grenfell fire, there was at least one flat door entrance open at some stage on every floor, so this was a set of circumstances that wasn’t realistic in terms of designing a smoke control system for a building like Grenfell Tower.

Kate Grange, QC, counsel to the inquiry, asked: “Is it your view that designing a system with just one single stair door being open, with all other doors being closed, was an unrealistic design assumption?”

“Once you’ve worked out how to produce an airflow through the open stair door, anything that weakens that or causes that to reduce, means that you can’t meet your offered design target,” Dr Lane responded.

Dr Lane concluded that the “fundamental issue is not the system type PSB chose, it’s the quality of the… system they designed”.

She wrote in her report on the smoke control system at Grenfell: “PSB failed to provide a smoke ventilation system which complied with the functional requirements of the building regulations.”

The inquiry also heard from expert witnesses on the ‘stay put’ policy and on the London Fire Brigade’s firefighting equipment tests.

Expert witness Professor José Torero said that it’s “essential” that the ‘stay put’ policy for high-rise buildings is “abandoned” because the risk of fires spreading externally cannot be properly assessed under current methods.

Dr Ivan Stoianov, a civil engineer and an expert in water supply networks, also said that the London Fire Brigade didn’t follow “even basic standards” in firefighting equipment tests. He concluded that water supply could’ve reached the top of Grenfell Tower on the night of fire and disputed the LFB’s conclusions that this wasn’t possible.