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Cyanide gas released as insulation boards burned may have contributed to deaths at Grenfell Tower.

Experts said the thermal lining, fitted in the cladding process, is said to give off the deadly gas when alight.

Prof Richard Hull said: “It has been an accident waiting to happen.

Fire toxicity experts claim their positioning - between the new cladding facade and the existing ‘70s brickwork of the building - meant every flat could have been filled with enough gas to kill those inside.

Three of those injured in the fire are known to have been treated with an antidote for hydrogen cyanide poisoning in hospital but it is thought the number of those affected may be higher.

(Image: Reuters) (Image: AFP)

(Image: Roy Cooper / Daily Mirror)

Pinning down what role it played in the deaths of the victims, now thought to be 79 or more, may never be known because of the victims’ condition.

Speaking yesterday Richard Hull, professor of chemistry and fire science at the University of Central Lancashire, told Sky News: “The outside wall of the building had 150mm of PIR foam (fitted), and once the fire had spread to that every flat would have its own source of PIR foam, which would have produced enough hydrogen cyanide to kill all the people in that flat.”

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(Image: AFP) (Image: PA)

The insulation was made of Polyisocyanurate (PIR), rigid plastic foam sandwiched between two sheets of aluminium foil to create 15cm-thick boards.

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Although PIR itself is flammable, the aluminium foil is supposed to disperse flames and prevent it catching fire.

It was fitted behind the cladding and in front of the old brickwork as part of the refurbishment process.

Professor Hull, who co-authored a peer-reviewed study in 2011 which established that PIR was the most toxic six insulation materials added: “It’s been an accident waiting to happen and unfortunately we’ve got to the stage now where the accident has happened and we’re standing here saying ‘I told you so’.

(Image: Getty)

“It would have been much better if people had listened to us earlier on when we published the report.”

The insulation board was manufactured by Celotex, who say if fitted correctly it meets regulations for use on buildings above 18m (59ft) tall.

Celotex is yet to comment on the cyanide claims.

Celotex said in a statement on its website: “As we previously stated, our records show a Celotex product (RS5000) was purchased for use in refurbishing the building. This product has a fire rating classification of Class 0, in accordance with British Standards. Celotex RS5000 is the insulation component specifically tested as part of a system to British Standard BS8414-2:2005. When the system is designed and installed in line with this, RS5000 meets the criteria set out in BRE Report BR 135 ‘Fire performance of external thermal insulation for walls of multi storey buildings.

“We will of course assist the relevant authorities fully with any enquiries they have.”