An amber alarm for hydrogen cyanide sounded on firefighters’ gas readers as they inspected Zane Gbangbola’s home the day he died.

Zane, seven, a pupil at St George’s Junior School in Weybridge, died after his family home in Thameside, Chertsey, was flooded on February 8, 2014.

He had been sleeping in the spare bedroom after watching television with his mother Nicole Lawler.

Surrey Comet:

Zane's parents Nicole and Kye met with Green party leader Natalie Bennett in the months leading up to their son's inquest

His family claims he was killed by hydrogen cyanide gas that leaked from a former landfill site behind their home, but this is disputed by Spelthorne Council and the Environment Agency.

Low levels of carbon monoxide were found in Zane's blood during a post-mortem examination, which concluded that this was the cause of his death.

The family had bought a number of electric pumps to remove floodwater from their home and later rented a petrol-powered one as back-up.

Stephen Schooling, a group commander at Surrey Fire and Rescue Service in the hazardous materials team, was called to the Gbangbola home at 4.55am on February 8, where he and colleague Karen Pointer entered the home to take gas readings.

Surrey Comet: Zane, seven, a pupil at St George's Junior School in Weybridge, had just passed his 7+ exams according to his mother

Mr Schooling told Woking Coroner’s Court on Friday that, after taking a background reading outside the home, the first reading inside was taken heading upstairs to the bedrooms where Zane was found.

He said: “At the top of the stairs, we had a reading of 2,000 parts per billion, but by the time we were in bedroom four [the spare bedroom] the reading rose to 2,500 parts per billion.”

Mr Schooling said the first gas reader they used, which does not detect which gas is present but measures the level of ‘organic compounds’ in the air, showed “a noticeable rise in there from the front bedroom and Zane’s room”.

The figure dropped to 1,700 parts per billion after deducting the background reading.

The crew went to a neighbouring house where the occupants had not been taken ill, and a reading of 1,300 parts per billion was taken.

Mrs Pointer then contacted Bureau Veritas, a testing and inspection company, to get confirmation of the gas reading’s significance from expert Bruce Juliffe.

Mr Schooling said: “Mr Juliffe’s advice to me over the phone was that this was a significant rise.”

The team then took a further reading in the home with another gas reader calibrated to detect hydrogen cyanide, carbon monoxide and hydrogen sulphide.

It gave a decreased gas reading in the upstairs bedroom of 1,000 parts per billion.

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Zane was described by his mother as a "gift"

Mr Schooling said: “We went round the whole property. As we were leaving we had an amber alarm for a low level of hydrogen cyanide.”

He explained that the alarm would sound at 10 parts per million of hydrogen cyanide.

Mr Schooling said that no one should be exposed to 10 parts per million of hydrogen cyanide “for any more than 15 minutes” in a working day.

The third sweep of the house was run with dräger tubes, which have crystals inside that react to dangerous gases, in the area where the alarm had been triggered.

The crew decided to close the front door of the house at this point, where previously the house had been “well ventilated”, according to Mrs Pointer.

The colour change of the crystals in the tube was “below the lowest threshold” for a reading to be conclusive.

Una Morris, representing the Gbangbolas, asked if at any point Mr Schooling or the team could smell petrol fumes in the house, to which he replied he had not.

But Mark Harris, representing the Environment Agency, said Mr Juliffe’s evidence suggested the readings from the alarmed meter were “more likely to be created from cross-contamination from nitrogen dioxide or hydrogen dioxide.”

Mr Schooling and Mrs Pointer both confirmed the petrol pump in the downstairs bathroom was off when they took their readings.

Jerry Toogood, the former manager of Surrey Hire and Sales who rented the petrol-pump in question to the Gbangbolas, denied telling them it could be used indoors with the windows open during the six-week inquest.