The family of a man who suffered “devastating brain damage” after inhaling hydrogen sulphide have lost their High Court fight against a drain cleaner manufacturer.

Adeniyi Ayannuga collapsed and was left in a permanent state after a friend poured some One Shot Instant Drain Cleaner containing sulphuric acid down the blocked kitchen sink at his flat in Peckham, south London.

Tito Gbadegeshin, who had previously worked with Mr Ayannuga at Southwest Trains, went to help the father-of-three clear the blockage but died after also inhaling the gas in the incident on New Year’s Day 2015.

Mr Ayannuga’s wife, Oluyomi, brought a claim against One Shot Products Limited alleging that its drain unblocker “materially contributed” to the formation of the gas and was “defective”.

The company argued that the hydrogen sulphide likely originated from a sewage pipe and was not caused by the product.

In a judgment on Thursday, Mrs Justice Yip dismissed the family’s claim, finding the events were a “tragic and unforeseeable accident”.

The High Court previously heard that, after an unsuccessful attempt to unblock the sink with a plunger, Mr Gbadegeshin visited and poured some of the drain cleaner down the plughole.

He went out of the kitchen, leaving the product to take effect, before returning and disconnecting some sink pipework.

Later finding Mr Gbadegeshin on the floor, Mrs Ayannuga called her husband, who went into the kitchen and also collapsed before she was also “overcome” by the fumes and lost consciousness.

In her ruling, Mrs Justice Yip said the claimant’s case about how the One Shot cleaner caused the toxic gas would require the presence of lime sulphur, found in some specialist plant and pet products.

The judge rejected that lime sulphur had previously been poured into the drain for use as a drain unblocker.

“It is not obvious why anyone would think a bottle of pet shampoo, a product for whitening the dead wood of a bonsai tree, or a plant pesticide might help with unblocking a sink,” she said.

Mrs Justice Yip continued: “The claimant’s case that lime sulphide had been poured down the sink after it became blocked is implausible.

“On the other hand, the defendant’s theory that sewer gas escaped from the waste system when Mr Gbadegeshin removed the pipe is scientifically sound and is consistent with what is thought to have occurred in other tragic and rare instances.”

She later added: “The use of One Shot was therefore coincidental and did not make a material contribution to the death of Mr Gbadegeshin or the injuries sustained by any of the claimants.”

The judge also found that the One Shot product – which now requires a licence to purchase following concerns about the unlawful use of concentrated sulphuric acid – is not defective or unsafe.

Mrs Justice Yip concluded: “The Ayannuga family have my utmost sympathy.

“I extend that sympathy also to those who mourn the loss of Mr Gbadegeshin.

“I know the trial was not easy for Mrs Ayannuga and the outcome will be bitterly disappointing.

“The claimants may be able to take some small comfort from the fact that their case was expertly presented and argued, allowing for the full exploration of the cause of the terrible events on 1 January 2015.”