The family of a man who suffered “devastating brain damage” after inhaling hydrogen sulphide is suing the manufacturer of a drain cleaner they claim contributed to the release of the toxic gas.

Adeniyi Ayannuga, 58, collapsed and was left in a permanent vegetative state after a friend poured the product 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, came 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, 51, is now bringing a claim against One Shot Products Limited at the High Court in London.

Her lawyers allege that their drain unblocker “materially contributed” to the formation of the gas and is “defective”.

But the company argues that the hydrogen sulphide likely originated from a sewer pipe and was not caused by the product.

In written submissions for the trial being heard before Mrs Justice Yip, Simeon Maskrey QC, representing the family, described their account of the incident.

He said that after an unsuccessful attempt to unblock the sink with a plunger, Mr Gbadegeshin visited and poured some One Shot Instant Drain Cleaner down the plug hole.

He left the kitchen leaving the product to take effect before returning and apparently disconnecting some sink pipework.

Mrs Ayannuga heard a noise, ran to the kitchen door and saw Mr Gbadegeshin on the floor.

She called her husband who went into the kitchen and also collapsed before she was also “overcome” by the fumes and lost consciousness.

The couple’s eldest son, who was 12 at the time, called 999 and described in a witness statement how the incident left him “frightened”.

“My first instinct was (that) everyone was dead and that now it is just me and my siblings left,” he said.

“I remember seeing the man, my dad and mum all on the floor in the kitchen not moving, I noticed a smell like rotten eggs, like a stink bomb, what children would use when the are playing pranks.

“I could smell it in the air.”

Mr Maskrey said paramedics arriving at the scene were aware of “an indescribable offensive smell” and the London Fire Brigade was alerted.

Elevated readings of hydrogen sulphide were later detected in the hallway to the flat and the block was evacuated.

A coroner later found that Mr Gbadegeshin died as a result of hydrogen sulphide intoxication, while Mrs Ayannuga was not permanently injured but has suffered post-traumatic stress disorder alongside two of her children, Mr Maskrey said.

In a witness statement, Mrs Ayannuga said: “What happened has ruined our lives. I am a ghost of myself. I was so depressed.

“I cried everyday for at least the first year.

“I still cry often.”

She said it took months for her to return to the family home, that she struggled to be alone there and found Christmas and New Year “very challenging now”.

Mr Maskrey said that mixing lime sulphur and the drain cleaner can produce hydrogen sulphide, adding that an issue in the case was whether there was a sufficient quantity of sulphur in the blockage to react with One Shot and produce a “lethal concentration” of the gas or if another explanation was more likely.

He said: “Whether rare or not and whether foreseeable or not if the One Shot did give rise to a lethal concentration of hydrogen sulphide when being used for the purpose for which it was sold, then it is not as safe as persons generally were entitled to expect and it is defective.”

The barrister added: “There was no warning that One Shot could react so as to create a lethal, or indeed toxic, gas.”

Neil Moody QC, representing One Shot Products Limited, said in written submissions that its “high strength” product comprised 91% sulphuric acid, water and bromothymol blue.

It has been produced for 32 years, with 16 million bottles sold and “no reported incident of the use of the product ever having caused hydrogen sulphide poisoning”.

He said the company accepted it was used by Mr Gbadegeshin but argued it “did not contain a defect” and “was of no causative effect”.

“It is an open question as to whether Mr Gbadegeshin poured other substances into the drain and, if so, what they were,” he said.

“There is also an absence of evidence as to what may have been poured into the sink so as to cause the blockage.”

Arguing that the claim should be dismissed, Mr Moody said that “on the balance of probabilities, the hydrogen sulphide originated from the sewer/soil pipe”.

He added that the family cannot prove the presence of the gas was caused by the product, with the incident remaining “unexplained”.

“Even if the use of the product did create hydrogen sulphide within the kitchen, there was nevertheless not a defect in the product; this was an unprecedented freak accident,” he said.

The trial at the Royal Courts of Justice is due to conclude on Friday, with judgment expected at a later date.

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