Carbon monoxide leakage cannot be detected by the senses
A couple died of carbon monoxide poisoning while they were watching television at home, an inquest in Bridgend has heard.
Douglas Macdonald, 65, and his wife Wendy, 48, were found by her daughter Kelly Ann Bowen in Caerau, Maesteg.
They had recently had building work on their home to remove the chimney, which eventually led to a build-up of the gas which killed the couple in July 2007.
Bridgend coroner Philip Walters recorded verdicts of accidental death.
Ms Bowen told the inquest she found her mother and stepfather after calling on them after dropping her children off at school.
She initially failed to get an answer when she called on their home and left, assuming they had slept in. But she later returned after their home helper called her to say she could not get an answer.
"I went back down and opened the door and saw Mam on the three-piece (suite) and my stepfather on the other three-piece (suite)," she explained.
"An ambulance was called for and they were certified dead at the house."
The inquest was told how high levels of carbon monoxide had been found in the bodies of both Mr and Mrs MacDonald.
The couple had recently had the back wall of their home rendered removing the chimney with the resultant hole filled in and tiled over, the inquest was told.
A British Gas investigation by regional technical manager Robert Hanford found a "down-drafting" zone had emerged in place of the missing chimney, preventing gases from the couple's back boiler dissipating when the wind was blowing in a certain direction.
He also discovered the boiler was producing "huge amounts" of carbon monoxide due to a lack of servicing.
Det Sgt Andrew Williamson of South Wales Police said they had investigated the builders who carried out the work, but decided not to prosecute them for gross negligence because the charge would be difficult to prove on account of the back boiler's history of poor maintenance.
The inquest also heard how an investigation by the Health and Safety Executive was continuing.
The coroner said: "Clearly, from the investigation that has been conducted by the authorities there were two problems involved.
"The first in that the boiler hadn't been serviced for some time and the work carried out was unsatisfactory in the sense that, as Mr Hanford explained, if the wind was in a particular direction there was a blow-back of gases that should have been taken out to the air.
"It wasn't necessarily going to happen straight away unless the wind was in a particular direction. At some time this was inevitably going to happen."