A father and his two young children died from carbon monoxide poisoning after an empty crisp packet blocked the inside of their chimney.
Trevor Wallwork, 50, and his two children Kimberley, 12, and Harry, nine, were watching television when the discarded crisp packet, which had been thrown on to an open coal fire, blew up 'like a hot air balloon' inside the flue.
The blockage prevented coal fumes from escaping and sent the invisible gases back into the room, overcoming the family with carbon monoxide poisoning.
Chief Fire Officer Mr Paul Coyle told an inquest that investigators found the empty crisp packet high up the chimney and used tongs to pull it out.
He said: "The flue had looked reasonably clean but I could not see the light shining up because of an obstruction. There appeared to be a large black rounded ball 1.2 metres from the top of the chimney."
It seems the flue became blocked by the plastic wrapping, the packaging expanded locking in air like a hot air balloon.
"The heated air in the bag passed up the chimney and expanded as it it did so. The bag was full of hot gases and they were not hot enough to melt the plastic."
He said as gases were no longer able to escape, they in turn produced combustion gases which were toxic and filled the living room.
The source of carbon monoxide was the fuel burning in the open fire. The level of carbon monoxide was said to have risen quickly and became 'very dangerous' as the family sat there unaware.
Coroner Alan Walsh described the tragedy as a 'sad and extreme' chain of events during the inquest at Bolton, in Greater Manchester.
He said: "I have found it to be one of the most tragic cases I have heard in the court after sitting here for over 12 years.
"For a father and two children to die followed by the death of his wife. I can't emphasise how sorry I feel."
Recording verdicts of accidental death he said: "The crisp wrapper may well have been put into the fire as it would have been the norm many many years ago.
"It got into the chimney and blocked it as it expanded. That would not have been foreseen by the family who had gone to watch TV.
"I find it sad and extreme. His wife was in hospital suffering from a terminal illness. He had being visiting her regularly, he was her carer. He was a a good father, a good man, a caring man who looked after his family and wanted to care for them.
"This was an extraordinary series of events, unimaginable and dramatic series of events, sudden and unexpected which occurred without any intention."
Mr Wallwork's step-daughter Vicky Barnes, 22, discovered the bodies at the home in Swinton, near Salford, the next day after he failed to drop the children off at a planned visit to his terminally-ill wife Susan in hospital.
Mrs Wallwork, who had been married to her husband for six years, lost her battle with breast cancer about six months later.