Three members of the same family who died after suspected carbon monoxide poisoning at a caravan park would have been "unconscious within minutes", investigators said today.
It is also believed there was no working carbon monoxide detector in the static caravan where the bodies of John Cook, 90, his wife Audrey, 86, and their 46-year-old daughter Maureen were discovered on Saturday afternoon.
It is believed the family may have been using a heater to keep warm at Tremarle Home Park, Camborne, in Cornwall, as the region experienced freezing conditions overnight into the weekend.
Police and fire crews today continued their investigations at the mobile home.
The cause of death is still to be determined, although an early reading from experts at the site revealed a potentially lethal level of carbon monoxide present within the caravan at the time it was taken, shortly after the grim discovery.
Mark Pratten, crew manager in prevention with Cornwall Fire and Rescue Service, said: "Carbon monoxide was at an extremely high level. A significant dose such as this would have been fatal.
"The investigation is continuing, but it would appear that the people inside the home would have slipped into unconsciousness within a few minutes (of the leak).
"They would then go into a comatose state very quickly."
He said if, as expected, carbon monoxide poisoning was responsible for the deaths, the Cooks would have died "very swiftly" after falling unconscious.
Flowers continued to mark the scene of the tragedy today, with neighbours on the quiet caravan park - tucked away on the edge of the Cornish town - paying their respects.
One bouquet read: "Why did this happen to lovely people like you?"
Another added: "May you all rest in peace together."
News of the tragedy has rocked the close-knit residential park, where many elderly couples live.
Neighbour Sue Issacs, 58, said: "Everyone here is in total shock. You never think that something like this would happen on your own doorstep.
"John, Audrey and Maureen were lovely people. It's so upsetting to think that three members of the same family have been wiped out in one go."
The alarm was raised at around 1pm on Saturday after the family failed to respond to knocks on the door from the couple's helper who became worried.
As well as claiming the life of John, Audrey and Maureen, their family dog, a five-year-old Jack Russell called Jannie, also died.
Friend Julie Boon, 55, said the whole community was left shocked and devastated.
She said: "I saw Maureen and her mum on Thursday morning when they were walking their dog.
"Maureen asked about my dog and her mum commented on the cold weather and then they went. That's the last time I saw them.
"They were a lovely family who loved their dog and their home. The whole community is shocked and devastated."
The three deaths come less than a fortnight after an elderly woman died of suspected carbon monoxide poisoning at her home in nearby St Ives.
Reports say that since the latest incident a number of local shops have sold out of carbon monoxide detectors.
Asked if the Cooks' caravan contained a working device, Mr Pratten said: "My understanding is that there was not."
He added: "As they say, carbon monoxide is the silent killer. It has got no taste and no colour, so it is vital that people equip their homes with a detector."
Although Devon and Cornwall Police are continuing to investigate, a spokesman said the incident was not being treated as suspicious.
Cornwall coroners in Truro confirmed they had received reports of the three deaths, but that no dates had yet been set for the opening of the inquests.