A woman and her elderly parents have died of suspected carbon monoxide poisoning at a caravan park in Cornwall.
The alarm was raised at the park near Camborne just before 1pm on Saturday after the couple's helper was unable to reach them, Devon and Cornwall Police said.
Firefighters were called to break into the static caravan at Tremarle Home Park, North Roskear, and found the bodies of three people, and a dog, inside.
The woman was in her mid-40s. The age of her parents is not yet known.
Inspector David Eldridge of Devon and Cornwall Police said: "Shortly before 1pm this afternoon, we were called to a caravan park near Camborne in Cornwall, where a helper had been unable to get a reply from an elderly couple who lived in the caravan. We were able to see that there was a figure sat in a chair but they were unresponsive to knocks at the door. Cornwall Fire and Rescue were called. They forced entry into the property and found that the three occupants were all dead."
An investigation into what caused the deaths is under way, but the incident is not being treated as suspicious.
A Cornwall Fire and Rescue Service spokesman said a crew from Camborne Community Fire Station attended the scene with a hazardous materials advisor after being called at 12.56pm. The Health and Safety Executive said it would not be investigating as the incident took place at a domestic address.
Stephanie Trotter, president and director of the independent charity CO-Gas Safety, said Carbon Monoxide was an incredibly lethal gas. "Less than 2% of CO can kill in between one and three minutes. It cannot be sensed using human senses of smell, touch, sight or hearing," she added.
"The Department of Health estimates that about 40-50 people die of CO and about 4,000 attend A & E every year in England & Wales alone. But the numbers could be much higher because there is no automatic test of CO on dead bodies, even in cases of unexplained death."
She added the charity was lobbying MPs to bring about changes to the Energy Bill currently going through Parliament - for more public awareness campaigns and for the gas emergency service to carry and use equipment to test gas appliances for CO.