An explosion which destroyed two houses was "most likely" caused by a heater's gas cylinder in one of the properties, an investigation has revealed.
Ten people were injured in Cloes Lane, Clacton, Essex, on 5 February 2014.
A report by the Health and Safety Executive (HSE) said a definite leak location had not been found but the cylinder was the "most likely" source.
A woman was caught up in the blast when she let her dogs out of the house's back door, the report said.
Her movements and air disturbance from the door may have ignited the mix of air and gas, it added.
"By opening the door this mixture was diluted to a concentration within the flammable range."
A man in his 70s and a woman in her 50s were badly burnt in the fire that followed the initial blast, and spent a number of weeks in hospital.
The investigation, which was carried out by an HSE inspector alongside officers from Essex Police, the county's fire service, engineers and scientists, found the butane (LPG) cylinder was being stored on a first floor landing in one of the houses.
The property did not have central heating, and its occupants used an "LPG fired cabinet heater" upstairs and an electric fire downstairs.
The report found a total of six butane cylinders around the house, as well as the one being used in the cabinet heater.
Gas incident investigation officer Steve Critchlow said: "The most likely explanation for the uncontrolled release of gas was due to a sticking pin in the butane cylinder gas valve after the regulator had been turned off."
But the report said there were "various failures of pipework" around the house, including in a kitchen cupboard, behind the kitchen gas cooker and in two other spots.
A Health and Safety Executive (HSE) spokeswoman said there was no evidence of any criminal behaviour.
"As a consequence, HSE is not proposing further action as a result of this investigation," she said.
"This was an unfortunate event to innocent members of the public which had profound and serious consequences," the spokeswoman added.