Carl Mills trial: Fatal Cwmbran fire spread in a 'split second'
A fire where three generations of a family died spread in a "split second" through the house after being started in the porch, a jury has heard.
Kayleigh Buckley, 17, her six-month-old daughter Kimberley and mother Kim, 46, died at their home in Cwmbran, Torfaen in September during the fire.
Carl Mills, 28, denies their murders.
A fire investigator told Newport Crown Court a recycling box was deliberately set on fire causing a devastating "flashover" into the house's hallway.
All three members of the family died in the house fire just hours after baby Kimberley, who was blind and deaf, had been discharged from hospital after being born prematurely.
The jury heard how an emergency 999 call was made at 03:27 on 18 September 2012 and fire crews arrived six minutes later to the property in the Coed Eva estate.
The court heard CCTV pictures of the house showed the fire from 03:22.
During Tuesday's hearing, fire investigator Andrew Peterson from South Wales Fire Service told the jury "a flashover" happened when everything in the hallway caught fire at the same time "in a split second".
Mr Petersen, who said the investigation into cause of the single-seat fire had taken five days, told the jury how the flashover had been fuelled by baby clothes, nappies and an overnight bag which were in the downstairs hallway.
He said: "A flashover is [caused] when all the contents start decomposing due to the heat before they get to their ignition temperature, so everything catches fire in a split second."
He told the jury how after spreading into the hallway, the fire rapidly spread upstairs because of a "chimney effect" and went into the attic of the house.
Mr Petersen said: "The fire has spread from the porch into the study and entrance. It's found another fuel source to intensify, and in this case the fire went up the stairs because that's a chimney effect."
The jury was shown pictures of the three bedrooms in the house including one with a cot in.
Mr Petersen said the fire was "attacking that room from two places" because it was coming up the stairs and also down through the loft.
Another photograph showed plasterboard falling from the ceiling.
Mr Petersen, under cross-examination by Patrick Harrington QC, did not disagree that there was a "massive fire" in the attic.
Mr Harrington said the upstairs windows in the 40-year-old house were "very small" and queried whether they would pass present planning regulations.
Mr Peterson agreed with Mr Harrington that the porch was open and the ceiling was made of plywood which were all "fuel substances".
Emma Wilson, a forensic scientist, told the court she believed the fire was started in the porch around 70cm (2.5ft) from the front door to the right-hand side and reached a temperature of 600-700C.
She told the jury once the fire had breached the front door, it took "seconds" to spread upstairs and for flames to pour out of the front bedroom window.
Ms Wilson said there "no evidence" to suggest an accelerant had been used to start the fire.
She said: "My opinion is this fire was started by a naked flame."
The court was told the orange and white tent which Mr Mills had been sleeping in in the front garden of the house had soot stains and a linear burn inside the tent.
Ms Wilson said the burn was not caused by the house fire but ignited separately.
The court had previously heard that Mr Mills, who is Kimberley's father, had become jealous of the attention Kayleigh gave to their daughter after she was born very prematurely along with a twin sister Angel, who was stillborn.
The prosecution say Mr Mills started the fire the night Kimberley was first allowed home from hospital aged six months after he had been drinking and wrongly suspected Kayleigh had another man in the house with her.
The jury heard he had sent texts threatening to kill the family and to set fire to the house.
The case continues.