A rescue worker who is also a structural engineer, who arrived at the disaster site 30 hours after the collapse, believes the fire may have started in cars in the ground floor carpark.
Urban search and rescue support engineer Graham Frost told the royal commission hearing this morning that six cars removed from the building during the recovery stage in the immediate disaster's aftermath were all burnt out.
"I think it's possible the fire started in these vehicles," he said this morning.
He believed the cars would have provided the fire with a fuel source for "some time".
Mr Frost spent five days at the site collating evidence he knew would be crucial for investigating authorities to later establish how the building failed and caused the deaths of 115 people.
Mr Frost said that it was obvious that the six-storey office block had failed in "a very non-ductile fashion".
He felt it was his professional obligation to record the condition of the building in its collapsed state.
Mr Frost told the commission hearing he was concerned that the diggers and other machinery working on the rescue and recovery might destroy "crucial evidence" that would be vital in later trying to establish the cause of the building's catastrophic failure.
While his primary role was to minimise the risk of danger to USAR and police teams working on the rescue and recovery, he spent five days taking photographs and making careful notes.
He took several photographs capturing specific building details, connections, and recording the collapse condition from various angles which would be "of interest to anyone investigating the building collapse at a future date".
Today (Wednesday), Mr Frost talked the hearing through many of his photographs, which he said highlighted potential areas of failure.
Columns were a "very weak element ... very highly stressed", he explained, while the spandrels, connecting the floors to the walls, had "very light connections" and were unable to "transfer much load".
The concrete floor slabs did not stay intact in the collapse, while the beams had separated from the concrete columns "very early on" in the intensive shaking of the magnitude-6.3 quake.
He concluded by identifying three potential areas of failure, which could have been triggered by the quake, beam to column connections, the concrete floor slabs, and a tension failure of the metal decking at "midspan" of the floor slabs.
The Canterbury Earthquakes Royal Commission hearing into the failure of the CTV building on February 22 last year started on Monday and is due to last eight weeks.
Earlier today, a witness who saw the CTV collapse described the building as "swivelling" in the intense shaking.
Matthew Ross was driving a van through Christchurch city centre when the quake hit, and brought down block in front of his eyes.
He told the third day of the royal commission of inquiry hearing into the collapse he approached the Cashel St and Madras St intersection when the quake hit.
He drove into the middle of the road to avoid a nearby church collapsing on him, and was clinging to his van's steering wheel when he saw the CTV building.
"The shaking was long and vigorous," Mr Ross said.
"Then there was a really firm jolt and it began to collapse.
"The building was turning either way. It was swivelling.
"I though the building was going to collapse over Madras St so I was surprised it went straight down.
"I could see the top floors were intact as they collapsed into the dust."
Around 15-20 seconds after the shaking stopped, the went over to the CTV site, which he said was "completely rubble."
He saw people walking off the top of the rubble, before a police officer told everyone to move away from the site.
The hearing continues.
