Exploding fiery cars have been pinpointed as the likely cause of the fire that engulfed the CTV building following its collapse, the Royal Commission of Inquiry has heard today.
USAR structural engineer David Frost has given evidence on day three of the inquiry into the collapse of the CTV building where 115 people lost their lives in the February 22 earthquake.
Frost said the six cars crushed underneath the CTV building may have provided the fuel source for the fire that broke out after the earthquake, which later consumed the building and killed some occupants who had survived the intial collapse.
"All vehicles were burnt out, I think it was possible the fire may have started in these vehicles and proved a fuel source for quite some time."
It has previously been suggested a gas cylinder inside the building may have started the fire.
The CTV building was still smouldering as rescuers hunted for survivors, but engineers who rushed to help in the days after the collapse also had another focus.
Forensic engineer Rob Heywood said: "I became concerned potential evidence was being lost and this loss may hinder further investigation into the building collapse."
In a balancing act between the search effort and the search for clues engineers asked police to cordon off an area of debris to protect it against people who were trying to bury it in rubbish. Samples were tagged and kept for further study.
And those samples revealed concerns about the building structure, including a lack of steel reinforcing in columns and weak connections to floor slabs.
Frost said he was surprised by the number of structural failings when he arrived at the site on the corner of Cashel and Madras streets 30 hours after the quake.
He said the building had collapsed suddenly and vertically after failing to absorb the shock of the 6.3 magnitude quake.
He said the roof had collapsed before the supporting south wall fell on top of it.
"The building collapsed vertically, almost immediately, before much horizon shaking had occurred due to overloading of the building elements designed for gravity load," said Frost.
"I believe it is also possible little or no horizontal loading was taken by the south wall and it may be it did not have an opportunity to perform as it should have."
Over 30 pieces of debris from the site and photos Frost took in the aftermath of February 22 have been exhibited as evidence at the inquiry.
For Brian Kennedy, who lost his wife Faye in the building, today's testimony brings a sense of foreboding.
"You're just waiting, what else is going to come out."
However, he said it is "a bit of a release too, because beforehand we seemed to know nothing about it".
Earlier, witness Matthew Ross described watching the CTV building disappear into a cloud of dust as he sat in his van clinging to his steering wheel.
Ross, director of Window Coverings, was in a van on Cashel St driving west towards Madras St when the quake struck.
Concerned a church he was beside would fall, he drove his van away and was still clinging to the steering wheel when the CTV building went down.
Ross said the building had been shaking both side to side and back and forth.
The top of the building was bending towards Madras St and he expected it would collapse in that direction.
"I was surprised when it began to drop straight down...I thought one of the bottom floors had given out."
"I could see the top floors were intact as they disappeared into the dust."
The hearing continues.