Survivors of a collapsed Christchurch building in which 18 people died in the February earthquake say they never felt safe working in it after damage caused by earlier quakes.
The Royal Commission of Inquiry investigating the Canterbury quakes is hearing evidence about the Pyne Gould Corporation building and what happened to it during the 6.3-magnitude quake on 22 February this year.
The main item to be discussed during this phase of the inquiry is a technical investigation report into the PGC building, which aims to explain why it collapsed.
Engineers assessed the building five times after the first big quake to hit Canterbury on 4 September 2010 measuring 7.1, and February's quake. Each assessment found that the building was still safe to enter, despite concerns raised by tenants.
Helen Guiney works for Perpetual Trust and was trapped in the PGC building for 21 hours after the February quake hit.
Ms Guiney told the hearing on Monday the building felt different following an aftershock on 26 December last year and there were obvious signs of damage, including large cracks.
She said the building also creaked more and she did not feel 100% safe in the building, despite the assessments saying it was safe to re-enter.
Ms Guiney said the last thing she saw on 22 February was the front window blowing out and tiles falling around her. She lay in the dark unable to move and called out to her colleague Jim Faithful until help came.
Another worker, Julia Stannius, told the hearing she also felt uncomfortable after the Boxing Day tremor and that if a truck went past it was possible to feel the building vibrating.
A lawyer assisting the Royal Commission says there was consensus among experts that the PGC building collapsed because the central core of the tower failed between levels one and two.
However, Stephen Mills said the role other factors may have played is also important.
"Determining what the critical structural weaknesses were in this building as accurately as possible goes directly to the question of what other buildings in New Zealand might have similar problems, and identifying that obviously matters a lot."
Robert Wynn told the hearing on Monday he was in his office which looked across to the PGC building on 22 February when he felt what he thought was an aftershock.
Mr Wynn looked out the window and saw the building drop, flattening and rotating as it came down. He said it fell fast like a controlled demolition between five to eight seconds into the quake and described the event as catastrophic.
The hearing continues on Tuesday when the engineers who inspected the building after the first quakes will give evidence.