"He looked utterly shocked and then blurted out 'You won't believe it but the bloody stairs have collapsed.' It took me a moment to register what he was saying, but he was quite insistent that the stairs had completely disappeared. "
The staff realised they were trapped in the building with no way out.
"There was just a gaping hole stretching down through the middle of the building with blackness both above and below."
Experiencing continual aftershocks and concerned about the possibility of a fire breaking out, Mr Cameron decided they had to get out of the building as soon as possible.
"I then explained to the staff we had a simple choice. We could stay where we were and await some form of rescue or we could attempt to escape down the side of the building. To await rescue necessarily meant some sort of crane being found and we had no way of knowing if and when such a crane may be available."
The staff began frantically tying electrical extension cords together to form a makeshift rope, but then discovered some actual rope in a Civil Defence kit in the building. Mr Cameron's office was about 30 feet from the carpark, and he thought if staff could be lowered to that level they may be able to escape down the car park ramps to the street.
After smashing a window with a sledgehammer, several men took the weight of each rope and began lowering people down to the carpark below. Over the next 90 minutes, 15 people were lowered to safety.
Mr Cameron and two other men remained in the building and were rescued by crane at around 4pm.
Earlier in the day, QC Stephen Mills said it was extremely lucky that no one had died in the staircase's collapse.
"It is by great fortune that no one was on the stairs at the time of the collapse. Had they been, then there would have been deaths. It's also by great good luck that no one tried to descend the stairs in the dark."
The stairs in the 18 storey building were pre-cast "scissor stairs", fixed at the top end of each flight, but designed to slide at the bottom end during an earthquake. The sliding movement was accommodated by a seismic gap of about 30 mm.
A report commissioned by the Department of Building and Housing last September said the stairs collapsed because the seismic gaps at the bottom landings were too small for the level of shaking experienced on February 22.
Minor structural damage was observed after the September 4 earthquake, including some cracking and deformation in a few flights of stairs.
Mr Cameron also told the commission he had been concerned about the state of the stairs following the September earthquake.
"Straight after we re-entered the building I was advised by a staff member that there was considerable damage to the stairwell and that it appeared quite serious."
Mr Cameron inspected the stairs himself and said he noticed "prominent damage", including sagging, vertical and horizontal movement, and "distinct cracking." He took photos of the damage.
Engineering firm Beca Carter Hollings & Ferner inspected the building on several occasions after the September earthquake. It was first given a red sticker, then this was changed to yellow, then green. When the sticker was changed to green, Beca said a further inspection of the stairways was needed.
However, no further investigation of the stairs was undertaken. The building's owner switched engineers, from Beca to Homes Consulting Group, and it was not clear whether Homes' engineers knew about Beca's recommendations to check the stairs.
"In any event, the follow up of the stair damage, including the inspection of the seismic gaps that Beca had recommended in its level two assessments, was never done," Mr Mills said.
