'Great fortune' nobody died in Forsyth Barr | Canterbury News | Local News in Canterbury

It was only by "great fortune" that no one died in the Forsyth Barr building on February 22, the Royal Commission of Inquiry has been told today.

The building's staircases collapsed in the magnitude 6.3 earthquake, leaving many people trapped, terrified, for several hours as aftershocks shook the building. Eventually, some escaped by abseiling down the side of the building or being lifted out by crane.

Addressing the commission this morning, QC Stephen Mills said it was extremely lucky that no one had died when the stairs collapsed.

"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."

Mr Mills recounted the tale of "Jane" who was on level 17 of the building when the quake struck. She and a group of four others began to feel their way down the stairs in the "pitch black" dark, but stopped at level 15 - below where the stairs had collapsed.

"If her and her party had gone any further they would have lunged into what was then a dark void. It's very lucky no one did."

The stairs in the 18-storey building were "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 30mm.

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. Photographs showing both cracking of the stairs, and what appears to be a sag in the stairs, were taken by a tenant after the September earthquake.

Engineering firm Beca Carter Hollings and 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 required.

However, no further investigation of the stairs was undertaken. The building's owner switched engineers, from Beca to Homes Consulting Group. 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.

Mr Mills said the stair's collapse raised concerns about their design.

"Scissor stairs are a concern because when one comes down the other usually come down as well ... Egress [emergency exit] stairs are supposed to be the last ones standing, the contrary has happened here where the stairs were the first down and the building stayed up."

He said the findings about the stair's collapse had wider implications for buildings in New Zealand.

"They are also relevant to other buildings in Christchurch and elsewhere in New Zealand where urgent investigations are now required to ensure that stairs can survive a very occasional earthquake with a magnitude considerably greater than that used for the design of the building as a whole."

The hearing continues.