The earthquake resilience of stairways in the Forsyth Barr building was compromised when they were installed, an inquiry into the Canterbury quakes has been told.
Fifteen flights of stairs collapsed in the 18-storey building during the devastating quake on 22 February last year, forcing some workers to abseil to safety.
The Royal Commission is investigating why the stairs collapsed. Several possibilites have been explored so far, including errors made by construction workers who installed the stairs in 1988.
A lawyer assisting the Royal Commission, Stephen Mills, said on Thursday that seismic gaps between the stairs and the building, which are designed to allow for movement in an earthquake, had been filled with debris.
The commission was shown photos of polystyrene in the 30-millimetre gaps, potentially limiting how much the stairs moved during the quake. Mr Mills would not say whether the debris was left accidentally or not.
A former tenant of the Forsyth Barr building on Thursday recalled helping colleagues abseil from a window.
Lawyer Grant Cameron says ropes were found in a Civil Defence cabinet in the building and it took 90 minutes to get everyone down.
Mr Cameron told the inquiry that he and two others were the only ones left when a crane came to their aid.
On Friday, the site manager responsible for the construction of the Forsyth Barr building will give evidence.