The Royal Commission of Inquiry into the Canterbury Earthquakes continues today looking into the failure of the Forsyth Barr building during the February 22 earthquake.
It is day two of the hearing, which considers whether the Christchurch office block complied with earthquake-risk requirements.
The site manager for the construction of the building and stuctural engineers who carried out a post-earthquake assessment of the site will today front the hearing.
The Royal Commission heard yesterday how workers in the Forsyth Barr building had become concerned about the stairs after the quake in September.
"It was clear that they had sagged somewhat as the paint on the wall had separated from the stair treads for most of the lengths of the flight," office worker Grant Cameron said.
When the earthquake struck on February 22 the stairs collapsed, leaving workers stranded.
"There was just a gaping hole stretching down the middle of the building with blackness both above and below," Cameron said.
"It was now plain that everybody was now trapped on their respective floors."
The stairs were compressed and failed catastrophically as the built-in 30mm seismic gap - designed to allow movement during quakes - was overwhelmed.
No one was in the stairwell at the time of the quake, but the Commission heard if there had been anyone there, they would have probably been killed.
Despite the concerns of workers the building was given a green sticker and recommended safety checks were never carried out.