Staff have returned to the Dunedin City Council's Civic Centre building, which was evacuated this morning after an electrical explosion.
Hundreds of staff were forced out of the building about 9.15am and firefighters called, after initial reports of a loud bang inside the council's third floor computer server room, the Otago Daily Times has been told.
A council spokesman said an uninterruptible power supply shorted out which triggered the non-toxic gas system to cool and reduce oxygen in the room.
No information had been lost as the council's production servers were hosted off site and staff began moving back into the building about 10am.
Dunedin Senior Station Officer Rob Torrance, who led the Fire Service's response, said firefighters entered the building with breathing-apparatus and with a thermal camera to track down the source of the explosion and determine how toxic the gas was.
It was possible the fire was connected to maintenance which had been going on in the room over the last week, he said.
The gas sprinkler system in the room was designed to suppress fire without damaging equipment.
