New Zealand’s rapid assessment system for earthquake-damaged buildings is being questioned after it emerged that buildings cleared for occupancy after the September 4 Christchurch quake were among those that collapsed in the February 22 quake.

The classification system itself may need reviewing if it gives building owners a false sense of security.

The guidelines for evaluating building safety after earthquakes give red, yellow and green stickers to buildings, with red meaning unsafe and green stating the building is “apparently OK” with no restrictions on use or entry, but further inspections or repairs might be needed.

The assessments are made by an engineer on a “walk-by” and are a temporary measure intended to help emergency controllers plan the disaster response.

The tagging system only applies during the emergency period. Building owners are expected to arrange for a more detailed engineering evaluation.

NZ Society of Earthquake Engineers Executive Officer Win Clark told insuranceNEWS.com.au some building owners may have relied entirely on a green sticker when reopening their buildings.

He says owners still have a responsibility to ensure buildings which been through a major event are safe, as damage may not be obvious.

The owners of the Pyne Gould Guinness and Canterbury Television buildings, which collapsed and took many lives, have told NZ media they had their own assessments done by structural engineers after the first quake on September 4.

Mr Clark says although the second quake was lower on the Richter scale, the ground shaking was greater.

“As an engineer you are concerned about the intensity of ground shaking at the building site,” he said. “It is quite probable and certainly has been demonstrated that a building can survive without any damage on September 4 and be significantly damaged in the second earthquake.”

An official inquiry into the building collapses will examine why some relatively modern buildings collapsed and whether building standards are adequate.

The Society of Earthquake Engineers wants the inquiry to include a thorough investigation into the technical aspects of the earthquake and its aftermath.

The emergency effort is being run from the Christchurch Art Gallery, opened in 2003 and with walls of glass that withstood the shaking.

Mr Clark told insuranceNEWS.com.au the gallery demonstrates that buildings can be designed to withstand earthquakes – but New Zealanders will eventually “need to have a discussion” about the level of response to the risk and recognise that no building can be completely earthquake-proofed.

He says there is “too much emotion involved” at present for such a discussion.

“There is a lot of science that needs to come into it – engineering science as well as social science.”