An engineering expert in disaster relief is concerned the red, yellow and green sticker system is being incorrectly applied to some earthquake-damaged buildings in Christchurch and causing confusion among owners.

"The same issues happening here in Christchurch happened in Haiti," says Unitec associate professor Regan Potangaroa, a member of RedR (Registered Engineers for Disaster Relief).

"People didn't understand what the red, yellow, green meant. They thought it was a structural check and it's not. It's an access guideline on whether people can go into buildings or not."

Professor Potangaroa, who was in Christchurch last week, says he's concerned the sticker system is being incorrectly used to assess seismic compliance and to guide the demolition process. He says he's seen a number of houses tagged red when that appeared to be overstating their condition.

"You don't need a PhD for some buildings. Some you look at it and it's a pile of rubble and it's going to be red. But between red and green there is a huge confusion about what the stickers mean."

He watched a two-storey historic house in Durham St demolished and was dismayed to see all the personal items still inside as it was flattened.

"Thinking about public safety, if the house did collapse to the left or the right, it would be hard to see it hitting the house next door - so you wonder about the tagging, but also the need to demolish it so quickly under the emergency requirements. It just didn't make sense."

Professor Potangaroa says he is concerned also that a demolition company has been claiming salvage rights on the houses it has been knocking down.

"My understanding of the emergency act is that is not the case. While you may have to knock the house over under the act, what's in the house remains the property of the owner."

He's also heard from Maori families not being able to go into their homes and take their family photographs.

"For Maori, these photographs are not pictures of dead people, they are living whakapapa. Having to leave them in the houses and not be able to take them down and take them with them is devastating."

His impression on reading statements on some red tags is that many of the assessments were done either by building inspectors or engineers who were judging what they saw against the Building Act or building codes. "What they should have been doing is just judging it under the access guidelines."

Professor Potangaroa, who is part of the multi-disciplinary team Resilient Organisations, which researches disaster recovery, is concerned about too much reliance on "top-down" emergency processes rather than getting out into the field to see what is happening.

"They are relying on the system delivering what they had planned for. They don't understand there is a human element to this.

"It's not all about activating their systems because there are extended emergency powers. It's not being reviewed enough. Common sense isn't being applied."

Placards are placed on buildings under the Civil Defence Emergency Management Act. The guidelines, which have been developed by the New Zealand Society for Earthquake Engineering, draw heavily upon North American experience - in particular the ATC-20 Proc.

A green sticker means the building has been inspected and there are no restrictions on use or entry.

Yellow means restricted use - parts may be off limits and people should enter only on urgent business and leave as soon as possible.

Red means unsafe: do not enter.