A short series of ear-shattering explosions was all it took to demolish Radio Network House in Christchurch.

The 14-storey building  is now a pile of rubble between Manchester St and Latimer Square.

Mark Loizeaux, president of Controlled Demolition who headed the project, said the implosion went better than planned.

"I really didn't think we would get the structure to roll to the north as far as we did, it went a bit further than I had hoped so I am lucky,'' he said.

Initial reports indicated there was no damage to nearby buildings.

A seismograph reading taken during the implosion showed the resulting ground velocity was about 12 millimetres per second.

''Which is very low,'' Loizaeux said.

"That's about the same as crawling one of the track machines across the site''

Greg Hedges, CEO of building owner Nor West Arch No.4, said it was sad to see it go.

''There have been good memories with that building, to see it like that its difficult,'' he said.

"I thought it was magnificent the way it went down.

''I must say I was slightly apprehensive after the first volley of explosions went and it was still standing, and then the second lot just brought it all down.

'LOUD AND DUSTY'

A Cashmere resident said it was like "a bomb going off" and was "loud and dusty".

Somerfield resident Marcella Cassiani said she "definitely heard it here".

"Three loud booms, a pause then three more. No shaking though, thankfully," she said. 

Debbie Sutton from Barrington heard "about three bomb like noises".

"I realised what it was and felt quite sad actually but also intrigued about how it all works," she said.

Naylor Love was the prime contractor and Ceres New Zealand was the subcontractor responsible for the demolition.

Ceres long-term recovery manager Bill Johnson said the implosion would be achieved byplacing small explosives charges in holes drilled in the support columns of the building.

A total of 60 kilograms of explosives was be used to bring down the building.

"By carefully controlling the sequence of the firing of the charges, the demolition of the building will occur by utilising gravity. The weight of the upper part of the building will destroy the lower portion," he said.

He said the implosion would result in minimal shaking as the lower levels of the building would absorb the energy of the impact.

He said the shaking could not be compared to a quake as the "vibrations were different".

An exclusion-zone fence will be installed, about a block in either direction of the Worcester St building, to ensure the safety of the public.

The cost of the implosion is close to $1 million and is covered by the owner's insurance.

In comparison, alternative methods of demolition were quoted at about $1.2m.

After the implosion, all public roads would be cleared before being reopened to traffic.

JAYDEN'S BIG MOMENT

The honour of pushing the button which will trigger the implosion was been bestowed on 6-year-old Queenstown boy Jayden Halliwell.

Eight demolition companies won a Trade Me auction to implode the 14-storey Radio Network House with a bid of $26,000, and they gave the opportunity to the Child Cancer Foundation, which nominated Jayden.

Jayden is undergoing cancer treatment and is staying with mother Justine at Ronald McDonald House in central Christchurch.

- © Fairfax NZ News

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