Implosion 'test case' for Christchurch

The demolition of Radio Network House could be a "test case" for further implosions in central Christchurch.

The implosion is expected to see the 14-storey Worcester St building come down in 7.7 seconds.

The demolition, which will take place on August 5, will be New Zealand's first building implosion.

Work is under way to strip the interior of the building so it will be empty when it implodes.

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

Ceres is partnering United-States based Controlled Demolition, which has carried out 9000 implosions worldwide.

Canterbury Earthquake Recovery Authority general manager of operations Warwick Isaacs said that because the implosion was the first in New Zealand, the method had been scrutinised by Cera engineers.

"We are satisfied that the contractors have covered all the key risks in great detail and that the demolition will be safe and successful."

He said the implosion could act as a "test case" for other suitable buildings in the city.

He was not aware of any other buildings earmarked for implosion.

"We're very excited that it allows the demolition of this building to come down in a much quicker fashion than what it would've come down,'' he said.

"So from our point of view, what that does is expedite the recovery of the central city and helps us move on with the rebuild more quickly." 

Building owner Greg Hedges said it was "ridiculous" that implosions had not been used to assist the rebuild.

"We're using outdated technology when this is available to use,'' he said.

''We see the big issue as trying to speed up the demolition of buildings that will in turn speed-up the building and recovery of Christchurch."

Ceres long-term recovery manager Bill Johnson said imploding the building would not only shorten the demolition process by about six weeks but also save money.

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.

Johnson said the implosion would be achieved by placing small explosives charges in holes drilled in the support columns of the building.

A total of 60 kilograms of explosives would 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.

It is not yet known who will push the demolition button, and the role could be auctioned to raise funds for charity.

"We're trying to sort out the liability of that," Johnson said.

"I've seen them go for $6000 ... Considering this is the first in New Zealand, I'm going to have high hopes." 

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.

Given the lack of activity in the area, the recommended zone was extended as a precaution, Johnson said.

Implosions have gone wrong in the past.

The Royal Canberra Hospital implosion resulted in the death of 12-year-old Katie Bender.

Nine other people were injured as large fragments of masonry and metal were flung up to 650 metres from the demolition site.

After the Radio Network House implosion, all public roads will be cleared before being reopened to traffic.

The Press