$60k bill to strengthen glass ceiling

The Dunedin City Council is facing a $60,000 bill to strengthen the Wall Street shopping mall's glass ceiling and protect against further spontaneous glass explosions.

It has also emerged other Dunedin building owners could face similar bills for buildings constructed before regulations were toughened two years ago.

The concern comes after two men - one in a wheelchair - escaped injury despite being showered with falling glass fragments when a ceiling panel spontaneously shattered inside the Wall Street mall in April.

The incident prompted an Australian construction industry source - visiting Dunedin when the mishap occurred - to warn the glass needed strengthening to prevent a possible repeat, which could have fatal consequences.

Council city property assistant manager Rhonda Abercrombie said this week the incident had prompted the council to pay for a protective film to be added under every glass ceiling pane in the shopping mall.

The film would prevent fragments falling if another piece of glass shattered, she said. Work began last month and was due to be completed next week.

The retrofit would cost about $60,000 and be paid for from an operational maintenance budget for Wall Street, she said.

Council staff had been advised a repeat was "very, very unlikely", but had decided to be "incredibly proactive", she said.

"There's no design flaw. The council didn't have to do it, but we made the call ... that we would take this precautionary approach."

Parker Warburton Team Architects Ltd was the lead architect behind the $34 million, council-owned shopping mall, which opened in March 2009.

Parker Warburton director Simon Parker said yesterday the mall was designed to meet the regulations of the day, but glazing codes had been toughened in 2010.

That meant the mall - and possibly other buildings in Dunedin - would need to be retrofitted if owners wanted to bring them up to the newer requirements.

"There's the potential for any building that was built prior to 2010 ... [to] also have this issue.

"There's certainly projects which were designed to the standard before it was upgraded which would be in the same boat."

April's incident was blamed on nickel sulphide inclusion, which could occur during the manufacture of float glass that was later toughened.

Nickel contamination meant nickel sulphide crystals, formed during glass toughening, slowly reverted to a larger form and expanded to trigger shattering.

The phenomenon was a "worldwide problem" that could affect one in 2500 sheets of glass, but 90% of those shattered before leaving the factory, Mr Parker said in April.

Australia had already adopted new regulations requiring toughened glass to be heat-soaked - causing faulty toughened sheets to fracture - and laminated before use.

Yesterday, Mr Parker said New Zealand had since adopted its own new rules partly in response to incidents such as that which had occurred in Wall Street and other buildings.

"There is certainly retrofitting ... going on throughout Australasia."

The film was being added underneath all 201 panes of glass inside Wall Street, and attached to the edge of each ceiling frame using structural silicone.

"In the event there is ever another breakage, the film just really holds all the glass, and then the film itself is attached to the edge of the frame, so it doesn't fall in.

"It's clear, so you'd never ever even know it was there."