SkyCity Convention Centre fire: 'Environmentally friendly' roof will be fully consumed by blaze, engineer says

Wednesday, 23 October 2019

The fire continues to burn in the Auckland Convention Centre, as seen from a nearby apartment

A huge fire at the SkyCity Convention Centre will keep burning until the flammable layers of straw in the roof are consumed, an engineer familiar with the project says.

The expert said there were measures in place to stop a fire spreading from inside the building to the roof, but no plan to prevent a blaze in the roof itself.

The fire is still burning, sending plumes of thick smoke across the city.

The fire was continuing to burn on Wednesday afternoon, with severe gales and rain forecast, after it broke out on Tuesday afternoon.

Auckland University associate professor of civil engineering Charles Clifton, who previously visited the building site as a consultant, said the building's roof was a sandwich panel made up of layers of straw.

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The straw was used for insulation and acoustics and was seen as more environmentally friendly than using polysiocynaurate, another insulation material, Clifton said.

'There's multiple layers of straw through the roof because they had to reach a very high insulation rating and acoustic rating.

'The reason the fire's still burning is the fire got into the straw. You've got the layers of straw and the layer of plywood on-top, with a bitumen membrane on it. So it is a flammable panel.'

Bitumen, a water-proofing membrane commonly used on flat roofs, is also flammable given enough heat.

An electrician working on the site said on Tuesday the fire started when a torch was being used on the bitumen membrane.

Clifton said laying the membrane was a time-consuming process that involved heating, with a blow torch, the joins between the bitumen strips to bond them together.

He was doubtful that the fire started during this process.

'The blow torches are very noisy when in operation doing this, and it is very unlikely that someone left a torch on at full power while they went on a break.'

The professor, who is currently on sabbatical in Italy, said the roof panel had a fire-resistant layer underneath it to stop a fire from spreading.

'The whole system is designed to stop a fire getting in from below the roof. There's no system for if a fire actually starts in the roof panels, because there's no envisaged scenario where that would occur.'

Clifton said he was surprised by news of the fire, saying in his 40 years in the industry the convention centre's building site was 'one of the most safety conscious and tightly-controlled I've seen'.

'They certainly were aware the roofing was flammable.'

He said the fire would burn out on its own after it had consumed the roof, because the roofing panels were the only combustible part of the building.

He believed the overall effect on the structure could be quite minimal, with little or none of the steel work needing to be replaced.

The fire's aftermath will be expensive, he said, with the clean-up likely exceeding the cost of replacing the roof.