The fact a toxic blaze has enveloped the Sky City convention centre is even more complex due to it still being under construction.

Fire crews from around not only Auckland but as far south as Hamilton have been fighting a fire at the $700 million building since 1.15pm yesterday.


But what exactly the firefighters are dealing with isn't known, however NZ Professional Firefighters Union president Ian Wright said it was one of the toughest they will ever face.

"This is as serious as it gets. This is a dangerous, dangerous fire."

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Wright said it was dangerous because he can read the smoke, but making it difficult was the fact it was still under construction.

"The building isn't finished. There maybe bits missing in the building, ceiling panels missing, walls missing, other things missing from there that you would expect to be there."

Wright said fighting fires like the one at Sky City were incredibly taxing on firefighters and despite wearing specialist gear, the dangerous toxins would still manage to seep there way into their skin after about an hour.

News of the serious wind warning due for the city would also be making crews nervous and would be another obstacle firefighters would have to overcome.

Firefighters get up close to the fire at the Sky City convention centre. Photo / Jade Fairweather
Firefighters get up close to the fire at the Sky City convention centre. Photo / Jade Fairweather

Working out how to tackle it was also difficult, and getting helicopters to dump 500 litre buckets of water wouldn't be an option.

"It's probably not appropriate to be dropping tonnes of water on there with helicopters, for starters.

"There's a whole lot of fire happening where you can't see it. It's under the roof, in the floors below and in the voids below, so in the buildings like this there's concealed ducting and concealed walkways and accessways and these can contain fire and make it difficult to extinguish."

The building's construction, in general terms, would have floors and ceilings which go up and across on the same floor and it was crucial - but difficult - for firefighters to get in those areas.

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"So what's happening in there with these firefighters, there will be thick black smoke, extreme heat and it will be really punishing. So it's not what you see from the outside with the people on the roof doing what they're doing, a lot of the hard work will be out of sight, in the dark with extreme heat and you're only feeling your way.

View of the fire from the NIWA webcam on the Sky Tower at the Sky City convention centre. Photo / NIWA
View of the fire from the NIWA webcam on the Sky Tower at the Sky City convention centre. Photo / NIWA

"We have thermal imaging cameras which can help us but we rely heavily on our training to move through the buildings like this, extinguishing fire as safely as possible.

"So it's not what you see, it's what you can't see."

Wright said there were dangers in dropping buckets of water from helicopters to help extinguish the blaze - especially that when you put it on fire it expands 1700 times.

Flames and smoke from the Sky City convention centre construction site as seen from Freeman's Bay. Photo / Debbie Cook
Flames and smoke from the Sky City convention centre construction site as seen from Freeman's Bay. Photo / Debbie Cook

"If you dump that you don't know what it's doing to the crews inside.

"What happens when you put water on a fire is, it expands 1700 times. So a litre of water that you put on will expand 1700 times into steam.

"We can use that to our advantage but it's also a disadvantage when there's firefighters in those environments.

"That water is expanding and of course steam can reach much higher temperatures than boiling water.

"In a building fire like that where you have an enclosed compartments, that 1700 times expansion can make conditions really, really dangerous and really, really uncomfortable."

Wright said the location of the fire wasn't so much difficult, it was more the fact they didn't have as many aerial appliances as they wanted.

A weary firefighter at the scene of the Convention Centre blaze. Photo / Dean Purcell.
A weary firefighter at the scene of the Convention Centre blaze. Photo / Dean Purcell.

"We have a shortage of aerial appliances in Auckland. Fighting a fire at any height over 6 or 7m or any multi storey building adds a layer of complexity but we do train for these fires ... these are the conditions that career firefighters, especially, practise for. This is one of the big ones."