The roof of the SkyCity Convention Centre on fire last night (Image: NIWA Weather)
The roof of the SkyCity Convention Centre on fire last night (Image: NIWA Weather)

ScienceOctober 23, 2019

Bitumen, plywood and straw: on the aflame SkyCity Convention Centre roof

The roof of the SkyCity Convention Centre on fire last night (Image: NIWA Weather)
The roof of the SkyCity Convention Centre on fire last night (Image: NIWA Weather)

Was the SkyCity Convention Centre construction site at higher risk of fire than any other construction site or building? Alex Braae asks the experts.

A fire at the SkyCity Convention Centre construction site has continued to burn this morning, after a night of lighting up the Auckland CBD sky.

The fire, which unconfirmed media reports suggest was sparked by an unattended blowtorch, has the potential to cause millions of dollars worth of damage and throws an already delayed and cost-overrun project into deeper turmoil.

Last night, a decision was made to abandon firefighting efforts on the roof. The roof was “sacrificed” in order to concentrate instead on protecting the wider structural integrity of the building and lower floors.

The materials used for the roof gave many pause for thought – reported as a combination of bitumen, straw and compressed plywood. It appears at first glance to be a uniquely flammable combination.

However, according to Michael James, the Immediate Past President of the NZ Chapter of the Society of Fire Protection Engineers, that is not the case, even though the materials are themselves combustable. More likely, he told the Spinoff, is that it was a panel with a waterproof membrane subsequently applied.

“The use of bitumen in waterproof membranes on roofs is common and almost always able to be applied in a safe manner,” said James.

“Typically when they’re applied they don’t catch on fire, and they don’t catch fire during their lifetime as well. So it is a bit unusual to see.”

Another expert had a somewhat different view. Stuff reported comments from Auckland University associate professor of civil engineering Chris Clifton, who said that “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.”

Clifton also expressed scepticism about reports that the fire had started after a blowtorch was left unattended.

As to the decision to abandon the roof to burn, while attempting to protect lower levels, Michael James said the key consideration would have been Fire and Emergency’s desire to protect their people.

Provided firefighters can prevent further spread, James didn’t see a particularly strong risk of the building imploding or collapsing. With the amount of water being poured onto it, the heat wouldn’t have risen to the point where it might have weakened the steel structure, he said.

However as a construction site, the chances are high that the fire has had an abundance of fuel to feed off, said AUT school of engineering professor John Tookey.

“Renovators at Windsor Castle in the UK caused a huge fire that burned for 12 hours. Similarly, workers on the reconstruction of the Mackintosh School of Art in Glasgow started a fire that almost completed destroyed this architectural icon. Ironically the reconstruction work was needed to repair the effects of a previous accidental blaze.”

He listed a range of factors that heighten risk, including subcontracted companies and operatives working for short periods in unfamiliar environments, potentially dangerous processes involving materials at high temperatures, and combustible materials either awaiting installation as new additions.

“All conspire to present extensive fire hazards on any commercial construction site,” said Tookey.

As well as that, the usual systems to prevent and halt fires wouldn’t have necessarily be in place, like how they would be for a completed building. That means that once started, fires become harder to stop.

Previously, the SkyCity Convention Centre was going to include the same cladding that proved so disastrous in the deadly Grenfell Towers fires in London. However, earlier this year that cladding was removed from the construction process, at a cost of $25 million.

Both SkyCity and Fletcher Building are likely to be badly affected by the fire. Fletcher Building had already incurred significant losses on the construction of the Convention Centre, after cost overruns went above their successful bid.

Parts of the CBD remain blocked off today, with warnings from health authorities to keep windows closed and avoid breathing in smoke.

The Spinoff’s science content is made possible thanks to the support of The MacDiarmid Institute for Advanced Materials and Nanotechnology, a national institute devoted to scientific research.

Mad Chapman, Editor
The Spinoff has covered the news that matters in 2021, most recently the delta outbreak. Help us continue this coverage, and so much more, by supporting The Spinoff Members.Madeleine Chapman, EditorJoin Members

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