In a world-first, an international team of scientists just managed to create a rare "fire whirl" amid a burning pile of forestry slash in Canterbury – yielding invaluable new data that could ultimately keep fire crews safer.
Video / Supplied
They’re nicknamed fire devils – and they’re one of the most dangerous and dramatic features of an extreme fire threat rising each year under climate change.
In a world-first, an international team of scientists just managed to create some amid a burning pile of forestry slash in Canterbury – yieldinginvaluable new data that could ultimately keep fire crews safer.
Before this month, what are called fire whirls or vortices had never been deliberately generated at scale, outside the lab – and for clear reasons.
They can stretch kilometres high, reach temperatures as hot as 1090 degrees Celsius, and are typically seen in cases of “extreme fire” - fast-moving masses of heat and flames that behave in ways that firefighters can’t predict.
Such was the spectacle of these spinning, burning whirlwinds that videos of them, filmed amid Australia’s catastrophic bushfires and recent major wildfires in California, have gone viral online.
As part of a multi-million dollar, Government-funded programme, scientists have been carrying out controlled burns to learn more about extreme fire characteristics.
Over four days this month, in a field near Twizel, fire crews and Department of Conservation staff watched on as a team of 24 researchers set alight nine piles of wilding pines.
From one of these piles, measuring about 20m in diameter, the scientists were able to generate a “smoke devil” that took up the flame and created a fire whirl.
Ready in place to measure temperatures and conditions was more than $1m worth of specialist equipment, including high-speed thermal infrared cameras, drones and meteorological heli-kites.
It proved the longest, sustained whirl they’d managed to produce – and by capturing it at rates of 10 to 100 times per second, they secured a trove of data to analyse.
Jason Forthofer, a US firefighter and Forest Service researcher, said it was the first time that scientists had attempted to generate such a large fire vortex in the field, anywhere in the world.
Given so little was known about what triggered their formation, studying a fire whirl within a running vegetation fire was thought nearly impossible.
The scientists produced this fire whirl from a pile of slash near Twizel earlier this month. Photo / Scion
“By isolating the whirls into large pile burns, we were able to control the location and timing of the whirl,” said Forthofer, a leading expert in them.
The team observed that, even with low intensity fires, the smoke plume stood up, despite continuous light wind, just before the vortex formed – indicating this pattern could still hold in variable conditions.
“With every fire whirl experiment the team learned the sensitivities of the variables that produce fire whirls in forest debris and wilding pines,” said Scion’s science lead, Hugh Wallace.
“These burns were aimed at increasing our understanding of thresholds: atmospheric, environmental, fire intensity and fuel condition that must be crossed to generate a fire whirl.
“When these are understood, we can better predict their cause and spread.”
A fire whirl created by the study team, as viewed from an infra-red camera. Photo / Scion
Scion science lead Shana Gross added that the freshly gleaned data would help scientists pin-point “watch out” signals for firefighters, indicating when a fire whirl was ready to form.
Another member of the team, the University of Canterbury’s Associate Professor Marwan Katurji, said the insights would also help improve fire models.
“These models provide us with critical spatial information for understanding the physical processes governing when and how these dangerous fire whirls can occur.”
Rural fires cause about $100m in damage to the country each year, but “extreme fires” have rural fire authorities more worried, as their unpredictable and dynamic conditions could put crews at greater risk - particularly if the fire spreads behind them.
Along with fire whirls, these dangerous blazes can include larger fire tornadoes; spotting, where embers and other particles are hurled ahead of the fire front, and “blow-up” conditions, where the inferno suddenly escalates in size and intensity.
A helicopter uses a monsoon bucket to fight the devastating wildfire at Nelson's Pigeon Valley in February 2019. Photo / Leon Menzies
Cases of extreme fire behaviour have already been seen in big events like 2019′s Pigeon Valley fire near Nelson, yet also unexpectedly in smaller ones, including a blaze that devastated 90ha near Hanmer Springs in 2016.
More recently, a modelling study found the same extreme conditions that led to Australia’s “Black Summer” could also form in parts of New Zealand – and more frequently than first thought.
That danger would only increase as our planet warms, with projections indicating that fire seasons will increase by an average 30 per cent by century’s end – while the direct economic cost of wildfires may balloon from around $142m a year today to $547m in 2050.
“More extreme fires also mean a greater risk that fire whirls will occur - making it critcally important to arm firefighters with information to help keep them safe in the field,” Wallace said.
