No other country on Earth has more bushfires than Australia. Bush fires spread quickly destroying everything in their path and they are extremely difficult for fire brigades to control. At the CSIRO in Yarralumla, researchers are using their Pyrotron – a combustion wind tunnel – to provide them with a unique insight into how fire behaves in the Australian bush.
Frequent events during the hotter months of the year, the fires occur due to the scorching climate of the Australian continent. With the size, intensity and frequency of large bushfires predicted to increase under climate change, understanding bushfire behaviour and mitigation has never been more important.
Victoria saw the majority of the deadliest and largest bushfires in Australia, most notably through the 2009 Black Saturday fires, when 173 people were killed, around 2,000 homes and structures were destroyed. Towns were gutted, and some were almost entirely destroyed, such as Marysville.
Major firestorms may result in severe loss of life. The most intense, extensive and deadly bushfires typically occur during droughts and heat waves, such as the 2009 Southern Australia heat wave, which precipitated the conditions during the Black Saturday bushfires in which 173 people lost their lives. Other major conflagrations include the 1983 Ash Wednesday bushfires, the 2003 Eastern Victorian Alpine Bushfires and the 2006 December Bushfires.
Since 2009, a standardised Fire Danger Rating (FDR) was adopted by all Australian states. During the fire season the Bureau of Meteorology (BOM) provides fire weather forecasts and by considering the predicted weather including temperature, relative humidity, wind speed and dryness of vegetation, fire agencies determine the appropriate Fire Danger Rating.
The study of free-burning fires in the open is fraught with difficulties and physical danger. Additionally, reproducible experimental conditions are essential for obtaining scientifically useful results. Researchers are now looking to use technology to predict how bushfires might spread in the hope of controlling them sooner.
CSIRO has become a world leader in research aimed at understanding and predicting fire behaviour and informing mitigation strategies.
The CSIRO (Commonwealth Scientific and Industrial Research Organisation) have been studying how bush fires spread. The CSIRO built the Pyrotron in 2008, but the scientists then waited until 2012 to have the monitoring equipment to enable modelling to be done in it.
In the field, experiments are dependent on the weather conditions: ”If it gets too hot, we can’t burn, if it’s raining, we can’t burn”, said the researchers. Due to the perennial hot and dry climate of Australia, Dr Andrew Sullivan said it was also dangerous to light and observe fires in the bush on high risk days, so there was a gap in scientific knowledge on how fires spread in very hot, and very dry conditions.
A new wind tunnel has been built to study fires burning freely in vegetation fuels. This tunnel achieves very low levels of turbulence without using a contraction section, thus enabling a large working section to be employed without major cost.
The Pyrotron is a long aluminium tunnel where wind and fire can be combined to model how real fires might spread. This type of apparatus opens up the window of opportunities for conducting actual scientific experiments.
An open-circuit blower fire-proof wind tunnel was constructed within a suite of experimental, budgetary and operational constraints to enable the safe study of bushfire fuel combustion under a wide range of reproducible burning conditions. The Pyrotron’s 25-metre-long ‘L’ shaped wind and fire tunnel enables researchers to study the chemistry of combustion and behaviour of bushfires under a range of simulated environmental conditions.
The Pyrotron is unique in Australia and one of only two in the world.
Key to achieving reproducible burning conditions is the reduction of unwanted turbulence in the upstream air flow. This was achieved without resorting to an expensive contraction section through judicious use of settling distance, perforated screens, straighteners and a large capacity fan.
The resulting design enables a working section with a large (2 x 22 x 2)-metre cross-section in which turbulence intensity was measured to be less than 0.6% of the mean flow for a range of air speeds (1.0 – 5.5 m s-1). Variation in spatial uniformity across the entire cross-section of the working section was less than 2.2% of the mean flow over the same air speeds.
As well as filming fires, researchers use sensors inside the tunnel to study fire behaviour in grasses, forest leaf litter and small logs. CSIRO’s Pyrotron is providing better information about emissions under different burning conditions, as well as the amount of carbon sequestered through charcoal formation.
How Fire Behaves in the Australian Bush with the Pyrotron
Frankly, no amount of digital pyrotechnics will detract from the fact that the Pyrotron is just a big metal tube with a fan. But it is progress. You see…
Researchers used to model the behaviour of fire in open fields. Yes, that’s exactly what it sounds like. They would literally set fire to a field in order to see what would happen… Hey! That’s what scientists do! 😉
Free-burning fires in natural vegetation (wildland or bushfires) exhibit a wide range of behaviours due to the natural variation in environmental conditions and the interactions between the vegetation, the weather, the topography and the fire itself.
The scientific study of bushfires in situ is fraught with difficulties, ranging from dealing with these variations in a suitably reproducible manner and providing a safe work environment, through to gaining satisfactory access to active wildfires or permission to light experimental fires under the conditions associated with wildfires.
Anyway, it was not perfect. Unsurprisingly perhaps… Not being able to control the wind meant they couldn’t test for a variety of specific conditions.
In the Pyrotron, the CSIRO fire-starters recreate a field of sorts, filling the floor of the tube with materials like those found on dry forest floors, then using the fans to create a model of those varied bushfire conditions. The Pyrotron allows bush fires to be studied safely, and in a controlled environment.
Unpredictable No Longer?
Unpredictable and capricious, bush fires are an erratic phenomenon. Sometimes, houses will burn, but kitchen tables are left intact. Garages will burn to the ground leaving cars inside untouched. According to Andrew Sullivan, the head of the Bushfire Dynamics and Application Group at CSIRO, the explanations for bush fire behaviour are more the stuff of science than science fiction:
“The thing to understand about fires, particularly landscape fires such as bush fires, is that they do follow physical processes […] where a fire appears to burn some houses and not others, there is a reason for that and that was because there was less fuel or a disconnection in the fuel.”
“While seeing one house standing in a row of burnt houses may look surprising, when the fire was actually burning you learn sometime later there was someone there to put the fire out. […] There are some very pedestrian explanations for what could be construed as supernatural events.”
Compared to wildfires in the U.S. or forest fires in Europe, Sullivan said what is unique to Australian bush fires was their ability to throw “spot fires” – that is to say, carry embers on the wind and start fresh fires at a massive distance from the fire front:
“There’s a great potential for them to start new fires — it allows bush fires to overcome breaks in fuel and topography. Spot fires can jump rivers or ridges – the fire throws spots over the break, those spots coalesce and form a new fire and off it goes.”
Spot fires are the result of burning debris lofted in the convection column of a fire being transported up to a great height, falling out of the convection column and transported downwind. Spot fires are one of the primary reasons that fighting fires in Australia is so difficult. The longest distance that an Australian bushfire can ‘spot’ is about 30 kilometres!
But the CSIRO also studies the ability for fires to restart sometimes days after firefighters believe they have been extinguished – the phenomena known as “escaped fires“. The burnt fuel can sometimes retain heat for long periods – even without oxygen. Escaped fires have many of the qualities of peat fires, which burn underground for months.
“To all intents and purposes it looks like the fire has gone out but when there’s a change of wind direction, there’s always residual heat in the char fuel. One of the biggest issues firefighters face is major changes in wind direction. One of the biggest causes of bush fires in Australia are ‘escaped’ fires. […] The ability to black out a fire edge takes an awful lot of effort and an awful lot of water because you’ve got this charring process that can retain residual heat for a long time, and that charring process is anaerobic – it doesn’t need oxygen. […] You need to keep an eye on an area that was previously thought to have been put out.”
While firebreaks – meeting the fire with a countervailing controlled fire running in the opposite direction – are one possible solution, old fashioned vigilance remains the only solution to Australia’s perennial bushfire seasons. With the pattern of bad fire weather recurring during the fire season, new fires are sparked by old fires with depressing regularity.
In January 2015, the researchers started modelling even more severe fire conditions, close to those of the Black Saturday bush fires in Victoria in 2009 which killed 173 people.
The results of the research will provide valuable information to fire fighters about how much time they have to attack a fire directly with water before it becomes a threat to lives and property.
CSIRO researchers are also developing a National Fire Behaviour Prediction System to provide managers with better models for simulating bushfire scenarios, and implementing prescribed burning, suppression, risk and biodiversity management programs. The prediction system consists of four primary components: fuel models, fuel moisture models, wind models and fire behaviour models.
The system is designed to predict bushfire behaviour in Australia’s main fuel types: eucalyptus forests, exotic pine plantations, grasslands, shrublands and Mallee heath. Importantly, the system will enable more accurate simulations of the impact of different climate change scenarios on fire risk.
The fire behaviour models predict fire characteristics such as the
rate of spread,
fireline intensity and
onset of crowning/spotting potential.
The Pyrotron fire-starters might not actually stop bushfires, but their research will help with containment and let the authorities determine the behaviour of them much more accurately, allowing them to warn residents in the future paths of these fires and hopefully, saving lives.
A preliminary model of the rate of growth of fire is expected to be ready before the end of the year.
Read more about CSIRO’s Pyrotron: