Tag: Black Saturday

The royal commission that is investigating the Black Saturday fires of February 7 in Australia was told by wildfire behavior expert Dr. Kevin Tolhurst that spot fires occurred a record 35 kilometers (21 miles) ahead of the main fire.  Dr. Tolhurst also had some other interesting observations about fire behavior during the fires. Two examples are spot fires occurring off the flanks of a fire, and researchers studying fire behavior of small fires and extrapolating that to assume fire behavior on large fires would be similar. The latter was an issue during the 1988 Yellowstone fires when crown fire behavior did not match the existing prediction models.

Here is an excerpt from The Australian:

Dr Tolhurst said researchers had developed “warped ideas” about bushfire behaviour because they had studied comparatively small fires. This had flowed through to training of fire fighters and advice given to the public. 

Dr Tolhurst, who has studied extended video of the February 7 fires, said most people expected a fire front that was like a “wave of fire”, which would pass in a matter of minutes. But during the Black Saturday disaster fire activity had lasted for hours in some cases, with up to an hour when radiated heat remained a danger. 

“There’s no one front of fire,” Dr Tolhurst said. “It’s not a continuous wave of fire going through.” 

The strong wind change caused by the arrival of a cold front late in the afternoon of Black Saturday created a “horror situation”. 

“That’s the worst situation you can have,” Dr Tolhurst said. 

Although cold fronts can bring cooler conditions, bushfires burn just as intensely for a number of hours after their arrival. The change in wind direction to a southerly or south-westerly will “blow out” the eastern flank of any fire burning at the time, pushing it in a new direction on a much wider front. 

The size of the new fire front and the speed it travels will “catch people out”, Dr Tolhurst said. 

He said 80 per cent of the damaged caused by bushfires in Victoria occurred after the arrival of a cold front and change in wind direction. Dr Tolhurst said the Black Saturday fires produced huge convection columns and pillars of smoke that made them burn more intensely. 

The convection columns caused air to be sucked into the fires at ground level, creating localised cyclonic winds of up to 120kph and snapping trees off three or four metres above the ground. Higher winds created by fires could carry smoke and embers in a direction different from the prevailing wind that was driving the main fire front. This meant spot fires could occur not just ahead of the main front, but off the fire’s flank. On Black Saturday spot fires occurred up to a record 35 kilometres (21 miles) ahead of the main fire, Dr Tolhurst said. 

It also made it difficult attempt to judge whether a fire was coming towards you by looking at the direction the smoke was blowing. Someone in the path of the fire could be “in the clear” in terms of seeing smoke. 

 

From The Australian:

THE climatic conditions leading to the Black Saturday bushfires were so extreme that fuel reduction would not have made any difference, a leading scientist has said.

David Karoly, from the School of Earth Sciences at Melbourne University, told a seminar last night the climatic conditions experienced in Victoria on February 7 were unprecedented, with temperatures so high the soil caught on fire.

Professor Karoly said the devastated area northeast of Melbourne had experienced a 12-year drought before the fires, which had already reduced the fuel load. “But fuel reduction burning would have made no difference. The fires would have been uncontrollable with minimal amounts of fuel.”

He said the fire was so intense that bare soil burnt in some places, and there were reports of the humus in ploughed ground burning.

“We had record high temperatures, a record heatwave two weeks earlier and record low rainfall. We also had record low humidity,” he said.

The previous three years had been so dry the region had effectively missed one year’s rain. The area was also experiencing an unprecedented sequence of days without rain.

“The preceding heatwave from the 28th to the 30th of January, when Melbourne had three days above 43C, was also unprecedented,” Professor Karoly said. “That heatwave would have kiln-dried everything.”

On the McArthur fire danger index, Black Friday 1939 was rated 100. Ash Wednesday in 1983 was rated 120, but in southern Victoria on February 7 this year there were unprecedented ratings of between 120 and 190.

The unprecedented climatic conditions of February 7 also showed up the shortcomings of bushfire modelling.

Kevin Tolhurst, from the School of Land and Environment at the University of Melbourne, said: “One of the things that has been shown to us with the February 7 case is our understanding of the propagation of wildfire is not well-described.”

He told the seminar that while they predicted the extent of the fire “pretty well” using their models, “it is the mechanism of how they get there that is not well understood”.

He said that information was imperative for everything from planning the design of houses to the decisions people make on whether to leave or stay and fight a bushfire.

Dr Tolhurst said fire modelling had been two-dimensional, but fire was a three-dimensional process. “The way the fire interacts with the atmospheric conditions isn’t currently accounted for in an adequate way in our fire behaviour models.”

 

From The Australian:

The Victorian Government was repeatedly warned of potentially fatal problems with its “stay or go” bushfire policy, including that people planning to go would not leave early enough and that those preparing to defend their homes were badly informed and ill-prepared.

Even the Country Fire Authority’s own research before Black Saturday showed a “significant proportion” of people in bushfire-prone areas had not adequately planned how to respond to a fire.

Problems with the stay or go policy, which encourages people to stay and defend their properties or leave early on days of increased threat, will be a prime focus of the Victorian bushfires royal commission.

Counsel assisting the commission, Jack Rush QC, has flagged that forced evacuations in areas considered indefensible might have to replace the policy after it apparently failed on February 7 when 173 people were killed.

Mr Rush told the opening of the inquiry on Monday that the stay or go policy was potentially confusing and open to misunderstanding.

An inquiry into bushfire preparedness by Victoria’s auditor-general warned that many people in fire-prone areas were poorly informed about risks, had dangerous misconceptions and were not ready to face a bushfire.

“A significant number of residents in wildfire-prone areas have not undertaken essential preparedness steps, have potentially dangerous knowledge gaps about fire behaviour and are planning inappropriate survival strategies,” the auditor-general concluded.

The inquiry found CFA advice to residents planning to go that they should leave before 10am on days of high fire danger was being widely ignored, with fewer than 5per cent saying they planned to leave that early. About 25 per cent of residents said they would wait until told to leave by emergency services, despite the fact that emergency services did not give such warnings during bushfires.

“If residents are relying on emergency services to tell them when to evacuate, this could be a fatal misunderstanding,” the auditor-general warned.

The report handed to the government in 2003 also found that in some areas many residents “held incorrect beliefs or knowledge that may lead them to make household survival plans that could place them in danger”.

Research commissioned by the CFA before the 2007-08 fire season found 56 per cent of residents wrongly believed a fire truck would be there to defend their homes and 51 per cent thought a firefighting aircraft would come to their aid.

Those “unrealistic” beliefs persisted, despite the CFA giving public warnings that it could not guarantee such help.