Earth, wind and fire

THE Black Saturday fires created 120 km/h winds, snapping trees in half. They created their own weather, triggering storm clouds and lightning strikes that started more fires. They fuelled flames that leaped 100 metres into the air and fireballs that barrelled ahead of a front and landed with explosive force in farmers’ paddocks.
And they fed on their own fury and destructiveness. The fiercer they became, the more strength they drew from the heat, wind and energy they had spawned.
The science behind them has been explained by fire behaviour expert Kevin Tolhurst in evidence to the Bushfires Royal Commission and in a report he produced for the inquiry on the physical nature of the fires that day.
Dr Tolhurst is senior lecturer in fire ecology and management at Melbourne University. He says the Black Saturday fires were unique in three ways: the speed of ignition, the intensity of the flames and the way they spread in ”pulses”, with prolific spotting up to 35 kilometres ahead of a front.
The Black Saturday fires were similar to previous Victorian fires in that they were at their worst following the cool change late in the day. The drop in temperature brings relief to baking cities but the associated change in wind direction can mean horror in country areas.
Cool changes ”turn the flank (side) of a long and narrow, cigar-shaped fire, driven by strong northerly winds, into a fire front several kilometres wide”, Dr Tolhurst says. ”Typically, about 80 per cent of the total area burnt occurs after this wind change.”
When five firefighters died at Linton in 1998 it was because a cold front turned a seemingly benign fire with flames less than half a metre high into a blaze with flames 10 metres high, he says.
On Black Saturday much of the bush was dried out from more than a decade of drought and 11 days of temperatures over 30 degrees. This meant it was easier for embers to bring fuel, such as bark or leaves, to kindling temperature of about 300 degrees.
They did not have to smoulder for long periods to dry the fuel because the fuel was already desiccated. Dr Tolhurst says the speed with which embers ignited spot fires was unique to February 7.
Even mountain ash and rainforest areas, usually moist, had been dried out.
”Normally you wouldn’t have a chance of trying to ignite or burn those areas . . . (but they) are the areas where the greatest fuel accumulation occurs so when they do burn, they burn with great intensity.”
A fire burning fiercely interacts with fuel, air, its own spot fires and the energy it produces to create a self-sustaining system. The more it consumes, the more it can consume.
The fires that day also set a record for spotting distance, due to the prevailing winds and the winds and heat the fires created.
The Kilmore fire on Black Saturday developed a smoke plume about 5200 metres from the ground and a huge white pyrocumulus cloud 8500 metres off the ground.
The plume acts like someone sucking on a straw, Dr Tolhurst says. As air rises into the plume, more air is drawn into its base. This vacuuming effect pulls on the thousands of surrounding spot fires, encouraging the burning areas to come together and form a whole, and drives the direction of the fire front. The formation of the pyrocumulus cloud adds further heat to the smoke column and reinforces the updraft of air.
If the atmosphere is unstable, it is easier for a parcel of warm air to rise. Thunderstorms develop in unstable atmospheres because warm moist air rises readily and forms thunderclouds.
Late on Black Saturday, pyrocumulus clouds developed into a fire-induced thunderstorm that produced lightning strikes and small fires in Melbourne’s water catchment forests, including the Upper Yarra and Britannia Creek catchments.
Bushfires create their own winds when air is whipped into the convection column at ground level.
”In the 2003 fires in Canberra, we saw the fire tornado that was a result of that convective effect,” Dr Tolhurst says. ”In the fires here on February 7 we saw trees snapped off – down at the Bunyip Ridge fire, for example, where the winds would have had to have been in the vicinity of 120 km/h or more.”
Fire whirls, balls, flares and willy-willies of flame are moving air filled with combustible gases, ”and the quickest way for these to rise is to actually spin in the same way as a tornado or willy-willy would rise by spinning. When it has got combustible gases in it, we get a fire whirl.”
A lot of people on Black Saturday saw ”fair dinkum fire flares or fire balls”, he says.
”The fuels were so dry and the temperatures were so high, the rate at which the volatile gases were given off was much quicker than normal, if you like, and so the likelihood of getting black smoke and these parcels of unburnt volatiles moving through the air is much greater.”
Those parcels of gases need to mix with air to ignite and often travel long distances through the fire zone before igniting when they hit fresh air at the edge of it. ”You only need to go down to Southbank to see the gas flares in front of the casino there. It is the same phenomenon. We see it separated from the source, and it won’t last, but it is there.”
Many people have described the noise of the fires that day as being like the rumble of dozens of freight trains or the roar of hundreds of jet engines.
That noise is not heard until the front is upon you, says Dr Tolhurst. Video of Marysville just before the fire showed it still and quiet, with hardly a flutter of leaves in the trees, because prevailing winds and the winds of the bushfire cancelled each other out. ”Often as the fire is approaching things will go calm,” he says.
Many things make up the roar of the fire front: ”One is just the strong winds associated with the fire, with updraughts and so on, so that you get the thrashing of leaves and twigs and branches and other material. You don’t even need much wind. The fire actually bursts the cells of the plants . . . the crackling of the cells as they explode with the heat from the fire is quite deafening.”
The Black Saturday fires burnt out 300,000 hectares and produced flames that leaped 100 metres in the air and had temperatures of up to 1200 degrees . ”The energy of the fires was equivalent to more than 1500 atomic bombs the size of the one used at Hiroshima . . . but bushfires release their energy in a ‘storm’, not a ‘blast’,” he says.
”The total amount of heat released from the fires on Black Saturday would have been sufficient to provide the total energy needs for all Victorian domestic and industrial use for a year. This energy was released in just a few hours.”
Dr Tolhurst told the commission the fires that day showed up holes in scientific knowledge and, therefore, in the advice given to the community.
Video around one fire observation tower showed severe flames for an hour and strong radiant heat for five hours in total. Dr Tolhurst says this phenomenon of ”areas of fire” that burn for long periods has not been studied adequately and is not reflected in fire advice that tells people they can shelter briefly in houses while a fire front passes quickly over.
Areas of massive spot fires that can burn for hours, rather than a passing front, are not captured well in scientific models or in training, he says.
”If a fire is only travelling at a maximum of five or 12 km/h per hour, why do so many kangaroos get killed, because they can travel much quicker than five or 10 kilometres an hour? It’s because they basically get surrounded by fire; they get engulfed in an area of fire. So we need to actually change our conceptual framework and follow that up with research that fits that pattern.”
1 Directly under the smoke plume and driven by a northerly wind: This is the fastest and most intense phase. The fire burns out relatively quickly but could still last for an hour. This kind of blaze destroyed Humevale and Strathewen.
2 To the left (or east) of the left-hand flank: This kind of fire will affect an area for a long period of time. The area could be struck by firebrands coming from high up in the air and travelling long distances. Running fires could go on for two hours or more but the process is more gradual, and its intermittent nature may leave people confused or disoriented. This kind of fire attacked Kinglake and Pheasant Creek.
3 After the wind change: The long flank (side) of the fire turns and becomes the front. There is a massive release of embers and spotting is prolific.
Areas that were previously in clear air will fill with smoke with little warning. Spotting may occur five kilometres ahead of a front that is now 20 kilometres long. The danger of getting caught, surrounded by fire, is very high. This happened in Marysville, Buxton and Flowerdale.
A million microscopic particles can enter your body in a single breath. The tinier the particles, the greater the threat they pose. A human hair is 70 microns wide.
15 MICRONS AND LARGER Half of particulates inhaled lodge in the mouth, nose and throat.
Possible effects Dryness, irritation, inflammation, chronic runny nose, nasal and throat cancers.
5-15 MICRONS Particles are deposited in trachea, pharynx and air passages in lungs.
Possible effects Breathing difficulties, cough, aggravation of existing heart and lung disease, influenza, bronchitis, lesions and lung cancer.
5 MICRONS AND LESS Tiniest particles penetrate the alveoli where lungs perform gas exchange. Some are removed by cells called macrophages; many will remain permanently.
Possible effects Pneumonia, emphysema, reduced blood and oxygen flow, loss of macrophages and alveoli.
2.57pm DSE spotter Colin Hind at Mt Despair tower sees start of fire at Murrindindi mill. Phones regional district officer at Broadford DSE.
3.06pm Operations manager and crews arrive about 3.30pm.
3.30pm Mt Gordon spotter Andy Willans tries to call Marysville CFA captain Glen Fiske to warn him town under threat. Cannot get through.
Calls local Pauline Harrow instead.
3.45pm Alert message issued that fire burning in Murrindindi area and moving S/E direction.
4.30pm Andy Willans reports spotting in Narbethong.
4.45pm First urgent threat message for Narbethong issued by DSE (crossposted on CFA website 10 minutes later.
4.47pmWarning announced on ABC.
5pm DSE air observer flies over blaze and says there is fire “all around Narbethong”.
5.27pm Urgent threat message issued for Marysville. “The communities of Narbethong, Marysville and Buxton can expect to come under direct attack from this fire. Healesville residents are advised to remain on high alert.”
5.34pm ABC broadcasts threat message for Marysville.
5.45pm – 6pm Map predicting fire would hit Marysville produced in the IECC.
6.20pm Spot fire in Marysville (before main fire).
6.30pm South-westerly wind change hits, Narbethong and Marysville spot fires merge.
7pm DSE office on fire (partially destroyed).
Fire contained by 6pm, March 5 2009
11.49am Kilmore East fire reported to CFA.
12.33pm Infrared “linescan” of fire area taken by aircraft.
12.40pm Awareness warning for Wandong and Clonbinane.
2.25pm Alert message for Wandong.
2.40pm Urgent threat message for Wandong.
3.05pm Urgent threat messsage for Hidden Valley 3.18pm First time a threat to Kinglake is mentioned on radio. “Kay” from Kinglake calls 774 ABC and reports smoke in the sky, believing it is from a fire at Kilmore. “If I didn’t know about those fires I’d say we’re about to be hit by a wall of flames.”
3.53pm Urgent threat messages issued for Whittlesea, Hidden Valley, Heathcote Junction and Upper Plenty.
3.30pm Fire spotting into Pheasant Creek and Strathewen.
4pm-5pm Spotting starts in St Andrews.
4.01pm 774 ABC broadcasts urgent threat message for Whittlesea and Hidden Valley.
4.10pm Kilmore ICC drafts an urgent threat message warning for Clonbinane, Mt Disappointment, Kinglake, Heathcote Junction, Upper Plenty, Humevale, Reedy Creek, Strath Creek.
4.24pm Seymour RECC asked to distribute the Kilmore message through its fax due to problems with communications.
4.24pm 774 ABC radio reports fire is south of Kinglake escarpment.
4.35pm Alex Caughey at Seymour RECC sends out the Kilmore urgent threat message to IECC and others (message inexplicably goes missing, never appears online).
4.35pm Urgent threat message issued by CFA for areas including Whittlesea, Humevale, Arthurs Creek, Nutfield, Eden Park and Doreen.
4.43pm CFA spokesman mentions Kinglake is under threat in an ABC radio interview. First official threat warning on ABC about Kinglake.
5.20pm Kilmore incident controller Stuart Kreltszheim asks for urgent threat message stating communities from Kinglake to Flowerdale will be directly affected to be issued (Kinglake West, Pheasant Creek, Wandong, Wallan, Humevale, Kinglake, Glenburn, Flowerdale). Strathewen never mentioned.
5.35pm Map predicting fire spread produced at IECC based on 12.33pm linescan. Predicts that by 9pm fire could hit Kinglake, Pheasant Creek, St Andrews and Smith Gully to Diamond Creek.
5.40pm Kinglake-Flowerdale urgent threat message sent.
5.50pm Kinglake-Flowerdale message “reviewed” 5.55pm Urgent threat message for Kinglake and Flowerdale appears on CFA website. First time Kinglake mentioned online.
6pm – 6.30pm Fire hits Kinglake 7.44pm CFA chief officer Russell Rees interviewed on 774 ABC radio.
Says fire is “putting enormous pressure on areas like Kinglake West and Kinglake”.First published in The Age.