Commission hears of bushfire’s ‘scale of fury’

Commission hears of bushfire’s ‘scale of fury’

27 May 2009

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Australia —

This week Victorians learned possibly more than they wanted to know about the disaster that befell them on Black Saturday.

With the evidence of fire behaviour specialist Dr Kevin Tolhurst, the commission uncovered excruciating new details of the precise scale of the fury unleashed on ordinary people.

Dr Tolhurst told the commission the February 7 fires released as much energy as 1,500 atomic bombs – enough to power the state of Victoria for a year.

“It is an enormous amount of energy and it is not surprising that it actually affects local weather conditions and has such destructive force,” he said.

The flames burned as hot as 1,200 degrees Celsius. Wet mountain ash forests that normally would not even support a flame were burning downhill, at night, with flames a metre high.

For the first time the commission saw video footage recorded by a camera mounted on a fire tower in the Yarra Valley between Healesville and the O’Shannassy Reservoir pointed towards Marysville.

In eerie, grainy tones, a plume of smoke appears in the distance at about 4:45pm.

The plume throws off an increasing number of spot fires that come closer and closer until the tower itself is first shrouded in smoke and then, by 6:15pm, is showered with sprays of burning embers.

Fast moving and super hot

By 6:30pm the smoke is so thick it has blocked out the sun. The south-westerly wind change comes through at 6:35pm and at 6:43pm there are bursts of flame flaring.

Dr Tolhurst pinpoints this as the most intense part of the fire passing the tower and estimates the air at the camera height on the tower would have been 150 degrees – without factoring in the radiant heat.

On Black Saturday the fire is said to have moved at an average speed of eight kilometres an hour.

At its height it covered 12 kilometres an hour. In bursts it could travel 600 metres in half a minute.

The commission heard the fireballs people have described are a real phenomenon. Volatile gases released by vegetation as it heats up burst into flames when they mix with the air.

Dr Tolhurst called for a better understanding of the way fire spreads and, critically, for that understanding to be passed on to the public.

To take the fire tower footage as an example, the blaze arrives as a massive number of spot fires, rather than any continuous fire front.

Dr Tolhurst says it is an important concept for people to understand.

“I think a lot of people sometimes think that it is going to be like a wave moving up on a beach, that it’s just going to come up, go past and continue on,” he said.

“In fact, there is an area of fire that can last for several hours, I don’t think we capture that very well in our models or in our training for people [so they] really expect this ‘area of fire’ rather than a ‘fire front’.

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