Crikey spoke to Andrew Sullivan from the department of Fire Behaviour & Management at CSIRO Sustainable Ecosystems about the Victorian bushfires:

What combination of factors made these fires so lethal?

There are several factors that affect fire behavior. Wind speed is the primary factor. The temperature and dryness of the air are the other factors. They affect what’s called the moisture of the fuel, that’s how much moisture is in twigs, bark and leaves.

The lower the moisture content, the easier it is for the fuel to ignite and burn. So under the very, very dry conditions that were occurring across Victoria, the fuel was very dry and could burn very quickly. Once it ignites, the wind spreads the fire across the landscape.

On Saturday you had a situation that hadn’t really occurred before in the history of Victoria, where you had winds and temperatures after an extended hot spell.

Given that the authorities had an idea of how bad the conditions were going to be on Saturday, should there have been a blanket order to evacuate rather than the traditional CFA advice to decide early to stay and defend your house, or leave?

The whole stay or go policy is based on the proviso that people have prepared their house or property and the knowledge that it will protect them in a fire and they can then get out of the house and put any spot fires out.

The ‘leave early’ policy is so you don’t get caught in the smoke, or run the risk of being caught in the smoke, to avoid the danger of running off the road. Getting caught on the road in a bushfire is one of the scariest things you can imagine, you can’t see, and the smoke is so thick and dark the headlights don’t work. And a car is nowhere near as good a refuge as being in a house in a fire.

Given the ferocity and speed of these fires, does this change the rule book on residents deciding whether to stay or go?

It’s hard to say, not being familiar with the precise situation.

I don’t know that it will change the rules about the ‘stay or go’ advice. The question is how long you have to decide. Usually you leave in the morning, when you know it will be a bad day, and then you’re not anywhere near the fire. But if those fires started in the afternoon then that makes it more difficult for people. You may not then have the time to go or evacuate so you have to spend more time preparing.

…But it does take a long time for a house to burn down, much longer than it takes for the fire to go past. That’s the proviso that the stay and defend policy is based on. The fire will come at the house quickly but then pass quickly. So for ten to fifteen minutes you shelter in the house, and in that time the house won’t burn down. It may start, but you should be able to put it out or at the very least, get out and watch it burn down.

How do you prepare for that kind of fire?

Make sure areas around the house are free of fuel, turning out gutters, ensuring that garden beds are nowhere near the house, that there’s a fuel-free path out of the house.

Kinglake reminded me very much of the Canberra fire, where there were green trees next to houses that had burnt to the ground. Which suggests the houses kept burning after the fire passed.

There were the same sort of conditions in Canberra. Extremely dry. In Canberra the fires came into suburban areas and then spread through the gardens to the houses, through mulch beds, through the side and back wooden fences.

Were the current fire alert systems adequate for these kinds of fires, on this kind of day?

There are systems that are in place to predict fire danger… and that’s the roadside signs that you see. People knew it was going to be a bad day. So the aim of systems like total fire bans is to reduce the number of total ignitions of bushfires on bad days. Because once they start it’s extremely hard to stop the fire spreading, there’s probably nothing you can do really.

People will have to do some analysis on what led these people to be on the roads at such a late time.

How is it that the public continue to be caught unawares, and that tragic mistakes such as people being caught on the road continue to be repeated?

I don’t know. That’s one question that puzzles me at the moment. In this day and age people shouldn’t die in fires.

Can we expect more of these kinds of fires in the future?

The research that’s been done suggests that the current incidents of extreme weather conditions will increase under climate change, it’s possible, we don’t know how exactly, but it is possible.

Peter Fray

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