We know that hot, dry and windy weather increases the risk of fires starting, but here’s what we know about what actually provides the spark.

The nine categories of bushfire ignition

Fire investigators have nine categories for the ignition sources of fires:

Smoking: Smoking isn’t as common a source of bushfire ignition as we might think. There have to be some really specific conditions for a flicked cigarette to spark a fire — temperatures generally need to be above 27°, and humidity below 22%. And the cigarette needs to land in a loose fuel bed, and at a quite specific angle, according to Richard Woods, who runs Wildfire Investigations and Analysis consultancy. Fires that start by the roadside are more likely to be ignited by burning pieces of carbon ejected from car exhausts than a cigarette butt, said Mr Woods, who is also an adjunct lecturer in wildfire investigations at Charles Sturt University. However, he warned that we’re currently facing weather conditions in which a cigarette could cause a fire, and we need to take every precaution we can to avoid providing a spark.

Burning off/debris: Burning off is a regular source of bushfire ignition.

Arson: The motivations for why people commit arson are varied and complex, but arson is behind a large number of bushfires.

Railway cause: Railway has its own category, as trains are a surprisingly common source of bushfires. Brake failure in trains can throw out a wall of sparks, sometimes igniting dry vegetation along the side of the tracks and across significant distances. Burning carbon embers thrown from train engine exhausts can also start bushfires.

Campfires: Embers from campfires, and campfires that aren’t properly extinguished are a bushfire hazard. Many popular campsites have moved away from open campfires, and provide fire rings to contain embers.

Equipment use: Chainsaws, angle grinders, mowers, etc. Using grinders or welding equipment outdoors is not permitted during a fire ban because of the sparks they throw.

Children: Children are also categorised separately, as they are often implicated in starting fires, but usually they’re considered to be out of curiosity rather than malice.

Lightning: It’s the most common ignition source in remote areas, but not all lighting is equally likely to start a fire, according to Mr Woods. “Positively charged lightning is far more likely to start a fire,” he said. “Positive charges only make up about 10 per cent of lightning strikes.” “In the recent fires of northern New South Wales and Queensland, it was reported that there was a big lightning band that went through the area.”

Miscellaneous: Power lines, firearms, blasting, glass refraction, electric fences, and more. Electric fences and power lines are also common sources of ignition, but glass refraction — where sunlight is concentrated through a discarded glass bottle — is so rare it’s almost a myth.

Army exercises: If army exercises turn out to be the culprit in the Gold Coast fire last week, it won’t be the first time, “There’s a case in New South Wales which occurred in 2013 that was known as the State Mine fire. What happened there was that they were doing controlled explosion of ordnance that caused a fire that then escaped.” according to Mr Woods.


Source: https://www.abc.net.au/news/science/2019-11-20/bushfire-ignition-source-how-we-know/11701132

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