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An Explosive Way to Fight Bushfires

Explosives have been used to extinguish oil well fires, and now the method is being investigated for bushfires that are out of control. The process is not dissimilar to blowing out a candle: it relies on a blast of air to knock a flame off its fuel source.

Dr Graham Doig of the University of NSW travelled to a high-explosives and bomb test site in a remote part of New Mexico to scale up tests he originally conducted at the University’s heat transfer and aerodynamics laboratory.

The New Mexico tests used a 4-metre steel blast tube – which contained a cardboard cylinder wrapped in detonation cord – to produce a concentrated shockwave and rush of air. This was directed at a metre-high flame fuelled by a propane burner.

“The sudden change in pressure across the shockwave, and then the impulse of the airflow behind it, pushed the flame straight off the fuel source,” Doig says. “As soon as the flame doesn’t have access to fuel anymore, it stops burning.”

Doig hopes the concept can now be scaled up to fight out-of-control forest and bushfires burning in remote parts of the world. He wants to test if it is possible to blow flames out of treetops and knock any loose, dry material in the trees that is fuelling the fire to the forest floor, where it will burn more slowly, if at all.

“Fire is very fast-moving if it gets up into the tree tops. If the fire is still smouldering or burning on the forest floor, it’s moving at a fraction of the speed, giving emergency services extra time to come in with water bombing or ground operations,” Doig says.

Doig speculates that the explosive charge could be carried into place by a helicopter before being unleashed on the fire.