Fighting fire with explosives
Building on a technique commonly used to extinguish oil well fires, Dr Graham Doig from the University of New South Wales' School of Mechanical and Manufacturing Engineering is examining whether explosives could be used to fight out-of-control forest and bushfires by blasting the flames out of treetops, slowing the fire and making it easier to fight on the ground.
The technique, which is akin to blowing out a candle, has long been used to extinguish oil well fires. This was pioneered by Myron M. Kinley, who while still in his teens helped his father, Karl T. Kinley, use dynamite to extinguish a fire resulting from an oil well blowout in 1913. Myron then further developed the technique and trained others, including Red Adair.
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Doig is conducting research to examine whether knocking a flame off its fuel source with a concentrated shockwave and blast of air from explosives could be adapted to fighting bushfires. With funding from UNSW and an American Australian Association Fellowship, Doig traveled to the Energetic Materials Research Testing Center in New Mexico.
At the high-explosives and bomb test site he was able to scale up tests he had previously carried out at UNSW. This involved the use of a 4-m (13-ft) steel blast tube containing a cardboard cylinder wrapped in detonation cord. This apparatus was used to produce a concentrated shockwave and rush of air that was directed at a 1 m (3.3 ft) high flame fueled 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," said Doig. "As soon as the flame doesn't have access to fuel anymore, it stops burning."
Doig now wants to test whether the technique could be used to blow flames out of treetops while at the same time knocking any loose, dry material to the forest floor, where it would burn more slowly and be easier to fight by conventional means.
"Fire is very fast moving if it gets up into the tree tops. If the fire is still smoldering 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," said Doig."We're thinking of this as being a potential way to stop a fast uncontrolled fire in its tracks and give you a lot more time to get things under control or evacuate people that are downwind of the blaze."
A potential way to implement the technology proposed by Doig is to use helicopters to carry the explosive charges into place before being detached. This would allow the charges to be delivered to locations that would be otherwise difficult to reach.
High speed video, taken at 20,000 frames per second, of the steel blast tube test can be viewed below. The second video uses a cut-off filter to make the explosive blast more visible.