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Fighting fire with explosives

Fighting fire with explosives
A flame is blown off its fuel source with a blast of air from explosives
A flame is blown off its fuel source with a blast of air from explosives
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A flame is blown off its fuel source with a blast of air from explosives
A flame is blown off its fuel source with a blast of air from 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.

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.

Source: UNSW

Fighting bushfires with explosives - clip 1

Fighting bushfires with explosives - clip 2

Mel Tisdale
With the setup as shown in the videos and the situation with an oil well, i.e. a fixed pipe at the seat of the fire, one can clearly set the distance between the point of detonation of the blast and the fire so that the remnants of the blast do not re-ignite the flame. This is clearly shown at the end of the videos. However, with an ill-defined and rapidly changing situation, such as that associated with a bush fire, I imagine that stopping the tail-end of the blast from reigniting the fire must be very difficult to manage successfully.
One has also to consider the fact that in the videos and with oil well fires the seat of the fire is in a metal structure. Like the top of a Bunsen burner this will not be very hot. With a bush fire, there will be countless glowing embers that will be refreshed by the inflow of air that always follows a blast.
I think using machine guns to create fire breaks would work better.
Daniel Gregory
Fight Fire with Fire.
Jay Finke
Ok lets throw more hot air on a fire. now I can see this has a use but it's kind of limited. what works good is cool air and fine mist of water.
Stephen N Russell
Use mortars, RPGs to fire TNT into fires or 105mm howitzers with modified shells. Awesome. Or use flame thrower to redirect flames away from homes??
Looks like the shock wave killed the fire before the air-blast even arrived. Why not dispense with the air-blast entirely - one or two directed shock-waves alone should be all that's needed?
The energy of shock waves dissipate quickly as a function of radius from center of explosion. In the video, the shock cannon muzzle is very close to the fire. I'd be surprised that the cannon will do anything to the fire if the distance between the muzzle and the fire were doubled. Once the shock has dissipated, the trailing vortex ring will likely do little but fan the existing fire with fresh oxygen.
I'd think this technique would be worth trying to knock down a tornado.