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Fighting Fire with Sound

Many “out of the box” ideas have been put forward to stop wildfires. As with any invention, they have drawbacks. That frequently means they are dismissed as not worthy of further consideration. Wildfire Breakthrough challenges this thinking. It is possible that one of these ideas could make a major difference in fighting wildfires. It is further possible that two of these ideas combined could actually provide fire fighters with a way of stopping wildfires when all else has failed. One example of what could be termed a wild idea is the use of sound waves

Scientists have long known that sound waves can extinguish flames but have struggled to explain exactly how. Sound is the result of an object vibrating (usually in air), the vibration travels through the air like 3600 ripples in a pond, pushing air forward as it goes. However, this is distinct from air moving forward as wind, which would serve to feed a fire rather than suppress it. In 2012, DARPA (Defense Advanced Research Projects Agency) demonstrated how flames can be suppressed using acoustics and offered up an explanation as to why. According to DARPA: “Two dynamics are at play in this approach. First, the acoustic field increases the air velocity. As the velocity goes up, the flame boundary layer, where combustion occurs, thins, making it easier to disrupt the flame. Second, by disturbing the pool surface, the acoustic field leads to higher fuel vaporization, which widens the flame, but also drops the overall flame temperature. As the same amount of heat is spread over a larger area, combustion is disrupted.”

Using sound to fight fire could deliver significant advantages. Sound can be created anywhere (except in a vacuum) and, crucially, it can be produced continuously, meaning that in particularly arid areas, sound could be used to combat fire. Moreover, sound could be controlled in such a way that it would not damage property or the environment.

Controlling the sound is key to the success of its use in firefighting. You wouldn’t just blast fire with deafeningly loud heavy metal and hope the flames retreat in fear. And the lab conditions created by DARPA were a far cry from any practical application. In 2015, two students at George Mason University in Virginia looked to have found the answer. As part of a research project, they discovered (through trial and error) that low frequency sound (or bass) yielded particularly impressive results. The sonic gun device they created is far more portable and less power hungry than the device DARPA used for its 2012 experiment. Clearly, though, there is a huge difference between a proof of concept sonic gun and something that could be used in the field.

This area of research should be included in the search for a solution. It is not beyond the realm of possibility that this technology could be optimised and scaled to fight wildfires. A safe and controllable sound-based solution would be music to the ears of firefighting organizations around the world.

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