Two students at George Mason University have developed a device that can put out a fire using sound. So far they have only tried it on burning rubbing alcohol in a skillet, so the usefulness on solid fuels is still in question.
However, in an article in the Washington Post, they mention forest fires:
Although the students originally envisioned their device as a tool to attack kitchen fires and to eliminate the toxic monoammonium phosphate used in commercial fire extinguishers, they can see more uses: in confined areas in space, or wide areas outdoors, such as forest fires. Not having to use water or foam would be a bonus in many situations.
Kenneth E. Isman, a clinical professor in the University of Maryland’s fire-protection engineering department, was quoted in the article:
The project also would have to address different types of fires — solid combustibles such as wood, paper or metals, or electrical equipment — and keep a fire from reigniting.
“One of the problems with sound waves is that they do not cool the fuel,” Isman said. “So even if you get the fire out, it will rekindle if you don’t either take away the fuel or cool it.”
DARPA has also experimented with suppressing fire using sound. The video below is only nine seconds long.
DARPA summarized their results:
IFS Phase II was completed in December 2011. IFS performers succeeded in demonstrating the ability to suppress, extinguish and manipulate small flames locally using electric and acoustic suppression techniques. However, it was not clear from the research how to effectively scale these approaches to the levels required for defense applications.
Remarking on the overall impact of the IFS program, Matthew Goodman, DARPA program manager, said, “We have shown that the physics of combustion still has surprises in store for us. Perhaps these results will spur new ideas and applications in combustion research.”
We have run across many out-of-the-box ideas for suppressing fires, including, an electric wand, a truck that puts out fires without water, a fire extinguisher bomb, dropping water in containers that when empty weigh 100 pounds, a disposable air tanker, a truck that dispenses dry chemical to suppress wildfires, a shoulder-fired rocket that launches a fire hose and nozzle into a structure, and suppressing a fire with directional explosives.
Meanwhile, wildland firefighters still put out fires with sharpened pieces of metal attached to the end of sticks.