You can put out a fire with nothing more than sound—and it doesn't even have to be eardrum-deadening, Marty McFly-flattening loud sound. This is Darpa's sonic fire extinguisher, and it sounds kinda like a foghorn.
The extinguisher was developed to fight fires in small spaces, like plane cockpits or ship holds. It uses speakers on either side of a liquid fuel flame. (It's not clear the decibel level or frequency of sound required.) Here's how Wired explains the demonstration:
The team arranged two speakers either side of a liquid fuel flame to demonstrate how fire can be controlled by amping up an acoustic field. The sound increases air velocity, which then thins the area of the flame where combustion occurs, known as the flame boundary. Once the boundary area is thinned, the flame is easier to extinguish. At the same time, the acoustics are disturbing the pool of fuel and creating higher fuel vaporisation - this widens the flame, thinning it out so it is less concentrated and cool enough to extinguish.
Pretty awesome. Here's looking forward to the day your surround sound system doubles as your fire extinguisher. [Wired]