DARPA uses sound to extinguish fires

US government agency DARPA (Defense Advanced Research Projects Agency) has developed a new “Instant Fire Suppression” system that is designed to put out flames in confined spaces using a “wall of sound”. Two speakers were placed either side of a liquid fuel flame to show that it can be doused by an increase in the acoustic field and, therefore, the air velocity. This has the effect of thinning the air around the area of the flame where combustion occurs – the flame boundary. At the same time, the change in the acoustic field is affecting the fuel, creating higher vaporisation. This widens the flame, thinning it out so it is less concentrated and cool enough to extinguish. And the good news is, the system doesn’t rely on the sound being loud to extinguish the flame. DARPA has spent two years researching the composition and chemistry of cold plasma. In the video immediately above, using a wand-like electrode device housed in ceramic glass and electronic field is created that emits an “ionic wind” that “displaces the combustion zone from the fuel source” which bends flames. This might seem like merely a stunt, but it will allow anybody caught in a fire in an enclosed space to dodge past the flames to make an escape. The system also prevents fires from spreading, localising them and making them easier to control. Now, DARPA just needs to reproduce these success stories on a much larger, and more practical scale.