Experiments from the past two centuries have shown the effects of sound on fire. In 2012, the U.S. Defense Advanced Research Projects Agency (DARPA) illustrated how noise from a large sound generator was used to extinguish a flame. Now, two students at George Mason University are applying the power of sound waves via a handheld sound generator to put out fires, with an eye toward eliminating the inconvenience of fire extinguishers and improving fire safety.
After a year of testing to see how fire responds to noise, electrical and mechanical engineering majors Viet Tran and Seth Robertson found the frequency range that would disrupt the oxygen flow necessary to fuel a fire. Between 30 and 60 Hz, a relatively low frequency range, the waves push the air molecules and oxygen molecules away from the fire at a rate that does not allow oxygen to fuel the fire any longer. In order to work, the frequency must remain constant, or else the fire will fluctuate and is less likely to extinguish.
Watch the students in action, in a video curated by Engineering TV, below:
After determining the right frequency, the students needed to design a sound-wave extinguisher that was small and safe enough for use in households. The prototype consisted of an amplifier powered with a small power source, connected to a frequency generator. They made a collimator out of a hollow cardboard tube to direct the sound waves at the fire.
Since only ethanol-fueled fire was tested, the handheld noise fire extinguisher still needs to be tested on fires started from other sources. If successful, it could revolutionize household fire safety, potentially end messes caused by fire extinguishers and water damage, and decrease risks for firefighters. Because of the high speed and far reach of sound waves, a large sound-generating device could also be set up on forest fire perimeters to improve forest-fire control.