Firefighters use water or chemicals to put out fires, but two engineering students at George Mason University have shown that it’s possible to extinguish a blaze using nothing but sound. Seth Robertson and Viet Tran built a device that looks like a traditional fire extinguisher connected to a power unit the size of a small messenger bag, that uses booming bass notes to snuff out flames.
The video shows Mr. Robertson aiming the extinguisher at a small fire lit in a kitchen skillet. As the device emits a low hum, the flames waver briefly and almost immediately vanish – no water, chemicals, or foam needed.
How does it work? As music notes get deeper, the amount of air required to produce them increases. That’s why bass guitarists need big speakers to amplify the notes their instruments create. A deep tone is essentially a blast of air, and the deep hum created by Robertson’s and Mr. Tran’s invention is essentially a regular series of these blasts. The flames are extinguished just as if somebody blew them out.
Why not simply blow out a blaze using an air compressor or similar device instead of employing an audible hum? It turns out that sound waves displace oxygen in a particular way, depriving fire of the air it needs to survive. Robertson and Tran found that a tones at higher frequencies caused flames to vibrate, but that deeper tones in the range of 30 to 60 hertz kept flames from getting oxygen.
The Defense Advanced Research Projects Agency (DARPA) built a similar device in 2012, but didn’t pursue the idea of extinguishing fire with sound. DARPA’s device is large and unwieldy, while Robertson’s and Tran’s is portable. It consists of an amplifier and a loudspeaker positioned at one end of a cardboard tube, which allows the user to point the sound waves in a certain direction. George Mason University is helping the two students secure a provisional patent for their device.
Would a fire extinguisher that uses sound be useful in everyday situations? Robertson and Tran think it could be used in households – perhaps mounted over a stove to automatically extinguish grease fires. Robertson also speculated to CNN that astronauts could use the device to put out blazes in space. Sound waves aren’t affected by gravity, he says, so they could be directed at a fire more easily than conventional chemicals.
The students still need to do more testing to see whether their device works on different types of fires, and whether it can keep a blaze from spontaneously reigniting. They’ve already begun working to secure a provisional patent on the unconventional extinguisher.