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Engineering students extinguish fire with sound

A pair of engineering students created a new type of fire extinguisher that uses sound waves to put out flames.

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Photo by George Mason University

Imagine if all you needed to put out fire was a subwoofer. It's an idea that has been toyed with, theoretically, over the years -- DARPA demonstrated an acoustic extinguisher in 2012, following prior experiments from other researchers. Now, for the first time, a handheld extinguisher exists that uses not foam, powder or water, but the waves produced by a low-frequency sound.

The prototype extinguisher was developed by computer engineering major Viet Tran and electrical engineering major Seth Robertson of George Mason University in Fairfax, Virginia. The pair hopes their design could revolutionise firefighting, particularly in the home.

The technology is based on the way sound waves displace oxygen as they move through physical space -- oxygen that fire feeds on. If you can suffocate a fire, you can extinguish it, so the pair set to work. They discovered that music is unsuitable -- the sound waves it produces are inconsistent.

A higher frequency sound caused the flames to vibrate, but that was all. The lower frequencies -- 30 to 60 hertz -- seemed to be the so-called "Goldilocks zone" at which the waves were able to effectively keep the oxygen from the flames long enough to suffocate them.

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Photo by Screenshot by Michelle Starr/CNET

The next step was the development of a portable, handheld extinguisher. DARPA's device, for example, was a large machine that can't be easily moved around. The prototype they developed consists of the sound frequency generator, a small amplifier, and a collimator made out of a cardboard tube with a hole at the end, to focus the waves in a specific direction.

This device was able to extinguish small, controlled fires created with an alcohol accelerant, proving that the concept is viable. Of course, the next step is further development -- testing the technique on different types of fires; seeing if it can keep these fires from reigniting, since the sound waves do not have a cooling effect like water does; and examining the feasibility of developing a device that could deal with larger fires.

If they can pull it off, though, it could be great news not just for homes -- the usage for which the extinguisher was originally envisioned -- but for fire departments too. According to the Washington Post, a local fire department has already requested to test the extinguisher on a structure fire.