"I throw more power into my voice, and now the flame is extinguished"

Physicist John Tyndall, 1857

There's been a recent breakthrough in fighting fires - using sound waves to extinguish flames. Since 1857, scientists have known that sound waves could put out a flame, but they weren't exactly sure why. There have been many experiments, even by the Department of Defense, that have had mixed results. But two students at George Mason University recently unveiled a portable extinguisher that resembles a small wastebasket. The extinguisher is actually a collimator (a tube that focuses the sound) that contains a sub-woofer and amplifier driven by an audio oscillator. Inventors Seth Robinson and Viet Tran simply aim the device at an alcohol-fueled blaze, and within seconds it's out.

Previous efforts in the lab by other researchers involved bulky containers with several loudspeakers. One research group played Nickleback's "How You Remind Me" through subwoofers until certain bass notes put out a candle. But the SMU engineering majors (since graduated) managed to break the portability barrier and figure out which bass frequencies are effective.

The device is still in the development stage, but efforts to bring it to market are progressing. They see immediate uses in the kitchen, on drones over forest fires, and even in space. The "no mess" snuffer will be a welcome sight in the space station to put out small fires. Because traditional chemical extinguishers spray liquids and gases, the remnants can float around a spacecraft and get into delicate electronic equipment.
So how does it work? Sound waves work by oscillating a medium, such as air or liquid. The wave motion of the sound extinguisher displaces the oxygen that fire needs. In addition, cooler air is brought in during the ebbing part of the wave. This is why you can blow out a candle.

How low does the sound need to be? Robinson and Tran tried ultra-high frequencies, which did vibrate the flame. But they found that frequencies between 30Hz to 60Hz were most effective. As a point of reference, 60Hz is AC electrical hum you might get in an old stereo when something's not plugged in right. You hear 30Hz (and below) coming from those annoying cars with really loud subwoofers. Maybe we shouldn't think of them as an irritating nuisance, but see them as a service to our community. Aren't they really just mobile fire extinguishers? Maybe we could deploy these headbangers to fires. I can see it now – a little red Honda Civic rolling to a fire with tinted windows, a huge spoiler on the back, a dalmatian hanging out the window, and Eminem's "On Fire" thumping from the trunk.

Watch fire being extinguished with sound waves.

Read more about their experiment in The Washington Post and in Physics World.

Did You Know?

• In 1857, John Tyndall of Ireland discovered that sound waves from his voice would put out a candle.
• Tyndall was the first to prove that the earth's atmosphere has a greenhouse effect.
• Tyndall invented a better firefighter respirator, which filtered smoke and noxious gas.
• Tyndall was the first to climb the Weisshorn, a major peak in the Alps.
• SMU's Seth Robinson's and Viet Tran's experimental device cost only $600 to make.
• Their first prototype was only tried on small alcohol-fueled fires.
• Music is not a good sound source to put out fires because of its inconsistency in tones.