It’s 2025, and a team of firefighters arrive on the scene of a massive conflagration. There’s trucks and ladders, but also a team of drones tethered to a massive generator. As the drones swarm the flames, they blast a guttural roar that sounds like the unholy offspring of a bullfrog and a lawnmower. Firefighters follow up with hoses and foam, and within minutes, nothing but wisps of smoke are curling up from cooling embers.
That vision of the future could be possible thanks to a small, sound-powered fire extinguisher developed by two college seniors, Viet Tran and Seth Robertson, both at George Mason University in Virginia. Tran was searching for an idea for a class project when he stumbled upon an old DARPA project that used sound waves to put out a small fire. The device was rather large—a person certainly couldn’t hold it. So he and Robertson set out to make it more practical.
Their extinguisher resembles an antique milk can connected to a well-ventilated amp. A bass speaker sits atop the barrel, which amplifies and directs the sound waves. Tom Jackman, reporting for the Washington Post, has more details:
They placed flaming rubbing alcohol next to a large subwoofer and found that it wasn’t necessarily all about that bass, musically speaking, at least. “Music isn’t really good,” Robertson said, “because it doesn’t stay consistent.”
They tried ultra-high frequencies, such as 20,000 or 30,000 hertz, and could see the flames vibrating but not going out. They took it down low, and at the range of 30 to 60 hertz, the fires began to extinguish.
“I honestly didn’t think it would work as well as it did,” Tran said.
The extinguisher works by pulsing air across the base of the flame, the boundary layer at which the combusted material produces the flame itself. The deep sound produces successive blasts of air which disrupt the process of combustion. Eventually, the flame peters out.
The waterless extinguisher could be used in a variety of situations. Tran suggests that they could be installed in kitchen hoods to quickly kill grease fires. Server rooms packed with computers could also benefit. And among fire departments, it’s likely to be combined with other tools available to firefighters, giving them a leg up on the biggest of blazes.
Watch Tran and Robertson's sound-based fire extinguisher in action.
Photo credit: Evan Cantwell/GMU