A decade ago, two college students built a fire extinguisher that snuffed out a fire using nothing more than a booming 10-inch subwoofer. The internet lapped it up, and Jimmy Fallon even booked a demonstration for The Tonight Show. But since that brief viral moment, there has not been much more than a whisper about the technology.
This is not for lack of trying. The college kids were not the first to prove the concept. DARPA was on the case in 2012, and a search of the scientific literature reveals dozens of researchers investigating the idea.
One startup now claims to have cracked the problem. Sonic Fire Tech has built an acoustic fire suppression system that does not just extinguish flames; it might also protect homes and other buildings from wildfires. The startup has raised a 3.5 million dollar seed round from investors, including Khosla Ventures and Third Sphere.
Wildfires cost the United States as much as 424 billion dollars annually. The problem has become so acute in places like California that insurers are refusing to renew policies after repeated blazes have reduced large swathes of the state to ashes.
Sonic Fire Tech has been developing its technology over the last several years. Michael Thomas, who is chairman of the startup’s board, had been tinkering with the idea of using sound to fight fires. When he hit a wall, he reached out to Geoff Bruder over LinkedIn. Bruder had worked for NASA, where he focused on heat and acoustics.
Bruder, the startup’s CEO and CTO, was intrigued with Thomas’s idea and set about building a prototype. He got a subwoofer and some parts from Home Depot and AutoZone to see if they could do any better than other people had. He recalled that they knocked a fire out from seven feet in his driveway.
The startup soon ditched the subwoofer and moved to lower frequencies. The problem with audible frequencies is that any system powerful enough to suppress a fire would be damaging to people’s hearing. Bruder said you have to throw a speaker design in the trash and start from scratch.
There are competing theories as to how exactly acoustic energy can disrupt combustion, but the soundless demonstrations certainly suggest that Sonic Fire Tech is onto something.
The new system uses a reciprocating piston much like those inside a car’s engine, but it is significantly larger. An electric motor turns a crankshaft, which pulses the two-foot piston to produce infrasound. This is the technical term for sound that is below people’s hearing range, or about 20 Hz. Since they designed everything themselves, they dropped the frequency to where it is below the audible range. This helps the sound transmit further and makes it safe.
Sonic Fire Tech’s current record is 25 feet. A bigger system could work as far away as 330 feet. The company plans to sell and install its system for about two percent of a home’s value, and it is talking with insurance companies to qualify the technology.
To protect a house, Sonic Fire Tech routes infrasound from a single generator through rigid ducts that sit on the roof’s ridge and under the eaves. On the ridge, they fire down the pitch to catch any fires that might start in debris in the gutters. Under the eaves, they are aimed toward the ground to suppress any flames that pop up near the walls. The system turns on when sensors detect a flame.
A home-based system draws around 500 watts of electricity. In case of a power outage, Sonic Fire Tech is drawing up plans to use lead-acid batteries for backup. Unlike sprinkler systems, it does not require a source of water, which can be in short supply in wildfire country.
The startup is working with PG&E and Southern California Edison to demonstrate the technology on homes, and it has signed a letter of intent with a chemical storage facility. The natural progression is that if the system gets certified as a sprinkler replacement, then you could just run a pipe into your house and protect your kitchen and everywhere you would need to protect.