Inaudible sound could be the next frontier in wildfire defense

Ten years ago, two students built a fire extinguisher capable of putting out a fire using nothing more than a booming 10-inch subwoofer. The Internet took advantage and Jimmy Fallon even booked a demonstration for “The Tonight Show.”

But since that brief viral moment, there have been nothing but rumors about the technology.

It’s not for lack of trying. College students weren’t the first to prove the concept. DARPA was on the case in 2012; and a search of the scientific literature reveals that dozens of researchers are studying this idea.

A startup now claims to have solved the problem. Sonic Fire Tech has built an acoustic fire suppression system that not only extinguishes flames, but can also protect homes and other buildings from wildfires. The startup has raised a $3.5 million seed round from investors including Khosla Ventures and Third Sphere, TechCrunch has learned exclusively.

Wildfires cost the United States up to $424 billion annually. The problem has become so acute in places like California that insurers are refusing to renew insurance policies after repeated fires reduced large swaths of the state to ashes.

Sonic Fire Tech has been developing its technology for several years. Michael Thomas, chairman of the startup’s board of directors, had been mulling over the idea of ​​using sound to fight fires, and when he hit a wall, he contacted Geoff Bruder via LinkedIn. Bruder had worked for NASA, where he focused on heat and acoustics.

“It’s kind of a new-age founding story,” Bruder, the startup’s CEO and CTO, told TechCrunch.

Bruder was intrigued by Thomas’ idea and set about building a prototype. “I bought a subwoofer and a few parts from Home Depot and AutoZone and said, ‘Hey, let’s see if we can do it better than others,'” Bruder recalls. “We put out a fire seven feet up in my driveway.”

The startup quickly ditched the subwoofer and moved to lower frequencies. The problem with audible frequencies is that any system loud enough to put out a fire would harm people’s hearing, Bruder said. “Basically, you have to throw a model of speaker in the trash and start from scratch,” he said.

There are competing theories about how acoustic energy can disrupt combustion, but the silent demonstrations certainly suggest Sonic Fire Tech is right.

The new system uses a reciprocating piston similar to that of a car engine, but it is significantly larger. An electric motor turns a crankshaft, which vibrates the two-foot piston to produce infrasound, the technical term for sounds below people’s hearing range, or about 20 Hz.

“Since we designed everything ourselves, we lowered the frequency to where we are below the audible range, which helps us transmit further and make it safe,” Bruder said.

Sonic Fire Tech’s current record is 25 feet. A larger system could operate up to 330 feet, Bruder said. The company plans to sell and install its system for about 2 percent of a home’s value, and it is in discussions with insurance companies to qualify the technology.

To protect a home, Sonic Fire Tech routes infrasound from a single generator through rigid conduits located at the roof ridge and under the eaves. On the ridge, they fire into the terrain to catch fires that might start in the debris in the gutters. Under the eaves, they are directed towards the ground to smother any flames that arise near the walls. The system turns on when sensors detect a flame.

A home system uses about 500 watts of electricity, and in the event of a power outage, Sonic Fire Tech plans to use lead-acid batteries as a backup battery. Unlike sprinkler systems, it does not require a water source, which can be scarce during wildfires.

The startup is working with PG&E and Southern California Edison to demonstrate the technology on homes and has signed a letter of intent with a chemical storage facility.

“The natural progression is if we get certified as a sprinkler replacement, then you can just put a hose in your house and protect your kitchen and anywhere else you would need to protect,” Bruder said.