How can sound put out a fire?

Ángela Karime Hernández Venegas, a student at CETis 78 in Altamira, Mexico, built a fire extinguisher with no water, no foam and no chemicals: a battery, a frequency generator set to 30 Hz, an amplifier and a speaker, aimed through a bucket. In October 2026 it won gold at the International Science and Invention Fair in Indonesia. It sounds like a low hum. So how does a sound put out a fire?

▶ Try it yourself in Sound Extinguisher Lab: change the pitch and the sound level, and watch the speaker’s push grow until the flame tears and goes out.

It isn’t the sound

A sound wave doesn’t carry air along. Each bit of air just shuffles back and forth as the wave passes, and not by much: at 99 dB and 60 Hz, about a hundredth of a millimetre. A flame doesn’t notice that. What it does notice is the air right in front of the speaker, which the cone shoves back and forth like a piston. Xiong, Wang and Huang measured both at a candle flame in 2021: at 100 dB the sound wave moved the air at about a centimetre per second, while the cone’s own wind reached about half a metre per second, and it was the wind that put the flame out. A tube in front of the speaker strengthened that wind and made the flame easier to put out.

About three millimetres

In a second experiment the same group held small propane flames 10 cm in front of a big speaker and played 50 to 70 Hz. The flame swung back and forth with the air, and it blew out when that swing reached about 3 mm, the same however the sound was made, and a little more for taller flames. Shaking the flame stretches the thin sheet where fuel meets air; stretch it far enough and it tears.

Half the pitch, four times the push

To make the same sound level, a speaker playing a low note has to move much more air with each stroke: for a compact speaker, the air it moves goes as one over the pitch squared. Halve the pitch and the push goes up four times. At 30 Hz the same sound level shoves about 1,100 times as much air as at 1,000 Hz. In the tool, which is calibrated to the 60 Hz lab test, a flame that needs 99 dB at 60 Hz needs only about 87 dB at 30 Hz, and would need about 148 dB at 1,000 Hz, far louder than any ordinary speaker. That is why these extinguishers hum instead of squeal. George Mason University students found the same in 2015: 30 to 60 Hz worked, high frequencies didn’t.

A puff, not a hose

VortexTech sends each push out of a bucket as a vortex ring, a spinning doughnut of air that holds together a little longer than a plain puff. Its maker says the rings cut the fire off from its oxygen, and her team reports more than 100 tests on small fires, including wood, flammable liquid and cooking oil. But a ring is still a puff. It spreads out within a short distance, and it doesn’t soak or cool the fuel the way water does, so a fire can come back. Acoustic extinguishers work on small fires, up close; they don’t replace a conventional extinguisher.

The tool is a model calibrated to one lab test, not a model of VortexTech, and it was measured only between 50 and 70 Hz. The film uses short excerpts of Ángela Hernández’s own videos (Karime vortex on YouTube), a woofer by barevids and a 2015 demonstration by George Mason University, credited on screen; the speaker, air, flame and numbers are drawn from the model.

Sources: C. Xiong et al., “Fluctuation and extinction of laminar diffusion flame induced by external acoustic wave and source”, Scientific Reports 11, 14402 (2021), nature.com; C. Xiong, Z. Wang and X. Huang, “Acoustic flame extinction by the sound wave or speaker-induced wind?”, Fire Safety Journal 126, 103479 (2021), doi; Tamaulipas Secretaría de Educación, ISIF 2026 gold medal; N+, Vortex Tech: cómo funciona el extintor acústico; Mexico News Daily, A Tamaulipas teen built a fire extinguisher that puts out flames using sound; TechXplore, George Mason University students’ sound-wave extinguisher (2015).