US military agency uses sound to put out fires
The US Defense Advanced Research Projects Agency (Darpa) is investigating ways to put out fires using sound.
Fires in enclosed spaces such as warships, ground vehicles and cockpits, are a big problem for the military.
Rather than use the age-old theory that water puts out fire, Darpa came to the problem with a fresh perspective - physics.
Despite successful laboratory tests, the team admitted they were unsure how it could be applied in the real world.
Darpa launched the Instant Fire Suppression (IFS) programme to look at radical new approaches to firefighting back in 2008.
Last year, researchers began experimenting.
"From a physics perspective, flames are cold plasmas. Darpa theorised that by using physics techniques rather than combustion chemistry, it might be possible to manipulate and extinguish flames," the agency explained on its information page.
Two approaches were selected - using electromagnetics and acoustics to suppress a flame.
One of the technologies explored was a hand-held electrode to suppress small methane gas and liquid fuel fires.
In another experiment the team of researchers used speakers to blast sound at specific frequencies that extinguish the flame.
"The acoustic field increases the air velocity. As the velocity goes up, the flame boundary layer, where combustion occurs, thins, making it easier to disrupt the flame," the website explained.
Although researchers succeeded in putting out small flames using both electric and acoustic techniques in the laboratory, it was not clear how to adapt these approaches to real-world applications.
Matthew Goodman, Darpa programme manager, said: "We have shown that the physics of combustion still has surprises in store for us. Perhaps these results will spur new ideas and applications in combustion research."