US military fights fire with electricity and sound
Traditional fire fighting techniques have relied on dousing flames with water or chemicals. But in an effort to fight fires in combat environments, DARPA has developed a groundbreaking technique where flames can be extinguished by using electricity and sound. But while the proof of concept has been established, the real challenge will be in bringing it to the real world.
The Pentagon has good reason to be concerned about fires. Back in 2008, a fire aboard the aircraft carrier USS George Washington burned for 12 hours and caused about $70 million in damage. The incident resulted in the founding of DARPA's Instant Fire Suppression (IFS) program with the stated goal of learning to better understand the fundamental properties of fire in order to transform the ways it can be extinguished.
A major revelation came in the way that the researchers framed the very nature of fire. According to physicists, flames are actually a cold plasma. This realization led DARPA to theorize that applied physics — not chemistry — could help them come up with a novel way of putting out fires.
And this is exactly what happened. By looking at the electromagnetic and acoustic nature of fire, the DARPA researchers were able to devise two different schemes for flame suppression — one that involved the application of electrons, and one with sound.
By using a handheld electrode, the DARPA scientists were able to suppress small methane gas and liquid fuel fires. The method works by creating an oscillating field that induces a rapid series of jets that displace the combustion zone from the fuel source. In other words, the electric field creates an "ionic wind" that blows out the flame.
And in the second experiment (see video in banner above), flames were extinguished by an acoustic field that was generated by speakers on either side of the pool of fuel. This resulted in two different effects. First, the sound waves increased the air velocity which thinned the flame boundary area, making it easier to disrupt the flame. And second, the acoustic fields disturbed the pool surface, causing the flames to widen and decrease in temperature. Essentially, the flame is extinguished as the same amount of heat is spread over a larger area — the speakers are blasting sounds at specific frequencies that extinguish the flame.
Now, while this looks great in the lab, translating these techniques to actual fire-fighting scenarios could prove to be difficult. DARPA's research indicates that these techniques will work well for small fires. Perhaps these systems could be used in small engines or other mechanisms where fires start out small. But as for whether we'll be able to douse a raging fire with electrons and sound — that's an open question at this point.
By George Dvorsky / io9.com
