In May 2008, a fire on board the USS George Washington aircraft carrier burned for 12 hours and caused around $70 million in damage. Thirty seven sailors were injured, but thankfully there were no fatalities. For almost half a century there have been no new methods for extinguishing or controlling outbreaks of fire. And so, in 2008 DARPA launched the Instant Fire Suppression (IFS) program.
This program sought to assess the feasibility of using novel flame-suppression approaches to extinguish unwanted flames. This began with an investigation into the fundamentals of fire, and understanding the effects of various flame suppression techniques.
Most normal fire-suppression methods (like the age-old bucket of water method) are targeted at one or more of the key ingredients in any fire. Removing fuel, heat or oxygen is good enough to defeat even the fiercest blaze. A fire simply cannot exist without all three of these components. This approach views a fire as a chemical reaction, and simply looks to alter the available components. The problem with these normal fire-suppression technologies is that they can be slow to use and extremely difficult in confined or obstructed spaces. This led DARPA to view the problem differently.
In the IFS program, DARPA has shifted focus and approached the fire-suppression problem from a physics standpoint. From this perspective flames are seen as cold plasmas, which DARPA theorized could be manipulated and controlled.
After investigation and narrowing down from a range of possibilities, DARPA selected two methods of flame suppression to take forwards and look into further. They noticed potential in the use of electromagnetics and acoustics in flame suppression.
Below is a video of the acoustic approach in action. Here, a lit pool of fuel is placed between two speakers. As sound waves at specific frequencies are generated, they interact with the fire in two different ways. Firstly, the acoustic waves increase the velocity of the air. This has the effect of thinning the flame boundary layer, which makes disruption of the flame easier. Secondly, the acoustic waves interacting with the surface of the fuel leads to a higher rate of vaporization. This widens the flame, spreading out its energy and reducing the overall temperature. These two effects in combination result in the flame being extinguished.
As you can see from the video, these techniques are effective in suppressing small flames, although the work is by no means complete. It isn’t yet clear how these techniques can be effectively scaled up to be useful in real world scenarios. The results so far have been promising though, and steps towards the future of fire suppression have definitely been made.
Matthew Goodman, DARPA program 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.”
With further research and innovation in fire-suppression technologies, perhaps it won’t be too long before dangerous fires like the one which blazed on board the USS George Washington are a thing of the past.