When the use of water, CO2 or spray-foam is as potentially as damaging as the flames itself, -how can fire be extinguished? Would you believe that sound waves could do it?
I came across an interesting article in the Acoustical Society of America Digital Library (1) (Sept. 2005) mentioning something I had read about more recently; the ability of focused sound waves of a low frequency to extinguish the flame of a candle.
Fire on a Submarine, Space Station or Capsule in Outer Space
The ability to extinguish a small but potentially deadly fire in a micro-gravity environmentsuch aboard a submarine, or enclosed vessel such as a submerged research vessel, would be a great asset. A on-board fire aboard a space capsule or orbiting space station is of special concern to NASA and other aeronautical agencies.
Spraying the fire with water would put out the flames under any condition, but water in weightlessness is just as hazardous as fire to the lives of astronauts in micro-gravity (zero-G) environments. This is also not to mention the immediate damage to vital computer systems and electrical life-support controls.
The same principles that apply water would also be the same for any kind of ‘foaming’ fire suppressant. The absence of gravity would make floating water or suppression foam debris a genuine hazard to astronauts whom could just as easily drown in floating over-spray.Wikipedia
A Carbon Dioxide (CO2) extinguisher would be nearly as bad of an option as well, as the air quality would be severally compromised and life-threateningly diluted with toxic-to-humans carbon dioxide by just seconds of CO2 extinguisher use in such a closed environment.
Donning spacesuits and ‘blowing the hatches‘ to open space would stymie the flames quite effectively but in a crisis this is equally untenable. Time being a major factor, the loss of any large volume of breathable atmosphere would likely not be limited to just small compartments of any station or craft. Re-pressurization would be a detrimental additional element, compounded to any damage already caused by a systems fire.
In the case of a submarine or submersible, CO2 or foam are the only real options. Letting water in to suppress flames is a definite wrong thing to do under any circumstances!
Something better seems to be the best all-around solution; extinguish the flames using a low-pulse of sound waves!
Flame-Killing Sound Waves
There is a sound frequency that is audible to the human ear that when directed towards a flame such as a candle or perhaps as large as a small accidental fire, will extinguish the flame in just seconds! The sound waves are not depriving the flame of oxygen, and the moving frequencies of sound are not ‘blowing the candle out’ by moving the air.
Scientists are equally mystified by the curious fact that sound can extinguish a flame and are somewhat at a loss to explain exactly why or how this works.
One theory why sound waves might extinguish flames is suggested by the Ideal Gas Law which states that temperature, pressure and volume are inter-related and thus, a decrease in pressure (low-frequency of sound waves) causes a corresponding decrease in temperature which could be what extinguishes the flame. Scientists are not quite sure why this works, or if this is even the reason.
The frequenciesthat seem to be at work are between 40-50 hertz (within the audible range of the human ear) and the sine-wave troughs that alternative between high and low frequency extinguish the flame in seconds.
Experiments to be done on NASA’s C-9B Aircraft (a.k.a. ‘The Vomit Comet‘) were mentioned in the Sept. 2005 article and data collected from these experiments would need to be compared and evaluated against the standard 1-g (Earth-based) environment.
Fire Extinguisher of the Future?
Someday, fire extinguishers may no longer be a matter of Class A, B or C but will be smaller, lightweight and require a set of long-life batteries. Instead of bulky overhead sprinkler systems in buildings, ceilings and walls will contain wafer-thin concealed fire suppression speaker systems producing a ‘brown note‘ for quickly suppressing a house or building fire.
Imagine a world without that no longer needs the standard bulky fire extinguisher. Maybe these fire-suppressing sound systems will be the iPOD app of the future; a FIRE SUPPRESSION program whereby you launch the program (just press the "PLAY" button!) and the handheld device is tossed near the fire and it squelches the flames with waves of low-frequency blasts, saving life and property!
- Cite: (1) Acoustical Society of America Digital Library (article: Sept.2005)