Gizmdo had a really cool blog post about how DARPA is building a sonic fire extinguisher. It has a pretty cool video about how the sound waves thin out the fire to the point where it put itself out. A lot of cool science going into how this happens. My best guess is that fires require a certain air : fuel ratio which the sound waves distort. Once that balance is fucked with, the fire puts itself out in a matter of seconds. There are other variables to consider as well. I believe the articles talks about how the sound waves fuck with how the liquid fuel is dispersed as well. This is a neat idea but like the blog post said, best used for confined space where environment cannot be a factor. This also seems to only work for liquid fuel where as a chemical fire or material fuel fire might not be affected... Either way, cool to watch and good to know.

Source: http://gizmodo.com/5925828/watch-a-machine-put-out-a-fire-with-sound