Trust NASA to figure this one out: how to start a fire with water. Astronauts onboard the International Space Station are now in the second round of experiments designed to shed light on this counter-intuitive but very real process, and the implications are significant.
The key in using water to start a fire is that the water isn’t regular drinking water. It’s supercritical water, a state that’s hard to achieve but has some really interesting properties. To become supercritical, water has to be compressed to 217 atmospheres and heated to above 703 °F. At that temperature and pressure, water ceases to be a liquid and becomes something between a liquid and a gas, a sort of superdense gas. Add organic material to that supercritical water and the immediate chemical reaction is oxidation, which is basically a fire without flames.
Supercritical water could be a fantastic tool in getting rid of unpleasant organic materials like sewage since human waste contains a fair amount of water. Hicks explains that when a stream of wet waste is pushed above the supercritical point, the supercritical water breaks its hydrocarbon bonds and reacts with oxygen. In short, the compressed and heated sewage ignites, burning cleanly and producing water and carbon dioxide as byproducts instead of the typical toxic products of an ordinary fire.