Ran into your reply and it reminded me of a conversation I had with a friend that works as an engineer related to fire. He told me that magnesium burns at 1500 degrees Celcius and the reason it continues to burn in water is that at 1500 degrees it actually separates the oxygen and hydrogen atoms and the hydrogen burns on its own. He said water will eventually extinguish the fire as the water will reduce the temperature below the temperature required to separate the Oxy and Hyd atoms stopping the processs and the burning. He did not recommend a Halon or chemical extinguisher since they do not have the desired cooling effect to stop the magnesium from burning at the high temperature required to create the phenomenon. I am going to run some typical racing extinguishers by him for a recommendation on what to use.