Metal fires are very dangerous when hit with water, the molten metal is cooled on the surface and returns to a solid. This surface cooled solid on top of the molten and still burning metal (Magnesium makes its own O2 when burning) traps the presser and allows it to build up, when the crust ruptures the metal sprays with explosive force and goes every where (burning). You don’t want to be there.
In the USAF we used a chemical called metalX to extinguish metal fires. I don't know what they use now that was in the early 80's
