If there was magesium in this fire, I think it is long burnt. It produces an incredibly bright light which isn't showing. You guys are right... it is hard to extinguish. It yanks the O2 right out of water to burn and produces free hydrogen which will burn explosively when ignited in air. There was a large plant here in Peterboro which used to cast magnesium for outboard motors, chainsaws and snowmobiles. Fires were quite common and they had their own fire crew. They had some sort of special sand that they covered it in to put it out, (so the story goes). They also used a lot of Acetone and other super inflamables. When the wind blew in the right direnction it smelled like a glue sniffers convention. Their insurance agent must have been a basket case. The factory is now vacant and the land worth less than zero because a lot of these solvents are in the soil.