In wildfire terminology, the black is the area the fire has already burned through. This area may contain some-still smoldering debris, but for the most part it is free of any fuels. For this reason, the black is the best place to be if a fire gets a little too crazy. The problem is... it's generally on the other side of the fire and hard to get to. But if you're threatened by a fire and can get to the black without putting yourself in danger, its probably a good idea. Otherwise, its time to deploy your fire shelter and hope for the best