Campfires are permitted at Black Rock but they must not be made directly on the surface of the playa. The standard fire container is the tub from a washing machine supported on bricks.
Fires on the surface will bake the clay in the soil like pottery and form a hard patch that does not weather the same as the rest of the desert.
Do not dump your ashes, charcoal and half burned wood on the playa, take it with you as trash and dispose of properly. If you just dump it it leaves a black area the BLM does not like and we have to clean it up. Plan ahead and bring a container that can hold the hot ashes.