The first fire is relatively small and is intended to dry out some of the moisture in the clay/earth around the kiln remaining after construction and before winter. After cooling and cleaning it out, a “floor” is created above the steel floor slats using thin boards and brown charcoal from previous charcoal runs. Then the wood (mostly Pine) is split and stacked vertically from back to front leaving only a small airspace at the top. The front will be filled with kindling and bark and then the opening closed up and mostly sealed before lighting. Controlling the air intake slows down the burn and prevents loss/crumbling/cracking of charcoal wood. read more about the kiln and making charcoal.