Two or three issues, at least, w/ burn scars -- discoloration from smoke & ash, discoloration & baking/firing of playa silt/clay from the heat, and leaving ash and other materials as trace.
Sheet metal or silica cloth prevent smoke & ash from contacting the playa, but should be overlaid w/ sand or dirt, layers of sheet metal separated w/ air space, maybe w/ noncombustible insulation of some sort. Or a metal pan kicked off the ground at least six inches.
Here's the proper link on the main website. Look for the art installation guidelines.