Skeptical observers have had a good understanding of the the fire walking trick (and that’s all it is) for many years.
It is essential to use low-density coals and to make sure the surface of the individual coals has been mostly converted to ash. Though the coals are very hot, the low density and the insulating effect of the ash combine to ensure that relatively little heat is actually transferred to the walker’s feet during the very brief period of contact during each step. It also helps if the walker’s feet are damp. In woo-woo events, this is usually done by having the marks, er, spiritual graduates, walk through wet grass on the way to the pit.