Occult House rules:

"Squares marked as Orange are considered to be 'Hellfire' Terrain. Hellfire terrain is treated as one elevation lower than surrounding terrain. Characters who begin their turn occupying a square of Hellfire terrain take 1 click of unavoidable damage, unless they possess either the 'Mystical' or 'Monster' keyword. Damage caused by Hellfire damage cannot result in a KO."

Pretty straight forward.