Section 18.2.5 states “[T]he elimination of all accidental causes to reach a conclusion that a fire was incendiary is a finding that can rarely be justified scientifically, using only physical data; however, the elimination of all causes other than the application of an open flame is a finding that may be justified in limited circumstances, where the area of origin is clearly defined and all other potential heat sources at the area of origin can be examined and credibly eliminated.” (Emphasis added.)