Due to the internal complexity, the human intent and the large physical distribution of a facility, a classification of the vulnerability of a facility or a distributed system to Intentional EMI based exclusively on shielding effectiveness is inadequate. This latter concept is more suitable for enclosures. Also, the hardening of such facilities against IEMI requires a correspondence between the electromagnetic zone boundary and physical access control boundary. Therefore a method, based on three key terms; Accessibility, Susceptibility and Consequence, is proposed here. Also, examples of how this method could be implemented are given here.