The equivalent distances relevant for zoning are given by the dimensions and building development of the controlled area of the CI processing department. If a sole-use property does not have a fence or similar as a perimeter boundary, the outer walls of the building delimit the controlled area.

A particularly high-risk situation exists if a controlled area around the installation site of a CI processing device does not include at least a sphere radius of 8 m. The handling of such circumstances requires individual consultation, detailed examination and case-by-case decision by the BSI.

A rarer case, for which an equivalent free space attenuation of 1000 m or more must exist (e.g. bunker, shielding enclosure), would lead to a declaration as "Zone 3".

An important aspect that is easily overlooked is the routing of metallic cables in the building infrastructure. Electromagnetic radiation can cross-couple onto cables and propagate there with very low attenuation. For example, power cables, air conditioning ducts, metal pipes (heating, cooling, water, etc.) can act as random conductors and enormously increase the range of compromised emissions. For this reason, there must be sole sovereignty over this infrastructure in the entire control area. If a CI processing agency shares a building with other departments and therefore the area boundaries run within a building, there is no longer complete control over the entire infrastructure. If the requirements of the National Zoning Model for the building infrastructure are not given, it is mandatory to use "Level A" devices in compliance with the minimum distances and installation specifications of the National Zoning Model or to use devices for zones 1, 2 or 3 in a shielding enclosure with filtering of all outgoing lines (power, data, etc.) that meets the technical requirements of the National Zoning Model for the corresponding building zone.