The basic assumption for the division of the building into fire zones and the resulting requirements, is to isolate the part of the building affected by the fire, in order to limit the possibility of fire spreading.

For tall and high-rise buildings, the fire zone is a building or a part of it, separated from other parts of the building by means of fire separation, a fire zone should be understood as a space separated in such a way, that the fire does not spread outside or inside the space within a certain period of time. The storey of the building is also a fire zone, where staircases and lift shafts are enclosed, closed with doors with a fire resistance class of at least El 30 and equipped with devices to prevent fuming or to remove smoke. It must be noted, that it does not follow from the above that each storey of the building must be constructed as a separate fire zone.
The area of ​​the fire compartment is calculated as the interior area, measured along the inner contour of the zone's external partitions, at floor level, without reducing the area of ​​the horizontal cross-section of the structure and internal partitions, but with an enlargement by the mezzanine area (if present). Acceptable fire zone area for high and high-rise buildings ZL I, ZL III and ZL V is 2500 m2. In the case of underground storeys, the permissible area of ​​the fire zone is 50% above area, tj. 1250 m2. The exception is the situation, when emergency exits from the underground storeys lead directly outside the building. The permissible area of ​​the basement fire zone is then this, like above-ground storeys.
If there are production rooms in the building, warehouse or technical, not functionally related to the part of the building included in the ZL, these rooms should constitute a separate fire zone. It must be noted, that the question of functional linkage is room-related, and not only to the devices they contain, therefore, the exemption from the obligation to create separate fire zones does not apply to fan rooms or boiler rooms. Solid fuel boiler houses with a total thermal capacity greater than 25 kW or fuel oil with a total heat output greater than 30 kW, they should be separated by internal walls and ceilings with fire resistance class El 60, while the doors or other closures therein – He 30. If these rooms are used as a gas fuel boiler room with a total heat output above 30 kW, solid fuel composition, a slag plant or a fuel oil storage facility, the internal walls and ceilings separating them should have the fire resistance class El 120, while the doors or other closures inside them -El 60. The fire resistance class of external walls in these rooms should be determined in accordance with the general requirements, according to the fire resistance class of the building. The exception is the external partitions of gas-fueled boiler rooms, located above the roof of the building, for which there are no requirements regarding the fire resistance class, provided, that they are made of non-combustible materials.