A rational, analytical approach to a fire engineering design of load-bearing steel structures is described. The method of design is directly based on the natural compartment fire concept and on strictly defined functional requirements and performance criteria. The method is permitted to be generally applied in Sweden , as one alternative, since about ten years. For facilitating the practical application, a comprehensive design basis has been worked out in the form of diagrams and tables for a direct determination of the maximum steel temperature during a complete compartment fire and the corresponding design loadbearing capacity of the fire exposed structure. The design basis is presented in a manual which has been given type approval for practical use by the National Swedish Board of Physical Planning and Building.