The present paper describes a rational analytical approach to a fire engineering design of loadbearing structures and partitions. The design method is permitted to be generally applied in Sweden, as one alternative, since about ten years. The method is directly based on the natural fire concept and strictly defined functional requirements and performance criteria. For facilitating the practical application of the design method to steel structures, a comprehensive design basis has been worked out in the form of diagrams and tables for a direct and quick 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 (4), which is approved for practical use by the National Swedish Board of Physical Planning and Building. The paper is organized in such a way that a reader, who only wants to be informed of the practical application of the design method, can limit himself to a study of chapter 3 and the explanatory example. Chapters 1 and 2 are supplementing this description with respect to the general design philosophy behind the design method and the connected structural fire safety characteristics.