To enable the description of safety-related software, the Unified Modeling Language is provided with well proven constructs as found, e.g., in corresponding subsets of the real-time programming language PEARL and in Function Block Di- agrams according to IEC 61131-3. These constructs are ordered in nested sets to fulfill the respective requirements of the four Safety Integrity Levels of IEC 61508. By adding to UML safety elements oriented at the prevailing safety standards, UML can be employed to design dependability structures for safety-critical systems. The safety elements are described in UML notations, and collected in a profile which can be incorporated into models of safety-related embedded real-time control systems.