Modern technical systems are increasingly built to exhibit self-x properties as, e.g., self-healing or self-optimization. For this, they require adaptation at runtime. This is even true for embedded or mechatronic systems which often operate in safety-critical environments. There, the effects of the adaptation with respect to safety must be analyzed carefully. However, not all parameters needed for safety analyses, e.g., the concrete system architecture, are known at design time. Consequently, safety analyses need to be executed during runtime. Current approaches of runtime safety analysis typically react to anomalies that already occurred in the system. Thus, unsafe system states cannot be excluded completely. We present a runtime safety analysis that prevents system states with an unacceptable risk that have not yet occurred. For this, we generate the reachable component structures at runtime and analyze them with respect to risk. The system is modified such that component structures with an unacceptable risk are not reachable any more and are thus prevented.