This thesis shall examine whether realistic values for the availability of safety-related loops can be mapped for the environment of NAMUR. Therefore, the standard bottom-up methodology is applied on typical safety-related loops installed within NAMUR member companies. The resulting bottom-up benchmark has more theoretical character and thus requires a plausibility check towards reality. For this purpose reliability data of safety-related loops operating in NAMUR member companies are collected. In the subsequent step they serve as input for a top-down benchmark based on field data. Evaluating the bottom-up benchmark by its top-down pendant mirrors large discrepancies. In order to gain more realistic bottom-up results the bottom-up approach is mixed up with the top-down methodology in a kind of hybrid approach. The resulting review for the bottom-up benchmark shows good congruency with the real performance of operating safety-related loops in the NAMUR environment.