1. A system comprising: a processor communicatively coupled to a memory; a model library stored in the memory and configured to model a safety system, wherein the model library comprises a plurality of subsystem models, and each of the plurality of subsystem models is configured to derive a reliability measure; a fault tolerance input; a maintenance policy input; and a dynamic risk calculation engine (DRCE) configured to be executed by the processor and configured to: use a user-defined set of the plurality of subsystem models, the fault tolerance input, and the maintenance policy input, to derive a system risk for an apparatus, wherein the system risk comprises an average probability of failure on demand (PFD); determine if an N-step ahead estimate of the average PFD exceeds a risk reduction factor (RRF), and if the N-step ahead estimate exceeds the RRF, then to command a proof test.