Verification & Validation

Another step in the safeguarding cycle is verification and validation (in fact these are two, closely related steps). Verification mathematically ensures the engineered safety function meets or exceeds the level of risk faced (PLachieved >= PLrequired) by documented the Probably of Failure per Hour to dangerous (PFHd) (expressed exponentially). The analysis must be done by a knowledgeable person in functional safety (preferably certified) who is third party to the design engineer. Typically, this is performed near or at the end of the engineering phase of a project.

Part of this analysis results in a validation checklist which identifies the expected reaction of the safety related part of the control system (SRP/CS) under demand conditions (i.e. Safe state of actuators based on input element conditions). Additionally, faults are injected into the SRP/CS to ensure the fail-safe nature of the design has been achieved in the installation. This documentation and procedure then become part of the user's periodic maintenance of the safety system.