Determining and verifying the safety integrity level of the control and protection systems under uncertainty

This concept of risk reduction is illustrated in Figure 2. The relative risk reduction (for the consequence N = const) is evaluated from the formula rF = Rt/Rnp = Ft/Fnp (1) where: Ft-a numerical frequency target (specified for a tolerable risk level); Fnp-the frequency of a hazardous event that could occur without the protective system considered.