The calibrated risk graph method is a semi-quantitative method for determining the required SIL for safety instrumented functions (IEC 61511-3, Annex D). Its basis is a graphical decision chart where, in addition to Demand Rate W and Consequence parameter C, additional factors F (exposure time) and P (probability of avoiding the hazardous event) enable ‚order-of-magnitude‘ steps to define the final SIL.
The standard does not quantify demand rate and consequence, therefore parameters W1, 2, 3 and CA, B, C, D must be ‚calibrated‘ in line with Client risk acceptance criteria. Consequence criteria are defined for personal safety, environmental damage and asset loss. The calibrated risk graph method generally results in more a conservative SIL-selection than the LOPA method.