Calibrated Risk Graph

Last updated: October 31, 2017

What Does Calibrated Risk Graph Mean?

The Calibrated Risk Graph Process is a process that is used to determine the safety integrity level for safety instrumented functions. The IEC 61508 standard specifies standard risk graphs, although their description is subjective and suffers from an interpretation problem of risk parameters.

As a way to overcome this, a modified risk graph based on a fuzzy rule-based system is implemented. This updated version of calibrated risk graph relies on fuzzy scales to assess risk parameters, resulting in calibration through varying risk parameter values. The outcomes are numerical values of risk reduction factor and are comparable directly with those given by quantitative and semi-quantitative methods. Semi-quantitative methods used in conjunction with the risk graph process include fault tree analysis (FTA), quantitative risk assessment (QRA), and layers of protection analysis (LOPA)

Safeopedia Explains Calibrated Risk Graph

The Calibrated Risk Graph Process and LOPA methods are commonly used to determine the required Safety Integrity Level for safety instrumented functions. The two remain the most popular methods in comparison to others outlined in the SIS standard for process sector IEC 61511. They are part of occupational risk assessment and identification.

The Calibrated Risk Graph Process determines if a Safety Instrument Function (SIF) is needed to reduce risk to a ‘tolerable’ level. If this is the case, the amount of risk reduction that any identified SIF must achieve, requires a method that is ‘calibrated’ to the risk associated with the said application. The standard BS IEC 61511 for this process sector identifies several methods: risk matrix, risk graph and Layers of Protection Analysis, (LOPA). Calibrated Risk Graph Process is applicable when the functions need to be ‘calibrated’ for that specific application. This is a team-based procedure with identifiable and quantitative parameters.


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