Safety Integrity Levels, Standards and Risk Measures

This figure shows the relationship of DIN V 19250 classes and SILs (safety integrity levels).

Figure: Standards and Risk Measures

As a required SIL increases, SIS integrity increases as measured by:

• System availability (expressed as a percentage)
• Average probability of failure to perform design function on demand (PFDavg)
• Risk reduction factor (RRF, reciprocal of PFDavg)

Reference: Triconex