How Does a SIF Achieve its SIL Target

For A Safety Instrumented Function (SIF) to achieve its target SIL, the IEC61511 standard requires that it meets three design requirements: PFDavg/PFH, Architectural Constraints and Systematic Capability. Many people consider meeting the PFDavg/PFH target sufficient, but this is not the case. A SIF is an Independent Protection Layer (IPL), which is required to satisfy 4 requirements:

S – must be specifically designed to prevent the consequence of the hazardous event
I – must be completely Independent from all other IPLs
D – must be designed to have sufficient defense against random and systematic failures
A – must be auditable in terms of being able to be tested and maintained

Therefore, meeting the random hardware failure dependability is the PFDavg/PFH and meeting the systematic failure dependability is the Systematic capability. The architectural constraint requirement is required to counteract any unrealist parameters used in the PFDavg/PFH calculations and determines the level of Hardware Fault Tolerance (HFT) required.

The webinar examines what’s involved with determining the PFDavg/PFH and the 9 key variables associated with this, as well as the importance of tracking Useful Life, and how to determine the HFT using the tables in IEC61508 or the table in IEC61511. It also looks at equipment qualification for the SIF and the use of IEC61508 certified devices or Prior Use justification to meet the systematic requirements.

What you will learn?
• What is involved with determining the SIL achieved by the SIF
• The importance of meeting the 3 design requirements
• How to meet the systematic requirement
• How to justify use of the equipment

#FunctionalSafety #ProcessSafety #SIL #IEC61511 #SIS #PriorUseJustification #SystematicCapability #PlantSafety #exida #IPL #ProofTesting

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