Functional Safety Assessment- FSA 1,2,3 as per IEC-61511
Functional Safety Assessment- FSA 1,2,3 as per IEC-61511
IEC-61511 Part 1 Clause 5.2.6 talks about Functional Safety Assessment
The standard calls for a procedure through which functional safety and safety integrity for each SIF can be evaluated. Actions laid out in the procedure should be executed by a multi disciplinary team consisting of technology, application and operation.
FSA Team should consist of following:
a) Stage 1,2,3- Senior Competent person not involved in Project Design
b) Stage 4,5 - Senior Competent person not involved in Operation and Maintenance
FSA Stage1:
It is a crucial step to ensure that any mistakes made early in the lifecycle do not result in an inadequate Safety Instrumented System (SIS).
Typically, in this stage the hazard risk analysis is evaluated and confirmed along with the HAZOP or LOPA reports. The SRS document is able to cross check every single SIF description in comparison with the IEC61511 chapter 10 requirements.
FSA Stage2:
This is critical for ensuring that the design meets all process safety requirements before implementation begins
Once the SIS has been built by the system integrator/manufacturer, then stage 2 of FSA shall be carried before shipping the SIS to the end user. Stage 2 FSA is executed during or along with the Factory Acceptance Test (FAT) as a witness test that all of SIF and SIS content as per SRS have been built correctly and tested. Typically, in stage 2, SIF design requirements, SIL target estimation, SRS requirements, safety PLC configuration, and application program functionality are evaluated and confirmed.
FSA Stage 3:
Stage 3 occurs after the installation, pre-commissioning, and validation of the SIS, as well as the development of operation and maintenance procedures. This stage ensures everything is tested and functional before the hazard is present, often marking the handover from the engineering
team to the plant owner/operator. This is often carried out with PSSR.
FSA Stage 4:
Stage 4 FSA, which is also mandatory, is conducted after gaining operational and maintenance experience. It verifies that the assumptions made during the design phase are correct, such as hazard frequencies and equipment failure rates, ensuring that the SIS continues to function effectively.
After gaining experiences in the operations and maintenance phase, a periodic FSA (stage 4) shall be carried to ensure that activities are being carried out according to the assumptions made during design, and that IEC 61511 requirements for safety management and verification are being met. The frequency for periodic FSA is often driven by regional regulatory authorities but is typically anything between 1 - 3 years. Typically, proof tests, SIF requests, and field-detected failures data are evaluated and validated.
FSA Stage 5:
Stage 5 FSA occurs after modifications to the SIS and prior to its decommissioning. Though not mandatory, it is essential for ensuring modifications are correctly implemented. This stage may involve combining assessments from Stages 1, 2, and 3, depending on the modification's scope.
FSA stage 5 includes a modification activity that shall not begin until a FSA is completed and after proper authorization. Once the modification activity is completed, another FSA stage 5 shall be carried out again to assess and confirm that the requested modification is meeting safety integrity requirements. The authorized Management of Change (MOC) procedure has been followed ensuring safety status and functional safety. Concurrently, as-built documentation is updated.