A functional safety assessment (FSA) is an independent investigation, based on evidence, to judge the functional safety achieved by one or more safety instrumented systems (SIS) or safety related electrical control systems (SRECS).
FSA requires an independent person from your project or plant to provide a truly objective judgement. FSA needs someone who is competent with functional safety requirements and has practical experience of projects involving functional safety.
For the 5 stages recommended by IEC 61511 for FSA, the following summary table provides a breakdown of the level of effort and key documents required to complete the FSA activity at the recommended different stages of the safety life-cycle:
# Key Documents
(after PHRA and the SRS has been produced
10 + # Drawings
(after the SIS has been designed)
FSA 1 + 15 + # SIS & SIF FAT RECORDS
(after I&C, validation & O&M manuals have been developed)
FSA 1 + FSA 2 + 10 + # SIS & SIF VALIDATIONS
(after gaining experience in operation and maintenance)
15 to 20 + # SIS & SIF PROOF TEST RECORDS
(after modification and prior to decommissioning)
* The level of effort will depend on the previous FSA stages completed and number of SIS and SIF being validated
** The level of effort may be affected by the age of the installation and available documentation.
*** The effort and required documents are only possible to estimate when the full size and scope of the modification is known.
A functional safety assessment (FSA) will only commence with a sound plan in place. Our typical methodology includes a series of "swim-lane" work processes which show the required steps and responsibilities.
For a new-build or major modification project, our planning will include scoping all the proposed stages of FSA, the required inputs at each stage, and the expected results.
For an FSA of an existing SIS in operation, our plan will show the extent and scope of the assessment to be conducted on the existing system. Any exclusions will be fully clarified at the outset.
For a new-build project we recommend that FSA is started as soon as the first SIL assessment has been completed. This may be before the safety requirements are fully developed, but from experience it is not wise to wait that long.
We use a combination of offline document review and site-based project team interviews to conduct our assessment
When the safety requirements specification is fully available, the FSA 1 activity can be finalised and formal reports can be produced.
Having conducted many FSA projects across chemical sites, oil & gas, power generation and pharmaceutical production, we have developed an extensive standardised protocol and checklist.
The checklist includes several hundred questions which each relate to each IEC 61511 edition 2 requirement. Our independent assessor uses document review and interview questions to elicit an argument that the objective and technical aspects of each requirement are met. This is supported by evidence documents provided by the project or client for FSA review.
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According to IEC 61511 edition 2
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