exida Services - Functional Safety for the Process Industries


Functional Safety Assessments

A Functional Safety Assessment (FSA) is defined as an investigation, based on evidence, to judge the functional safety achieved by one or more SIS and/or other protection layers. exida has become recognized as the global leader in functional safety certifications with a strong global acceptance and a growing base of technology. In addition, exida is ANSI accredited to ISO/IEC 17065, the general requirements for bodies operating product certification systems.

exida functional safety assessors have for many years performed numerous Functional Safety Assessments with scopes ranging from small skids and turbomachinery to complete plants. In many cases, the exida FSA report is the proof our customers need to satisfy local authorities with regard to the functional safety achieved. The exida FSAs are a combination of procedural and evidence documentation review and an in person physical inspection. exida’s tool based approach ensures comprehensive, efficient, and timely results.

Using a third party independent assessor removes bias and ensures an honest assessment of the state of your functional safety standard compliance. Our customers praise us for our thoroughness, knowledge, and real life practical understanding.

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The IEC 61511 functional safety standard defines 5 Functional Safety Assessment Stages:

Stage 1

The Stage 1 FSA, is defined to occur after the Hazard and Risk Assessment has been carried out, the required protection layers have been identified and the SRS has been developed. Thought this Stage 1 FSA is not mandatory per the IEC 61511 standard, it occurs at and important place in the Safety Lifecycle, namely after the hazards have been identified and the need for Safety Instrumented Functions has been defined. Any mistakes in the early phases in the lifecycle will have an in adequate Safety Instrumented System as result.

Stage 2

The Stage 2 FSA, is defined to occur after the SIS has been designed, so after the conceptual design is completed. The Stage 2 FSA is not mandatory per the IEC 61511 standard; however, it occurs at and important place in the Safety Lifecycle, namely after the SIS is designed but before the implementation of the SIS is initiated. Ensuring your conceptual SIS design is meeting the requirements as defined in the process safety requirements specification and that the design 

Stage 3

The Stage 3 FSA, is defined to occur after the installation, pre-commissioning and final validation of the SIS has been completed and operation and maintenance procedures have been developed. The Stage 3 FSA is mandatory per the IEC 61511 standard. Simply said at this stage in the functional safety lifecycle you want to make sure that everything is in place, tested, and functional prior to the hazard being present. For many projects this represents the handover between engineering contractor and owner/operator of the plant.

Stage 4

The Stage 4 FSA, is defined to occur after gaining experience in operating and maintenance. The Stage 4 FSA is mandatory per the IEC 61511 standard. The objective of this FSA is to ensure that the assumptions made during the analysis and design phases of the safety lifecycle are correct, i.e. are the hazard demand frequencies as estimated, are the SIF equipment failure rates as predicted, are the various layers of protection as effective as assumed, etc. In addition this is a good time to review if the assumed proof test frequencies during the conceptual design are maintained and if all test results are adequately documented. 

Stage 5

The Stage 5 FSA, is defined to occur after modification and prior to decommissioning of a SIS. Thought this Stage 5 FSA is not mandatory per the IEC 61511 standard, it is essential to make sure that modifications are implemented correctly. Strictly speaking if one would follow the safety lifecycle, a modification would trigger a stage 1, 2, or 3 FSA, however depending on the size of the change, one could argue that combining all 3 into a single assessment as suggested by the Stage 5 FSA is more practical. Part of the Stage 5 FSA, is the review of operational experience (Stage 4) as well as impact analysis documenting the required modification.