Functional Safety Audit and Functional Safety Assessment are both mandatory activities identified within IEC 61511. The standard establishes the recommended safety lifecycle stages for Functional Safety Assessment.
Stage 1 - After the hazard and risk assessment has been carried out, the required protection layers have been identified and the safety requirement specification has been developed.
Stage 2 - After the safety instrumented system has been designed.
Stage 3 - After the installation, pre-commissioning and final validation of the safety instrumented system has been completed and operation and maintenance procedures have been developed.
Stage 4 - After gaining experience in operating and maintenance.
Stage 5 - After modification and prior to decommissioning of a safety instrumented system.
The standard does not specify the timing of the FS Audit, however considering the intended purpose of the FS Audit such activities may take place at any of the completion of any stage of the safety lifecycle, as well as being performed at a fixed multi-year interval during the SIS operational phase.
In addition, planning will need to include consideration that any of the findings & recommendations identified from either audit or assessment can only practicably be incorporated into the system if they are detected early e.g. If an assessment requires to revise a system design, but the plant is already commissioned, it will be very difficult to implement this recommendation due to the timing and cost constraints.
So the project manager and project planner should always seek to consider that the benefits of the audit and assessment process for identifying faults in the system are scheduled and resourced as early as possible and that FS Audits and Assessments are valued as an essential tool for managing the risk impact on project technology non-compliance, cost elevation and schedule delays.