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The Importance of Functional Safety Assessment and its Application
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Eventually, the design of the safety system will need to satisfy the requirements as identified within
the SRS. This will need to consider all the assumptions made during the hazard and risk analysis
phase. Therefore, an FSA will need to be performed after the safety system is designed so as to
ensure that functional safety is not compromised. This is identified by the stage S2 in
Figure: 2Note also that any design, development and production tools used during any phase of the SIS safety
lifecycle shall also be subject to an independent FSA.
When the safety systems are installed, commissioned and validated against the requirements of the
SRS, such activities are again subject to an FSA as this is the stage after which the system is put into
operation. Any risk reduction measures implemented will now need to be reviewed and assessed for
ensuring all the functional safety requirements are met. This is identified by the stage S3 in
Figure: 2Once the safety system is in the operation and maintenance phase, then periodic FSAs are required
to be performed so as to confirm that the safety system is operated and maintained based on the
identified assumptions and credited layers of protection defined during the hazard and risk
assessment phase. This is defined by stage S4, as identified in
Figure: 2.
Any modifications arising out of efficiency improvements or process modifications, will be subject to a
formal FSA prior to implementing the solution.
Stage 5, as identified in
Figure: 2,ensures that full or part decommissioning of the safety system
does not compromise on functional safety and that the activity does not create any additional plant
hazards.
FSAs are therefore implemented not only during the early development of the Greenfield project
execution, but should be undertaken as part of the conventional management and technical reviews
throughout the entire life of the operating plant.
5. Responsibilities and Intended Users
Functional Safety Assessment is primarily the responsibility of the Asset Owners who are accountable
for maintaining the license for operation of the plant. The safety standards do not provide detailed
guidance on who are responsible for the FSAs, however, it mandates that FSAs shall be undertaken
by organisations who are responsible for the respective lifecycle phase deliveries.
As the Asset Owners are ultimately responsible for the entire safety lifecycle associated with their
process plants, the onus of ensuring that the FSAs are performed during all lifecycle phases across
the entire supply chain resides with them.
Organisations responsible for the respective phases of the safety lifecycle are subject to the ‘stage
FSAs’. These shall typically cover, but is not limited to the following:
v
Hazard & risk assessment
v
SRS development
v
Suppliers of safety devices, safety instrumented systems and their sub-suppliers
v
Installation
v
Commissioning
v
Validation
v
Operations
v
Maintenance
v
Modification & Implementation
v
Decommissioning