190 / 1143
d) It is all about calculations related to random failures
SIL validation is of course necessary but it is important not to get too obsessed with the numbers.
The IEC process is order of magnitude, not a numerically precise exercise. The parameters we use to
determine the SIL (demand rates, risk reduction etc.) are in most parts rough estimates, as are the
failure rates we use in the reliability calculations. Too often I see people arguing over which
reliability modelling method to use when in reality the difference between the best to worst
approaches are second order at best. This focus on the numbers can lead to less attention being
paid to other areas of SIL validation, such as hardware fault tolerance requirements, or ensuring that
the equipment meets the safety manual constraints when demonstrating systematic compliance.
e) Operations is just about proof testing
Operations is about maintaining, and demonstrating maintenance, of the required SIL throughout
the plant life. This is much more than proof testing. It involves management of change, data
validation and collection, training and much more. Operations readiness preparation is a complex
and wide ranging subject.
4) IMPLEMENTATION SHORTCOMINGS
As a result of all or some of the factors described, projects can get into problems during execution.
Problems arise typically as a result of the following failures:
Lack of an experienced (or any) FS manager
Lack of an adequate (or any) FS management plan
HAZOP report quality and lack of clear links to all the later phases
Lack of understanding about tolerable risk definition
Lack of understanding about regulatory vs contract requirements
Contractual issues between EPC designers and operator
Poor management of change, in design and in operations
Lack of organisational connection between engineering and operations at an early stage
The first stage in minimising these potential shortcomings is by ensuring that the designer (e.g. EPC)
appoints an experienced FS manager, preferably as early as FEED or bid in order to:
Fully understand and clarify the contractual FS scope e.g. conflict of referenced standards,
full life cycle or hybrid, any client FS standards
Have a clear understanding of the regulatory and contract requirements
Ensure the project starts with a well-defined FS scope that is understood by the team. These
issues affect the design including ICSS.