What is Operation and Maintenance for a Safety Instrumented System?

For a SISSafety Instrumented System the “Operation and Maintenance” (O&M) phase is more than just operating and maintaining. The objective is to make sure that the SIS achieves it’s SILSafety Integrity Level level over the entire life of the plant and to ensure that the assumptions on which the SIL target were based are - and remain - true.

O&M activities are challenging at the best of times – but if the way these activities are to be carried out is not considered during earlier lifecycle stages (and at the SRS stage in particular), they may be made very difficult to implement.

O&M activities include:

• Proof Testing – to ensure the SIS can operate as it should, by finding any dangerous undetected failures. (The “undetected” failures that proof testing is targeted to reveal are those that are “undetected” by internal diagnostic tests).
• Management of Bypasses (if these have been allowed / specified by the SRSSafety Requirements Specification).
• Initial and on-going training of Operators and Technicians.
• Analysis of data (from proof test results, spurious trips, demands, bypass quantity and duration etc).
• Routine inspection and maintenance activities.
• Monitoring to ensure that the assumptions made during H&RAHazard and Risk Assessment are and remain true. Such as what is the actual BPCSBasic Process Control System failure rate? has the occupancy of a particular area changed? If any of these values vary from those assumed in the H&RA, the required risk reduction (and therefore the SIL) may change.

Technical author

Dil Wetherill

CEO - Method Safety and Security

Dil launched Method Functional Safety in 2013. He now delivers training courses and provide consultancy on all aspects of functional safety.

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