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Use of Leading & Lagging Indicators - Good Practice For SIS

The IEC61511/ISA-84 Process Industry Sector Standard is predicated upon a performance-based Safety Lifecycle (SLC) to help reduce risk and to provide a foundation for the development, operation and maintenance of Safety Instrumented Systems (SIS).  The SLC is composed of three phases: Analysis, Design/Implementation (Realization) and Operation and Maintenance.  As a performance-based standard, End Users are required to develop Key Performance Indicators (KPIs) to facilitate performance monitoring.  The basis of this is to ensure that the performance targets defined within the Safety Requirements Specification (SRS) for the SIS can be met and sustained throughout the life of the SIS.

This paper outlines how KPIs based upon Leading and Lagging Indicators can help in maintaining performance and to help prevent potential future incidents from occurring.  Accidents, such as the Texas City Isomerization Unit explosion in 2005, highlighted the need for such indicators and was a key recommendation in the Chemical Safety Board’s final, published, report on the accident.

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