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Is there a "hidden" SIS in your legacy automation system?

When looking at modernizing a programmable process control/automation system e.g. those based on Distributed Control Systems (DCS), Programmable Logic Controllers (PLC) or even Direct Digital Control (DDC), particularly one that has been in service for some time (say 15+ years), have you considered compliance to current process safety standards like IEC 61511/ANSI S84? “Protective functions” such process interlocks, emergency and process shutdowns that are implemented in the legacy system need to be accounted for and safety assessed in the new design. These functions may well reveal a “hidden” Safety Instrumented System (SIS) that was part of the legacy system, and now needs to be part of the new system.

In many cases, “replacement in kind” automation modernization projects do not consider these “latent” safety functions; they have been, at best, overlooked and at worst, ignored. If these safety functions are not properly implemented in the modernized system, the facility may not have the proper protection from process hazards that a modern Integrated Control and Safety System (ICSS) can provide.

A best practice in automation modernization is to ensure process HAZOPS and Layers Of Protection Analysis (LOPA) are updated as part of the project and the results used to determine if a SIS is required as part of the replacement system’s architecture.

Has anyone got a story about finding the “hidden SIS” as part of your automation modernization project?

1 Reply

  • If you are thinking about migrating ABB Bailey NET 90 / INFI 90 BMS or Boiler controls to DeltaV, this is a very valid point and is often overlooked. Be aware of safety functionality in your legacy DCS, and ask your Emerson LBP about DeltaV SIS and Industrial Energy Solutions to appropriately accommodate migration of your safety functionality!

    Joel Galmor

    Modernization Consultant