Intrinsic Safety / Safety Instrumented Systems

Closing the loop on process safety

Process safety metrics based on leading indicators can help head off incident and injury

By Keith Larson

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Industry puts substantial effort into ensuring that plants are designed and built to run safely. By their very nature, however, the safety instrumented systems (SIS) that often carry a lion's share of the plant's risk reduction measures are seldom called into action. How then can operating companies be sure that operations continue to be as safe as they were 20 years ago when the plant was built?

Indeed, the passage of time and poor visibility can conspire to erode the ability of a plant's established safety instrumented functions (SIFs) to provide adequate risk reduction, according to Nasir Mundh, global director, safety services, Schneider Electric. Mundh, together with colleague Farshad Hendi, safety services practice leader, discussed how Schneider Electric is helping its customers to better understand and track the leading indicators that point to increased risk—before an incident or injury occurs.

Unlike lagging indicators such as are revealed in post-event data collection or a running tally of incidents and injuries, leading indicators work like a yellow traffic light between green (safe) and red (unsafe) states. "Leading indicators determine how likely things are to go wrong, and consequently, how likely they are to have an incident or injury in the future," Mundh said.

Leading indicators of increased risk typically can be found in three areas: functional safety documentation, operational data and maintenance data.

"Often it's the quality of the functional safety documentation that may indicate increased risk," Hendi said. For example, mismatch between documented operational and maintenance procedures and what the operators and maintenance techs actually do is one red flag of increased risk. Other documentation to check for accuracy and currency include hazard and risk analyses, safety requirements specifications, functional design specifications, SIL verifications and change records.

While such measures are primarily qualitative checks that rely on people and work processes, technology also can help to identify and provide visibility of leading indicators in the midst of operational and maintenance data. Schneider Electric's SIF Manager software, for example, can be used to gather and plot metrics related to SIF performance, such as trip frequency and time in bypass. These metrics, in turn, are compared against design expectations to pinpoint any troubling drift.

These types of process safety metrics are but the first step in a "closed loop" approach to process safety that Schneider Electric has begun to promulgate across its process automation and safety offering to ensure that design integrity translates into ongoing operational integrity. "It requires a continuous cycle of measurement, comparison, validation and correction," Mundh said, "all while providing visibility to safety leadership."