Some of you reading this may not be aware or familiar with the terms “leading” and “lagging” indicators, when applied to Functional Safety.  The concept isn’t new but does provide significant benefit when applying this to Functional Safety because, if used correctly, these indicators can help significantly improve performance.  Let’s not forget that the IEC61511 standard is a “performance-based” standard and not prescriptive (i.e. tells you what you need to do but not how to do it).

In simple terms, “leading” indicators are an indication of the likelihood of having (or preventing) incidents from occurring that could have catastrophic consequences.  For example, by simply looking at how mechanical integrity is implemented, in terms of when and how proof testing is conducted, including timely repairs and maintenance, which will have an impact on the Safety Instrumented Systems overall integrity.  “Lagging” indicators, on the other hand, involve documenting incidents, failures, near misses, etc.  The fact that a relief valve (for example) goes off is an indication that all is not well with the process; an event which should be captured.

There are prime examples of where not paying attention to leading and lagging indicators has resulted in catastrophic events, such as the Texas City Isomerization Unit explosion in 2005.  The plant had experienced many years of incidents: releases, fires and fatalities that had largely gone ignored, resulting in a decline in infrastructure and poor maintenance.  Had leading and lagging indicators been used then things may have been different.

If this article has peaked your interest, then watch out for a webinar on the use of leading and lagging indicators to help improve process safety.

Tagged as:     Steve Gandy     SIS     Safety Instrumented Systems     lagging indicators     IEC61511     Functional Safety  

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