It always amazes me that when teaching our FSE 100 Functional Safety Engineering course, the number of times I find that end users in the class are not really measuring the performance of their SIS. In most cases, they are doing some measurements, but not thoroughly.
It was partly for this reason that some of the changes to IEC 61511, in the 2016 edition, focused on measuring performance. After all, IEC 61511 is a performance-based standard that requires end users to “periodically” measure performance and is why a Functional Safety Assessment (FSA 4) is now required to measure performance. If we don’t do this, then how do we know that our SIS is achieving its target performance, as defined in the SRS?
Setting up the Key Performance Indicators (KPIs) to measure performance isn’t difficult to do, and there are different ways to do this (the use of Leading and Lagging Indicators is one method). One example is performing proof testing per the SRS. If the SRS specifies a proof test interval of 12 months and is only performed every 18 months, then this will have a detrimental effect on the integrity of the SIFs (e.g., if the SIF was designed to be SIL 2, it could soon degrade to a SIL 1). Not analyzing any trips to root cause and/or investigating near misses are also other KPIs that should be recorded. Near misses such as relief valves being triggered is an indication that all is not well, and this should be recorded and investigated. The number of Functional Safety Assessments and Functional Safety Audits being performed should also be recorded since these will help identify any non-conformances. These are just examples of KPIs that will give an indication of how well functional safety is being performed and followed.
Accidents such as the Texas City Isomerization Explosion in 2005 was the result of management not following up on incidents and audit reports that highlighted serious deficiencies to ensure the proper resolution of these problems. Undertaking regular performance checks will enable potential serious problems to be identified and corrected before becoming major issues. The IEC 61511 committee has recognized that end users are not following through on the Operations and Maintenance (O&M) requirements properly, which is why the requirements have been strengthened. If end users don’t follow through on the O&M requirements, this may lead to future consequences.
Always remember, if you think safety is expensive, then try an accident!