We are going to continue discussing the results from exida’s recently published industry benchmark survey on the practices for the use of alarms as safeguards and IPLs. Over 200 safety practitioners from around the world provided responses. This entry will discuss the relationship between alarms identified as safeguards and those that become IPLs.
One industry reference defines a safeguard as “a potential protection layer that has yet to be evaluated in a LOPA to determine effectiveness and independence” .
Respondents provided feedback to the following question:
What percentage of the alarms that are considered during a Layer of Protection Analysis (LOPA) were identified during a Process Hazard Analysis (PHA)?
Ideally 100% of the alarms that are considered in a LOPA would have first been identified as a safeguard/recommendation in the PHA. Figure 2 shows that in practice, this is far from the case. Only 12.4% of the respondents indicated that all (100%) of the alarms in the LOPA had come from the PHA. 51% of the respondents appear to frequently identify new alarms during LOPA that were “missed” during the PHA. This would seem to indicate poor PHA practices. Failing to identify alarms during a PHA could signal various issues, such as a lack of thoroughness, lack of documenting all safeguards in order to save time, or a lack of understanding of the process. This blogger wonders whether this pattern is unique to the treatment of alarms or is present for other safeguards as well.
If you would like to view the complete paper, click here.
Also, if you would like to learn more on this topic, or to understand the full detailed report, please register to attend tomorrow’s webinar.
 Hartmann, H., Scharpf, E., and Thomas, H., Practical SIL Target Selection: Risk Analysis per the IEC 61511 Safety Lifecycle, exida, Sellersville, PA, (2012).