(80a) Use of Human Reliability Analysis to Supplement LOPA for Scenarios Dominated By Human Error

There are many scenarios and situations for which Layers of Protection Analysis (LOPA) may not apply as a suitable methodology or may be difficult to use. One such case is when a scenario is dominated by human error and yet there does not appear to be a way to have one or more IPLs. This paper illustrates Human Reliability Analysis ([HRA], including Human Reliability Event Tree [HRET]) which can be an alternative and it illustrates how to augment LOPA and SIL Verification calculations for human error probability estimates. Cases include:

• HRA / HRET used for the risk assessment of the re-built Phillips Polyethylene Plants (Pasadena, TX) following the explosion in 1989 that 23 workers. This occurred during on-line maintenance to clear a large product discharge line. This HRET was required as part of the settlement between Phillips and the US Government.
• Risk assessment of a task at a copper smelter that was addressed using LOPA, while incorporating human-error-prevention IPLs that perhaps other sites have not considered. A list of human error prevention IPLs is shared in the paper
• HRET used to augment SIL V to account for the human error appropriately (SIS standards and ANSI/ISA Technical Reports ignore these large terms.)

This paper will help the implementor understand how to get the most from LOPA in high human error scenarios and when it is appropriate to consider an alternative approach.