Layers of Protection analysis ( LOPA)


Layer of protection analysis (LOPA) is a special form of event tree analysis using fault propagation modelling to determine fairly accurately the frequency of an unwanted event.


LOPA Methodology

  • Define the unwanted impact.
  • Determine and list all of the initiating events that can cause the unwanted impact.
  • Determine and list all the layers of protection that are available for preventing an initiating event from propagating into the unwanted impact.
  • Quantify the frequency of the initiating event(s), based on historical data and engineering judgment.
  • Quantify the effectiveness of the layers of protection in terms of probability of failure on demand (PFD), based on historical data and engineering judgment.
  • Calculate the resulting frequency of the unwanted impact.

Benefits of LOPA

  • Lowers the life-cycle cost of SIS.
  • Supplements existing procedures (e.g., hazard matrix, risk graph).Adding LOPA does not require an organization to completely change other procedures.
  • Neither excessively complicated nor time consuming.
  • More accurate than purely qualitative estimates.
  • Identifies potential gaps in the plant’s overall protection that can often be fixed very economically.

Role of NIST in conducting LOPA workshop

  • Scheduling and planning the session
  • In house Competent and Certified functional safety expert who has vast experience in Operation and technical scribe
  • Verify thoroughly the process documents and conduct sessions in systematic manner
  • Training of LOPA methodology to stakeholders
  • Prepare comprehensive report with priority
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