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