Which quantitative risk assessment tool is commonly used to determine the necessary risk reduction for a single hazard, often after a PHA?

• A. HAZOP
• B. QRA
• C. LOPA
• D. Bow-tie

Answer: (C)

LOPA, or Layers of Protection Analysis, is the method used to determine how much risk reduction is needed for a single hazard after a PHA. It focuses on one initiating event and the protection layers that stand between that event and a consequence. By estimating the frequency of the initiating event and the probability that each independent protection layer will fail on demand, you can quantify the residual risk and compare it to a predefined risk target. If the risk is too high, LOPA guides you to add or strengthen protections until the target is met. This makes it well suited for sizing the necessary risk reduction for a specific scenario after a PHA. HAZOP is qualitative hazard identification, Bow-tie diagrams map barriers and pathways, and a full QRA analyzes risk across many scenarios and the entire facility with more data.