Definition:
Semi-Quantitative Risk Analysis/Assessment (SQRA) is a method combining qualitative severity descriptions with numerical likelihoods to prioritize hazards. This is a hybrid approach to bridge the gap between qualitative (QLRA) and fully quantitative methods (QRA). This analysis usually uses order of magnitude estimates and not specific calculations to the decimal point. Because of this, it reduces the level of subjectivity and is more actionable.
It combines the more qualitative aspects, such as expert judgment and experience, with numerical scoring or categorical ranking. Risk matrices are often used.
The very common Layer of Protection Analysis (LOPA) is the most typical example. As LOPAs are so common now, an SQRA is arguably the most common type of risk analysis. Another common example is a risk graph.
Key Points:
- Faster than a full QRA.
- Often uses calibrated risk matrices.
- Uses order of magnitude estimates.
See Also: QRA, QLRA, LOPA, risk graph
Example:
Using a 5×5 risk matrix with numerical frequency estimates to prioritize mitigation actions. A biogas company’s functional safety program decides to execute their H&RA via a HAZOP and its SIL Selection via a LOPA. This would be a semi-quantitative method.
Cited Source:
- CCPS Guidelines for Hazard Evaluation Procedures.