Definition:
Qualitative risk assessment (QLRA) is a risk assessment method that uses categorical descriptors (such as high/medium/low or color-coded matrices) to evaluate the severity and likelihood of risks. It is often a very simple matrix with color codes. It does not assign numerical values to probabilities or consequences.
A QLRA cannot be used by itself to meet the robust requirement of a H&RA per IEC 61511-1.
A QLRA can still be used in the functional safety lifecycle, especially early and for large projects. A QLRA can quickly indicate where further investigation is warranted. Later phases would use more advanced methods.
Key Points:
- Uses a simple matrix with categories like high/medium/low to rate likelihood and severity.
- Supports early-stage hazard identification and prioritization.
- Does not produce numerical risk values.
Example:
In a batch reactor system, a team performs a HAZOP and identifies a potential overpressure scenario. They rate the likelihood as “possible” and the consequence as “major,” placing it in the “medium risk” zone on the plant’s risk matrix. This flags the scenario for a deeper review.
Cited Source:
- CCPS Guidelines for Hazard Evaluation Procedures.