Hazard and Operability Study (HAZOP)

Guide words are short standard terms — 'No', 'More', 'Less', 'Reverse', 'As well as', 'Part of', 'Other than' and similar — that are combined with process parameters such as flow or pressure to generate deviations from design intent. IEC 61882 makes them the engine of the method because they impose completeness: instead of hoping a team imagines every failure, the study marches through every meaningful guide-word-and-parameter combination at every node. This procedural exhaustiveness is what makes HAZOP more reliable than free-form brainstorming at finding the rare, dangerous deviation that would otherwise be overlooked.

Both are systematic hazard-identification techniques, but they enter the problem from different directions. FMEA starts from components and asks how each can fail and what effects the failure has. HAZOP starts from the process and its intended parameters and asks how each can deviate, using guide words, then traces causes and consequences. HAZOP therefore naturally captures operability and process-interaction problems, including those not tied to a single component failure, while FMEA excels at component-level reliability. The CCPS guidelines present both as complementary members of the hazard-evaluation toolkit, often used together.

No. HAZOP is a qualitative hazard-identification method: it finds deviations, their causes and consequences, and the safeguards in place, and recommends actions where residual risk seems intolerable, but it does not compute probabilities or quantified risk. When a quantified judgment is needed for a critical scenario uncovered by the HAZOP, analysts typically follow up with semi-quantitative or quantitative techniques such as layer-of-protection analysis, fault-tree analysis or event-tree analysis. In practice HAZOP serves as the structured front end that decides which scenarios deserve that further quantitative scrutiny.