1What is HAZOP?
L'HAZOP (HAZard and OPerability study) analyses a process node by node (a homogeneous facility section, such as the feed line between pump P1 and reactor R1). For each node it systematically applies guide words (NO, MORE, LESS, REVERSE, OTHER THAN, etc.) to process parameters (flow, pressure, temperature, level, etc.) to generate deviations and then analyses their causes and consequences.
Its strength is systematic coverage : combining guide words and parameters forces the team to examine deviations that unstructured discussion might miss, such as NO FLOW on the feed line.
2Method steps
- Divide the process into nodes — homogeneous sections with a defined operating state, based on the facility model.
- Select relevant parameters for each node, such as flow, pressure, temperature, level and composition.
- Apply guide words to each parameter to generate deviations (for example MORE + pressure = overpressure).
- Identify the causes of each deviation.
- Identify consequences that may result.
- Record existing measures and rate scenario severity and likelihood.
- Issue recommendations for deviations that are not adequately controlled.
Do not blindly combine every guide word with every parameter. The team must filter physically plausible combinations for the node to avoid overwhelming the analysis with irrelevant cases.
3Example completed in Polyodos
Section to be completed — step-by-step example using a reactor-feed node and MORE FLOW deviation, with Polyodos screenshots.
4Common mistakes
| Mistake | Why it is a problem |
|---|---|
| Defining overly broad nodes | A node spanning an entire unit makes parameters inconsistent—inlet and outlet pressure differ. Node boundaries must follow process-state changes. |
| Confusing a deviation with a cause | MORE FLOW is the deviation; a valve stuck open is a cause. Reversing them loses the guide-word × parameter logic central to HAZOP. |
| Performing HAZOP alone | HAZOP depends on combining process, instrumentation and operations perspectives in a workshop. Performed alone, it loses much of its detection value. |