Hazard Analysis
What is HAZOP? A Complete Guide to Hazard and Operability Studies
Vinit Pandey · Published 3 November 2025 · Updated 28 June 2026
In short: HAZOP (Hazard and Operability Study) is a structured, team-based technique for identifying hazards and operability problems in a process by applying standard guide words to process parameters at each node of a P&ID.
- P&ID Node
- Parameter
- Guide Word
- Deviation
- Cause
- Consequence
- Safeguard
Key takeaways
- Applies standard guide words (No, More, Less, Reverse, Other Than) to each P&ID node
- Requires an independent, trained facilitator and a dedicated scribe
- Every deviation is checked for cause, consequence, and existing safeguards
- Findings feed directly into LOPA and SIL determination
A HAZOP study is the most widely used process hazard analysis technique in the chemical and process industries. It was developed in the 1970s by ICI and has since become a near-universal expectation for hazard identification ahead of plant commissioning.
The technique divides a process into 'nodes' — sections of the P&ID with a consistent design intent — and systematically applies guide words such as No, More, Less, As Well As, Part Of, Reverse, and Other Than to process parameters like flow, pressure, temperature, and level at each node.
For every credible deviation generated this way, the HAZOP team identifies possible causes, potential consequences, and existing safeguards, then judges whether additional safeguards or design changes are warranted.
A well-run HAZOP requires an independent, trained facilitator, a dedicated scribe, and representation from process engineering, operations, instrumentation, and where relevant, maintenance.