A hazard and operability study (HAZOP) is a structured team review of a design, node by node, asking how deviations from the design intent could occur and what they would lead to.
Team and preparation
A facilitator, a scribe and a team with process, operations, instrumentation, mechanical and safety knowledge. Up-to-date P&IDs, cause and effect matrices, operating procedures, relief valve data and equipment design conditions.
Nodes
A node is a part of the process with one design intent: a vessel with its inlet line, a pump and its discharge, an exchanger. Write the design intent with numbers ("receive 30 m³/h at 2 bar g, hold 20 min surge"). Too large a node loses detail; too small wastes time.
Guide words and parameters
Guide words applied to parameters create deviations:
| Guide word | Meaning | Example with "flow" |
|---|---|---|
| No / none | complete negation | no flow |
| More / less | quantitative increase or decrease | high flow, low flow |
| As well as | something in addition | flow with contaminant |
| Part of | only part | wrong composition |
| Reverse | opposite | reverse flow |
| Other than | complete substitution | wrong material |
| Early / late, before / after | timing and sequence | step done too early |
Parameters: flow, pressure, temperature, level, composition, reaction, phase, and operations such as start-up, shutdown, maintenance, sampling and draining.
Good records
For each credible deviation: specific causes (not "operator error" in general), the consequence without safeguards, the existing safeguards (named, with tags), the risk ranking, and a recommendation with an owner. Consequences written "without safeguards" are what LOPA needs.
From HAZOP to LOPA
Rows with high severity and a SIF or several safeguards as protection go to LOPA. Keep one cause per row so each LOPA scenario maps to one HAZOP row.
In First Out AI
HAZOP worksheet tab: nodes with design intent, drawing, equipment and conditions; guide word, parameter, deviation, causes, consequences, safeguards, S, L (risk = S × L, colour coded), recommendation and owner. Recommendations collect in the action list. Load the example nodes to see complete records, or import your worksheet from Excel.
Written for First Out AI as engineering guidance. It supports engineering work and does not replace it; check every value against your standards, certificates and company rules with a competent functional safety engineer.