HAZOP Guide Words Reference Card
Quick Reference for Facilitators & Team Members | SANS 1461 Compliant
| Guide Word | Meaning | Common Parameters | Example Deviation |
|---|---|---|---|
| NO / NONE | Complete absence | Flow, Power, Signal, Level | No flow through cooling pump |
| MORE | Quantitative increase | Flow, Pressure, Temp, Level | High pressure in reactor vessel |
| LESS | Quantitative decrease | Flow, Pressure, Temp, Level | Low temperature in distillation |
| AS WELL AS | Something extra present | Composition, Phase, Contaminants | Water contamination in acid |
| PART OF | Something missing | Composition, Components, Steps | Reactant B missing from batch |
| REVERSE | Opposite direction | Flow, Rotation, Sequence | Reverse flow in return line |
| OTHER THAN | Complete substitution | Material, Operation, Mode | Wrong chemical loaded |
| EARLY | Action before intended | Sequence, Timing, Operations | Valve opens before safe state |
| LATE | Action after intended | Sequence, Response, Alarms | Interlock activates too late |
| SOONER/LATER | Duration deviation | Batch time, Residence, Process | Reaction completes early |
NO / NONE / NOT
Complete negation of design intent — nothing happens
Facilitator Prompt
"What could cause this process parameter to be completely absent? What happens if there's zero flow, zero pressure, zero signal?"
MORE / MORE OF
Quantitative increase beyond normal operating range
Facilitator Prompt
"What if this parameter increases significantly above normal? Consider control system failures, operator errors, and upstream upsets."
LESS / LESS OF
Quantitative decrease below normal operating range
Key Difference: LESS vs NO
LESS = reduced but still present (pump running slowly). NO = completely absent (pump stopped).
REVERSE / OPPOSITE
Logical opposite of design intent — direction reversal
⚠️ Most Overlooked Guide Word
REVERSE is frequently skipped. Always ask: "What if flow direction reverses? What if the sequence runs backward?"
AS WELL AS / PART OF
Qualitative change — extra present or component missing
Facilitator Prompt
"What contaminants could enter this stream? What component of the mixture could be missing?"
OTHER THAN / INSTEAD
Complete substitution — something entirely different
Human Error Focus
OTHER THAN scenarios often involve human error. Ask: "What if an operator makes a mistake? What if the wrong material is delivered?"
✅ HAZOP Facilitator Checklist
Before the Workshop
- Distribute reference cards to all participants
- Explain each guide word with facility examples
- Clarify LESS vs PART OF difference
- Emphasize REVERSE is mandatory
- Review node definitions and P&IDs
During the Workshop
- Apply all guide words systematically
- Consider startup, shutdown, abnormal ops
- Don't combine multiple deviations
- Trace consequences to worst credible outcome
- Document all safeguards, even obvious ones
Before Moving to Next Node
- All 7 primary guide words applied
- Timing deviations considered (if relevant)
- At least one cause per deviation
- Risk rankings assigned
- Recommendations specific and actionable
Pro Tips for Effective HAZOP Sessions
- Keep sessions under 3 hours — fatigue reduces effectiveness after this point
- One deviation at a time — don't let the team jump ahead or combine scenarios
- Consider all operating states — startup and shutdown often have different hazards
- Never dismiss a deviation — document it even if quickly ruled out
- Use the "What if" extension — "What if this happened during a power outage?"
- Track action items live — assign owners before moving on
| Mistake | Solution |
|---|---|
| Skipping "obvious" deviations | Apply all guide words systematically, even if outcome seems unlikely |
| Combining multiple deviations | Consider each deviation separately; combined scenarios come later |
| Only considering equipment failure | Include human error, external events, and process upsets as causes |
| Stopping at immediate consequence | Follow the consequence chain to the worst credible outcome |
| Ignoring existing safeguards | Document all protective measures before ranking risk |