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Stop your HAZOP workshop to look up guide words? Download our printable reference card used by 100+ South African facilities. Covers all 10 guide words with parameter-specific examples and facilitator prompts.

HAZOP Guide Words: The Complete Reference Card for Facilitators

Quick Links: Download PDF | View Table | Facilitator Tips
Every experienced HAZOP facilitator knows the frustration: the team is in full flow, ideas are being generated, and then—someone asks "Wait, what does 'Other Than' mean again?"
Momentum stops. Energy dissipates. Time is wasted.
This free downloadable reference card is designed to keep your HAZOP workshops running smoothly. Print it, laminate it, and hand one to every team member before the study begins.

Why Guide Words Matter for MHI Compliance

Under SANS 1461:2018, MHI risk assessments require systematic hazard identification using recognized methodologies. HAZOP (Hazard and Operability Study) is the gold standard because:

  • Systematic coverage – Guide words ensure no deviation type is missed
  • Legal defensibility – Structured methodology stands up to audit
  • Team alignment – Common vocabulary prevents miscommunication
  • Documented rigor – Clear records for your Safety Report
    ❌ What happens without proper guide words: A South African petrochemical plant missed a critical "REVERSE flow" deviation because the team didn't systematically apply all guide words. The consequence? A near-miss incident that could have contaminated drinking water supplies.
    ✅ With systematic application: Every parameter, every guide word, every deviation considered—no shortcuts, no gaps.

The 10 Standard HAZOP Guide Words {#full-reference-table}

Quick Reference Table

Guide Word Meaning Common Parameters Example Deviation
NO / NONE Complete absence Flow, Power, Signal No flow through pump
MORE Quantitative increase Flow, Pressure, Temp, Level More pressure in vessel
LESS Quantitative decrease Flow, Pressure, Temp, Level Less temperature in reactor
AS WELL AS Something extra present Composition, Phase Water as well as acid
PART OF Something missing Composition, Sequence Part of reactant missing
REVERSE Opposite direction Flow, Reaction, Sequence Reverse flow in pipeline
OTHER THAN Complete substitution Material, Operation Other than normal chemical
EARLY Timing deviation Sequence, Reaction Early valve opening
LATE Timing deviation Sequence, Response Late alarm activation
SOONER/LATER Duration deviation Batch time, Residence Batch finishes sooner

Detailed Guide Word Breakdowns

1. NO / NONE / NOT

What it means: Complete negation of the design intent. Nothing happens when something should.
Parameter Matrix:

Parameter Deviation Typical Causes Questions to Ask
Flow No flow Pump failure, closed valve, blockage What stops flow completely?
Pressure No pressure Leak, open vent, supply failure How could pressure be lost?
Level No level Drain open, massive leak, evaporation What empties the vessel?
Signal No signal Sensor failure, cable break, power loss What stops the signal?
Power No power Outage, breaker trip, cable damage What causes complete power loss?
South African Example:

At a Secunda chemical plant, a "No cooling flow" deviation identified during HAZOP led to the installation of a redundant cooling pump. When the primary pump failed 6 months later, the backup prevented what would have been a runaway reaction. The HAZOP paid for itself in one incident.
Related reading: What Happens After Your HAZOP Study?

2. MORE / MORE OF

What it means: Quantitative increase above normal operating bounds.
Parameter Matrix:

Parameter Deviation Typical Causes Questions to Ask
Flow High flow Control valve fails open, pump over-speed What increases flow beyond normal?
Pressure High pressure Blockage downstream, overcharging, runaway What increases pressure dangerously?
Temperature High temp Cooling failure, exothermic reaction What overheats the system?
Level High level Outlet blocked, overfilling, seal leak-in What overfills the vessel?
Concentration High conc Over-dosing, evaporation, reaction What increases concentration?
Critical Insight:
"More temperature" and "More pressure" often occur together. When facilitating, consider: What happens if BOTH occur simultaneously? This combined deviation is where many major incidents originate.
Learn More: Consequence Modeling Explained shows how we model these high-consequence scenarios.

3. LESS / LESS OF

What it means: Quantitative decrease below normal operating bounds.
Parameter Matrix:

Parameter Deviation Typical Causes Questions to Ask
Flow Low flow Pump wear, partial blockage, leakage What reduces flow gradually?
Pressure Low pressure Leak, relief valve open, demand increase What drops pressure unexpectedly?
Temperature Low temp Heater failure, excess cooling, ambient What undercools the system?
Level Low level Excess withdrawal, small leak, evaporation What slowly empties the vessel?
Mixing Low mixing Agitator failure, baffles missing What reduces mixing effectiveness?
Warning for Facilitators:
Don't confuse "LESS" with "NO." Less flow means reduced flow—the pump is still running. No flow means complete stoppage. Each generates different causes and consequences.

4. AS WELL AS

What it means: Something extra is present that shouldn't be there.
Common Contaminants:

Contamination Type Sources Consequences
Water Leaks, condensation, cleaning Hydrolysis, corrosion, reaction
Air Vessel opening, seal failure Oxidation, combustion
Impurities Raw material, degradation Quality loss, catalyst poisoning
Other phase Phase change, entrainment Pump damage, blocked filters
Particles Rust, scale, debris Erosion, blockage
Case Study - Omnia Chemical:
An "As well as water" deviation in a concentrated acid system was dismissed as unlikely. Three months post-HAZOP, rainwater ingress caused a violent exothermic reaction. The lesson: every "As well as" deviation deserves genuine consideration—not dismissal.
See also: HAZOP for Different Industries

5. PART OF

What it means: Something is missing that should be present.
Application Areas:

Context What's Missing Consequences
Composition Key reactant Incomplete reaction, quality loss
Sequence Step skipped Unsafe state, product loss
Phase Liquid phase gone Pump cavitation, dry running
Components Catalyst missing No reaction, batch loss
Control Signal missing Loss of control
Facilitator Tip:
"Part of" is often confused with "Less." Here's the difference:
  • Less = reduced quantity of the same thing (less reactant A)
  • Part of = missing component from a mixture (mixture lacks ingredient B)

6. REVERSE

What it means: The logical opposite of the design intent, especially direction reversal.
Common Reverse Scenarios:

Deviation Typical Causes Critical Consequences
Reverse flow Check valve failure, pressure reversal Contamination, siphoning
Reverse rotation Phase sequence error, wiring mistake Pump damage, no output
Reverse reaction Equilibrium shift, temperature change Unexpected products
Reverse sequence Operator error, PLC failure Dangerous state
The Most Overlooked Guide Word:
In our experience, REVERSE is the most commonly skipped guide word. Teams assume check valves work and pressure differentials don't change. But the gold mining incident in North West Province (cyanide solution reverse flow contaminating clean water) proves otherwise.
Related: Qualitative vs Quantitative Risk Assessment

7. OTHER THAN

What it means: Complete substitution—something entirely different happens.
Deviation Types:

What Changes Examples Critical Questions
Material Wrong chemical loaded What if the wrong material arrives?
Operation Wrong procedure followed What if operators do something different?
Destination Material goes elsewhere What if routing is wrong?
Mode Wrong operating mode What if we're in the wrong state?
Never Skip This:
"Other Than" scenarios include human error and procedural failures—the dominant causes of major industrial accidents. A Bhopal-scale disaster often starts with an "Other Than" deviation.

8-10. Timing Deviations: EARLY, LATE, SOONER/LATER

What they mean:


  • EARLY: Action happens before it should

  • LATE: Action happens after it should

  • SOONER: Duration is shorter than intended

  • LATER: Duration is longer than intended

    Timing Matrix:

    Deviation Process Example Batch Example
    Early Valve opens before stable conditions Catalyst adds before heating complete
    Late Interlock doesn't activate in time Cooling starts after reaction runaway
    Sooner Reaction completes faster than expected Batch hits spec early
    Later Reaction takes longer than expected Batch not complete at schedule
    Critical for Batch Operations:
    If your facility runs batch processes, timing guide words are essential. Continuous processes often skip these; batch processes cannot.

    Facilitator Quick-Reference Card {#facilitator-tips}

    Before the Workshop

    • Distribute this reference card to all participants
    • Explain each guide word with examples from your facility
    • Clarify the difference between LESS and PART OF
    • Emphasize that REVERSE is not optional

    During the Workshop

    Situation Facilitator Action
    Team skips a guide word "Let's pause—we haven't considered [guide word] yet"
    Team dismisses deviation too quickly "What would make this deviation possible?"
    Team combines multiple deviations "Let's separate these and address one at a time"
    Team gets stuck "Think about startup, shutdown, and abnormal operations"
    Energy drops "Let's take 5 minutes, then tackle REVERSE scenarios"

    Quality Check

    Before moving to the next node, verify:

    • All 7 primary guide words applied (NO, MORE, LESS, AS WELL AS, PART OF, REVERSE, OTHER THAN)
    • Timing deviations considered if relevant (EARLY, LATE, SOONER, LATER)
    • At least one cause identified for each credible deviation
    • Consequences traced to worst credible outcome
    • Existing safeguards documented

    Download Your Free Reference Card {#download-section}

    What's Included

    📄 HAZOP Guide Words Reference Card

    • Print-ready format (save as PDF)
    • All 10 guide words with examples
    • Parameter-deviation matrix
    • Facilitator prompts for each guide word
    • Common mistakes to avoid
      📊 HAZOP Worksheet Template
    • Pre-formatted with all guide words
    • Risk ranking matrix included
    • Action tracking built-in
    • Signature blocks for approval

    How to Download

    1. Click the link below to open the resource page
    2. Press Ctrl+P (or Cmd+P on Mac) to open print dialog
    3. Select "Save as PDF" as your printer/destination
    4. Click Save to download your PDF

    ➡️ HAZOP Guide Words Reference Card - Open and save as PDF
    ➡️ HAZOP Worksheet Template - Landscape format for HAZOP sessions
    ➡️ MHI Compliance Checklist 2026 - Track your compliance status

    Need all resources in one place? Visit our Free Resources Page for all downloadable templates.

    How This Supports Your SANS 1461 Compliance

    The SANS 1461 standard requires systematic hazard identification as part of every MHI risk assessment. Using guide words correctly ensures:

    1. Comprehensive coverage – No deviation category overlooked
    2. Auditable methodology – Clear records for Department audits
    3. Defensible results – Structured approach that holds up under scrutiny
    4. Quality recommendations – Deviations linked to actionable safeguards
      MMRisk (CI MHI 0013) applies this systematic approach to every HAZOP we facilitate. Our clients pass Department audits because our methodology is rigorous, documented, and SANS 1461 compliant.

    Related Resources

    HAZOP Fundamentals

    Detailed Guide Word Application

    HAZOP Examples

    MMRisk (CI MHI 0013): Professional HAZOP facilitation with systematic guide word application across South Africa. Contact us to schedule your next study.