HAZOP Guide Words, No, More, Less, Reverse, As Well As, Part Of, Other Than.
HAZOP guide words are the seven standard deviation modes used in a hazard and operability, HAZOP study to systematically explore how a process parameter, flow, level, pressure, temperature, composition might deviate from design intent. The seven guide words are NO, complete absence, MORE, quantitative increase, LESS, quantitative decrease, REVERSE, opposite direction, AS WELL AS, qualitative addition, PART OF, qualitative decrease, and OTHER THAN, substitution. Combined with the process parameters, the guide words generate the deviation tuples that drive HAZOP node analysis per IEC 61882.
What HAZOP Guide Words, No, More, Less, Reverse, As Well As, Part Of, Other Than means.
HAZOP methodology emerged in the 1960s at ICI, Imperial Chemical Industries as a structured technique for identifying hazards in process plants. The guide words are intentionally simple and universal. By applying each guide word to each parameter at each node in the process, the HAZOP team systematically considers what could go wrong. The discipline forces the team to consider deviations they might miss in unstructured brainstorming. The guide-word framework is documented in IEC 61882, Hazard and operability studies, Application guide and is the foundation for LOPA, SIL determination, and IEC 61511 safety lifecycle work.
How are guide words applied per parameter.
For Flow. NO no flow, pump failure, blocked line, valve closed. MORE more flow, control valve open, demand increase. LESS less flow, partial blockage, pump cavitation. REVERSE backflow, downstream higher pressure. AS WELL AS contamination, cross-connection. PART OF missing component, multi-component feed. OTHER THAN wrong material, mis-loaded feed. For Pressure. NO is rare, vacuum is more meaningful. MORE overpressure, relief device required. LESS underpressure or vacuum. REVERSE typically does not apply. AS WELL AS, PART OF, OTHER THAN typically do not apply to pressure. For Temperature. MORE overheating, cooling failure. LESS underheating, heating failure. The qualitative guide words rarely apply. Each parameter has guide words that apply meaningfully and guide words that the team marks as 'not applicable.'
What is a HAZOP node.
A HAZOP node is a section of the process selected for analysis as a unit. Nodes are typically scoped at the equipment level, one node per major equipment item or at the function level, one node per identified process function. Feed preparation, reaction, separation, distillation. Node boundaries are drawn on the P&ID and explicitly listed. Each node has design intent, the conditions the process expects at this point, and the HAZOP team applies the guide words to each parameter to develop deviation scenarios. A typical complex process plant has 50 to 200 HAZOP nodes.
What follows the HAZOP guide-word application.
Each, node, parameter, guide word, cause combination that produces a credible deviation goes into the HAZOP worksheet. The team identifies the consequence, what happens if the deviation occurs, the existing safeguards, the layers of protection currently in place. Instrumented protection, relief devices, mechanical integrity, procedural controls, and the risk-matrix severity and likelihood. Where the existing safeguards are inadequate, the team writes a recommendation, typically an additional layer of protection, often a new SIF. Recommendations track through to closure as the design progresses.
Common questions
Why are there seven guide words and not more.
Do HAZOP guide words apply to batch operations.
What is the difference between HAZOP and LOPA.
Can a HAZOP team use software to generate guide-word combinations.
Run it on your drawings.
Upload a drawing set, get every document populated and classified, export to the format your team uses.