Hazop Guide Words: LESS
temperature#vessel#brittle fracture to viscosity#pipe#general
HAZOP guide words and deviations — IEC 61882:2016 guide words applied to common process parameters across node types (pipe, vessel, reactor, heat exchanger, pump, compressor, control loop, batch step), with typical causes, consequences, and safeguards
| guide word | deviation key | context | deviation description | likelihood class | node type | process parameter | severity class | standard | typical causes | typical consequences | typical safeguards |
|---|---|---|---|---|---|---|---|---|---|---|---|
| LESS | temperature#vessel#brittle fracture | brittle fracture | Low temperature causing brittle fracture risk in pressure vessel | unlikely | vessel | temperature | catastrophic | IEC 61882:2016 Table 3; CCPS Guidelines for Hazard Evaluation Procedures 3rd Ed.; ASME Sec VIII Div 1 | Cold ambient temperature; loss of heating; refrigerant leak; depressurization chilling; cold feed introduction | Brittle fracture of carbon steel; loss of containment; explosion; structural failure | Low-temperature alarm; minimum temperature interlock; MDMT verification per ASME Sec VIII; impact tested steel for low-temperature service |
| LESS | temperature#vessel#general | general | Temperature lower than intended in vessel | possible | vessel | temperature | moderate | IEC 61882:2016 Table 3; CCPS Guidelines for Hazard Evaluation Procedures 3rd Ed. | Loss of heating; steam failure; cooling control failure; low ambient temperature; cold feed introduction; process fluid flashing | Freezing and pipe blockage; product solidification; brittle fracture; loss of fluidity; slow reaction rate; condensate formation | Low-temperature alarm (TAL); heat tracing; insulation; low-temperature trip; minimum temperature interlock |
| LESS | viscosity#pipe#general | general | Viscosity lower than design intent | unlikely | pipe | viscosity | minor | IEC 61882:2016 Table 3; Crawley et al. HAZOP: Guide to Best Practice 3rd Ed. | High temperature; dilution with solvent; change in composition; degradation of polymer | Reduced pump efficiency; increased seal leakage; insufficient film thickness for lubrication; product off-spec | Viscosity analyser; temperature alarm; composition monitor; operating procedure |
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