| guideword,meaning,parameter,example_deviation,example_cause,example_consequence,example_safeguard |
| NO/NOT,Complete negation of the design intent (the intended event does not occur at all),Flow,No flow in process pipe to reactor,Control valve CV-101 fails closed; pump P-201 fails to start; blocked line upstream,No feed to reactor — potential runaway if exothermic reaction already in progress; catalyst damage,Low-flow alarm FAL-101; reactor temperature high alarm TAH-201; interlock on reactor feed shutdown; pump duty-standby auto-changeover |
| NO/NOT,Complete negation of the design intent,Reaction,No reaction in batch vessel,Catalyst not loaded; incorrect raw material; temperature too low to initiate,Off-spec batch; undetected unreacted hazardous material in product stream; downstream explosion risk on concentration,Batch recipe interlocks; temperature confirmation before heat release; in-process quality sample; production hold and test procedure |
| NO/NOT,Complete negation of the design intent,Level,No level in separator,Bypass valve left open draining vessel; upstream failure; drain left open,Loss of liquid seal in separator — gas breakthrough to liquid outlet; overpressure in downstream liquid line; downstream fire,Low-level alarm LAL-201; low-low level shutdown LSL-201LL; operator checklist for drain valve position before startup |
| MORE,Quantitative increase above the design intent,Flow,More flow through heat exchanger shell side,Upstream control valve CV-202 fails open; increased upstream pressure; pressure regulator failure,Tube overloading; elevated pressure on tube-side — tube failure; flammable or toxic material release to cooling water or atmosphere,High-flow alarm FAH-202; pressure relief valve PRV-HX101 on shell; shell inspection programme for tube integrity |
| MORE,Quantitative increase above the design intent,Temperature,High temperature in reactor,Excessive steam supply; blocked cooling water; runaway exothermic reaction; loss of agitation,Decomposition; runaway reaction; vessel overpressure; BLEVE potential for flammable material; toxic gas release,High temperature alarm TAH-301; high-high temperature shutdown TSH-301HH (trips steam supply + activates quench); relief valve RV-R01; agitator low-speed trip |
| MORE,Quantitative increase above the design intent,Pressure,High pressure in gas storage vessel,Thermal expansion (solar radiation); upstream compressor runaway; blocked outlet; external fire (BLEVE scenario),Vessel failure; BLEVE; fragment projection; vapour cloud explosion; multiple casualties,Pressure relief valve PSVX-01; rupture disk upstream of PSV; high-pressure alarm PAH-401; fire-fighting water system; vessel support design for fire case |
| MORE,Quantitative increase above the design intent,Level,High level in atmospheric tank,Inlet control valve fails open; level transmitter failure; operator inattention during filling,Overflow of flammable / toxic material; tank berm exceedance; environmental spill; fire risk,High-level alarm LAH-501; high-high level shutdown LSH-501HH (closes inlet valve); independent level gauge (sight glass); overfill protection device per API 2350 |
| MORE,Quantitative increase above the design intent,Concentration,Higher concentration of hazardous component in reactor feed,Sampling error; supplier batch variation; metering error; wrong raw material loaded,Runaway reaction; product out of spec; potential detonation for peroxide-forming substances,Inlet analyser AIC-601; feed ratio control; batch record verification; raw material QC certificate check |
| LESS,Quantitative decrease below the design intent,Flow,Less flow in cooling water to reactor jacket,Cooling water pump degradation; partial valve closure; fouling in cooling water circuit,Inadequate heat removal; reactor temperature rise; runaway risk; potential decomposition of thermally sensitive material,Low cooling water flow alarm FAL-701; temperature rise alarm TAH-301; interlock on reactor agitator speed and steam supply |
| LESS,Quantitative decrease below the design intent,Temperature,Low temperature in cryogenic storage vessel,Refrigeration system failure; excessive heat ingress; warm product fill; vacuum jacket failure,Vapour generation; pressure build-up; relief valve lifting; potential vessel embrittlement if temperature falls below design minimum metal temperature,Low temperature alarm TAL-801; high pressure alarm PAH-401; refrigeration duty-standby; boil-off gas management system; vessel material specification for cryogenic service |
| LESS,Quantitative decrease below the design intent,Level,Low level in suction vessel,Outlet valve opens unexpectedly; downstream demand increase; metering error,Pump cavitation; loss of flow downstream; potential air ingestion; product quality impact; pump seal failure,Low-level alarm LAL-201; pump auto-stop on low-low level LSLL; inlet control valve override to maintain minimum level |
| LESS,Quantitative decrease below the design intent,Pressure,Low pressure in reactor (vacuum scenario),Condenser flooding; outlet valve opens; steam condensation with no vent; cold snap with no nitrogen padding,Vessel designed for pressure operation only — implosion; ingress of air into flammable atmosphere; oxygen contamination of product,Vacuum relief valve VRV-R01; nitrogen padding system with N2 supply alarm; pressure monitoring with low-pressure alarm PAL |
| AS WELL AS,Qualitative modification — something in addition to what was intended,Composition / Flow,Contaminant in process stream — water in anhydrous reactor feed,Condensation in delivery hose; improper purging after hydrotest; water hold-up in dead leg,Decomposition of water-sensitive catalyst; violent reaction with moisture-reactive material; steam generation causing overpressure,Moisture analyser on feed; purge and dry-out procedure after maintenance; line draining checklist; dead-leg elimination programme |
| AS WELL AS,Qualitative modification — additional hazardous material present,Two-phase flow,Gas and liquid carried together in normally liquid line,Vaporisation due to pressure drop; gas ingestion at pump suction; dissolved gas release,Surge and slug flow causing pipe vibration; fatigue failure; flow measurement error; pump damage; high vibration and noise,Separator upstream of pump; vortex breaker; flow pulsation dampener; vibration monitoring on pump and critical pipework |
| PART OF,Qualitative modification — only part of the intended event occurs,Composition,Partially complete chemical reaction — low conversion,Catalyst poisoning; insufficient residence time; low temperature; reactant ratio imbalance,Unreacted hazardous material in product stream; downstream processing of out-of-spec stream; potential for secondary undesired reaction,In-line analyser on reactor outlet; batch sample testing with hold procedure; residence time interlock on continuous reactor |
| PART OF,Only part of intended transfer completes,Flow (partial),Partial transfer of batch to next vessel — incomplete drain,Pipe partially blocked; valve does not fully open; pump operates below design duty,Wrong batch composition in receiving vessel; heel material causes contamination in next batch,Level confirmation in source and destination vessels before process step sign-off; batch management system check |
| REVERSE,Logical opposite of the design intent,Flow,Reverse flow in single-direction line,Downstream pressure higher than upstream; pump fails while line is pressurised; siphon effect on drain line,Back-flow of product (possibly hazardous) into wrong vessel or to atmosphere; contamination; overfill,Non-return valve (check valve) NRV-101; backflow prevention device; interlock preventing simultaneous opening of inlet and outlet valves; reverse flow alarm in DCS |
| REVERSE,Logical opposite — reversed rotation or direction,Rotation,Pump / compressor reverse rotation,Single phasing of motor; incorrect phase connection after maintenance; loss of supply phase,No flow or reduced flow; potential seal failure; motor overheating; damage to impeller,Anti-rotation device on pump; phase rotation indicator on motor starter; electrical protection relay; pre-start check procedure |
| OTHER THAN,Complete substitution — something completely different from design intent,Material / Service,Wrong material charged to reactor,Label mix-up; look-alike containers; wrong tank connection; material substitution without MOC,Uncontrolled reaction; toxic gas release; equipment damage; potential fatality; fire/explosion,Material labelling and colour-coding; two-person verification on material loading; unique connection fittings (key locks); MOC procedure; pre-charge verification checklist |
| OTHER THAN,Deviation in utility service — wrong service applied,Utility,Wrong utility connected — instrument air connected to nitrogen line or vice versa,Physical connection error during maintenance; connector not uniquely designed; labelling failure,Instrument air in purge system — oxygen ingress into inerted system; fire/explosion; or nitrogen in breathing air line — asphyxiation,Unique connection fittings for different services; colour-coding of pipe and hose connections; cross-connection prevention programme; pressure and composition check after reconnection |
| OTHER THAN,Operating mode deviates from intended,Operating mode,Maintenance mode operated instead of production mode (or vice versa),Logic controller fault; software update error; HMI display error; operator selection error,Safety instrumented system bypassed; safety interlocks defeated without authorisation; process run outside safe operating limits,Access control on operating mode selection; mode change requires authorised sign-off; SIS bypass log and management procedure (IEC 61511 management of functional safety); proof testing programme |
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