Hazop Guide Words: BEFORE
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 | typical causes | typical consequences | typical safeguards |
|---|---|---|---|---|---|---|---|---|---|---|
| BEFORE | sequence#batch_step#general | general | Step performed before prerequisite step in batch sequence | unlikely | batch_step | sequence | catastrophic | Operator sequence error; incorrect procedure; BMS logic fault; step-skip due to instrument failure | Wrong order of reagent addition (exotherm or reaction hazard); charging before vessel is at correct temperature or pressure; risk of reactive hazard | Sequence interlock in BMS requiring prerequisite step completion before enabling next step; operator confirmation; SOP with step-by-step checklist |
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