# HAZOP Guide Words and Deviations Reference Table > Source: https://netray.co/tools/chemical-plant-hazop-guide-word-reference > Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems. > Section: Free Tools ## Short answer Combine HAZOP guide words with process parameters to prompt deviations, with typical causes and consequences to speed up your node discussions. ## Category ehs-workforce ## Industry Chemical Manufacturing ## Audience - Process safety engineer - HAZOP facilitator - Chemical engineer ## Tool **Kind:** worksheet **Mode:** reference **Columns:** #### Guide word **Key:** guide **Type:** text #### Parameter **Key:** parameter **Type:** text #### Deviation **Key:** deviation **Type:** text #### Example cause **Key:** cause **Type:** text #### Example consequence **Key:** consequence **Type:** text **Rows:** #### Blocked line, closed valve, pump trip, empty source tank **Guide:** No / None **Parameter:** Flow **Deviation:** No flow **Consequence:** Reactor starved of feed, loss of cooling, pump running dry #### Control valve fails open, wrong pump speed, bypass left open **Guide:** More **Parameter:** Flow **Deviation:** More flow **Consequence:** Overfilling, off-ratio feed, exotherm from excess reagent #### Partial blockage, fouled strainer, worn pump **Guide:** Less **Parameter:** Flow **Deviation:** Less flow **Consequence:** Poor mixing or heat removal, off-spec product #### Check valve failure, pressure higher downstream **Guide:** Reverse **Parameter:** Flow **Deviation:** Reverse flow **Consequence:** Contamination of upstream equipment, reaction in wrong vessel #### Incorrect hose connection, mislabeled tote **Guide:** Other than **Parameter:** Flow **Deviation:** Wrong material **Consequence:** Unplanned reaction, toxic release, product loss #### Blocked outlet, runaway reaction, external fire, blocked vent **Guide:** More **Parameter:** Pressure **Deviation:** High pressure **Consequence:** Vessel overpressure, relief device lifts, loss of containment #### Condensing vapors, pump-out with blocked vent, steam condensation after cleaning **Guide:** Less **Parameter:** Pressure **Deviation:** Low pressure or vacuum **Consequence:** Vessel collapse, air ingress into flammable systems #### Cooling failure, heater control failure, fouled exchanger **Guide:** More **Parameter:** Temperature **Deviation:** High temperature **Consequence:** Runaway reaction, decomposition, boil-over #### Heating failure, cold ambient, wrong utility **Guide:** Less **Parameter:** Temperature **Deviation:** Low temperature **Consequence:** Freezing, crystallization or blocked line, reaction accumulation #### Level transmitter fault, outlet blocked, overcharge **Guide:** More **Parameter:** Level **Deviation:** High level **Consequence:** Overflow, carry-over into vent or downstream equipment #### Leak, drain left open, instrument fault **Guide:** Less **Parameter:** Level **Deviation:** Low level **Consequence:** Pump cavitation, heater exposed, loss of liquid seal #### Overcharge of reagent, evaporation, dosing pump fault **Guide:** More **Parameter:** Concentration **Deviation:** High concentration **Consequence:** Faster reaction, corrosion, exotherm #### Dilution with water, dosing failure, wrong recipe **Guide:** Less **Parameter:** Concentration **Deviation:** Low concentration **Consequence:** Incomplete reaction, off-spec product, unreacted raw material #### Cross-connection, residual from previous batch, water ingress **Guide:** As well as **Parameter:** Composition **Deviation:** Contamination or extra component **Consequence:** Side reaction, quality failure, hazardous byproducts #### Charging step skipped, empty hopper, ratio controller fault **Guide:** Part of **Parameter:** Composition **Deviation:** Component missing **Consequence:** Incomplete reaction, unstable intermediate #### Catalyst overcharge, accumulation then sudden start, agitator restart **Guide:** More **Parameter:** Reaction **Deviation:** Faster or larger reaction **Consequence:** Thermal runaway, gas evolution, overpressure #### Agitator motor trip, shaft or coupling failure **Guide:** Less **Parameter:** Agitation **Deviation:** Poor mixing **Consequence:** Stratification, hot spots, delayed reaction then surge #### Utility header fault, power failure **Guide:** No / None **Parameter:** Utilities **Deviation:** Loss of cooling water, steam, nitrogen or instrument air **Consequence:** Loss of temperature control, loss of inerting, valves moving to fail position #### Operator action, batch controller logic, delayed sample result **Guide:** Early / Late **Parameter:** Time or sequence **Deviation:** Step too early or too late **Consequence:** Wrong addition order, incomplete hold time, reaction accumulation #### Procedure not followed, bypassed interlock, abnormal operation **Guide:** Other than **Parameter:** Operating mode **Deviation:** Startup, shutdown or maintenance state **Consequence:** Exposure to hazards not present in normal operation **Notes:** Guide words are prompts, not a complete list of deviations. Tailor parameters and causes to your node, and record safeguards, risk ranking and actions in your own HAZOP worksheet. ## Content **Intro:** A HAZOP study works by applying guide words such as no, more and less to process parameters such as flow, pressure and temperature, then asking what could cause that deviation and what would follow. This reference lists the standard combinations with chemical plant examples, so facilitators and team members always have prompts at hand. **Sections:** #### How to use it in a session **Body:** Divide the process into nodes, such as a reactor with its feed lines and vent, then walk each node with the table open. Filter by parameter, read the deviation aloud and ask the team for credible causes. Record the consequence, existing safeguards and any actions in your HAZOP worksheet. The examples in the table are starting points. Not every combination is meaningful for every node, and discarding a combination with a reason is part of a good study. **Bullets:** - Filter by parameter when working through a node line by line - Use the 'Other than' and 'Early / Late' rows to cover startup and batch sequence - Export to Excel to build your study template #### Where HAZOP fits in process hazard analysis **Body:** HAZOP is one of the accepted methods for process hazard analysis, alongside what-if, checklists and FMEA. In the United States, OSHA process safety management for covered processes requires a hazard analysis that is revalidated at least every five years. HAZOP suits continuous processes and complex batch units well because it is systematic. For simple utility systems a what-if review may be enough, so match the method to the risk and the available process knowledge. #### Common mistakes **Body:** Studies fail when the team lists only the normal operating mode, accepts 'operator will notice' as a safeguard, or skips batch sequencing and human factors. Another common problem is stopping at the consequence without judging whether safeguards are independent and adequate. Keep the drawings current, include operations and maintenance staff, and track every action to closure. **Bullets:** - Do not count alarms as independent of the control system they depend on - Review the P&IDs against the plant before the session - Track actions to closure in a system, not an email thread **Cta:** Netray can help link HAZOP actions and management of change items to maintenance and quality records in your ERP so that follow-up does not depend on spreadsheets. **Faq:** #### What are the standard HAZOP guide words? **Answer:** The commonly used set is no or none, more, less, as well as, part of, reverse and other than. Many teams add early, late, before and after for timing and sequence deviations. They combine with parameters such as flow, pressure, temperature and level. #### How often should a HAZOP be repeated? **Answer:** For processes covered by OSHA 29 CFR 1910.119 the hazard analysis must be updated and revalidated at least every five years. Changes to the process, incidents and new information may require earlier review under your management of change procedure. #### Is HAZOP suitable for batch processes? **Answer:** Yes, but add time-based prompts and sequence steps because many hazards come from the wrong order or timing of additions. Treat each recipe phase as a node or use a sequence-based variant of the method. #### Do I need a facilitator? **Answer:** A trained facilitator and a dedicated scribe greatly improve quality and speed. The facilitator manages the method and discussion while the scribe records causes, consequences, safeguards and actions. ## Search terms hazop guide words, hazop deviations list, hazop parameters and guide words table, hazop study example chemical plant, no flow more flow less flow hazop, hazop prompt list, process hazard analysis guide words --- Talk to an engineer: https://netray.co/contact?intent=erp_ai | Machine catalog: https://netray.co/agent/catalog.json