Structure design intent, deviations, causes, consequences, safeguards and actions for an invented cooling node; no risk score or suitability approval is produced.
HAZARD & OPERABILITY · 1.0.0
HAZOP · a structured deviation worksheet
Start with design intent, challenge it with a guide word, and record the reasoning. This is qualitative teaching support: no numerical risk score, automatic safety approval or claim of completeness.
One hypothetical cooling-water node
N-01 runs from the cooling-water pump discharge, through a strainer, to the heat-exchanger inlet during steady operation. The lesson examines less flow. The drawing is conceptual, not a P&ID; no real vessel limits, installed protection or operating authority are implied.
Intended flow is from pump through strainer to heat exchanger. The node boundary includes pump discharge, strainer and heat-exchanger inlet. Less flow is a hypothetical deviation downstream of a fouled strainer.
From intention to a reviewable action
A competent facilitator and a multidisciplinary team examine credible deviations using current process information. A guide word prompts discussion; it does not discover causes, evaluate safeguard adequacy or prove that all hazards have been found. Record an uncertainty explicitly instead of filling it with an unsupported claim.
This is a reasoning sequence, not a mathematical risk equation. A worksheet field being filled is not evidence that its content is correct.
Guide words used in this exercise
These are original teaching definitions for a small selected subset. They are not an IEC table or a complete HAZOP vocabulary. Other nodes, operating modes and parameters need a team-selected examination strategy.
No
The intended flow is absent. Do not interpret “no temperature” or “no pressure” as a ready-made deviation.
More
The chosen parameter is above the stated design intention or range.
Less
The chosen parameter is below the stated design intention or range.
Reverse
Flow goes against the intended direction. Applicability and causes must be established.
Work the example, one question at a time
Define the node boundary, operating mode and design intention. Obtain the approved flow requirement and pressure/temperature envelope before any real assessment.
Combine parameter “flow” with guide word “less”. Describe the actual deviation as cooling-water flow below the design requirement.
Consider strainer fouling as one possible cause and reduced heat removal as a consequence. Establish the real causal chain, including equipment response and escalation.
Record the assumed alarm and trip separately from evidence. Their existence, response, coverage and independence are unverified; the worksheet gives them no protective credit.
Specify the missing drawings, curves, limits and functional-test records. Assign the verification recommendation to an accountable role and keep it open until the responsible team accepts adequate evidence.
Reviewable record
JavaScript enables the form; the full lesson and teaching row remain readable below.
Local-only form. No network requests or persistent storage. CSV is downloaded only on your click and includes the current assumptions. Save it before leaving if you need the record.
Completed teaching row
“Completed” means that the example row has been written. Its action remains open and its assumptions remain unverified. Load worked example copies this exact scenario and row into the form.
Node boundary
N-01: cooling-water pump discharge, strainer and heat-exchanger inlet
Design intent
During steady running, deliver the required clean cooling-water flow from the pump to the heat exchanger within the approved pressure and temperature envelope. No numerical operating limits are supplied in this fictional exercise.
Operating mode and excluded interfaces
Steady running only. Start-up, shutdown, maintenance, parallel equipment and external interfaces require separate examination.
Current assumptions and missing process data
Fictional cooling node. No vessel drawings, measured limits, trip test records or team review have been provided. Listed safeguards are candidate claims awaiting evidence, not credited independent protection layers.
Row 1
Parameter
Flow
Guide word
Less
Deviation from intent
Cooling-water flow below the design requirement.
Credible cause(s)
Strainer fouling progressively increases resistance; inspect the actual flow path and operating conditions before judging credibility.
Consequence(s)
Reduced heat removal can raise cooled-equipment temperature; sustained operation may cause equipment shutdown or damage. Wider consequences need separate analysis.
Existing or claimed safeguards
A low-flow alarm and high-temperature trip are assumed for teaching; existence, independence, coverage and response are unverified.
Evidence, references and gaps
Missing: approved P&ID revision, pump/system curves, flow limits, alarm/trip cause-and-effect and recent functional-test records.
Recommendation / next action
Confirm the design flow requirement; review fouling detection and strainer-maintenance criteria; verify alarm/trip response using approved procedures.
Responsible owner or role
Exercise lead (role only)
Action status
Open
Preparation and limitations
A real study needs a competent facilitator, appropriate design/operations/maintenance expertise, a recorder, defined boundaries and an agreed study plan. This four-row interface cannot replace a team session.
Use current approved P&IDs, equipment and material data, design limits, control narratives, cause-and-effect diagrams, operating procedures and relevant incident/test records. Revisions and missing information matter.
Examine start-up, shutdown, maintenance, abnormal operation, interfaces and relevant combinations separately. The selected node, modes and guide words do not cover every hazard.
A named safeguard is only a recorded claim. Do not infer independence, reliability, functional coverage or adequate response time from its presence in a row.
An owner and a status help track follow-up, but “closure proposed” is not closed. Evidence must be assessed by the authorized technical team; this tool never grants closure.
The worksheet contains no severity/likelihood scale, risk multiplication, tolerability test, SIL determination or operating permission. Quantitative follow-on methods need their own justified assumptions and data.
Method sources
IEC 61882:2016’s public scope covers guide-word-based studies and their preparation, examination, documentation and follow-up. The standard’s proprietary tables are not reproduced here. MOD guidance provides an accessible account of team, facilitation and information needs.