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Use a practical Management of Change process to screen plant modifications, control temporary changes, update documents, and protect critical safeguards.

Management of Change: Stop Small Plant Changes Becoming Major Risks

A fitter replaces a failed valve with one that has the same flange size. The new valve uses a different metallurgy and closes faster. Production sees a routine repair. The process engineer sees two questions: can the material tolerate the service, and can the faster closure create a pressure surge?
That gap is where Management of Change (MOC) earns its place in process safety.
MOC gives your team a controlled way to review changes before they reach the plant. It connects engineering, operations, maintenance, training, drawings, procedures, and startup approval. A good system catches modest changes that can weaken a safeguard or invalidate an assumption in your HAZOP study.

Download: MMRisk Management of Change Screening Form (PDF) or use the print-friendly version.

Which changes need an MOC?

Start with a broad rule: review any change to chemicals, process technology, equipment, procedures, control logic, staffing, or operating conditions unless your team can demonstrate that it is a true replacement in kind.
Common triggers include:

  • changing a raw material, catalyst, concentration, or supplier specification;
  • increasing throughput, pressure, temperature, inventory, or batch size;
  • altering pipework, relief paths, alarms, trips, interlocks, or control logic;
  • installing a temporary hose, bypass, spool, blind, or power supply;
  • revising an operating, maintenance, sampling, or cleaning procedure;
  • changing shift structures, responsibilities, contractor support, or minimum staffing;
  • extending equipment service beyond its inspection interval or design life.
    Organisational changes deserve the same attention as hardware. Removing an experienced shift role, combining maintenance teams, or changing an emergency duty roster can affect response time and decision quality even when the P&ID remains untouched.

Replacement in kind needs a technical test

Teams often use "replacement in kind" as a shortcut. Appearance and fit do not prove equivalence.
Before classifying a replacement as equivalent, confirm:

Check Questions
Design duty Does it have the same pressure, temperature, flow, and containment duty?
Materials Are metallurgy, gasket, seal, lubricant, and chemical compatibility unchanged?
Function Does it fail in the same position and at the same speed?
Protection Does it preserve alarm, trip, relief, and isolation performance?
Maintenance Are inspection methods, spares, competency, and intervals unchanged?
Documentation Do drawings, procedures, data sheets, and training remain valid?
If one answer changes, route the work through MOC screening. The review can remain proportionate. A small, understood change may need a short checklist and one competent approver. A complex modification may need a HAZOP, LOPA, relief review, or specialist design verification.

A seven-step MOC workflow

1. Describe the proposed change

Name the equipment, location, reason, scope, duration, and owner. Attach the marked-up drawing or procedure. Phrases such as "upgrade pump" or "improve line" leave too much room for interpretation.

2. Establish the technical basis

Record the design calculation, failure history, production requirement, inspection finding, or legal obligation behind the proposal. This gives reviewers something concrete to test.

3. Screen the hazards

Ask how the change can affect containment, ignition, reaction, overpressure, toxic exposure, isolation, human workload, emergency response, and nearby equipment. Review the effect on existing safeguards, not only the new component.
A change that affects a major-incident scenario should connect back to the MHI risk assessment, BowTie, HAZOP, or QRA that defined the original risk.

4. Define required actions

Actions can include:

  • updating P&IDs, cause-and-effect charts, data sheets, and procedures;
  • testing alarms, trips, relief devices, and shutdown functions;
  • revising inspection plans, spares, and maintenance tasks;
  • training operators, maintainers, contractors, and emergency teams;
  • completing a Pre-Startup Safety Review.
    Give each action an owner and due date. Separate work that must close before startup from work that can close after startup under an approved risk control.

5. Obtain competent approval

Use reviewers who understand the affected disciplines. Operations alone cannot approve a relief-system change. Engineering alone cannot confirm that a new procedure will work during a night shift with one field operator.

6. Verify the installation in the field

Compare the finished work with the approved package. Check tag numbers, materials, valve orientation, instrument ranges, software versions, set points, labels, and removed temporary items.

7. Close the change

An MOC remains open until the plant records match the plant. Confirm that documents, training, inspection tasks, and outstanding actions are complete. Record the startup date and the person who accepted the change into operation.

Temporary changes need expiry dates

Temporary arrangements often survive because they solve an immediate production problem. A hose installed for one week becomes part of the plant. A bypass stays open after testing. An alarm override remains in place after the technician leaves.
Every temporary change needs:

  • a named owner;
  • an expiry date;
  • a visible field identifier;
  • operating limits and compensating controls;
  • a review before extension;
  • a restoration or permanent-design plan.
    Include temporary changes in shift handovers and routine plant inspections. A spreadsheet that only the engineering office can see will not control a bypass in the field.

MOC, PHA revalidation, and the MHI system

Your MOC register provides evidence that the facility manages risk between formal reviews. It also gives the next PHA revalidation team a traceable history of modifications, incidents, temporary changes, and revised assumptions.
South Africa's MHI framework expects duty holders to manage major-incident risks across the establishment lifecycle. MOC supports that duty by keeping the physical plant, operating practice, and risk documentation aligned.
MMRisk helps facilities design MOC workflows, review complex modifications, facilitate hazard studies, and verify readiness before startup. Contact our process safety team when a change affects a major-incident scenario or a critical safeguard.

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