Management of change (MOC)

Management of change begins from an uncomfortable fact: a design reviewed as a whole is safe as a whole, and every subsequent change re-opens the question locally. MOC procedure requires that a proposed change — to equipment, process conditions, materials, procedures or documents — be described, its technical and safety implications assessed by people competent to see them, approvals obtained at a level matching the risk, and the affected documentation updated before or promptly after implementation. In the process industries the discipline is regulatory, born of accidents caused by modifications nobody re-analysed; its formal boundary is the replacement-in-kind test — like-for-like replacement needs no MOC, anything else does.

The boundary is where the process erodes. "Minor" changes, urgent changes, temporary changes that become permanent — each is a category of modification that slips past review precisely because it seemed too small to need one, and the accident record of the process industries is substantially a record of such changes. The second erosion is documentary: changes managed and approved but never propagated into the drawings, so the facility drifts from its documentation one authorised increment at a time — an as-built problem being manufactured in real time.