Decommissioning is expensive and can be a complex operation involving a series of distinct phases, including cessation of operation, site preparation, decontamination, dismantling (demolition) and disposal. Each decommissioning phase has associated risks, which need to be identified, controlled, and minimized as far as reasonably practicable. A risk-based approach has been recognized, both for ensuring safety and reducing the total decommissioning period with cost savings. A traditional hazard and operability (HAZOP) study can be conveniently extended to decommissioning HAZOP, which is a guideword-based collective multidisciplinary study identifying types of risks associated with decommissioning and allocates actions to the contractor and specialists departments for implementation. A decommissioning HAZOP enables to address the hazards and risks of decommissioning activities holistically, addresses all major contingencies, and results in safe decommissioning within budget. The presented decommissioning HAZOP study itself was completed ahead of time, without accidents. While there are other methods, decommissioning HAZOP and risk assessment was recognized as one of the effective methods for achieving the safety and project cost objectives.