Expect the unexpected: managing decommissioning  risk

Demand for decommissioning and dismantlement is rapidly increasing, but for divers, such projects are among the most technically demanding and potentially hazardous operations they undertake.

That is why IMCA has published new guidance on diving operations in support of subsea decommissioning and dismantlement projects, a document developed to help diving contractors, operators and project teams better understand the risks associated with these projects and, critically, how those risks can be managed effectively.

While decommissioning shares similarities with offshore construction and inspection, repair, and maintenance activity, it is fundamentally different in one important respect: uncertainty. In construction, teams generally know exactly what they are building. In decommissioning, that certainty often no longer exists. What appears on paper may bear little resemblance to what divers encounter offshore. Many offshore installations have been operating for decades, and ownership may have changed several times. Drawings may be incomplete, outdated or missing, and equipment may have been modified without records being retained. Structures may have degraded, accumulated marine growth or changed significantly from their original condition, and it is here, in the gap between expectation and reality, where risks emerge. 

One of the strongest themes running through the new IMCA guidance is the need to challenge assumptions – assumptions about structural integrity, historical records, residual hydrocarbons and pipeline contents, or about the condition of lifting points, which can all create serious hazards if left unverified. The industry has already seen incidents where divers have been injured because infrastructure did not behave as expected once excavation or cutting work commenced. In some cases, assumptions that systems had been flushed or isolated correctly exposed divers to hazardous chemicals. In others, changes to planned work scopes were not adequately reassessed as operations evolved subsea. The lesson is clear: decommissioning demands a dynamic approach to risk management, and robust management-of-change processes are essential.

The guidance also emphasises the importance of managing simultaneous operations. Decommissioning campaigns often involve multiple vessels, contractors, and activities taking place concurrently. Diving operations may occur alongside heavy lifting, flushing operations, explosive severance activity, or dismantling. Without rigorous coordination and communication, risks can escalate very quickly. 

Another area that deserves greater attention is contamination and residual hazards. Even after cessation of production, hydrocarbons, chemicals, hydrogen sulphide, drill cuttings and naturally occurring radioactive materials may still be present. These hazards are not always visible or fully understood from historical documentation alone. 

The guidance reinforces the need for detailed planning, verification, and monitoring before divers break containment or recover infrastructure to surface. Importantly, it also highlights newer or less widely recognised risks, such as microbiologically generated H2S arising from long-submerged equipment and biofouling. 

Technology and engineering controls also have a critical role to play. Wherever practicable, ways should be explored to reduce diver exposure through remote methods, remotely operated vehicle intervention, and alternative cutting or recovery techniques. The objective should always be to minimise both the duration and consequence of diver exposure. 

Ultimately, safe decommissioning depends on mindset as much as procedure. Project teams must ‘expect the unexpected’. They must be prepared to stop work when conditions differ from assumptions, reassess risks continuously, and maintain a culture where questioning and verification are encouraged, rather than seen as obstacles to progress.