Subsea CCS injects captured CO₂ into geological formations beneath the seabed. Getting it there needs pipeline, wellheads and injection structures, and that infrastructure is inspected and maintained the same way gas infrastructure is. It's one of the few new niches that already has projects up and running.
Of all the sectors pitched as the future of offshore energy, CO₂ storage is probably the one that gets the fewest headlines and has the most installations already running under water. That makes it an interesting case for commercial diving, because it isn't a promise: it's infrastructure that exists and needs maintaining.
How it works, in short
The idea is to capture CO₂ at an industrial source — a cement plant, a steelworks, a power station — compress it to a dense state, transport it and put it into a porous geological formation at sufficient depth, sealed by an impermeable layer that stops it rising.
In the offshore variant, that formation lies beneath the seabed. It can be a deep saline aquifer or a depleted hydrocarbon reservoir, which has the advantage of being very well characterised geologically and of having demonstrated over millions of years that it holds gas in.
The physical route the CO₂ takes
From the capture plant, the CO₂ goes to a terminal, is transported by pipeline or by ship, and reaches an injection facility. From there it goes down a well into the formation. Each of those legs has components that, when they are in the sea, fall within the remit of commercial diving and ROVs.
What's underwater on a CCS project
The list looks very much like that of a gas development, and that is exactly the point.
Pipelines
The pipeline carrying CO₂ from shore or from the terminal to the injection point. It's inspected for the same reasons as any other: external corrosion, coating integrity, condition of the supports, free spans (free spans) caused by seabed movement, and impact protection in traffic areas.
Injection structures and wellheads
Injection wells have their own protective structure, valves and connections. All of that requires visual inspection, checking the state of the cathodic protection and, sometimes, cleaning so you can actually see what you need to see.
Moorings and terminal structures
When the CO₂ arrives by ship, there's a terminal with its own mooring system and loading arms. Maintaining those moorings and chains is classic diving work, very similar to that on monoboyas.
The technical peculiarity of CO₂
CO₂ under transport conditions behaves in a way that demands careful design. It's a fluid that changes phase easily with variations in pressure and temperature, and a sudden loss of pressure produces very sharp cooling. That shapes the choice of materials, start-up and shutdown procedures, and integrity criteria.
On top of that, in the presence of water CO₂ forms carbonic acid, which is corrosive. That's why controlling moisture in the stream is a critical operating parameter, and why integrity inspection programmes are strict.
None of this changes what a diver does with their hands, but it does explain why these installations carry more scheduled inspection than others and why it's documented in more detail. For anyone who makes a living from inspection, that's good news.
Reusing infrastructure, and decommissioning
One of the economic arguments for offshore CCS is that it allows existing assets to be reused: depleted fields as storage and part of the pipeline network as transport. Before anything is reused, it has to be shown to be fit for purpose, and that means detailed inspection campaigns on installations that have been in the water for decades.
It's a nuance worth understanding well, because it touches directly on the sector's other big stream of work, decommissioning. An installation reused for CO₂ is one that isn't decommissioned yet, but does need to be assessed. Either way there's work in it, only the order changes.
What diver profile fits
The dominant profile is inspection. A diver with an underwater inspector certification and real experience in pipeline and structural integrity fits here far better than a profile geared only towards construction.
On top of that come the usual requirements: a commercial diving certification recognised in the market where the projects are, current offshore survival training, and a clean bill of medical fitness. The certifications required are no different from those for any other work on an energy installation.
And saturation work
It depends on the depth of the installation. In shallow water it's handled with surface-supplied diving; on deeper developments, underwater work tends to be ROV-led, with the saturation diver coming in when hands-on work is needed on components the robot can't handle. It's the same logic as the rest of the sector, and it's explained in the comparison between saturation and surface-supplied diving.
How to read this if you're starting out
It isn't worth redirecting your training towards CCS. What is worth doing is knowing it exists, understanding that it draws on the same set of skills as the rest of offshore, and keeping it in mind when reading job ads: more and more inspection campaigns will turn up whose end client isn't an ordinary oil company.
The practical conclusion is a reassuring one. The energy sector changes product more easily than it changes physics: as long as there's steel under water, someone will have to look at it, measure it and fix it. Anyone who can do that well will have somewhere to work, whatever the name of the fluid running through the pipe.
What's the difference between inspecting a CO₂ line and a gas line
On paper, not much. In practice, three nuances that an experienced diver ends up noticing.
The first is frequency. A carbon storage installation has monitoring obligations that go beyond mechanical integrity: it has to be shown that the CO₂ is staying where it was put. That means environmental monitoring and periodic inspection campaigns with documented criteria.
The second is sensitivity to leaks. On a natural gas pipeline, a leak is a safety and production problem. On a CO₂ line it's also a regulatory and reputational problem, because the entire point of the project is that the gas doesn't get out. The practical consequence is a very low tolerance threshold for any sign of a defect.
The third is how young the infrastructure is. Many of these installations have been in the water for only a short time, so the work is less about repair and more about setting a baseline: the first detailed inspection that every later one will be compared against.
What setting a baseline means
It's a campaign in which the initial state of everything is recorded: wall thicknesses, geometry, the exact position of each element, coating condition, cathodic protection potentials. It's meticulous work that depends heavily on the quality of the record, and it usually needs more diver time than the routine inspections that follow it.
The monobuoy, the terminal and the mooring
When the CO₂ arrives by ship instead of by pipeline, there's a part of the installation that is pure classic commercial diving work: a mooring system with chains and anchors, a submerged connection, a transfer system.
That whole set-up is inspected with the same routine as any hydrocarbon terminal: measuring wear on critical links, checking shackles, reviewing the state of the cathodic protection and verifying the geometry of the mooring. Anyone who has worked on chain and mooring line inspection is on familiar ground from day one.
Specific risks and how they're managed
CO₂ isn't toxic in the sense of being a poison, but it's an asphyxiant through oxygen displacement, and it's denser than air, so it tends to collect in low areas and confined spaces. That risk sits in the surface installation, not in the water.
For the dive team, managing it comes down to the usual measures: isolating and locking out the affected part of the installation, a permit to work signed off by the person responsible for the installation, gas detection in the areas where work is being done on deck, and a pre-job briefing explaining what has been isolated and what hasn't.
It's important to understand that the dive team doesn't invent these measures: they're imposed by the installation's safety management system, and the supervisor's job is to make sure the team understands and follows them. The chain of command works exactly as it does on any other process platform.
How a diver gets onto this kind of project
There's no specific door in. You get in the same way you get into any offshore work: through a subsea services contractor holding the inspection and maintenance contract for the installation.
That means the requirements are the contractor's and the country's where it operates. In northern Europe, where most of the projects are, that means a certification recognised in that market, current survival training and an up-to-date medical. The medical certificate and survival training both expire, and without them you don't get on board no matter how much work there is.
A word of advice on expectations
Offshore CCS is a real but small sector. No diver today lives exclusively off it, just as none lives exclusively off floating wind. What a sensible professional does is keep a profile that lets them work on whatever comes up in their region, and accept that the mix of clients changes from one year to the next.
In closing
Subsea CO₂ storage isn't a new sector for commercial diving: it's the same sector with a different fluid inside the pipe. It calls for rigorous inspection, careful documentation and discipline working alongside live installations, which is exactly what the trade has been doing for decades.
For anyone starting out, the useful takeaway isn't "train for CCS". It's that integrity inspection, with both its technical side and its reporting side, remains the most transferable and durable skill in this trade, and that it's never a bad bet. The route into it is laid out in the guide to training and the qualification options in the one on certifications.
Frequently asked questions
What is CCS?
It stands for carbon capture and storage. It involves capturing CO₂ from an industrial source, transporting it and storing it permanently in a deep geological formation, which offshore lies beneath the seabed.
What does a diver do on a CCS project?
The same as on a gas installation: inspecting pipelines and structures, checking cathodic protection, working on flanges and supports, supporting interventions and cleaning structures. The difference is in the fluid flowing through it, not in the task.
Is oil and gas infrastructure reused for CCS?
On some projects, yes, because both depleted fields and part of the pipeline network can be put to use. That reuse requires very detailed integrity inspections before the step is taken, which in itself generates inspection work.
Is it a sector with stable employment for divers?
It's still small compared with oil and gas or offshore wind, but unlike other niches it already has installations in operation. The sensible way to see it is as an extra client for a diver already trained, not as a separate career.
Is subsea CO₂ dangerous for the diver?
CO₂ is denser than air and displaces oxygen, so the main risk is a confined atmosphere at the surface and in the installation's enclosed spaces. The control measures are the usual ones: isolation, permit to work and gas detection, managed by the installation.
Published 4 September 2026 · By Arthur More, professional saturation diver
Photo: Slaunger · CC BY-SA via Openverse
This article is part of our in-depth guide to how dangerous commercial diving really is — the complete picture, with sources.
This article is part of our in-depth guide to how dangerous commercial diving really is — the complete picture, with sources.
This article is part of our in-depth guide to how dangerous commercial diving really is — the complete picture, with sources.
This article is part of our in-depth guide to how dangerous commercial diving really is — the complete picture, with sources.