They translate early technology pathways into verifiable requirements and notations.
LR, ClassNK, and DNV have incorporated OCCS into their rule development.
It reveals much about feasibility and future minimum requirements.
Engage class societies early in OCCS projects.
Classification societies face a fundamentally new challenge with Onboard Carbon Capture and Storage. Unlike established technologies such as scrubbers or ballast water treatment systems, no internationally harmonised regulatory framework exists for OCCS. The IMO has not yet adopted a binding standard, which means that class societies are effectively acting as the first rule-makers.
DNV has established an initial formal framework with its OCCS(Capture) notation. This notation covers the capture system but deliberately excludes storage and CO2 transfer. Lloyd's Register works with Guidance Notes that follow a risk-based approach — similar to the treatment of novel fuel systems under the IGF Code. ClassNK has initiated Joint Development Projects with Japanese shipowners and technology suppliers to gather operational experience in parallel with rule development.
The technical assessment fields include pressure vessels, chemical storage (amines, sorbents), waste heat utilisation from the exhaust stream, intermediate CO2 storage on board and transfer in port. Each of these fields requires specific material approvals, safety assessments and documentation. The handling of amines in particular — which serve as absorbents in many OCCS systems — raises questions about health protection, storage and disposal.
For operators, this means: an OCCS project without early class involvement risks considerable delays. The approval procedures are not yet standardised, and each class society brings its own priorities and timelines. Those who understand the process and begin the dialogue early gain six to twelve months' advantage over late entrants.
The documentation requirements for OCCS systems go beyond what operators are accustomed to from conventional installations. Class societies typically require a comprehensive risk assessment (HAZID/HAZOP) covering all operational states including emergencies and maintenance scenarios. This is supplemented by material certificates, pressure vessel calculations according to recognised standards and evidence of electrical safety in hazardous areas.
A frequently underestimated aspect is the interface between the OCCS supplier and the existing vessel documentation. The Safety Management System (SMS) must be extended to include OCCS-specific procedures — from daily operational monitoring to emergency shutdown. Class societies review not only the hardware but also whether the management system adequately covers the new technology.
Operators should further note that a class society notation is not automatically recognised by port state control authorities of other flag states. The regulatory landscape remains fragmented, and proactive coordination with both flag state and port state can prevent subsequent operational disruptions.
DNV, in collaboration with Seatrium (formerly Sembcorp Marine) and technology provider Carbon Ridge, applied the first formal OCCS notation to a concrete vessel project. This pilot process demonstrated just how extensive the approval effort truly is — from basic engineering to sea trials, considerably more months elapsed than for comparable retrofit projects without novel technology.
At the same time, this process created valuable precedents. The checklists, inspection protocols and risk matrices developed along the way form a foundation from which subsequent projects can benefit. For operators seriously evaluating OCCS, knowledge of these pilot projects and their outcomes represents a considerable informational advantage.
Engagement should follow three phases. Phase 1: Pre-consultation (concept stage) — clarifying whether the chosen class society offers an OCCS notation at all and which requirements apply. Phase 2: Design review — submission of technical documentation for the specific system and vessel. Phase 3: Accompaniment during construction and commissioning.
A common mistake is to skip Phase 1 and begin directly with the design review. This means that fundamental questions — such as the acceptability of certain sorbents or the required redundancy — are clarified only late in the process, jeopardising the entire schedule.
Operators planning an OCCS retrofit or newbuilding often underestimate how the absence of a harmonised standard affects the project schedule, not only the technical scope. Because each class society is still developing its own approach, the approval timeline cannot be estimated by analogy with a scrubber retrofit or a dual-fuel conversion, where established rule sets and precedent cases shorten the review. Budgets should include contingency for iterative rounds of technical queries, particularly around novel elements such as amine storage, intermediate CO2 handling and waste heat integration, where class reviewers themselves are often evaluating a configuration for the first time.
A realistic project plan separates the class approval track from the yard construction track and treats the two as only loosely coupled in the early phases. Construction milestones that assume a fixed approval date risk slipping across the board if a single technical query takes longer to resolve than anticipated. Operators who build schedule buffers around the class dialogue, rather than around yard capacity alone, are less likely to face costly idle time or contractual penalties tied to delivery dates that never accounted for the novelty of the approval process itself.
Fleet operators considering OCCS across several vessels face a further complication: different ships in the same fleet may be classed with different societies, each with its own notation, documentation expectations and technical priorities. Treating every vessel as an isolated approval case wastes the learning gained on the first project. A more efficient approach consolidates the technical dossier — risk assessments, material certificates, SMS amendments — into a common core that each class society reviews against its own specific requirements, rather than rebuilding the submission from scratch for every hull.
Where a fleet spans multiple flag states as well as multiple class societies, coordination becomes more demanding still, since a notation accepted by one class society is not automatically read the same way by every port state authority. Operators who appoint a single internal owner for the OCCS approval process across the fleet, rather than leaving each vessel's project team to negotiate independently, tend to accumulate institutional knowledge faster and avoid repeating the same clarifying questions with each class society on every subsequent vessel.