Enclosed Space Entry Rules Are Changing: What IMO's New Resolution Actually Adds

What's Changing

IMO Resolution MSC.581(110), adopted December 2025, revokes and replaces the previous enclosed space entry guidance (Resolution A.1050(27)). It isn't a minor wording update – it adds real new structure to how enclosed space entry is supposed to be managed aboard ship, and the UK's MCA has now reached out to industry, via trade bodies including British Marine, for input on how UK regulations and guidance should align with it.

The New Requirements Worth Knowing

• A mandatory Enclosed Space Register – a formal, maintained record of which spaces aboard the vessel actually qualify as enclosed spaces, rather than this being left to informal crew knowledge or memory.
• A formal Enclosed Space Emergency Response Plan – a specific, written plan for exactly this scenario, distinct from a vessel's general emergency response arrangements.
• New defined terms – including “Connected/Adjacent Space” and “Trapped Hazardous Atmosphere,” closing a real gap: a space physically connected to a known enclosed space, or one where a hazardous atmosphere could become trapped even without classic enclosed-space characteristics, wasn't always clearly captured by the older guidance.
• Tighter gas-detection and testing requirements, and more specific rescue-procedure expectations.

Where This Sits Against Existing UK Rules

The underlying UK law – the Merchant Shipping and Fishing Vessels (Entry into Enclosed Spaces) Regulations 2022 – has been in force since May 2022 for SOLAS ships and May 2023 for everything else, including fishing vessels. Guidance under that law has already been updated once for the IMO shift: MGN 659 (M+F) Amendment 3, published 6 January 2026, incorporates elements of the direction MSC.581(110) confirmed. The MCA's current industry outreach is about the next stage of alignment – working out how UK domestic rules and guidance should fully reflect the new resolution's specific requirements (the Register, the Emergency Response Plan, the new defined terms).

Why Your Input Actually Matters Here

This is a genuine opportunity to shape how a real operational requirement gets implemented before it's finalised, not after. Requirements like a formal Enclosed Space Register or a written Emergency Response Plan can be built as genuinely useful working documents crew actually reference, or as another compliance form nobody opens after the initial sign-off – and that outcome depends heavily on what practical detail gets fed back at exactly this stage. If your company is a British Marine member, or you have a route to respond via your flag state or trade association, this is worth a look while the detail is still being worked out, not after it's locked in.

What to Do Now, Regardless of the Consultation Outcome

1. Check whether your vessel already has an Enclosed Space Register, even informally – if not, start one now rather than waiting for a mandate to force it.
2. Review your current emergency response arrangements specifically for enclosed space rescue – is it a dedicated plan, or folded into a general emergency response document that doesn't address this scenario's specific rescue challenges?
3. Familiarise your team with the new terms – Connected/Adjacent Space and Trapped Hazardous Atmosphere – since they capture real hazard scenarios the old guidance's language didn't clearly cover.

Test Your Knowledge

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Related Reading

• Silver Condor – a real case where a life-saving procedure existed on paper but the equipment access hadn't been checked in practice