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On board a vessel, maintenance almost never kills through the tool. It kills through the atmosphere. A ballast tank, a peak tank, a chain locker, a bilge well: the oxygen there has been consumed by rust, or displaced by an inert gas, and the man who climbs down passes out in three breaths. What follows is always the same: a second man goes down to rescue him without equipment, then a third. It is the leading cause of multiple fatal accidents on board merchant vessels.

That reality explains why the safety of maintenance work on board cannot be handled as it is ashore. On an industrial site, you evacuate and the emergency services arrive within fifteen minutes. At sea, the crew is at once the worker, the rescue party and the only resource available, sometimes several days from the nearest hospital. The prevention arrangements have to be sized for that constraint.

This article covers the four permits to work that structure a job on board, isolation applied to a vessel's energy sources, the management of competence in the STCW sense, and what the resolution adopted by the IMO in June 2025 changes for enclosed spaces.

The framework: what the ISM Code requires

Unlike the shore-based industrial world, where occupational safety is a matter of national law, the safety of operations on board a merchant vessel is structured first and foremost by the ISM Code.

Its chapter 7 requires the company to establish procedures, plans and instructions for key shipboard operations, identifying those that bear on safety and pollution prevention. That is the foundation of the permit to work system. Its chapter 8 deals with emergency preparedness, from which the drills follow. Its chapter 6 requires every newly joining seafarer to receive documented familiarisation before taking up their duties.

The vessel also remains subject to the labour law of its flag State, which may add requirements of its own. But it is the company's SMS that will be examined in an audit, and it is the SMS that defines in practical terms who authorises what, on what basis and with what record.

The four permits that frame a job on board

A permit to work system is not an administrative formality: it is a stopping mechanism. It obliges someone to check, before the work starts, that the conditions are met — and to answer for it.

These permits often overlap. Welding inside a ballast tank means three permits at once: enclosed space entry, hot work, and isolation of the circuits running through the tank. It is precisely in those combinations that accidents occur, because one of them is forgotten.

Enclosed spaces: what resolution MSC.581(110) changes

This is the most significant regulatory development on the subject in ten years, and it is recent. The IMO adopted resolution MSC.581(110) on 27 June 2025 at the 110th session of its Maritime Safety Committee, revoking and replacing resolution A.1050(27) in force until then.

The main contributions, from the point of view of organisation on board:

• A register of enclosed spaces must now be kept on board. It lists the spaces concerned, their particular hazards and the conditions of access to them. It is a living document, not a list drawn up once and for all.
• A dedicated emergency response plan for enclosed spaces must be established. It addresses directly the improvised rescuer scenario, which remains the dominant cause of multiple casualties.
• New definitions widen the scope: connected space, adjacent space, trapped hazardous atmosphere. A space can be dangerous without anyone having entered it, through communication with another.
• Detection equipment must be suited to the cargoes the vessel actually carries, with particular attention to CO₂ and to solid bulk cargoes.

These recommendations sit alongside two SOLAS requirements already in force: regulation III/19.3.6, which requires enclosed space entry and rescue drills, and regulation XI-1/7, which requires a portable atmosphere testing instrument to be carried on board.

What to do about it in practice. Review your SMS procedures and your detection equipment in the light of the new text, and approach your flag State to find out the arrangements it adopts for applying it. A register of enclosed spaces that does not yet exist on board is a non-conformity that will show up at the next audit.

Isolation applied to a vessel's energy sources

Isolation — lock-out tag-out in international usage — follows the same sequence everywhere. What changes on board is the range of energies involved and the fact that the person who authorises is also the person who operates the plant.

1. Separation. Cut every source: electrical at the main switchboard or at the feeder concerned, starting air, hydraulics, steam, pressurised sea water lines.
2. Locking. Physical locking of the isolating device. Each person working fits their own padlock: as long as one padlock stays in place, putting the equipment back into service is impossible.
3. Identification. A tag carrying the name of the person working, the date and the nature of the job. On board, where the team is small and everyone knows everyone, this is the step most readily skipped — and the one missing when the next watch starts the machine again.
4. Verification. A start attempt or an instrument reading. It is the only tangible proof that the separation has worked.
5. Dissipation. Removal of residual energy: pressure left in a hydraulic accumulator, trapped steam, a loaded spring, a charged capacitor, and heat — an exhaust manifold takes hours to come down.

Two maritime specifics deserve to be underlined. The first is redundancy: shutting down one generator set out of three does not remove the need to isolate it, because automatic load management can start it again on its own. The second is the watch handover: an isolation that spans a change of watch has to be handed over explicitly, otherwise the officer coming on will not know why that valve is shut.

Competence: what really applies at sea

Managing qualifications on board is not a matter of national electrical authorisations or of shore-based plant operator permits. It rests on three levels.

STCW certificates first: they define who may perform which function, with what limits of power or tonnage, and they carry flag State endorsements. Their validity expires, and an expired certificate is a classic ground for a remark at port State control.

Specific safety training next: advanced fire fighting, survival craft, first aid, and depending on the vessel, training related to dangerous cargoes.

Familiarisation on board last, required by chapter 6 of the ISM Code. It is specific to this vessel: where the isolating switches are, how this extinguishing system works, what the particular features of this engine room are. It is the most neglected and the most frequently raised in audits.

The critical point is rotation. Ashore, a qualification is checked on hiring. On board, the team changes completely several times a year, and the question "who, today, is qualified for this job" has to be answerable instantly. That is the role of the Crew module, which tracks certificates, medical examinations and individual expiry dates.

Chemicals on board

Solvents, degreasers, paints, water treatment products, refrigerants: the engine room and the paint store hold a considerable quantity of them, in poorly ventilated compartments. Every product must have its safety data sheet, available where the product is used and not in a binder in the master's office.

The information that matters at the moment of the job comes down to four points: the personal protective equipment required, incompatibility with other products stored nearby, what to do in case of exposure, and the handling of residues — which falls under MARPOL and is not thrown over the side.

What a CMMS changes in practice

A paper permit system works as long as the team is stable and nobody is in a hurry. It gives way in exactly the circumstances where it is most needed: a short port call, a crew change, a breakdown to be dealt with urgently.

A marine CMMS brings three things here.

The permit attached to the work order. The task does not open until the check points have been validated and time-stamped. It is that binding character which makes the difference with a form filled in after the event.

The competence check at assignment. The system compares the qualifications the task requires with those actually held and in date, and blocks the assignment where there is a gap. That removes an entire class of human error.

The proof. Every permit issued, every isolation applied and lifted, every drill carried out leaves a dated and attributed record. In an ISM audit as in a port State control inspection, it is this documentary continuity that distinguishes a system applied from a system written down. The digital engine room logbook carries the same logic for day-to-day operation.

The condition, as always on board, is that it works offline. A permit that cannot be issued because the satellite link has dropped will not be issued at all: the work will be done anyway, without a record.

Frequently asked questions

Does national labour law apply on board?

The labour law of the flag State applies to seafarers, but the safety of operations on board is structured first by the international instruments — ISM Code, SOLAS, STCW — and by the company's safety management system. It is the latter that will be examined in an audit.

Who issues a permit to work on board?

It depends on the permit and on what the SMS provides for. Enclosed space entry and hot work typically fall to the master or to an officer he designates; machinery isolation, to the chief engineer. The constant rule is that the person who authorises must not be the person who carries out the work.

Is a permit needed for a ten-minute job?

If the job falls into one of the four categories, yes. Duration does not reduce the risk: a two-minute entry into an unventilated ballast tank is fatal. Brevity is in fact an aggravating factor, because it serves as the argument for skipping steps.

What exactly does the new resolution on enclosed spaces say?

Resolution MSC.581(110), adopted on 27 June 2025 at the 110th session of the Maritime Safety Committee, replaces A.1050(27). It introduces a register of enclosed spaces kept on board, a dedicated emergency response plan, new definitions covering connected and adjacent spaces, and clarifies the suitability of detection equipment for the cargoes carried.

How often should the crew be drilled?

SOLAS regulation III/19.3.6 requires enclosed space entry and rescue drills. Beyond the required interval, the useful question is whether the drill has ever been run with the actual recovery harness, in the actual space. A classroom exercise prepares nobody for anything.

In summary

The safety of maintenance work on board rests on a simple principle: nobody starts before somebody else has checked and taken responsibility for it. The four permits give that principle form, isolation makes it physical, and competence management ensures that the right person does the work.

What is most often missing is not the procedure but its continuity: between two watches, between two crews, between ship and shore. That is what 91�鶹��Ʒ is designed to hold — permits linked to work orders, qualification checks at assignment, a record that stands up in an audit, all of it usable offline. The marine CMMS is developed in Marseille by seafarers and deployed on more than 700 vessels. Request a demonstration on your own procedures.

This article presents the international framework for information. The way IMO resolutions are applied depends on your flag State and on the type of vessel. Refer to your safety management system and to your classification society.

Isolation is only as good as the rights behind it: role and permission control with an audit log proves who authorised what, and when. Safety and maintenance are steered in the same tool, whose components our maritime CMMS guide describes.