Start hereRules checked 20 October 2026
Most enclosed space accidents happen during jobs that were planned.9 What failed was one step in the chain: a test done with the fan still running, an attendant who went in to help, a permit used again the next morning, a hold access nobody had listed as dangerous.
In June 2025 the IMO replaced its 2011 recommendations with resolution MSC.581(110), Revised recommendations for entering enclosed spaces aboard ships. The Maritime Safety Committee invited the 34th IMO Assembly (24 November to 3 December 2025) to revoke the old resolution A.1050(27), and class society notices now treat it as superseded. The new text adds an Enclosed Space Register for every ship, a carbon dioxide limit before entry, a ban on single-person entry and an eight-hour maximum for permits. This lesson walks through the whole chain in order, and shows who does what.
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In this lesson
- One entry from register to rescue drill
- In plain words
- In detail
- What the rules say
- Flag and class notes
- Key numbers
- What inspectors find
- Quiz: 6 questions
Try it
One entry from register to rescue drill
In plain words
Think of an entry as a chain; break one link and people can die. Know which spaces are dangerous. Think about what the space held and what is next to it. Get a signed permit, valid for at most eight hours. Isolate the space and ventilate it, then stop the fan and wait before measuring, or the reading lies. Measure from outside, high and low, and go in only on the right numbers. Never go in alone: a trained attendant stays at the entrance with radios and rescue gear. Keep testing while people are inside. If someone collapses, raise the alarm; rescuers go in only with breathing apparatus and a plan. Practise it at least every two months.12
In detail
What changed from A.1050(27) to MSC.581(110)
| Topic | MSC.581(110) (adopted 27 June 2025) |
|---|---|
| Register | Ship-specific Enclosed Space Register listing spaces, connected and adjacent spaces, hazards, mitigations and how the atmosphere changes with the cargo or contents (2.8, 4.1, 4.2) |
| Definitions | New: connected space, adjacent space, trapped hazardous atmosphere (2.2 to 2.4); competent person, responsible person and attendant kept and redefined (2.5 to 2.7) |
| Who may authorise | The master or a responsible person at management level (master, chief mate, chief engineer, second engineer) authorised by the company (2.6, 5.1) |
| Permit | Validity based on the risk assessment and never longer than eight hours (5.2); leaving the space unattended voids it (appendix 2, note 1) |
| Single-person entry | Not permitted (3.11) |
| Gas limits | Adds CO₂ below 0.5% by volume to the oxygen, flammable and toxic limits (7.4) |
| Gas detection | At least two sets on all ships, two more where vapour-emitting cargo spaces are regularly entered (7.3) |
| Time pressure, SIMOPS | Company should allow adequate time and set criteria for simultaneous operations (3.5, 3.10) |
| Shore personnel | Schematic plan of safe and unsafe spaces at the gangway, signs on doors, joint risk assessment with terminals (6.1 to 6.3) |
| Emergency | Ship-specific emergency response plan, reviewed after each drill (4.1, 11, appendix 1) |
The register and risk assessment
The Register, kept on board and ashore, should record for each space its layout and access, physical hazards (vertical ladders, openings, heat, slippery surfaces), connections to other spaces, specific hazards such as the effect of the ballast water treatment method on the tank atmosphere, the ventilation equipment and how long it takes to achieve safe air changes, lighting, means of atmosphere testing, locking and “safe” or “unsafe” signs, and the rescue equipment needed.1
The competent person’s assessment then places the entry in one of three bands: minimal risk; no immediate risk but a risk could arise during the work; or a risk to health or life. The first two follow the general precautions; the third adds the precautions of section 9 (breathing apparatus and more).1
The permit
MSC.581(110) appendix 2 gives a model permit in five sections:1
| Section | Completed by | Main content |
|---|---|---|
| 1. Pre-entry preparation | Master or responsible person | Ventilated; isolated; tested (O₂ 20.9%, LFL below 1%, toxic below 50% OEL, CO₂ below 0.5%); frequent re-testing arranged; continuous ventilation; access and lighting; rescue equipment (hoist, winch, tripod) ready; attendant; officer of the watch informed; communications tested; equipment inspected |
| 2. Pre-entry checks | Each entrant | Permission received; section 1 complete; communication procedure and reporting interval agreed; evacuation understood |
| 3. Unsafe atmosphere | Responsible person and entrant together | Trained in the breathing apparatus; air supply, low-pressure alarm and mask checked; personal gas monitor, lighting, harness and lifeline |
| 4. Personnel entry | Responsible person | Names, time in, time out |
| 5. Completion | Responsible person | Job complete; space secured against entry; officer of the watch informed |
The permit becomes invalid if ventilation stops or any listed condition changes.1
Ventilation and testing
Ventilate until the assessment’s target is reached, then stop the fan for about 10 minutes and test.1 Steady readings needed for entry:1
- Oxygen 20.9% by volume. Anything lower, or any trace of flammable or toxic gas, means treating the space as unsafe (6.5.3).
- CO₂ below 0.5% (5,000 ppm).
- Flammable gas below 1% LFL where the assessment shows it may be present.
- Toxic gases below 50% of their occupational exposure limit.
If the numbers are not met, ventilate more and test again later. Restart the ventilation for the work and keep it running. Testing continues “frequently” while people are inside, and more often when conditions change: hot work, cleaning sludge, painting, changes in temperature, trim or list.1
People and equipment at the entrance
- Attendant: trained, stationed at the entrance, in contact with those inside, and the one who starts the emergency procedure. Under no circumstances should the attendant enter before help has arrived.1
- Communications tested and evacuation signals agreed before entry.1
- Personal gas detectors on everyone who enters, calibrated and tested, monitoring oxygen, CO₂, flammable gas, toxic gases including CO and any other gas in the risk assessment.1
- Rescue and resuscitation equipment at the entrance, tested; with work in several holds, at a central point.1
- Daylight or normal working hours where practicable, so reserve personnel are available.1
When the atmosphere is known or suspected to be unsafe
Section 9 applies when the space cannot be made safe or has not been tested. Then:1
- wear positive-pressure breathing apparatus, and only trained people enter;
- no air-purifying respirators, dust masks or canister masks, because they do not supply clean air;
- EEBDs are not suitable for entry into enclosed spaces;
- wear a rescue harness and, unless impractical, a lifeline;
- wear protective clothing where chemicals can contact the skin (lesson 6).
Breathing apparatus used for entry is normally the ship’s self-contained breathing apparatus (SCBA). SOLAS II-2/10.10 governs the fire-fighter’s outfits; the Marshall Islands, for example, points to its own notice on fire protection maintenance for SCBA checks.4
Rescue
MSC.581(110) appendix 1 gives a model emergency response plan: sound the alarm with the location; muster; consult the Register or permit for the space’s layout; rescue team dons SCBA and waits for the on-scene commander; master considers telemedical advice and, at sea, a port of refuge; the commander briefs the dangers and leads; casualties are brought out one at a time with a stretcher where possible; first aid and CPR once clear of danger.1
Drills
SOLAS regulation III/19.3.3 requires crew with entry or rescue duties to take part in an entry and rescue drill on board at least once every two months, and III/19.3.6 lists what each drill must include: checking and use of PPE, communication equipment and procedures, atmosphere measuring instruments, rescue equipment and procedures, and instruction in first aid and resuscitation.2 MSC.581(110) asks that drills cover spaces from the Register and different aspects each time.1
Work it out
What the rules say
- MSC.581(110) section 3.11 says the company should ensure that single-person entry into an enclosed space is not permitted.1
- MSC.581(110) section 5.1 says no one should open or enter an enclosed space unless authorised by the master or a nominated responsible person and the ship’s safety procedures have been followed.1
- MSC.581(110) section 5.2 says the permit’s validity should be set by the risk assessment “and should never be longer than eight hours”.1
- MSC.581(110) section 7.4 recommends steady readings of 20.9% oxygen, CO₂ below 0.5% by volume, flammable gas below 1% LFL and toxic gases below 50% of their OEL before entry.1
- MSC.581(110) section 8.3 says ventilation should be maintained while the space is occupied, the atmosphere retested and recorded after a break, and everyone should leave at once if ventilation fails.1
- MSC.581(110) section 8.5 says the attendant should under no circumstances enter before help has arrived and the situation has been evaluated.1
- MSC.581(110) section 9.2 says positive-pressure breathing apparatus should always be worn in a known or suspected unsafe atmosphere, and that EEBDs are not suitable for entry.1
- SOLAS regulation III/19.3.3 requires an enclosed space entry and rescue drill at least once every two months for crew with entry or rescue responsibilities, and III/19.3.6 sets its contents.2
- SOLAS regulation III/19.4.2.5, added by MSC.350(92), adds the risks of enclosed spaces and the on-board procedures for safe entry to the instructions that crew members must receive.2
Flag and class notes
- Marshall Islands Marine Notice 7-041-1 (Rev. Jan/2026) turns MSC.581(110) into flag requirements: drills at least every two months per SOLAS III/19.3.3 and III/19.3.6 and RMI regulation 7.41.7, with two national additions (checking sampling hose length for double bottoms and calibrating instruments); SCBA mandatory in any known or suspected unsafe atmosphere; EEBDs never to be used for entry; drill and training dates recorded in the logbook, with an explanation if a drill was not held.4
- Antigua and Barbuda SOLAS Circular 2026-002 encourages owners to build MSC.581(110) into their procedures and points to the UK Code of Safe Working Practices for Merchant Seafarers (COSWP) as recognised good practice.5
- Port state control uses these texts as the yardstick in campaigns: the 2015 Paris and Tokyo MoU campaign questionnaire covered risk awareness, atmosphere testing equipment and training, emergency duties and drills.6
- Some national rules set different safe ranges, which MSC.581(110) acknowledges in a note to section 7.4; follow your flag’s figure where it is stricter.1
Key numbers
| What | Value |
|---|---|
| Maximum permit validity | 8 h1 |
| Ventilation stopped before pre-entry test | about 10 min1 |
| Oxygen for entry | steady 20.9%1 |
| CO₂ for entry | below 0.5% (5,000 ppm)1 |
| Flammable gas for entry | below 1% LFL1 |
| Toxic gas for entry | below 50% of OEL1 |
| Single-person entry | not permitted1 |
| Entry and rescue drill | at least every 2 months2 |
| Drills observed satisfactory, Tokyo MoU 2015 | 93% of 4,4877 |
What inspectors find
- In the 2015 Tokyo MoU campaign, 96% of inspections found evidence of two-monthly drills, but only 74% gave satisfactory answers to all ten questions.7
- The Paris MoU found 7.9% of observed drills unsatisfactory in the same campaign.8
- Investigations repeatedly find unequipped rescue attempts: the attendant or a colleague goes in, as on Sally Ann C and Berge Mawson.310
- The Sally Ann C report quotes audits where enclosed spaces were entered without permits or risk assessments; one ship had paperwork for only one of five fresh water tank entries.3
- On Berge Mawson the ship-shore safety checklist had little value once cargo work began, stevedores were unsupervised and accesses were left unlocked.10
FAQ
Can the attendant also be the person who tests the atmosphere?
MSC.581(110) does not forbid it, but the roles differ. The competent person makes the assessment and tests; the attendant’s job is to stay at the entrance and raise the alarm. Whoever tests must be trained in the instrument.
Can we use the EEBD as an emergency set while working in a tank?
MSC.581(110) section 9.2 says EEBDs are not suitable for entry, and the Marshall Islands forbids their use for entry. They are escape devices with a short duration. If the atmosphere may be unsafe, wear SCBA.
Does the permit need renewing after lunch?
If people left the space and it was unattended, the model permit says the permit is void and a re-inspection is needed. In any case, MSC.581(110) section 8.3 requires a retest and record before re-entry after a break.
Do shore workers fall under the ship's permit?
The recommendations apply to shore personnel working on board. The ship should give them hazard information, post a plan of safe and unsafe spaces at the gangway, and agree a joint risk assessment and permit arrangements with the terminal or contractor before they enter.
Quiz6 questions
Sources
- 1
IMO Resolution MSC.581(110), Revised recommendations for entering enclosed spaces aboard ships (adopted 27 June 2025), resolution paragraph 3 and Annex, sections 2 to 11 and appendices 1 and 2. https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.581(110).pdf
- 2
IMO Resolution MSC.350(92), Amendments to SOLAS (adopted 21 June 2013, in force 1 January 2015), Annex, regulation III/19 paragraphs 3.3, 3.6 and 4.2.5. https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.350(92).pdf
- 3
Isle of Man Ship Registry, Casualty investigation report: Sally Ann C, enclosed space fatalities and near fatality, 13 March 2015, Summary, section 2.4 and appendix 2. https://www.iomshipregistry.com/media/1124/cr-sally-ann-c-enclosed-space-fatalities-and-near-fatality.pdf
- 4
Republic of the Marshall Islands Maritime Administrator, Marine Notice 7-041-1, Entering enclosed spaces: safety precautions (Rev. Jan/2026), sections 1.4, 5 and 6. https://www.register-iri.com/wp-content/uploads/MN-7-041-1.pdf
- 5
Antigua and Barbuda Department of Marine Services and Merchant Shipping, SOLAS Circular 2026-002, Enclosed space entry (17 March 2026), paragraphs 4.3 and 4.5. https://abregistry.ag/wp-content/uploads/2026/03/SOLAS-Circular-2026-002-Enclosed-Space-Entry.pdf
- 6
West of England P&I Club, Port state control: Paris and Tokyo MoUs concentrated inspection campaign on crew familiarisation for enclosed space entry (31 July 2015). https://www.westpandi.com/news-and-resources/news/port-state-control-paris-and-tokyo-mous-concen-(4)/
- 7
Tokyo MoU results of the 2015 concentrated inspection campaign on crew familiarization for enclosed space entry, as reported by The Maritime Executive. https://maritime-executive.com/article/strong-commitment-to-enclosed-spaces-safety
- 8
Paris MoU preliminary results of the 2015 concentrated inspection campaign on enclosed space entry, as reported by MarineLink (23 February 2016). https://www.marinelink.com/news/satisfactory-performance405552
- 9
InterManager, The analysis of enclosed-space accidents on board ships, IMO document III 12/INF.17 (15 May 2026), Annex paragraphs 15 to 18. https://hksoa.org/wp-content/uploads/2026/06/III-12-INF.17-The-analysis-of-enclosed-space-accidents-on-board-ships-InterManager.pdf
- 10
MAIB on behalf of the Isle of Man Administration, Report 5/2025, Berge Mawson (March 2025), Synopsis. https://www.iomshipregistry.com/media/qoucqgn3/2025-5-bergemawson-reportandannexes.pdf
Rules checked 20 October 2026. VSL Safety is not an approved training provider and doesn't issue certificates. These lessons don't replace STCW training, or the manufacturer's training and certification that service technicians need.
