What has to be finished before anyone signs an enclosed space entry permit (MSC.581(110))

On 27 June 2025 the IMO Maritime Safety Committee revised the recommendations for entering enclosed spaces by resolution MSC.581(110). The resolution invites the Assembly to revoke the earlier A.1050(27). As recommendations they carry no force of their own. What the preamble recalls, though, is that the entry and rescue drills of SOLAS regulation III/19.3.6 and the atmosphere testing instruments of regulation XI-1/7 are Convention obligations.

The order in the recommendations is clear. The register is made, the risk assessment is done, the atmosphere is tested, and then the permit is issued. The permit confirms that the work before it is finished; it is not a document that stands in for that work.

This article goes through what has to be finished before the permit is signed, in the order of the text. The definitions, the register and the risk assessment, who issues and for how long, the four readings, the rules during entry, and the signature boxes on the form in the appendix.

A space is enclosed if it has any one of three characteristics

2.1 Enclosed space means a space which may contain a hazardous atmosphere or lack of oxygen and has any of the following characteristics: .1 limited openings for entry and exit; .2 inadequate ventilation; or .3 not designed for continuous human occupancy.

The condition is any of the following. All three do not have to be present; one is enough. The text gives cargo holds, bilge spaces, ballast and other tanks, pump-rooms, chain lockers and engine crankcases as examples.

Paragraphs 2.2 and 2.3 define connected spaces and adjacent spaces separately. A space joined by a single door counts as connected even if the door is watertight, and it is treated as holding a hazardous atmosphere until testing proves otherwise.

There are three roles for people.

2.6 Responsible person means a person in a management level on board a ship (i.e. master, chief mate, chief engineer officer or second engineer officer) of competency and authorized by the shipping company to permit entry into an enclosed space. 2.7 Attendant means a person maintains a watch over those entering the enclosed space, to maintain communications with those inside the space and to initiate the emergency procedures in the event of an incident occurring.

The responsible person is a management-level officer whom the company has authorized to permit entry. The attendant keeps watch at the entrance, maintains communications with those inside and starts the emergency procedures. The competent person in paragraph 2.5 has the operational-level competency to judge whether a dangerous atmosphere is likely to be present. These are roles rather than ranks, but the attendant cannot leave the entrance.

The register and the risk assessment come before the permit

4.1 The company should ensure that a risk assessment is conducted to identify all enclosed spaces on board the ship and that the identified enclosed spaces are recorded in the Enclosed Space Register, which should be maintained on board the ship as well as ashore.

The first purpose of the risk assessment is to find every enclosed space on the ship. The result goes into the Enclosed Space Register, kept both on board and ashore. Paragraph 4.2 lists twelve items for the register. The layout of the space and its access points, physical hazards, connections to adjacent spaces, ventilation equipment and the time it takes to ventilate for safe entry, means of atmosphere testing, locking and signage, and rescue equipment.

4.8 Throughout the assessment process, there should be an assumption that the space to be entered is considered as hazardous until positively proved to be safe for entry.

The assessment starts from the assumption that the space is hazardous. Until positively proved safe, it remains a hazardous space. Paragraph 4.5 splits the outcome three ways. Minimal risk to health or life, no immediate risk but one that could arise during the work, and an identified risk. The third outcome brings in the additional precautions of section 9. Positive-pressure breathing apparatus and rescue harnesses are among them.

The permit is issued by the master or a nominated responsible person and runs no longer than eight hours

5.1 No person should open or enter an enclosed space unless authorized by the master or a responsible person nominated by the master and the appropriate safety procedures laid down for the particular ship have been followed.

Opening is covered as well. open or enter. Lifting a manhole cover is already something that needs authorization. The authority sits with the master or a responsible person nominated by the master.

The validity of the permit should be specified based on the risk assessment and should never be longer than eight hours.

Paragraph 5.2. The validity comes out of the risk assessment and can never exceed eight hours. Note 1 to appendix 2 adds one more thing. If the people inside leave the space and it is left unattended, the permit is void and a re-inspection is required. Going back into a space that was vacated for a meal on the same permit runs into this note.

Paragraph 5.3 says other permits may overlap. Energy isolation, electrical isolation, hot work and working at height permits are the examples. One enclosed space permit does not authorize those tasks.

There are four pre-entry readings and they are taken with the ventilation stopped

7.4 After completion of a suitable risk assessment targeted to the space to be entered steady readings of all of the following should be obtained: .1 20.9% oxygen by volume; .2 the level of carbon dioxide has been checked and is less than 0.5% by volume (5,000 ppm); Note: National requirements may differ when determining the safe atmosphere range for gases stated above. .3 less than 1% of lower flammable limit (LFL) on a suitably sensitive combustible gas indicator, where the assessment has determined that there is potential for flammable gases or vapours; and .4 less than 50% of the occupational exposure limit (OEL) of any toxic vapours and gases.

Item	Reading that allows entry	Note
Oxygen	20.9% (by volume)	The same value as normal air
Carbon dioxide	Less than 0.5% (5,000 ppm)	National requirements may differ
Flammable gas	Less than 1% of LFL	Where the assessment found flammable potential
Toxic gases and vapours	Less than 50% of OEL	Which gases to test for is set by the assessment

Note that the oxygen criterion is a single value, 20.9%, rather than a range. Paragraph 6.5, item .3 says that if the reading is below 20.9%, or shows even low levels of flammable or toxic gas, the space is treated under section 9 as one whose atmosphere is known or suspected to be unsafe. Paragraph 7.7 adds that testing for flammability or oxygen is no substitute for testing for toxicity.

7.6 Any gas testing should be carried out with ventilation to the enclosed space stopped, and after conditions have stabilized, in order to obtain accurate readings.

Testing is done with the ventilation stopped and after the atmosphere has settled. A reading taken while the fans run measures the air being blown in, not the atmosphere of the space. Note 2 to appendix 2 says ventilation should be stopped for about 10 minutes before the pre-entry tests. Paragraph 7.5 has the space ventilated further and retested if the conditions are not met, and allows entry only when all of them are.

Single-person entry is not permitted and the attendant never enters first

3.11 The company should ensure that single person entry into an enclosed space is not permitted.

It is written as something the company ensures. Making sure that a quick look inside is not allowed on board is a matter of the company’s system.

8.5 In the event of an emergency, under no circumstances should the attendant enter the space before help has arrived and the situation has been evaluated to ensure the safety of those entering the space to undertake rescue operations. Only properly trained and equipped personnel should perform rescue operations in enclosed spaces.

What the text forbids is the attendant going in on seeing a colleague collapse. under no circumstances. Paragraph 11.1 extends the same words to everyone on board and to shore personnel. Rescue entry follows the agreed rescue plan and nothing else. Paragraph 11.2 writes into the text that the urge to enter is immense, and that it is always to be resisted.

Paragraph 8.3 has anyone inside leave immediately if the ventilation fails. Before re-entry after a break, the atmosphere is retested and the result recorded.

The form in the appendix closes with three signatures

The example permit in appendix 2 has five sections. Section 1 is the pre-entry preparation checked by the master or the nominated responsible person. Ventilation, isolation, the four readings, rescue equipment, the designated attendant, notice to the officer of the watch and the communications test are here. Section 2 is checked by each person entering. Whether permission was received, whether section 1 is complete, and what reporting interval in minutes was agreed. Section 3 is for a space whose atmosphere is known or suspected to be unsafe, checked jointly by the responsible person and the person entering.

Once sections 1 to 3 are complete, the master or nominated responsible person, the attendant and the person entering each write the date and time and sign. Section 5 is closed by the responsible person after the job. The times of job completion, securing the space against entry and informing the officer of the watch go there.

THIS PERMIT IS RENDERED INVALID SHOULD VENTILATION OF THE SPACE STOP OR IF ANY OF THE CONDITIONS NOTED IN THE CHECKLIST CHANGE

That sentence sits at the foot of the form. If the ventilation stops or any one condition on the checklist changes, the permit is void. It is void even with hours of the eight still to run.

Worth confirming

The passages above are from the annex to MSC.581(110). The resolution takes the form of inviting Governments to bring the recommendations to the attention of shipowners, seafarers and ports and to urge their application. Where flag State law or the company SMS sets a stricter standard, that standard applies.

As the note to the readings says, national requirements for the safe atmosphere range may differ. Paragraph 3.9 has the company’s internal audits and the Administration’s external audits verify that these procedures are followed. This article covers the body of the resolution and appendices 1 and 2 only, and does not go into section 10 on cargo hazards by ship type.

You can consult the cited source documents

These links lead to the official publishers of the documents discussed here. Match the edition and provisions cited in the article, and check subsequent amendments and flag-state implementation before applying them.

• IMO · MSC.581(110)

Continue with the related operational guidance

• The five steps of a shipboard risk assessment and the order of preventive measures (MLC Standard A4.3 and the ILO guidelines)
• The headcount that makes a safety committee mandatory and the boundary between safety representatives and the master’s designee (MLC Standard A4.3)