Introduction

The International Maritime Organization (IMO) has adopted Resolution MSC.581(110), providing revised recommendations for entering enclosed spaces aboard ships. These guidelines, adopted on 27 June 2025, aim to prevent the continued loss of life resulting from personnel entering shipboard spaces where the atmosphere is unable to support life due to oxygen depletion, oxygen enrichment, toxicity, or flammability. It is suggested that Members review their Safety Management Systems to incorporate the recommendations of Resolution MSC.581(110) for the safety of their crews and for prevention of risk to Personnel on board their ships.

The revised recommendations adopted by Resolution MSC.581(110) on 27 June 2025 introduce several critical updates to safety procedures for entering enclosed spaces. The most significant changes focus on enhanced definitions, the mandatory Enclosed Space Register, and rigorous new standards for Carbon Dioxide (CO₂) monitoring.

Significant changes are as follows:

a. Section 2

The revisions provide a more granular understanding of hazardous areas beyond the immediate entry point:

Connected space: This is defined as any space connected to a source space containing a hazardous atmosphere via a door. It must be treated as hazardous until testing proves otherwise.

Adjacent space: This is defined as a space sharing a common boundary with a compartment which may contain hazardous atmosphere. Such space has no openings whatsoever, temporary or permanent and is designed to be a contiguous barrier.

Trapped hazardous atmosphere: A hazardous atmosphere that may be trapped in a connected space in a manner that causes that space’s atmosphere to fill and/or to empty at a different rate to the source space.

Competent and Responsible Persons: Clearer distinctions are made between operational-level competency (Competent Person) and management-level authority (Responsible Person).

Attendant: A person maintain watch over those entering the enclosed space, maintains communications with those inside the space and initiates emergency procedures in the event of an incident.

Enclosed space register: Means a ship-specific register which lists all enclosed spaces on board, along with their connected spaces and adjacent spaces, their hazards, associated risk mitigations if applicable, and how the atmosphere in these spaces may change depending upon the nature of the cargo carried or the content of the space, and which forms a part of the safety management for the enclosed spaces.

b. Section 3 and 4

There is a requirement for a ship-specific Enclosed Space Register. This is a comprehensive safety document that must include:

A physical layout of the space, including all access and egress points.

Identified connections to adjacent spaces.

Estimated time required for ventilation to achieve safe air changes.

Specific hazards, such as the effects of ballast water treatment or oxygen-depleting cargoes.

c. Section 5

The rules regarding the Entry Permit have been tightened:

Validity Period: The permit validity must be based on risk assessment and capped at a maximum of eight hours.

d. Section 6

Careful management of access (entry points) to enclosed spaces, on ships especially bulk carriers and general cargo vessels where shore personnel regularly enter cargo spaces for loading and unloading operations.

It is recommended that basic schematic plans to be placed on ship access points like gangways clearly indicating which spaces are safe to enter and which spaces are unsafe. Enclosed spaces entry procedures to be complied with by ship/shore personnel to be part of this plan.

e. Section 7

Another critical revision is the mandatory inclusion of Carbon Dioxide (CO₂) in atmospheric testing:

Mandatory CO₂ Testing: Ships must carry equipment to test for CO₂ in addition to the standard gases.

The space to be entered once steady readings of all the following is obtained:

Oxygen: 20.9% by volume.

CO₂: Less than 0.5% by volume (5,000 ppm).

Note: Check National requirements as well which might differ from these levels.

Flammable Gases or vapours: Less than 1% of the lower flammable limit (LFL).

Toxic Vapours: Less than 50% of the occupational exposure limit (OEL).

All ships are required to carry at least two sets of gas detection equipment as per SOLAS regulation XI-1/7. A ship which may carry a cargo capable of generating hazardous vapours and which requires regular entry into the cargo space for cleaning or inspection is required to carry two additional sets of gas detection equipment. The use of flexible hoses or fixed sampling lines will assist with safe testing of remote areas within the enclosed space without the need to enter the space.

f. Section 10

This section lists Hazards related to specific type of ships or cargoes.

g. Section 11

The revisions reinforce following the ship-specific enclosed space emergency response plan in case of emergency.