Technical Notices

INSB Class draws the attention of Shipowners, Managers, Masters, and INSB Surveyors to IMO Resolution MSC.581(110), Revised Recommendations for Entering Enclosed Spaces Aboard Ships, adopted on 27 June 2025, which replaces the previous IMO recommendations and introduces enhanced safety expectations, procedural clarity, and training requirements.

This Circular is issued to highlight the key changes and expectations arising from the revised IMO recommendations and to provide guidance on their effective implementation within the Safety Management System (SMS).

This Circular updates the guidance contained in INSB Class Circular ISM 39/2025.

1. Background and Safety Context

Despite long-standing guidance, fatal accidents related to enclosed space entry continue to occur, often involving multiple casualties during attempted rescues. Investigations consistently identify:

• Inadequate risk assessment
• Failure to recognize enclosed spaces
• Insufficient atmosphere testing and monitoring
• Lack of effective supervision and rescue preparedness
• Complacency and procedural non-compliance

IMO Resolution MSC.581(110) strengthens the previous framework by placing greater emphasis on human factors, training effectiveness, leadership, and operational discipline, moving beyond a checklist-only approach.

2. Key Enhancements Introduced by IMO Resolution MSC.581(110)

Based on a review of the revised IMO recommendations and aligned industry guidance, the following key enhancements and expectations are highlighted:

2.1 Clearer Identification of Enclosed Spaces

• Expanded clarification on spaces that may be considered enclosed, including those not normally entered or temporarily enclosed.
• Emphasis on vessel-specific identification and marking of enclosed spaces.

2.2 Strengthened Risk Assessment Requirements

• Mandatory task-specific risk assessment prior to each entry.
• Consideration of previous cargoes, residues, cleaning agents, and biological activity.
• Explicit evaluation of human factors, fatigue, and competence.

2.3 Enhanced Atmosphere Testing Requirements

All ships should carry at least two sets of gas detection equipment as required by SOLAS regulation XI-1/7, Any ship which may carry a cargo capable of generating hazardous vapors and which requires regular entry into the cargo space should carry two additional sets.

Based on the results of the risk assessment, the atmosphere should be tested using calibrated instruments before entry and during entry:

• Oxygen content: 20.9%
• Carbon dioxide (CO2): less than 0.5% (5,000 ppm)
• Flammable gases or vapors: less than 1% of LFL (The assessment has determined that there is potential for flammable gases or vapors)
• Toxic gases: below 50% of applicable occupational exposure limits

 2.4 Permit-to-Work and Control Measures

• Enhanced expectations for the enclosed space entry permit, ensuring:
  • Defined roles and responsibilities
  • Clear authorization and supervision
  • Communication arrangements
• Emphasis on strict adherence to permit conditions.

2.5 Training, Drills, and Competence

• Improved guidance on quality and effectiveness of training, not merely frequency.
• Enclosed space drills to reflect realistic scenarios, including:
  • Use of Rescue equipment
  • Communication
  • Rescue coordination
• Focus on ensuring crew understand why procedures exist, not only how to complete them.

2.6 Rescue Preparedness and Emergency Response

• Clear reinforcement that no person shall enter an enclosed space for rescue without proper equipment and procedures.
• Emphasis on:

• • Dedicated rescue plans
  • Availability and readiness of rescue equipment
  • Avoidance of impulsive rescue attempts

 2.7 Enclosed Space Entry Permit

• • Entry should be conducted under an Enclosed Space Entry Permit (5.2)
  • The validity of the permit should not exceed 8 hours (5.2)

2.8 Enclosed Space Register

Each ship should maintain an Enclosed Space Register containing, as a minimum:

• Identification of enclosed spaces
• Space-specific hazards
• Ventilation and atmosphere testing methods
• Information on connected or adjacent spaces
• Emergency rescue equipment requirements

The register should be managed as part of the SMS and reviewed periodically

3. Impact on Safety Management Systems (SMS)

Shipowners and Managers are expected to:

• Review and update SMS procedures related to enclosed space entry to align with IMO Resolution MSC.581(110).
• Ensure procedures are ship-specific, practical, and clearly communicated.
• Verify that enclosed space entry documentation, permits, and checklists reflect the revised recommendations.
• Reinforce a safety culture where enclosed space entry is treated as a high-risk operation, regardless of perceived routine.

Ship management companies are recommended to incorporate the following into their SMS in accordance with MSC.581(110):

• • Enclosed space entry procedures
  • Risk assessment processes
  • Permit-to-work systems
  • Emergency response plans and Enclosed Space Register
  • Training, drills, and authorization

4. Guidance to Shipowners, Managers, and Masters

INSB Class strongly recommends that:

• All crew are made fully aware of the revised IMO recommendations.
• Enclosed space entry procedures are reviewed, practiced, and enforced.
• Masters exercise clear leadership and control over enclosed space entry operations.
• Lessons learned from drills, near misses, and incidents are recorded and acted upon.
• Entry into enclosed spaces is avoided unless absolutely necessary.

5. Guidance to INSB Class Surveyors

INSB Class Surveyors are requested to:

• Verify that vessels are aware of IMO Resolution MSC.581(110).
• Confirm that enclosed space entry procedures have been reviewed and updated, where applicable.
• Assess the effective implementation of procedures during audits and inspections, including:

– Crew familiarity

-Permit usage

– Training and drills

• Raise observations where procedures exist but are not effectively implemented.