ISM News
From ISM News Update nr. 139: Resolution MSC.581(110), CO2 as a risk
July 2026
Other news from this ISM News Update:
- Safety improvement sheet no.13 – Caught in Action
- Emission Control in the North Atlantic
- Updated ISPS Security Interpretations for ships flying the flag of the Netherlands
- Safety Improvement Sheet No. 14: Disrupted GPS Signals
- Ship Security Plan, Cyber Security measures and Cross Reference for download
Additional information on Resolution MSC.581(110), specifically on CO2 as a risk
In the last ISM Newsupdate Nr 138 we informed about the revision of Resolution MSC.581(110). These revised recommendations entered into force on 3 December 2025, replacing the previous guidance issued in 2011.
The most important change is that carbon dioxide (CO₂) has now been explicitly included as a gas that must be assessed whenever there is a potential risk of its presence. Previously, the focus was primarily on:
- Oxygen (O₂)
- Flammable gases (LEL)
- Hydrogen sulphide (H₂S)
- Carbon monoxide (CO)
Under the revised recommendations, CO₂ must also be measured where it may accumulate, for example in:
- Cargo holds
- Bulk cargo spaces carrying wood pellets, grain, biomass or similar cargoes
- Spaces adjacent to fixed CO₂ fire-extinguishing systems
- Tanks
- Void spaces
- Other enclosed spaces where CO₂ accumulation is possible
In addition, the recommended atmospheric acceptance criteria prior to entry have been updated. Before personnel enter an enclosed space, the atmosphere should be verified as follows:
- Oxygen: approximately 20.9 vol%
- Carbon dioxide (CO₂): less than 0.5 vol% (5,000 ppm)
- Flammable gases: less than 1% of the Lower Flammable Limit (LFL)
- Toxic gases: below 50% of the applicable Occupational Exposure Limit (OEL)
These changes have significant implications for portable gas detection equipment.
Many existing 4-gas detectors (measuring O₂, LEL, CO and H₂S) are no longer sufficient for all enclosed space entry applications. As a result, many shipowners are upgrading to 5-gas detectors equipped with an CO₂ sensor. We advise making a thorough risk assessment to find out whether the CO₂ measuring is applicable for your vessels.
The revised guidance also places greater emphasis on personal gas monitoring. Instead of relying solely on a pre-entry atmospheric test, personnel entering enclosed spaces should ideally wear a personal multi-gas detector that continuously monitors the atmosphere throughout the entire entry.