One cargo, two kinds of hazard
A booking described simply as “DRI fines” is not specific enough to plan this voyage. The IMSBC Code’s DIRECT REDUCED IRON (D) schedule covers by-product fines with moisture content of at least 2% that have been aged for at least 30 days. It classifies the cargo in Groups A and B: it may liquefy if its moisture exceeds its transportable moisture limit (TML), while reactions with air or water can produce heat and flammable hydrogen. The same schedule warns that oxygen may be depleted in the hold and enclosed adjacent spaces. Identifying the applicable schedule is therefore the first operational decision, not a paperwork detail. ([wwwcdn.imo.org](https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.539%28107%29.pdf))
Build the evidence before the cargo reaches the ship
The shipper must provide certificates addressing natural preparation and ageing for at least 30 days and confirming that the cargo does not meet the criteria for class 4.2 materials. The stockpile temperature must be measured and logged over three consecutive days before loading; cargo above 65°C must not be loaded. On completion of loading, a further certificate must establish that material larger than 12 mm is no more than 3% by weight, moisture is at least 2% but below the TML, and cargo temperature does not exceed 65°C. These are separate checks: an acceptable moisture result does not answer the temperature or particle-size questions. ([wwwcdn.imo.org](https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.539%28107%29.pdf))
The schedule also calls for the shipper to give the master comprehensive information about hydrogen evolution and factors affecting its rate, and to provide contact details for expert advice throughout the voyage. Use that information to test the proposed passage against weather, possible ventilation interruptions and access to suitable ports of refuge. A route on which the ventilation system may be unusable for longer than the estimated time for hydrogen to reach the schedule’s limit needs reassessment, not just a note in the handover file. ([wwwcdn.imo.org](https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.539%28107%29.pdf))
Loading ends with a measured waiting period
Prepare clean, dry cargo spaces free of salt, old cargo residue and combustible debris. Because these fines are dense, spread them so a loading pile does not overstress the tank top. Record the temperature of each lot loaded. If weather permits and there is no precipitation, the schedule provides for hatches to remain open after loading and thermocouple placement to let the cargo cool and stabilize; otherwise they are to be closed and sealed immediately, with temperature and hydrogen monitoring begun. ([wwwcdn.imo.org](https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.539%28107%29.pdf))
Departure is not simply the moment the last grab is discharged into a hold. The schedule specifies a wait of 24 hours after loading, or longer if needed, to verify sealed holds and at least 12 consecutive hours of stable cargo temperatures no higher than 65°C and stable head-space hydrogen no higher than 1% by volume. Build that observation period into the loading and sailing plan rather than treating it as an unexpected delay. ([wwwcdn.imo.org](https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.539%28107%29.pdf))
Ventilate the surface, not the body of the cargo
For DRI (D), ventilation is a controlled response to measured hydrogen. The schedule requires certified-safe mechanical surface ventilation capable of at least 1.2 cubic metres per hour per tonne in each loaded hold when needed, with capacity to reduce hydrogen to 0.2% by volume or less. Gas is to be extracted, not displaced by blowing outside air into the hold; air must not be directed into the cargo body. Limit ventilation periods to what is needed to keep hydrogen below 1%, so the system does not introduce unnecessary oxygen and moisture. Before loading, check that the system works and that the specified spare equipment and a person able to install it will be aboard. ([wwwcdn.imo.org](https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.539%28107%29.pdf))
Record hydrogen, oxygen and cargo temperature at least daily during the voyage, increasing monitoring when readings, weather or equipment problems warrant it. The schedule calls for a time-based hydrogen prediction curve before sailing and updates when conditions change. If hydrogen approaches 1%, check ventilation, increase surface ventilation where possible, guard against ignition and monitor more often. A rising reading is a prompt to act and reassess the passage—not a reason to open a hold without considering the schedule’s precautions. ([wwwcdn.imo.org](https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.539%28107%29.pdf))
Keep the discharge threshold separate from entry clearance
Immediately before opening a hatch for discharge, measure hydrogen in that hold. If it exceeds 1% by volume, the DRI (D) schedule says not to open the hatch: apply additional ventilation until the reading falls to 1% or less, and take care to avoid sparks during opening. That threshold permits the hatch-opening decision; it does not certify the hold or a connected space safe for people to enter. ([wwwcdn.imo.org](https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.539%28107%29.pdf))
The schedule prohibits entry into a loaded hold or enclosed adjacent space until it has been ventilated, tested and found gas-free with sufficient oxygen. IMO’s enclosed-space recommendations likewise warn that hazardous atmospheres can persist in connected spaces even after a hatch is opened. Keep atmosphere testing and entry control as a distinct task in the discharge handover. ([wwwcdn.imo.org](https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.539%28107%29.pdf))
Resolution MSC.539(107): 2023 Amendments to the International Maritime Solid Bulk Cargoes (IMSBC) Code · Resolution MSC.581(110): Revised Recommendations for Entering Enclosed Spaces Aboard Ships