Direct Reduced Iron: IMSBC Code Schedule and Carriage

Direct reduced iron (DRI) is a metallic-iron intermediate product shipped under the IMSBC Code in four distinct schedule entries, each reflecting a different physical form and hazard severity. The central risks are re-oxidation with self-heating, evolution of flammable hydrogen gas when the cargo contacts water, and oxygen depletion in enclosed cargo holds. Schedules DRI (B) and DRI (C) require full nitrogen inerting and prohibit water-based firefighting; DRI (A) hot-briquetted iron is the safest form for sea transport; and the DRI (D) schedule for passivated by-product fines, mandatory from 1 January 2025, takes a different approach built on aging, moisture control, and hydrogen concentration monitoring rather than inerting.

What direct reduced iron is and where it fits in steelmaking

Direct reduced iron is iron metal produced by removing oxygen from iron ore without melting the ore. The reduction happens in a shaft furnace or rotary kiln where a reducing gas, predominantly a mixture of hydrogen and carbon monoxide derived from reformed natural gas, reacts with iron ore pellets at temperatures of around 800 to 1,050 degrees Celsius. The result is a solid sponge-like metallic iron product that retains the external shape of the original ore pellet but now has metallic-iron content of approximately 90 to 94 per cent on a total iron basis, with residual iron oxides, gangue minerals, and carbon making up the balance.

DRI occupies a specific position in the steelmaking value chain. It is used as a charge material in electric arc furnaces (EAFs), where its consistent chemistry, low tramp-metal content, and controlled carbon make it attractive as a substitute for or supplement to scrap steel. EAF steelmakers particularly value DRI when scrap prices are high or when scrap-quality variability is a problem. The cargo is also used in basic oxygen furnaces as a coolant charge alongside hot metal.

Global seaborne DRI trade runs at roughly 10 to 20 million tonnes per year. The main producing countries are those with access to cheap natural gas for the reduction process: Iran, the UAE, Saudi Arabia, Venezuela, Trinidad and Tobago, Russia, and India are historically the largest exporters. Receiving steelworks cluster in Türkiye (which runs among the world’s largest EAF sectors), southern Europe, Egypt, and increasingly East Asia. HBI, the densest and most stable form, dominates the maritime trade because it handles shipping better than pellets or fines.

The production technology most widely deployed is the MIDREX direct reduction process (developed by Midrex Technologies, a subsidiary of Kobe Steel) and the HYL/Energiron process (developed by Tenova and Danieli). Both produce DRI in pellet or lump form; HBI is produced by pressing freshly reduced DRI through a roll press at temperatures above 650 degrees Celsius before the product cools, which closes the internal pore structure and produces the dense, pillow-shaped briquette that characterizes HBI.

Re-oxidation: the fundamental hazard

DRI is thermodynamically unstable in air and in water. The reduction process creates metallic iron with an enormous internal surface area from the porous sponge structure of the original ore pellet. That surface area is available for oxidation by atmospheric oxygen and by liquid water the moment the product leaves the reduction vessel.

Oxidation with oxygen proceeds as a dry reaction:

This is an exothermic reaction. In bulk, particularly in a cargo hold with limited heat dissipation, the liberated heat raises the cargo temperature, which in turn accelerates the oxidation rate. Left unchecked, temperatures can rise high enough to cause smouldering and cargo ignition. The UK P&I Club’s “Carefully to Carry” guidance records temperature exceedances above 200 degrees Celsius in cargo hold incidents.

Oxidation with water takes a different and more immediately dangerous path:

This reaction produces hydrogen gas. In the enclosed atmosphere of a cargo hold, hydrogen concentrations can build to within or above the flammable range (4 to 75 per cent by volume in air). An ignition source, such as a spark from opening a hold hatch or operating electrical equipment, can then initiate an explosion. This is the mechanism that destroyed the MV Ythan.

The two reactions interact. Oxygen-driven self-heating raises cargo temperature, which can drive water out of the cargo as steam or, if the hold atmosphere contains moisture, condenses on cooler surfaces and drips back into the cargo. That water then drives hydrogen evolution. The combined effect is a self-reinforcing hazard cycle that makes DRI management at sea a multi-parameter control problem rather than a single-point check.

The four IMSBC Code schedules

The IMSBC Code regulates DRI under four individual schedule entries. The table below summarizes the key distinctions:

All four schedules are classified Group B under the IMSBC Code (materials possessing chemical hazard which could give rise to a dangerous situation on a ship) and as MHB (materials hazardous only in bulk). All prohibit the use of water as a firefighting medium. None is a Group A liquefaction cargo (though DRI (D), discussed below, has a transportable moisture limit requirement because of its higher water content).

DRI (A): Hot-briquetted iron

The IMSBC Code designation “DIRECT REDUCED IRON (A) Briquettes, hot-moulded” covers what the industry calls hot-briquetted iron, abbreviated HBI. HBI is produced by pressing freshly reduced DRI at briquetting temperatures above 650 degrees Celsius before the iron cools. The hot-pressing collapses most of the internal porosity that makes cold DRI pellets reactive, producing a dense pillow-shaped briquette with a bulk density of approximately 2.4 to 2.6 tonnes per cubic metre. The reduced surface area compared to pellets cuts the re-oxidation rate substantially.

HBI is the safest DRI form for sea carriage. The IMSBC Code does not require nitrogen inerting for DRI (A). The schedule does require that the moisture content at loading not exceed 1 per cent by weight, that fines content (particles below 6.3 mm) not exceed 5 per cent, and that dust content (particles below 0.5 mm) not exceed 2 per cent. The briquettes must have been cooled to below 65 degrees Celsius before loading. Continuous temperature monitoring is required during the voyage, and the hydrogen concentration in the free space of the cargo hold must be measured before and during the voyage; if hydrogen exceeds 1 per cent by volume, ventilation is required.

Hold preparation for HBI requires that the hold be clean and dry, that no aluminium components or equipment be present in the cargo space (aluminium reacts acceleratedly with moisture in the presence of iron), and that bilge systems be operational and tested.

The master must not sail until satisfied that cargo temperatures have stabilized at all measuring points. The shipping document must state: “DIRECT REDUCED IRON (A) Briquettes, hot-moulded” and include certification from a competent person that the cargo meets the Code requirements for moisture, fines, and dust content, and that it has been cooled to the required temperature.

HBI is the dominant form in seaborne DRI trade. Major exporting terminals at Point Lisas in Trinidad and Tobago, Lebedinsky GOK through the port of Murmansk (Russia), and several Venezuelan and Middle Eastern facilities ship HBI in handysize, supramax, and occasionally panamax bulk carriers.

DRI (B): Lumps, pellets, and cold-moulded briquettes

DRI (B) is the most tightly regulated and most hazardous of the commercially significant DRI forms, covering cold DRI in the form of sponge iron lumps, pellets, and cold-moulded briquettes, all of which retain the high internal surface area of the reduction process.

The moisture content must not exceed 0.3 per cent by weight at loading. Above this threshold, hydrogen evolution rates during a typical voyage can be high enough to create a flammable atmosphere even within a nitrogen-blanketed hold. The fines content at loading must not exceed 5 per cent (particles below 6.3 mm) and dust (below 0.5 mm) not exceed 2 per cent.

The central operating requirement is nitrogen inerting. Before loading begins, dry inert gas (nitrogen is the specified preference) is introduced at tank-top level in the cargo hold so that it purges air upward and out of the ventilators, displacing the oxygen-containing atmosphere. The inert gas blanket must then be maintained throughout the voyage. The ship must have the means to maintain oxygen concentration in the cargo hold atmosphere at below 5 per cent by volume at all times, and must have calibrated instruments capable of measuring both oxygen and hydrogen concentrations within the hold without requiring personnel to enter the hold or compromising the inert atmosphere.

Temperature monitoring at multiple locations within the stow is mandatory. The departure conditions are a cargo temperature below 65 degrees Celsius at all measuring points and a hydrogen concentration in the cargo space free space below 0.2 per cent by volume. Neither condition is a one-time check; both must be confirmed stable before sailing.

On voyage, readings should be taken regularly. If temperature rises above 65 degrees Celsius or hydrogen exceeds 0.2 per cent, the master must investigate and act. The Code does not permit opening hatches to ventilate as a response because this would introduce oxygen and accelerate re-oxidation. The prescribed response for elevated temperature or oxygen ingress is to resupply nitrogen to restore the inert atmosphere.

Fire or smouldering discovered in a DRI (B) hold must not be fought with water. The Code specifies dry sand or dry inert solid material as the extinguishing medium, and maintaining or restoring the nitrogen atmosphere. Water application to a burning DRI cargo would produce rapid hydrogen evolution and could cause an explosion inside the hold.

The ship must be fitted with a nitrogen supply system capable of maintaining the inert atmosphere, with connections at the cargo hold. Shipboard nitrogen generators (membrane-type or pressure-swing adsorption units) are common on DRI carriers. Alternatively, nitrogen from pressurized cylinders or a liquid nitrogen tank can supply the holds, though the quantities required for a multi-week ocean passage make liquefied nitrogen supply more practical for longer voyages.

The shipping document must bear the correct IMSBC designation: “DIRECT REDUCED IRON (B) Lumps, pellets, cold-moulded briquettes.” Any misleading or incorrect designation, such as calling cold DRI pellets “HBI” to avoid the inerting requirement, is a Code violation and has contributed to several incidents.

DRI (C): By-product fines

DRI (C) covers the fine particulate by-product generated during DRI production and handling, with particle sizes predominantly below the 6.3 mm threshold that defines the fines fraction. The schedule has the same moisture limit (0.3 per cent) and the same nitrogen-inerting requirements as DRI (B), but is listed separately because the higher surface area of fines creates faster oxidation rates and larger hydrogen evolution potential per tonne than the coarser DRI (B) material.

DRI (C) is a relatively small volume cargo. The fines fraction of DRI production is commercially less valuable than pellets or HBI, and the stringent shipping requirements make it difficult to transport economically. Some DRI producers blend fines back into the reduction feed or pelletize them before export; others accept the maritime schedule requirements and ship under DRI (C) certification.

The same departure conditions apply: cargo temperature below 65 degrees Celsius at all measuring points and hydrogen concentration in the free space below 0.2 per cent. Nitrogen inerting must be maintained throughout the voyage. The fines require particular attention to cargo containment, since fine particles can migrate into bilge systems and form a paste that interferes with drainage; bilge well covers and strainers must be inspected and in place before loading.

The MV Ythan incident in 2004 (discussed in detail below) was caused by cargo that was effectively DRI fines, though the cargo had been certified and loaded under a misleading description. That incident was the direct regulatory driver for the inclusion of a dedicated DRI fines schedule in the IMSBC Code.

DRI (D): By-product fines with moisture content at or above 2 per cent (passivated/aged fines)

The DRI (D) schedule is a new entry, introduced by IMO Resolution MSC.539(107) as part of the 07-23 amendment set. Voluntary application was permitted from 1 January 2024; the schedule became mandatory from 1 January 2025.

DRI (D) addresses a cargo that the DRI (B) and DRI (C) schedules did not cleanly accommodate: by-product DRI fines that have been intentionally exposed to atmospheric air for an extended period, a process called “aging” or “passivation.” During aging, the most reactive sites on the external and internal surfaces of the DRI particles react with atmospheric oxygen and are converted to stable iron oxide. Once the surface is passivated, the bulk of the remaining metallic iron is substantially less reactive than fresh DRI. The process takes a minimum of 30 days under open-air conditions.

The critical hazard distinction from DRI (C) is that aged DRI (D) fines have a higher moisture content (at or above 2 per cent by weight) and a lower self-heating rate than dry, fresh DRI fines. The primary hazard from DRI (D) is not self-heating driven by oxygen reaction, but hydrogen evolution driven by the reaction of residual metallic iron with the water already present in the cargo. Because the cargo contains enough water to sustain hydrogen production over time, the IMSBC Code approach for DRI (D) is fundamentally different from DRI (C): surface ventilation to control the hydrogen concentration, rather than nitrogen inerting to exclude oxygen.

The shipper must provide the master with a certificate from a competent person confirming that the cargo has been naturally aged for at least 30 days before loading. The moisture content must be monitored, and the cargo must be below its transportable moisture limit to prevent liquefaction risk. Hydrogen concentration in the cargo hold atmosphere must be measured after loading and during the voyage. If hydrogen concentration approaches an elevated threshold, the Code calls for surface ventilation, not for nitrogen injection.

DRI (D) is also classified Group B MHB and prohibits water firefighting, for the same reason as all DRI schedules: water adds to the moisture burden and can significantly increase hydrogen evolution.

The re-oxidation and self-heating mechanism in detail

Understanding the DRI hazard at a mechanistic level is important for officers managing the cargo on a voyage, because the controls are specific to the chemistry.

The metallic iron in DRI is in the alpha-iron (ferrite) crystal structure, as it was in the original ore but now without the bound oxygen. The surface area available for reaction depends critically on the particle’s internal pore structure. A DRI pellet reduced from a 12 mm iron ore pellet may contain hundreds of square metres of internal surface area per kilogram. A cold-moulded briquette has somewhat less due to the compaction process, but still far more than a hot-briquetted HBI product.

Dry oxidation by atmospheric oxygen is thermodynamically favorable at all temperatures above absolute zero, but the kinetics are slow at ambient temperatures on an HBI surface and faster on the porous DRI pellet surface. As cargo temperature rises (from the initial oxidation heat, from ambient conditions, from solar heating of the hold), the oxidation rate increases. The Arrhenius relationship means roughly a doubling of reaction rate per 10 degrees Celsius temperature rise. A hold temperature of 65 degrees Celsius is therefore not just a monitoring threshold; it is the point at which the self-heating rate can outpace the heat dissipation capacity of the inert-gas-blanketed hold, leading to runaway temperature rise.

Water contact, even as vapour condensing on cold cargo surfaces, introduces the wet-oxidation pathway and hydrogen generation. The rate of hydrogen evolution from DRI (B) pellets in contact with water at 25 degrees Celsius can be on the order of millilitres of hydrogen per gram of DRI per hour, depending on the degree of reduction and the surface area. A 20,000-tonne cargo of DRI (B) pellets with a small percentage of wet spots could, in principle, evolve hydrogen at a rate sufficient to reach explosive concentrations in a sealed hold within hours. This is not a theoretical concern; it is the mechanism behind the MV Ythan tragedy.

Oxygen depletion is a secondary hazard for personnel. As DRI oxidizes in an enclosed hold, oxygen is consumed. In a partially inerted hold or in the early stages of loading, the oxygen concentration can fall below 18 per cent (the broadly accepted minimum for safe working) without any visible indication. Personnel who enter a hold to inspect a DRI cargo without atmospheric testing and appropriate breathing apparatus are at risk of rapid incapacitation. This hazard applies even to DRI (A) HBI holds before inerting is established.

Documented incidents involving DRI at sea

The MV Ythan (2004) is the most-cited DRI casualty. The vessel loaded a cargo described and certified as HBI at Palua, Venezuela, in late February 2004. The cargo was, in reality, a mix of HBI fines that did not meet the DRI (A) schedule requirements. Fines have substantially higher surface area and reactivity than HBI briquettes. The fines were wet; the moisture content was above the thresholds that applied even to the then-current DRI schedules under the BC Code predecessor to the IMSBC Code. On 28 February 2004, while the vessel was off the Colombian coast, explosions occurred in four of the five cargo holds in rapid succession. The ignition source is believed to have been work or opening of a hold in a hydrogen-rich atmosphere. Six crew members died and the vessel was lost.

The MV Adamandas (2003) was a vessel carrying DRI fines whose cargo condition deteriorated so severely during a dispute over the voyage that French maritime authorities ordered the vessel sunk at sea with its cargo and bunkers on board, rather than risk attempting cargo discharge.

Both incidents preceded the IMSBC Code and occurred under the BC Code, which had DRI schedules but with less-specific requirements. The Ythan disaster, in particular, was the principal driver for the introduction of the dedicated DRI (C) fines schedule in the 2009 edition of the IMSBC Code, which entered mandatory force on 1 January 2011.

The UK P&I Club’s “Carefully to Carry” guidance and various P&I club circulars from Skuld, North Standard, and the Shipowners’ Club have documented additional incidents involving:

• Temperature runaways in DRI (B) pellet cargoes during long ocean passages, where port-state control or underwriters required discharge and inspection before the ship was permitted to continue.
• Holds found to have leaked nitrogen during the voyage, with the inert atmosphere compromised and oxygen levels rising towards ambient before detection at intermediate atmospheric checks.
• Cases where cargo certified as DRI (A) was found on inspection to contain a fines fraction exceeding the 5 per cent schedule limit, effectively making it a DRI (B) or DRI (C) cargo without the required inerting preparation.
• The problem of HBI fines, which are generated as a by-product of HBI handling and transport and which have been shipped under misleading descriptions that understate their reactivity.

These incidents collectively show that the documentary and operational requirements of the IMSBC Code are not merely bureaucratic: they represent the minimum controls necessary to prevent casualty.

Hold preparation: the pre-loading sequence

Hold preparation for DRI is more demanding than for most Group C bulk cargoes and requires a defined sequence:

1. Inspection and cleaning. The hold must be clean, dry, and free from any residue of previous cargo, particularly anything that could react with iron or with nitrogen. All aluminium components in the cargo space (aluminium ladders, staging, strainers) must be removed before loading DRI (B), DRI (C), or DRI (D), because aluminium reacts with water in the presence of iron at an accelerated rate.

2. Hatch cover integrity. Hatch cover sealing must be verified with hatch cover tightness testing (hydraulic or ultrasonic). A leaking hatch cover can allow ingress of rain or sea spray, which creates moisture contact with the cargo and triggers hydrogen evolution. A leaking hatch also allows inert nitrogen to escape, compromising the atmosphere.

3. Ventilation system status. Ventilation trunks and closures must be confirmed functional and capable of being sealed. For DRI (B) and DRI (C), ventilation is closed for the voyage to preserve the inert atmosphere. For DRI (A) and DRI (D), ventilation will be open for some monitoring or control operations, so the closures must be in good working order in both directions.

4. Instrumentation check. Oxygen analyzers, hydrogen detectors, and cargo temperature monitoring probes must be calibrated and operational before loading begins. These instruments are required to be capable of measuring hold atmosphere conditions without hold entry: typically via sample lines run from the hold through dedicated gas-sampling manifolds on deck.

5. Pre-inerting (DRI (B) and DRI (C)). Dry nitrogen is introduced at tank-top level and the hold is purged. The purge continues until the oxygen concentration in the hold atmosphere is confirmed below 5 per cent at representative measurement points. For a standard handysize or supramax hold of 10,000 to 15,000 cubic metres gross volume, the nitrogen quantity required to achieve initial inerting is substantial. Pre-inerting at loading terminals in Trinidad and Tobago and at Middle Eastern DRI ports is typically done using terminal-supplied nitrogen.

6. Confirmation before loading commences. The master and the competent person acting for the shipper must both confirm that the pre-loading conditions are met and that the cargo documentation is in order. Loading should not commence if any condition is not satisfied.

7. During loading. Temperature monitoring during loading detects any abnormally reactive cargo before the full parcel is loaded. Cargo temperature at or near the discharge from the conveyor, and at various levels in the developing stow, should be monitored continuously. If temperatures exceed 65 degrees Celsius at any point during loading, loading should be halted.

8. Post-loading confirmation. After loading is complete and hatches are closed, a waiting period is necessary to allow temperatures to stabilize throughout the stow and for the hydrogen concentration in the free space to stabilize. The Code requires that the master be satisfied that both temperatures (below 65 degrees Celsius at all measuring points) and hydrogen (below 0.2 per cent by volume for DRI (B) and (C), below 1 per cent for DRI (A)) have stabilized before sailing. This may require a delay of several hours at the berth.

Monitoring on voyage

Once at sea with DRI (B) or DRI (C), the master maintains an inert atmosphere in the cargo holds throughout the voyage. Monitoring has several components:

Temperature. Fixed temperature probes in the cargo stow transmit readings continuously or at short intervals. A rising temperature trend without a corresponding rise in ambient temperature is the primary early indicator of accelerating re-oxidation. A rate of rise greater than 2 degrees Celsius per day (a common threshold used in industry guidance, though not codified in the IMSBC Code at a specific numeric value) warrants immediate investigation of the hold atmosphere and, if oxygen ingress is confirmed, resupply of nitrogen.

Oxygen concentration. The cargo hold atmosphere is sampled through the sampling lines and the oxygen content is measured by paramagnetic or electrochemical analyzer. Oxygen concentrations above 5 per cent indicate that the inert atmosphere has been compromised, either through hatch cover leakage, through sampling-line faults, or through consumption of the available nitrogen supply. Corrective action is to resupply nitrogen.

Hydrogen concentration. Hydrogen is measured by catalytic-bead or thermal conductivity detector on the same sampling lines. Elevated hydrogen readings indicate water-iron reaction is occurring in the hold, which either means moisture was present in the cargo at loading, has condensed into the cargo from the atmosphere, or has entered through a leak. Hydrogen concentrations approaching 0.2 per cent on voyage should be treated as a developing hazard requiring close observation. Concentrations approaching 1 per cent (25 per cent of the lower explosive limit) require immediate reporting and action. Opening the hold to ventilate, which would be the reflex response for many cargo incidents, is the wrong action for DRI because it would admit oxygen and accelerate re-oxidation.

Atmosphere in the free space. Both oxygen and hydrogen are measured in the headspace above the stow. For multi-hold ships carrying DRI in multiple holds simultaneously (common for handysize and supramax vessels carrying 4 to 6 holds of DRI (B)), each hold must be monitored independently, since conditions can vary by hold.

Personnel entry into DRI holds during a voyage is prohibited without an enclosed space entry permit, complete atmospheric testing at the entry point and at depth, and emergency rescue equipment standing by. Even a nitrogen-inerted hold at 2 per cent oxygen is immediately life-threatening to any person who enters without breathing apparatus.

Firefighting: the no-water rule and what to do instead

The prohibition on water firefighting for all DRI schedules is absolute under the IMSBC Code. For DRI (A) the hazard level is lower, but water contact with any DRI cargo at sea still produces hydrogen gas and accelerates oxidation. For DRI (B) and (C), applying water to a hold fire would produce a rapid surge of hydrogen into an already-confined atmosphere and could cause an explosion.

The prescribed response to a hold fire in a DRI cargo is:

1. Maintain or restore the nitrogen inert atmosphere.
2. Seal the hold as completely as possible to cut oxygen ingress.
3. Apply dry sand or dry inert solid material if the fire is accessible and at the cargo surface.
4. Do not ventilate (which would admit oxygen).
5. If the hold is sealed and inerted and temperature continues to rise, do not open the hold hatches suddenly, as this could create a sudden explosive mixture when the accumulated hydrogen meets air.

The Code explicitly prohibits carbon dioxide as well as water for DRI hold fires. The inert-gas approach is preferred. This makes DRI cargo a genuine challenge for maritime fire response, because the instinct of crews and shore teams is to apply CO2 or water to cargo fires.

The 2004 MV Ythan explosions illustrate what happens when hydrogen accumulates and then meets an ignition source in an enclosed hold. The practical lesson is that preventing hydrogen buildup is vastly preferable to managing it after the fact. The cargo controls, the inerting, and the pre-departure atmosphere checks exist to ensure that a hold fire never develops.

DRI and the electric arc furnace steelmaking trade

The maritime DRI trade is closely tied to the economics and geography of electric arc furnace steelmaking. EAF producers in Türkiye consumed roughly 8 to 10 million tonnes of DRI in recent years, making the country one of the largest maritime DRI importers. Egyptian EAF producers at Alexandria and Port Said consume DRI from Middle Eastern suppliers via the Mediterranean. Indian EAF producers at Vizag and elsewhere have increasingly imported DRI as domestic supply of sponge iron from coal-based rotary kilns remains volatile.

The reduction from iron ore happens predominantly by the gas-based MIDREX and HYL/Energiron processes. Coal-based DRI production (rotary kiln processes, mostly in India) produces a lower-metallization product that is typically not exported by sea; the coal-based product is consumed directly at or near the production facility. Maritime DRI trade is almost exclusively gas-based product.

The hydrogen-based direct reduction process (H-DRI), which uses green hydrogen rather than reformed natural gas as the reducing agent, is under commercial development. HYBRIT (a joint venture of SSAB, LKAB, and Vattenfall in Sweden) commissioned a pilot direct reduction facility using hydrogen in 2021, and H2 Green Steel is building a large commercial plant in Boden, Sweden, targeting production from 2026. H-DRI product would be chemically similar to conventional gas-based DRI in its handling hazard profile: still metallic iron, still porous, still subject to the same IMSBC Code re-oxidation and hydrogen-evolution hazards when shipped by sea.

Trade volumes are sensitive to the spread between natural gas prices and scrap steel prices. When natural gas is cheap relative to scrap, DRI production expands and maritime trade rises. When gas prices spike (as they did in Europe during 2021 to 2022 following supply disruptions), DRI production margins tighten and trade volumes fall. This cyclicality means DRI carrier specialists, including companies such as Interorient Navigation, Vale, and several Middle Eastern shipping groups, manage a variable trade calendar.

Vessel types carrying DRI are predominantly handysize (25,000 to 40,000 DWT) and supramax (50,000 to 65,000 DWT) bulk carriers configured for the inert-gas and monitoring requirements. Some Panamax carriers (65,000 to 80,000 DWT) are used for HBI cargoes where the inerting requirement does not apply. Capesize vessels are not normally used because DRI cargoes are relatively dense (HBI: 2.4 to 2.6 t/m3; DRI pellets: 1.6 to 2.0 t/m3 stowage factor) and hold capacities can be filled before cargo weight fills the ship.

Relevant IMSBC Code amendments and their history

The IMSBC Code entered mandatory force on 1 January 2011, superseding the BC Code under which DRI had previously been regulated. The transition preserved the basic DRI schedule structure but brought tighter and more specific requirements:

Amendment 01-11 (IMSBC Code, 2009 edition, mandatory from 2011): Introduced the DRI (C) by-product fines schedule, driven by the 2003 to 2004 incidents. Before this, DRI fines had been shipped under a general DRI schedule that did not specify inerting or departure conditions specifically for fines.

Subsequent amendments (02-15, 03-17, 04-19, 05-21): Progressive refinement of the DRI schedules, tightening the moisture limits, clarifying the competent-person certification requirements, and revising the aluminium prohibition.

MSC.500(105) (amendment 06-22, mandatory from 1 December 2023): The 2022 amendments adopted at MSC 105. Updated individual cargo schedules and added new entries. The DRI schedules continued to be refined in terms of the certification and testing requirements.

MSC.539(107) (amendment 07-23, mandatory from 1 January 2025): Introduced the DRI (D) schedule for passivated by-product fines with moisture content at or above 2 per cent, adding the 30-day aging requirement and the hydrogen-monitoring-with-ventilation approach as a distinct control framework from the nitrogen-inerting approach of DRI (B) and DRI (C). Voluntary application was permitted from 1 January 2024.

The introduction of DRI (D) reflects a recognition by the IMO’s Carriage of Cargoes and Containers Sub-Committee (CCC) that aged, passivated DRI fines represent a different hazard profile from fresh DRI fines and that a regime requiring full nitrogen inerting for material that has already partially oxidized and stabilized is technically disproportionate, provided the aging and moisture requirements are met and the hydrogen evolution rate is managed through ventilation control rather than inert-gas suppression.

Certification and shipping document requirements

The IMSBC Code imposes specific certification requirements on shippers of all four DRI schedule types. The shipper must provide:

Cargo declaration. The correct IMSBC schedule designation, the cargo quantity in tonnes, the moisture content, the metallic iron content, the fines and dust content percentages, the maximum cargo temperature at time of loading, and the hydrogen concentration in the free space at time of sailing (or the measured reading at confirmation of stability before sailing).

Competent-person certificate. Signed by an independent competent person, confirming that the cargo meets the schedule requirements. For DRI (D), the certificate must specifically confirm aging of at least 30 days and the TML determination.

Compatibility of schedule designation with actual cargo. The master has an obligation to satisfy themselves that the cargo description and the physical form of the cargo are consistent. Misclassification (notably, calling DRI (B) pellets or fines “HBI” in the shipping document to avoid the inerting requirement) is a documented practice that has contributed to casualties. The master may request to see the producer’s technical documentation and reject cargo that cannot be matched to its declared schedule.

Any consignment that cannot be classified under an IMSBC Code schedule should not be loaded. Where there is doubt about the correct classification, the shipper and the master should seek guidance from the flag state administration or a P&I club surveyor.

Interactions with other cargo hold systems

DRI interacts with several other shipboard systems in ways that deserve attention:

Inert gas plant capacity. Dedicated DRI carriers are fitted with nitrogen generating plants sized to maintain hold atmosphere over a 30-day voyage, with capacity for resupply after sampling-line maintenance losses and minor hatch leakage. A general-purpose bulk carrier without a permanently fitted nitrogen generator cannot carry DRI (B) or DRI (C) safely; the operator must arrange a portable nitrogen generating unit or liquid nitrogen supply before accepting the cargo. The marine inert gas systems article covers nitrogen generator types (membrane-type and pressure-swing adsorption) and their integration with cargo hold systems.

Bilge systems. DRI fines migrate into bilge systems and form a wet paste. Bilge well covers with fine strainers must be in place and regularly checked. Bilge pumping during a DRI voyage, if required by water ingress from condensation or hatch leakage, will discharge water that may contain dissolved iron and fine particles; port-state discharge requirements apply.

Cargo hold ventilation. For DRI (B) and DRI (C), the marine cargo hold ventilation system must be fully closed during the voyage. Ventilation duct openings into the hold must be sealed. For DRI (A), ventilation is surface-only and is used to manage any hydrogen that does evolve; the ventilation rate must be sufficient to prevent accumulation in the cargo hold headspace.

Fire detection. Fixed fire-detection systems in DRI cargo holds must use point-type heat or temperature sensors, not ionization or optical smoke detectors, because the iron-oxide dust in the hold atmosphere can trigger false alarms in smoke detectors during loading. The marine fire detection and fixed fire fighting systems article covers the relevant sensor types and their compatibility with solid bulk cargo holds.

IMSBC Code group framework. The IMSBC Group B cargoes article covers the broader Group B classification, which encompasses materials posing chemical hazard in bulk. DRI is among the most hazardous Group B cargoes handled in significant commercial volumes, along with charcoal, calcium hypochlorite, and ammonium nitrate fertilizer.

Limitations

This article covers the DRI schedule requirements as established in the IMSBC Code through amendment 07-23 (MSC.539(107), mandatory from 1 January 2025). It does not constitute regulatory advice and does not substitute for the current edition of the IMSBC Code and applicable national legislation.

The DRI (D) schedule requires specific aging certification that must be verified on a per-consignment basis. The 30-day aging period is a minimum; some producers apply longer aging under defined conditions, and the competent person assessing the cargo must confirm that the passivation is adequate. The IMSBC Code does not specify a test method for passivation adequacy equivalent to the TML tests for Group A cargoes; shipper and master judgment, supported by the competent-person assessment, governs.

Hydrogen evolution rates from DRI vary significantly with the degree of metallization, the moisture content, the surface area of the particular product, and the temperature. The departure thresholds (0.2 per cent for DRI (B) and (C), 1 per cent for DRI (A)) are the Code minimums; a prudent master with rising hydrogen readings during the pre-departure stabilization period may elect to delay sailing until the rate of change is clearly declining, even if the absolute value is below the threshold.

The no-water firefighting rule is absolute under the current IMSBC Code. Masters and crew should be trained specifically on DRI firefighting constraints before the vessel enters the trade.

Flag state requirements may impose additional obligations beyond the IMSBC Code baseline. Classification society requirements may also be relevant, particularly for vessels that have been specially fitted or certified for inert-gas carriage of DRI.

See also

• IMSBC Code
• IMSBC Group B Cargoes
• Iron Ore: IMSBC Code Schedule and Carriage
• Iron Ore Pellets: IMSBC Code Schedule and Carriage
• Pig Iron: IMSBC Code Schedule and Carriage
• Marine Inert Gas Systems
• Marine Fire Detection and Fixed Fire Fighting Systems
• Marine Cargo Hold Ventilation

Related calculators

• IMSBC - Direct Reduced Iron (A)
• IMSBC - Reduced Iron Briquettes
• IMSBC - DRI Fines (C)
• Bulk Iron DRI Passivation
• IMSBC - Pig Iron
• IMSBC - Iron Swarf
• IMSBC - Iron Ore