Direct reduced iron (DRI) in various forms is described in the International Maritime Sold Bulk Cargo (IMSBC) Code, (hereinafter, the Code). The latest addition, which becomes a mandatory part of the Code from January 2025, is the entry for the Type D, by-product fines with a moisture content of at least 2%. This entry runs over multiple pages and contains large amounts of important information and guidance. In this Circular, the main points of the Type D entry are summarised, and, where appropriate, additional guidance and observational notes have been added.
It should be noted that this Circular is for guidance only and the relevant entries from the IMSBC Code, which are appended to this Circular, remain the primary source of carriage requirements which should be relied upon.
Background
Direct reduced iron (DRI) is formed by passing hot reducing gases, such as hydrogen, methane and carbon monoxide, over iron ore, which is usually in the form of lumps or pellets. This produces a highly porous iron material which has a very large internal surface area available for re-oxidation. The principal hazards associated with DRI are its ability to undergo self-heating through oxidation and its ability to generate hydrogen from reaction with water/moisture. When stowed within the confines of a cargo hold, hydrogen produced by reaction with water can form an explosive atmosphere inside the hold, presenting a risk of explosion.
The principal forms of DRI are Type A (hot-moulded briquettes) and Type B (pellets), but fines are also generated during manufacture and handling (via abrasion) and from filtering particles out of off-gases. Fines are not generally suitable for inclusion with Types A and B, so these are screened out and handled separately.
Formerly, fines would be shipped under DRI Type C, but the IMSBC Code entry for this type defines the moisture level of the cargo as not exceeding 0.3%. That low moisture level is often not feasible due to handling practices for fines, such as outdoor storage and handling being subject to rain.
In addition, the Code calls for DRI (C) cargoes to be shipped under inert gas, as for DRI (B). Inert gas is intended to exclude air (oxygen), thus limiting self-heating due to reaction with oxygen. However, as set out below, self-heating is typically not the main issue with fines. Instead, the prevalent risk is the generation of flammable hydrogen gas due to reaction with water, leading to a scenario where the holds need to be ventilated in order to maintain low hydrogen concentrations, below the lower explosive limit plus a margin of safety.
With the production of DRI(C) fines having a moisture content not exceeding 0.3% being difficult to achieve, in the IG Clubs’
experience shippers often sought to ship such cargoes under exemptions in accordance with section 1.5 of the IMSBC Code.
Those exemptions often sought to avoid shipment under inert gas, instead using mechanical ventilation as an alternative arrangement, but this proved difficult due to the need for tripartite agreement. Therefore, there was a need for industry to work collectively to seek a more permanent, but safe, long-term solution.
Accordingly, Amendment 07-23 to the Code introduces a fourth DRI schedule: DIRECT REDUCED IRON (D) (By-product fines with a moisture content of at least 2%).
Like DRI (C), DRI (D) is described as a by-product of the manufacturing and handling process of DRI (A) and DRI (B) but has a higher moisture content (≥2% as compared to ≤0.3% for DRI (C)).
There is also reference in the new DRI (D) schedule to the risk of liquefaction if shipped with a moisture content exceeding its transportable moisture limit (TML). DRI (D) is therefore classified as both a Group A and Group B cargo.
The principal hazard associated with DRI (D) fines is the generation of hydrogen, due to the relatively high moisture content and reaction with water. By contrast, the dense packing of the fines often reduces oxygen/air ingress into the bulk, with the result that the propensity for self-heating through atmospheric oxidation reactions is reduced, often to non-problematic levels. As such, there is no requirement in the DRI (D) schedule for purging the cargo hold with inert gas to prevent an explosive atmosphere from forming, nor in keeping the cargo hold tightly sealed to exclude oxygen ingress, whereas there are such requirements for DRI (B) and DRI (C). Instead, a regime of controlled mechanical surface ventilation and regular gas concentration measurements should be introduced in order to keep the hydrogen concentration within the holds below a designated limit.
The IG has previously issued Circulars on DRI cargoes due to a number of incidents, some of which have resulted in fatalities. Whilst these advisories were issued nearly two decades ago, given the seriousness of those casualties and a cargo that potentially emits hydrogen, the IG has supported independent expert input to the International Maritime Organisation on the drafting of revised DRI schedules, including this latest one for DRI (D).
Hazards of DRI (D)
The entry for DRI (D) leads with a reference to a potential temperature increase when the material is handled in bulk; and the risk of overheating, fire and explosion due to the reactivity of the cargo with air and water to produce hydrogen gas and heat.
Whilst DRI (D) will react with oxygen and generate heat, its dense packing and the very small spaces between particles are often such that oxygen/fresh air is not able to diffuse into and through the stow to the same extent as with other types of DRI types, particularly the larger briquette/pellet forms. This low permeability means that self-heating is considered a secondary hazard. The primary hazard observed is hydrogen generation, due to the reaction between the DRI and water / moisture. The focus of the new DRI (D) schedule is on the measurement and control of the hydrogen gas concentrations in the ullage spaces.
Although self-heating is considered a secondary hazard, the reaction with air can lead to oxygen depletion in the cargo spaces, and possibly also adjacent spaces, where flammable gases (i.e. hydrogen) might also accumulate. The Code therefore stipulates that no person shall enter a loaded cargo space (or enclosed adjacent space) unless such space has been ventilated and found to be gas-free.