Loss prevention advice on the carriage of Direct Reduced Iron (DRI) and its derivatives

We refer to our Loss Prevention Advice of December 1997, which references our circular of July 1982, which was prepared following the 23rd session of the IMCO (now International Maritime Organisation) Sub-Committee on Containers and Cargoes in January 1982, in which a working group recommended certain amendments to the entry for Direct Reduced Iron (DRI) in the IMO Code of Safe Practice for Solid Bulk Cargoes (the BC Code).  The committee's recommendations were subsequently ratified by the IMO Maritime Safety Committee.

DRI is classified as a Group B cargo according to the BC Code; that is, a cargo that possesses a chemical hazard that could give rise to a dangerous situation on a ship, and in particular, it is a Material that is Hazardous only when transported in Bulk (MHB).

DRI (A) and DRI (B)

Since 1982 two types of Direct Reduced Iron have been recognised in the BC Code.  The first type is the highly reactive, low density DRI in the form of lumps and pellets (from about 6mm to 25mm in size) and cold moulded briquettes.  This material was originally entered in the BC Code under BC No. 015.  The second, less reactive type is the high-density variety of DRI that is obtained by compressing the product at temperatures in excess of 650^oC, and is known as Hot Briquetted Iron HBI, or Hot Moulded Briquettes HMB.  A briquette will typically measure about 120mm x 90mm x 30mm thick and should have a density greater than 5000 kg/m³, (5 g/cm³).  This material was originally entered under the BC Code No. 016.

The entries for DRI were amended in the 2005 edition of the BC Code.  The high-density, hot briquetted material is now entered as Direct Reduced Iron (A), and the more reactive, low-density material is Direct Reduced Iron (B)

DRI and HBI Fines

Recently, there has been a trend to offer DRI and its derivatives in the form of fines that are generated as a by-product from the manufacture of DRI and HBI. 

Although the BC Code defines "fines" as material less than 4mm in size, in practice fines cargoes often have particle sizes that are considerably less than 1mm in size, the cargo then being a dust or powder rather than discreet pieces.  The 2005 edition of the BC Code restated a limit on the proportion of fines that may be included in a cargo of the high density DRI (A) material, "Fines (under 4mm) not to exceed 5%".  However, the entry for the reactive, low density DRI (B) material quotes this limit as a characteristic, leaving uncertainties regarding the requirements for the carriage of a cargo comprising mainly fines. 

Following a number of serious incidents involving DRI and HBI fines, the matter has been addressed at recent sessions of the IMO Sub-Committee on Dangerous Goods, Solid Cargoes and Containers (DSC) in 2005 and 2006.  DSC circulars have been issued, but no amendments to the BC Code had been notified at the time of writing this advice.  The Association is aware of a number of explosions that have been caused by the ignition of hydrogen that has been produced from cargoes of HBI fines.  Moreover, the Association considers that there is no reason why 4mm pieces of DRI will not self-heat to auto-oxidation (see below).  Therefore, until official guidance is published to the contrary, the Association recommends that cargoes of DRI and HBI fines be treated for the purpose of carriage by sea as the reactive, low-density DRI (B) material as described in the BC Code. 

Members should be aware that cargoes of DRI/HBI fines have been described by many names that seek to avoid using the term "DRI".  Examples have included Orinoco Remet Fines; Orinoco Iron Fines; Orinoco Iron Remet; Metallic HBI Fines; Re-oxidised Fines; Iron Oxide Fines; Re-oxidised DRI; Venezuela Iron Concentrate.  Owners and Masters should be wary of any bulk cargo offered for shipment under trade names or abbreviated names and insist on a full product description, which should preferably contain a quantitative chemical analysis and include proper technical and alternative names.  If Members have doubts about any cargo that is offered, they should seek advice from the Association.

The Hazards of DRI

The principal hazards of all cargoes of DRI and its derivatives are twofold.  Firstly, they will react with the oxygen present in the air, thereby producing heat and depleting the atmosphere of the oxygen that is essential for life.  With DRI (B), the former effect can run away in spectacular fashion, leading to auto-oxidation of the iron in which the stow becomes incandescent as the temperatures approach 1000^oC.  The cargo is then said to be on fire and burning much in the way that charcoal behaves. 

Whilst self-heating is dangerous and alarming, it is a gradual and progressive event that can often be diagnosed early, affording Masters time to consult the Association, obtain advice from suitably qualified experts and institute suitable safety measures. 

Self-heating to dangerously high temperatures can be successfully prevented in most practical applications by compressing the DRI into Hot Briquetted Iron at the manufacturing stage, DRI (A).  The Association is not aware of any fines cargoes that have undergone self-heating to the auto-oxidation stage, although there is no theoretical reason why 4mm pieces of DRI will not self-heat to auto-oxidation.

The second hazard is again related to the reactivity of iron, this time with moisture or water.  The result is the generation of hydrogen gas, which is explosive over a very wide range of concentrations and, in practical situations, displays an alarming readiness to be ignited.  Explosions of hydrogen in air are extremely violent and rapid: flame speeds may exceed 1000 m/s and pressures exceeding eight bar may be generated in a fraction of a second.  An unfortunate Master has no time in which to react to a hydrogen (or any other gas) explosion.

All three types of the material will evolve hydrogen to a greater or lesser extent on contact with water.  Seawater is more aggressive than fresh water, producing a greater degree of self-heating and higher evolution rates of hydrogen.

For the guidance of Members, we set out below a list of those countries known to have exported DRI, and whether they are known to be currently shipping:

DRI (A), High Density Type

DRI (B), Low Density Type

Low Density DRI Pellets, Lumps, Cold Moulded Briquettes and DRI/HBI Fines, DRI (B)

The current IMO BC Code entry for DRI (B), direct reduced iron pellets, lumps and cold moulded briquettes contains "Shippers' Requirements" that read as follows:

Prior to shipment, DRI should be aged for at least 72 hours, or treated with an air passivation technique, or some other equivalent method that reduces the reactivity of the material to at least the same level as the aged product.  Hatches should be sealed.  All ventilators and other openings should be closed to maintain an inert atmosphere.

A. Shipper should provide necessary specific instructions for carriage, either:

1. prior to loading, provision should be made to introduce the inert gas at tank top level so that the whole of the stow can be maintained at a low oxygen level throughout the voyage. 
2. Maintenance throughout the voyage of cargo spaces under an inert atmosphere containing less than 5% oxygen.  The hydrogen content of the atmosphere should be maintained at less than 1% by volume; or
3. that the DRI has been manufactured or treated with an oxidation- and corrosion- inhibiting process which has been proved, to the satisfaction of the competent authority, to provide effective protection against dangerous reaction with sea water or air under shipping conditions.

B. The provision of paragraph A may be waived or varied if agreed by the competent authorities of the countries concerned, taking into account the sheltered nature, length, duration, or any other applicable conditions of any specific voyage.

Unquote

In relation to paragraph A (2), in the early 1980's major manufacturers in Germany used a chemical "passivation" process to inhibit oxidation/corrosion.  However, there was a serious fire on board a ship carrying this product.  More recently, in the early 1990's a Russian manufacturer of low density DRI (B) pellets claimed its product was passivated, but several DRI fires have occurred in the Russian material shipped from Black Sea Russian and Ukrainian ports when it became wetted with sea water.  More recently, serious doubts have been expressed regarding its resistance to the effects of fresh water, there being at least one instance of auto-oxidation which was likely caused by fresh water.  To date no passivation process has been proven to be effective when the material is wetted with sea water, and therefore DRI (B) pellets, lumps, cold moulded briquettes or fines cannot be shipped under the dispensation given in paragraph A (2).

The Association therefore continues to believe that the only proven method of carrying the low density product DRI (B) safely is by maintaining the cargo holds in an inert atmosphere throughout the voyage.  The prescribed and most effective method of providing an inert atmosphere is by injecting the inert gas at the bottom of the stow in order to force out the air within the stow.  This should be done after completion of loading and the closure and sealing of the hatch covers.  Thereafter, the oxygen level must be regularly monitored and maintained below 5% by volume.

On present information, the Association has reservations that the requirement of maintaining the cargo in an inert atmosphere can be waived on the grounds of the length or nature of the contemplated voyage in the case of the low-density DRI (B) material. 

Members are advised to ensure that the terms of their charterparties permit the carriage of direct reduced iron pellets, lumps, cold moulded briquettes and fines in accordance with the recommendation that the cargo should always be carried in an inert atmosphere whatever the nature or length of the voyage contemplated.

It should be noted that the charterparties offered for the carriage of the Russian DRI pellets may contain a clause requiring not only that the vessel be seaworthy at the commencement, but also throughout the voyage.  Thus it may be found that the vessel would be at fault if seawater entered a hold and the cargo started to self-heat or produce hydrogen, even if caused by heavy weather damage.

The following recommendations to Masters and Owners should be acted upon before loading all forms of DRI:

(a)      The shipper should provide the Master or his representative with appropriate information on the cargo in writing and sufficiently in advance of loading to enable the precautions that may be necessary to be put into effect.  The cargo information should include:

• the Bulk Cargo Shipping Name, not just a trade name
• the total quantity of the cargo offered
• information on stowage factor
• the trimming procedures
• the likelihood of shifting, including angle of repose
• the conditions under which the cargo may become dangerous
• the nature of any flammable or toxic gases that may be generated by the cargo
• flammability, toxicity, corrosiveness and propensity to oxygen depletion of the cargo
• self-heating properties of the cargo, and the need for trimming if appropriate

In addition, a competent person recognised by the national Administration of the country of shipment should certify to the ship's Master that the DRI, at the time of loading, is suitable for shipment.  The Master should be assured by the "competent person" that, in certifying the stability and suitability of the cargo for shipment, he has considered the period and conditions of storage of the cargo before loading and its temperature.  Shippers should certify that the material conforms to the requirements of the BC Code, 2005 Edition. 

Additionally, the Master should receive information on the specific hazards of the type of DRI being offered for carriage, particular instructions on the necessary precautions to be taken during loading, carriage and discharge of the cargo, and guidance as to the measures to be taken in the event of a problem arising.

(b)      The hatches should be inspected and hose tested before loading to ensure they are watertight.  Ultrasonic testing is also acceptable.  This should be performed by the ship unless it is included as part of a pre-loading survey performed by shippers.  All cargo spaces should be clean and dry.  The Master should ensure that bilge lines, sounding pipes and other services lines within the cargo space are in good order.  Bilges should be sift-proof and kept dry during the voyage.  Wooden fixtures such as battens etc. should be removed.  Where possible, adjacent ballast tanks, other than double bottom tanks, should be kept empty.

(c)      The ship should carry an appropriate instrument for measuring the concentrations of hydrogen and of oxygen in the cargo spaces.  The detector should be suitable for use in an atmosphere that is depleted of oxygen and should be properly calibrated and in good working order.  Crew should be versed in its correct usage.  Closed cargo spaces containing any form of DRI should be assessed for safe oxygen levels prior to personnel entry.

(d)      Only certified safe electrical equipment and associated wiring should be installed in any cargo space or adjacent closed spaces or deckhouses where flammable gases may accumulate.  In such spaces, through runs of cable should be suitably mechanically protected, should have no joints and preferably be of a type approved for oil tankers or be enclosed in heavy gauge screen steel conduits.

(e)      During loading and discharge, proper precautions should be taken against the effects of dust on deck machinery, navigational aids and radio communications equipment.  Any dust accumulated on decks or elsewhere during loading or discharge should be washed off as soon as possible to prevent adhesion. 

(f)      The temperature of the cargo should be monitored during loading and, if more than 65^oC, the Master should reject that cargo and suspend loading.  Cargo that has already been loaded and which is found to exceed 65^oC can remain on board whilst it cools, but no further cargo should be added.  If the temperature of any part of the cargo at the end of loading is in excess of 65^oC, sailing should be postponed until it is clear that it is falling.  If it continues to rise the master should call for the assistance of the local P & I correspondent and the "competent person" providing the certificate of suitability for shipment.

(g)      During cargo handling, "NO SMOKING" signs are to be posted on decks and in areas adjacent to cargo compartments, and no naked lights should be permitted in these spaces.  No smoking, burning, cutting, chipping, grinding or other potential source of ignition should be allowed in the vicinity of the holds.  Movable cargo lights, if used, should be not less than 10ft (3m) from the coaming and be in a position where they are not likely to be broken during operations, and not over the square of the hatch. 

(h)      As far as is reasonably practical the DRI should not be dropped from a height into the hold.  Cargoes should be trimmed reasonably level to the boundaries of the cargo space so as to minimise the risk of shifting and to facilitate total flooding of the hold by water, should this be necessary in case of emergency.

(i)       Loading, and transfer between ships, during rain is unacceptable.  In such conditions, all loading operations should be suspended and the cargo holds should be closed.  Hatches that are not being worked should be closed.  The BC Code does not impose any special requirements on the discharge of DRI cargoes.

The following recommendations to Masters and Owners refer to the loading and carriage of the low-density DRI (B) and DRI/HBI Fines:

(j)      During loading the DRI (B) must either be protected from exposure to rain or snow, or else loading should be stopped and the hatches covered.  DRI (B) that has been exposed to wetting on an open-conveyor or elsewhere should be rejected.  Should wet cargo be loaded into a cargo hold, it should be removed as soon as possible together with sufficient surrounding cargo to ensure that only dry material remains on board.  Consideration should be given to rejecting all the cargo in the affected hold.

(k)      Before loading, the ship should be fitted with a means of introducing inert gas at several points at tank top level in the hold so as to be able to force out effectively the air within the stow.  On completion of loading the hatches should be closed and sealed by tape and/or expanding foam.  Care must be taken not to use a flame to soften the bitumen tape, because hydrogen accumulated in the hold could be ignited and cause an explosion.

 All ventilation openings should be effectively sealed, as should the coaming drains and any other openings in the cargo space.  Thereafter, inert gas should be introduced to achieve the required oxygen level of 5% (maximum).  This may conveniently be supplied from a shore-based supply, thereby reducing the on-board capacity required.

(l)       It is recommended that at least four thermocouples per hold be incorporated within the stow at approximately half depth and their leads routed to a suitable opening that can be effectively sealed.  Positioning of the thermocouples can be achieved by suspending cargo operations briefly when the hold is half full and placing the instruments just below the surface of the stow, and then resuming loading.

(m)     The cargo temperatures and the concentrations of oxygen and hydrogen in each hold should be monitored at regular intervals throughout the voyage and properly recorded.  Readings should be taken in such a manner as to minimise the loss of the inert atmosphere.  Monitoring of the oxygen concentration will indicate whether air has entered the hold and whether more inert gas is required to maintain the oxygen concentration below 5% by volume.  The vessel should carry sufficient inert gas to permit the holds to be topped up throughout the voyage so as to maintain the oxygen concentration below 5% by volume.  The preferred inert gas is nitrogen, but if this is not obtainable, carbon dioxide may be used provided that the cargo is not hot.  It should be noted that the on-board supply required for topping up must be additional to the ship's carbon dioxide system, if fitted.

(n)      If water enters a hold containing DRI (B), hydrogen is likely to be evolved with the development of heat.  If oxygen is present above the prescribed limit, the heat may be sufficient to cause the auto-oxidation of the cargo and/or ignition the hydrogen.  For this reason every precaution should be taken to exclude water.  Particular attention should be paid to bilges, adjacent ballast tanks and the water tightness of the hatches, ventilators and other openings on the weather deck.  Inspection of these openings should be made regularly throughout the voyage, particularly after heavy weather, and any defects should be remedied.  Should heavy weather severely damage the hatches so that they cannot be repaired and water enters the hold, the ship should make for the nearest suitable port and seek assistance.

(o)      Hydrogen gas is liable to escape even through small openings.  Care should be taken to guard against its possible accumulation in adjacent enclosed spaces.  These should be tested periodically, especially after encountering heavy weather.

(p)      If monitoring indicates a hydrogen concentration approaching 1% by volume (i.e. 25% of the lower explosive limit), and/or rise in temperature above 65^oC, a dangerous situation may be developing, and advice should be sought.  If a fire situation does develop, the ship should make for the nearest suitable port.  Water, steam or additional carbon dioxide should not be used at this stage to counteract the fire as a dangerous reaction with the cargo may result.  If, however, nitrogen gas is available, then this should be introduced into the hold to contain the fire.

(q)      If a DRI fire is developing it is likely that hydrogen is also being produced. The opening of the hatch covers could produce a spark that could ignite the gas and cause an explosion.  In such circumstances, hatches should not be opened without expert advice, which may be obtained through the local P&I correspondents.

(r)      DRI reacts with oxygen in the air reducing its concentration in the atmosphere in a hold to levels that are dangerous to humans.  Therefore normal procedures for entry into confined spaces where there is a depleted oxygen concentration should be followed.  Entry into a hold without breathing apparatus should be prohibited at any time unless the hatch covers are completely open and the holds effectively ventilated. 

The following recommendations to Masters and Owners refer to the loading and carriage of the high-density DRI (A), Hot Briquetted Iron (HBI) or Hot Moulded Briquettes (HMB)

(s)      The main hazard arises from the evolution of hydrogen if water enters the stow.  For this reason, effective ventilation should be carried out whenever possible.  A mechanical ventilation regime is preferred and should be such as to avoid the possibility of igniting gas/air mixtures.  Care should be taken to avoid drawing moisture or water into the holds.  Ventilation should be such that escaping gases cannot reach living quarters on or under deck.

(t)      Prior to loading, the briquettes may have been stored in the open and therefore exposed to rain. 

This is not necessarily objectionable provided that the cargo is not obviously wet at the time of loading.  However, loading should cease during periods of rain and the holds should be closed.  The bottom layer of piles on the quay prior to loading may be excessively wet and should be rejected if obviously wet.

(u)      The Master should be assured by the "competent person" that all practical steps have been taken to ensure that the cargo delivered to the ship does not contain more than the permitted 5% fines (material less than 4mm in size).  The bottom layer of piles may contain excessive 'fines' and again should be rejected if the material is obviously different to the rest of the cargo.  Where possible, any fines should be distributed throughout the stow and not accumulated in one area.  As the density of the cargo is extremely high, care should be taken to ensure that the cargo is evenly spread across the tank top and is not piled in the centre of the hatch.  As far as is practical, dropping the briquettes from a height into the hold should be avoided to prevent fragmentation and disintegration.

(v)      On completion of loading and prior to sailing if weather and circumstances permit, the hold should be left open as long as possible to allow the cargo to cool (it is likely to heat up a little after loading) and to allow the dissipation of any moisture or hydrogen that may have been evolved.

(w)     Slight emissions of steam are normal and should clear with adequate ventilation.  If steaming persists or worsens, this signifies that potentially dangerous chemical reactions are taking place within the cargo that are generating significant quantities of hydrogen.  Advice should be sought from the local P&I correspondents and/or the "competent person".

(x)      The concentration of hydrogen in the hold atmosphere should be regularly monitored using a suitable instrument.  This is especially important after periods when ventilation has been suspended.  Advice should be sought from a suitably qualified expert if the hydrogen concentration exceeds 1% by volume in air, which is equivalent to 25% of the lower explosive limit.

(y)      Should the Master suspect a serious abnormality in the temperature of the cargo during the voyage he should seek advice the local P&I correspondents and/or the "competent person".  It might ultimately be necessary to make for a port of refuge and seek assistance.  Ventilation should continue in the meantime so as to ventilate any hydrogen that would likely be evolved.

Any decision to carry DRI in contravention of this advice should be discussed with the Association before loading commences.

This Circular supersedes all previous circulars on this subject.