The real risk of bauxite liquefaction

There has been some debate on the issue of the liquefaction potential of bauxite cargoes, not least because bauxite cargoes can be made up of particles of varying sizes and dimensions including fine particles, smaller particles as well as lumps and rocks.

Under the IMSBC Code bauxite has been described as Category C, neither prone to liquefaction (Category A) nor possessing a chemical hazard (Category B).

In practice, however, Skuld has had experience of shipments of bauxite which appeared to show signs of liquefaction and indeed expert advice on the issue would suggest that depending on the composition of the cargo, it is possible for liquefaction to occur.

This is particularly the case where water is introduced to the cargo to pre-filter it to separate fine and large particles, or when the cargo has undergone some other form of partial processing/crushing.

Depending on the particular circumstances of any given shipment, it would appear that bauxite may come with the risk of liquefaction. As such it may not be safe to assume that simply because a cargo has been declared by the shippers to be Category C that in fact it is.

Category shift

Under the Code, bauxite is stated to be a Category C cargo, with the following cargo composition: size: 70% to 90% Lumps – 2.5 mm to 500 mm; 10% to 30% powder. When the cargo consists of such a particle size and distribution – with over two thirds of the cargo being in the form of lumps – the IMSBC Code appears to state that the cargo is not prone to the risk of liquefaction. That may not be a safe assumption to make: actual composition and moisture content will impact the risk of liquefaction.

The expert advice received is that a cargo with 70% of particles ranging from 2.5 to 10 mm and 30% powdered cargo with particles sizes under 2.5 mm could, depending on moisture content, in fact display signs of being prone to liquefaction and thus act like a Category A cargo, rather than a Category C cargo as it is categorised. The IMSBC Code, in Appendix 3 of the 2013 edition, does states that any fine grain material containing moisture may potentially display flow characteristics and thus should be tested.

Where the cargo is of a different composition as stated in the Code, particularly with a greater amount of fine particles, then there should be no doubt as to the potential risks and the likely situation that the cargo may in fact qualify as a Category A cargo.

Skuld understands that for some shipments cargo may be pre-filtered to take out particles and lumps above 100 mm in size. Furthermore, larger particles may be subject to crushing to reduce the size of the particles to meet the preference of receivers for smaller particle sizes.

This in itself may not be an issue, assuming the cargo is sufficiently dry and has a moisture content below the Transportable Moisture Limit (TML), which is 90% of the Flow Moisture Point (FMP).

It would appear, however, that cargoes may not only be subject to significant water introduction by way of rainfall, but that the process of filtering the cargo may involve the use of significant quantities of water under pressure.

If the cargo is pre-filtered and/or crushed to reduce the size of particles, fines and powder as well as subjected to large intakes of water (be it by way of rainfall, high pressure hoses or other) then it would change the nature of the cargo as described in the IMSBC and thus give rise to the risk that it may liquefy. In such circumstances, the cargo needs to be considered as a Category A cargo and one which is prone to liquefy.

Red mud

A by-product of the processing of bauxite into aluminium is so called red mud. Given the composition of bauxite, the red mud produced contains a lot of iron oxides (up to 60%) and thus becomes of potential interest as an iron source cargo in itself.

It is, however, a cargo that comes with two significant risks. Firstly, it is highly prone to liquefaction and may actually be produced in a liquid state and secondly, the mud has a very alkaline level (as a consequence of the industrial ‘Bayer process’) and thus is hazardous due to its caustic properties.

Charterers and operators need to consider very carefully before loading such a cargo given that it may present significant risks to crew and vessel. This cargo has been shipped from Asian sources, but described as ‘iron oxide’ or ‘iron ore’ and declared incorrectly as Category C in shipment documentation.

Skuld has repeatedly warned about the risks of liquefaction that come with the carriage of bulk mineral ore cargoes. Just because a cargo is described as Category C in the IMSBC and in cargo documentation, does not mean the cargo actually tendered for loading is of that nature. Skuld has seen a number of cases where cargoes were mis-described including:
• mis-description as to the particle size and composition of the cargo
• mis-declaration of cargo as being Category C, even though the IMSBC listed it as Category A
• failure to provide moisture content information
• failure to provide proper TML and / or FMP information
• failure to follow the IMSBC with respect to sampling, testing and cargo certification in advance of loading
• and cargoes given different names to disguise their true nature.

Charterparty check

Charterers, operators and brokers should carefully check in advance where their cargo will be loaded and the description of the cargo as declared and should ask for clear and full cargo declaration descriptions to be incorporated into the fixture. Charterparties should contain suitable liquefaction risk clauses, which address issues that include:
• apportionment of risk of liability, time, cost and other delay factors
• use of surveys and arrangements for testing
• and liberties to refuse loading unsafe cargoes and to take action to protect a vessel experiencing a risk scenario.

Masters and chief officers should be instructed to refuse to load cargo that is not properly documented and/or which appears to come with a visible issue or have an issue ascertained by testing. Masters and crew should also be educated about the possible risks and carefully monitor loading, being instructed to refuse to load any cargo that appears to have an issue. In particular, it is important to watch out for obvious signs of accumulated water on barges and cargo stockpiles; splatter of cargo in the holds during loading; failed can tests; and free water accumulation on top of cargo in the holds.

This article was prepared with the assistance of Brookes Bell and is re-published with the kind permission of Skuld.