Iron Ore Fines What is Liquefaction?
In fine grained moisture laden cargo the spaces between cargo grains are filled with both air and water. Whilst at sea the cargo is subject to forces due to the vibration and rolling of the vessel. These forces cause the inter-grain spaces to contract. The water in the spaces between grains is subject to a compressive force but as it is a liquid it cannot be compressed. This has the effect of reducing the inter-grain frictional force that holds the cargo in a solid state. Where enough moisture is present the reduction in inter-grain friction due to the ship’s motion and vibration can be sufficient to cause the cargo flow like a liquid i.e. to liquefy.
Consequences of Liquefaction
The most significant consequence for the vessel resulting from liquefaction is cargo shift leading to loss of stability. This may produce dangerous angles of list and in some instances the resulting loss of stability can be such that the vessel and the lives of those onboard are lost. It is therefore imperative that seafarers are aware of the types and condition of cargo that may give rise liquefaction.
The International Convention for the Safety of Life at Sea (SOLAS) Chapter VI – Carriage of Cargoes - provides the general framework for the carriage of all cargoes.
Shipper’s Duties In respect of cargoes with particular hazards, such as liquefaction, SOLAS is explicit in requiring the shipper to provide the master, or his representative, with the appropriate cargo information sufficiently in advance of loading to enable the necessary precautions for safe carriage to be put into effect. The format of such information is also supplied in IMO circular MSC/Circ.663. Additionally there are specific provisions for additional information to be supplied for cargoes which may liquefy in the form of a certificate of moisture content and transportable moisture limit (TML).
As such shippers are obliged to provide appropriate cargo information to the master before loading commences.
SOLAS, Chapter VI Part B, Regulation 6.2, states that “Concentrates or other cargoes which may liquefy shall only be accepted for loading when the actual moisture content of the cargo is less than its TML.”
Therefore, a master should not accept such a cargo for loading without first receiving the appropriate documentation certifying the moisture content and TML of the cargo with the moisture content shown to be less than the TML.
Terminal Representative’s Duties
SOLAS, Chapter VI Part B, Regulation 7, deals with the loading, unloading and stowage of bulk cargoes and introduces the Code of Practice for the Safe Loading and Unloading of Bulk Carriers (BLU Code). The BLU Code is included as a supplement of the IMSBC Code.
The BLU Code, although primarily concerned with arrangements between the terminal and the ship to ensure safe and efficient cargo operations in port, does under section 3.3.3 state that:
“The terminal representative should be satisfied that the ship has been advised as early as possible of the information contained in the cargo declaration as required by chapter VI of SOLAS 1974 as amended.”
A question confirming that the cargo information has been received is also included in the recommended ship shore safety checklist at Appendix 3 - question 12 - of the BLU Code.
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