The London P&I Club has published a booklet to provide guidance about the risk of cargo liquefaction. It offers practical advice on the loading and the carriage of bulk cargoes which may liquefy and the risks associated with liquefaction, plus the precautions to be taken to minimize these risks.
Cargo liquefaction is described as the phenomenon that is triggered by an increase in water pressure that makes solid bulk cargoes (granular materials that are loaded directly into a ship’s hold) turn from a solid-state into a liquid state, causing a ship to tilt and potentially capsize. It can occur when cargo is loaded into the hold – this often involves a fall from significant heights, or when it is exposed to agitation by the ship’s engine vibration or movement of the waves.
It is important that the master should not accept concentrates or other cargoes which may liquefy for loading without being provided with the appropriate documentation certifying that the moisture content of the cargo is less than the TML.
Prior to the commencement of loading the master should satisfy himself and confirm that:
– The cargo holds are clean and dry, and the bilges have been tested.
– The hatch covers close correctly and are weathertight.
The following should also be carried out by the shipper and the master:
– The shipper should provide the master well in advance with the appropriate information on the cargo as per requirements found in Section 4.2.2 of the IMSBC Code.
– This information should be accompanied by a declaration by the shipper (Section 4.2.3).
– The master should check, based on the information provided on the cargo declaration, whether the cargo can be safely carried on board the vessel or whether additional information is required.
– The shipper should provide the master with a signed certificate of the TML, and a signed certificate or declaration of the MC issued by an entity recognized by the Competent Authority of the port of loading (Section 4.3.2).
– The master should check that the laboratory test undertaken ashore to determine the TML of a cargo has been conducted within six months of the date of loading the cargo3 (Section 4.5.1).
– The master should check whether the testing of the MC of the cargo that is being presented is as near as practicable to the time of loading, and not more than seven days (Section 4.5.2).
– If there has been significant rain or snow between the time of testing and loading, check tests (laboratory tests, not can tests) should be conducted to ensure that the moisture content of the cargo is still less than its TML.
It is a master’s responsibility to ensure that his/her vessel is safely loaded. If a shipper’s declaration has not been provided and has not been forthcoming, then the master should not start loading and immediately notify the vessel’s owners.
Loading should only commence when the shipper has fulfilled the requirements outlined above and the master is satisfied with the information he has been provided with. The master should also complete the ship shore safety checklist as recommended by the Code of Practice for the Safe Loading and Unloading of Bulk Carriers (BLU Code4).
The master and owners may consider the appointment of an experienced, independent cargo surveyor in order to check the shore-side stockpile and if necessary take samples. In most ports, the master may not be allowed to go ashore to inspect the stockpile.
During loading the master should:
– Arrange for the deck to be adequately manned so as to carry out a visual inspection of the cargo being loaded.
– Be aware of the build-up of water pools or splatter on the bulkheads – this indicates excessive moisture.
– Continue to systematically carry out and record ‘Can Tests’ as described above.
– Restrict the ingress of water and not load during periods of rainfall.
– Make sure that the hatch covers of all non-working holds are kept shut.
– Ensure that, if the cargo is being loaded from barges, the barges are adequately covered during periods of precipitation and water ingress. If this is not the case, the master should not accept any cargo from these barges unless the moisture content has been re-established.
– If the vessel encounters prolonged periods of precipitation during the loading period, request check tests to ensure that the MC of the cargo is still less than its TML.
– Prior to completion of loading, ensure that the cargo is reasonably trimmed (as per dry bulk cargo good practice).
– On completion of loading, ensure that the hatch covers are closed and secured as required.
If during loading the master has reason to suspect that the MC is in excess of the TML, he/she should stop loading the cargo and inform the owners. The master may issue a ‘Letter of Protest’ and seek further advice from the P&I Club.
During the voyage
Monitor the cargo holds regularly to check for any sign of accumulation of free water in the cargo. Although these inspections may not provide a true representation of the cargo condition, they may provide an indication of how the cargo has behaved since it was loaded. However, this should only be carried out if it is safe to enter the holds, as mineral cargoes tend to deplete oxygen levels.
If it is not already part of the ship’s routine, sound the cargo hold bilges on a daily basis. Although free water is expected to drain it can hold the moisture towards the bottom of the hold and develop a wet base.
If necessary, consider ventilation of cargo as and when appropriate. This will depend on the advice contained in the IMSBC Code for that particular cargo loaded. Monitor the vessel’s motion, in particular the rolling period. A change in the rolling period may provide a warning of a reduction in the vessel’s GM.
If the master or owner has any reason to suspect that the cargo liquefaction is or may be occurring, they should immediately:
– Contact their P&I Club;
– Contact the nearest coastal state authority;
– Consider heading to the nearest port or place of refuge;
– Consider measures to reduce the vessel’s vibration/motion.
Key facts about cargo liquefaction
Cargo liquefaction may occur without additional water content (e.g. from rainwater) if the inherent moisture content is already too high, yet undetected by improper checks/tests, agitation alone will cause liquefaction to happen.
– Space between particles reduces
– Air is expelled
– Water pushes particles apart
– Loss of shear strength
– Solid cargo becomes liquid
– Centre of gravity shifts
– Free surface effect
– Ships may capsize
Read the booklet in pdf format: London Club Cargo Liquefaction booklet