Liquefaction of cargo vessels involve a lot of risks. But, there are mitigating actions to reduce these risks. DNV GL has published a guideline for the design and operation of vessels with bulk cargo that may liquefy because Cargo liquefaction is the most significant factor in lives lost at sea for bulk carriers.
Iron ore fines, nickel ore and various mineral concentrates have the potential to transform into an almost fluid state, threatening the stability of the vessel.
Since 2009, at least six ships of more than 40,000dwt have been lost to suspected liquefaction of cargo.
DNV GL has been approached by concerned owners and operators for support and advice to increase awareness and building competence around the phenomenon, but also to offer some strategies, both in design and operation, to reduce the risks.
The following are the guideline for safe cargo liquefaction:
- Make sure that cargo is correctly identified and properly documented.
- Ensure the time interval between testing for moisture content and loading is no more than seven days.
- Retest in the event of rain, appointing an independent surveyor.
- Perform a can test or similar to verify the moisture content,
- Load in a non-homogeneous pattern, raising the centre of gravity by ballasting the top wing tanks.
- Loading condition and structural strength should allow item 5.
- Trimming is necessary to ensure cargoes are at reasonable level.
- Permanent structural boundaries or specially designed portable divisions to confine any shift or liquefaction of cargo.
The IMSBC Code suggests safety through specially constructed or fitted ships from a stability and strength point of view even if the cargo liquefies or shifts.
The guideline also examines how, why and for which bulk cargoes are subject to liquefaction risks. The Transportable Moisture Limit (TML) is also explained. The aim of the guideline is to provide ship designers, yards, shipowners and other stakeholders in the shipping industry a basis to assess the risks and begin the process of making their vessels and their operational processes safer when it comes to the risks of liquefaction.
Source: DNVGL
