New Guidelines to Avoid the Biggest Risk to Bulk Cargo Vessels

WORLDWIDE – Norwegian classification society DNV GL has published a set of guidelines for the design and operation of vessels with bulk cargo that may liquefy, with the intention of raising awareness of the risks of liquefaction and describes mitigating actions to reduce these risks. Liquefaction is a phenomenon in which a soil-like material is abruptly transformed from a solid dry state to an almost fluid state. Many common bulk cargoes, such as 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.

The guidelines focus on both the operational and design aspects of cargo liquefaction and makes a number of recommendations to reduce the risk of liquefaction in daily operation. The main risk for a vessel carrying cargo that may liquefy is of course shifting of the cargo. Such movement may be caused by liquefaction, or by sliding of the cargo. The two processes are different, but the possible consequences are the same: listing, capsize and structural damage. Morten Løvstad, Business Director of Bulk Carriers at DNV GL, said:

“Cargo liquefaction is probably now the most significant factor in lives lost at sea for bulk carriers. While the general safety level of modern bulk carriers has been significantly improved over the last decades, recent incidents have shown that cargo liquefaction remains a major safety issue. Since 2009, at least six ships of more than 40,000 dwt have been lost to suspected liquefaction of cargo.

“These incidents have shown that cargo liquefaction is an issue that has not been sufficiently dealt with, and concerned owners and operators have contacted us for support and advice. With this guideline we wanted to help our customers by not only increasing awareness and building competence around the phenomenon, but also to offer some strategies, both in design and operation, to reduce these risks.

The design guidelines look at the potential of carrying cargoes with high moisture content on board specially constructed or fitted ships, in compliance with the International Maritime Solid Bulk Cargoes (IMSBC) Code. Such vessels can remain safe both from a stability and strength point of view even if the cargo liquefies or shifts. Løvstad continued:

“Under the IMSBC code such vessels must have permanent structural boundaries or specially designed portable divisions to confine any shift or liquefaction of cargo, but detailed requirements are lacking. It is clear, however, that stability and structural strength have to be specially considered, and our guideline sets out criteria for them, based on DNV GL procedures and rules.”

The guidelines also examine how and why liquefaction can occur, which bulk cargoes are subject to liquefaction risks, explains the Transportable Moisture Limit (TML) and presents the effect of liquefaction on a vessel. 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.

Copies of the guidelines ‘Bulk Cargo Liquefaction’ can be downloaded here.