London P&I Issues Warning on Cargo Liquefaction
On Tuesday, three days after the mysterious loss of the South Korean ore carrier Stellar Daisy, the London P&I Club released a new guide to managing the risk of cargo liquefaction – the dangerous phenomenon associated with damp mineral ores.
Each load of a bulk commodity contains moisture and air in addition to the cargo itself. Vibration and motion cause the cargo to compact over time, and if there is enough moisture, the settling process can displace all of the tiny air pockets between each grain of ore. Under certain circumstances, this consolidated wet cargo may liquefy and generate an enormous free surface effect, thanks to its high density and the unobstructed width of a bulker’s hold. Even worse, it may flow suddenly to one side of the vessel and stay put. Each progressive roll may shift more and more of the cargo to the same side, eventually resulting in a capsize.
To guard against the risk of liquefaction, London P&I recommends that the master should be certain that proper tests and precautions have been taken prior to loading, including the use of an independent cargo surveyor if necessary. A simple "can test" performed by the crew can provide an indication of an excessively wet cargo. While under way, regular monitoring of the holds and the cargo bilges can give the crew an early warning of a developing problem with liquefaction – and may give the master the chance to head into a port of refuge.
Some observers have suggested that liquefaction may have been a factor in the Stellar Daisy's sinking, as she was carrying a cargo that has relatively high potential for the phenomenon. A Chinese steel mill source told Platt's that the Daisy was carrying iron ore fines, either the Sinter Feed High Silica Tubarao or Sinter feed High Silica Guaiba grades. However, the root cause of the sinking is still unknown, and investigators say that it is too early to draw conclusions. The only known factors are water ingress and structural failure: two survivors told rescuers that she broke in half before she went down.