Another problem with certain bulk commodities is that of liquefaction, created by moisture migration. Moisture migration is caused when vibration at sea progressively causes the water content of a cargo to rise to the top of the hold which might eventually lead to a dangerous free surface, perhaps shifting violently from side to side. Accordingly, commodities liable to such problems are allotted a TML – transportable moisture limit, representing the maximum moisture content of that cargo considered safe for carriage in ships. Certain commodities – eg: concentrates, are particularly prone to liquefaction and should never be carried without first checking the moisture content. Where such cargo is contemplated, it is common practice to include a clause in the contract of carriage reading such as:- .. Cargo to be loaded. stowed. carried and discharged strictly in accordance with IMO and/or local authority regulations and recommendations”. and Certificates should be issued by the shippers relating to the properties and the moisture content of the cargo to be loaded. The “Code of Safe Practice for Solid Bulk Cargoes” referred to earlier, provides information on both the transportable moisture limits of various commodities as well as details of how the moisture content of a particular commodity can be tested and assessed.