Bulk cargo. The IMO “Code of Safe Practices for Solid Bulk Cargoes” defines this cargo as:
“A cargo consisting of solids in particle or granular form, with or without entrained moisture, generally homogeneous as to composition, and loaded directly into a ship’s cargo spaces without bagging or packaging.”
Huge volumes of cargo in international trade are transported in bulk form in specialised bulk carriers. However, small percentages of the different bulk commodities may still be fixed for ships which are not specialised bulk carriers, for example, general cargo ships and there will then be important cosniderations to be taken into account. The main hazard with some dense bulk cargoes is stress or lack of stability, caused by improper weight distribution. In purpose-built ore carriers these problems are minimised because of planned loading instructions from the ship designer and also the strength and design of the ship itself.
There are various categories of hazard with bulk cargoes. For example,
(a) improper weight distribution can result in structural damage;
(b) improper stability or reduced stability can occur during the voyage because of cargo shift; the improper stability can be excessive, where the vessel is too “stiff” with a large metacentric height because high density cargo, such as iron ore, is loaded too low down; it can also be deficient;
(c) some commodities heat spontaneously, e.g., coal and ore concentrates. Toxic or explosive gases can be emitted, e.g. from coal;
(d) severe corrosion can be caused by some bulks such as sulphur ;
(e) determination of quantity loaded can be difficult (see “draft survey”);
(f) some cargoes, such as ore concentrates and similar finely divided materials, liquefy when shipped in a damp state; they may appear to be in a relatively dry granular state when loaded yet may contain sufficient moisture so as to become fluid under the stimulus of compaction and the vibration which occurs during a voyage; in the resulting viscous, fluid state the cargo may flow to one side of the ship with a roll one way but not completely return when the ship rolls the other way; the vessel may progressively reach a dangerous heel;
(g) damage can be caused by improper cargo-handling methods; e.g., ‘‘pouring’’ of heavy lumps of a high density bulk cargo can damage the bottom of the hold; grabs used for discharge can also damage the vessel’s structure.
Therefore, before loading any solid bulk cargo, the master and shipowner should obtain detailed, comprehensive and current information from the shipper.
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