Hazards of Bulk cargo and High density cargo.

All the points below will be applicable for bulk cargo and some of them will also be valid for High density cargo.

Structural damage

Great care is required to avoid over stressing the vessel and doing structural damage. Carefully planning of the load and the discharge must be made, and at all times the maximum loading of the tank top must not be exceeded.

In addition, the maximum loading for each hatch must not be exceeded. Care must be taken to ensure that the peak height of an untrimmed cargo is not excessive thereby increasing the tank top loading.

In tween deck vessels, high density cargoes such as iron ore should be loaded in the lower hold only to avoid damage to the tween deck.

Shifting

Some cargoes may have a tendency to shift across the ship in heavy weather and so correct trimming of the cargo is required. Some cargoes such as grain may need extra measures to be taken to secure the surface. For example, bulk grain may be over stowed with bagged grain.

As a general rule all cargoes should be trimmed level or nearly level. and whenever possible spaces should be filled as fully as practicable without putting excessive stress on the structure.

Liquefaction

Some cargoes, particularly metal concentrates, may become semi‑liquid on top when loaded “wet”. This is due to the vibration of the ship at sea causing the moisture in the cargo to migrate to the surface.

The surface may then act as a liquid and seriously affect the stability of the vessel. Examples of this are coal, duff and lead concentrates.

Gas Production

Explosive gasses such as methane and poisonous gasses such as carbon monoxide may be produced by some cargoes. For example coal

Self‑Heating

Some cargoes are liable to heat up on voyage. Temperatures should be taken and a log kept of each space. For example coal and steel swarf.

Corrosive

The cargo itself may be corrosive or the liquid draining out of the cargo into the bilge’s may be corrosive. In some ships severe damage has occurred. For example coal and sulphur.

Dust Very dusty cargoes may be hazardous to humans and the environment and so measures may have to be taken to control the level of dust created e.g. stop load/discharge in high winds. For example alumina and phosphates.

Cargo Liquefaction

Liquefaction is a phenomenon in which solid bulk cargoes are 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 are examples of materials that may liquefy. Liquefaction occurs as a result of compaction of the cargo which results from engine vibrations, ship’s motion and rolling and wave impact that further causes cargo agitation.Liquefaction results in a flow state to develop. This permits the cargo to slide and shift in one direction thus creating free surface effect and reducing the GM thereby reducing stability. Shippers declaration should be thoroughly examined by the chief officer before loading any bulk cargo. He must make sure that the moisture content of the cargo to be loaded should not exceed the transportable moisture limit to avoid liquefaction during the voyage. Often shippers declaration turn out to be faulty. Spot checks can also be carried on board ships to check the moisture content.

Prior to Loading

The master is to have approved stability information containing comprehensive information on the ships stability and distribution of cargo and ballast for standard conditions.

The master is not to accept concentrate or other cargoes that might liquefy unless the moisture content is lower than its transportable moisture limit, If the moisture content is above the transportable moisture limit the master must satisfy the authorities that there is satisfactory stability in the event of a shift and that the ship has adequate structural integrity.

If loading a cargo with chemical properties that might create a potential hazard, for example coal, appropriate precautions for safe carriage are to be taken.

The owner is to ensure that the master is given the required information.

The master is not to accept cargo for loading unless he has been provided the required information and he has calculated that the stability would be sufficient.

Cargo Loading Manual

The owner is to ensure that the master is provided with a cargo loading manual that includes:

Loading and Unloading Plan

Before loading or unloading the master and terminal representative are to agree on a plan which:

Ensures that the maximum permissible forces and moments on the ship are not exceeded.
Includes the sequence, quantity and rate of loading or unloading.Copies of the plan and its subsequent amendments are to be sent to the appropriate port State authority. (In the United Kingdom this will be the port or harbour authority who will keep the plans for at least 6 months)

Loading, Unloading and Stowage

The master is to ensure that bulk cargoes are loaded and trimmed reasonably level to the boundaries of the cargo space.

When bulk cargoes are carried in tween decks the master is to ensure that tween deck hatches are closed when the loading information indicates unacceptable stress of the bottom structure if they are left open.

The tween decks are not to be overloaded, and the cargo trimmed from side to side or secured by longitudinal divisions.

The master and terminal representative are to ensure that the unloading methods do not damage the ships structure.

The master is to ensure that ship’s personnel continuously monitor cargo operations, check the ship’s draft regularly and record draft and tonnage observations. If significant deviations form the plan are detected, cargo or ballast operations are to be adjusted to correct the deviations.

The master and terminal representative are to ensure that loading and unloading proceed according to the agreed plan. If the maximum permitted forces or moments are exceeded the master has the right to suspend operations and should inform the appropriate port State authority. The master and terminal representative are to take corrective action.