COAL CARGOES

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Coal Slurry
This is a mixture of solid coal containing water and is obtained as a by-product during mining. The coal particle size is usually less than 1 mm. It is regarded as a cargo that may liquefy due to its high moisture content.

Coal Duff
This is a mixture of coal and water with the largest coal particles around 7 mm. Less liable to liquefaction than coal slurry, but does require its moisture content to be monitored.

Coke
Solid residues obtained by distillation of petroleum products, or half burnt coal with less gas content but with a tendency to absorb moisture at up to 20% by weight.

Small Coal
Contains particles of coal less than 7 mm in size; small coal is likely to develop a flow state due to its high moisture content. Spontaneous Combustion
Some coals are liable to spontaneous combustion due to the presence of moisture that causes exothermic oxidation (a reaction that results in production of heat) of coal at ambient temperature. If this heat is not dissipated, the temperature rises and the coal may ignite.

Corrosion
Some types of coal react with water to produce acids that can cause excessive corrosion of the ship’s structure, known as `cargo corrosion’. As a result of the chemical reaction during the process of forming acid and then corrosion, colourless and odourless gases such as hydrogen are produced.

Precautions for Carriage of Coal

General precautions for the carriage of coal include:

  1. The Master should be informed about the cargo in the `Cargo Information Form’ ( ie. Shipper’s Declaration/Cargo Information ) and the material safety data sheet (MSDS) prior to loading.
  2. The precautions that need to be taken depend upon the information provided, eg if the cargo is liable to emit methane, then the Master should refer to the IMDG Code to obtain the loading, stowage and carriage information.
  3. It is, therefore, imperative that the cargo information be supplied to the Master prior to commencing loading, or they may not allow the operationBefore loading cargo:
    1. oi) Bilge wells should be cleaned, residual cargoes removed, suction tested and covered with taped down double wrapped burlap.

    oii) Hatch top wheels and associated equipment should be greased to ensure that no sparks are caused during opening and closing.

    oiii) Electrical cables, cargo hold lights and any other electrical instruments within cargo holds should be checked for insulation damage to ensure that they are safe for use in an atmosphere containing explosive gases. On bulk carriers, as no lighting is needed, the fuses should be pulled to isolate electricity.

    oiv) Ships that carry coal are required to carry instruments to measure:
    a) Methane, oxygen and carbon monoxide levels in cargo holds
    b) cargo hold temperature (between 0-100°C)
    c) the pH of bilge water.

    The installation of these instruments or the taking of measurements, should be possible without entering the cargo space. Arrangements should also be made to calibrate and test the instruments.

    1. Extra monitoring should be implemented when coal is loaded in holds adjacent to hot areas, such as heated fuel DB tanks and engine room bulkheads.
    2. The ideal place to monitor the temperature of the load is the centre of the stow. If the temperature is measured from the side, top or corners of the hold it must be remembered that the temperature at the centre of the cargo will be several degrees higher.

     

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    VIII.Except where the shipper provides specific instructions to ventilate the cargo, compartments containing coal should only be ventilated for the first 24 hours after departure from the loading port. There should be regular monitoring of atmosphere to check the concentration of pH of bilge water. Ventilation should only be continued if the amount of methane rises above the acceptable level. Coal should also be ventilated prior to discharge owing to the danger of the build-up of gases that could be ignited by a spark from the opening of the hatches.

    1. The gases may escape the cargo compartment to adjacent stores, mast houses, etc. These spaces should also be monitored on a regular basis.
    2. If any suspected problem is observed during the passage the shipper should be contacted, not only to update their information but also to seek any clarification.Special Precautions for Coals Emitting MethaneIf the shipper has declared that the cargo is liable to emit methane or the methane concentration in the cargo compartment is above 20% of the Lower Explosive Limit (LEL), the following additional precautions should be taken:
      • Surface ventilation should be maintained
      • hatch covers should not be opened until the accumulated gases have been removed. Hatch covers should then be opened carefully ensuring no sparks are initiated
      • all enclosed spaces such as store rooms, tunnels and passageways, etc, should be thoroughly monitored for methane
      • enclosed hatch covers should be ventilated.Special Precautions for Self-Heating CoalsIf the shipper has declared that the cargo is liable to self-heat, then the following additional precautions should be taken:
        • If required, the Master should seek additional guidance from the shipper on the adequacy of the existing precautions
        • if analysis of the atmosphere of the cargo compartment indicates an increased carbon monoxide concentration,

         

        1. iv) if the hold temperature exceeds 55°C or the carbon monoxide concentration rises steadily, expert advice should be sought.
          • then
          1. i) the hatch covers should be closed after loading and additional seals appliedii) surface ventilation should be kept to minimum

            iii) carbon monoxide concentration should be regularly measured and recorded