is sometimes misinterpreted as CH4 emission. This can lead to holds being ventilated, which worsens the self-heating.


Coal that is liable to self-heat should not be loaded on board vessels if its temperature exceeds 55°C. This is because self- heating reaction rates increase exponentially as temperatures rise. As shippers’ declarations may not be reliable, proper temperature measurement before loading is very often appropriate, for example in Indonesia, even if the coal is not declared as liable to self-heat. Temperature measurement of the coal to be loaded needs to be done at multiple points, to pick up hot spots. The temperature should preferably be measured below the surface, because if there is any self- heating the bulk will be hotter than the surface. If that cannot be done, then freshly exposed coal should be measured before it has been able to cool.


Once coal is on board, temperatures are more difficult to measure. Temperature sounding pipes within the holds are often used, but their readings are of limited value because bulk coal transmits heat poorly. Therefore, the focus should be on temperature measurement before loading.


The IMSBC Code indicates that coal stows should be trimmed ‘reasonably level’ to the hold boundaries. This is to minimise the exposed surface area, and to avoid cracks, hence minimising air entry and self-heating. It is good practice to take photos of the coal stows at the completion of loading to show the final trim, and to record the ullage size.


Holds and adjacent spaces must not be entered without proper precautions to ensure that the atmosphere is safe, because coal often removes O2 from air and produces toxic gases such as the odourless carbon monoxide (CO). If there are delays of more than a few hours with no loading, consider closing the holds and measuring gases in the meantime.


Once holds are full, the IMSBC Code provides that, unless indicated otherwise, ventilate for the first 24 hours after departure from the load port, and measure gases once


during this period, after closing vents for a suggested period of not less than 4 hours. With self-heating coal that might not be declared as such, venting may worsen self-heating. It is often best to measure gases early within the first 24-hour period, after closing vents for the suggested period for measurement, and to repeat gas measurements frequently thereafter until conditions are seen to be stable. This is to check early for excessive CH4 / flammable gas and CO.


If CH4 / flammable gas concentrations remain below 20 %LEL, then holds should remain closed and unventilated. This is to exclude air / O2 and hence minimise the potential for self-heating.


If CH4 / flammable gas is increasing and above 20 %LEL, ventilation needs to be considered as a priority, to avoid explosion risks, which are more acute than self-heating. However, the %LEL action level for ventilating also depends on the ventilation history, the O2 and CO levels and other factors.


Ventilation can hide self-heating problems. This can suppress CO measurement results, the best indicator of self-heating. Therefore, gas measurements need to be assessed carefully and ventilation needs to be controlled correctly, to avoid both explosion risks and self- heating. If gas measurements indicate that CO is rising above 50 parts per million (ppm) in unventilated holds, that indicates that the coal has propensity to self-heat. Gard recommends seeking expert advice if the CO level is above 50 ppm, as is indicated in the IMSBC Code. In such cases gas measurements should be taken at least every 12 hours until the situation is stable.


For coal with any self-heating tendency, once the vessel arrives at the port of discharge it is recommended to keep all cargo holds and vents closed and to measure gases until the discharge operation is ready to start. This applies to all holds individually meaning those holds that are not actively being discharged should remain closed. Pre-discharge surveys should not cause holds to be opened, allowing air / O2 entry to the holds, unless discharge is to commence very shortly, or gas measurements have shown that there is no self-heating tendency.


If coal is showing signs of problematic self-heating, then it should be discharged all in one go, without delays. It is preferable to have a discharge plan to facilitate this, if it is possible within ship loading and stability limits. If there are any significant delays during discharge in any holds, consider re- closing those holds and measuring gases.


In case of severe self-heating or fire in coal, the IMSBC Code mentions avoiding using water when at sea. Røyset said that Gard’s experience was that spraying water could help to suppress heating and fire, usually at anchor or alongside. Care however must be taken to keep within loading and stability limits, for example by pumping out water to an appropriate tank. Fresh water is preferred because seawater is often detrimental to the end use of the coal.


Concluding remarks


Given that cargo declarations may be unreliable and faced with the prospect of catastrophic losses to people and property, Gard said that it was important that care be taken at each stage, from loading to discharge, to monitor loading temperatures and, critically, gas levels on board.


The writer noted that coal has other characteristics not addressed here. For example, some coal can also liquefy or produce acidic liquids which may corrode the vessel’s structure.


62 | ISSUE 107 | MAR 2024 | THE REPORT


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