Cargo hold ventilation requirement for Container ships
The sea transportation of containerized goods involves many complexities; therefore, they need close supervision from the moment the containers being loaded onboard until safely delivered at destination. Each year cargo damage claim is on the rise, and many such claims could have been easily avoided if safety precautions and due diligence rules properly-being exercised.
Insufficient knowledge, inadequate skill training, and lack of information sharing are the root cause of many cargo damages on board a container ship. Thus, not understanding cargo stowage plans and ventilation requirements, especially for reefer cargo or D.G. cargo, can lead to a potential damage claim. We have summarized below some critical guidelines on cargo hold ventilation requirement onboard a containers ship.
Cargo holds ventilation onboard a containership is very important as it minimizes the risk of harm or damage to cargo. A proper ventilation system assures the quality of the transported goods by preventing the formation of condensation in cargo spaces, reducing the harmful heating of the shipment, and removing potential hazardous gases from cargo spaces. Cargo holds of container ships are fitted with two basic types of ventilation systems, namely natural and mechanical. Mechanical ventilation could be of either the supply or the exhaust type.
Container ships certified to carry D.G. cargo underdeck, are fitted with mechanical ventilation fans meeting SOLAS special requirements for ships carrying dangerous goods.
Such fans operate in the exhaust mode and are capable of providing at least six air changes per hour to remove vapors from upper or lower parts of the cargo spaces as appropriate.
Cargo holds designated for carrying refrigerated containers that may be fitted with additional ventilation fans that operate in the supply mode.
The operation of these ventilation fans will provide forced ventilation required for the operation of reefer container refrigeration units. When carrying D.G. cargo in such cargo holds, care must be exercised to operate only exhaust mode ventilation fans, if fitted, by reversing the direction of reversible fans to operate in the exhaust mode.
Condensation on the surface of the cargo:
Condensation can form on the cargo as a result of climatic conditions. Cargo sweat can always occur when the cargo's temperature is lower than or equal to the dew point. It can also occur during transportation from temperate latitudes, e.g., from northern-hemisphere winter to the tropics.
Proper cargo hold ventilation is also effective in controlling hull corrosion caused by the presence of moisture and free water inside cargo holds. The cargo's temperature within a container can vary according to place and time (e.g., during a cooling or warming process).
Moisture and free water in cargo holds could result from sweat, which might be either ship's sweat or cargo sweat and from other sources like rainwater, leakages, etc.
Such moisture and free water will accelerate corrosion and cause deterioration of structural members and plating within the cargo hold.
Hull corrosion caused by such reasons can be effectively controlled by carrying out proper ventilation which must be planned and undertaken on passage as necessary.
Two broad rules of ventilation
As a general rule inside a cargo compartment loaded with containerized cargo there are two broad rules of thumb which can be borne in
mind
Cold to Hot - Ventilate Not
Hot to Cold - Ventilate Bold
During a voyage from a cold area to a warmer area, the cargo will generally remain cold while the structures of
the vessel will get warmer, and the dew point of the outside air is likely to be above the temperature of the cargo –
therefore do not ventilate. Whereas during a voyage from a warmer area to a colder area the steelwork of the vessel
will become colder while the shipment will remain warm and ship's sweat is likely to occur, at the same time the dew
point of the outside air is expected to be below that of the air inside the hold, therefore ventilate to avoid the formation of
ship's sweat.
These examples are simplified, and in practice, all appropriate measurements must be taken, and ventilation/no ventilation must be carried out, bearing in mind all the circumstances, day-to-day.
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