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Ventilation requirement for various type cargoes
Proper ventilation is extremely important for all cargoes, although the types of ventilation for different cargoes are widely varied, and you should be guided accordingly by the reference publications, with advice available from the Company on request.
It is the responsibility of the Master to ensure that entries are made correctly in the deck log book concerning items which could affect the condition of cargo, and this will later assist the Owners in documenting their case in the event of a claim. For example, weather conditions during loading, discharging and during sea passages. Also cargo left standing on dockside during rain, wet or otherwise contaminated/damaged cargo being placed on board or rough handling by stevedores.
Holds drying up
The correct log book entries are extremely important and you are to instruct the Deck Officers accordingly. An appropriate starting point for those faced with decisions as to when to ventilate a particular cargo, is to consider what the objective of any such ventilation is. In this respect cargo type is important, and can be broadly classified into several basic categories.
a) Cargoes in bulk or in permeable packages which are liable to evolve toxic or otherwise hazardous gases.
b) Cargoes of fresh vegetables and fruit.
c) Cargoes in bulk or in permeable packages which do not possess the characteristics of those in categories 1 and 2 but which are liable to be damaged by wetting, or absorption of water vapour.
The objective of ventilating cargoes in category a) is to minimise the concentration of hazardous gases within the atmosphere of a ship's hold. Some of these cargoes - for instance certain types of ferrosilicon and coal - are listed in the IMDG code and/or in the IMO Code of Safe Practice for Solid Bulk Cargoes, with specific recommendations concerning ventilation.
When readily available information on any particular cargo is lacking and doubts exist, specialist advice should be sought.
Fresh vegetables and fruit
The same applies to cargoes in this category where the different objective of ventilation is to remove heat and other products of active cargo metabolism and where aspects of stowage are importantly inter-related.
Attention will therefore be focused in this article on the appropriate ventilation regimes for the wide range of cargoes of radically different nature which fall into the above mentioned category c).
Standard bulk and bagged cargoes
These can be further sub-classified into the following broad categories:
These three categories can conveniently be referred to respectively as zero, low and high moisturecontent cargoes.
- cargoes which contain no inherent moisture such as unpackaged steel products. Some cargoes of very low moisture content which are in impermeable, and non-moisture-containing (e.g. plastics) can also be conveniently placed in this category.
- cargoes which contain very low levels of inherent moisture or alternatively no inherent moisture, but where the packaging (e.g. jute bags or fibreboard cartons) may naturally contain comparatively low levels of moisture. Examples are refined sugar in plastic-lined jute bags, and canned goods in fibreboard cartons.
- cargoes in bulk or in permeable packages which contain appreciable amounts of inherent moisture. Examples are grains, cocoa beans etc and processed products derived there from such as flour, soya bean meal etc.
Reducing the humidity. Humidity and condensation can cause damage to cargoes and also to the holds or tanks containing them. Dehumidifying of the areas prevents these problems, and the two most widely used systems employ either refrigeration or desiccant.
In the refrigeration systems the air is cooled, and the amount of water vapour it can hold is reduced, with the excess condensing on the chiller surface. The condensed water has to be either collected into a container or pumped away. In the desiccant method, a medium (silica gel, for instance) is used to absorb the moisture from air before it is blown into the hold to replace the humid air. Heat is then used to dry the desiccant. The released water vapour is vented outside the controlled atmosphere.
Dehumidifier A substance or a machine used to reduce humidity in holds or cargo tanks. Calcium chloride and silica gel are water-absorbing chemicals (desiccants) commonly in use.
Related information :
Cargo sweat and ships sweat & recommended ventilation methods
Risk of ship sweat and how to minimise
Requirement of bilge monitoring at sea
Preventive measures against cargo which may liquefy
Causes of bulk carrier hull damage and failure in operation
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- Handling water ingress problems in bulk carrier, investigation and countermeasures
- Survival and safety procedure for bulk carriers
- Monitoring hull stresses during rough sea conditions
- Precautions against bulk cargo which may liquefy
- Cargo damage survey guideline
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