Goods with a low water content (< 1.5%) (WCC 1) and low, 3rd order biotic activity (BA 3)
These goods undergo only biochemical and microbial degradation processes and include hygroscopic crystalline goods, such as sugar, salt, fertilizer (potash) and chemicals which reach their flow moisture point at φ > 70%, resulting in an abrupt change in the adsorption isotherms; in the event of further water vapor adsorption, they deliquesce, leading in the case of sugar to syrup formation (see Fig. 5 in Section. 10.2.7). They require particular humidity/moisture and possibly ventilation conditions (SC IV).
Where temperature differences are too severe, water vapor release may occur, which may result in lump formation (agglomeration) and often in complete hardening; transporting the containers on deck may therefore be disadvantageous. If the goods are container dry, they do not require any ventilation; ventilation then only becomes necessary if moisture has to be removed, which is impossible with standard and bulk containers; however, transport in standard and bulk containers may be possible if additives are incorporated (to prevent lump formation). It may be necessary to close any fan outlets present.
In practice, if no additives are incorporated, moisture and agglomeration damage occur repeatedly in containers.
Goods with a low water content (> 1.5 to ≤ 30%) (WCC 2) and low, 3rd order biotic activity (BA 3)
These are typical hygroscopic goods with distinctive sorption behavior (S-shaped adsorption isotherms), which include many foodstuffs, semiluxury items and animal feedstuffs, such as dried fruit, spices, tea, tobacco. They are goods in which respiration processes are suspended, but in which biochemical, microbial and other decomposition processes still proceed. They must not suffer any moisture damage (mold, rot, fermentation, postfermentation) or desiccation damage (fragmentation, drying-out). This group also includes packaging materials (lumber, cardboard, paperboard) and pallet lumber, except that these are generally biologically inactive. These goods require ventilation (SC VI), which is impossible in standard containers. However, such goods may be transported without damage in standard containers if the water content of goods, packaging and pallets is kept so low that a correspondingly low equilibrium moisture content < 75% (mold growth threshold) is established, which corresponds to a temperature/dew point difference of > 6°C: the greater this difference, the lower the risk of sweat water upon cooling in the container (see Section 10.2.8). The goods should therefore be "container dry".
Notes on damage prevention (see Section 10.3.7)
Moisture damage caused to hygroscopic goods in standard containers by the formation of condensation water may be reduced by:
- Reducing the water content by pre-drying of goods, packaging, pallets and container flooring
- Laying paper dunnage
- Suspending a plastic sheet with condensation reservoir
- Using non-hygroscopic packaging materials, e.g. shrink film wrappings, aluminum foil in plywood chests, e.g. for tea, film lining impervious to water vapor for example for dried milk and sugar bags
- Suspending a nonwoven fabric, which is attached beneath the container ceiling
- So as to be able to transport bulk cargo in a standard container, a liner bag made from a strong woven plastic fabric can be suspended in the container. Since container bulk cargo is very often hygroscopic, the liner bag is also available combined with an integral nonwoven fabric.
- So-called sealed packages combined with the desiccant method for container transport of high quality technical goods
- Using ventilated containers for particularly sensitive hygroscopic goods, such as coffee, cocoa, rice, spices
Goods with a low water content (> 1.5 to ≤ 30%) (WCC 2) and 2nd order biotic activity (BA 2)
Due to their distinctive sorption behavior and high biotic activity (respiration and degradation processes), these hygroscopic goods separated from their parent plant require particular temperature, humidity/moisture and ventilation conditions (SC VI). Ventilated containers (known as "coffee containers") are appropriate, at the very least.
Natural ventilation takes the form, as is known, of the inlet of air through openings in the sides of the lower side rails; the air is heated by the cargo in the container, rises and may leave the container again through slots in the upper side rail.
This warm, moist air is able to escape, so that even the container ceiling dries off and/or no sweat develops (see Section 10.3.7).
If stowed in the hold, the ventilated container requires more intensive hold ventilation or a stowage space where this ventilation may reach it to the necessary degree.
For product groups with a tendency to self-heating, such as shell fruit, oil-bearing seeds/fruits, the "coffee container" is preferable to the standard container.
Particularly problematic with regard to containerization are cocoa beans (vapor damage, mold damage, total loss of aroma) and pepper (release of large quantities of water vapor, self-heating) and these goods must accordingly never be transported in a bulk container.
Goods with a high water content (> 30% to ≤ 90%) (WCC 3) and high 2nd order biotic activity (BA 2)
These include highly perishable goods with a high water content, such as bananas, pineapple, citrus fruit, pomaceous and stone fruit, berry fruit, vegetables, potatoes and onions. Since these are living organisms separated from the parent plant, the respiration processes have to be specifically controlled (e.g. "dormancy temperatures"; particular temperature, humidity/moisture and ventilation conditions (SC VII) are therefore required, as is intensive ventilation. Refrigerated containers with a fresh air supply, i.e. thermally insulated refrigerated containers with a fully air-conditioned atmosphere, or CA containers (controlled atmosphere containers SC VIII) are necessary.
Meat and fish also belong to this group, but their biotic activity is only 3rd order (BA 3), so meaning that only particular temperature and humidity/moisture conditions (SC VI) are necessary and they are generally transported in low-temperature refrigerated containers.
Goods with a high water content (> 90%) (WCC 3) and 1st order biotic activity (BA 1)
These are living organisms with fully maintained intrinsic metabolism, in which anabolic metabolic processes predominate: examples are livestock (animals for breeding and for slaughter), zoo animals and poultry. Loss-free transport in livestock containers, e.g. of horses, pigs, zoo animals, must be ensured by the provision of food, water and care.
Summary and future prospects
The above statements reveal that different goods display a range of sensitivities to climatic stresses, depending on their water content and biotic activity, and that containers range accordingly from the flatrack for goods not subject to any conditions, through standard containers, ventilated containers, refrigerated containers with full air conditioning or CA containers with a controlled atmosphere to livestock containers for living animals, which latter place the most stringent requirements on storage climate conditions (see Table 3, Allocation of some product groups to container types).
