Last week, an importer was asking us how to avoid the formation of mold on the shoes they ship from China to Chile. The goods stay up to 50 days inside the container, so that was an extreme case.
I suspect the materials are not treated against mold, in the first place. We suggested taking some samples randomly in the factory before production, and testing them in a laboratory. But that kind of test takes 3 weeks (which is sometimes longer than production)!
Another way of avoiding this problem is to absorb the humidity inside the container, by placing desiccants–some in each export carton, and some others outside the cartons.
The key is to place enough desiccants (at least 4 kg per 20′ container for those outside the cartons, from what I heard), but also to select desiccants that work for long enough. Once they are full of water and can’t absorb anything anymore, they start releasing water back into the air!
In my search, I came across a very interesting page on the website of Superdry, a supplier of container desiccant.
Under conditions of 90% humidity and 30 degrees, 1 cubic meter of air contains nearly 30g of water. And it can get worse during freight, because of condensation:
Fundamentally there are two different kinds of condensation :
Cargo sweat: This occurs when moving cargo from a cold or temperate climate to a tropical one. The air containing moisture or water vapour condenses-out on the cargo or its packing.
Container sweat: This is water vapour in the air condensing or forming on the inside surfaces of the container when moving from tropical or temperate climates to cooler areas.
Fungi, moulds and mildew do not usually cause any problems below approximately 55% Relative Humidity.
The effect or onset of corrosion is a function of many variables where humidity and time are also present.
Has anybody got problems because of humidity inside containers?