Very simply, Damp and Condensation can form when warm air holding water in a vapour, cools down and that cooler air can no longer hold the same amount of moisture. This moisture collects on a cold surface in very tiny tiny,  droplets almost a mist ( that’s the mist you see on your windows ) and  those tiny, tiny droplets joins hands to  form even bigger droplets that can then start running down your walls or windows or dripping off the ceiling or they  quickly get absorbed into the nearest water absorbing material.  If the air warms up again these droplets are again transformed back into vapour which is then held in the air, returning back into droplets when the air cools again. In a Shipping Container for example or a tin roofed shed, the most usual place for these droplets to meet up is on the ceiling which is usually the first coolest place and these droplets may run to the lowest area of the ceiling and form dripping points. This can keep happening every day it’s like a micro rain cycle, the result is the top of your stored items gets damp regularly and in the worst cases some areas get sodden and start growing  bacterial fungi things or black spots!

Why and what is container moisture damage?

Where does the airborne moisture come from … well Primarily it is already in the AIR and of course everything organic has moisture in it, Paper, and more especially Cardboard,  Fabrics, Materials, Books, Soft Furnishings, Bedding, Mattresses, Carpets, Wooden Pallets, and your Breath generates a lot (think, cave paintings, in a dry stable atmosphere they lasted thousands of years, then they get discovered, the public  go and look at them, and they start deteriorating).

Container moisture is caused by changes in temperature, which occur when vessels pass different climate zones. A container that is loaded in a tropical environment, for example in Hong Kong, where the air is warm and humid, and then shipped to, for example Scandinavia, where temperatures are far cooler, will most likely suffer from cargo damage caused by container rain – if the container is not protected against moisture.

What happens inside a container during transportation is that the warm, humid air condenses. Like the dew running down a can of fizz on a hot summer’s day, condensation begins to form on the cargo, the inner ceiling, and the walls of the container. Condensation takes place on the coldest available surface, and when the warmer air hits a colder surface (the container sealing), given the right heating and cooling cycles in the container, the moisture release could be so significant that it would seem to be “raining” from the ceiling. This could happen repeatedly every 24 hour unless the relative humidity (Rh%) is reduced. The container flooring by itself can hold up to 100 litres of water!

So, when your container arrives and the cargo is wet inside, and the interior smells of mould and mildew, this is most likely what has happened!

Did you know that approximately 10% of all containerised goods are discarded by moisture related damages? This is an incredibly large amount that goes to waste, not only causing large economic losses, but also affecting our nature. So, what is causing container rain? And more importantly, how can it be prevented? In this article I will tell you just that, and also teach you a few tricks on how to protect your cargo.

The importance of moisture protection inside containers

Discharging ten percent of your cargo is very expensive in the long run. Looking at one consignment only, it may not be the end of the world, but looking at all shipments you do in one year – or ten years – the amount of money you lose is huge. Selling your cargo instead of having to discard it, could greatly benefit your profit. If your shipment is completely destroyed by moisture and fungus, you will have to discard everything, and make an additional transport for your customer. If the shipment is urgent you might even have to choose an expedited transport option instead of short sea freight – which is much more expensive. In addition to large economic losses, and unnecessary waste of our nature, the effects of cargo damage can often translate into lost revenue, and jeopardise the credibility for manufacturers or retailers, of almost any product.

A few tricks on how to protect your cargo from moisture and fungus

Apart from temperature fluctuations, which you cannot affect, there are a few things you may want to consider to avoid container rain. In general, all containers hold moisture to some extent, as air always holds water (warm more than cold). But also the cargo may contain moisture. Cargo with a high fibrous construction, such as furniture, handicrafts, agricultural products, clothes and other fabrics, hold a certain amount of moisture at origin that can be released under the right cooling conditions. Also the packaging material, including pallets, cartons and cardboard, contains moisture. The type and amount of cardboard used, can greatly contribute to moisture release. When shipping containers over sea, take into account, both the material of your goods and the material of the packaging, and make sure to use the right packaging material for your cargo accordingly.

Using ventilation is a good fix to prevent the moisture from turning into container rain. A common mistake is to cover the ventilation inside the container, in the belief that moisture from outside will enter through the ventilation. This is completely wrong – the ventilation is there to remove excessive moisture! Covering it will only make it worse, as the humid air cannot be released when the humid air inside gets warmer, contributing to more container rain.

Another way to reduce the moisture inside containers is to make sure not to have the pallets standing outside. Wood absorbs moisture, especially if the air is warm and humid. A standard EUR-pallet can absorb up to 20 litres of water, and a standard 40 feet container accommodates about 40 pallets. Doing the maths, you will realise there can be a huge amount of water inside the container – 800 litres of water is almost like having two full bath tubs with water! The price of LCL consolidations is usually based on kilos and cubic meters. This means, if your cargo has an unnecessary weight, you will also pay an unnecessary amount of money. By paying attention to the details of your shipment, you may be able to reduce the likelihood of container rain, and protect your goods from moisture and fungus.

The best way to prevent containerised goods from getting damaged

If you are shipping high value goods that are fragile, or if your factors are such that there is a high probability of container rain, you should consider using desiccant. Desiccant (similar those little sachets of Silica Gel which is made of a hygroscopic substance used as a drying agent) prevents the build-up of moisture in the air to levels where it may cause damage. This is done by using absorbing bags based on calcium chloride, which is a liquid brine in its natural state, and is converted into a dry material by removing the water through heating. It will quickly and automatically absorb water from the surrounding atmosphere when exposed, in order to transform back to its natural state. This means you can close the container, open it weeks later, and the goods are still in perfect shape.