Moisture Damage A Checklist

Sea Containers are an economical and safe way of shipping almost any kind of cargo. But putting a cargo into a closed strong box also entails a constant risk of moisture damage for every kind of cargo on every voyage.

  • Metals corrode, discolour and loose their shine
  • Cargo and packaging get moldy, soft, crumbled and discoloured.
  • Bad smell
  • Physical damage from water, ice, things gluing together, caking etc.

Such damage may result in substantial losses and costs. Yet obviously not every shipment suffers moisture damage, and most of those that do, suffer only limited damage. In fact, lots of moisture damage remains unrecognized, because it is considered “normal”. Very few shippers have a good system of feedback from the receivers of their goods. There may be lots of things they don’t know.

The pattern of moisture damage may seem random. The moisture processes are examples of strongly non-linear physics. That means that very small differences in the cargo and voyage conditions can have a huge effect of the outcome. That is why you may have 4 perfectly safe shipments and the 5th may be a disaster. This means that there is always a risk of moisture damage in the next shipment, even if the last one was ok.

Moisture Damage can be Prevented

All containers contain moisture from the time of loading and in the cargo. No container is airtight. Moisture will move in and out of the container during the course of the voyage – “Container Breathing”.

The objective of a moisture protection program is to prevent the build up of moisture in the air to levels where it may cause damage. This is done by reducing the amount of the moisture entering the container and by using “Absorbers” to remove moisture from the air.

We like to present the InterDry Power Desiccant moisture protection program as a kind of checklist of things that should be arranged as well as possible. And it is to be noted that many of the items on the list can be influenced only to a degree. Yet even small changes can result in big improvements. In some cases a few tens of grams of water in the wrong place is enough to cause significant damage.

Storing pallets inside or outside is often enough to make the difference between no damage and “disaster”. Simply adjusting the temperature of the cargo at loading can prevent damage. Thus it is well worth to make what improvements are at all practical, and the balance will then have to be taken up by the packaging and the absorbers.

Is the Container Tight?

A minimum requirement is of course that the container is watertight against rain and spray. That is usually the case, but especially the bottom side and the doors are vulnerable to damage that may not be noticed.

Check the seals. Certainly no container is airtight, but a container in good condition allows air (and moisture) to move in and out of the container only slowly, over hours perhaps. That significantly reduces the amount of moisture moving into the container under common circumstances. (Container Breathing)

Tape the vent holes if you are shipping a dry cargo. For a moist cargo, such as agricultural commodities, it is usually better to leave the vent holes open.

Is the Container Dry?

A container that has been washed before loading, brought in from outside into a warm loading area or stored in a humid place, may contain lots of water. In particular, attention must be paid to the container floor. The humidity of the wood should not be above 18%.

All pallets and other wooden dunnage must be dry. Preferably the moisture content should not above 18% and certainly not above 20%. It is easy to check the humidity with a small handheld device commonly used in the construction industry and costing a couple of hundred euros.


Is the Cargo Dry?

Some cargoes are entirely dry and don’t contain any moisture, e.g. pure metal products without corrosion protection or surface treatment.

But most cargoes contain moisture, if only in the packaging that usually include wood, cartons, paper etc. Most of this moisture is bound in the material and is not easily released, but even a small percentage can cause problems. Even if the product appears dry at loading is no guarantee against things going wrong in a container where temperatures may later on reach 60-70C.

Some cargoes unavoidably contain a large mounts of moisture, even after having been made as dry as practical. They require a more sophisticated moisture protection installation.

Is the Loading Dry?

You can easily destroy all the other precautions you have taken by loading the container under the wrong conditions.

Particular attention should be given to the storage of containers, pallets and dunnage. Not to speak of the cargo. Even under a tarpaulin dry pallets or crates stored outside, can quickly absorb significant moisture.

Wet or snowy tarpaulins, truck wheels or even shoes may introduce a lot of water into the container. Again beware of wood, including the container floor, that may look dry but in reality be very moist.

A more subtle consideration is to make the cargo have the same temperature as the container during and after loading. It is especially dangerous to load a cool cargo under warm and moist conditions. A moisture containing warm cargo loaded into a cold container, e.g. a reefer, is also a problem.

As the doors on the container are closed a certain amount of air is enclosed. Under normal conditions the amount of moisture contained in the air is usually insignificant in comparison with that which will be exchanged with the outside and the cargo during the voyage. But when loading under tropical conditions the amounts of moisture involved may be greater by a factor 10 or more, and special consideration will then need to be taken to quickly absorb the surplus moisture.

Is the Cargo well packaged and stuffed?

Even a completely sealed package may suffer moisture problems as a result of temperature variations.

Most packaging materials let moisture though and moisture will move both into and out of the packages during the voyage. This can be advantageous in a dry container, where the cargo will dry out into the container air. But it is of course a danger if there are moisture problems in the container.

A properly designed moisture protection considers the entire logistic chain and may involve a combination of absorbers placed within the cargo as well in the container and several layers of barriers with different properties chosen so that the net effect of the moisture migration is positive. To stop the moisture migration through using sealed alufoil bags is usually too expensive.

It is usually an advantage if the cargo is closely stuffed and there is as little free air as possible in the container. The pallet wrapping should have openings at least on the bottom. If mold or condensation is observed on the inside of the wrapping it is too tight.

Use InterDry Power Desiccant correctly

There are different types of absorbers with different properties. Calcium Chloride based absorbers are by far best suited for use in the container. For several reasons, perhaps most importantly because they do not risk re-evaporation of already absorbed moisture, the InterDry absorbers are by far the best and safest of the Calcium Chloride absorbers.

Other types of absorbers, so called “desiccants”, are more suitable for use inside packages. Whether one should have absorbers both in the container and within the packages, and in which proportions, depend on many considerations. Most importantly one must consider the entire logistic chain, and the need of protection before and after the container transport.

Generally, however, the container transport is the worst part of the logistic chain. It usually makes economic sense to provide as much of the moisture protection as possible in the packages. Using standard formulas to calculate the amounts otherwise required within the packages often lead to very large amounts of desiccants.

How many InterDry Bags or Poles are required depends on the cargo, how long the voyage is and what risk of damage is acceptable. For a dry cargo 4 Picollos 1000 are often sufficient in a 20 ft container.

Systematic Follow Up

Every transport is in some sense unique. The best way to optimize the moisture protection is to gather systematic feedback on all shipments.

Some things to note are:

  • Is the container dry. Are there any signs, e.g. discoloured carboard, bad smell, mold or insects, that indicate that the container at some point has been wet?
  • Is there any moisture damage on the packaging? On the cargo? In that case is there a pattern of damage – only on top, only in the centre of the cargo etc?
  • How much water has collected in the InterDry Absorbers? Is the amount about the same in all the absorbers or does it differ according to placement?
  • Temperature/weather at arrival.

To get much more information on what has happened during the voyage, it is possible to put an electronic logger in the container that records temperature and humidity throughout the voyage.

More regularly one can use the so called Alfasensor moisture indicators. They are a pair of simple stickers that can be put anywhere in the container, e.g. on an absorber or somewhere in the cargo. They will indicate how long the humidity has been above a certain set level giving much information about the voyage

About moisture and condensation in shipping containers

Q: How do InterDry absorbers help to solve moisture problems?

InterDry absorbers contain Calcium chloride that very aggressively grab and absorb moisture from the air. They dry the air. When there air is dry, there are no moisture problems.

Q: Can InterDry absorbers solve all moisture problems?

Well, not all. Some cargoes may be so wet that any reasonable number of InterDry absorbers get overwhelmed. But InterDry absorbers can reliable protect even very difficult cargoes that may contain tons of moisture, such as coffee beans, wood products or paper.

Q: I load my container under dry conditions and it is very tightly sealed. How come I still experience moisture problems?

Your cargo or the packaging, including container floors, pallets and crates, contain moisture that is evaporated into the air during transport. Wet packaging material is the most common cause of unexpected moisture problems.

Q: I have shipped the same cargo for years with InterDry absorbers without any trouble, but now I have a lot of damage. Have you changed the poles?

Check your container and your packaging material. Did you just start to store your pallets outdoors? Does your forklift drive into the container with snow on the wheels? Did you just change supplier of crates? You can’t tell by looking whether wood are carton is dry. The moisture properties of wood and cartons have an exponential character. It makes a huge difference if your pallets moisture content should be 20% instead of 17%, say.

Q: I ship consumer goods in tubes/cans/jars etc that contain no moisture, yet I still have problems.

Consumer goods are often shipped with a lot of cardboard packaging. Even if the boxes seem dry they could literally hold tons of water.

Q: Each container of my cargo of peanuts/coffee/cocoa contains tons of moisture. What difference does it make that InterDry absorbers absorb a few litres during a voyage?

All the important things that happen have an exponential character. That means that a small change in circumstances can have a huge effect on the outcome. InterDry absorbers create circumstances that allow almost all of the moisture to remain in the cargo even while the level of humidity in the air is lowered by a crucial amount, sufficient to prevent damage. It is a question of ”leverage”.

Q: Does it make a lot of difference that my cocoa beans have a moisture content of 8% instead of 7%?

Yes, such a difference could be all the difference between no damage and disaster. The moisture behaviour of most agricultural products have a strong exponential character.

Q: My cargo of peanuts had suffered damage in the centre even though the outside of the cargo looked fine and there was were no signs of condensation?

Lots, if not most, damage to cargoes is caused by prolonged periods of elevated humidity without any condensation (Container rain, Container sweat, Super Saturation Event). It is common that cargoes loaded at cool temperature and then moved into warm condition suffer damage in the centre of the cargo as a result of a difference in temperature between the outside and the centre of the cargo. Warm air from the outside of the cargo becomes humid as it moves into the cooler centre. InterDry absorbers protect against this effect even though the absorbers are mounted on the container walls.

Q: I had damage to my cargo even though I used lots of silica gel and there was no condensation. Would it help to switch to InterDry absorbers?

Calcium chloride absorbs moisture even when the humidity is not very high. This protects the cargo against damage caused by prolonged periods of elevated humidity. Some kinds of steel start to corrode at 70% relative humidity, moulds can grow at 80% relative humidity and at near 90% relative humidity lots of things go wrong. Yet, InterDry absorbers are also at their most efficient protecting against condensation. Most other products, such as silica gels, are really effective only in very humid conditions and in protecting the cargo against condensation damage.

Q: What is so great about InterDry absorbers anyway?

Well, they will not fall off the wall, get punctured during loading and unloading, leave a wet puddle on the cargo or run out after half the voyage. They are installed in seconds without ladders and take up no cargo space. The capacity of each absorber is big, so fewer is required. The cost of an installation is very competitive, even against much inferior alternatives.

Q: How many absorbers do I need?

The number of InterDry absorbers required to protect the cargo depends on the cargo, the temperature conditions during the voyage, the length of the voyage – and just how safe you want to be. For some really dry cargoes e.g.. steel coils or household removals, 2-3 InterDry absorbers are enough. For a lot of ”normal” goods 4-6 InterDry absorbers is about right. Some cargoes with very difficult moisture properties on long voyages may require up to 16 InterDry absorbers.

Q: Do I need to line my container with kraft paper?

Lots of containers are lined with Kraft paper primarily for reasons of hygiene or to simply isolate the cargo from direct contact with the container walls. The liner will act as a kind of sponge, catching and absorbing any droplets of water and then re-evaporating the moisture into the air. If liner is used without InterDry absorbers it could contribute top a kind of pumping effect, drawing moisture out of the cargo. When used together with InterDry absorbers the liner will act as a buffer in extreme conditions, and will prevent any container rain from reaching the cargo. Much the same can be said for so called dew cloths.

Q: My container is absolutely filled with cargo. Will the InterDry absorbers still work?

Moisture diffuses very effectively, even through a seemingly compact cargo. Experience shows that InterDry absorbers will make a difference even to mould growth inside cartons in the cargo. It is, however, necessary that some free space is left in front of each InterDry absorbers. If some InterDry absorbers have collected less water than others inside a container, there may be a problem with air access to those absorbers.

Q: I have problems with mould growth inside my shrink-wrapped pallets. Will InterDry absorbers help?

Yes, so long that there is some access of air through the top and bottom of the pallets. If this is not possible, a spiked roller may be used to tear holes in the shrink wrap.

Q: My shipments of steel/galvanised components/aluminium/ machinery etc arrives corroded, stained or discoloured despite heavy packaging. Will InterDry absorbers help?

You can forget about your tectyl, coatings, oil-paper and plastic wraps that are expensive both to apply and remove. Your container can probably be equipped with a sufficient number of InterDry absorbers to protect against any damage at less cost than your present packaging.

Q: I got some brine on my hands while removing used InterDry absorbers . Is it dangerous?

No it isn’t. Calcium chloride is non-toxic and environmentally safe. It is the second biggest constituent of sea-salt and is liberally sprinkled over icy roads in cold countries. The brine is somewhat similar to very salty seawater, and may cause irritation and rashes if left to dry on the skin. We recommend that you wear gloves and goggles when handling used absorbers, but should you get splashed by brine just wash off immediately with lots of fresh water.

Q: Can I re-cycle my used absorbers?

The absorbers can not be re-used but can be disposed of environmentally friendly. It doesn’t contain any harmful chemicals.

Humidity in shipping containers

Container ship Bahia Laura

1. Relative humidity measures the amount of moisture in the air. It is expressed in a percentage of how much moisture the air could possibly hold. The wetter or damper the air is, the higher the relative humidity. The drier the air feels, the lower the relative humidity. Thus, 100% humidity is actually rain.

2. When stuffing a container in any climate, you also stuff the actual humidity contained in the air at the place of packing.

3. When closing the container, the humidity is contained in a very small space. As the container is moved from one climate to another, the humidity vaporizes up into the ceiling of the container, where it will start to rain down onto the cargo. Either the humidity will start to soak into the cargo or run along the surface of i e steel products. It can also turn into water that runs towards the bottom of the container. Nordic Container Desiccant actually “catches” the moisture before it vaporizes.

Container Ship

4. As soon as the climate changes, the moisture will either vaporize again or really start making trouble among your different products being shipped, if you do not use a desiccant. The longer the transportation time – the more damage may possibly develop.

5. You may have seen your cargo being loaded in perfect condition. But have you ever opened a container full of molded furniture? Or rusty motor equipment? Or rice sacks full of mildew? Or fruit covered in fungus? The customers do not like it. They will blame you. They will lose money and time, they will lose their customers and they will make claims to you. Then you will lose money and time, and possibly even the client. Since there are many parties along the transportation chain, many may be blamed for damaged goods – like manufacturers, traders, shipping lines and forwarders. Why be among them?

Container ships at the Port of Oakland

Container ships at the Port of Oakland (Photo credit: mental.masala)

6. Other desiccants being used are i.e. silica gel. Silica gel is the most common type of desiccant in use today. It is a porous sand and can absorb moisture in the air, often up to 40 % of it´s weight. However, silica gel absorbs moisture best in small, confined spaces and often end up getting saturated in a very short time span, making it unsuitable for container shipments. When saturated, it will not help catching the moisture anymore. Be aware that some silica gel – the blue contains cobolt – is toxic, and can not be disposed of any which way.

7. The best insurance there is – using Nordic Power Desiccants. The effect is 40 – 60 % better than other products in the market.


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