Humidity in Freight Transportation
HUMIDITY IN FREIGHT TRANSPORTATION
– Guillermina Rosas; Commercial and Services Manager – Assistcargo Spain
Those who ship goods and materials by sea know what damage can be caused by condensation inside containers, since more than 10% of goods transported in containers suffer serious damage precisely from condensation. Condensation is the consequence derived from the combination of a high level of environmental humidity and the natural thermal alternation during day and night. It is created after a rapid decrease in temperature that causes the moisture particles to move from a gaseous state to a solid state, which causes the humidity present in the air to become water. Reducing the amount of humidity inside a container will eliminate the dew or condensation point, which is the phase in which humidity transforms into liquid form.
Sea transport of a container can take weeks or months before reaching its destination, although container transport is an economical and safe way to ship most types of cargo, placing the cargo in a closed steel box means a constant risk of moisture damage caused by container rain. For container rain to occur, two important conditions must be met:
- Temperature variations during shipping
- Excess humidity
All containers contain moisture from the moment of loading and none are completely airtight. Moisture will enter and leave the container during the journey, known as “container breathing.” During a journey, the temperature in the container will rise each day and drop at night, this temperature fluctuation means that the air expands during the day, spreading out of the container, and then contracts, introducing cool, moist sea air. at night. This is called container breathing. Temperature variations are difficult to eliminate and mitigating them involves a high cost.
Hot air can contain more moisture than cold air. When the temperature drops, the humidity increases. If the air cools enough, some of the moisture can condense. The dew point is the temperature to which air must be cooled to become saturated with water vapor. The air pressure and water content are assumed to be constant. When it cools further, the water vapor carried in the air will condense and form liquid water (dew). When air is cooled to its dew point through contact with a surface that is colder than the air, water will condense on the surface. A drop in temperature of 5° is usually enough to cause problems. Water will condense on the coldest surface available, which will usually be the roof or walls of the container, from there, it can drip onto the cargo and cause damage, also known as container rain.
Moisture damage materializes in many ways and affects all types of products. Exposure to moisture over a period, which does not necessarily have to be long, can damage goods transported within a container in many ways. Often, just a small amount of excess moisture is enough to cause devastating damage that can render goods unsaleable, unfit for human consumption, or unsuitable for subsequent manufacturing processes.
The most typical damages related to humidity are:
- CORROSION
- MOLD AND FUNGI
- DAMAGED PACKAGING
- CRUSHED PACKAGING
- BAD SMELL OR CHANGES IN SMELL
- BAD TASTE OR CHANGES IN FLAVOR
- RAISED LABELS
- CAKING
Metal parts are sensitive to corrosion and rust, which can weaken the metal or cause discoloration. Rusted metal requires special and cumbersome treatments after transportation to restore original characteristics. Relative humidity describes exactly how much moisture is present in the air at a given temperature. The more moisture there is, the faster the metal will rust. For example, corrosion is unlikely to occur in clean air with a relative humidity of about 45% or less. If the relative humidity increases to approximately 60%, the risk of corrosion also increases. As relative humidity increases, the degree of corrosion and rust formation increases exponentially.
Mold affects the organic load, especially food and agricultural products, along with the development of bad odors and tastes or changes in odor and taste. For mold to grow, the relative humidity must be above 75% (although research shows this could be a problem at even lower relative humidity, such as 50%) and the temperature must be between -5° C and +55 °C (the optimal temperature for mold and mildew is 20-30 °C). There must also be mold, which in many cases is a given, since the goods cannot be protected from that during storage or handling. Therefore, the simplest way to protect goods from mold and mildew is to reduce the humidity level.
Excess moisture also causes irreversible damage to the cargo packaging which could eventually collapse as the packaging is hygroscopic and will absorb moisture. Excess moisture could also be the reason for labels peeling off glass bottles or food cans.
In dry goods such as powder products, moisture damage appears in the form of caking. This is because dry powder is often also hygroscopic and will attract moisture.
Moisture damage is a threat to the quality of your goods and can lead to high costs. Insurers estimate that approximately 12% of all damage during container shipping is related to humidity.
Damage due to humidity transcends the merely economic issue, since it also affects the environment and leads to inefficient use of available resources.
But these costs are just the “tip of the iceberg”, as many overlook the hidden costs: Repackaging, Decontamination, Production interruption, Bad will, weakening of the supplier/customer relationship, Brand damage, Environmental waste/damage, Loss of business opportunities, Seasonal sales, Loss of income due to canceled deliveries.
