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What is humidity?

  • Humidity is the amount of water vapor in the air. Water vapor is the gaseous state of water and is invisible. Humidity indicates the likelihood of precipitation, dew, or fog.
  • Higher humidity reduces the effectiveness of sweating in cooling the body by reducing the rate of evaporation of moisture from the skin. This effect is calculated in a heat index table or humidex.
  • The amount of water vapor that is needed to achieve saturation decreases as the temperature increases. As the temperature of a parcel of water becomes lower it will eventually not reach the point of saturation without adding or losing water mass.
  • The differences in the amount of water vapor in a parcel of air can be quite large. For example, a parcel of air that is near saturation may contain 28 grams of water per cubic meter of air at 30°C, but only 8 grams of water per cubic meter of air at 8°C

Container rain



What is container rain?

  • Container rain 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.
  • When ships travel between South Asia and Europe, and pass the Suez Canal, the container temperature could rise up to 80 degrees Celsius! What happens inside the container during transportation is that the warm, humid air condenses.
  • Like the dew running down a can of coca-cola 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!



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