Container rain

Container rain, also known as container sweat, is the term used to describe the condensation that takes place within a sealed shipping container resulting in moisture damage to imported goods. Warm air can hold more moisture than cold air. When the temperature goes down, the relative humidity (percentage of the moisture that can be retained by the air – moisture-holding capacity – at a given temperature and pressure without condensation) will increase. If the air is cooled enough, some of the moisture may condense. The dew point is the temperature to which air must be cooled to become saturated with water vapor. It is assumed that air pressure and water content are constant. When cooled further, the airborne water vapor will condense to form liquid water (dew). When air cools to its dew point through contact with a surface that is colder than the air, water will condense on the surface. A temperature drop of 5° is often enough to cause problems. Water will condense on the coolest available surface, which usually is on the container ceiling or walls. From there it may drip down onto the cargo and cause damage.

Given that the temperature and pressure can fluctuate drastically from day to night, the container rain phenomenon can happen as often as every 24 hours during the journey of the supply chain.

For container rain to happen, two main conditions are needed:

● Temperature variations during shipment

● Excess moisture