Moving objects between temperatures

As an object moves from a low temperature store into a warm display area there is a risk of transient condensation. This happens because the object surface is colder than the dew point of the warm room.

This risk can be removed by ensuring that the object warms in isolation from the room air. This means wrapping it in plastic and putting it into an insulating bag, then waiting for equilibrium. Overnight is sufficient equilibration time for almost any conceivable load of objects being transferred. There is no need for conditioning chambers at intermediate temperatures, individually humidity controlled.

A similar risk attaches to the return of the object to the cold store. This is because the container of the object, a film can for example, will cool down quickly while the object inside retains a higher temperature. If the object is hygroscopic, it will release water vapour which will condense on the inside of the container. The condensate will dribble down and may re-enter the object as liquid water. To avoid this, there must never be more than a 7 C temperature difference between any two points within the container. An insulated bag will solve this problem. In practice this means that cool stores must have a temporary cooling off space for objects coming back from the warm. Likewise, warm rooms which regularly receive shipments from a cold store need a warming up space.