The points on figure 9 represent the result of passing air in any quantity through a perfectly insulated room. In practice the air change will be held to the minimum needed to ensure adequate ventilation and the room will lose heat to the outside, bringing the summer temperature closer to the standard specification. Note that an extremely massive and well insulated building is not necessarily the correct structure. Careful design is necessary to get the optimum result from simple strategies. This dehumidification system is used in the museum stores of the Danish National Museum.
Underground storage provides great temperature stability.
In general, dehumidification is preferable in store rooms, because the air change can be kept small. In rooms used by people the necessary air exchange, and the need for reasonable warmth, often makes heating a more attractive route to a low RH in a cool climate. Summary Observations on collections of photographs show that the rate of deterioration is very variable, depending as much on the quality of the processing as on the inherent stability of the materials. The current standard for storage climate is a compromise that will still allow the deterioration of badly manufactured or processed film but demands expensive equipment that is not necessary for the survival of film and prints that are in good condition. The standard emphasises the importance of the room climate but observation suggests that pollution of the microenvironment by relatively few decomposing negatives is a frequent cause of damage to sound material nearby.