In the Swedish Civil Defence shelters and command centers in rock have been used since the 40-ies. The location offers good shielding against weapon effects and also possibilities for energy conservation. However, the difference between the outside climate and the climate in the subsurface space must be considered carefully in order to avoid disadvantages with high humidity and increased corrosion. Principles for a good handling of the climate control are discussed. Tests with alternative ventilation and climate control have been performed. Means to reduce corrosion in high humidity areas are recommended
The experience of large scale subsurface construction for Civil Defence in Sweden goes back to the years after World War II. It was especially the threat of a future nuclear war that lead to the construction of large shelters in rock, capable of receiving from 1000 to 10000 persons each in an emergency situation. Those shelters were all situated in city areas and designed for use in peacetime, mostly as garages, frequently including repair shops, in other cases as storage rooms. Smaller rock shelters of different size down to a capacity of around 100 persons were already built both in industrial and housing areas, sometimes close to local train stations. Those smaller shelters have not always had a peace time use. The experience is, however, that passive shelters often suffer from corrosion problems and the tendency is to look for a peacet1Jre use if the shelters are Subjected to a general overhaul and repair works. During the last three decades a system of command centers for civil defence has been built, with many of the units situated in rock. From a rather sparse and robust equipment in the early units, the command function has gradually been more advanced. Especially the units completed during the 70-ies have a sensitive equipment, leading to rigorous demands on the inner climate. Increased demands are not only related to the equipment but also to the per-sonnel and today's standard for the personnel is quite similar to modem office standard. Both because of the need for improvements in older -shelters and the increased demands on the modem command centers, research has been initiated in order to find out roost economical ways to construct and maintain undergroun:1 installations. Before going into details a brief summary will be given of some basic facts of importance when looking for practical solutions.
Rock caverns are characterized by a rather constant temperature. During periods, when the outer air temperature is considerably higher than the inside temperature, this might give conditions with a high relative humidity of the inside air. It may also happen that condensation of water occurs on the rock surfaces causing drip and corrosion problems even if there are no water leaks from the outside coming through the rock. The situation will be discussed in connection with some meteorological data. TABLE 1 gives some data on air temperature and water content in air valid for 8 different places in Sweden.