The Wieliczka Salt Mine in Poland contains many historic carvings and sculptures in salt, created over the centuries by the miners and other artisans. The mine is listed as an endangered World Heritage site because these unique artifacts are deteriorating because of dissolution by water. A team of U.S. and Polish scientists and engineers conducted a continuous year-long study of temperature and humidity conditions at multiple locations within the mine to determine the likely sources of moisture at key locations, and to make recommendations for mitigation of the threat.
The data show that conditions favoring the precipitation of moisture from the entering ventilation air stream occur between April and October, and that the volume of water condensed in the mine increases rapidly with increasing external temperatures. Chemical sampling indicates that entering air pollutants are deposited on the surfaces within the mine, but that they do not significantly affect the deliquescence point of the salt. However, surface soiling due to airborne particulates is observed. The Kinga Chapel and the Museum are key areas where the seasonal and diurnal oscillations in relative humidity do not exceed at any time the critical relative humidity of 75% above which strong water absorption and dissolution of the salt occur. But St.Anthony's Chapel is the site of strong condensation, with observed humidities of 75% or more, and therefore suffers badly from surface dissolution.
The recommended solution is installation of a suitable sized dehumidification system at the mine ventilation inlet. If the relative humidity is maintained below critical levels in the St. Anthony's Chapel area, then conditions in the remainder of the historic portions of the mine can be expected to always be satisfactory. An independent engineering consultant visited the mine and used the research study's observations to provide hardware recommendations and cost estimates for a system adequate to protect the St. Anthony's Chapel area, so as to preserve all of the mine's artifacts for future generations.
Lynn Garry Salmon <>{