The key exchange stations are used to safely trap keys of a machine or system. No secondary keys can be removed from the exchange station until all primary keys have been inserted and trapped. The primary keys remain trapped until all secondary keys have been returned. In conjunction with other components, the exchange station serves to increase the number of identically coded keys. It is thus the interface between the switch-off components of the system and the interlocks at the guards. It is used in precipitators, steel or power plants, or mines etc.