A cartridge holds a perishable dielectric load, e.g. blood plasma, during heating n a heating chamber by means of an electromagnetic field from an emitting element. A conducting container of the cartridge is arranged between the emitting element and the perishable dielectric load. The conducting container holds dielectric matter and is arranged in contact with a load container for the perishable dielectric load, so that energy from the electromagnetic field is bridged into the perishable dielectric load. A first surface of the cartridge faces the emitting element and contains a recess for receiving any fluid having leaked out from the conducting container and/or the load container. A transmitter module for generating the electromagnetic energy repeatedly measures an impedance of the perishable dielectric load and the conducting container. If, due to any fluid being located in the recess, the impedance deviates substantially from a previous measurement, an alarm signal is generated.
