Messer has developed the DuoCondex process for waste gas cleaning. This involves the flow of waste gas being conducted through special condensers that are cooled with liquid nitrogen. The extremely cold temperatures of the liquid nitrogen (minus 196 degrees Celsius) cause the harmful substances to be frozen out in the condensers, allowing them to be separated from the waste gas flow. When the condensers are frozen over, they are heated, causing the harmful substances to melt and flow into a container in liquid form. They are then disposed of. The liquid nitrogen that is used to cool a DuoCondex unit’s condensers vaporises in the apparatus and exits the unit in a gaseous state. The gas can then be easily conducted into the shredder, where it acts as a protective gas, virtually eliminating the risk of fire or explosion. This is necessary because an increasing number of refrigerators using pentane-foamed insulation are also being processed. Pentane-foamed insulating materials are environmentally friendly and are now being used in place of CFC materials. These refrigerators therefore account for a constantly increasing percentage of appliances being recycled. However, pentane is flammable and requires effective protection against fire and explosion.