A centrifugal drum for a separator having a vertical axis of rotation, including a drum bottom part and a drum cover fastened to the drum bottom part by a locking ring. The gas mixture comprises a hydrofluorocarbon gas, an optional hydrogen-containing gas, an optional fluorine-rich fluorocarbon gas, a nitrogen gas, an oxygen gas, and an inert gas. , a 95%-distillation temperature of 250\xb0 C. A second conductive layer is connected to a sink voltage and separated from the first conductive layer by an insulating layer of a predetermined thickness.