When processing human plasma protein solution an unacceptable virus enrichment must be prevented. The nanometer filter cascade described in this application is used for this purpose. It ensures that existing viruses and/or viruses introduced by a later contamination are removed so that the human plasma is suitable for further use and that the final product cannot cause any damage to health. A special requirement of this process technology is to ensure that the medium is transported pulsation-free and that the flow speed of the product is as gentle as possible. The plant must be CIP cleanable and sterilizable.