The guideline is only valid for such processes which use inerting as a preventive measure to avoid dust explosions. The use of inert gas during fire fighting to reduce the risk of an explosion or while emptying a silo are governed by different conditions.
VDI 2263 Blatt 2-1992 Referenced Document
DIN 2403:1984 Identification of pipelines according to the fluid conveyed
VDI 2263 Blatt 1-1990 Dust fires and dust explosions; hazards, assessment, protective measures; test methods for the determination of the safety characteristic of dusts