Partial inerting – A possible means of eliminating the brush-discharge-ignition hazard with explosive gases and vapours?

It was found that the brush discharge ignition hazard with IIA gases/vapours (propane) can be eliminated by reducing the oxygen/nitrogen volume ratio in the atmosphere to the order of 15/85. The condition is that the diameter of the earthed electrode ≤ 40 mm. Published information on whether an oxygen/nitrogen ratio of 15/85 is acceptable as regards the oxygen deficiency hazards is contradictory. With IIB gases/vapours (ethylene) the oxygen/nitrogen ratio must be reduced to at least 10/90 to eliminate the brush-discharge-ignition hazard. Lowering the oxygen/nitrogen ratio to this level will undoubtedly present a substantial oxygen deficiency hazard to humans.

► Brush discharge ignition of IIA gases can be eliminated if the O2/N2 volume ratio is reduced to ≤15/85.
► The condition is that radii of curvature of earthed electrodes ≤20 mm.
► Whether or not this is acceptable in terms of oxygen deficiency hazards to humans is unclear.
► With IIB gases an O2/N2 ratio << 15/85 is required for eliminating the brush discharge ignition hazard.
► When assessing the brush discharge ignition hazard all MIEs must be determined by identical methods.