This depends on the door size but also the room size
By re-circulating internal facility air and forcing it across an opening, Enershield Air Barrier technology creates a 'Virtual Door'.
Membrane generators do not need electricity which makes them ideal for explosion-proof locations. If they include an oxygen analyser, they need minimal current rated at 120 VAC, 0.25A. The standard PSA nitrogen systems have an electrical rating of 120 VAC, 2.0A.
In air, oxygen is the most reactive gas and is present in significant volume. The balance of gases are either trace or in the case of argon, not reactive. In addition, oxygen content can be easily and directly measured with an analyzer. Therefore, a 99% nitrogen stream is really 1% oxygen and 99% nitrogen and other gases.