So there’s where I’m confused. The PADI nitrox manual says “If you ever need to use air in an enriched air cylinder, no problem. Take it to an enriched air fill center. They treat the fill as enriched air in all aspects, including marking it EANx21 (“enriched” air with 21% oxygen), analyzing the contents and completing all records. If an enriched air cylinder that has been prepared for oxygen service (for partial pressure filling) is accidentally filled from a conventional air source, it must be cleaned and serviced by someone qualified to service enriched air equipment before being exposed to more than 40% oxygen again.” There are also a lot of posts on this thread suggesting that air blended into nitrox isn’t the same as the air going into regular tanks, but is “hyper” or low hydrocarbon or some such thing. Do what’s up with that?