The SCUBA industry seems to make a great mystery out of gas mixtures. Which is not surprising. I remember when a small cabal of dive shops coined the sexy misnomer "NITROX" to make it seem like they were selling something magical and special...instead of a gas mixture that any welding [sic] shop could put together.
And it still seems that way, a bigger cabal and bigger mysteries, although calling it "EAN" instead of "NITROX" is arguably no improvement. "OEA" or oxygen-enriched-air, just doesn't have that sexy sell. And whether 40% is a magic number, or whether *everything* should just be "oxygen clean", well, if you're breathing it, air should be free of petrochemicals anyway, perhaps?
Yeah, there's nothing in the magic "high oxygen" mixes that needs to be cleaned out before you use that same gear for "air". Although that's not a bad idea...maybe the shops need to start charging customers for "retrofit cleaning" to put nitrox gear into plain service, the same way they want to charge for oxygen cleaning before they upgrade already. A great new profit opportunity! Mr. Barnum would have seized on that years ago!