I don't think industrial oxygen bottles are rated for human use(something about the type of compressor used to compress it if I recall)

Really not to concerned about losing air supply down the small bunker....that would require like a mud-slide or something..and I live on high ground..plus the shelter's top is about 2 feet or better above ground.

I suppose if you had a dozen people in it..and tornados smashed the protruding ventilators plus piled debris on the door available air could be an issue.

I do notice that the ventilators have thick formed steel
plates bolted over the vent holes inside the shelter..I suppose to reduce the chance of storm driven debris peircing it's way into the shelter's interior verticaly.

Not something I'm very concerned about though. The door isn't hermaticaly sealed...shelter has 8" and 6" ventilators(not sure why two differing sizes?).