Not to hijack the thread, but I always remember being struck by a comment that John Chatterton said during a seminar. He was saying "in the old days" people used to dive air to 230 feet and deeper, pushing the ppO2 of air above 1.6 ATA, but he could never recall anyone ever toxing on air.
Hardly a scientific survey, but I remembered wondering at the time (given how little we know about CNS toxicity) if there was something in that - it was not purely a feature of partial pressure, there was some kind of accelerated risk curve for richer mixes.
The value of 1.6 ATA is not a hard number. I've seen reports where people have suffered oxygen toxicity at 1.2 ATA. Everyone can dive any gas with partial pressure of oxygen beyond 1.6 bar and not suffer an O2 hit. With a small enough sample I'm sure it is very likely you never see anyone take an O2 hit at 230 feet and deeper.
However, if you talk to people who dive beyond 220 feet on a regular basis they will tell you they dive hypoxic blends (i.e. less than 21% oxygen).
There is nothing magical about air that makes it different from EANx.