@DevonDiver
So what is the max on air when you teach? 50m?
Yep, 50m with TecRec. TDI and some others use 55m.
But, as a caveat, that's based on the diver, the conditions and the mission. The Tec50 course is a relatively straight-forward 4-tank dive. I teach in tropical warm water (albeit very variable viz) and little current on the sites used. I wouldn't do 50m for penetration, or in any conditions that I felt were unreasonably taxing.
With the new Tec45-tmx and Tec50-tmx options, I can suggest that students use trimix to gain their qualification. This means a process of evaluation can be conducted on the course build-up dives. If there are noticeable, hazardous, performance-degrading narcosis issues then an additional 2 dives qualifies and allows graduates to set prudent ENDs.
The deepest air dive I've planned in recent years was circa 60m. It was supposed to be a double body recovery from a crashed air force jet. There was no helium available. Sadly (for the families concerned) the wreckage was never located and the dives didn't happen.
Personally, I don't have big issues with narcosis. I put that down to experience, muscle memory, very ingrained protocols and having dived enough that very few unique problems arise. .That said, I'm intimately aware of narcosis issues from my old deep air diving days - it only takes one unforeseen and relatively novel issue to arise to cause confusion. Problems amplify rapidly once that happens.
My personal choice would always be to dive at a max END of 30m; but the reality of living in the Philippines is that helium is very expensive and stocks can be unreliable. Deep air OC diving between 30m and 50m is just a reality, when cost and availability are considered as factors. Relative to the cost of living and income here... I can live for a month for the cost of helium on a full trimix OC dive...