I am on the road and do not have access to my materials. The PADI nitrox course and book I used for my course nearly 20 years ago were decidedly different from what is done today in terms of content covered. Those changes reflect changes in thinking about nitrox and diving in general. As a current nitrox instructor, I know that there have been no changes in the tables themselves, and they still use the same partial pressure standards.
My final exam consisted of 50 questions, and they involved a lot of math. You had to use (but not memorize) all sorts of equations for MOD, equivalent air depth, etc. I remember distinctly that I got one wrong, question #31. I don't recall the content, but I remember the number because I took the course at Cayman Brac and the instructor made a big joke about my missing question #31, as if it were a mark of shame. (The joke was that apparently it was more common for people taking the course to barely get enough right to pass.)
So what happened after that? I recently saw an email from someone at PADI headquarters who was answering a different question, but what I read there applies to this question. What follows comes both from that email and from my own observations.
- I became as obvious to them as it did to me when I took the course that pulmonary oxygen toxicity was simply not a threat to recreational divers. You had to be doing some really unusual diving to make it happen, even according to the knowledge available then.
- Research indicated that recreational divers using the 1.4 standard could pretty much dive all day without consequences.
- They realized that pretty much nobody was using the tables anymore.
- Anyone getting nitrox can refer to a table for MOD. They aren't sitting down and deriving it mathematically every time they get a fill.
- In short, they realized that nitrox is not the big bad boogeyman everyone used to think it was.
And so we have two camps--1) the old school people who believe everyone should still take the old style high octane class, and 2) the people who think it will only take a few minutes to add what people need to know about nitrox to the OW class and make it part of beginning certification. The second group thinks having a separate class that teaches so very little of importance is a "money grab."
The current class is right between those two extremes.