It turns out almost all the organizations follow the same training standards set out by the WRSTC (World Recreational Scuba Training Council). The big exception

It turns out almost all the organizations follow the same training standards set out by the WRSTC (World Recreational Scuba Training Council). The big exception is CMAS which past level 2 no longer is comparable to the WRSTC program tracks since it allows for decompression diving on air down to 40m (level 2) and 56m (level 3). This means even with an advanced or master diver certificate from PADI, (NAUI, SDI, SSI, etc...) the tables you learn to use do not go beyond decompression limits (requiring mandated decompression stops on your ascent) since they stop at 30m. It used to be 40m but I believe the standard has become more conservative since I was last teaching. NAUI does have supplemental training that goes beyond WRSTC standards but a lot of that has to do with the science and ecology of the underwater world more generally. All open water level certs (usually the most basic level cert) expects students to be fully autonomous (with their buddies) by the end of the course. If you sign up for an open water dive in southern. California for example, it is rarely a guided experience and most people form groups of 2-3 on the boat and go and enjoy the water, coming back within an 1-1.5 hours. Almost everywhere else I have worked, it is expected (by the guests...) that all dives in open water are lead by a certified dive master and not self lead in small groups. I personally think this is a result of the way the standards and incentives work for dive operators to encourage that dependency on their outfit and keep the money flowing in. Generally recreational diving is very safe but even working as an instructor for a few years at a few different outfits, there is always a handful of fatalities. I really like the comparison to Skydiving someone else made, except its a much more subtle danger since you dont actually need to be in top physical shape to do this activity (even though it is required by the certification agencies). The only other thing I find interesting is all the certification agencies are for the INSTRUCTORS (hence the I in PADI, NAUI, SSI...). These orgs are outfits that enable recreational scuba operators to have a standardized set of empirically derived safety limits to protect the instructor and shop liability (not the student's). More often than not, especially in far flung, remote diving destinations, caution is thrown to the wind and people do not always follow the prescribed standards. Source: OWSI (Open water scuba instructor) with multiple agencies as well as CMAS level 3 diver