One of the most common questions I get from my students is what the progression of courses should be. There are a couple of ways to answer this question depending on where in training someone is and what type of diving someone is most interested in doing. Let’s split this up into a couple of categories and approach it from each perspective. We’ll look at this from the perspectives of both the open water diver and the overhead diver that are interested in doing some decompression dives.
If an open water diver is interested in pursuing decompression diving but has no real desire to do overhead dives, then the answer may seem obvious. It’s just a matter of signing up for an Advanced Nitrox/Decompression Procedures (AN/DP) course and going from there. This isn’t necessarily the best way to approach it, though. I’m not an advocate of deep air diving. While AN/DP certifies divers to dive to depths of 140 or 150 feet deep (agency dependent), I don’t think this is a good idea in most situations. One of the things I like to do with my students is find out where their personal helium depth begins.
Narcosis is pretty much immediate as soon as we begin our descent. We are affected by the nitrogen even at 20 feet deep. However, the effect is so minimal we don’t usually notice it and it won’t affect our ability to respond to issues that may arise. This usually doesn’t occur until people hit the 60-80 foot depth range. But even at this depth, most divers will insist they are not feeling the effects of narcosis. While, I don’t feel it’s necessary for a majority of divers to dive trimix at 60-80 feet, I do believe that divers need to recognize they are affected at that depth, even if only slightly. The need to begin using helium in breathing gas usually doesn’t start until about 100 feet deep. This number varies with different divers, but most will find that anything deeper than 110-120 has a significant effect on reaction time. It can be pretty easy to find that personal helium depth during a supervised dive and some simple exercises.
If a diver is interested in extending bottom time but remaining relatively shallow (Read: below their personal helium level), then AN/DP is an appropriate course. My AN/DP course trains divers how to plan and conduct dives in the 100-120 foot depth range beyond no decompression limits (NDL) with the appropriate amount of standard and accelerated decompression stops. We focus primarily on learning about the various decompression models available out there and how to implement them into our dive planning. We then go out and do some dives.
If a diver is interested in doing deeper dives, though, then there’s a better way to approach this. I offer a course called Advanced Recreational Trimix (ART). This course trains and certifies divers to a depth of 160 feet with minimal decompression. I offer it in conjunction with Decompression Procedures (ART/DP). It’s very similar to the AN/DP course with the major difference being additional discussion time about helium as a breathing gas as well as how it affects our decompression. We also conduct deeper dives utilizing helium in our gas mix. AN/DP is not a prerequisite for ART/DP. A diver can sign up directly for ART/DP without any decompression training or experience.
To summarize, if you want to do longer dives in the 100′ depth range, AN/DP is the course for you. If you want to do deeper dives, then you should consider ART/DP. Knowing the type of diving you want to do will be helpful in making this decision, but if you’re not sure, then save yourself some money and time by taking ART/DP.
Now, let’s look at this from the overhead or cave diving perspective. The same discussion applies to the cave diver in regards to longer dives vs. deeper dives. The difference for cave divers is when to sign up for an AN/DP or ART/DP course. My advice has always been to do this mid-way between the cave training. Complete the Cavern and Intro/Basic Cave diver courses, get some experience diving caves, and sign up for a decompression course. This allows us to complete the training in caves as long as we still adhere to the gas management rules of the Intro/Basic Cave diver.
So why not wait until after completing cave diving training? While agencies don’t typically require AN/DP before completing the final cave diving course, not having AN/DP will limit what can be done during training. A cave diving course is there to teach divers how to cave dive. Learning how to conduct decompression dives should be left to the decompression diving courses. Some cave instructors won’t even accept students into a cave diving course unless they’ve completed AN/DP first. I don’t currently do that, but it’s been something I’ve considered.
I haven’t taught anyone at the cave diving level that didn’t first complete the AN/DP course, but not having AN/DP would make it necessary to spend a few extra hours discussing decompression theory and how it affects us on the longer dives. It also means we may end up turning dives on time rather than gas pressure in order to minimize our decompression obligation. One of the agencies I teach through also allows me to incorporate the use of stage cylinders during the cave course with students who have completed AN/DP or ART/DP.
So, in summary, the progression of training for cave divers I recommend is 1. Cavern, 2. Intro/Basic Cave, 3. AN/DP or ART/DP, and 4. Cave. This progression allows students to get the full benefit of each course and allows us to conduct a majority of the training in caves. We can also do a mix of open water and cave during the AN/DP or ART/DP courses if the student desires.