IANTD Advanced Nitrox Course

At about the same time as I got my dry suit, I signed up for Advanced Nitrox, which covers the knowledge and skills necessary for accelerated staged decompression using enriched air (a.k.a. Nitrox). The certification is intended to employ mixtures of up to 50% Oxygen, which is not that much more than the PADI Enriched Air Diver Specialty, but the applications are quite different, as the IANTD course is designed for extended range diving into depths beyond the recreational limit of 130 feet and/or the no decompression limits.

The classroom sessions, covered many of the same topics of the Open Water and Enriched Air Courses, but in much more depth. Oxygen Toxicity especially is covered in much more detail, with greater attention to the CNS Clock, and the Pulmonary or “Whole Body” exposure calculations using Oxygen Tolerance Units and Unit Pulmonary Toxicity Dose. Having been interested in science my entire life, I ate this stuff up, and scored a perfect mark on all the tests. The final test I scored 19 out of 19 on a 20 point test because everyone in the class, including the instructors, agreed that there was no correct choice in the answers provided for one of the questions.

On the evening of July 13, 2006 I tried out a set of doubles for the first time at Big Bay Point in Lake Simcoe. I didn’t own my own set at the time and borrowed a set of 85 cubic foot steel tanks from Dave, a certified technical diver and assistant instructor who assists at the shop from time to time. I also used my Seaquest Raider BC, which although lacking a backplate is a reasonable but not ideal technical BC. It was also only my second dive in my dry suit, which made it all the more challenging.

The main point of the dive was to get familiar with the equipment. I had bought my Apeks ATX50 regulators (2 ATX50 first stages, with an ATX50 primary second stage and an Egress backup second stage), and had to sort out a problem right away with a leaking port plug, and then with the plastic tie on the regulator that was pressing against my lips, which Brad rotated slightly in place. We started out in about 4 feet of water and Brad signaled to me to swim around a bit. I went off about twenty or thirty feet into slightly deeper water as the dry suit, even with the doubles and 12 pounds of lead, wasn’t a comfortable swim so close to the surface. This was the one and only time that Brad has ever yelled at me, because he lost track of me and was concerned about my safety. Putting the whole thing down to a communication error, we continued with the dive down to a maximum of 48 feet, and an average of 21.

I didn’t have an SPG for my technical regulators, but the tanks had been filled to 3000 PSI and even with my high air consumption with the unfamiliar equipment we felt that at the relatively shallow depths that there would be plenty available.

After doing some switches between the primary and backup regulators, the next exercise was a “doff and don”, which with doubles in a dry suit and integrated weights is a real workout. Big Bay Point also has a thick silt bottom, so all the struggling you need to do creates a massive silt-out, which fortunately clears pretty quickly in the current. Once the scuba unit is off your back, it is very negatively buoyant, which is the opposite of an unweighted human in a dry suit. So you have to pull yourself down by the straps and wriggle back in, which is a lot of effort. I helped out this year’s class and they had exactly the same difficulty.

I can’t remember exactly what point in the dive it was, but at one stage I found myself breathing water because the plastic tie on my primary regulator broke (after being weakened at the beginning of the dive by rotating it) and it separated from the mouthpiece. I retrieved the regulator and took a few breaths from it, then switched over to the backup. All good – I passed my first equipment failure challenge. It would not be my last.

In the dry suit, I could not reach the tank valves. This is a mandatory skill in technical diving and the problem dogged me for quite some time until I figured it out, helped by some new equipment. I did the rest of my technical training in a wet suit, which was much, much easier in all respects. With a water temperature of 20C (68F) and a bottom time of 39 minutes, I could have just about used my 3mm wet suit (the only one I had other my 25 year-old suit that I swore never to use again), along with a hood. The hood makes a huge difference I’ve found, and is good for another 4-5C with any exposure suit configuration.

It was to be over a year before my next technical training dive. My class had pretty much broken up for various reasons, including lack of money for technical diving equipment. It turns out that a lot is required and you might as well budget $5,000 to get into it. The big ticket items are the BC, Tanks, and regulators, but accessories will run up the tab as well. Then of course unless you want to only dive with tables you’ll need two computers, or one computer and a bottom timer. The two computers are a nice way to go but good ones are really expensive. I like planning the dive with tables but using a computer on the dive, so I have an idea of what to do if the computer breaks, but can get the advantage of a multi-level dive in shortening the required decompression time.