4 Ways to absorb nitrox
BSAC Advanced Nitrox Diver
Advanced nitrox courses require the use of decompression stops and relevant equipment as well as surface marker buoys, and are aimed at the more aspirational diver.
The BSAC offers a basic one-day course and its advanced course, which is open to BSAC Sports Divers with 20 qualifying dives. Theory takes about seven hours and is followed by two training/assessment dives with relevant skills. The course, as with other BSAC courses, can be taught in a school or coaching scheme environment. Southern Regional Coach Andy Hetherton, my instructor, will travel to a member's home if there are enough candidates, otherwise courses are available on pre-set dates at pre-arranged locations.
Slower but no less effective is to learn through a BSAC branch, which can cost half as much as through a school.
For the BSAC and IANTD courses you need specialist equipment. Rent rather than buy before doing a course, because only afterwards will you know your needs and what suits you personally.
Andy Hetherton spent two evenings with me on the theory, going through course materials on his laptop. Course presentation depends on the individual instructor - some use paper, others projectors, but the result is the same.
Although the BSAC course explains how to solve nitrox problems, divers are encouraged to rely heavily on the tables rather than calculations, as there is less chance of error creeping in. BSAC nitrox tables are straightforward to use for mixes of 27, 32, 34 and 36 per cent. From 36-40 per cent the 36 per cent tables are used, which gives an additional margin of safety.
There is no use of the Equivalent Air Depth concept or need to add in residual nitrox times for a subsequent dive.
These tables minimise the need for calculations, recommending a good surface interval, increasingly shallow dives and increasingly rich mixes as a dive series progresses. I found the presentation of the course materials and tables excellent, making the information easy to find.
The BSAC Advanced Nitrox Course envisages a maximum bottom mix of 40 per cent and a maximum deco mix of 50 per cent, using a 3-7 litre pony cylinder with an oxygen-compatible regulator.
After passing the 30-question theory exam, it was time for the test dives. These are done with simulated deco stops at 9m and 6m, using the handy BSAC Nitrox Dive Conduct Slate, for four scenarios: "planned dive", "just longer", "just deeper" and "worst case". These dives made clear how important practical skills are, especially buoyancy, when it comes to decompression.
We travelled to the Breakwater Diving Centre/AquaSport Hotel in Portland Harbour for the first dive off Portland Bill. As well as deploying the SMB, I had to locate and switch on the simulated deco mix and exchange regulators, while maintaining buoyancy and a level attitude in a knot of current, with 3m visibility. I struggled.
The second dive was in the harbour, on the wreck of the Countess of Erne. The 9m stop was done with difficulty, as we were being pushed by the tide against the wreck; the 6m stop we did as a drift.
I had a lot to think about, and needed to practice the use and configuration of my new equipment. I had clearly outgrown my "entry level" console/depth gauge; it's hard to monitor depth without a wrist gauge while attempting to control the SMB and maintain relaxed buoyancy at the deco depth.
Andy suggested I continue my practice in a more controlled environment and give a lot of thought to setting up my deco kit for my own convenience. A nitrox dive computer beckoned.
Wiser, and not a little chastened, I realised there was far more to diving on nitrox than a paper qualification and a couple of pre-dive plans. Conditions had been challenging enough in the Red Sea, and mindful of UK diving conditions the self-reliant diver has to carry kit for any eventuality. Without practice it might not be possible to complete deco stops safely in less-than-perfect conditions.
Appeared in DIVER - July 1999