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I attended the Combined Nitrox course in November not really knowing what to
expect. I had read the course plan but not a lot else. Many of my club members had
it in their pony cylinder; a few of the more advanced divers had the green stickers on
their main cylinders. I had heard it referred to as the Devil's gas, adding to the aura. I
had also just seen the Diver article saying I needed a complete set of new kit; which
did not bode well.
The first day was theory, long, but not too soporific. We received the theory books
and tables. The lectures explained the, who, what, when, where, why and how. There
ware lots of references towards the exam, highlighting points to remember. The
theory pointed out that I did not have to go out and buy lots of new kit: bother, and
Christmas just a few weeks away. The BSAC Nitrox tables made all the calculations
very straightforward. The examples were chosen to make you think just a little bit
more than blindly read off tables. We then went to the dive shop to play with the
Oxygen analyser and collect our cylinders for the following day
The next day was practical, Stoney in November. The rain stopped and the clouds
blew away, it was still cold!
Having assembled with the kit and retested the O2 percentage in the cylinder, we
went diving. With a higher percentage of Oxygen there is a higher risk of O2 toxicity.
This means with Nitrox there is a Maximum Operating Depth that must not be
passed. Nitrox is not a gas for deep diving.
For the exercise we were set an MOD of 18m. On the helicopter 18m does not give
you much to see, the tail and the top. The instructors kept trying to entice us lower; a
few succumbed. We then tied of our SMBs and deployed them. Up to 9m to simulate
decompression stops and to switch regulators simulating the use of a pony with a
higher Nitrox concentration. Hanging around maintaining depth not that easy, and
this was in still water. The stops were conducted horizontally. This is the preferred
way to off gas as it keeps the whole body at the right depth; this is also how the
tables are calculated. Up to 6m for even more switching. With not much swimming
around you did start to get cold. Then out for 'Show and Tell' as to who got caught out by the instructors.
Lunch was taken with the multiple-choice exam. Not too hard, given the excellent
hints/teaching the day before.
Cylinders were refilled, with double filtered air, reanalysed and back into the water for
the next dive. Basically this was the same as the previous dive but with the added
difficulty of launching the SMB mid water. Again no real problems nobody followed
the SMB up or sank whilst deploying. Having got changed, it was into the bar for the
debriefing (and a drink). All of us had passed.
I had attended the course only planning to only use Nitrox as a deco gas, but having
attended the course I will now get one of my main cylinders O2 clean, if only for
running training at Stoney.
On the way home I was less tired than normal, one of the perceived benefits of
Nitrox, but I had also dived less than a normal Stoney visit.
What else did I get out of it: it was good to dive with others to see their
configurations, and pick up some extra tips.
All in all a good weekend well spent. I will be recommending it to other members of
the club.
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