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Trimix for Beginners |
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TDI, (Technical Diving International) ran the course, which consists of a day of theory followed by four open water dives. I should say BSAC do not run this course. It is, however, recognised and accreditation is given in the form of a logbook sticker. A day in June saw our happy throng converge on Jacks house, just South of London. John Dunwell, Ray Mckee, Jim Ackroyd Marc Beaumont and myself, were amongst the students, all from the Yorkshire region. I think we were all a little apprehensive of the technical content
that we envisaged being crammed into us. We needn't have worried, as
Jack is an entertaining instructor, who was able to de-mystify the black
art for us in layman's terms! Contrary to what many people think about Trimix, it does not give you shorter decompression times than air. Due to the molecular consistency of Helium, tissues absorb the gas at a higher rate than nitrogen. This results in Deco times far longer than doing the equivalent dive on air. The benefit comes from having a clear head, reducing the nitrogen in your breathing mixture reduces the onset of narcosis. By altering the amount of Helium in the mix, you can decide how "narked" you want to be, by setting the "equivalent narcotic depth". This means that you could dive to 60m, but have a gas mix which is the equivalent of diving to 30m on air. To dive to 60m on air, is not recommended! So what are the downsides? Well, as mentioned, far longer deco stops.
Also the necessity to carry more cylinders for the other mixtures of gas
you need such as Nitrox 36, 50 or 70. This reduces Having all passed successfully, we arranged a date for the practical side of things. Unfortunately due to the weather, our original plan to dive from the South Coast was changed to dive at the National Diving Centre in Chepstow. Suitably equipped with twin cylinders, and two side slung cylinders containing different nitrox mixes, we descended the shot line to 50m. Having dived to this depth (and,er, greater!) on air, it was a revelation to have such a clear head. Some people find that Narcosis affects them in a pleasant way, feeling mildly drunk. I, on the other hand seem to suffer a bout of paranoia, being extremely annoyed with everything and everyone! Despite the depth, and the long decompression schedule, I found it to be one of the most relaxing dives I've had. So, trimix isn't for everyone, but you should not be put off by the thought that it is too difficult, or that it is a black art, or any other misconception. It is involved, but not beyond the realms of possibility for a Nitrox diver, with a few years experience, who wants to dive deeper. It is expensive, so I for one won't be diving it every weekend, nor would I want to. I do want the option though, to dive wrecks just that little bit deeper, and with a clearer head, and thus more safely, when I want to. The depth limit for introductory trimix, and the BSAC maximum for trimix dives, is 60m. To go deeper, there is another course, and more expense! At this level, using a rebreather becomes a viable option to buying shares in Air Products or BOC! Chris Storey
Here are some related links. Extended
Range Diving (ERD). The article to which Chris refers
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the amount of time
spent decompressing (compared to breathing the "bottom mix" or
air). This may mean a change in your usual equipment configuration,
possibly changing to a harness and wing, from a BC. And finally there is
cost. Allowing for a set of new equipment, the relevant training
required to obtain a trimix qualification etc, there is the cost of the
actual gas itself. Typically, to use nitrox, we buy a 50l cylinder of
oxygen, which for the cost of the gas alone, is about £20. The cost of
the same amount of Helium is around £80. The cost of a twin cylinder
fill for the course was £30. Compare that to the club's charge for a
36% Nitrox fill for the same size cylinders, which is under £5!
