TDI Nitrox

[Lancashire Lad]

Hi,

Has anyone done the TDI basic nitrox course.  I believe it is a one day course, all theory.  A local dive centre has offered our club places on one of these courses next year and I wondered if it was any good?

Thanks

[Jay]

I've not done it myself (I'm PADI nitrox) but I've heard that TDI is the organisation to go for for anything technical (and yes, I DO class nitrox as a basic form of technical diving).

Once I get my Divemaster early next year, I'd like to do advcanced nitrox and extended range diving and I'll probably do that with TDI even though PADI have started branching out with their Tec courses.

Regards

[Eddie]

I'm thinking about doing the PADI nitrox course, for us none tech divers whats the difference/advantage of using nitrox over air? I have been 45 meters on air and had no problems, is it worth the extra costs? ok so I'm a dummy!

[Davey Willo]

I don't think you'd want to go to 45m on Nitrox Eddie :eyecrazy:

[Eddie]

I told you I am a dummy when it comes to tech stuff.. you  still havn't answerd my question! any offers???

[Jay]

Ok - here goes. Diving recreational nitrox involves a pay-off between depth and extended no-deco dive times or reduced surface intervals when conducting multi-dives. When you learn to dive, you are not told about the toxic effects of oxygen at depth because these do not kick in until you reach depths much greater than recreational limits (approx 60m or greater). You ARE taught that your greatest gas enemy is nitrogen (partially because of narcosis but more because of your obligation to 'off-gas' nitrogen that has saturated into your fat tissues at increased pressures. Under pressure, gas molecules are compressed into smaller sizes and therefore nitrogen (which is classed as 'inert' at surface pressures) is absorbed into mainly fatty tissues and, if you surface too quickly, will expand back into bubble formation and cause problems in your bloodstream, spine, skin or any number of other places (hence safety stops, deco stops etc). When you surface from a dive, you are still getting rid of this excess nitrogen and therefore need to take previous dives into account when planning multiple dives either on tables or when diving on your computer.

Nitrox is a slightly inaccurate term used for gas that contains more O2 than 'air' (and therfore LESS nitrogen - less nitrogen in the mix means less is absorbed and therfore less time is required to get rid of it) - with me so far?

Whats the catch? Well, all gases are subject to a principle called 'partial pressures'. The partial pressure of a gas is the pressure it exerts in relation both to the ambient (external) pressure and its percentage within the breating mix. For example - at the surface, the ambient pressure is 1 bar (1 atmosphere) and the percentage of O2 within air is 21%. If we multiply the pressure by the percentage, we get the partial pressure of O2 within air at the surface which is 1 x 21% = 0.21

This is well within limits. The recommended safe maximum partial pressure of O2 is 1.4 (1.6 as a maximum) although US Navy use a partial pressure of over 2.

So, with a maximum 'safe' ppO2 (or partial pressure of oxygen) of 1.4, the maximum safe depth for O2 usuage is 1.4 / 0.21 = 6.67 bar = 56.67m

Make sense so far?

OK, if we increase the O2 content to 40%, then the maximum safe depth is reduced to 1.4 / 0.4 = 3.5 bar = 25m. The pay-off is that diving at 25m on 40% nitrox (or EAN 40 as it is also known - Enriched Air) is equivalent to diving on air to 16.6m therefore you absorb as much nitrogen at 25m on EAN 40 as you would diving to 16.6m on air for the same time. (By the way, 'air' is also nitrox - called nitrox 21 or EAN 21)

So the benefits are increased bottom time for shallower dives but an increased awareness of O2 toxicity.

What are the problems of O2 toxicity? The main one is the threat of convulsions at depth which would probably cause you to lose your regulator and drown!

I know this are probably inaccuracies here (Ammers - I await your input) but this is nitrox for the recreational diver.

Regards

[Eddie]

Cheers Jay for the excelent explanation, just goes to show your never to old to learn something new! :book2: I think I will stick to good old plain air! less complicated... :ogle:

[Jay]

Its really not complicated and it does have great benefits - it does place more emphasis on dive planning (especially dive plans and max depths) but hey, we all do that anyway! Seriously though, if you are on a liveaboard for example and they do nitrox then you can easily do 3 dives a day all week.

I really liked the course - learned a lot.

Regards

[Davey Willo]

Eddie

Although Jays explanation was full of facts it may also have been slightly confusing so to help out an old fool from Holland let me try to simplify it a little :biggrin:

The use of Nitrox has become popular amongst recreational divers for a few different reasons.

[1] It allows you to dive your average dive profile that you would dive on air, using your standard computer or tables  to a max depth of say 30m (not quite right but close enuff I think) but because of the reduced amount of nitrogen in the mix you will exit the water with less nitrogen in your system thereby reducing the risk of a DCI hit. Safer diving!

[2] But If you were to use a nitrox computer or tables then again because of the reduced amount of nitrogen in the mix you could dive for longer before you reached the same levels of nitrogen in your system giving longer bottom times. Great for when you don't want a good dive to end just yet.

[3] Now this one isn't proven but most nitrox divers will tell you, that they feel much more refreshed after a dive on nitrox than they do on plain old air.

On the flip side....The danger of nitrox is that if you exceed the maximum depth for that mix the increased oxygen becomes your enemy rather than the nitrogen, instead of getting narked and having reduced capabilities which in itself is dangerous, you may reach a level of oxygen toxicity or an 02 hit which is usually fatal as the spasms that follow mean you are no longer in control of anything.

Hope that helped mucka, I'm no expert as I've not yet taken my course but I believe that those are the basics.

Best regards
Dave. :thumb:

[Eddie]

That's what I like about YD.. nobody takes the Mickey when someone asks a question that they should know the answer too! thanks Dave but, after a look at the costs (replacing 1st & 2nd stages, computer etc.) I think I will stick to air..