Staging the ascent
TDI Advanced Nitrox and Decompression Courses
Does your No Decompression Limit (NDL) rather than your air supply bring you up from a dive?
Do you wish that you could stay down on that wreck a bit longer but find that your computer doesn’t agree?
If that’s the case, then it’s time that you considered Nitrox.
For those of you that are not quite sure what that is and what it does, then have a look at the PADI Specialties page on the web site. In essence, it is a breathing gas that contains a percentage of oxygen greater than the standard 21%. As there is less nitrogen in the gas, your NDL is therefore greater which means you can stay down longer. Clever or what!? Just about every diver gets into Nitrox diving particularly those that dive regularly.
Having said that, there is only so long you can stay down on one tank of air. That’s fine during a Red Sea trip where dive times are restricted to about 60 minutes, but what happens in the middle of the English Channel? We usually find ourselves diving on a wreck at 30mtrs or deeper where even on Nitrox, the NDL fast approaches. The deeper we go, the less oxygen we can have in our mix and we arrive at the NDL that much sooner. That’s where Decompression diving comes in.
Most of you will have at least heard of decompression diving, coming up from the bottom in stages and stopping at various depths to get rid of the excess nitrogen in your system. Most of you probably think that this type of diving is only for ‘Teckies’ and you have to have more tanks than sense. Well think again. The art of ‘deco diving’ is to enable you to have the buoyancy skills and the ability to read a dive table in order for you to safely extend your dive past the NDL if you want to!
|There you are at 35mtrs, on the wreck that has 12mtrs viz, and you’re wearing a 15ltr tank and a pony bottle. Sound familiar? OK. You’ve been down a whole 12 minutes and your computer tells you that there is just two minutes until you reach your NDL but you still have 150 bar. Tough. You’re coming up! Your pony bottle doesn’t count ‘cos that’s only for emergencies. What if you could extend your bottom time on that dive by another 15 to 20 minutes and then just do a slightly longer safety stop of 8 minutes or so? Yeah? Now you’re interested! For those of you that have already been out with us on club trips in the UK, you will have seen a lot of staff members spending a lot longer under the water than the other divers and that’s after doing only 10 or 15 minutes decompression. Well you can do that too without the twin sets if that’s what you want.|