How can the air we breathe be so harmful to us, after all isn’t oxygen good for us? Well, we do know from our Enriched Air aka Nitrox class that under pressure can become toxic to our body and cause a host of issues.
We can avoid all of those issues by paying attention to our dive computers and by setting our oxygen levels on our computers correctly. Let me provide an example that actually happen to me of all people. A day before we went to the crater I was showing a diver how to set the oxygen limits on one of my dive computers. This particular computer you can actually set up to 99% oxygen. By the way at that level the maximum dive depth is 13 feet. Well instead of making sure it was set back to regular old 21% air, I must have left it at 99%. Well you can just imagine the grief that the computer was giving me after only 5 minutes of the first dive at the crater. As most of you know that dive is usually between 16 and 25 feet. Well after 5 minutes my computer was telling me that I was approaching my oxygen limit for 24 hours. And after 10 minutes I was way past that limit. I knew I was fine and I knew what had happened. But of course my computer didn’t know that I was fine and actually diving 21% or just regular old air.
Of course I finish both of the dives with the class and one extra for the advanced open water students. At this point I was curious what the computer would actually do. I was definitely on the naughty list as far as it was concerned. But after 14 hours of being out of the water the computer was much happier and allowed me to reset it to 21%. After 3 more dives with the class the computer was showing only 5% of my daily oxygen exposure had been reached.
Nitrox (Enriched Air) just what is it and what benefit does it have for our diving? Nitrox is any blend of air that has over 21% oxygen, hence the tern Enriched Air Nitrox or EAN, with the most common being around 32% oxygen.
The first benefit in diving Nitrox is that by using air that contains less nitrogen we are loading less nitrogen into our bodies therefore at least in theory we are adding a safety margin against decompression illness. With less nitrogen in our scuba cylinders there is even less need to push the limits of the dive tables or our computers. On the regular PADI dive table a dive to 60 feet for 45 minutes leaves us in the pressure group of “S” while on Nitrox of 32% the same dive leaves us in the pressure group of”M”. That is quite a large difference in nitrogen loading.
Which brings us to the next benefit of Nitrox, longer bottom times or shorter surface time. Using our 60 foot dive of before if we look at the regular dive table 60 feet shows a maximum bottom time of 55 minutes and our Nitrox 32% table shows 90 minutes. A huge amount of extra time to spend under water, but not many can make a tank last that long.
So how about shorter surface time? In our 60 foot dive for 45 minutes on the regular PADI table we would be an “S” diver and after a 1 hour surface interval we would have off gassed down to a “G” diver which would allow us only 34 minutes at 60 feet or 54 minutes if we only go to 50 feet. On Nitrox 32% the table is much kinder to our bottom time. If we dive the same 45 minutes and our pressure group is “M” if we want to go right back to 60 feet for 45 minutes our surface time is less than 4 minutes. But since we are safe divers we stay on the surface for 30 minutes which drops us to “H” pressure group and that gives us up to 60 minutes of allowable bottom time.
One last benefit of diving with Nitrox is that you may feel less tired after a day of diving. There is no science that I can point you to, but after 4 or 5 dives a day I know I am less tired