I hesitate to take the thread off on a tangent, but, I thought I ought to reply after the comments that my post created after I stated you feel better on Nitrox.
To some degree I understand that it is a subjective measurement.
However, from a personal point of view, and for those I dive with, we generally find air diving far more exhausting than the same dives on Nitrox. If anything we do far more extreme dives when we dive Nitrox, than when we are forced to use air. I am also aware that in an ideal world you would do a double blind study.
The best example I have is our Scapa experiences. Other trips have repeated the experience.
Scapa is located in the Orkney Isles. (Off the top of Scotland, where the German first world war fleet where scuttled). The dives are cold water dives. It is exceptional to do more than two dives a day. Often these include decompression. The capital ships lay between 42m and 24m, these are the morning dives. There are a few deeper dives, but these are not from the fleet. The afternoon dives are the block ships, these are extremely tidal, and shallow, these are the afternoon dives.
In the summer, the weather can be anything from a comfortable 20C and sunny, to snow and sleet. I've experienced just about every variation, from lazing in the sun to sweeping the snow off the deck before diving.
My first trip involved diving air, twin 10 litre cylinders. It was noticeable that in the evenings the whole group where generally washed out.
The second trip I was Nitrox qualified. Although Nitrox was still difficult to get other than from one 'technical' boat. We where able to get a fill by leaving the cylinders on the boat overnight.
My buddy and I both dived twins, with 3 litre cylinders of 50% Nitrox. Decompression was never to exceed more than 30 minutes (first dive). We decompressed on the 50%, after the end of the first dive, following an air table. What Nitrox was left, was then used for as long as it would last on the second dive, either for compulsory decompression, or for a 5 minute safety stop.
In general, we where more than twice as long in the water than the rest of the group .
On this occasion, we where not washed out after diving, this was even more noticeable towards the end of the week.
The third trip my buddy and I used Nitrox on the bottom and a rich mix for decompressing (on an air table).
We did have to medivac one of the air divers out for recompression half way through the week. (I subsequently found out he had a PFO - three chamber trips later!)
These days Nitrox is readily available, and the skippers prefer divers to use it.
Our practice now is to fill an optimum mix for the second dive. Then air top it for the following mornings dive (giving you a weak Nitrox), then optimum mix for the afternoon. This keeps the O2 costs down. Some will accelerate the stops, some will follow the bottom gas profile. Anyone accelerating a stop will chuck another 5-10 minutes on the end for safety.
It is extremely rare that we will have a diver diving air in Scapa, when we do, they are always far more fatigued than those using Nitrox.
Whilst I accept this isn't a proper study, the consensus is that we feel better on Nitrox. We don't always use Nitrox, especially on weekend trips, but on longer trips we always use Nitrox if we have the opportunity.
*** To some degree this is not an issue for me, I dive CCR, so I am always on the best mix.***
Whilst I am talking about UK diving. It is some of the best diving you can get any where in the world. However, you never quite know what you are going to get until you hit the water. Also, if you like wreck diving, we have had centuries of conflict, and bad weather, so our coastline is littered with wrecks, for history and marine life. Just remember, regular UK divers use a drysuit!
Gareth
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