Posted by North Coast Diver on June 02, 2005 at 16:48:47:
In Reply to: Deep air diving posted by FARMHAND on May 31, 2005 at 17:34:24:
In current times there is the modern notion of the "best mix" for scuba. Air (21/0) is a great mix to about 50 feet, but not really great any deeper. Air is an ideal mix to 20 ft, at which depth you have virtually unlimited NDL times with air.
You can dive air as deep as you dare, but you would not be diving the "best mix" if you were deeper than 50 ft on air. Inexperienced divers do not understand this concept. They think air is fine to 100 ft or more for various reasons, such as they have been doing it for a long time, or there are tables that give you data for those dives, etc.
The best mix minimizes your N2 loading as well as exposes you to minimal narcosis effects at your planned maximum operating depth.
If you cannot get nitrox or trimix fills, then you have to ask yourself the question, how deep is it wise to go with compressed air, even though tables give you data for depths that are not wise.
For any dive deeper than 100 ft the narcosis is going to be significant with air or nitrox.
But even at only 100 ft with compressed air, the N2 loading is very significant. You would be much better off diving with nitrox at 100 ft than with air due to nitrox's lower N2 loading compared with air.
When you only have air available to you, it makes sense to limit your planned MOD to 50 ft. That allows you to dive as many dives in a day as you like with air, with an 80 cu ft tank (smaller if your frame is less than the normal male frame), and with a 1 hour surface interval between dives.
If you can get nitrox or trimix fills, then it makes no sense to dive air deeper than 50 ft ever.
Nobody can tell you how to dive. It is your body and your certification and your gear. But if you are diving air deeper than 50 ft you won't be viewed as a modern conservative diver.
I have dived with air to 185 ft, and 173 ft, and 156 ft (several times). I don't recommend it to others. I don't do it myself without a specific reason, such as not having trimix or nitrox available to me. The great thing about nitrox and trimix training is that the training makes you a better, more conservative diver.
The great thing about having dived with trimix to 250 ft is that depth has no particul allure anymore, and planned depth becomes more of an issue of the "best mix" than it does with reaching any particular depth.
When you plan a dive trip to a resort, it is smart to ask them if they provide nitrox. If they do, that means you can dive practically as many dives in a day as you want. If they do not have nitrox, then book with a different facility in order to get your money's worth for the trip, if you like to dive a lot.
[Let the flamers begin.]