Which expert is right? re:Nitrox on air tables

[BigJetDriver]

As others have mentioned here, both men were right, it depends upon how you look at the question.

When I first looked at this question, back in the days when PADI was still calling it "voodoo gas", I talked to researchers and statisticians about it.

As we know, Mark Twain famously said: "There are liars, damn liars, and then there are statistics." What the consensus on the subject was is that there is a very slight increase, statistically, on the side of safety if you use Nitrox but run Air Table times and depths. They all agreed, however, that it was so small as to be meaningless in practical terms.

The true benefits of Nitrox are (1) that it gives you more bottom time, and (2) that you feel better at the end of the day if you dive Nitrox. (That last is called "anecdotal evidence". This means that people in the field report it, but that the boffins don't have their name on the study yet!)

The DCIEM (now DRDC) tables have always been described as more conservative than others available, but the real arbiter of what is conservative in your case is YOU. No model can accurately judge how well hydrated you are, for instance, when you start any particular dive.

Hope that helps a bit. I would suggest that you take the nitrox class from the agency of your choice.

Cheers!

Rob Davie

 

[grf88]

As an "older" diver I can attest to the benefits of Nitrox. Even staying well within the NDL I can extend my bottom time over air while at the same time increasing my margin of safety as compared to getting close to the NDL on air. The combination of Nitrox and deep stops leaves me feeling much better at the end of a weekends diving than I did before. I can even drive home without having to pull over for a nap.

 

[lamont]

in addition to nitrox and conservative profiles, don't forget slow ascents...

and suuntos on the least conservative setting are more conservative than the PADI RDP...

 

[Michael Freeman]

I may be missing the point, but why don't you use that money to buy a good dive computer and set it to a more conservative setting? You could also do both, get the nitrox class and use a nitrox computer and set it to a more conservative setting.

That way you get credit for shallow parts of the dive, but if you actually did a square profile it would actually push you to be safer then the tables.

Just my 2 cents.

 

[DA Aquamaster]

Or just dive nitrox with an air computer to get the same multilevel benefit.

I have just turned 40 and can still claim to not be a member of the "over 40 crowd". But none the less I have found the combination of deep stops, slow ascents and saftey stops to be valuable in avoiding fatigue at the end of a long diveweek end with 6-8 dives in it.

 

[Charlie99]

I have found the combination of deep stops, slow ascents and saftey stops to be valuable in avoiding fatigue at the end of a long diveweek end with 6-8 dives in it.

My experience has been similar. Before I developed better control of my ascent rates and also started doing deep stops, I found that nitrox would reduce fatigue levels when doing multiple dives per day. Once I started spending more time in my ascent + deep stops + safety stop, the air vs. nitrox difference disappeared.

 

[Charlie99]

One also went on to say the PADI dive tables for mutiple dives are among the MOST aggressive (as opposed to conservative) tables there are.

Any other opinions or thoughts?

The U.S. Navy tables, and those derived from USN (NAUI, SSI, YMCA, .....) assume that the critical compartment is the 120 minute compartment and track only that compartment. PADI tracks the 60 minute compartment, and uses the special X, Y, and Z rules (look at the back of the PADI RDP) to extend surface intervals for those unusual cases where the limiting compartment is slower than 60 minutes (basically, extremely long, shallow dives that are uncommon on open circuit). The PADI table does a better job of tracking N2 for typical no-stop recreational dives. That is why it generally allows more bottom time on repetitive dives as compared to USN-derived tables.

Tables are very crude devices for tracking N2 loading. The crudeness of a table will add a highly variable amount of conservativeness. For example, on most tables, you plan and calculate the dive as if it were all at the deepest depth. If you spend some of the dive shallower, then obviously, using a table has added some conservatism. Similarly, by use of an excessively slow compartment, the USN-derived tables add a highly variable amount of conservatism. I prefer to use a table that is more suited for the types of dives I am doing.

Charlie Allen

 

[tkrock]

As long as your not worried about bottom time, Nitrox can and will help!!!!

 

[jbd]

US Navy tables had a 6% failure rate,.....

Where do you get this statistic from? I have recently read an article that indicates that this is not quite true. I will try to find it.

 

[StSomewhere]

Using nitrox to extend bottom time effectively cancels the so-called safety factor. The NDL is still the NDL.