Nitrox/Time to Fly

[lmorin]

Elsewhere, DandyDon has extolled the virtues of using various nitrox mixes to reduce DCS likelihood caused by post-dive flying. However, I have not seen this issue directly discussed by others, and particularly, I have not seen DandyDon's position either supported (it sounds logical to me) or seriously criticized. So, the question is, Does nitrox use reduce the necessary off-gassing interval before flying, or are there other factors not related to the accumulated nitrogen load that support the use of existing air-based, time-to-fly rules?

 

[HowardE]

Does nitrox use reduce the necessary off-gassing interval before flying, or are there other factors not related to the accumulated nitrogen load that support the use of existing air-based, time-to-fly rules?

While I'm not Dr. Deco... I know that offgassing occurs at the same rate regardless of the mix your're diving. If you compare the times to move to lower pressure groups on your RDP you'll notice that Nitrox and Air have the same offgassing rates. I would say that time to fly should not be reduced.

 

[M_Bipartitus]

Also from a non-offical....

It would only make a difference if you had less of a nitrogen load in your body due to, say making the same dive you would have made on air thus having less nitrogen in your system. It would be the same as choosing to make your dives shorter with the same mix.

That being said most cert organizations suggest a fixed time 12, 24 hours between diving and flying. These are based on a worst case senerio, and being conservative. There are a few computers that use a calculated time to fly, but this is uncommon.

 

[String]

Surely youd just use the EAD of the dives performed and go from there to computer the no fly as you would with air ?

 

[DandyDon]

Elsewhere, DandyDon has extolled the virtues of using various nitrox mixes to reduce DCS likelihood caused by post-dive flying.

Well you really gotta discount such based on the source. You can tell from my profile that I am not an expert on anything.

Surely youd just use the EAD of the dives performed and go from there to computer the no fly as you would with air ?

Yep, that would be the logic of any discussion I've offered along these lines. I'd used the EAD and the NOAA Dive Manual table on Flying After Diving. I have used this approach myself - at the end of a week of diving all Nitrox for overall less N2 buildup, as well as specifically on 20 ft shallow training dives in the morning with an afternoon flight. But then, I am a cowboy about such, so study the details yourself.

 

[sky50960]

Well, more %o2 --> les N2--> equivalent depth is less important than with EAN 21%-->off gassing time is reduced and of course also time before flight.
just use your dive computer(time before flight), deco software or decompression equation to verify it.

 

[M_Bipartitus]

Well, more %o2 --> les N2--> equivalent depth is less important than with EAN 21%-->off gassing time is reduced and of course also time before flight.
just use your dive computer(time before flight), deco software or decompression equation to verify it.

This is only true if the dive is the same. This is not true if you dive to the limit of s computer or table. For example, if you compare the two situations

2 identical dives to the same depth and time, then you will have less dissolved N2, hence less time untill off gassing is complete.

2 dives, only difference between dives is that you choose to ascend and take your safety stop when the computer says you have 5 min remaining. In this case the off gassing time is about the same since you have made a dive to the same limit. The air dive is likely much shorter.

Moreover, I suspect most people on a dive trip will be trying to get in as much bottom time as they can, so they are likely go to the limit of what ever gas they have, so the second case is more relevant to most people.

 

[Dr Deco]

Hello Imorin:

For the residual nitrogen in your body with nitrox, you would use the equivalent air depth and follow that pressure group. [By extension, if you were to dive with no nitrogen and only oxygen, you would have no nitrogen at all, and therefore you would have no required surface interval.]

Dr Deco :doctor:

 

[lmorin]

Thanks for all the feedback. It is logical and reasonably consistent across posts (a relative rarity??). DAN, however, is sticking by its published recommendations. From a DAN email response to my query: "The flying after diving recommendations remains the same regardless of the breathing gas used. Keep in mind that EAN has lower nitrogen content so this can actually add a margin of safety to the guidelines."

 

[Dr Deco]

Hello Imorin:

DAN is combining caution with simplicity. :icosm12:

There is a lot to recommend in that approach.

Dr Deco :doctor: