Nitrox and air

[Rank66]

Hello fellow divers,
I'm taking a nitrox class next month but had a question about the use of nitrox and air on the same day. Can you dive using nitrox, say on your first dive, then switch to air on your second dive?

 

[Doc]

Yes.

Additional calculations are involved.

 

[Docc]

Hello fellow divers,
I'm taking a nitrox class next month but had a question about the use of nitrox and air on the same day. Can you dive using nitrox, say on your first dive, then switch to air on your second dive?

You can even use air and nitrox on the same dive if you have separate bottles of each.

 

[merxlin]

You might even need to go the other way (air first then nitrox) if your first dive is deeper than the MOD for your mix.

 

[GrumpyOldGuy]

Yes you can. You do need to be very careful if you use a computer to set it to the right mix (21%) when you switch back to air. It is easy and dangerous to forget.

 

[ivobj]

No problem, just be careful with planning, and remember, usually for air/nitrox computers, don't switch to air mode, you must specify nitrox 21% in your air dive instead of air mode, or the computer won't perform correct calculations.

 

[Teamcasa]

Hello fellow divers,
I'm taking a nitrox class next month but had a question about the use of nitrox and air on the same day. Can you dive using nitrox, say on your first dive, then switch to air on your second dive?

Generally, the first dive of a multi-dive day has the deepest dive first so most cases, air is used first.

In addition, Nitrox helps in increasing your bottom time so the following shallower second and third dives don't present a NDL problem.

In any event, consult your dive planer to work out your dives ahead of time and should your planed profile change, re-calculate.

 

[Crowley]

I agree with most of the above. Make sure your computer is set for the blend you are using during the dive, regardless of which gas mixture you use first, there are potential problems associated with either using Nitrox NDLs whilst diving with air, or vice versa.

In practical recreational diving, which mix you use first depends on what you're doing. If I was doing a 30 metre / 100ft wreck dive followed by an 18m/60' reef dive I'd have a 32% mix for the deep wreck dive and air for the second. Given that my nitrox supplier only ever mixes 32% except by special request, if I was doing a 40m/120' dive first then I'd use the air, since the 1.4ata maximum operating depth (at least by PADI standards) for a 32% mix is 33 metres.

Other people will tell you that recreational enriched air limits are wayyyyyyy too conservative and you can push those boundaries a lot further. This may be true - but unless you have the training and experience, don't push anything!

Safe diving,

C.

 

[Dan Weidert]

The argument could be (and has been) made that you are diving nitrox in both cases. Just a different blend :blinking:
Dan

 

[boulderjohn]

The concerns already expressed about your computer are important. In most modern computers, you just set the oxygen percentage for your dive. No big deal to change from dive to dive.

In some computers that were designed in the earliest days of nitrox, it can be a big deal. Some of them (Suunto Cobras, for example) have different settings for air and nitrox, and when you are in a dive sequence, you cannot change from one to the other. If you want to switch during a dive day, which is fairly common, you MUST have your computer set on nitrox from the start. When you are diving air, you set the nitrox setting to 21%. If you do air first on the air mode instead of nitrox 21, you will not be able to switch to nitrox for the other dive.