Nitrox: Multiple Dives per Day

[badfrog88]

I haven't taken a nitrox class, yet, but I have bought the SSI Enriched Air Nitrox manual. After the first read through of the manual I have to say I'm a little disappointed. I'm not sure what I was expecting, but the manual seems a little too basic.

Anyway, on to my question: In the section "Planning Your Nitrox Dives", on page 4-22 it says "Many Nitrox divers like to take at least an hour surface interval between Nitrox dives and any other subsequent air dives. It is also common to limit the use of Nitrox to just the one or two deepest dives of the day." (emphasis mine)

Why would this be the case? Wouldn't it be better to use nitrox at the end of the day (if using both air and nitrox during the same day) and use the extra O2 to help off gas the nitrogen?

I know this is something I could/should ask my instructor, but I haven't signed up for a class yet. Based on the SSI manual I may look at another agency.

[mike_s]

the only reason you'd want to do less nitrox dives is oxygen saturation and oxygen toxicity.

But for a manual to say you can only do one or two nitrox dives a day is crazy. I wonder if their manual is old and outdated back to the days of everyone thinking that Nitrox was "VooDoo Gas".

BTW.... you'll find many people, me included, that have done 5 or more Nitrox dives in a day without problem. You just need to compute your Po2 & O2 saturation, or let your dive computer do it for you.

[TxHockeyGuy]

Originally Posted by badfrog88

I haven't taken a nitrox class, yet, but I have bought the SSI Enriched Air Nitrox manual. After the first read through of the manual I have to say I'm a little disappointed. I'm not sure what I was expecting, but the manual seems a little too basic.

Anyway, on to my question: In the section "Planning Your Nitrox Dives", on page 4-22 it says "Many Nitrox divers like to take at least an hour surface interval between Nitrox dives and any other subsequent air dives. It is also common to limit the use of Nitrox to just the one or two deepest dives of the day." (emphasis mine)

Why would this be the case? Wouldn't it be better to use nitrox at the end of the day (if using both air and nitrox during the same day) and use the extra O2 to help off gas the nitrogen?

I know this is something I could/should ask my instructor, but I haven't signed up for a class yet. Based on the SSI manual I may look at another agency.

The reason some people use Nitrox just on deeper dives (up to the MOD) is because it allows them to stay down longer at those depths and they use cheaper air on subsequent dives because it still allows them the bottom time they want. Remember you can use Nitrox to increase bottom time or to increase safety depending upon how it is used, but you can't do both.

So many people think Nitrox is a voodoo gas. In a nutshell it you are ongassing less Nitrogen and therefor can stay down at a given depth for longer. The class is required because you need to know about oxygen toxicity so you don't go past your MOD and so you understand the oxygen clock. It really just isn't that difficult.

If you want to play around to see what you can do I suggest doing a set of virtual dives on the air tables using EAD (Equivalent Air Depth) which should be discussed in your SSI book. That will let you mix in Nitrox and Air dives to see which has benefits for what.

[badfrog88]

The SSI book does discuss EAD. I'll do some virtual dives as suggested.

[MEL-DC Diver]

TxHockeyGuy pretty well nailed the emphasized portion of your post. The chief reason is bucks. They are trying to get the biggest bang for their buck, so to speak.

[Damselfish]

Basic Nitrox isn't all that complicated. But your quotes from that manual I don't get. When I took the PADI class they did recommend 1 hour between Nitrox dives (though if you're on a 2 tank boat trip that usually doesn't quite happen. ) But specifically saying an hour between Nitrox and subsequent air dives makes no sense to me, since the purpose of a decent SI is to help keep down the accumulated O2 exposure, and you'd have less exposure with air. I also don't see it as that common to limit Nitrox to a couple dives. Yes, some people will do this, mainly to save money, and they'll try and pick the most advantageous dives to use it on. But I don't see any other reason to switch back and forth. You have to be watching the various limits of course, but it's unlikely for accumulated O2 exposure to be an issue in your average rec diving. If I'm someplace with Nitrox I usually use it for all dives, can be 5 a day on a liveaboard. Some places (including most liveaboards) will even have a deal for unlimited Nitrox.

[medictom]

I haven't looked at an SSI book for a while for EANx, but does the course at least give an overview of EAD END and OTU's which are all thing's you take into account on a mixed gas dive.
Last week I had to use 3 different mixes for a dive in L. Manitoba to help search for a relic. I used 36 30 and a 50/50!
You really have to watch your OTU's!!

[BSea]

Originally Posted by medictom

I haven't looked at an SSI book for a while for EANx, but does the course at least give an overview of EAD END and OTU's which are all thing's you take into account on a mixed gas dive.
Last week I had to use 3 different mixes for a dive in L. Manitoba to help search for a relic. I used 36 30 and a 50/50!
You really have to watch your OTU's!!

The basic course covers just 1 mix per dive (if I remember correctly). And being that it's recreational nitrox, it doesn't go above 40%. So your 50/50 is way beyond the scope of the course. It does go into EAD, but END is mainly for trimix I believe, and wasn't mentioned in the course that I remember.

[cummings66]

Many and common are two buzz words in the text they have. I don't limit my Nitrox usage to two dives a day. I'll do up to 4 a day on Nitrox, but be warned you need to watch the O2 clock because you can push it.

Diving Nitrox is simple really, but now you have to watch something in addition to Nitrogen when you plan the dives. In reality from what I gather the agencies teaching Nitrox courses teach it similar to air diving when it comes to SI's.

[thesmoothdome]

I did multiple days of 5 dives a day on a 32% mix with absolutely no problem and never came close to my o2 limit.