Question How to dive nitrox for the first time

[Mike_4635]

I have seen multiple instructors telling students to dive an air setting. Again, IMO, that alone is not especially dangerous but it gains nothing over setting your computer correctly, setting a comfortable (to you) gradient setting and then using the gray matter between the ears to say, hey, let's go up or shallow up or end the dive before approaching the NDL.

I have several times been on boats or at a dive locations where divers set for air and exceeded NDL and locked themselves out or pushed MOD depth.

I certainly can and do run hour plus dives on 80cf in that magic 60-100 feet zone. Tank volume is not for me (or many divers) the limiting factor, it is NDL.

I understand DCS is scary and inconvenient if it happens but I think that card is over played. Anecdotal, yes, but I have done thousands of dives and due to application of some common sense have never been bent. I have seen people get bent and they all did something really stupid and one fellow paid for it by spending his life in a wheel chair. Now that is inconvenient .

One issue that I seen setting your computer as air instead of your nitrox is your o2 retention is not calculated correctly. I was diving on a liveboard in Turks and Caicos. Did 5 dives a day over 6 days. Turks can be some deep dive. My Oceanic computer start to warn me about my o2 level on s couple of dives and had to limit my depth. After seeing a dive with oxygen toxicity in Truck, I am very aware of my o2 retention level.

 

[TrimixToo]

One issue that I seen setting your computer as air instead of your nitrox is your o2 retention is not calculated correctly. I was diving on a liveboard in Turks and Caicos. Did 5 dives a day over 6 days. Turks can be some deep dive. My Oceanic computer start to warn me about my o2 level on s couple of dives and had to limit my depth. After seeing a dive with oxygen toxicity in Truck, I am very aware of my o2 retention level.

And *this*, right here, is IMO the best reason not to set your computer to air while diving nitrox. I was about to bring this up but you beat me to it. Good on ya.

 

[EFX]

One danger of setting your dive computer for air when diving nitrox is exceeding the MOD. The MOD for air is 187 ft. The MOD for EAN 36 is 95 ft. Your DC will never give you a warning for exceeding the MOD of the gas you are actually using.

 

[Nemrod]

And *this*, right here, is IMO the best reason not to set your computer to air while diving nitrox. I was about to bring this up but you beat me to it. Good on ya.

That is what I meant by pushing MOD.

 

[TrimixToo]

That is what I meant by pushing MOD.

They are both important. You should not exceed the MOD and you should not ignore the O2 clock.

 

[NothingClever]

Only on ScubaBoard could we take a simple, straightforward question, especially in the Basic Scuba sub-forum, and completely careen off the rails with absolutely asinine answers and techniques.

 

[TravisD]

Seriously, who taught you this?

I’m not asking for a specific name, but was this a technique you got from an instructor, a dive buddy or something heard in resort chatter?

I just checked the SSI Instructor Manual for Nitrox, and under "The Benefits of Breathing Less NIitroge", under "Nitrox use and Decompression Sickness" it lists. "Setting your computer for EAN21 (or using air tables) increases safety margin".

It goes on later to say "While treating nitrox as though it were air. may somewhat reduce the risk of decompression sickness, it does not eliminate it. Additionally, divers who treat nitrox as air must still keep their exposure to elevated partial pressures of oxygen within acceptable limits." There's a couple of other things listed on why you might want do dive an Air setting with Nitrox.

The student book has similar verbiage too.

 

[babyhippo]

-decide if you'll set your computer to PO2 1.4 or 1.6, I'm partial to 1.6 myself.

- understand which dives will benefit from Nitrox, those dives for which Nitrox may possibly offer a slight benefit, and those dives where you're just wasting your money filling your tanks with enriched air.

Generally speaking Nitrox is effective to the point of being worth the expense and extra steps when diving between 60-100' but there are exceptions outside that range.

I’m going to Moalboal, Oslob and Malapascua. They are not going to be too deep that’s why I plan to dive on Nitrox.

 

[babyhippo]

- Check that the gas analyser is calibrated, calibrate it if needed
- Analyse your gas
- Calculate your MOD
- Correctly label your cylinder with MOD, gas mix, your name
- Plan your dive - you will now be limited by gas, not just NDL/no-stop times
- Discuss with your buddy what gas are they diving (hopefully similar gas mix, if they are on air and you use nitrox, change your buddy)
- Set computer(s) to correct gas mix

Repeat each day

Thanks for the detailed points. Can you also talk a bit about what’s normally going to happen in the dive shop on the day and where do I start?
Like is the DM going to lead me to my tank and give me an analyzer so that I can do the checking?
The places I’m going to, Moalboal, Oslob, Malapascua, are all touristy sites and will probably be very busy. Do you have other practical suggestions for me to make sure everything is ready to go before we get in the water/on the boat?
Thanks again!

 

[uncfnp]

Thanks for the detailed points. Can you also talk a bit about what’s normally going to happen in the dive shop on the day and where do I start?
Like is the DM going to lead me to my tank and give me an analyzer so that I can do the checking?
The places I’m going to, Moalboal, Oslob, Malapascua, are all touristy sites and will probably be very busy. Do you have other practical suggestions for me to make sure everything is ready to go before we get in the water/on the boat?
Thanks again!

Each boat/shop will have their own standard procedure. Not specific to your trip but typically the shop will analyze and mark the tank after they fill it. There should also be a log book. You then confirm the gas and sign the log. Some divers don’t personally check their tank. Others will watch as staff uses the analyzer. Other times the diver themselves will use the analyzer. The unit is usually nearby but other times you will have to ask for it.

If you choose to use the analyzer make sure you know how. An inaccurate reading is not much better than no reading. And sensors can be easy to damage and expensive to replace. Plus different analyzers operate a bit differently. Get the staff to demonstrate before you try.