Question How to dive nitrox for the first time

[halocline]

It is very relevant in recreational diving. If your buddy is on air and you are on nitrox, you need to discuss no-stop times. You don’t want your buddy to shoot to the surface because OMG their computer showed 1 minute of deco while you were at 15 minutes NDL.

MODs might be different. Liveaboards - especially in Egypt - might call anything between 25% - 35 % as 32%. You never know when you might need to breathe your buddy’s gas.

Your buddy might be a slob who didn’t analyse their gas or dive at 1.6. So definitely worth having a discussion.

You said “if they are on air and you are on nitrox, change your buddy” I said “there is no need to change your buddy, this is recreational diving…”

Nobody said anything about not discussing the differences in the divers’ gas. Again, it’s very common on recreational dive trips to have some divers on nitrox and some on air, diving together, and somehow they all survive just fine. You want to argue that too?

 

[Nemrod]

@ttc008 why did you get your nitrox certification?

Some people do it to extend bottom times. I did it for enhanced safety/reduce nitrogen load. For this reason, I don't switch my computer's dive mode.

I also recommend against this practice. While not inherently dangerous this practice requires discipline and technical understsanding. I see divers setting air when they are on 32/36. Many dive groups can do hour plus dives with 32/36 even on a conservative setting. But the air setting on the computer will end that dive much earlier. So, the diver thinks, well, I am really on Nitrox so I can continue the dive for a few more minutes while the manta rays play, what is the harm? And then upon surfacing the computer locks out (and some computers will stay locked for 24 hours). The captain and DM get upset and sit the diver out and even if they do not sit the diver out for busting BT and deco, what computer does the diver now use! So if one has the discipline to stick to the air profile and is aware of their MOD then I suppose it is okay. But that diver will be ending their dive earlier than their buddies and will miss all the cool things that always occur after the air hogs depart. The best part of having a low SAC and using Nitrox is that long after everyone else is gone to the surface, me and the DM get to enjoy the silent world alone for a few minutes. Priceless.

 

[Still Kicking]

It was mentioned but bears repeating ....NEVER trust an analysis you didn't do yourself or at least witness. Mistakes happen when filling tanks -- your safety depends on knowing the mix you're diving and setting computer/tables accordingly.

 

[DreadnoughtNH]

- 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

This is the way.

 

[NothingClever]

- Correctly label your cylinder with MOD, gas mix, your name

I’d only make one set of numbers (your MOD) visible to others to thoroughly prevent confusing the dullard on the team (me).

In much smaller text, the cool kids put their O2 percentage down to the tenth on the neck of the cylinder as positive confirmation they’ve analyzed their gas.

So, if you’re diving a tank of 36% EANx, your tank will show:

29m / ttc008

And on the neck on a small label, you’ll write 35.9 (or whatever precise mixture your gas analyzer shows) and the date.

 

[KatieMac]

I also recommend against this practice. While not inherently dangerous this practice requires discipline and technical understsanding. I see divers setting air when they are on 32/36. Many dive groups can do hour plus dives with 32/36 even on a conservative setting. But the air setting on the computer will end that dive much earlier. So, the diver thinks, well, I am really on Nitrox so I can continue the dive for a few more minutes while the manta rays play, what is the harm? And then upon surfacing the computer locks out (and some computers will stay locked for 24 hours). The captain and DM get upset and sit the diver out and even if they do not sit the diver out for busting BT and deco, what computer does the diver now use! So if one has the discipline to stick to the air profile and is aware of their MOD then I suppose it is okay. But that diver will be ending their dive earlier than their buddies and will miss all the cool things that always occur after the air hogs depart. The best part of having a low SAC and using Nitrox is that long after everyone else is gone to the surface, me and the DM get to enjoy the silent world alone for a few minutes. Priceless.

No, it doesn't end the dive earlier. It just gives more conservative NDLs. Shallow up a bit when NDLs are low and magically, the NDLs go up. There is great stuff to see at 40 feet as well. The dive isn't over.

And if you spend a bit more time deeper, the computer assigns a longer safety stop. My computer assigned a 5 minute SS on a recent 78 minute dive.

 

[BRT]

A couple of missing puzzle pieces:

- select the % O2 mix you will use based on the dive profile and available blends

- make sure you understand the maximum operating depth (MOD) limitations for the mix that you select

If those don’t make sense to you, talk to an instructor.

Lance

And there is the nitrox course in a nutshell.

 

[EFX]

I got my nitrox cert in 2023 as a dry course at the end of a dive trip but haven't dove nitrox since yet. I want to try nitrox on my planned october trip to cebu (moalboal, oslob, malapascua) but honestly I don't think I remember much from the course.

I will certainly do a full review of the course materials before the trip which I think are still available because the cert was with SSI. However, from what little I do remember, apart from the theory and the science, nitrox doesn't change much "how" I dive except that I need to check the gas and set my computer to nitrox mode, right? If there's a lot more I should do in practice then I better shut up and go back to the first page of the textbook now, but I just want to get a basic sense of where I am at the moment. Thanks in advance!

I've been nitrox certified for many years. In terms of the mechanics of putting together your equipment, the actual swimming underwater, and the feeling of diving nitrox (at least for me), there is no difference between nitrox and air. Definitely review the course materials especially MOD and make sure you have the gas tested and you set your computer correctly.

 

[boulderjohn]

No, it doesn't end the dive earlier. It just gives more conservative NDLs. Shallow up a bit when NDLs are low and magically, the NDLs go up. There is great stuff to see at 40 feet as well. The dive isn't over.

I see. So all you have to do to avoid getting shorter bottom times is shorten your bottom time.

 

[arkstorm]

@ttc008 why did you get your nitrox certification?

Some people do it to extend bottom times. I did it for enhanced safety/reduce nitrogen load. For this reason, I don't switch my computer's dive mode.

I think this practice made more sense before the age of dive computers, i.e., diving an air profile on nitrox (paying close attention not to exceed MOD) to introduce a layer of conservativeness to the dive table profile.

However, dive computers let us fix a level of conservativeness while still deriving the full benefit of a real-time gas loading calculation. To maximize this benefit, the computer needs to know what gas you are actually breathing.