Question How to dive nitrox for the first 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.

 

[KatieMac]

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

Longer bottom times is not the only reason people dive nitrox. Some people want to reduce their nitrogen load. Diving nitrox with the computer set to air adds a safety margin.

4 Divers Who Should Be Diving Nitrox - Are You One of Them?

Some types of divers will benefit more than others from diving nitrox. See if diving with enriched air is a good choice for you!

sundiversroatan.com

 

[scubadada]

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.

Sorry, running an air profile while diving nitrox is simply not the right thing to do. Many good reasons have already been posted.

You do not always have the option to "shallow up" when the profile is relatively square such as on a reef drift dive, on a wreck, or simply if the topography is deeper.

An adaptive safety stop does not help you when diving an air profile on nitrox. it only reflects that you came relatively close to your air NDL or exceeded a certain depth.

There are many better ways to increase your safety while diving nitrox. You could stay farther away from you your NDL or you could set the computer to a more conservative setting.

Out of interest, what computer do you dive and what settings do you use? The adaptive safety stop makes me think it may be a Shearwater, not sure if other brands also run this.

 

[boulderjohn]

Longer bottom times is not the only reason people dive nitrox. Some people want to reduce their nitrogen load. Diving nitrox with the computer set to air adds a safety margin.

4 Divers Who Should Be Diving Nitrox - Are You One of Them?

Some types of divers will benefit more than others from diving nitrox. See if diving with enriched air is a good choice for you!

sundiversroatan.com

Lets of people say it is one or the other. It isn't. You can have longer bottom times and greater safety.

People who think that way always assume divers will dive to the maximum allowed time on nitrox, but you don't have to do that. On the PADI RDP, the maximum bottom time for a dive to 80 feet is 30 minutes. On the PADI RDP for EANx 36, the maximum bottom time is 55 minutes. If you do the dive for 40 minutes, you get 33% more bottom time and significantly less nitrogen loading.

 

[gamon]

There’s no need to ‘change your buddy’ if one diver is on air and the other on nitrox. Just make sure the buddy understands the MOD. This is recreational diving, there are mixed nitrox/air dive groups all the time.

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?

So what it's common, you keep saying that as if because it's done that way often, it's somehow beneficial. It's not, at least to the diver who is paying for Nitrox and took the course so he or she can use it.

It's not about survival it's about longer, more enjoyable dives.

Of course there's a need to dive with a buddy who is on Nitrox, otherwise you're going to get a shorter bottom time than you paid for. Whether or not there are "mixed air/nitrox groups all the time" doesn't mean it's a good idea. Because it's not. No different than a dive charter that forces a diver to team up with an instabuddy of unknown skills, health, experience, etc because the charter doesn't want to pay a crewmember to do it.

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.

Fooling your computer is not a good idea. At all. If you want to dive conservatively, then do so. No need to play around with crazy ideas like setting your computer for the wrong mix.

 

[boulderjohn]

Here is the story of a recent dive I did that may be instructive.

I was planning to do a 2-tank dive to a wreck with a maximum depth of 130 feet, and I had my tanks filled with EANx 29 just in case I decided to go to the maximum. I ended up, however, buddying with a skilled diver with 32%. He did not know the wreck, and I agreed to show him around. We had almost identical computer algorithms.

On both dives, we went to a deck at 110 feet, his MOD, and we worked our through various rooms before ending up at the highest point of the wreck. I had milked my time through ascending as well as I could, but when I reached my NDL and it was time for us to head up the ascent line, he still had a pretty decent amount of NDL time remaining. We both had plenty of gas remaining.

We had only a 3% difference in our nitrox mixes, but he still had to end his dives early because of me. Think how early he would have had to end his dive if I had been using an air profile instead of 29%.

 

[gamon]

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.

You are wrong on so many levels. Setting your computer for air WILL shorten many or most dives for all practical purposes, just like most dives can be made longer if it's possible to shallow up regardless of whether the mix is air or Nitrox.

Not all dives can be "shallowed up", because in many scenarios there's simply nothing to see once you leave the bottom.

 

[Subcooled]

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!

Nitrox, a blend of nitrogen and oxygen, contains air as a special case (Nitrox 21).

The only differences that you need to be aware of are:

1. The maximum dive depth is no longer -56m (-184ft) but something much less. If you venture too deep and experience oxygen toxicity, it will most probably be your last experience, so please, check the max depth for the nitrox mix and respect it. Oxygen toxicity may not be immediate, but with time and depth its probability increases. It would be a healthy thing, in the long run, to be able to verify (measure) what the oxygen percentage is in your tank(s).
2. The computer will warn you of depth and calculate everything for you as long as you turn on the nitrox mode AND DIAL IN THE O2% CORRECTLY.

Having too much oxygen is rarely a problem unless you venture to deep. In some extreme cases though, long term effects of too much oxygen can irritate and damage lungs, even severely. I woudn't worry about this on your weekly 60 minute dive (deco included) to one hundred feet breathing Nitrox 32. Technical divers, rebreather divers, gas blenders and operators of hyperbaric chambers at hospitals need to know a lot more.

 

[Sascha314]

@KatieMac
You are fooled if you think you are reducing your nitrogen load by ascending a bit if coming close to it - well at least if we are speaking about 30m.

Actually you then may load more tissues to the max than if you do an honest dive - speaking from the model. Afaik there is some evidence that doing this increases the risk of a dcs hit.

And "extending" the safety stop has probably been a real deco stop.

 

[Subcooled]

I was talking about oxygen load. Oxygen toxicity and such. Not about the proper off-gassing of nitrogen.

But yes, there are slower and faster tissues, and sometimes the slower tissues become a problem with nitrogen. The Subsurface dive log can show a tissue loading heatmap, which is very enlightening to those studious enough. One might offgass the fast tissues (blood) while still ingassing slower tissues and the suffering from that.