Question How to dive nitrox for the first time

[boulderjohn]

Right. If it's a mixed gas group led by a DM and all divers must surface together, and do the same surface intervals then Nitrox is almost pointless.

Certainly true when it comes to single dive DCS risk. But you might want to use Nitrox anyway if this is one of many dives you are doing in a short time. Or if you believe it helps with subclinical side effects of diving such as fatigue.

I still usually use it. They used to call it Geezer Gas. I'm a geezer.

I generally try to avoid such dives to the greatest extent possible, but sometimes you have no choice. Unless it's super shallow, I'm doing the nitrox.

 

[arkstorm]

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 think it is also relevant to ask when this concept was taught because I seem to remember this idea being presented in the PADI EAN manual in the late 90's / early 2000's, i.e., prior to computers with conservativeness settings. I would agree that this concept is obsolete today.

 

[johndiver999]

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.

what are you talking about? ttc008 and what does 29 minutes mean?

I put the mix on the tank.

 

[boulderjohn]

what are you talking about? ttc008 and what does 29 minutes mean?

I put the mix on the tank.

I'm pretty sure it means an MOD of 29 meters.

 

[Nemrod]

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 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 .

 

[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.