Nitrox computer diving air profiles

[NAM001]

Hi sup

i ran a set of dives on a spreadsheet i have. 80 ft 35 min 40% o2 1 hr Si on the seventh dive you exceed daily otu and 24 hr cns is 100+.

Granted it is not a realistic scenerio but mathise possible jsut the same. the dives aquire about 55 otu's per dive. and max's are hat 180 per dive 300 per day. The cns is about 17% per dive. Once again no one ould ever do this but if one did a better mix may be 36 or 32 to stay ith in the imits of the 7 dive scenerio.

I'd be interested in hearing about a day when you thought you could exceed or even approach your O2 clock.
It's next to impossible unless you are doing very technical dives, and pretty stinkin hard without a rebreather with a constant PPO2.

But, that's for another class.
At any rate... You can either calculate your MOD and don't dive deeper than the MOD with your computer set on air. Or you can set your computer on the mix you are using and not dive it to its limits. Or, best case, dive two computers one set on air, one set on nitrox. But, don't overthink it.

 

[DiveNav]

..... So, I was thinking I could do a few things:

1. Dive Nitrox profile ....
2. Dive the air profile ......

Could you describe better what you mean by "Nitrox profile" and "Air profile"?
What gas mix are you planning to use?

Alberto (aka eDiver)

 

[Superlyte27]

Well, if i'm doing 4x dives a day, I usually go for 60+ minutes on my local shore dives. I see from my book the NOAA tables give me for 24 hr limits 180 minutes at 1.4. I guess i'd have to be diving a fairly rich mix and/or consistently hitting the MOD to get that. Not having dived Nitrox before, I'm just theorising at the moment and not sure what to expect on the liveaboard either.

Thanks for all the replies. It's been a good learning experience.

You're whole dive isn't at 1.4ppo2. Do one dive and look at your average depth. You'll quickly learn that running out of Oxygen clock is pretty friggin unlikely.

Let's say you were planning on doing 4 60 minute dives at 1.4ppo2. So, 32% at 112'? 4 Times in one day? Really? Do you generally do a buttload of deco in a day?

It's just not going to happen. Most people don't stay at max depth for the entire dive. So when you come up from 112' to 75', well, now you're not at 1.4ppo2. When you come to 30' you're really not at 1.4ppo2. You're doing 60 minute dives, but I'd guess less than half of that is spent at max depth. So, lets say your average depth was something more realistic like a 1.2 or 1.1... What's the maximum allowable for 24 hours?

---------- Post added May 20th, 2013 at 05:11 PM ----------

Hi sup

i ran a set of dives on a spreadsheet i have. 80 ft 35 min 40% o2 1 hr Si on the seventh dive you exceed daily otu and 24 hr cns is 100+.

Granted it is not a realistic scenerio but mathise possible jsut the same. the dives aquire about 55 otu's per dive. and max's are hat 180 per dive 300 per day. The cns is about 17% per dive. Once again no one ould ever do this but if one did a better mix may be 36 or 32 to stay ith in the imits of the 7 dive scenerio.

LOL< Keith, I could plan a moron dive too and max CNS. But that's kinda dumb dontcha think? And that's also assuming the entire dive was done at max depth. There's almost always something to look at a bit shallower. The point is... no recreational diver and most OC technical divers are not reaching their oxygen clock maximums.

 

[scubadada]

I'd be interested in hearing about a day when you thought you could exceed or even approach your O2 clock.
It's next to impossible unless you are doing very technical dives, and pretty stinkin hard without a rebreather with a constant PPO2.

But, that's for another class.

Hi Superlyte27,

Approaching or exceeding the NOAA O2 exposure is not difficult. I do most of my diving in Boynton Beach FL at about 60 ft. the entire dive is at 60 ft prior to ascending. The normal nitrox mix is 36%, making the pO2 1.0. The NOAA limit at this pO2 is 5 hrs per day. I often do 4 dives and come close to or exceed the 5 hour limit. To boot, I often dive multiple days, easily exceeding the O2 limit. I also go up to Jupiter and get in several deeper dives or dive the Castor in Boynton Beach to 110 feet or so. Dive 32% on the Castor. My Oceanic computers become uncomfortable but still give me the information I need. There you go.

 

[Sir-Dive-A-Lot]

Could you describe better what you mean by "Nitrox profile" and "Air profile"?
What gas mix are you planning to use?

Alberto (aka eDiver)

I meant by dialing in the actual FO2 i'm using, (say 32%) into the computer.
With air profile, I mean entering 21% as my FO2, even though i would really be breathing a higher mix.

 

[Superlyte27]

Hi Superlyte27,

Approaching or exceeding the NOAA O2 exposure is not difficult. I do most of my diving in Boynton Beach FL at about 60 ft. the entire dive is at 60 ft prior to ascending. The normal nitrox mix is 36%, making the pO2 1.0. The NOAA limit at this pO2 is 5 hrs per day. I often do 4 dives and come close to or exceed the 5 hour limit. To boot, I often dive multiple days, easily exceeding the O2 limit. I also go up to Jupiter and get in several deeper dives or dive the Castor in Boynton Beach to 110 feet or so. Dive 32% on the Castor. My Oceanic computers become uncomfortable but still give me the information I need. There you go.

So, you're doing what exactly?
You're diving 60' and never ascending except when the dive is over. What's your bottom time. What's your surface interval. Are you fitting 4 or 5 dives in the day without hitting deco? Again, I find it hard to believe that you are staying at 60' the entire dive. Most people don't lay on the bottom. So if you're really at 50' or even 53' instead of 60' well then your PPO2 is at .9 and your 24 hour Oxygen Clock is 6 hours not 5.

I'd like to see some profiles from a computer to see what the average depth really is. I'd be surprised if the max depth was 60' and the average depth was 60'. I could be wrong, but I've never seen it. Again, the Castor sits in 110' of water, that's to the sand. How many divers are laying in the sand when the wreck is 50' tall. The top of the wreck is just 60' from the surface.

Of course it is possible to reach your oxygen clock. It's just not very likely unless people are dumb enough to spend a whole dive laying in the sand. And if that's the case, then there are issues bigger than not planning their diving correctly. The point is people aren't oxtoxing all over the place.

 

[scubadada]

Hi Superlyte27,

No reason to be insulting. I was just pointing out it's not impossible, or even that difficult, to hit the NOAA O2 limit.

In Boynton Beach, my average depths are about 53-55 feet and my bottom times are about 75 minutes. No I don't generally go into deco. I often do 4 dives per day and othen dive multiple days. My surface intervals are generally around an hour, the O2 clock is per day. My average depths on the Castor are around 80 feet with run times around 50 minutes, usually close or just into deco. I don't lay around in the sand

Best, Craig

 

[ajduplessis]

Craig,

Superlyte27 is not insulting you. He is merely pointing out that you cant exceed the O2 clock if you stick to recreational diving profiles using recreational nitrox, they are designed not to put you at risk if you follow the recreational "rules". You indicate 4 dive on EAN36 to 60ft (PPO2 1.01) with 1 hour SI's. If you do these 4 dives as square profiles with a 60min BT you O2/CNS clock would only be 50%!!! I think you are adding the clock times without taking into consideration decay times during SI or the fact that the PPo2 will drop as you ascent and perform your SS.

Even if you increase depth to 90 feet (PPO2 1.4!!!!) for the same time (60min BT) your clock will only be 92% (not ideal, but still safe) !!!!!!!!!!!!!!!!!

---------- Post added May 21st, 2013 at 01:09 PM ----------

@KWS: If I am not mistaken the OTU limit per day is 1440, not 300.

The information I provided is based on a quick manual calc, I expect to be corrected if there is mistakes.

 

[scubadada]

Hi Superlyte27 and ajduplessis,

Sorry if I misinterpreted comments. Perhaps my basic problem is a misunderstanding of the NOAA oxygen exposure limits and how that exposure is captured by my Oceanic dive computers. As mentioned in previous posts, I was under the assumption the daily exposure limit is 5 hours at a pO2 of 1.0, 6 hours at 0.9, etc. I believe that's how it is reflected by my computers.

You learn things every day, thanks

 

[ajduplessis]

You are correct in that the single exposure @ PPO2 1.0 relates to 5 hours. But there is decay over time, thus this time accumulated during the "pressure" portion of the dive will come down (decay) as you ascent and surface. Remember that there are single exposure times and also daily exposure (multi dive - OTU). The agencies don't cover these topics in depth during Nitrox courses as they do in an advanced nitrox/deco course. I believe the reason could be that if you stick to the recreational parameters for nitrox diving that you will always be within the NOAA limits, thus only the focus on PP02/depth.