Nitrox as air? Anyone do this?

[oly5050user]

Not a good idea....statitics wise no safer than putting correct mix in computer. You will lose out on the shorter surface intervals afforded by nitrox, and how will you keep track of O2 exposure! and any mod warning your computer may offer. if you really want to do this put computer in nitrox mode with 21% mix, but I would not recommend it.

 

[tursiops]

I think that might be their point. It doesn't matter.


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I guess I was trying to be too subtle...
I think the statement "It's interesting to see the difference between the two computers. (Especially the ascent rate indicator.)" is complete nonsense. Yes, the computers will be different if one is on air and the other on Nitrox.....but the ascent rate indicator only knows about depth changes per minute....and has no idea what the gas mixes are. I don't know if boat sju had something clever in mind, or was just blowing smoke for fun. I suspect the latter.

 

[HungoverDiver]

if you really want to do this put computer in nitrox mode with 21% mix, but I would not recommend it.

That has all the same disadvantages... Nitrox mode with 21% is the same as putting it on air.


Sent from my iPhone using Tapatalk

 

[boat sju]

Relax tursiops. Sorry, I got a bit off topic there and wasn't being clear. What I was talking about was the difference between the ascent rates of the computer that's in my bc pocket, which is remaining fairly stable on my hip, vs. the one on my arm and being raised to eye level during ascents. Pocket computer ascent rate looks good while the one on my arm usually reads "fast". My other post did make me sound like a moron though.

 

[oly5050user]

That has all the same disadvantages... Nitrox mode with 21% is the same as putting it on air.


Sent from my iPhone using Tapatalk

you are wrong..this way computer keeps track of your O2 exposure, so if you want to go to a nitrox mix of on next dive, let's say 32% it would be a closer measurement of you O2 clock

 

[tursiops]

Relax tursiops. Sorry, I got a bit off topic there and wasn't being clear. What I was talking about was the difference between the ascent rates of the computer that's in my bc pocket, which is remaining fairly stable on my hip, vs. the one on my arm and being raised to eye level during ascents. Pocket computer ascent rate looks good while the one on my arm usually reads "fast". My other post did make me sound like a moron though.

LOL - Got it.
I wear both on my arm (one on each) so they both show "fast" now and then.....

 

[HungoverDiver]

you are wrong..this way computer keeps track of your O2 exposure, so if you want to go to a nitrox mix of on next dive, let's say 32% it would be accurate measurement of you O2 clock

That doesn't make any sense. Maybe we are talking about two different scenarios (and I'm assuming recreational scenario)

Your O2 clock is dependent on time and PO2:

[TABLE="width: 450"]
[TR]
[TD="class: backgrnd_lightblue, colspan: 3, align: center"]NOAA PO2 and Exposure Time Limits for Working Divers[/TD]
[/TR]
[TR]
[TD="class: image_caption, width: 150, align: center"]Oxygen Partial Pressure (PO2) in ATA[/TD]
[TD="class: image_caption, width: 150, align: center"]Maximum Duration for Single Exposure in Minutes[/TD]
[TD="class: image_caption, width: 150, align: center"]Maximum Total Duration/24 Hr. Day in Minutes[/TD]
[/TR]
[TR]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]1.6[/FONT][/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]45[/FONT][/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]150[/FONT][/TD]
[/TR]
[TR]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]1.5[/FONT][/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]120[/FONT][/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]180[/FONT][/TD]
[/TR]
[TR]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]1.4[/FONT][/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]150[/FONT][/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]180[/FONT][/TD]
[/TR]
[TR]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]1.3[/FONT][/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]180[/FONT][/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]210[/FONT][/TD]
[/TR]
[TR]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]1.2[/FONT][/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]210[/FONT][/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]240[/FONT][/TD]
[/TR]
[TR]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]1.1[/FONT][/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]240[/FONT][/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]270[/FONT][/TD]
[/TR]
[TR]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]1.0[/FONT][/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]300[/FONT][/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"][FONT=Verdana, Arial, Helvetica]300[/FONT][/TD]
[/TR]
[/TABLE]

If you are diving EAN32 and set your computer as such, it will track your O2 exposure as a function of time and PO2, which is a function of depth. Say you keep PO2 around 1.2, you get 210 minutes/day, which 3.5 hours of bottom time, which is pretty reasonable even on a liveaboard. If you do the same dive, but set your computer to EAN21, then you may have activated the clock function, but it isn't actually calculating anything useful, since it will inaccurately calculate your PO2 across your dive profile (since you are breathing EAN32). And this will underestimate your total O2 exposure.

Now if you are actually dive air, and you want to clock your O2 exposure, you can set your computer to EAN21, but you'd need to reach a PO2=1.0 to even be on the chart. On air that's 4.7 ATM which is outside recreational limits. You also get 5 hours/day at PO2 = 1.0. And that pressure now you are working against NDL, so you'd have nearly a negligible time added to your O2 clock assuming you remain with rec limits.

This is why every dive computer I know of doesn't calculate O2 clock when set to air.

Perhaps I'm missing something, but what advantage would you have for setting your computer to EAN21 when diving air?

 

[Storker]

what advantage would you have for setting your computer to EAN21 when diving air?

Fewer button presses to set your mix to 21% if you dive both air and nitrox on the same trip?

Also, some PDCs, like mine, revert to 21% a few hours after setting the mix. So "setting my computer to EAN21" for the first dive of the day requires absolutely zero button presses, while setting my computer to air requires me to change from nitrox mode to air mode.

 

[rhwestfall]

Perhaps I'm missing something, but what advantage would you have for setting your computer to EAN21 when diving air?

Subsequent dives on other mixes.....

 

[oly5050user]

That doesn't make any sense. Maybe we are talking about two different scenarios (and I'm assuming recreational scenario)

Your O2 clock is dependent on time and PO2:

[TABLE="width: 450"]
[TR]
[TD="class: backgrnd_lightblue, colspan: 3, align: center"]NOAA PO2 and Exposure Time Limits for Working Divers[/TD]
[/TR]
[TR]
[TD="class: image_caption, width: 150, align: center"]Oxygen Partial Pressure (PO2) in ATA[/TD]
[TD="class: image_caption, width: 150, align: center"]Maximum Duration for Single Exposure in Minutes[/TD]
[TD="class: image_caption, width: 150, align: center"]Maximum Total Duration/24 Hr. Day in Minutes[/TD]
[/TR]
[TR]
[TD="width: 150, bgcolor: #ffffff, align: center"]1.6[/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"]45[/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"]150[/TD]
[/TR]
[TR]
[TD="width: 150, bgcolor: #ffffff, align: center"]1.5[/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"]120[/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"]180[/TD]
[/TR]
[TR]
[TD="width: 150, bgcolor: #ffffff, align: center"]1.4[/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"]150[/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"]180[/TD]
[/TR]
[TR]
[TD="width: 150, bgcolor: #ffffff, align: center"]1.3[/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"]180[/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"]210[/TD]
[/TR]
[TR]
[TD="width: 150, bgcolor: #ffffff, align: center"]1.2[/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"]210[/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"]240[/TD]
[/TR]
[TR]
[TD="width: 150, bgcolor: #ffffff, align: center"]1.1[/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"]240[/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"]270[/TD]
[/TR]
[TR]
[TD="width: 150, bgcolor: #ffffff, align: center"]1.0[/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"]300[/TD]
[TD="width: 150, bgcolor: #ffffff, align: center"]300[/TD]
[/TR]
[/TABLE]

If you are diving EAN32 and set your computer as such, it will track your O2 exposure as a function of time and PO2, which is a function of depth. Say you keep PO2 around 1.2, you get 210 minutes/day, which 3.5 hours of bottom time, which is pretty reasonable even on a liveaboard. If you do the same dive, but set your computer to EAN21, then you may have activated the clock function, but it isn't actually calculating anything useful, since it will inaccurately calculate your PO2 across your dive profile (since you are breathing EAN32). And this will underestimate your total O2 exposure.

Now if you are actually dive air, and you want to clock your O2 exposure, you can set your computer to EAN21, but you'd need to reach a PO2=1.0 to even be on the chart. On air that's 4.7 ATM which is outside recreational limits. You also get 5 hours/day at PO2 = 1.0. And that pressure now you are working against NDL, so you'd have nearly a negligible time added to your O2 clock assuming you remain with rec limits.

This is why every dive computer I know of doesn't calculate O2 clock when set to air.

Perhaps I'm missing something, but what advantage would you have for setting your computer to EAN21 when diving air?

True you will not get accurate measurement of o2 exposure. But at least there would be some measurement especially if using nitrox on subsequent dives. I would again suggest just entering correct mix in computer and stay within Ndl limits.