Keeping Cobra in Nitrox mode @ 21% 02 when using air?

[azstinger11]

Thanks everyone for clarifying. That instructor gave some other "interesting" advice. Luckily I wasn't his student, he just saw my computer and made that comment.

 

[USN Ras]

Worth noting that if you dig into your manual (at least on my Cobra II) that Suunto includes a 1% safety margin built into the NITROX mode which changes things a bit. Basically, for EAN32, it computes as EAN33. Which makes me wonder if the air mode is calculating the same way at 22%?

 

[Bubblesong]

Worth noting that if you dig into your manual (at least on my Cobra II) that Suunto includes a 1% safety margin built into the NITROX mode which changes things a bit. Basically, for EAN32, it computes as EAN33. Which makes me wonder if the air mode is calculating the same way at 22%?

Does it include a safety margin on the depth as well? Reducing how deep you can go on that same Nitrox?

 

[tursiops]

Does it include a safety margin on the depth as well? Reducing how deep you can go on that same Nitrox?

Yes, according to some other threads, which I cannot find right now.

Added later, after post #15: I suspect those "other threads" might be wrong, but maybe not. If Suunto is trying to protect you from too much oxygen by adding a percent to what you say is the percentage, then adding a percent so your MOD is a bit shallower would be a consistent protection. Should be easy to tell if you have a Suunto: in plan mode, what is the MOD for 32%? if it says 111 ft, it is not adding a percent, If it says 106 ft , it IS adding a percent. None of this adding-a-percent stuff affects the nitrogen uptake/offgas calculations, so NDLs should be unaffected.

 

[tursiops]

Worth noting that if you dig into your manual (at least on my Cobra II) that Suunto includes a 1% safety margin built into the NITROX mode which changes things a bit. Basically, for EAN32, it computes as EAN33. Which makes me wonder if the air mode is calculating the same way at 22%?

I'm not sure this is true. What the manual says is: "As a safety precaution, the oxygen calculations in the computer are made with an oxygen percentage of 1% + set O2%." But it is referring to oxygen limits, as in OTUs. In the manual, appendix 10.3, under Oxygen Exposure, it explains more fully.

 

[GreggS]

We have two identical Suunto DC.
Monday, I dove air the two morning dives, rested7 hours, then Two night dives.
One Suunto, set to 21% Nitrox, (air) for morning dives, easily reset to 32% Nitrox.
The other was set to air for morning and I couldn't reset to Nitrox for evening. 24 hours after dives, I was able to reset preferences to 21% Nitrox for this other computer, and that is how I will leave them.

This the only reason to keep a Suunto in Nitrox mode all the time. They will allow you to change the Nitrox mix but will not allow you to change modes within 24 hours of the last dive. There is absolutely no difference in air mode vs. Nitrox 21%.

I keep mine in Nitrox mode at all times.

 

[northernone]

Same NDL times on 21% nitrox or air mode for me on the Suunto Zoop.

It is convenient to leave it on 21% nitrox so you don't get locked out if you need to switch to nitrox.

It since died unpredictably and I lost a couple hundred dives so I'm not a fan of them. (Though I could have paper logged and the loss was my own doing)

 

[USN Ras]

Yes, according to some other threads, which I cannot find right now.

Added later, after post #15: I suspect those "other threads" might be wrong, but maybe not. If Suunto is trying to protect you from too much oxygen by adding a percent to what you say is the percentage, then adding a percent so your MOD is a bit shallower would be a consistent protection. Should be easy to tell if you have a Suunto: in plan mode, what is the MOD for 32%? if it says 111 ft, it is not adding a percent, If it says 106 ft , it IS adding a percent. None of this adding-a-percent stuff affects the nitrogen uptake/offgas calculations, so NDLs should be unaffected.

Yes, if set to 32%, MOD is listed at 106 ft, 31% shows 111 MOD.

 

[mddolson]

I used my Cobra in nitrox mode 21% with air for the reason mentioned above. In the original model it would lock you out 24 hrs, changing modes after a Nitrox dive.

 

[GloryDayz]

Thanks for the tips folks, my new (used) Cobra-1s are set to 21% Nitrox as we prepare to go to Coz and get Nitrox certified.