Nitrox Question

[jrwalsh20]

BTW, Laurie; the best manual for really understanding Nitrox, IMO, is the TDI Nitrox manual. Not the advanced Nitrox, but the TDI basic Nitrox. If you can work your way through that, and do the tests without consulting the book, you will understand Nitrox.QUOTE]


Couldn't agree more, i used this exact manual for my Nitrox last summer, it made it very easy.

 

[Jax]

The Oc1 has a 50% Defaut feature where, unless you turn this feature off, 10 minutes after your first nitrox dive it will set to EAN50 automatically.

Page 87 of this manual...
http://www.oceanicworldwide.com/pdf/12-2761-r02 Eng.pdf

The manual for that computer says on pg 86 that it will default to 50%. That's my guess as to what happened to you.

http://www.oceanicworldwide.com/pdf/12-2761-r02 Eng.pdf

Thank you, Tina, John;

Could someone help me understand why a computer would be designed to do that?

And once a Fraction of O2 number is set for any gas, the Air option is disabled for 24 hours? (even though one could set the FO2 to 21)

 

[bleeb]

However, on the next dive, which was in the 60-70 foot range, I noticed that the reading started climbing from 1.4 to 1.6 to 1.7, all the way to 1.81. When I saw that, I immediately went shallower and watched the gauge until it again reached 1.4.

The OP seems to be saying the reading was climbing during the dive. While it doesn't seem unusual for a particular make and model of computer to change ppO2 limits between dives, I've never heard of one that changed while the dive was under way. Also, a computer which primarily displays the ppO2 limit value seems a bit unusual. If anything, I would have thought it would display the current ppO2, which wouldn't climb without a significant depth excursion. Laurie S or any other OC1 users, what other parameter might the computer have been displaying? Every computer manufacturer seems to want to do things differently, but does the OC1 calculate it's version of O2 saturation or O2 clock as a decimal value like that? The ones I'm familiar with tend to go with percentages or minutes.

The Oc1 has a 50% Defaut feature where, unless you turn this feature off, 10 minutes after your first nitrox dive it will set to EAN50 automatically.

 

[Majickyl]

I find it a pretty stupid feature, but if I had to guess I think it is a safety feature to avoid oxygen saturation.

If you forget to change your mix, the computer assumes you are diving something rather high and doesn't let you get too deep.

My computer has the opposite feature where it will revert to air, shortening my bottom time and leading to more conservative profiles. But if I use that feature I HAVE to know my MOD, because the computer will not let me know if I'm getting past it.

Personally, I turn off the "computer knows best" features and set my mix manually before every dive.


---
Tina

 

[Jax]

The OP seems to be saying the reading was climbing during the dive. While it doesn't seem unusual for a particular make and model of computer to change ppO2 limits between dives, I've never heard of one that changed while the dive was under way. Also, a computer which primarily displays the ppO2 limit value seems a bit unusual. If anything, I would have thought it would display the current ppO2, which wouldn't climb without a significant depth excursion. Laurie S or any other OC1 users, what other parameter might the computer have been displaying? Every computer manufacturer seems to want to do things differently, but does the OC1 calculate it's version of O2 saturation or O2 clock as a decimal value like that? The ones I'm familiar with tend to go with percentages or minutes.

As I read the manual, the computer computes your current partial pressure of O2 according to the input fraction of O2 and your current depth.

If the computer defaulted to the EAN50, as it seems, then her PPO2 would rise as she descended.

 

[Majickyl]

The OP seems to be saying the reading was climbing during the dive. While it doesn't seem unusual for a particular make and model of computer to change ppO2 limits between dives, I've never heard of one that changed while the dive was under way. Also, a computer which primarily displays the ppO2 limit value seems a bit unusual. If anything, I would have thought it would display the current ppO2, which wouldn't climb without a significant depth excursion. Laurie S or any other OC1 users, what other parameter might the computer have been displaying? Every computer manufacturer seems to want to do things differently, but does the OC1 calculate it's version of O2 saturation or O2 clock as a decimal value like that? The ones I'm familiar with tend to go with percentages or minutes.

Her ppO2 was changing during the dive based on depth. Yes it would take a significant excursion at low mixes, but set at EAN50 the 10 ft between 60 and 70 is the difference between 1.4 and 1.6.

The OC1 does display ppO2 and uses a bar graph for O2 accumulation.

 

[Cave Diver]

Thank you, Tina, John;

Could someone help me understand why a computer would be designed to do that?

And once a Fraction of O2 number is set for any gas, the Air option is disabled for 24 hours? (even though one could set the FO2 to 21)

It keeps you from going too deep w/ nitrox.

If it defaulted to air and you were diving 36% and not paying attention to the setting you might end up going deep and toxing. By defaulting to 50% it forces you to stay shallower because no recreational divers are going to be on a mix that rich.

 

[Charlie99]

Several people have said the computer will default to EAN50 after 10 minutes. That's not quite correct.

It will default to 50% O2, 79% N2.

Yes, this is a physically impossible mixture, but this default mixture conservative calculations for both deco and O2 exposure.

Could someone help me understand why a computer would be designed to do that?

If you forgot to set the mix, then it's reasonable to default to a conservative mix.

 

[Majickyl]

Several people have said the computer will default to EAN50 after 10 minutes. That's not quite correct.

It will default to 50% O2, 79% N2.

Yes, this is a physically impossible mixture, but this default mixture conservative calculations for both deco and O2 exposure.

Wow, that's actually pretty cool. Conservative on both ends. I don't think that feature's as stupid as I did 10 minutes ago.

 

[CAVDVR93538]

It may sound stupid, but it is a safety feature. Many of the computers default to 50% if you change to anything other than air as your mix. This usually happens at midnight.
As a couple of the other posts indicated to make you change the setting every day for oxygen toxicity clock. The current Eanx classes have a computer version and also the place that you bought the computer from could have pointed that out to you. Maybe they did and you forgot or they didn't at all. It is good that you recognized that something wasn't right, many get complacent and just do what ever the computer says, knowledge is bliss, knowing what is happening is much, much better.
If you set it on air, it stays set. I have done this on accident by for getting to set the computer. Your habit should be to not only analyse the mix you are diving, but to also make your computer is set at the correct mix, especially if you are diving a mix greater than 21%.
Be careful!