Atom 2.0 FO2 50% default purpose

[Eric S'pore]

I just got my atom 2.0 one week ago. No dive yet.
Instructions are quite clear eace2:except one point: what is the intention behind this "FO2 50% default" function.
When FO2 50% default is set ON, and FO2 gas1 set for a numerical value (let say 32%),further dives will be calculated based on 50% O2 for oxygen and 21%O2=79%Nitrogen for Nitrogen calculation.

What is the benefit coming from this Oxygen penalty(OTU and PO2) for the following dives?
When and why should I choose this option ?

Thanks in advance for your kind support.

 

[TheTrickster]

The reason for defaulting to 50%, is purely a safety feature. It is there, so if you forget to test your gas on a repetitive dive and set your Atom to the right mix, it will become very conservative and stop you from going very deep - beeping at you, giving you pp02 warnings...

An example would be:

First dive on 32% - MOD (@1.4) = 33.7m
Second dive on 38% - MOD (@1.4) = 26.8m

If you didn't set your ATOM2 to reset to 50% after each dive and you forgot to set the mix to 38%, it would think you are still on 32% - quite happily letting you go to 33mtrs, without warning and letting you have a oxtox/cns attack...

 

[Doug Krause]

Let me take this a step further...

The 50% ON setting actually defaults to 50% O2, 79% Nitrogen - in the event that you switch to anything between 21-50% without telling the computer what you're doing.

I dive mine with it OFF, as I suspect most do. I don't have a problem with leaving it ON in the event that I'll forget to set my mix - I never do. It is a good backup - but, remember that a "new dive" is defined as one that begins after a 10 minute transition period on the surface. With the setting ON - should you begin a dive, then surface to help a buddy, grab more weight from the boat, debrief students, etc - then, descend again... the computer will default to 50/79.

Hope that helps,

 

[DiveMaven]

Nice to hear that you turn yours off too, Doug! We turned ours off the minute we started diving nitrox.

 

[H2Andy]

you will find this feature in many computers

as stated, it's a safety feature to make sure that (assuming you are certified to and dive up to 40% Nitrox) and you forget to set your O2 setting for the second dive after diving enriched air, you don't accidentally exceed your 1.4 or 1.6 PO2 with whatever mix you are diving

in other words, instead of risking you getting ox toxed by diving too deep for the mix you forgot to set (and that the computer doesn't know what it is), it will set your mix to 50% to keep you shallow and away from ox tox dangers

of course, if you dive with mixes over 40% that feature won't help you much, but that's advanced nitrox territory

 

[Eric S'pore]

Thanks to all of you. F02 50% Default has no more secret.