Oceanic Atom 2.0 Gas Switching from Nitrox on first dive to Gas

[SnorkleFL]

I just purchased two Atom 2.0 wrist computers for me and my wife to dive together with. We dove 32% Nitrox mix on the first dive. It would not let us switch to air on the second dive. The manual seemed to indicate that you could not set the second gas to a lower FO2 setting for the users second dive. I asked the dive instructor if there was any reason that you should not use air after using Nitrox on the first dive and he said no. Is there a way to turn off this lock that will not let you use a lower fraction of oxygen for your second dive?

 

[ronbeau]

I just purchased two Atom 2.0 wrist computers for me and my wife to dive together with. We dove 32% Nitrox mix on the first dive. It would not let us switch to air on the second dive. The manual seemed to indicate that you could not set the second gas to a lower FO2 setting for the users second dive. I asked the dive instructor if there was any reason that you should not use air after using Nitrox on the first dive and he said no. Is there a way to turn off this lock that will not let you use a lower fraction of oxygen for your second dive?

The NAUI Nitrox course that I took said that it is ill-advised to go from a richer to a leaner mix on subsequent dives within the same day.

In other words, if your first dive was done using EAN32 the second dive should be done using EAN32 or EAN36 but not anything lower than EAN32 (such as air).

Most compter manufacturer's won't let you switch the computer from Nitrox to air within a 24 hour period.

Your only option within the same24 hour period is to set it for EAN21 which is effectively air. I only do this when diving the following day but less than 24 hours from the completion of the last dive of the previous day. I never switch to a leaner mixture on second or subsequent dives within the same day.

 

[Daxter]

I sent you a PM I think will help you out. You are not setting up mutipule gases at the start of your first dive. Before your second dive go to where you set the Nitrox % on your first dive and increase the % past the 100 mark and the next number will start over at 21%(air) after your surface interval. Have not tried to dive nitrox then air but for any dive after your surface interval it should let you set it to a lower %. Reason that it should let you do this if your first dive is checked at 34% and you check the next tank for your second dive and it happens to be 32% the watch should let you adjust it.

 

[Daxter]

Now that I think about it I did do this in Coz last month. I was set up for first tank air and second tank 36%. We had a norte blow out 2 days so on one of the following days we did 4 tanks, two in the morning and two later so the watch will go from air to nitrox to air to nitrox. As stated above you just use 21% for air.

 

[yyidus]

I own a VT3, but I assume it's the same concept:
You can't go back to 'air' on a dive within 24hrs of a Nitrox dive. You CAN go to '21% EAN' which is the same as air, but leaves it computing your PO2. Simply keep raising the oxygen level to 100%, and then it will wrap around to 21%. Also, unless you set it NOT to default, if you do not go to EAN21 on your next dive, it will instead go into this funky mode when it assumes you have 78% nitrogen and 50% oxygen in your tank -- i.e. conservative on both nitrogen loading and oxygen tox. So be sure to set it back to EAN21 if you're going to use air.

I think what you're confusing about 'not going to a lower EAN' is for multi-tank diving. If you have multiple tanks set up on a dive (each one with its own transmitter) then your first tank has to be a lower %O2 than the second, and onwards. This doesn't affect multiple-dives. Just multiple tanks (and from reading your posting, it doesn't sound like you're using multiple tanks).

 

[SnorkleFL]

That may be it. The manual reads tank 1 and tank 2 etc... I guess you would just reset it after every dive on Tank 1. I did not try that. The manual is a little hard to understand. Thanks for the response.

 

[fppf]

The 3 different tank settings are for advanced deco diving. You can program 3 different gas mixtures for bottom, travel, and deco gas.

The reason you can not set the computer back to "air" is because it is running your Oxygen window calculation. You need to wait 24 hrs to reset your oxygen window just like your nitrogen window before you can set it back to air. When diving Nitrox and air within 24 hrs just set the PO2 to 21%, which is air. The difference is the computer will keep track of your oxygen window for any future nitrox dives.

If your only using 1 tank, and thus 1 gas mixture you would only set "tank 1" setting.

 

[SnorkleFL]

Thank you all for your assistance. I thought Tanks 2 and 3 were for dives 2 and 3. Here is the response from Oceanic:

Thank you for your purchase of the Oceanic Atom 2.0 dive computer. The
gas switching protocol for the Atom 2.0 will only allow you to go to
progressively richer O2 mixes, but will not let you go from a richer mix
to a leaner mix. This is because the gas switching feature was
originally designed for use by technical divers, who typically go from
their main gas source to a secondary gas source with a richer mix as
they ascend, and finally to a third gas source with a high O2 mix at the
end of the dive, in shallow water, to accelerate the offgassing of
nitrogen. Unfortunately, there is no way to circumvent this feature.

However, this limitation only applies when you are gas switching from
one gas supply to another during a single dive. If you are using
different mixes on successive dives, you can get around this restriction
by not performing a gas switch, but rather by simply changing the FO2 of
your primary gas during your surface interval between dives. If you plan
to use Nitrox 32% on Dive #1, you can program that mix into GAS 1 using
the SET F menu. Once you complete Dive #1, during your surface interval
you can go back into SET 1 and reset GAS 1 from 32% to AIR. There is no
restriction against doing this, and your no-deco times for Dive #2 will
be adjusted to account for your residual nitrogen times from Dive #1, as
well as for the new, leaner gas mix. Details on changing the FO2
settings on your Atom 2.0 computers can be found on pages 48-52 of the
Atom 2.0 Operating Manual.

 

[Dan Watkins]

Thank you all for your assistance. I thought Tanks 2 and 3 were for dives 2 and 3. Here is the response from Oceanic:

Thank you for your purchase of the Oceanic Atom 2.0 dive computer. The
gas switching protocol for the Atom 2.0 will only allow you to go to
progressively richer O2 mixes, but will not let you go from a richer mix
to a leaner mix. This is because the gas switching feature was
originally designed for use by technical divers, who typically go from
their main gas source to a secondary gas source with a richer mix as
they ascend, and finally to a third gas source with a high O2 mix at the
end of the dive, in shallow water, to accelerate the offgassing of
nitrogen. Unfortunately, there is no way to circumvent this feature.

While I understand the reasoning, there is an instance where one may want to go from rich to lean. Say you are diving a single tank of EAN32 and you have pony bottle with just air as a bail out bottle. Since it is just a bail out bottle, you may not want to pay for a nitrox fill. Now if for some reason you need to switch to the bail out bottle, and ascend, I would want to be able to switch to the air mix and have the computer calculate my nitrogen loading using the switch to the FO2 of 21%.

I was thinking about this and while there is no way to circumvent this feature, I think I have a work-around that will let you do it anway...

You set GAS1 to Air, and GAS2 to your EAN32. If you are using a transmitter, make sure you punch in your main transmitter S/N to GAS2 instead of GAS1.

The computer automatically makes you start out with GAS1, but after you desend 5 feet and the computer goes into normal dive mode, immediatly do a gas switch to GAS2 (which is your richer EAN32 main tank), and simply dive on GAS2. If you had to later switch to your bail out air mix, you just switch back to GAS1. It is working the gas switches backwards, but I think this would work. I have yet to try it.

And SnorkleFL, back to your original question, I believe you already have your answer, GAS2 and 3 are for switching, not subsequent dives. With just one tank you just use GAS1 only, and you can set it to any FO2 you want for subsequent dives.

 

[Doug Krause]

That will work Dan.