Diving 32% Nitrox with "Air" Algorithms

[Chavodel8en]

I fully agree with you on setting dive computers to the accurate gas mix being far preferable, but setting a clock ahead is totally reasonable for the OCD among us (but in my defense I only set the time 7 minutes early, 10 minutes does seem rather excessive...).

LOL, try ~24 minutes. I kept backing up the computer as I adjusted my "I really have 10 more minutes to sleep." 24 minutes works, bc I tell myself "I really have 20 more minutes to sleep"

 

[KenGordon]

This is basic so mods feel free to delete.

When diving CCR (very new to me) I keep my PPO2 at 1.3 but my off board backup computer is set to 1.2. Which means one computer is essentially doing what the OP mentions for deco and O2 calculations......

On CCR you do care about oxygen exposure so this actually matters. You also REALLY care about bailout TTS (in the end it is what limits dive times).

For the OP, the second point applies to OC. If you lie to your computer this way you get shorter NDL and longer stops. If you over run NDL for whatever reason then you will have longer stops than necessary and may run low on gas.

I have seen this happen with a pair of divers, one much less experienced, both on 32% but one with the computer set to 32 and one air. Fortunately the stops were on the shot line and so there were plenty of people to donate gas.

 

[KenGordon]

Well if I set my offload to 1.3 I'm lying to it as well because I won't be 1.3 the entire time especially if I bail out.

The controller will be doing its best to match 1.3. They turn out to be quite good at that, if you set your bailout to match then the NDL/stops do match well.

When you bailout you need to tell your backup you have bailed out too, otherwise your stops will probably be too short.

 

[shark_za]

My only comment on this is the risk for O2 issues are in the single figure % ranges while NDL limits can be closer to the 90% ranges.
You are always pushing the NDL the longer you dive.
You ignore the O2 risks because they are so low like when diving with Air .
Knowing they are there is important but its a non event.
When doing a few hours deco at high PPO2 you need to really pay attention, this is when the O2 risks are near or over the 100% mark.

 

[100days-a-year]

Basically, your average basic trained scuba diver isn't going to run into issues with Oxtox or 02 clock doing basic dives, basically.

I did 2hr SI for the most part and did a dive every two hours from dawn to dusk most of the days I was diving for quite a few years and often using nitrox and an EDGE. Thousands of dives and my buddies did the same and some had been doing it since before nitrox or computers.
They key seemed to be using a lean mixture for the depth and not doing super long dives, which wouldn't then be basic.

 

[Ken Reid]

In the interest of adding "conservatism" to our diving, my wife and I when diving the tropics (mostly shore diving on Bonaire ) dive 32% Nitrox. But to increase safety, we still keep our computers set to Air. We fully understand and adhere to the 111ft MOD for 32% and we even augment that by agreeing to stay inside of 100ft max depth as a rule. We just keep our computers set to AIR to add in some more "conservatism" . We then plan and dive the AIR algorithms ....... and NEVER go below the MOD for 32% Nitrox.

Anyone else do this........or does anyone have a reason why not to do this?

This was pretty common practice years ago. I remember it being mentioned in the training vids for SSI. Pretty sure it was also mentioned in the old PADI and IANTD vids too but don't quote me on that one. For your average open water diver not getting into deeper depths and multiple dive days, I can see a case being made for it but....
With technology improvements the potential benefits of such things are questionable. Most computers allow you to set the conservatism. If you want to be more conservative, change the settings. You now are coving all basis and you have an accurate record of your dive.

 

[BoltSnap]

Plenty of dc have no conservatism setting!!

Which ones? Modern ones?

 

[tursiops]

Plenty of dc have no conservatism setting!!

Which ones? Modern ones?

Some of the older computers did not have a labeled conservatism setting. Instead they let you set the altitude to "one or two mountains" to add a cushion to NDLs.

 

[scubadada]

Ha, Oceanic computers give you one mountain, 3001-4000 ft.

 

[BoltSnap]

Some of the older computers did not have a labeled conservatism setting. Instead they let you set the altitude to "one or two mountains" to add a cushion to NDLs.

Thank you for reminding me. Yes, I think like the early Suunto "Solution" DC but that's their way of adding conservatism which means they had a way to add conservatism.

This was in early to mid 90's, not terribly relevant to today, 30 years later. I doubt that there are many of them in operation/use today.