NDL or O2 limit

[Wookie]

For once I disagree with Wookie!

If you are diving 32%,using Al 80 tanks,not going beyond a pO2 of 1.4 (111feet) and staying out of deco it is pretty much impossible to be O2 limited. I tested this pretty extensively on V-planner and could not get O2 limited even doing 12 dives a day.

O2 limit at a pO2 of 1.4 is 180 minutes a day. Over 5 dives thats 36 minutes at 111 feet per dive ,thats WAY over NDL's. (The O2 contribution on the shallow part of the dive is negligible)

Diving 36% O2 limits MIGHT be a problem,but not on 32% within the above parameters.

Following NOAA guidelines O2 loading from a dive just disappears abruptly at 24 hours.Obviously that does not reflect reality but O2 loading over multiple days is only going to be a problem with technical dives and/or high O2 mixes.

Ian, you are a tech diver, therefore calculate your CNS O2 percentage and your OTU's for any particular dive. I assumed (by the nature of the OP's question and the fact that this is in the basic SCUBA discussion forums) that the OP will not be calculating his oxygen exposure, but will be relying on a computer to do it for him. You are absolutely correct, there is no real risk of over-exposure to oxygen diving NTX32 5 or 6 times per day at recreational depths as long as they are not all repetitive to 130 feet. However, recreational dive computers don't necessarily calculate O2 exposure the same way that v-planner, NOAA tables, or IANTD tables do. I'm not too sure how O2 uptake is calculated on the Pelagic or Suunto computers, but I have seen them limit a diver (a normal diver, running 40-60 min bottom times in 60-130 feet multi-level) by day 3 of a trip. I've seen it alot. I dive a Uwatec, and have NEVER seen it over about 40% CNS O2 except the one time I left it at 32% and did an hour at 180. (I was on trimix and usually put it in gauge mode, but forgot.) If you are on air diving those same profiles, even with 2 hour surface intervals, you will start to be NDL limited by dive 3 every day. I also assumed that this was the OP's first liveaboard and that he will make every dive available to him, as most new (and fanatic) divers will do.

I made some assumptions and apologize,

Frank

 

[redacted]

On my trips to the FGB diving EAN32, my dives are O2 limited by the 2nd day on my Oceanic Data +. My PPO2 rarely exceeds 1.2 but I do calculate my MOD based on 1.6 and do occasionally exceed 1.4. My older Oceanic does have a more conservative O2 algorithm than my buddy's newer Oceanic computers so he is often NDL limited while I am O2 limited. The differences are rather small and don't really limit our dives in a practical sense as we usually start our ascent at about 1000 psi in HP 100s.

 

[ianr33]

Interesting the variety of experiences people have with this. I'm convinced its impossible to exceed NOAA limits doing 5 NDL dives a day on 32% if you stay within 1.4.

With my Aeris computer the O2 loading is a complete non event,even doing repetitive hour long cave dives to around 100 feet. Frank dives a lot and has never seen his O2 loading exceed 40%. I seem to remember reading that some computers treat O2 exposure extremely conservatively if you go just the slightest bit over 1.4. Maybe that explains the differences ?