How much Nitrox is too much?

[Doc Intrepid]

You might want to think about getting (even just borrowing) a computer that tracks your O2 exposure so you can see what it actually is. Unless you're diving square profiles, you're probably not coming anywhere near the daily O2 limits.

Bingo.

As an "instructor and dive guide" you are not likely to be diving square profiles exclusively. Your profiles are probably far more "sawtooth-shaped" than square.

Terry's advice is sound - get a computer that tracks O2 exposure at real-time depth and time increments (including SI), to get a more valid idea of your total O2 exposure over a 'multi-dive per multi-day' period.

As James describes above, I suspect your actual exposures are considerably lower than you expect. And as b1gcountry notes, actual long-term exposures documented by the WKPP suggest that the currently established theoretical limits may be considerably more conservative than most divers realize.

I suspect you're nowhere near exceeding what your body can tolerate, but in any case, the first thing to do is get valid data - verify your actual O2 exposures using a computer rather than trying to estimate based on gross time and depth records.

FWIW.

Doc

 

[Mr Carcharodon]

The established table is based on the idea that someone can safely breathe pure oxygen (at the surface) for an entire day. Within any 24 hour period, you don't want to exceed 1440 (i.e. 24*60).

The NOAA Diving Manual puts a limit of a 300 minute exposure at 1 ATA within a 24 hour period. The pressure at which there is no limit is somewhere around 0.5 ATA (see E. Baker's paper on Oxygen Toxicity Calculations). Of course NOAA is probably being conservative, but I do not what to find out.

 

[Blackwood]

The NOAA Diving Manual puts a limit of a 300 minute exposure at 1 ATA within a 24 hour period. The pressure at which there is no limit is somewhere around 0.5 ATA (see E. Baker's paper on Oxygen Toxicity Calculations). Of course NOAA is probably being conservative, but I do not what to find out.

That 300 minute exposure relates to CNS, not OTU.

As FDOG noted, the NOAA REPEX table lists 850 as the limit. The US Navy table (I believe, don't have it handy) lists 1440 as the limit.

 

[Selachimorpha]

Thanks for all the replies guys, I was thinking in terms of OTUs. Yes you are very correct about the profiles not being square, especially here in the northern red sea, where pretty much every dive site extends from just below the surface to anything up to about 800 meters at our deepest walls, which lends itself ideally to multi-level profiles. You can spend the whole dive at 30 meters or your whole dive at 5 meters, but most of the dives are best with a combination of depths to explore the reef fully. So I never spend much time at the deepest portion of the dive, unless I am doing wreck dives.

I am not overly concerned about the effects of this type of diving in terms of oxygen, was just curious about the responses, some very nice information presented here. I think I may borrow a computer from the dive centre for the week and leave it in 21%, then switch mine to 32% and see what it has to say about the OTUs.

 

[imwright1985]

that would be the easiest way to do it since we dont dive squarish profiles too often. If you didnt have access to a 2nd comp im sure you can find a program or find the math out for OTU and plug it all in that way to see where your at.

 

[b1gcountry]

Since the limits for OTUs are linear, you can also just take your average depth, convert to ata, and multiply by time and O2% to get the number of OTUs from any given dive.

eg: 60 min at 33' avg diving 25% = 2ata * 25% * 60 min = 30 OTUs.