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I thought the OP was talking about no deco dives. 32% and 1.4 ppo2 is 114 feet. The US Navy air tables give a NDL of 15 minutes at that depth. The NDL from the PADI or NAUI tables may be slightly different, but it is definitely not one hour. It would take a lot more than three no deco dives in 24 hours to reach the limit for o2 exposure with 32% nitrox. It might not even be possible.
The OP was talking about sport dives and so am I... Since you mentioned the US Navy tables, let's use them (and I'm doing this from memory and in imperial units so forgive any slop... I am sure you'll get the picture and understand my concerns).
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To return to the OP's question. Here's an example...A basic nitrox user on a liveboard fills a cylinder with EAN39 or 40 and does a mid-morning dive (11:00) to 80 to 85 feet. The EAD is about 60 feet and I think her oxygen depth would be about 1.4 bar... or close to it. She is using the US Navy tables and they give her a 60 minute bottom time within the NDL. But that's cutting it close to the NDL so she stops and sucks back surface supplied oxygen on the hang bar which sits at 15 feet. She remains there for 8 minutes.
She surfaces, has some food, play deck quoits, watches a moving and does an afternoon dive. Same mix same depth but only stays down 30 minutes.
She goes to the salon, has a chat, reads a magazine, and opts into a twilight dive with some buddies who want her to model for them while they take snaps... same reef and a similar dive to her afternoon dive but on this one, she is in the water for 40 minutes... this puts her close and so she hangs on the bar again for 10 minutes.
She has a drink, eats supper, plays guitar, sings, goes to her cabin and sleeps. So far today she has been in the water for about 130 to 140 minutes with an oxygen partial pressure of about 1.4 bar (and that's NOT taking into account her time on the hangbar breathing oxygen at about 1.45 bar). Her bottom time is close to the 24 hour limit but no cigar.
She wakes at 07:00 and decides to do a pre-breakfast dive... Because some Muppet has told her she cannot exceed NOAA's 24-hour CNS limit doing sport dives, her dive plan does not take into consideration her 24 hour CNS loading. She plans a similar dive to the one she did the previous morning except she plans only a 45 minute bottom time.
Now, I'm OK at maths and not so great with arithmetic but hasn't she just done more than 180 minutes bottom time within a 24 hour period? She did four dives... a couple of them close to the NDL but that's common. Hell, unfortunately that's normal.
My intent here is to answer the OP's question as clearly and responsibly as practical in a public forum. I'm kind of compelled to, since I work for a training agency, training divers and instructors is part of my full-time job, I have to write textbooks about this stuff and I have been teaching nitrox programs since TDI first introduced them in 94. Hell, I'm no expert. But I have done a few dives using nitrox, and think that validates my methods.
You may be comfortable ignoring the NOAA limits on your dives, but the OP did not ask about diving in a cavalier fashion. He asked a reasonable question and I think my answers have been equally reasonable.
To restate what I posted already...
I believe that many, many divers using nitrox on multi-day, multi-dive profiles come close to exceeding or in fact exceed NOAA daily limits for CNS toxicity.
I think there are many situations where the total bottom time over a 24-hour period approaches 180 minutes... the NOAA daily limit for an oxygen partial pressure of 1.5 and 1.4 bar. That's only three hours. Sport dives on live-aboards of one hour plus are the norm in my experience. Doing three in a day is not uncommon. In fact, three dives a day is conservative. Add to this the practice of hanging off the back of the boat sucking surface supplied oxygen for a few minutes after every dive and our punter is getting awfully close.
My opinion is based on observation. I am not pulling this out of a hat. High daily doses that approach NOAA's limits are real not imagined.
As an aside... basic nitrox certified divers are not restricted to 32 or 36 mixes, and in any event, it is the oxygen pressure and time of exposure that should concern us. Oxygen pressure is a function of depth and fraction of oxygen. Citing a mix without associating it to a depth and time renders the example meaningless.
I strongly suggest you do not consider half times when calculating daily limits. I can post an article I wrote covering this but it actually deals with technical not sport exposures. The tenets are the same but we will spend the next 487 posts dealing with bull****... PM me your email address.