Nitrox discussion (Split from "Reasons not to use Enriched air" thread in Basic)

[ianr33]

). The most 1.6 ata bottom time you could squeeze out in 24 hours is 57 min. The 24 exposure limit is 150 minutes. So what is it that you are talking about?
.

Hate to admit it but you're correct on that

I'm still not going to dive 32% to 130 though. IMHO it would be safer to dive 28% and do a few minutes deco.

Thats the way I would risk manage a 130 foot dive. (Well actually I would do it on air with O2 for deco but thats another thread)

 

[Thalassamania]

Hate to admit it but you're correct on that

I'm still not going to dive 32% to 130 though.

Believe me, I'm not going to grab you by the scruff of the neck and drag you down to 1.6 on NOAA-32. That's your (and everybody's) personal decision. But making such a dive does not make one a "dangerous fool." I dare say I know many risk adverse divers who would choose diving to 130 on 32 as the less risky option.

 

[dumpsterDiver]

The arguement made for 1.6 exposure at 130 (with 32%) was that there was a problem with the oxygen clock for 3 repet dives.. Thall.. shows that the no-deco limits will be the governing constraint.

However, if someone were to use a "rich mix" at a shallower depth (say using 40% at 100 ft) it would be closer to getting the diver into oxygen trouble rather than deco, especially if the SI were an hour or so.. yes?

 

[Thalassamania]

Yes, and if I used 100% at 18 feet ...

 

[dumpsterDiver]

Sorry I guess it was pretty obvious

 

[almitywife]

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A ScubaBoard Staff Message...

Split from “Reasons not to use Enriched air” thread in Basic Scuba Forum



G’day divers

This is a copied & cleaned up thread thread that was in Basic Scuba and placed it in this forum for further discussion & education. I think i have cleaned it up but if there is anything glaring i have missed please report it or pm me to look it over.

Please note the rules for the new Advance Forum and keep it on topic, relevant and workplace friendly. Name calling is still against TOS and posts will be deleted.

alot of work went into this thread & it has alot of good information and members have reacted positively to it - please use it as an example to mentor and learn is all i ask.

Many thanks

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[Bottomfeeder Brodie]

great job of editing...all the irrelavent opinions are all gone

 

[ronbeau]

Most seizures last two to three minutes and resolve, but there is a period of reduced awareness and confusion afterward which varies tremendously in time. If the stimulus causing the seizure is not removed, you can have repetitive or continuous seizures, known as status epilepticus. A person who is actively seizing probably has a closed glottis, and should not be moved upward in the water column until the active convulsion has ended. Subsequent to that, it would be desirable to move them upward as quickly as is safe, to reduce the ppO2.

Few people have survived oxygen toxicity seizures underwater. It requires the immediate presence of a buddy who recognizes the problem and takes precisely the right actions immediately.

That said, oxygen toxicity seizures are extremely unlikely if O2 concentrations are kept below 1.4 ATA. It's easy to do the vast majority of dives that recreational divers will do on 32% and respect that limit. One might lose out on a few, deeper dives. Use of a standard mix in this way also permits keeping one's computer (or one's mental computations) set the same way all the time. Cumulative OTUs are not much of a concern unless one is doing multiple deep or long dives on multiple days.

I do all my diving on 32% if I can (which I can at home). But I pay a blanket fee for a year's NITROX which is an extraordinary deal, so it makes it very reasonable financially for me. I do dive 32% on trips if I can, although I have shaken my head at myself for paying the extra for NITROX to do 15 foot deep cave dives in Mexico

So, to answer the OP, there are disadvantages to diving NITROX all the time if a) you want to do particularly deep dives; b) you are diving multiple times over multiple days, or c) if it substantially increases your cost for shallow dives where the increased bottom time is irrelevant.

Lynn, I am confused by the portion of your post highlighted above in bold text. Your posts are always well thought out and well written so I must be misinterpreting something. Assuming the OP is staying well within the MOD for the mix I would think NITROX would be ideal for the highlighted activity.

What am I missing?

 

[TSandM]

Really, the only way you can run into cumulative oxygen toxicity is by diving a lot at your max ppO2 over multiple days. I haven't sat down to calculate exactly how often and how long you would have to dive to run up your OTUs, but I remember having done so at one point, and it is possible to push into levels that aren't recommended.

 

[ronbeau]

Really, the only way you can run into cumulative oxygen toxicity is by diving a lot at your max ppO2 over multiple days. I haven't sat down to calculate exactly how often and how long you would have to dive to run up your OTUs, but I remember having done so at one point, and it is possible to push into levels that aren't recommended.

Thank you for the clarification.

I think I found the OTU information you mentioned in my "NAUI NITROX Diver" textbook.

From page 39 of "NAUI NITROX Diver"

In all cases, a recreational diver's single dive time will be limited by the no-decompression limits as well as the diver's gas supply.
These will be less than the NOAA single dive oxygen exposure limit, and the controlling limit, if it arises at all, would be the 24-hour oxygen exposure limit.
Even then, only the most dedicated and determined NITROX diver would possibly exceed the 24-hour limit.
(A diver using EAN 36 and diving to the maximum dive times allowed by the NAUI EAN 36 Dive Tables would have to perform seven square-profile dives to 27 meters (90 feet) with dive times of 50 minutes for the first dive and 24 minutes for each repetitive dive with a minimum surface interval of 2 hours and 39 minutes between each dive.)