Of course 32% is the most common but it seems 30% should be for the many systems in the 100 ft range, keeping the 02pp below the 1.4 or 1.5 range.
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Of course 32% is the most common but it seems 30% should be for the many systems in the 100 ft range, keeping the 02pp below the 1.4 or 1.5 range.
I agree,and prefer a lower mix for deeper,high flow systems. I know at one time 34% used to be banked,which always made me nervous,and I would thin it out with air. What is real scarry,when nitrox was first really introduced we used to dive Ginnie with 36% to 38%,and Ginnie used to really pump then-surprised in retrospect that we didn't have more cases of oxtox.Quote:
Originally Posted by stairman
I dive 30%. I think it is the best choice for a number of reasons.
In high flow systems like Ginnie and JB where the depth can reach 90-100ft, I think it is crucial to keep the PO's low. The extra exertion just tips the scale IMO.
When you look at studies the incidence of tox at 1.4 is very low, but at 1.2 it is significantly lower (on my iPhone so don't have the numbers, but is way lower on the curve).
The extra minute or two of deco is insignificant to me.
Here in cave country almost everyone (except Jim Wyatt, he pumps 30%) pumps 32%. I always squirt some air in before filling to bring the % down.
Well, I keep my setpoint to 1.0 for most dives and only up it on deco, does that count?
Dive safe,
Celia
i agree, 32% is definitely aggressive for a lot of the "standard" Florida caves. And for the shallower ones, it matters less anyway since the deco is less. Dropping to 30% would be really nice.
I have made a point to mention the studies and present a case to a couple of the local shops.
The response I get is, "Well everybody likes 32%, that is what they are used to.".......:smt100
Some people have actually claimed that "All of the standard Nitrox tables are for 32%":roll:
Or my favorite, "I like the extra O2 to lower my chances of getting bent." To which I always reply, "Yeah, I would much rather tox than get bent....."
Since females seem to be more susceptible to O2 hits, I always have my wife dive a 1.0 or lower on a high current, high work type of dive.Quote:
Originally Posted by amphipod06
I work at an open water shop that still teaches there are two nitrox mixes, 32% and 36%.Quote:
Originally Posted by Marc Bryan
Good Ol' NOAA I & IIQuote:
Originally Posted by Slüdge
If I dive with several stages at Devils I mix it to 29 %. It sseemed that 30 was still pushing the O2 still higher than I prefered.
Bob Klauck
If I have to do any of my reevaluation dives in Ginnie, they'll be on 30% -- helium :)
If I am doing multiple stages (therefore longer exposure to cns clock and otu's), or we have a flood (to a max depth of 110' after that I like a little HE), I cut it down to 28%.
The floods are a time when the shops should definitely cut the O2 back.
When we was at Little River last month, we had them top off with air instead of 32%. I dont like running the limits that close. I could see 30% being a good choice at JB and Ginnie as well.
I don't think it's a big deal at Ginnie, at least in the places I go. 100 ffw with 32% gives about a 1.28 PPO, which is perfectly sane.
Actually, for myself, I prefer to dive 32/30 there. No, it's not a standard gas. But so far so good :-)
I think it all depends on the amount of time your going to be in there. I just did a dive in Ginnie that went near 4hrs by the time deco was over and I ran 1.2 (approx 30%) all the way in and 1.3 (approx 32%) on the way out with pretty much everything from the catacombs out at 1.4. At the end of the dive my CNS according to the computer was 102% but when I hit deco I was less than 80 so I'm fine going over on CNS if I'm in a relaxed deco environment (sleeping in a crack in the eye).
It's all personal choices and there is a lot that factors into it and your reactions could vary from day to day. All that said, I'd go with 32 and wouldn't give it a thought if I was doing 1-1.5 hr run times two or three a day at Ginnie for a weekend.
Maybe it's "perfectly sane", but wouldn't 30% be even more so? For me the extra risk is not worth a few extra minutes of hang time.Quote:
Originally Posted by BobK
I have stated my reasons for the 30%, I am curious what yours are for the 32%.
Quote:
Originally Posted by Marc Bryan
Okay I’m going to preface this by saying Ox Tox underwater is a really really bad thing and would be worse than DCS on any day. That said…
Navy divers in water recompression treatment includes O2 exposures to just shy of 3ATA (I beleive 60 FSW is the switch but it's been a long time sense I've looked at the tables it could be deeper). Chamber rides can also hit a 2 during their runs depending on what they are treating. OTU/CNS is just like any other dive/deco table and very conservative for 99% of the population on 99% of the days they dive.
If you want to dive 30% good on you, if you want to dive 32% good on you to. I personally like higher PPO2 and lower PPN whenever possible for narcosis and deco (I don’t mind deco but if something comes up I’d rather be able to get out sooner). I’m even known to throw some HE in there even on shallow stuff just to make work of breathing easier among other things.
Most fill stations bank 32%, but most will also pump whatever mix you want. FYI, EE banks 30%, with 30% helium.Quote:
Originally Posted by Marc Bryan
It is up to you do decide what mix is right for you. Until the majority of divers request 30%, the fill stations will bank 32%.
Dives are getting longer => percentages getting lower.
Marc,Quote:
Originally Posted by Marc Bryan
There is one shop (really close to you) where the analyzer almost always says 31 percent on my tanks when I check it, which I think is good.
Well then, I suppose 21% is even more sane then 30%. Probably could push it to 18%, then I bet your risk of Ox Tox would be virtually zero.Quote:
Originally Posted by Marc Bryan
OTOH, Given the number of dives in Ginnies over the years (10s of thousands ?) and the number of Ox Tox incidents with diver's using 32% or greater (I don't know of any, I suppose there has to be at least a few), I don't see what the issue is.
As others have said, it's really a personal choice on balancing deco time with "risk of Ox Tox". I don't personally see any significant risk at PPO's of 1.4 and below for the amount of dive time I do at Ginnie. If you're going for all day dives lowering your PPO is probably a good idea. It's all part of planning the dive.
There was at least one, 3/9/02. It is on the IUCRR website.Quote:
Originally Posted by BobK
I have a fill station at home. I fill for myself, a few friends and students. I have banked and dive EAN30 for a long time now in order to keep the PPO2 lower.Quote:
Originally Posted by stairman
How about for dives where you work very hard? Would you consider reducing PPO2 in that event?Quote:
Originally Posted by BobK
Is swimming against relatively high flow in a cave considered "work" to you? It is to me....
Speaking as a former US Navy Diving/Salvage officer....I have done chamber rides & surface supplied working dives with PPO2's exceeding 2.0. The difference is we were on a mask in the chamber or in a hard hat where the convulsions from a tox event does not cause us to drown.....just gets bruises on your noggin'Quote:
Originally Posted by sea2summit
I use 1.3 which gives me @ 1.25 in the loop. How long are your dives running? In my old age I don't do dives much over 3 hours.Quote:
Originally Posted by amphipod06
Bill
I usually show in Cave Country with air in my doubles from local diving, do a short shake down dive to check gear with the 21%, then top off on 32% for next several dives. This usually gives me 27-30% 02 for several dives, then I'll top off on air to keep it down around 28-30%...or do some short or shallow dives toward the end.
I also tend to keep air in my buddy bottle when solo so I have something lower to go to if I start to experience symptoms of ox tox.
That's because sometimes I get to fill the banks...:smt081Quote:
Originally Posted by WEPIV
You may want to look into getting tri-mix training. It will change you outlook on reducing PPN by adding O2.Quote:
Originally Posted by sea2summit
Right Idea.... wrong gas
It may not be hang time, if you have to get out of the water early it could be the difference between a deco obligation or none. You'd have to run the numbers to find out how much though.Quote:
Originally Posted by Marc Bryan
For me, I don't see much of a difference and you have to draw the line somewhere, there is no way to remove all the risk from this sport/activity. Most places pump 32% and it's within the ppO2 for all the major cert. agencies... good enough for me.
Copy that and thank you sir...Quote:
Originally Posted by Marc Bryan
iDeco - 90ft - 50 minutes - o2 deco - One minute extra deco.Quote:
Originally Posted by OneBrightGator
I'll stop beating the dead horse.
Does anyone have any links to actual reference papers documenting some of the harms of diving what is typically assumed as a save P02 of 1.4 for OC divers? I was having a similar discussion w/ other divers and we were looking for real science.
Expecting to get flamed for my post I googled a bit and found a lot using "navy maximum exposure oxygen".
This one was really good http://www.dtic.mil/cgi-bin/GetTRDoc...c=GetTRDoc.pdf
You must be an old man. I'm a young 53 year old :-) and don't consider Ginnie to be working very hard. I have noticed over the years that my going slower and taking it easy getting down the main line and then off to a jump somewhere has resulted in my gas consumption going down significantly. So I probably don't work as hard as some do who are in a bigger hurry. I've never scootered in a cave either.Quote:
Originally Posted by Jim Wyatt
But honestly, cave diving isn't my most stressful diving. I know this is somewhat off topic, but I think it relates.
I spear dive a lot in the ocean. When speardiving, I typically run PPOs of 1.3 or 1.4, diving to 100 - 120 FSW. And I have fought many fish, some to 70 pounds while doing those dives. I fought a fish once that kept me at 120 FSW so long that I had to let the fish go so that I had enough gas to make the surface. After the exertions on those kinds of dives, I don't feel that the Ginnie outflow is really that tough. I know guys who regularly are diving 1.6 PPOs several times a day doing this. I don't recommend it, but doing know of anyone toxing with this practice.
30% vs 32% at the Ginnie depths is, in my opinion at least, picking nits. We've all seen or heard of accepted practices scaling back from 2.0 PPO to 1.6 PPO to where we are now - 1.2 - 1.4 on a working dive, with 1.6 as acceptable deco. I've not seen an particular evidence that these current levels are risky. (I've not seen any evidence of man-cause globel warming either, but I digress) If someone is running a marathon dive then sure, cut the levels back further. But for recreational cave dives in the 1 - 3 hours range I just don't see this as an issue.
The good news is you all can ignore my ramblings and dive whatever mix you want. If 1.0 PPO is your comfort level, you should absolutely dive that. So far, there are no scuba police :-)
So what's the difference between 28% & 30% then? Or 26%? Or 24%?Quote:
Originally Posted by Marc Bryan
I imagine the difference between the number of ox-tox cases from 1.19 ppO2 vs. 1.12 ppO2 is even smaller.
Quote:
Originally Posted by BobK
LOL - Some days I feel older than others for sure!! :)
There are some places in the back of Devil's out past the Henkle where the flow is pretty darn high & there is virtually nothing to pull on without causing damage. I consider these places hard work because I find myself breathing hard while diving there. One point back there, where there are no pull points it is a bit deeper than 105 feet. So...coupled with swimming against high flow (no pull points) and the 105 foot depth I opt for 30%.
But, as you say I too see no evidence of man made global warming, and do not believe it. I also agree you have the right to dive ANY PPO2 that you see fit.
So this paper is in support of higher P02...or at least 1.6 while at rest during deco.Quote:
Originally Posted by sea2summit
Anyone else have any studies/science that support 1.2 P02 while open circuit diving?
It makes sense to me in a way but I want actual proof.
There is a HUGE difference in the propensity for 02 tox seizures during exertion, and resultant increased metabolic demand, as opposed to the resting state where the baseline metabolism is low. Patients at rest in a hyperbaric chamber can tolerate 2-3 ATA of pure 02 without seizing; this level of 02 would invariably induce seizures with even minimal exertion during a dive.
There are many unknown variables resulting in ones' individual susceptibility to 02-induced seizures, but one of the most recognized risks is the increased metabolic demand of exercise.
FWIW, I dive 31% in Ginnie, just not comfortable with 32% given the exertion levels necessary at times.
I ran several nitrox blends from 21 to 32% through decoplanner for a 3 hour dive at 100 feet with a single deco gas at 100% O2. The O2 toxity clock stayed under 100% during the dive for all mixes (of course dropping for lower PO2 mixes), but in all cases exceeded 100% during deco with the final O2 clock upon surfacing being virtually the same for all bottom mixes. The reason for this was that dives on lower PO2 ran longer deco at the higher PO2.
Bob
We played with basically the same thing today and it is true that at best you only save a few percent on the CNS clock if you back off on the PO2 - at least with the more conservative models in general use today.Quote:
Originally Posted by addexdiver
On the other hand, there are advantages to having a lower PO2 on the higher work portions of the dive, and on deco, you can at least add in some air breaks.
It does however also creates a potential argument for pumping 80% as a deco gas rather than 100%.
I agree that it does not save your CNS clock much to grant the change in banked gases, and i heard about the working part of a dive. Where are you diving that you are at 110' and working hard? No to 80%!!! Just use 100%, I never saw any benifit to it or why people use it.
There was a more recent one, can't recall the exact date but it was after Halloween back in 2007... witnessed by the buddies.... two diff gas analyzers at the scene... 32% +/- 0.5%...Quote:
Originally Posted by FW
Dive safe,
Celia
I try to keep it at 1.0-1.1 during the dive and then up it while on deco...Quote:
Originally Posted by BillBowden
Avg dives 120 mins long...
Dive safe,
Celia
not to mention there is a huge difference not just in a chamber but in the difference between a wet diver and a dry diver. It has to do with the body being suspended in fluid. for instance we teach in the Marine Corps that cns o2 tox becomes a risk at 1.3 ata in a wet diver and 1.6 ata in a dry diver. Now I have done treatments in a chamber that divers have been subjected to ppo2 levels reaching 2.0 ata. On a tt6(treatment table) for instance a diver is slammed to 60fsw as quick as possible then put on o2 right away. the length of the tt with out extensions is 4hr48 minutes which they are on o2 for the entire table with brief air breaks. Now this table is used to treat serious dcs, Arterial gas embolism, or symptoms reacurance. So you take a diver that has been on a 95 minute dive @20fsw with a mk-25 which is a 100% o2 rebreather then throw him in a chamber on a tt6 for age and his ppo2 is going to be well above 2.0 ata and we have seen this happen with no signs of cns o2 tox and then again we have seen it in divers with much less exposure. the moral being everyone is differentQuote:
Originally Posted by divindoc
Agreed! Your last line says it all - "everyone is different" - we know what the tolerable levels of 02 exposure are for the general diving population, but there is a wide range of individual variation in that equation, so what's right for me may not be right for you or the next guy. Being conservative with pp02 just makes common sense.Quote:
Originally Posted by adam0321
And further to that - based on other published Navy testing I have read - not only is there high variability of onset of CNS O2 toxicity symptoms from person to person, but also for the same person day to day...what is right for you today may not be right for you tomorrow....so maybe, "everyone is different every time" better describes it.Quote:
Originally Posted by divindoc
Makes coming up with hard rules that everybody wants, kind of tough to do. There is not much warning, and not much you can do except switch to a significantly lower O2 content gas if you are functionably able to and if you even have it or blow yourself to the surface and take the associated DCS issues if you can.
Particularly insidious.
As times and depths are pushed, be very, very careful folks...and my opinion, expect the problem to happen during deco, not on the dive.
Bob
on deco?? hmm not sure about that. I guess its as good a place as ever. i would think you would be more likely to discover onset during an exertion enduced dive. For instance I know going into jb against the flow you are working harder. It is true that ones o2 toleration does vary day to day. And dive to dive. exertion,cold water,diet,exericse,dehydration etc etc. where I think the divier gets in trouble is they assume since every one is so different that there is such a "fudge Factor" built into the tables that since they have been diving xx amount of years or have xx amount of dives under there belt that they "can take it" . Now in my humble opinion the navy (and Marine Corps) tables are built using young healthy well trained divers. At nedu(naval experimental diving unit) they put the tables to the limit every day to see what the human body can take. Bit the bottom line is every one on any day is different. And the most important thing that I tell our students all the time is "there is no gutting out a diving injury"