Why not 30%?

[WEPIV]

That's because sometimes I get to fill the banks...

Copy that and thank you sir...

[Marc Bryan]

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.

iDeco - 90ft - 50 minutes - o2 deco - One minute extra deco.

I'll stop beating the dead horse.

[JDostal]

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.

[sea2summit]

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

[BobK]

How about for dives where you work very hard? Would you consider reducing PPO2 in that event?

Is swimming against relatively high flow in a cave considered "work" to you? It is to me....

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.

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

[OneBrightGator]

iDeco - 90ft - 50 minutes - o2 deco - One minute extra deco.

I'll stop beating the dead horse.

So what's the difference between 28% & 30% then? Or 26%? Or 24%?

I imagine the difference between the number of ox-tox cases from 1.19 ppO2 vs. 1.12 ppO2 is even smaller.

[Jim Wyatt]

You must be an old man. I'm a young 53 year old and don't consider Ginnie to be working very hard. I've never scootered in a cave either.

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.

[JDostal]

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

So this paper is in support of higher P02...or at least 1.6 while at rest during deco.

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.

[divindoc]

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.

[Bob Cree]

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