Scrubbing with EANx

[Shcubasteve]

Hello all,

I’ve had a few discussions lately about the effectiveness of ‘scrubbing off’ with a high ppo2 mix during a series of deepish no-stop dives and would like to hear more opinions. So far, the benefits of more complete outgassing and shorter surface intervals are weighed against increased equipment/task loading and the hazards of hot mixes at depth.

I understand that breathing 1.4-1.6 pp02 will create a large pressure gradient resulting in more efficient outgassing (o2 window),- what I don’t understand is how effective (or ineffective) breathing, say 80% for a 5-10 minute during a series of dives would be… I’ve ran some vplanner scenarios with minimal results- does anyone have any empirical evidence as to the effectiveness of so-called scrubbing off

Thanks for the help
Steve

 

[rjack321]

The rule of thumb for 100% O2 is that 1 min on O2 is roughly = to 2 mins on your backgas. So just extend your stops from 5 min to 10min, poof you got most of the benefits with few drawbacks. Its easier and simpler. You are way way better off adding deeper stops to your profile vs. just stacking time on the final stops though.

Regardless deco mixes are for deco dives though. Don't push a simple dive into deco territory for an extra couple minutes of BT without understanding what you are doing with proper training.

 

[Doc Harry]

There is no evidence that breathing Nitrox reduces your risk for decompression illness (DCI) during recreational diving. Intuituvely, it makes sense that using Nitrox would reduce your risk for DCI. However, the incidence of DCI is so low in recreational diving that it would be difficult to show, statistically, that there is a benefit.

The risk of carrying hyperoxic mixtures (e.g, EAN80) for a dubious benefit in recreational diving is not worth it.

 

[Crowley]

I agree - certainly too much for recreational diving and whilst there may be theoritical benefits for different "no-stop diving" which maybe does not strictly fall into the "recreational" defenition, they would be minor compared to the benefits of a good old fashioned safety stop.

Breathing a higher percentage of oxygen will of course speed the release of nitrogen from the body, it is why we give pure O2 to people who get bent - by as you rightly identify, creating a greater pressure gradient in the lungs which causes the nitrogen to diffuse more rapidly across the alveolar wall.

I think well established conservatism with regard to teaching, tables, computers and conservative dive practise have minimised the risk of DCS whilst we appreciate that from time to time it does occur. The type of diver "no-stop" diver who pushes boundaries and follows dive practices that deliberately increase their risk of DCS without appropriate training are not likely to be the sort of people we can trust to learn about hyperoxic mixes, and the statistical risk of the bends for persons who do follow good practice is so low that as Doc Harry writes, they give us very little information at all.

If a diver who understands what they are doing and thinks they are pushing boundaries where they feel that switching gases during ascent would be beneficial, then there are plenty of Tec courses available for people just like that!

Safe diving,

C.

 

[Shcubasteve]

The rule of thumb for 100% O2 is that 1 min on O2 is roughly = to 2 mins on your backgas.... .

Exactly what I was looking for. Thanks

 

[rjack321]

Exactly what I was looking for. Thanks

Problem is this is for deco dives. And software like Vplanner is not setup to demonstrate this relationship or even plan no-deco dives.

Just extend your stops and add deep stops, most are ad hoc anyway:
1,1,2,2,4 from 50ft up to 10ft is alot easier and more useful than 3mins at 15ft or EAN80. Its 2.5x more time than a conventional safety stop which is alot on a recreational profile.

Also get more hydrated, install a pee valve if you need to.

 

[1_T_Submariner]

Why use 80%? Not 100% O2. I don't have training to this level just simply curious. Seems like at 80% you would have to take all of the same handling/equipment percautions as 100%.
Thanks.

 

[dumpsterDiver]

I scrub with oxygen commonly when doing 5-6 repetative dives in the 100-130 range on nitrox, often with several of them extending into the Deco zone on the computer. Usually, I have less than 5-7 minute deco on the computer for any one dive. BTW. to be "safe", I always punch in 1% less rich mix in my computer.

I have a one gas computer, do deep stops and don't "take credit" for the accelerated oxygen deco which is usually less than 2-3 miutes. I always clear the deco on the computer.

The oxygen appears to help a lot with headaches and general decrease in fatigue. We've seen some people get a little bent doing these kinds of dives, but I personally think the pure oxygen helps, even if it is only a few minutes. One of our buddies, get crippled doing this kind of diving and he now uses a walker to get around. Apparently, it doesn't work that well for everyone.

 

[MaxBottomtime]

Why use 80%? Not 100% O2. I don't have training to this level just simply curious. Seems like at 80% you would have to take all of the same handling/equipment percautions as 100%.
Thanks.

The Bakers Dozen - 13 reasons why we do not use 80/20. by George Irvine

 

[Doc Harry]

Not to hijack the thread, but George's diabtribe misses the point of 80/20. For those of us who have neither a booster nor an unlimited supply of full-pressurized oxygen tanks, 80/20 is sometimes what you get when you have top off with an EAN40 continuous blend in order to get the needed volume.

It's not that I can't maintain my buoyancy, it's that my oxygen tanks decrease in pressure every time I transfill into my deco bottle. At some point, you've got to top off with EAN40 to get enough volume.

If you're George Irvine and can afford to get a $5,000 booster or new, fully pressurized oxygen cylinders every time you need to fill your deco bottles, then I guess you can have it perfect every time. The rest of us have to deal with real physics, and we can't realistically plan a deco dive with only 500 PSI of 100% O2 in our deco bottles.

Back to the question of the OP, in the world of recreational diving profiles there is no proven benefit of even a gas as rich as EAN40 in reducing risk of DCI.

The Bakers Dozen - 13 reasons why we do not use 80/20. by George Irvine