Current best practice for deco gas: 75% vs 100%

[cerich]

Early in the tech era, there were extensive disagreements on the best gas to use for the shallow stops with advocates for pure O2 and 75%. What is the current practice? Does it still vary by agency?

no, it was 80% not 75%

 

[rjack321]

no, it was 80% not 75%

If anything the use of 80% has declined IMHO
There are more CCR divers than ever and hence boosters to support them
More boosters = easier to fill OC deco bottles full with 100% too
80% is recognized as less than ideal for most dives
The certification of tech divers with terrible buoyancy unable to hold a 20ft stop has perhaps declined, or maybe with the proliferation of intro to tech and GUE-F courses there are far fewer people arguing that plus/minus 8ft on a stop is "good enough" (although there are still tons of them holding on the line, they just hold on at 20ft now)

I have no data to support this but 80% was never popular or widely used in the PNW. Boosters have long been common here and we don't have swells.

 

[cerich]

If anything the use of 80% has declined.IMHO
There are more CCR divers than ever and hence boosters to support them
More boosters = easier to fill OC deco bottles full with 100% too
80% is recognized as less than ideal for most dives
The certification of tech divers with terrible buoyancy unable to hold a 20ft stop has perhaps declined, or maybe with the proliferation of intro to tech and GUE-F courses there are far fewer people arguing that plus/minus 8ft on a stop is "good enough" (although there are still tons of them holding on the line, they just hold on at 20ft now)

I have no data to support this but 80% was never popular or widely used in the PNW. Boosters have long been common here and we don't have swells.

I was replying to the first post by the OP where he said back in the day the debate was pure oxygen or 75%.

I'm not sure I am following your point, actually I am sure I'm not

Nobody was using saying 75%, it was 80% and in truth in the very early tech dive days 80% was what almost everyone did and it was WKPP that started the 100% debate even before GUE started in 98.

80% makes no sense to me even today

 

[rjack321]

I'm not sure I am following your point, actually I am sure I'm not

Everyone but the OP figured out he meant to say 80% lol.

I was just pointing out that 80% was never really that common here unless you go back over 25 yrs (before my time). And that the proliferation of boosters has reduced the only real selling point (other than buoyancy being crap) on why people were using it in the first place.

The use of 32% as a deco gas has similarly pretty much evaporated. People aren't rushing to get off that nasty helium "early" like they used to

Edit: So unless you have an unusual or rare circumstance, 100% became a "best practice" in the 2000s. The 80% proponents finally got boosters and stopped arguing about it.

 

[Billy Northrup]

80% makes no sense to me even today

I'll do it for no other reason to avoid the sausage party at 20.

 

[rjack321]

I'll do it for no other reason to avoid the sausage party at 20.

Is that what you are actually doing? Or on a hypothetical dive?

 

[Billy Northrup]

Is that what you are actually doing? Or on a hypothetical dive?

I've done it many time especially when I know the rebreather guys are going to be there awhile. I can hang at 30 for what I need and blow around them to 10... Sometimes surface current is ripping and I can hide at 30 instead of getting tossed at 20. Strictly environment driven, not because I have an axe to grind on a mixture.

 

[tursiops]

@kensuf
love #1-equipment solution to a skills problem. Painful fact of so much in this industry

Do you know what his thought on using 50% would have been for sea conditions?
100ft for 100mins on EAN32 with 50/80, 20ft last stop
89mins deco backgas
39mins deco O2
58mins deco on 50%

I really don't much care what he said or why he said it.

 

[kensuf]

When I did my trimix training through TDI, having been UTD before that, I could not help but recognize the snarky references to George Irvine in the course materials, and to the Baker's Dozen article in particular. My instructor had never heard of either DIR or George Irvine, and he did not know what I was talking about. I showed him the Baker's dozen article and showed the clear reference to it in the TDI course, and he immediately said it ignored some of the reasons people used 80%, one of which was the difficulty many people face getting fills of 100%.

I never liked the article myself.

• It it repetitive--some of the items are essentially rewording the main idea of other items.
• It focuses heavily upon getting the maximum PPO2 in order to maximize his concept of the oxygen window, a concept then embraced by the DIR community (and really no one else) and now thoroughly debunked.
• Like much of what came out of Florida diving in those days (and to some extent today), it assumes the whole world is like Florida, with a dive shop on every corner where you can get whatever you want whenever you want it. (OK, I exaggerate.) In the world in which I dive, you can only breathe mixes other than air if you bring your own O2 and He with you. Breathing pure O2 on our dives would be a challenge as our O2 supplies dwindled if I did not bring along my booster.
• The final item is the typical gratuitous GI3 insult that did so much to tear the diving community apart.

My purpose in linking the bakers dozen article had less to do with the actual content, but was in response to the comment that someone was surprised people have been arguing the pros/cons for years.

Personally, my reasons for preferring o2 over 80% fall under the following:

1. Best treatment for DCS, or other diving injuries except CNS oxtox, is 100%. I like to have 100% on-hand on deco dives for this case anyway, means there's one less bottle to fill.

2. Ease of blending 100%.

3. Less inert gas in the final stops.

While there are things George used to preach that I still believe in (cardiovascular fitness for deco diving, benefits of helium, a few others), there are other things he used to preach that I disagree with; doing the 10' stop at 20' is one of them, second stages finger tight is a second, and using deep stops to shorten the shallow stops is a third.

 

[boulderjohn]

While there are things George used to preach that I still believe in (cardiovascular fitness for deco diving, benefits of helium, a few others), there are other things he used to preach that I disagree with; doing the 10' stop at 20' is one of them, second stages finger tight is a second, and using deep stops to shorten the shallow stops is a third.

Are you OK with the oxygen window theory and the use of the S-curve on decompression profiles?