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

[tbone1004]

Why do such a long BT in the ocean?

That's what he would have said.

brought it out to make the times work more than anything. I would obviously much rather do a pair of hour dives

 

[PfcAJ]

brought it out to make the times work more than anything. I would obviously much rather do a pair of hour dives

Right.

You can ALWAYS find some depth/time/gas combo that creates a ridiculous dive plan. Solution? Don't to stupid stuff.

 

[kensuf]

George and I did the hydro together in 1997. We only used 50% as a deco gas, total run-time was 43 minutes (25 on the wreck).

I think AJ's right. Long deco's in the ocean incorporate a lot of risk that needs to be thought out before ever splashing.

 

[Ryan Mcshane]

didn’t George say the longest runtime he would do in the ocean is 90mins?

 

[Sevenrider860]

The argument was 100% over 80%. I've never heard of anyone "standardizing" on 75%.

Here's a reprint of the original "Baker's Dozen" that was published around 1996.

Baker's Dozen 80/20

Thanks for the link! The 100% or 80% discussions I am aware of. 75% is a new one for me and I have never run across that as being an intentional mix.

 

[rjack321]

didn’t George say the longest runtime he would do in the ocean is 90mins?

That is still the rough barometer and has been in the Fundamentals book all this time as well. Having been chased off Lake Huron by 4ft waves and lightening (in June) I'd say it applies to most big waters. That was after a 100min runtime dive and if the boat had to hang out for us for an hour longer we would have been in a world of hurt.

Edit: George didn't scooter stuff from shore like many people do nowadays. I don't exactly know where that falls in the spectrum. Personally I would do longer than 90mins for those kinds of dives (perhaps up to 2 to 2.5 hours) but 3, 4, 5+ hours hanging out in 20ft with surge or boats overhead seems imprudent.

 

[boulderjohn]

The argument was 100% over 80%. I've never heard of anyone "standardizing" on 75%.

Here's a reprint of the original "Baker's Dozen" that was published around 1996.

Baker's Dozen 80/20

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.

 

[rjack321]

I thought it was fascinating that the Thai cave rescue used 80%. Not as a deco gas. They used it because if one of the full face masks was dislodged from one of the kids in a restriction they would be so saturated with O2 that they might be resuscitated without brain damage. They could get full fills of 80% by transfilling and a compressor and didn't need a booster for those. Made a lot of sense given the circumstances.

 

[tbone1004]

@rjack321 you have a citation on 80%? I was listening to an interview and they said that they were on 100% for the ride out. The 80% for that would make sense if they didn't have a booster, but only bringing up because the interview was with one of the divers and said they were on pure o2

 

[rjack321]

@rjack321 you have a citation on 80%? I was listening to an interview and they said that they were on 100% for the ride out. The 80% for that would make sense if they didn't have a booster, but only bringing up because the interview was with one of the divers and said they were on pure o2

a quote from one team member about 80% is in here
Thai cave rescuers on making the daring rescue

different member also quoted about using 80% here
The Thai cave rescue - how they did it

the wiki page also quoting 80%
Tham Luang cave rescue - Wikipedia

Seem like they probably used 80%