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

[tbone1004]

In my universe for a 200ft 20min 18/45 dive everyone would bring one 40 of 50% and one 40 of 100%.

If you can't handle multiple gases & switches then stick to <25-30min deco exposures until you have the experience and training to do this dive properly.

is the 6 minutes of deco saved worth the hassle of a gas switch? Is it worth the risk of an extra 14 minutes of deco if you have a bottle failure? Whether you can handle it or not is irrelevant IMO, it's about whether that's the best choice of gases for that dive and if you're planning on lost deco gas, the second bottle of 50% gives you a LOT more benefit than a bottle of O2

 

[rjack321]

Do what you want. I've had deco regs fail a couple times, its not a big deal. I don't do more than 30mins on each OC bottle in the ocean and 2x 40s with 50% and 100% work perfectly for this dive. I don't know anyone bringing a spare "team" deco bottle although I've occasionally thought about it for remote cave dives.

On CCR I would bring a single 80 of 50% for the deco gas. I don't plan for 2 major failures (CCR and the deco bottle) but in theory I could use a buddy's 50% if I did have 2 majors, planning for 3 majors is getting beyond ridiculous.

 

[JohnnyC]

I'm not plussed about bringing 50% and 100% as opposed to two tanks of 50% because 100% has other practical uses beyond saving a couple minutes of decompression.

It's always good to have 100% available.

 

[Michael Guerrero]

I've only ever heard of 80% vs. 100%. 80% mainly advocated for to reduce oxygen stress and if you are in rough seas. I've personally only used, seen, and been taught 100% for my last deco gas. I don't have an issue with 80% other than it's not as good as 100%, especially considering that you can take air breaks to vastly increase your oxygen tolerance.

 

[TrimixToo]

I've only ever heard of 80% vs. 100%. 80% mainly advocated for to reduce oxygen stress and if you are in rough seas. I've personally only used, seen, and been taught 100% for my last deco gas. I don't have an issue with 80% other than it's not as good as 100%, especially considering that you can take air breaks to vastly increase your oxygen tolerance.

A friend says 100% irritates his throat too much and 80% is tolerable. I never found that to be the case for me, but YMMV.

 

[Billy Northrup]

I think one must clearly define the dive and conditions first otherwise it's a s**t show of correct answers. Maybe terrain features dictate a different gas, run time on the boat, hell what you had on hand in the garage works right? Do your time and then some. Spend it cleaning up, get tucked away, writing down wet notes for improvements next dive and exit like a boss.

 

[Sevenrider860]

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%.

Out of curiosity, where are you getting the information about the disagreements between 100% and 75%? Can you provide links to the papers (I am assuming early tech era was prior to the Internet) that document the discussions and disagreements?

 

[kensuf]

Out of curiosity, where are you getting the information about the disagreements between 100% and 75%? Can you provide links to the papers (I am assuming early tech era was prior to the Internet) that document the discussions and disagreements?

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

 

[tbone1004]

@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%

 

[PfcAJ]

@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%

Why do such a long BT in the ocean?

That's what he would have said.