50% O2 and and O2 for deco...........WHY? also labelling tanks........WHY?

[NAM001]

you can deco twince as fast on 100 than on 50. youalso have to be at 20 ft for 100 instead of 70 for 50. The shalower you are the less continued ongassing that occurs. youcan use both 50 and 100 with stops at 70 and 20 but it maeans youhave to carry 2 tanks.

The thing about tank markings is that if the % is that off,,, the tank would not have been accepted by a dir diver. Also the tanks are marked with MOD and not %o2. Everyone in your group sees the tank you are sucking from has a depth marked on it that is deeper than your present depth. One more reason to carry one tank. You dont pick the wrong one. Number of tanks, sizes, and mixes are determined by the dive and standard practices. As far as standard gasses goes deco is 50 and/or 100. Back gas has its standard mixes in the DIR world as well.

So ok guys

i am wondering what the advantage of using 50%o2 and 100% O2 for deco is over other gasses like 40% which let you offgas at a deeper depth.

do any agencies use standard gasses because i know TDI don't?

also why do mainly dir divers permanantly label tanks for 50 and 100 percentwhat id you analyse it and it is 46 percent and the mod changed?

thanks

 

[Hickdive]

Its not the 1.6 that makes oxygen great. It's the zero inert gas.

Yes, but a common refrain for those who use 80% is that it is somehow "safer" because you can use it deeper. I was simply pointing out that if you set your MOD on the basis of ppO2 then that "safety" is illusory since you'll be at 1.6 regardless of the actual mix.

I use O2 at 6m for precisely the reason you cite.

 

[Redshift]

Yes, but a common refrain for those who use 80% is that it is somehow "safer" because you can use it deeper. I was simply pointing out that if you set your MOD on the basis of ppO2 then that "safety" is illusory since you'll be at 1.6 regardless of the actual mix.

I use O2 at 6m for precisely the reason you cite.

Yes, you can use it deeper, but I have never seen anyone change the stop from 6m to 10m because they had EAN80. The stop is still at 6m, it will be less efficient, but with the safety margin of allowing for depth changes for instance in heavy seas.

---------- Post added April 5th, 2014 at 10:27 AM ----------

2) Is getting out of the water as fast as possible really your #1 priority?

I guess you're saying the priority is to be safer and with less inert gasses. But the runtime in this exercise is a measure of how much inert gas there is and how fast it's being released. And what it seems to be showing is that it's more efficient to use 40% and 80% than 50% and 100%. But we'd need to see how large % of the M values were being reached at each stop although they are already limited by the chosen GF.

I wonder if there have been studies focusing on these differences. We all know that sometimes perception is different from reality. And that some gas choices have been made not only thinking of decompression itself, but taking into account other factors such as ease of mixing, volume needed, etc.

 

[Bobby]

Wow, some responses are a bit scary. Yes 80% and even 40% can produce a better deco profile compared to O2 & 50%. O2 does not have to be blended making it easier and 50% is also a fairly straight forward blend. Back when not many of us had O2 analysers standard gases were developed making it easier to blend. Profiles were also generated from tables or personal computers then written down for dives. Again standard gases made things much easier to stay on the profile. Mixed gas diving was also so new to recreational diving that having standard gases helped get people generally on the same page.

Today I use O2 simply because it is easier, cheaper, and faster to fill. If I am doing a big dive with a lot of decompression the profile may make more sense to take the time to blend 80%. A lot of profiles will get you out of the water faster and cleaner with 80%. Also gas management can be better using 80% as the deeper deco gas volume requirements can be large when leaving the 30 foot stop on the deeper mix.

There is a place and reason for standard gases as well as a place and reason to use other mixes such as 80 or 40%. The depth, run time, & profile dictate which gases will work best for a particular dive.

Bobby

Sent from my Transformer TF101 using Tapatalk

 

[kwinter]

I use 80% instead of 100% because I do think it is safer by a small margin. Ongassing occurs because of partial pressure gradient differentials. Just because there might be 20% inert gas does not mean it will fight like a salmon to go upstream and ongas. Bouncing seas can change your depth as someone already pointed out. But even more important to me is the oxygen exposure. While OxTox would be extremely rare and unlikely, the consequences of it are far more serious than being bent. Extended deco at 6m on 100% would require air breaks as the O2 clock ticks away relentlessly. The deco schedule using 80% vs 100% is only marginally different, but far safer. Keep in mind that if you suffer DCS, it will be an hour or so later when you are on the surface while you are breathing air and have plenty of help. If you tox and seize even at your 3m stop, you are very likely going to die. Risk equals probability times severity. OxTox might be very low probability, but severity far outweighs DCS.

Just my worthless opinion.


Please pardon any typos. Sent from my iPhone using Tapatalk

 

[HowardE]

UPDATE

so i have just been running some profiles on v planner and see very little difference between 40 nd 80 as to 50 and 100, so fo example a dive to 60m for 30mins on 18/35 and a deco gasses of 40 and 80 is a 88 min runtime and 50 and 100 is a 92 min runtime, so if 50 and 100 is better then why is ti longer? surely 100 02 off gasses faster. wow

anyone care to explain.

50 and 100% aren't "Better", they're just the gasses that some groups use to make things easier so people don't actually have to think.

If you ask some people, they'll tell you that 100% is actually worse for several reasons.

It's a pure oxidizer. Oxygen will destroy your equipment, o-rings, etc. Even if you're using viton, oxygen is working against your gear. Oxygen on long decompression dives requires many people to need Oxygen breaks, and includes symptoms of the Lorrain Smith effect (Pulmonary Oxygen Toxicity).

So SOME people would agree with you that using 40% and 80% might even be better for decompression in some cases, this would require actually analyzing your dive plan and being a free thinking individual.

However... This would require custom labeling of the tanks so that you and others around you can clearly read the markings on the tanks. IT is true that mislabeled tanks have killed more than just a few people.

 

[PfcAJ]

Baker's Dozen 80/20
BAUE Bottle Marking

 

[wedivebc]

Baker's Dozen 80/20
BAUE Bottle Marking

It's funny how GUE tends to downplay GI3s influence on modern diving yet you guys still drag out this dusty old lunatic rant every time this subject comes up.

This is the internet equivalent of fossilized dinosaur crap.

 

[PfcAJ]

It's funny how GUE tends to downplay GI3s influence on modern diving yet you guys still drag out this dusty old lunatic rant every time this subject comes up.

This is the internet equivalent of fossilized dinosaur crap.

He's got some good points even if you don't like the guy.

 

[Hickdive]

I use 80% instead of 100% because I do think it is safer by a small margin. Ongassing occurs because of partial pressure gradient differentials. Just because there might be 20% inert gas does not mean it will fight like a salmon to go upstream and ongas. Bouncing seas can change your depth as someone already pointed out. But even more important to me is the oxygen exposure. While OxTox would be extremely rare and unlikely, the consequences of it are far more serious than being bent. Extended deco at 6m on 100% would require air breaks as the O2 clock ticks away relentlessly. The deco schedule using 80% vs 100% is only marginally different, but far safer. Keep in mind that if you suffer DCS, it will be an hour or so later when you are on the surface while you are breathing air and have plenty of help. If you tox and seize even at your 3m stop, you are very likely going to die. Risk equals probability times severity. OxTox might be very low probability, but severity far outweighs DCS.

ppO2 80% at 10m = 1.6 Bar.
ppO2 O2 at 3m = 1.3 Bar

I'm not sure why the former would be considered "safer" than the latter, let alone "far safer". Even if I use my O2 at 6m the ppO2 only equals that of 80% at 10m and the CNS clock runs up at the same rate using O2 at 6m as it would using 80% at 10m.