40% O2 mix at the safety stop

[Bismark]

Carrying a single bottle of 100% O2 is probably not a very good idea.

When I carry a single bottle, like this, it normally has EAN 50 in it. And then, I am normally wearing my twin tanks, as well.

This isn't "Nereas bashing day", but why do you believe carrying a single bottle of 02 is not a very good idea? Maybe you should be more specific about the particular dive you are using. Do you believe that 50% on a dive to 90' for 50 minutes (well within the range of your doubles) is better than using 100% for the deco? I am truly very interested in your rationale for using 50% as the best deco gas for this type of dive.

 

[hypertech]

No, holding depth is not a "tech skill". But rescuing a toxing diver is hardly a common "rec skill."

Why would that affect this analysis? Someone diving EAN40 may ox tox at 80', or for that matter, someone diving air could ox tox at 100' or maybe even less. 1.6 isn't a magic number. A diver may tox way above that or way below. Air has a MOD too so this isn't isolated to EAN or pure O2.

That risk applies equally across all diving anywhere near a MOD limit. Whether that is EAN40 at 100' or O2 at 20'.

I'm not saying it isn't a valid point - it most certainly is. This scenario doesn't create that risk - it is always there.

 

[RiverRat]

I'm just starting out and for the dives I'm doing I've got a single 30 of 100% I deco on. It goes with me throughout the dive. Some guys are doing 80/20 and that's ok. Maybe they're just a little a timid of 100% O2 at our stage in the game. But all the research I've done says it's best to get on O2 at 20fsw. I'm running some deeper profiles (but not diving them just yet) in vplanner and it seems a 50% gas is looking good for the deeper stops on your ascent and that can really cut down deco time especially on trimix dives. But that is also in combination with getting on O2 at 20. Even 80/20 at 20fsw the PPO2 is just not that high. And that's what you want to get the benefit of washing out the dissolved gas.

 

[Tomeck]

Again, good intentions but faulty information presented in a much to summary-like fashion.

I used V-Planner for the comparison with 40, 50 and 100% and I found 50% is shorter with trimix. Maybe 70% is shorter with air.

 

[Thalassamania]

I'd check v-planner for bugs, because that result denies the laws of physics and (at least my poor understanding) of physiology.

 

[PfcAJ]

There is somthing even more fundamentally flawed with this entire thread that no one has mentioned yet. Since when is it considered a good idea to breathe gas that the individual diver has not analyzed?

40%, 100%? Who knows because YOU didn't analyze it. It could be 100% helium for all you know.

The deco advantage of all 3 gasses in question (100%, 50% and 40%) are negligible for recreational profiles while simultaneously increasing the risk of having an issue (wrong gas, bad reg, gas turned off, supply bottle low, etc).

Bottom line is don't trust someone else to put gas in the water for you. A little bit of planning and education can eliminate this added (and unneeded) complexity from your dive.

Dive safe,
AJ

 

[RiverRat]

No, holding depth is not a "tech skill".

No but it's certainly a skill you need to be really good at to do tech diving. You can get away with a wide variance in Rec diving, but in tech diving you need to really tighten the "window" for holding your stops, especially on your high ppo2 stops. I think it's one of, if not the most important "skill" you need.

 

[OldNSalty]

Maybe next time I'll start out by stating that I am not a tech diver...Bismark and others, you are correct-there is a lot of info but I have a question/observation...several arguments revolve around the divers skill (or lack of). The few dive shops I have talked about regarding a NITROX course are all very proud of the fact that no diving is required in order to get certified for this. "In and out in just a couple of hours" they tell me. So how do they know rather I have normal skills, great skills or just suck?

And on a side note-why even come in at all? Not putting any course down but if it is just that simple then give me the book and charge me to come in and take the test.

I actually don't wish to do it that way-I have been searching for someone in the area who has a good course but can't find anyone. (well, I find people but...)

 

[Thalassamania]

There is somthing even more fundamentally flawed with this entire thread that no one has mentioned yet. Since when is it considered a good idea to breathe gas that the individual diver has not analyzed?

That's not the issue here, there is an assumption that the team knows what it is doing.

40%, 100%? Who knows because YOU didn't analyze it. It could be 100% helium for all you know.

If the truth be known I rarely analyze my own gas, unless I brewed it. But a competent team member does.

The deco advantage of all 3 gasses in question (100%, 50% and 40%) are negligible for recreational profiles while simultaneously increasing the risk of having an issue (wrong gas, bad reg, gas turned off, supply bottle low, etc).

The kinds of issues that you identify are such Bozo the Clown stuff that they do not warrant discussion except in the most basic of training.

Bottom line is don't trust someone else to put gas in the water for you. A little bit of planning and education can eliminate this added (and unneeded) complexity from your dive.

Dive safe,
AJ

I trust team members to put gas in the water for me all the time. They'd trust me with their lives too.

Remember, there's no such thing as "safe," all you can do is intelligently minimize risk.

 

[RiverRat]

Remember, there's no such thing as "safe," all you can do is intelligently minimize risk.

Nice I'm going to lift that for my tagline, now I'm done screwing off at work and I'm going home