Nitrox course. What's the point?

[Blackcrusader]

Hello. I am not deco trained. I might be one day but that’s currently not the case. My OP was about Nitrox but not as opposed to air for safety. However, your posts tend to make me think that diving without planning for deco is not safe.

What you could say Dody is that doing dives without planning are not safe. Let's take the vacation diver. They do not plan their gas or most likely even know what their air consumption is. They do not understand about SAC rates. I've met many they are decent divers but do not have the knowledge as the dive plan is simple, follow the guide do not exceed a certain depth and and are told not to exceed NDL in fact most DM's will tell people to ascend when they get to 5 minutes to NDL.

Now do I plan my gas usage for a max depth 30m dive when diving on air or nitrox and not exceeding NDL. No I don't. Most of these dives the vacation divers are not capable of staying at 30m for long on air as NDL is not far away and also they need to ascend to shallower depths to make sure they have enough air for an hours dive. They normally follow the guide. If I am buddied up with an instabuddy then I monitor their air and bring them shallower to get them to have a longer dive for say an hour.

So lets take a sac rate of 25l/min which BSAC recommends for a new diver planning a dive. A vacation diver will have less than 50 bar after 20 minutes staying at 30m on an AL80. So they would not be able to stay deep enough even on air to get to NDL. Your sac rate was 20l/min before and is better now but it changes with your dives as some are less comfortable than others. So the vacation diver who stays deep sometimes gets a very short dive 25 minutes. If shallower say 40 minutes.

Deco diving is not dangerous, what is dangerous is people who are not trained thinking it's OK to exceed NDL and not understand the required air to do the deco stop and safely complete the dive. Also my dive computer is setup to give me longer times to NDL than the default on most computers. A lot of divers are on the default settings and that's a good thing as well. So I have to be careful also not to let my dive instabuddy exceed NDL on their dive computers as sometimes they just tag along not looking at the NDL properly.

I know you are planning your dives on your sac rate but that too is a risk when you sac rate varies a lot. Some of us the sac rate does not vary so much. That's just experience and skills. You are doing fine for someone with 50 or 60 dives since November. A lot of new divers would never have asked the questions or tried to understand things the way you have.

No internet back when I was taught so did not have the ability to just get information as you can today. For your original question, using nitrox is better for multiple back to back dives even if you set your computer to 21% as normal and do not exceed 34m depth. Better if you say stuck to max at 30m if on nitrox 32%. If you use nitrox 32% on your computer you will have longer times to NDL. So then as you are gas planning for yourself and your wife you can decide do you want to do a dive at 25m for a longer time to NDL then ascend to shallower depths or even end the dive.

 

[Centrals]

What do you mean OW tec diver? Do you mean an OW level who does planned Deco dives?
You do that in the BSAC Sports diving courses as a novice.

You ought to read what and who have been said!
Post the question to the respective person.

Are you telling me that BSAC Sports diving course including deco on 100% 02?

 

[barth]

I understand your point.
I agree we must not confuse new divers.
And I give no importance on the name given as "rec" or "tech".
For me the correct concept to give to all new divers is that they should not stop their training after the first OW course. It is not safe to dive with just this low level of knowledge, in the assumption that if one stays within the NDL there is no risk.
Better to get further training and reach the level when you can do safely deco dives.
Only at that point a diver is "complete" and can dive safely, knowing that, when sht happens, he has the resources (knowledge, skills, expertise, equipment, amount of air, etc.) to replan the dive, doing the deco if required.
I understand that this is just my opinion, and some major agencies prefer to sell a number of useless "specialty" certs instead of teaching the discipline and knowledge required for safe deco diving.

You can have a long discussion about a complete diver.

when I want to do a deco dive I will bring deco gas and at least 2 tanks with backgas. Skills that would be required in my opinion would be at a high level, much higher then rec divers and rec instructors. Failures during tech training were very realistic. All problems were solved underwater.

I don’t understand that divers do deco dives without decogas and without the right skills like gue rec3. The standards for rec3 are lower then tech 1. Most people who dive with rec 3 do regret their choice and will do tech 1 after rec.

When I had Gue fundamentals I was doing deco dives with backgas. After doing tech 1 in 2016 I did never a dive again with backgas for deco.

I’m not telling other people what they should do or how they should dive. This is just my opinion.

But I do understand that agency’s are not teaching deco to an advanced openwaterdiver. I do understand that there is separate tech training.

 

[Edward3c]

You ought to read what and who have been said!
Post the question to the respective person.

Are you telling me that BSAC Sports diving course including deco on 100% 02?

I’ve stayed away from reading this thread, but I need to provide some prospective to @BLACKCRUSADER statements on BSAC training. Some of the things he claims to be BSAC training were provided by his instructor, additional to the Sports Diver (SD) syllabus.

In the 1980s when he said he was trained, Nitrox was not in the syllabus. Even today a newly minted SD has to undertake additional training to reach 35m or to use gasses greater than 36% O2. Diving below 35m as a SD requires Trimix training, see here.

 

[Storker]

Nope, never have seen that. What does it say?

"Safety stop required". See left side, halfway down

 

[Centrals]

I’ve stayed away from reading this thread, but I need to provide some prospective to @BLACKCRUSADER statements on BSAC training. Some of the things he claims to be BSAC training were provided by his instructor, additional to the Sports Diver (SD) syllabus.

In the 1980s when he said he was trained, Nitrox was not in the syllabus. Even today a newly minted SD has to undertake additional training to reach 35m or to use gasses greater than 36% O2. Diving below 35m as a SD requires Trimix training, see here.

Thank you ever so much to explain certain standard of BSAC.
Cheers.

 

[Celt]

If you dive them both to the NDL, then the safety levels are comparable, though I would give a slight nod to the EAN dive as you’d be breathing less N2 during the ascent and Safety Stop.

I can’t get my head around this, if a computer calculates a dive to NDL. Surely it calculates the same amount of offgasing needed on the assent no matter what gas is been used. Therefore there is no difference in the nitrogen loading at the end of the dive. What I missing. Are you saying that 2 divers using the same computer set to the same conservancy . One dives 21% O2 to NDL the other dives 32% O2 to NDL the computer sends one of them to the surface with a greater nitrogen loading?

 

[chillyinCanada]

My advice: Get out, learn some and don't talk about stuff you don't know anything about.


Since you admit to never have even seen a drysuit, how do you know that the freedom of movement is different than in a wetsuit? My advice: Get out, learn some and don't talk about stuff you don't know anything about.

English not being Dody's first language, may make it more difficult for him to be light when attempting to express humour.

I'm sure that you understand this better than many.

 

[mc42]

Ok, but let's go back on topic.
Nitrox.
Please tell me what of the two following options is safer:
1) Dive 30 min at 30m with air tables, so you are beyond NDL and you need to make a mandatory deco stop of 3m at 3 meters. Of course you must be deco-trained and deco-equipped.
2) As there is Nitrox-32 in your tank, a 30m/30 min dive is considered within NDL, so an unskilled basic OW diver can do it without any additional precaution.
For me, 1) is safer than 2).
And for you?

I believe if you use the US Navy table (which I think you're using since that also gives a 3 minute decompression for the air dive), you will see that the repetitive groups are different between the two dives, indicating that there is less residual nitrogen after the nitrox dive (group H vs J). For the nitrox calculation, I'm using an equivalent air depth of 80ft with the tables.

I also ran your scenarios in Subsurface using the Bühlmann ZHL-16C algorithm just to compare what that model would say about nitrogen load after the dive. The air dive with the 5 minute deco stop results in a Gradient Factor of 111% compared to the 32% profile (97% GF) upon surfacing. These indicate extra nitrogen from the air dive, but also show that you would be surfacing with tissue saturation beyond the Bühlmann M-Value limits.

To get the same 97% GF as the nitrox dive, you would need your air deco stop to be 9 minutes long. If you added a 3 minute safety stop to the nitrox dive to match the air dive, it would reduce the surfacing GF to 85%. To get your air dive to a surfacing GF of 85%, you would need to extend the deco stop to 15 minutes.

Obviously run your own research and check my work, but what I've pieced together for your scenario is both models (tables and Bühlmann) indicate higher residual nitrogen, and one has the dive exceed M-value limits which increases DCS risk. The 32% nitrox dive is safer than the air deco dive when viewed with these two considerations. It's also safer in the basic sense that it's an NDL dive and the diver can get directly to the surface.

 

[Blackcrusader]

You ought to read what and who have been said!
Post the question to the respective person. Are you telling me that BSAC Sports diving course including deco on 100% 02?

I never wrote such a thing I wrote that BSAC Sports divers learn deco diving and are recreational divers.