Nitrox course. What's the point?

[Blackcrusader]

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 Edward3c All these changes for the better. Question, do the new standards mean the older standards divers were taught under no longer apply? No more deco air dives at 40m with deco stops ( ps we always had steel 120 with 230 bar or around 3500 liters of air in tank and other tanks on the shot line at depth as well. )

Again this thread has veered of from just getting nitrox certified to deco and technical dives and what not which Dody has no intention of doing. Nitrox use is better for dives where you can get longer times to NDL and better over multiple dives in several days or more of diving. As he dives with his wife they can get the benefit from that. I've not always used it as my dives are at vacation resorts and often that is shallower than a lot of vacationers dive and also do not exceed NDL. Some of my vacations are diving with friends who are instructor level as well as TDI Advanced Nitrox Decompression certified some with other tec certs.

Most dive centers don't want DM's doing deco dives as they are there to take out the vacation divers. Some dive centers will let you do deco dives with an appropriate DM or instructor but usually has to be arranged in advance.

So Dody is the multilevel diver staying within NDL limits and probably dive times of an hour more or less. Pretty much how I dive now. I may do more dives on nitrox with 32% setting rather than 21% setting as I also tend to do. I don't always need the longer NDL times and sometimes you are in a mixed group where some are on nitrox and some on air. If I get an instabuddy using Nitrox I switch to Nitrox.

 

[Gareth J]

Right.

But to be a mite more serious: IMNSHO the rec/tec dichotomy is yet another sharp black line drawn through a grey area. What's the difference between a "mandatory safety stop" and a 5 min deco stop at 3m? Again IMNSHO, zero. For me, the big difference comes with accelerated deco and gas switches. Not between a "mandatory safety stop" and a backgas deco stop or two.

As always, YMMV

I would say that a mandatory safety stop is an oxymoron.

Look, you can always take these discussions to absurdities.

Should I always carry bailout with my rebreather? Yes. Well what about in 2 feet of water in the shallow end of a swimming pool? No. Ok, how about 3 feet...?

Why do I need to plan for deco? Because you can no longer surface directly once you have a virtual overhead. But what if it's only 2 minutes of deco and I'm running very conservative gradient factors and I know that my personal tolerance for decompression stress is excellent, etc...?

So yes, just because a line is arbitrary, doesn't mean that it's not useful. We should be telling new divers that once you incur a virtual overhead, no matter what arbitrary algorithm decisions you made to get there, you are now obligated to have done the appropriate training and planned this deco ahead of time, so that you have enough gas to make it to the surface safely. If that can be done by BSAC and called recreational or sport diving or whatever, fine.

I have highlighted a statement in red.

Just to be clear, a safety stop is not mandatory.
It is a recommendation.

Particularly for new divers.
A safety stop is a recommended stop. [1]
It is not required to complete the decompression schedule you are following.

It is important to know that if you have any issue, and still have No Stop Time remaining, you can go directly to the surface.

If you have an incident or problem, you can/should, skip the safety stop and go directly to the surface.
Managing an incident or problem underwater is far more dangerous than on the surface, it is far more dangerous to be on the surface, than in the boat (or on shore).
If things are starting to go wrong, have gone wrong, or you are concerned, make a controlled ascent to the surface with your buddy.

Under normal circumstances you should do the safety stop.

Gareth

[1] Safety stops where introduced to reduce ascent speeds by making divers attempt to stop at 3m for the safety stop.
It provides two safety benefits

• It slows ascent rates
• It gives an additional period of time for the body to off gas where the pressure change is greatest

So yes it does give you some additional safety, and the safety stop ideally should be included on all dives.

 

[Gareth J]

I have highlighted a statement in red.

Just to be clear, a safety stop is not mandatory.
It is a recommendation.

Particularly for new divers.
A safety stop is a recommended stop. [1]
It is not required to complete the decompression schedule you are following.

It is important to know that if you have any issue, and still have No Stop Time remaining, you can go directly to the surface.

If you have an incident or problem, you can/should, skip the safety stop and go directly to the surface.
Managing an incident or problem underwater is far more dangerous than on the surface, it is far more dangerous to be on the surface, than in the boat (or on shore).
If things are starting to go wrong, have gone wrong, or you are concerned, make a controlled ascent to the surface with your buddy.

Under normal circumstances you should do the safety stop.

Gareth

[1] Safety stops where introduced to reduce ascent speeds by making divers attempt to stop at 3m for the safety stop.
It provides two safety benefits

• It slows ascent rates
• It gives an additional period of time for the body to off gas where the pressure change is greatest

So yes it does give you some additional safety, and the safety stop ideally should be included on all dives.

Following the above post, which was particularly for new divers or divers not qualified, or not doing decompression dives.

A follow up.

If you are doing a dive that has a compulsory decompression stops. Then you will need to access the risk relating to the incident / problem and the risk of DCI, and the consequences for each.
If you have 5 minutes of stops after a single dive, the risk of a bend is probably low, so probably missing the stop is not a serious problem.
If you have 60 minutes of stops to do, the risk is high.

We cannot fix drowning, we can potentially fix a bend!

The reason 'technical' training is important for those undertaking dives involving compulsory decompression stops, is that it becomes a requirement that you can manage most issue in water, and resolve them. Hence carrying redundant gas in case of gas loss, etc. Better skills, so that your tendency to panic is reduced, your anticipation of problems is improved. A lot of technical diving relates to a mental attitude to the dive.
Cave diving is another thing again. With open water technical diving there is a possibility to go up to the surface. If you are in a cave, there is no possibility.
Reading a book (or the internet) does not impart the skills that you acquire with a good technical instructor.

 

[Angelo Farina]

Or is your point just more training and a broader skill set is better. And maybe extra gas and redundant gas.

Yes, this is exactly my point....
And sorry for not having been clear about one point. I was meaning that in both cases 1) and 2) the tank is filled with Nitrox32... In case 1) I simply plan the dive as if it was air, considering the extra oxygen just as an additional safety factor.
In case 2) I plan the dive as a Nitrox dive, so I get it within NDL instead of being a deco dive.
As said, the topic here is Nitrox, and if it is worth or not to take a Nitrox course (which for me means ending using Nitrox tables, or the computer in Nitrox mode).
The answer, for me, is that I prefer not to rely on Nitrox theory, following the Nitrox course. I prefer to get a deco training course...

 

[Angelo Farina]

Many divers don't plan at all, they just watch their NDL timer count down and slowly ascend until their tank is low.

Which is exactly what I consider very dangerous...
Those divers "ride the NDL" and are constantly on the edge between no DCS and some DCS...
When some sht happens, you are beyond that edge...

 

[ToneNQ]

Which is exactly what I consider very dangerous...
Those divers "ride the NDL" and are constantly on the edge between no DCS and some DCS...
When some sht happens, you are beyond that edge...

I don't overtly disagree, but I'd suggest there's residual risk rather than its very dangerous. Most computers are more conservative than recreational tables and much more than the US Navy tables. If the computer fails and you're inside NDL, ascend and you're good. Conduct a precautionary safety stop if the margins are tight.

 

[Belzelbub]

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?

The computer calculates the NDL as the amount of time you can remain at the current depth without incurring deco obligations. At that point, it has no idea what is going to happen next. If you go up a bit, the computer will recalculate and display a new number.

If using a dive computer that displays surf GF, both dives to NDL will show the same at NDL = 0. Assuming of course that the same GFs were used. The EAN diver will now offgas more N2 due to the richer mix.

 

[doctormike]

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

View attachment 636797

Yup! Exactly. An oxymoron. Printed on a waterproof slate by a big training agency. They should have hire a copy editor.

 

[Gareth J]

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?

@mac64

You answered your question yourself .

If two divers enter the water as a buddy pair. One on Air (Nx21), on on Nitrox 32 (Nx32). Both dive with the computers set for air.

Dive Option 1
One diver is breathing 79% Nitrogen, one diver is breathing 68% Nitrogen.
When they leave the bottom following the air profile, the diver using Nitrox has less nitrogen in their system (tissues), than the diver on air. Hence the diver using Nitrox has a safety buffer.

Dive Option 2
One diver is breathing 79% Nitrogen, one diver is breathing 68% Nitrogen.
The diver using air dives with the computer set to air, does a square profile and follows the NDL dive time, surfacing
at the limit of the NDL.
The second diver (Nx32), does the same square profile, with his computer set to Nx32. He files the NDL dive time, surfacing at the limit of the NDL.
The computer (Nitrox table) gives the second diver a longer dive. When he leaves the water, he has the same nitrogen saturation as the air diver had when he left the water at the end of his dive.

The two options produced to different risk factors.
Option 1 gave the Nitrox diver a 'safer dive' (with regards to DCI), than the air diver. Because although haveing the same dive as the air diver, his had less nitrogen in his system at the end of the dive.
Option 2 gave the Nitrox diver the same 'risk' of DCI as the air diver, i.e. he dived to the edge of the NDL, but he had a longer dive.

The air diver could reduce his risk of DCI, if he choose to ascend with 10minutes of NDL left on every dive.
The Nitrox diver could follow the same practice, choosing to ascend with 10 minutes of NDL left on every dive, he would have the same risk as the air diver, but longer dives.


In the above example we are assuming a perfect profile to the same depth for each diver. (i.e. how a table is calculated.)

To my view, diving to the edge of the NDL is aggressive diving.

 

[Storker]

a safety stop is not mandatory.

I kinda agree, but to me "required" means "mandatory". And this is an official publication from the biggest certifying agency in the world. Which I used to make a rhetorical point about deco being a hard black line drawn through a fuzzy gray area.

Me? If at all possible I do a safety stop, or at least spend quite a bit of time in the shallows. Because I can without getting bored¹ (my dives are usually more or less triangular profile), because I think it's a good idea, and because my Suunto gets annoyed with me if I blow it off and punishes me by shortening my allowed bottom time on dive #2. At the same time, if SHTF and I owed some three to five minutes I wouldn't think twice about going straight up to the surface if that was what I had to do to avoid drowning. My risk of getting bent would increase, but it wouldn't be the end of the world. But I always plan my dives as no-stop, because overheads - physical or virtual - is my personal hard no.

And this is why I dislike - more and more - that hard dichotomy between no-stop/"rec" diving and staged deco/"tech" diving. And the reason my hard black line is drawn at accelerated deco and gas switches, which takes quite another skill set than just diving backgas and spending a few minutes in the shallows before.

My "rec" PADI RDP allows me 56 min at 18m, albeit with a required safety stop of 3 min at 5m. My national tables allow me 60 minutes at 18m without a deco stop, but if I'm willing to spend 5 min at 3m, I can stay for 70 min, almost a quarter of an hour more than my RDP allows me with a 3 min mandatory stop. The PADI RDP is "rec", my national tables are apparently "tech".

There is no universal hard black line, a competent diver has to find out where their personal hard line is drawn. I know where mine is drawn.


¹ And if I do get bored, I can always do a few drills with my buddy just to pass the time.