CMAS & BSAC vs others Schools depth limit on Air

[Diver0001]

I am not sure that is strictly true. Which agency other than GUE prohibits diving beyond 40m on air?

Even the PADI Tec50 includes this in the description "Your Tec Deep Instructor may also introduce you to using trimix on the last open water dive."

Notice the 'may'.

I claim the 40m limit generally applies to divers trained at a level which is unlikely to include appropriate redundancy, how to handle the likely decompression and generally enough experience.

Tec 50 is not a recreational course.

Perhaps I should have been more specific by pointing out that it is a generally accepted best practice for recreational diving. In tec diving we've often dived beyond recreational limits.

Any way you look at it.. even if you want to nit pick about definitions and semantics, I personally believe that the 40m limit is reasonable. Should be be called an "absolute limit" as in the PADI materials? Maybe not.... but it's a "reasonable best practice" none the less. Can you go 30cm deeper or 30 seconds longer without dying? Obviously. But at some point, reasonably logical people will want to set a realistic limit for students to stop them from hurting themselves. I see no reason to view 40m as out of line in this context.

R..

 

[EastEndDiver]

Remy I have a question............why are you so fixated on Deep Diving? You have less than 24 dives according to your profile you have a long ways to go before you are trained /qualified for 50M dives.

 

[Dr. Lecter]

I am aware of this, and I try to keep it in mind throughout my dives. It may very well be a factor, but I don't know there is much more I can do about it. But since the feeling clearly increases with depth, wouldn't that suggest narcosis more than CO2 retention?

Gas density and WOB also increase with depth.

 

[Akimbo]

… But since the feeling clearly increases with depth, wouldn't that suggest narcosis more than CO2 retention?

Not necessarily since gas density/work of breathing also increases with depth. More than just keeping it mind, stop and do slow deep ventilation-breathing the next few times it happens. With no perceptible change it is Narcosis. With reduced symptoms is CO2. Also try doing some heavy physical work 20' shallower to see if similar symptoms appear.

For example, let’s say your Narcosis symptoms don’t subside at 130' after relaxing and deep breathing after multiple attempts. That is clearly Narcosis. Now let’s say they reappear at 100-110' under heavy work. That is likely CO2 exacerbating Narcosis symptoms. What is the message? Be careful to avoid situations that require heavy work deeper than 100' and consider making that your depth limit since you could find yourself in unanticipated demanding conditions like currents compounded by a rescue.

There is also a REMOTE possibility that your regulator is not performing well at depth, increasing the work of breathing. Unfortunately you can’t accurately test it even on a high-quality bench testing system at a dive shop. It requires something like an Ansti Breathing Machine that most manufacturers have. These machines actually pressurize the regulator to various depths and measure inhalation and exhalation resistance at various RMS rates. The simplest way to eliminate the regulator as a variable is to try another high-quality regulator for a few dives.

 

[Lorenzoid]

Thanks, Akimbo. I've tried various tweaks to my breathing, including what I thought was ridiculously exaggerated slow, deep breathing, and it doesn't seem to make a difference. I've also used various regs--no difference. My current reg set, HOG, is just two years old. It has always been this way for me. Of course, my little experiments where at various points on a dive I try breathing differently are hardly scientific. It's entirely possible that by the time I try changing my breathing I have already built up too much CO2. I may never figure it out, but staying shallow seems to work for me at this time. I may try helium someday, and then we will finally have an answer.

 

[Dr. Lecter]

Thanks, Akimbo. I've tried various tweaks to my breathing, including what I thought was ridiculously exaggerated slow, deep breathing, and it doesn't seem to make a difference. I've also used various regs--no difference. My current reg set, HOG, is just two years old. It has always been this way for me. Of course, my little experiments where at various points on a dive I try breathing differently are hardly scientific. It's entirely possible that by the time I try changing my breathing I have already built up too much CO2. I may never figure it out, but staying shallow seems to work for me at this time. I may try helium someday, and then we will finally have an answer.

Well, sort of Helium, as a much lighter gas than N2, produces noticably easier WOB and thus reduces CO2 retention.

I also have no doubts you'll notice a difference in perception on helium much below 130' - I just personally haven't found that it is the kind of binary difference from air that most low END advocates describe.

 

[Akimbo]

Well, sort of Helium, as a much lighter gas than N2, produces noticably easier WOB and thus reduces CO2 retention.

I also have no doubts you'll notice a difference in perception on helium much below 130' - I just personally haven't found that it is the kind of binary difference from air that most low END advocates describe.

Agreed. I was on a project where we alternated air and HeO2 on dives between 160 and 180' four times a day for weeks in the early 1970s. We got to the point where we couldn’t tell the difference without talking into the regulator testing for the Donald-Duck voice. We were cold anyway.

With all the distractions of being underwater it is hard to detect WOB compared to chamber dives where most people notice it right away. Funny thing, people still do strange things on Helium.

 

[rivers]

GUE has the strictest limits on air

0 m (they only dive EAN32)

Not true. While the preference is for 32% in the 0-30m/100ft range, in Rec 1, they do teach air tables (or at least how to figure out air equivalency time) as well because they realise it isn't always easy or possible to get nitrox.

 

[chrisch]

came across that the European schools teach air dives down to 53 and even 56m on air, of course this is in the Divemaster/Dive supervisor levels, but basically they fall in the recreational side....

I think you are mistaken in all honesty. Divemaster or any supervisory grade training does not increase your ability to push air as a deep gas. It is generally agreed throughout most of Europe that 40m is the functional limit for air, after which trimix is the better choice. For historical reasons there are agreed limits that mainly (as best I can see) bother the insurance companies not divers. Dive tables don't show limits in the same way a car's speedometer doesn't show either it's maximum or permitted speed.

The 40m "limit" is based around narcosis. In some places it is hard (or impossible) to buy helium and deep air diving is undertaken. It is very much a calculated risk and a sensible diver will undertake special training to do it. Where helium is available it is strongly recommended by all agencies that you use it for deep (35m plus) diving. Air can theoretically be breathed to about 130m - google for "Yuri Lipski" if you want to learn more about deep air diving.

Chris
IANTD Deep Air
CMAS 3 Star.

 

[Remy B.]

---------- Post added October 17th, 2014 at 12:34 PM ----------

I just read that, it was a chart that was comparing the depth according to the maxium recreational level, it said CMAS 3 start and divemaster down to 56m and the BSCA to 50m.

Equivalent Diving Qualifications: BSAC, PADI, CMAS, NAUI, etc - SCUBA Travel

Of course it doesn't mean that what was published in that site is correct.

For what I understand and read from others, 40m was the safer depth limit, ( less likely for serios narcosis and be able to spend some time deep and go up with some extra air and stay in NDL) and I guess it is as well related to not enter so quick in to Deco. The 50m was getting to close to the limits I guess, kind of a 10m safety buffer and according to the tables it is more like a touch "click a selfie I been here" and go back up, taking in account nothing go bad and you will not enter Deco, with the 40m limit you have some time to resolve a problem maybe and still have some air as well.

Not saying my perspective of what I understood is correct, but it make some sense to me that 10m safety buffer.

Long time ago I did read ( don't remember which book but it was a book ) that the 53m was the gate of lala land.