12 meter procedure - any good?

[dmaziuk]

4 min is the half-time for ZHL-16A, the ZHL-16C half-time is 5 min, but the result is essentially the same. Tissue 1 will be 92% saturated(vice 96% saturated) after 18 min.

ObNitpick: no. You choose 4 or 5 minutes for the fastest nitrogen TC for your implementation. There is not such option for He. Also I have not seen neither 'A' nor 'C' numbers for He.

So a trimix implementation of ZH-L16 will have the 'B' set for helium(*), and for nitrogen it can have either 'B' or 'C' set with either 4 or 5-minute first tissue compartment.

*) Unless they find the 'C' numbers for He.

Exactly what the vendor might call their particular implementation is anybody's guess.

 

[L13]

ObNitpick: no. You choose 4 or 5 minutes for the fastest nitrogen TC for your implementation.

I stand corrected.
SubSurface (and I think Garmin, but not sure) chose 5 minutes.

 

[Rollin]

@Rollin - what’s the skill qualification and experience level of the divers you will be training?

Level is rescue diver to dive masters.
Most of them will stay within 30m for 99.9% of their dives, but some have ambition for more technical diving.
But even if they were only rescue divers and AOW, for myself it is very difficult to use presentations of the federation with data I don't understand or not fully endorse.

 

[mr_v]

50/75 works well for me. I ascend very very slowly and like to hang around at 20' for sometime after deco's cleared.

 

[NothingClever]

Level is rescue diver to dive masters.
Most of them will stay within 30m for 99.9% of their dives, but some have ambition for more technical diving.
But even if they were only rescue divers and AOW, for myself it is very difficult to use presentations of the federation with data I don't understand or not fully endorse.

Given the skill qualifications and experience, I'd stick to approved technical course material and prioritize your focus on:

1) Quick review of historical figures and their scientific contributions
2) Principles of decompression
3) Procedures and standards to conduct decompression
4) Basic overview of safety procedures
5) Technical diving techniques

I would leave any discussion of technique (like the 12m topic) to the very last. You want to impart to the audience reliable, vetted information. This is not the right audience for artistic license or esoteric discussion. Going into technique or letting the audience drift into discussion of technique before first grasping the basics will likely disrupt an otherwise efficient opportunity to learn foundational information.

 

[Rollin]

Going into technique or letting the audience drift into discussion of technique before first grasping the basics will likely disrupt an otherwise efficient opportunity to learn foundational information.

I understand. But again, why teaching stuff that is obsolete? In the course, VPM is considered a new and promising algorithm and deep stops are mentioned as probably adding safety to your dive.


As I said, I try to be as well informed as I can be. And I will inform my students the newest insights in decompression strategies, newbies or not. In the case of 5 minutes @ 12meters, it is apparantly quiet useless but not dangerous. For the air and time used, you would be better off with a normal safety stop.

That's what I will tell them. Not more, not less.

 

[boulderjohn]

I understand. But again, why teaching stuff that is obsolete? In the course, VPM is considered a new and promising algorithm and deep stops are mentioned as probably adding safety to your dive.


As I said, I try to be as well informed as I can be. And I will inform my students the newest insights in decompression strategies, newbies or not. In the case of 5 minutes @ 12meters, it is apparantly quiet useless but not dangerous. For the air and time used, you would be better off with a normal safety stop.

That's what I will tell them. Not more, not less.

I was a TDI instructor when they updated the curriculum with new texts, with the decompression theory materials coming almost straight from TDI instructor Mark Powell's Deco for Divers. Mark was big on VPM and deep stops then--not so much now. Shortly after they updated the course, thinking started to shift away from both VPM and deep stops.

That shows the danger agencies face when they decide to incorporate the latest thinking into the course materials and then spend a fortune creating those materials. What do they do when that decision turns into a really big "Oooops!"?

About that time, I dropped out of TDI and went to PADI's tech program. They had incorporated deep stops into their trimix curriculum as well. When the trend went away from deep stops, I pointed out to PADI headquarters the problem in the course. It specifically told divers that they needed to keep up with the latest research, and it also told them to do deep stops, in opposition to the latest research. They responded by telling me that I was doing the right thing in explaining that to students, and I could skip the deep stop requirement. A few months later, they made it official, telling all instructors there was no longer a requirement for deep stops in the course. It is up to the instructor to keep abreast of those things, though, because the course materials have not changed.

 

[RobPNW]

Would be nice to mention normal Buhlmann with Gradient Factors and sticking to them.

For NDLs, you can do safety stops which could be extended if you feel it's required. Safety stops for NDL (no decompression limit) diving are normally done around 5m/16ft.

For decompression dives, you'll plan it using your preferred gradient factors -- 50:80 or thereabouts -- and follow that plan using the computer. Should the bottom phase be rather strenuous, then you'd extend your final stop by a few minutes, e.g. add a safety stop. The final ascent from the last stop (3m/10ft or 6m/20ft) would normally be done slowly, possibly 1m/3ft per minute.

If you're feeling rather more 'vulnerable' to decompression sickness, then adjust the GF-high down from 50:80 to 50:75 or 50:70 to extend the final stop on the computer. Lots of people have opinions on Gradient Factors, these numbers are used by at least a couple of the people mentioned above.

Is there any guidance of GF settings and different health conditions. I had a heart event years ago and I am considered to have a heart condition. Is there any good source to makes recommendations on that sort of thing?

 

[Rollin]

That shows the danger agencies face when they decide to incorporate the latest thinking into the course materials and then spend a fortune creating those materials. What do they do when that decision turns into a really big "Oooops!"?

Thank you John.

On one side, you have this printed material, but this federation has been clever by using a ring binder, so new insights could be incorporated by changing only a few pages at minimal costs.
Then, there are the powerpoints, which can be changed quickly and for free.


As I understand, the problem are some older veterans being not really into admitting they were 'wrong' all these years. I use ' ', because of course, the whole community was very much into deep stops and VPM. In aftermath, it is easy to critice. And I don't.

 

[boulderjohn]

Is there any guidance of GF settings and different health conditions. I had a heart event years ago and I am considered to have a heart condition. Is there any good source to makes recommendations on that sort of thing?

Here is an article by David Doolette: Gradient Factors in a Post-Deep Stops World
Here is an article I wrote a couple years ago: Evolving Thought on Deep Decompression Stops

Both of those deal with decompression diving, and NDL diving is different.

In NDL diving, the first GF is pretty meaningless, unless you violate those NDLs. After that, it is a matter of your decision as to how close you want to come to the limits. Remember first that the "limits" are not a bright line between safe and unsafe. If you dive to those limits, you should be pretty safe. The second GF tells you how close you are coming to those limits.

I am an older diver myself, and I am pretty cautious. When I am doing an NDL dive, I set my computer for a GF high of 85, but I generally stay in the water on a safety stop until I get a SurfGF number in the 70 range.