Issues with CCR standards

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

wedivebc

CCR Instructor Trainer
ScubaBoard Supporter
Scuba Instructor
Messages
5,552
Reaction score
1,379
Location
Vancouver Island
Recently TDI has made some changes to the standards which are causing me some issues when teaching CCR classes:

First they state a maximum of PO2 1.4 is to be used in all diving applications. This prevents me from using pure O2 at 20ft for bailout deco and also prevents me from performing an O2 flush at 20 ft to verify cell function.

The required breathing rate (SAC) for bailout is way too conservative at 1CFM if we are to use rule of thirds on top of that. Almost all instructors I know use a set of conservative factors based on regional and environmental considerations. No need to add anything to that.

The END factor of 100ft (PPN2 3.16) is also way too conservative. My dive planning for CCR has always involved using 1.6 PO2 limit for bailout deco gas and 4.0 PN2 for diluent and bottom bailout. Heliair for diluent and a 32% nitrox blended with helium for bottom bailout fit these limits quite nicely.
The limits imposed by the new standards are just too restrictive. How about letting your instructors do what we are trained to do without imposing unrealistic limitations?
 
Hi Dave - Is this TDI standard just for Meg or is it supposed to be across all RBs? I just finished a rEvo crossover through TDI and we did O2 flush at 20 to verify cells as part of the standards. Also had to do a bailout swim to calculate RMV rather than using a standard. I don't know about END since my CCR mix was years ago and we didn't go into that in the crossover.
 
Recently TDI has made some changes to the standards which are causing me some issues when teaching CCR classes:

First they state a maximum of PO2 1.4 is to be used in all diving applications. This prevents me from using pure O2 at 20ft for bailout deco and also prevents me from performing an O2 flush at 20 ft to verify cell function.

The required breathing rate (SAC) for bailout is way too conservative at 1CFM if we are to use rule of thirds on top of that. Almost all instructors I know use a set of conservative factors based on regional and environmental considerations. No need to add anything to that.

The END factor of 100ft (PPN2 3.16) is also way too conservative. My dive planning for CCR has always involved using 1.6 PO2 limit for bailout deco gas and 4.0 PN2 for diluent and bottom bailout. Heliair for diluent and a 32% nitrox blended with helium for bottom bailout fit these limits quite nicely.
The limits imposed by the new standards are just too restrictive. How about letting your instructors do what we are trained to do without imposing unrealistic limitations?

While I agree that there's some overly conservative rules there I don't agree with 1.0 RMV being too conservative. I actually think it's not conservative enough in most cases. When you factor in the additional respiratory drive created by increased CO2 and cold gas hitting your lungs your RMV is going to be much higher than that. Granted that may not be the case in all bailout situations but aren't we supposed to plan for the worse case scenario?
 
The RMV is NOT very conservative. I know the time I flooded my loop back in a cave, I wasn't anywhere near 1.0. I can go back through my log book, but I'm guessing I was over 2.0

The rest of the stuff is against what I was taught though. I will be doing an O2 flush at 20'. I will be using 100% O2 for bailout on deco. I don't care about the 100' END either. I'm usually close enough to 100' END
 
Last edited:
Right, you flooded the loop and immediately bailed out. What if you had a scrubber failure resulting in increased CO2 in your loop? Would that have been the case? Not likely.
 
This is from the TDI CCR Unit specific Mixed gas standards


Part 2-TDI Diver Standards
13.3.docx



Page 159 of 206

2. No dives shallower than 40 meters / 130 feet, other than the 1 air diluent configuration dive
3. Equivalent narcosis depth not to exceed 30 metres / 100 feet
4. Calculate all off-board gas at 45.30 litres /1.06 cubic feet per minute usage to cover stress situations
5. PO2 not to exceed manufacturer recommendation or a working limit of 1.3 bar during the bottom phase of
the dive and 1.4 bar during the decompression phase of the dive
6. All dives to be completed within appropriate fixed PO2 decompression tables
7. All dives to be completed within CNS percentage limits with a recommend maximum of 80 percent of the
total PO2 CNS limit
8. The student is only certified for CCR mixed gas diving on the rebreather being used
That and the following line from the same document
3. Bailout gas supply in a minimum of 2 separate off-board oxygen clean cylinders; calculated at 45.30 litres
/1.06 cubic feet per minute usage to cover stress situations
These limits are all well and good but portion of my mixed gas course involves calculating and verifying bailout supply and we are likely to arrive at that same number but whats the point if TDI just comes along and says that's what it is?

The PO2 of 1.4 is the biggie for me. I can't use O2 or do an O2 flush at 20 ft under the current standards. Would someone from TDI please explain how we are suppose to do a proper deco. Please don't say we have to use 80% for deco gas!!!!!
 
It would be interesting to know if these limits were imposed by a manufacturer, by all manufacturers, or if they were made up by someone at TDI without regard to the manufacturers?
 
I agree. I don't like the automatic 1.0 ppO2 the TDI imposes. If they stated a minimum, that would be okay, but it seems they are imposing 1.0 regardless of the student's RMV. I noticed the overhead CCR courses also had that. I think that may be where that originated.

It appears someone wasn't thinking too much about the specifics here.
 
Right, you flooded the loop and immediately bailed out. What if you had a scrubber failure resulting in increased CO2 in your loop? Would that have been the case? Not likely.

I re-read my post, and it was exactly opposite of what I meant to say. I have since edited. My point should have been that 1.0 is no where near conservative enough. And you can read about why I believe that here... Closer Than I Would Have Liked It To Get. - Underwater Adventures Ultimate Cave Diving
 
It would be nice to get Doppler's take on this, as he's pretty involved with TDI technical instruction.
 

Back
Top Bottom