YD Scuba Diving Forums banner
1 - 13 of 13 Posts

·
Technical Dive Instructor
Joined
·
384 Posts
Discussion Starter · #1 ·
Dear colleagues.

I am a TDI Instructor and myself not (yet?) GUE certified. I dive with a lot of tech divers from all over the world, coming from all sorts of training agencies, and therefore have to accommodate for a lot of different procedures.

With DIR becoming more and more popular and widespread, I am currently bringing myself up to date with their procedures. My own dive gear has been almost hogarthian for years (because it makes sense!), and I will probably take my own GUE courses in the future (time allowing), but for now I just have a few questions about DIR procedures regaring hypoxic mixes and travel gasses, as I could not find straight answers on the web:

Which travel mix is considered a DIR standard gas?

Is the EAN50 used to travel at the beginning of the dive, if back gas becomes normoxic after a few metres, and the gas volume used is considered in the gas planning?

What are the general DIR procedures regarding the travel gas?

Thanks, and dive safely!
Scubademon
 

·
aka Chimp 1 or Mavis...
Joined
·
10,108 Posts
Hypoxic mixes are 15/55 or 10/70.

15/55 I would use 50% to get to 6m and change.

10/70 (I haven't done) but would probably use deep deco to 6m as 50% bottle would be leash clipped.

Regards
 

·
Technical Dive Instructor
Joined
·
384 Posts
Discussion Starter · #3 ·
Thanks, Gareth, for the swift reply!

Okay, then it IS legit to touch the 50 to travel, very good :) It makes sense to use a deeper deco gas, if the tank is leash cliped in the beginning of the dive.

As well, I need to say that I am glad to get proper answers here at YD. Being new here, I was a bit concerned to post anything, as people seem to attack you quite viciously in other forums, when a non-GUE certified instructor asks anything related to GUE procedures. Those "get your fundy courses sorted out first, before opening your mouth" answers there are not very helpful, so I really appreciate that people here still have manners ;-)

All the best,
Scubademon
 

·
Registered
Joined
·
1,601 Posts
Can i hijack the thread and ask about the leash? Is it clipped off to a rear d-ring, or still clipped off to the hip ring but the leash allows it to be tucked behind the base of the twinset.

Ive carried three stages, all clipped left, and managed ok. But i breathed the bottom stage down to near empty but it was massivly buoyant and a pain. In the end i clipped the front of the stage to my hip d-ring and it was ok but not the most fun.

And yes ..... i'm not gue trained but its interesting to hear how others do this. I've tried left right but find the right side too cluttered with stage, long hose, reel and torch battery.
 

·
Technical Dive Instructor
Joined
·
384 Posts
Discussion Starter · #5 ·
Leash is clipped to the hip d-ring. When you choose the plastic tubing (and of course overall lenght of the leash) long enough, tanks will very comfortably sit on your butt cheeks! Measurements depend on your physique ;-)
 

·
Registered
Joined
·
1,601 Posts
surely this only works with tanks that are slightly negative to neutral as opposed to neutral to slightly positive?
 

·
Technical Dive Instructor
Joined
·
384 Posts
Discussion Starter · #7 ·
This generally works with slightly negative, neutral and postive tanks, hence all Aluminium stages, but it does not work with steel cylinders!
 

·
aka Chimp 1 or Mavis...
Joined
·
10,108 Posts
Scubademon, no worries. You can touch it but make sure you take it into account during your gas planning. However, going from SFC to 6m to switch to backgas then bottom stage (switching from bottle to bottle would be messy) isn't going to use much :)

Liamm. There are normally only 2 bottles clipped forward. For a 10/70 dive, I would expect 10/70 bottom stage and 21/35 deep deco forward with 50% and 100% clipped rear. The leash is clipped to the hip d-ring (4 clips in total there, spg, leash, 2x forward bottles) and the bottles then sit behind the twinset.

Regards
 

·
Mexican Dive Bum
Joined
·
516 Posts
The largest number of stages I have used is 4 - Bottom stage of 10/70, 21/35, 50% and O2. If I remember correctly (it was 2005), we had the 21/35 clipped forward and all the others on the leash. Breathed the 21/35 initially and did a gas switch onto 10/70 back gas, bottle rotation and switch to the bottom stage at 40m or thereabouts. Gareth is right about meticulous planning for travel gas - we had to resolve an issue (cross-clipped bolt snap) at the switch on the way down and used a bit more 21/35 than we had planned for. Deco was fine, but we did not have a massive amount left for "air breaks" at 6m and did the last gas break on 10/70 at 6 and a bit metres, which is not ideal. We took the pragmatic decision to do this (rather than skip the break or use 50%) as we had support divers in the water.

Having said that, I have not done Tech 2 (only just done Tech 1), so may be talking bollocks. I am sure that nice Mr Walker will be along in a minute to give the official GUE position.
 

·
Technical Dive Instructor
Joined
·
384 Posts
Discussion Starter · #11 ·
Thanks, Lanny, for this!
This procedure sounds logic and makes a lot of sense. Gas planning has to be done properly, and I always add another minute or two anyway, to be on the safe side, should a delay on travel gas occur (plus usually boost the tank pressures higher than planned, too).
 

·
Registered
Joined
·
4,880 Posts
It's less an official GUE position and more what the dive requires. We try, particularly at this level of diving, to train our divers to think rather than follow blanket rules. If you are using two gases by all means enter on 50 per cent. However, a dive requiring hypoxic gas would almost certainly require 3 deco gases or an intermediate trimix such as 21/35. Given that the 50 per cent bottle will be required for extended stops, I'd retain it and enter the water on one of the bottles which would be less critical on the ascent phase of the dive.

One dive I can think of I learned to enter on 35/25 as, when entering on 50 per cent once I then ran out of that gas on deco. Now I use the RB I enter on 50 per cent as it makes for a better profile and, using so much less than before, I'm not worried about the gas I use.

I realise that you are probably talking about sea diving - where the amount used is very small. But the principles remain the same. Hypoxic mixes may not be used in the majority of dives but on the RB80 this is a very common problem as breathing even 21 per cent through the unit shallow can be lethal.
 

·
Technical Dive Instructor
Joined
·
384 Posts
Discussion Starter · #13 ·
Hi Clare!

Thanks for the answer! I like you say that divers at Hypoxic Trimix level should be trained to think, rather than blindly follow standards! This is exactly what I think and teach! Unfortunately, I found that many GUE divers are somewhat unflexible concerning procedures, and would not consider anything, unless it has been written down in the DIR bible ;-) .

I am completely with you, concerning the intermediate mix, and travelling on deco mix should be avoided, if there is another 'non-deco' gas that can do the job. On a dive with only hypoxic back gas and 2 deco mixes, bringing another tank into the game just for travelling, would be more hassle than it's worth.
 
1 - 13 of 13 Posts
Top