Rebreather Discussion from Brockville Incident

[Dsix36]

Without the ability to isolate the ADV on the rEvo I certainly would be too concerned to dive 10/50 diluent in 30ft of water as it isn't necessary and could potentially be fatal but that is just my opinion and the risk that I am willing to take especially on a rebreather.

It can certainly be done and with someone who has a lot of skill and ability it could be done safely.

I hope you respect my differing opinion and I dont mean to disrespect at all. A few of my dive buddies do it frequently. It is such a personal preference thing I presume as I have not been trimix trained yet but I don't think I will be persuaded otherwise once I do.

Garth

I understand and respect your concern. I felt the same way until I had more experience and built up my comfort level. I have done multiple shallow, as in 10-15', dives with 10/50. My rEvo has no shutoff for the ADV either. I have adjusted the ADV so that I can feel a definite "pull" on my lungs when it fires. I know exactly when it is about to fire and can halt my inhale to add oxygen if I so desire at that time. This is not necessarily the best option for dil, but it is almost all that I ever use. I know the dangers and feel that I can manage the risk successfully, but at the same time would never advocate this for others, especially some that is new to RB diving.

That is not true, and yes I did begin Mod 1 with mix. (And here's a secret, I'm not the only one...)

I also began my training with mix. It was 21/35 until such time as I was able to get 10/50 fills. I had over 50 hours on my first rig before I ever had air in the dil tank.

 

[nadwidny]

I use 12/65 all the time and I too had 21/35 for my Mod 1 class.

 

[Garth]

I understand and respect your concern. I felt the same way until I had more experience and built up my comfort level. I have done multiple shallow, as in 10-15', dives with 10/50. My rEvo has no shutoff for the ADV either. I have adjusted the ADV so that I can feel a definite "pull" on my lungs when it fires. I know exactly when it is about to fire and can halt my inhale to add oxygen if I so desire at that time. This is not necessarily the best option for dil, but it is almost all that I ever use. I know the dangers and feel that I can manage the risk successfully, but at the same time would never advocate this for others, especially some that is new to RB diving.



I also began my training with mix. It was 21/35 until such time as I was able to get 10/50 fills. I had over 50 hours on my first rig before I ever had air in the dil tank.

Don! Good to here from you. I am a new rebreather diver and do not have your experience. I don't know if I ever will dive with 10/50 in 30ft but I have no issue with others doing so of course.

Just be careful partner. I need your flame in the dark ccr forum places that are filled with noise... :-D

Thanks for the Reply!! Hope all is well

Warm Regards
Garth

 

[Superlyte27]

Without the ability to isolate the ADV on the rEvo I certainly would be too concerned to dive 10/50 diluent in 30ft of water as it isn't necessary and could potentially be fatal but that is just my opinion and the risk that I am willing to take especially on a rebreather.

It can certainly be done and with someone who has a lot of skill and ability it could be done safely.

I hope you respect my differing opinion and I dont mean to disrespect at all. A few of my dive buddies do it frequently. It is such a personal preference thing I presume as I have not been trimix trained yet but I don't think I will be persuaded otherwise once I do.

Garth

Garth: I do respect your differing opinion. There are things I fear about my rebreather. This is not one of them, probably because I know that even on 10/50 at the surface, I could breathe for probably 5 minutes before passing out. Or it might be because I know how quickly I can switch to my bailout. The other thing I know is that I can hear my ADV. So, is there a chance I might mix the wrong gas in my loop? Yup, but that could happen with any gas, not just 10/50. Could it be that my ADV fires out of control, flooding my loop with an unbreathable mix at 10'? Yes, but I'll know it immediately and I can turn off that bottle or switch to bailout or both.

I really think the issue is minimal. And I like not having to reprogram my computer each fill. I know that it always has 10/50 in it. Not air, not 15/25, not 13/40... It's just easier, and it breathes very good.

 

[HIGHwing]

Absolutely, 21/35 for Mod 1. I owned my rebreather for about 14 months before I put something other than trimix in the Dil. So I stand by my statement WOB @ 40m is something I can solve for $3.00.

Regarding the comments about the ADV, mine is not exactly "silent". I might go so far as to say it's never released gas into the loop without my knowledge. Another thing I've noticed is I swear I can hear a squeaky sound on high He mixes while pre-breathing. Could just be me.

 

[gianaameri]

10/50 breathes like a dream from 1' -300' without issue in my opinion.

10/50 breathes better than any other more dense mix.

To reduce WOB one can reduce the max. operating depth of the rebreather (i.e. dive it to 30 meter using Air diluent instead of 40 meters) or use a less dense Diluent mix or both.

In theory, Heliox 10/90 is the best mix down to 100 meters to reduce WOB... but that creates other problems/risks (especially shallow).

In the first instance, it is preferable to buy a rebreather which has been designed to have a WOB which is within the USN max. safe limit.

There is still a risk.

Unbelievable as it may seem, the military lab which rubber stamped the early release of rebreathers to the general public made a scientific miscalculation.

A tiny mistake at some stage, and the WOB of those early rebreathers was not say 0.5 j/l, but say 5 j/l (as an example)... a decimal place off.

With Heliox at 100 meterss (i.e. using one of the least dense gases) the WOB was still way too high (well above the USN safety limit).

It would not be enough to use Heliox to reduce the WOB because the apparatus WOB was just so bad to start-up with.

Furthermore, no one publicly really knew what the WOB was so the apparatus would still be used with Air diuent to 40 meters... exposing the diver to a WOB which was well above the USN safety limit (i.e. as Dr. Mitchell explained us excessive WOB may lead to CO2 Retention and unconsciousness and drowning without warning).

Of course, the brain tissues and any MRI scan of the deceased would show everything normal and no evidence of death by CO2 Retention - the rebreather "silent killer" (hence no evidence that the rebreather may have caused the fatality).

So, before you buy, in addition to asking the manufacturer for the WOB, Hydrostatic Imbalance, and Elastance of the unit, if you care about your family and kids also request copy of the official test report carried out by a reputable independent safety lab... and of course buy a unit with a low WOB... to start-up with (don't buy second-hand).

If you buy a new and modern unit with a low WOB, then you do not need to de-rate it, or use Heliox/Trimix for dives to 40 meters.

Cheaper and easier to use Air - and safer - for dives to 40 meters (i.e. if there is two ways to do something, do it the safer and cheaper way and use Air diluent for shallow dives).

I use N32 Diluent (safer in many ways) rather than 10/50 (or Air) for all my shallow cave dives.

---------- Post added July 22nd, 2013 at 03:16 AM ----------

That is not true, and yes I did begin Mod 1 with mix. (And here's a secret, I'm not the only one...)

Your instructor should be sacked, or training agencies revise their standards to reflect the training methodogy you and others are accustomed to.

Sent from my HTC Desire C using Tapatalk 2

---------- Post added July 22nd, 2013 at 05:02 AM ----------

So I stand by my statement WOB @ 40m is something I can solve for $3.00.

No, you cannot solve it on some rebreathers and that solution (i.e. using a less dense diluent gas) causes other risks and problems (need not elaborate as to the additional risks of hypoxic mixes in OC or rebreathers).

If a rebreather has a very poor WOB to start-up with, even with Heliox you will still be well above the USN WOB limit.

 

[HIGHwing]

Why are USN standards relevant and IANTD standards not? Can you point to training accidents where students performed poorly in training due to less narcosis on the deeper dives? Is not IANTD being forthright in basically admitting a CCR is a complex machine; the last thing we need is a student with 300 minutes running a new piece of equipment narc'ed to hell. This seems exactly like the progressive safety movement you'd endorse. What gives?

And BTW, I said "I" as in "me". I can solve that issue on my rebreather for $3.00. How exactly is 21/35 so wildly different than 21/00? If people buy boxes which do not allow Trimix or limit their training to Air-Dil, that's a shame. Most of the "trained in Florida", "diving it deep every weekend crowd" started with Mix (I'm talking about in the pool on mix) and continually dive mix for everything. The answer to the unspoken question is diving mix every dive is how you get payback on a CCR. My advice is plan accordingly.

 

[rongoodman]

We all start with Air Diluent as part of our Mod. 1 training (no more, no less, the same as those who do the PADI Tec Rec training).

Did you start your rebreather diving with Air Diluent, or Trimix?

I just finished MOD 1 on my Prism 2 with an IANTD instructor and from the first day in the pool it had 21/35 in it. If you're concerned about WOB using air for diluant, the solution seems obvious.

 

[gianaameri]

How exactly is 21/35 so wildly different than 21/00 on a training dive within the NDL?

In a cave with multi-level diving it is very different.

I yo-yo dive (and on DPV) all the time and not a chance I would do it with He if I can possibly avoid it.

I use N32 down to an MOD of about 21 meters. It does not expose me to any of the risks of He. I use less O2 from the O2 bottle(s). I can use it more safely in SCR Bail-out emergency mode.

It is denser than 21/35 or Air, but given that my rebreather has a low WOB to start-up with (at 40 meters on air Diluent it is well within 10% of the USN max. safe WOB limit), then I consider it acceptable to use N32 Diluent at 21 meters MOD with yo-yo diving.

If my rebreather had a WOB in Air Diluent at 40 meters above 3.0 j/l (just to put a number), I would not use it with any gas. I just would not put my mouth to it in the first instance.

There is a trade-off between reducing WOB by using He in the mix, and the inherent risk of using Trimix instead of Air or N32.

If I were to go to 30 meters or deeper in a cave, I would definitely use 18/45 (i.e. from 26 meters up to 50 meters) and Heliox 12/88 (i.e. up to 100 meters), but for shallow dives I'd just stick to a rebreather with a good WOB (or de-rate the Air Diluent MOD a little), rather than use a rebreather with a poor WOB and add He to the mix.

 

[HIGHwing]

In a cave with multi-level diving it is very different.

I made that very point to you pages ago, remember saving oxygen and possibly using SCR mode (which we know you'll never do because you bring enough OC gas) in an overhead and such. Unless you're counting an indoor pool as an overhead environment you're stretching a bit with this one. I'm just saying.

Mod 1 using 21/35, Mod 2 using 10/50 no one said anything about caves, as clearly in caves we'd consider 32/35 to achieve easier WOB, Reduced END, and advantage of increased available oxygen molecules in the dil. <- I dunno why I put the smilie, but it seems like we need one to start the day in this thread.

As a side note, we're putting all the "secret rebreather planning strategies" out in the open here without yelling, screaming, or tantrums. I can imagine those reading along are learning a bit about the details. Actually a very interesting thread.