How Many Off Board DIL's to allow for?

[divingtactics]

Doing some future equipment planning for dives to 130m - still yet to get the MOD3 training but like to be prepared equipment wise.

If you are planning to plug in DIL from off board tanks, how many would you allow for? 2, 3, 4? One at a time of course.

My thinking is that for a deep dive like that, you only need two, one for the bottom phase and one for a normoxic range.

The reason to plug off board is to allow one to supply heaps of gas to the BOV in the event of a CO2 hit. Also interested in others reasons.

Comments please.

 

[jkaterenchuk]

How about the idea of keeping a shallow breathable gas in your onboard CCR DIL tank and only used the hypoxic bottom gas plugged in once you have gotten deep enough?

John

 

[Dave Sutton]

^^^^

What he said.

One offboard manual add valve on the rig and a quick disconnect hose on every bottle and you'll be golden.

NEVER have a gas on a BOV that you cannot breathe from at the depth where you are. That means normoxic gas at the surface. And unless you like to climb ladders with a stage bottle attached that means normoxic inboard and a system to switch BOV gas.

Should I post yet another link to the YouTube video of my symposium presentation? It may not be all correct and there's plenty of room for other ideas but it will raise a lot of discussion for you to consider.




Dave


.

 

[Andy Del]

How about the idea of keeping a shallow breathable gas in your onboard CCR DIL tank and only used the hypoxic bottom gas plugged in once you have gotten deep enough?

John

Ah, maybe not , John. One word, Sven.

When planning at any depth, one's connected gas is also bailout gas and this is what needs to be planned for.

On the ~120m dives I did with Sven before his accident, I had bottom mix in my back gas and an 11 litre cylinder of the same gas plumbed in. This is what I started and finished the dive with. In addition, there were bailout tanks for a team of (usually) 3 divers.

Everyone had an 11L of bottom mix. (in the region of 10/80)
We carried as a team:

• 2 11l cylinders of 15/55
• 1 11L of 21/35
• 1 11L of 40%
• 40% on deco station
• 100% on deco station

as a minimum. Each diver had three stage tanks. There was enough gas for any one diver to complete their deco OC from the end of the bottom phase of the dive. We also had surface support in the form of a diver, and more gas on a boat that could be brought down and given over.

We also recognised that having 2 divers with CO2 issues meant there was a problem and it was a real cr@p day at the office. 3 divers bailing out? In reality, the chances of this are so slight as to be not an issue. The alternative was not to dive as gas requirements were too great.

That was then. Today, prepping up for some deeper dives with a different buddy, we are going to be a team of 2, with inwater and surface support.

We will be taking 3 stages, the depth will determine exactly what gasses are used, but there WILL be bottom mix and a travel gas as a minimum. The dive plan will determine the last gas, either a milder travel of deco mix. Essetially, it's the same plan using different rebreathers.

I know some experienced and respected divers maintain they wish everything to be pluggable into everything else, so they have the most options in the event of issues. Our jury is still out, but the position of having just bottom gas plugged in to the loop and ADV and all other gas to be OC has some merit WRT 'keeping it all simple' principals.

This is a legacy that Sven has also left me. I have the gear configuration layout he sketched out... it's enough to confirm my KISS ideals.

cheers

Andy

 

[divingtactics]

^^^^

What he said.

One offboard manual add valve on the rig and a quick disconnect hose on every bottle and you'll be golden.

NEVER have a gas on a BOV that you cannot breathe from at the depth where you are. That means normoxic gas at the surface. And unless you like to climb ladders with a stage bottle attached that means normoxic inboard and a system to switch BOV gas.

Should I post yet another link to the YouTube video of my symposium presentation? It may not be all correct and there's plenty of room for other ideas but it will raise a lot of discussion for you to consider.




Dave


.

Thanks Dave, I have your presentation downloaded from YouTube and have watched it a couple of times - it was that, which got me thinking. My plan is to connect into my DIL first stage via a QC6 that feeds an Omniswivel CV-1 check valve, this way, it is connected from the surface but valve turned off and the onboard valve is turned on for the start of the dive and then at 20m during ascent the onboard valve is turned off and the offboard valve is turned. Reverse on ascent.

Drysuit would be fed separately via 50% bottle.
Onboard would be 18/45 and deep mix would be 8/72 or something similar.

The issue with this plan is that if one forgets to turn on/off valves, then one is breathing a normoxic gas below it's depth if one has to bail out. Andy, is this what you are getting at?

Dave, why do you suggest a QC on every tank, is this in case the bottom tank has an issue and you need options. My thinking is that if your bottom tank has an issue, the dive is thumbed. Maybe it makes sense to have two bottom gasses available to connect in. If I am using the onboard for Normoxic, then I still only have a requirement for two QC fittings. I have four available that I've used on my Satori project but have a mate that will need the same setup as me, so not sure if I should sell him two of the four I have.

Great discussion lads, keep it coming.

 

[jkaterenchuk]

Andy, I am not sure I am following what you are saying with respect to how it impacts the number of gases that can be plugged in. On the surface it would seem if you have to go OC due to a CO2 hit then your going to use the same amount of gas regardless of it coming thru the BOV or thru a 2nd stage on the tank regulator. I am not too familiar with the details of the accident you mentioned so that might be why I seem to not be understanding your post so please give it another try.

Just as a side note I do have all my BO tanks plumbed with QD's that allow them all to be plugged in to the BOV, both MAV's and Drysuit/Wing LP inflators just in case I need backup options.

John

 

[Andy Del]

Hi John

What was asked about breathing the wrong gas at depth is exactly what I'm getting at. Sven died as he was mistakenly using air (back-gas) as diluent on a 120m dive. This was due to having his back-gas on and not connecting his off-board to his ADV. In the heat of the moment, following a 6 hour drive, an early morning start and the excitement of the dive, it's all too easy to forget a simple thing like this.

I think if I were to have a CO2 hit on the surface art the start of a dive there's a HUGE screw up happening. Regardless, if at the start or end of a dive, there's a whole atmosphere to breathe out there. Therefore, the bottom gas is plugged in and bailout is for bailout.

Of course, there's more than one way to skin this cat, but having been involved in a fatal dive accident due to the wrong gas being breathed, I tend to err on the conservative/simple side of things.

Hope that puts things in a clearer light...

cheers

Andy

 

[jkaterenchuk]

Hi John

I think if I were to have a CO2 hit on the surface art the start of a dive there's a HUGE screw up happening. Regardless, if at the start or end of a dive, there's a whole atmosphere to breathe out there. Therefore, the bottom gas is plugged in and bailout is for bailout.

Of course, there's more than one way to skin this cat, but having been involved in a fatal dive accident due to the wrong gas being breathed, I tend to err on the conservative/simple side of things.

Hope that puts things in a clearer light...

cheers

Andy

I agree that breathing the wrong gas is a major concern. Sorry for the loss of your friend.

In my post I did not mean surface from a depth location perspective but rather from a examination perspective as in looking only quickly and not very deeply into the details.

Thanks, John

 

[Andy Del]

Hi John

No worries, this is a subject which deserves lots of talk, discussion, agreement and of course :trophy: disagreement!

I'm rather fortunate to be diving with a group who are happy to discuss things, and also accept there is more than one way to 'skin the cat'. Right now, our extended family of divers comprise of:

2 x JJs
3 x Inspos
1 x Poseidon / Prism (really, he's a great guy! why do you all say that
??)
1 x rEvo mini
2 x OC dinosaurs

Suffice to say, post dive discussions are lively, spirited and convivial, as would be in the presence of fine cheeses, dips, pate, caviar, hotdogs, cake, brownies and espresso!. Which boat and where to mount the BBQ???

cheers

Andy

 

[divingtactics]

Our jury is still out, but the position of having just bottom gas plugged in to the loop and ADV and all other gas to be OC has some merit WRT 'keeping it all simple' principals.

The more I think about this, the more I like this scenario. Hypoxic DIL from the surface is obviously breathable with the solenoid addition of extra oxygen into the breathing loop. The only time it is not breathable is if you are on the BOV, but chances are that this is not going to be at the start of the dive but at the end if something has gone wrong mid dive. In this case you would most likely not be on the loop or BOV anyway and instead using an OC reg on one of your bailout bottles. This way, it takes out the earlier mentioned issue of forgetting to plug/unplug/turn on valves or turn off valves. If I only have bottom gas pluggable, then I can never plug the wrong gas in at depth and suffer an O2 hit.

This has certainly been a worthwhile discussion to date and I'd like to thank everyone for their participation.

 

[jkaterenchuk]

The more I think about this, the more I like this scenario. Hypoxic DIL from the surface is obviously breathable with the solenoid addition of extra oxygen into the breathing loop.

Are you sure a solenoid trigger by the ppO2 reading on the O2 cells and the injection algorithm of the electronics can keep up with adding O2 to make the volume of a hypoxic gas added to the loop via the ADV enough that the final mixed breathed is not Hypoxic?

Not something I want to bet my life on. I always isolate the ADV when close to the surface.

John

 

[seppu]

hi
i have only on my deep gas a qc6 connector.to many things can go wrong.
and if the shit hit the fan,i would not breath 2-3 hours thru the bov.no thanks,prefer a standard reg.

 

[Aaen]

Typically what i do is i have no offboard dil's, i use what is on my back and the rest are bail out gases. Now that being said, they are all plumbed to be connected if need to be to the offboard dil mav and are programmed into my shearwater if i need to switch them if say the opv blows or something. Regardless i would probably still just bail out or go scr mode and end the dive if my dil runs out, which it shouldn't as well all plan our dives right? But the option is there if need be.

I know many whom advocate switching dils at depth and do dil flushes etc, to shave 5-10 minutes here or there from the deco schedules, i would prefer to dive one dil from the surface to the bottom to eliminate potential screw ups. I personally feel switching dils etc at depth is a recipe for disaster.

Regards


Steve

Sent from my iPad using Tapatalk HD

 

[divingtactics]

Are you sure a solenoid trigger by the ppO2 reading on the O2 cells and the injection algorithm of the electronics can keep up with adding O2 to make the volume of a hypoxic gas added to the loop via the ADV enough that the final mixed breathed is not Hypoxic?

Not something I want to bet my life on. I always isolate the ADV when close to the surface.

John

Is this a trick question....?

Ok, from the surface, at the start of the dive, I will be looking at my HUD and controller, both show me PPO2 of every cell, starting setpoint is .7 As soon as I start to descend, the PPO2 will raise of course and even if I have a DIL of 8% O2, it is breathable at 10m even if the loop gets completely flushed - above that, I'm not going to be DIL flushing. By the time, the first amount of gas makes it way around the breathing loop, I will be at a safe depth. If there is an issue with low PPO2, I will just manual add some oxygen via the MAV, but I really doubt this would be an issue. To date, I have never seen my PPO2 lower on descent, given my current DIL is normoxic, the amount of O2 in the loop from the DIL is minimal (.21), when my starting setpoint is .7 The solenoid is making up the remainder and that is done on the boat before I ever enter the water. The volumetric difference between .21 and .08 is next to nothing, so I feel confident the solenoid won't even batter an eyelid to make up the difference as a little more DIL gets added during the first 10 metres of the dive.

On return, my PPO2 is at 1.2 as a minimum at 6m and I'm not adding DIL as all my gas volumes are expanding on ascent of course. DIL hasn't been added since I left the bottom and I have a DIL flow stop anyway if I need it. I'm still of mixed opinions on if I like it or not. On a dive to 130m, which is what this discussion was based on, I will be conducting a very slow and controlled ascent up a shotline. At 4m, immediately prior to final ascent, I switch my setpoint back to .7 but no DIL is going to be added. The only time any DIL might get added is if I ran the loop volume too low and after a 130m dive, I've been in the shallows for quite some time, so the loop volume is not likely to change much. Will I be breathing off the BOV in OC mode, not at that depth, I would be on an OC reg of normoxic if there was an issue with the loop and there was no way I could stay on it. If the solenoid dies, I manual add, if the controller dies, I fly by the back up computer and Shearwater HUD.
From my understanding, the JJ controller uses an adaptive algorithm, so it will learn to keep up with my oxygen consumption regardless of my DIL PPO2.

There will be plenty of lead up dives to this big one too and I expect that it won't happen for at least a couple of years, it is going to take some logistical planning and I'm in no hurry.

 

[jkaterenchuk]

Is this a trick question....?

No it is not a trick question but you seem to have a good grasp of the mechanics of what is going on so I suspect you do not need anymore of my input.

Your free to choose whatever procedure you wish when diving hypoxic mix.

I will leave you to ask others as well as researching the details of those that have died near the surface on a CCR while using hypoxic mixes when a perfectly planned dive did not go according to the plan.

John

 

[Gtzav]

Interesting discussions

What I do :
BOV is connected only to my deep bailout.

At the start of the dive I run my rebreather as an O2 rebreather : ADV closed , bailout off ( if there is a long shallow swim ).

At 6m I check to see 1.6 or so and open my ADV and bailout.

On the way up again I close the ADV and at the shallow deco stops I also close the bail out tank that is connected to the BOV
This of course means I don't have a BOV at the shallows ..... But I prefer that than having to change / disconnect / connect or have manifolds
I prefer a simple solution.

On the other hand all my bail out / safety tanks have QC ( dry suit QC) so they can all be plugged in for SCR or emergency use

Note I only dive in caves so above maybe isn't applicable to fast descend wreck dives

 

[Tiptopperoo]

I don't like the idea of having a non breathable gas connected to my BOV at anytime.

Still keeping with the KISS principal this is how I would plan it.

Normoxic 18/45 in my 3L on board.
Hypoxic 10/70 or whatever as my deep dil/bailout with QC6 connected.

On the surface everything is all connected up, but the Hypoxic valve is turned off and the onboard DIL is on.

Once I pass 10m (or wherever my deep bailout becomes breathable), I turn on the offboard deep DIL, and turn off the onboard.

As I come up and my offboard becomes hypoxic again, I turn off dil/DBO and turn back on the onboard.

Most problems happen at the surface, but the worst problems will happen at depth. I feel this solution allows me to mitigate both those situations with minimal fuss.

If we are doing these dives, then we should be able to handle a gas switch, and we have most likely done our fair shair of gas switches and shutdowns in the past. If you can't get your head around turning one valve off and one valve on, then I think you have bigger problems than planning a 130m dive.

 

[Andy Del]

Is this a trick question....?

Ok, from the surface, at the start of the dive, I will be looking at my HUD and controller, both show me PPO2 of every cell, starting setpoint is .7 As soon as I start to descend, the PPO2 will raise of course and even if I have a DIL of 8% O2, it is breathable at 10m even if the loop gets completely flushed - above that, I'm not going to be DIL flushing. By the time, the first amount of gas makes it way around the breathing loop, I will be at a safe depth. If there is an issue with low PPO2, I will just manual add some oxygen via the MAV, but I really doubt this would be an issue. To date, I have never seen my PPO2 lower on descent, given my current DIL is normoxic, the amount of O2 in the loop from the DIL is minimal (.21), when my starting setpoint is .7 The solenoid is making up the remainder and that is done on the boat before I ever enter the water. The volumetric difference between .21 and .08 is next to nothing, so I feel confident the solenoid won't even batter an eyelid to make up the difference as a little more DIL gets added during the first 10 metres of the dive.

On return, my PPO2 is at 1.2 as a minimum at 6m and I'm not adding DIL as all my gas volumes are expanding on ascent of course. DIL hasn't been added since I left the bottom and I have a DIL flow stop anyway if I need it. I'm still of mixed opinions on if I like it or not. On a dive to 130m, which is what this discussion was based on, I will be conducting a very slow and controlled ascent up a shotline. At 4m, immediately prior to final ascent, I switch my setpoint back to .7 but no DIL is going to be added. The only time any DIL might get added is if I ran the loop volume too low and after a 130m dive, I've been in the shallows for quite some time, so the loop volume is not likely to change much. Will I be breathing off the BOV in OC mode, not at that depth, I would be on an OC reg of normoxic if there was an issue with the loop and there was no way I could stay on it. If the solenoid dies, I manual add, if the controller dies, I fly by the back up computer and Shearwater HUD.
From my understanding, the JJ controller uses an adaptive algorithm, so it will learn to keep up with my oxygen consumption regardless of my DIL PPO2.

There will be plenty of lead up dives to this big one too and I expect that it won't happen for at least a couple of years, it is going to take some logistical planning and I'm in no hurry.

Just to add to the mix (pardon the pun) we are diving our JJs a hybrid units now, with a Pelagian valve instead of the O2 manual add they come with.

Wkle this ads a small level of complexity to things, it also simplifies others, so on the surface, I get a constant flow of O2. I also start the dive with a loop of O2.

On descent, I let the ADV do its job and simply keep an eye on my PO2 - the Pelagian valve is gently closed for descent BTW. Setpoint goes up to 1.3 close to the bottom, I will reset this for different depths.

During the bottom phase, the Pelagian valve does it's job and I simply adjust the flow to keep things stable. Again, a slight adding o complexity, but now I have a CCR that can continue to be dived with no special change in technique if my primary electronics. Just keep going on the HUD. If that fails, cwell, it is a nasty day at the office...

On ascent, the valve helps keep PO2 stable, and on deco - 6m and up, I can boot my PO2 to whatever I like and have it stable with no change in technique. O2 after 6m, and no need to change setpoint, have the solenoid working overtime, etc. etc.

Seems to work for us... naturally, YMMV!

cheers

Andy

 

[Dave Sutton]

Your free to choose whatever procedure you wish when diving hypoxic mix.

I will leave you to ask others as well as researching the details of those that have died near the surface on a CCR while using hypoxic mixes when a perfectly planned dive did not go according to the plan.

John

Absolutely wise advice. Those that ignore the past are destined to repeat it.

Paul Blanchette would be alive if he had not had 10% lined up to his rig when he jumped. He was dead very quickly.

You should never ever EVER have gas lined up to an open circuit regulator that is in your mouth that you cannot breathe at the depth where you are. An ADV *is* an open circuit regulator that is effectively *in your mouth*. Having gas you cannot stay concious on lined up to an ADV is a good link to be connected to just a few other links to forge an error-chain. Why play with this?


Dave

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[divingtactics]

@john (jkaterenchuk) - I appreciate your input and apologize if my remark sounded smart alec, I'm just trying to work this whole process through.

@Tiptopperoo - Dave, this is what we've been talking about, till Andy mentioned Sven and I remembered his death and all that surrounded it, Syd Project guys were excellent for releasing information, so we could all learn from it. It didn't really affect me then as I was OC, but it affects me now on CCR and made me rethink about this strategy and if there was another or better way.

@Dave Sutton - I suspect that either way, their seems to be an element of gas risk. Sven had wrong gas at depth, Paul it seems had wrong gas on surface.

@Andy Del - not sure I wish to hybrid my JJ just yet or ever for that matter. I'd need to realize the benefits of it to me. While it simplifies some aspects, it possibly adds another element that could fail or another procedure. I'm not closed to the idea, but would just need to research it more and see if it suited me.

@Gtzav - an interesting solution, switching to BOV could be fatal on the surface.


Hmmm, not one system seems to be perfect. I can now potentially see more likelihood of real issues/incidents with having hypoxic mix on the surface connected to the BOV/Loop than switching between a backgas/offboard valve shut/open issue, so today, I'm leaning back again to Normoxic in backgas and hypoxic offboard like Dave (Tiptopperoo) and I have been talking about.